CA1107351A - Glow discharge heating apparatus - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention provides an AC glow discharge heating apparatus comprising a pair of electrodes opposing each other through a predetermined gap, and means for applying an AC voltage across said pair of electrodes to cause a glow discharge across said gap and a heated liquid heated with energy that enters heat into said pair of electrodes wherein said pair of electrodes are disposed to oppose each other on end surfaces formed into the substantially same shape while being supported only on one portion of said electrodes.

Description

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B~CKGR~U~D OF TIIE INVENrrION
This invention relates to a glow discharge hcating apparatus ror heating a liquid through the utilization of a glow discharge established between a paLr of elec-trodes involved and is a S divisional application of our copending Canadian Patent AFplication Ser1al No. 299,801 filed on March 2~, 1978.
Japanese laid-open patent application No 106252/1976 describes and claims a glow discharge heating apparatlls for heating a liquid by utilizing a phel-omenon that a glow discharge occurring between a pair of cathode and anode ~0 electrodes heats the cathode electrode to an elevated tcmpera-ture. The glow discharge heating apparatus disclosed in the cited patent application comprises a hollow cylindrical enclosure, a tubular cathode electrode coaxially entended and sealed through the enclosure, and having both ends open, a hollow cylindrical anode electrode disposed in the enclo-sure to surround ~he cathodc electrode substantially through-our the length thereof to form an annular discharge gap therebetween, a source of DC voltage connected across the cathode~and~anode electrodes to cause a glow discharge ~20 therebetwcen. The cathode electrode is heated with the glow dlscharge to directly heat a llquid flowing there-througll.
lleating apparatus of thls type re-ferred to have ~; instantaneously heated the liquid Wit]l the simple construc-~;~25 ~ tion and still with the high efflciency. Ilowever, where high currents are required to establish the glow discharge betveen tl~e electrodes, it has been difficult to sustain ; the stabllizedl g~low disFharge tl-erebe~wecn. There have ' ~, ~

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been a feax that the glow ~ischarge will -transit to an arc discharge as the case may be. Also the electrodes have been heated to be axially expanded. This might result in a fear that the appara-tus is broken.
Further it has been difficult to reliably control the glow discharge because of the absence of a control circuit for s-tarting and extinguishing the glow discharge.
Accordingly it is an object of the present invention to eliminate the disadvantdges of t~e prior art p~actice as above described by the provision of a new and improved glow discharge heating apparatus capable of always sustaining a stabilized glow discharge.
It is another object of the present invention to provide a new and improved glow discharge heating apparatus including means for absorbing thermal strains developed in electrodes thereby to provide a construction difficult to be broken.
It is still another object of the present invention to provide a new and improved glow discharge heating apparatus including a control circuit for easily controlling a glow discharge occurring across a pair of electrodes involved.
SUMMARY OF THE INVENTION
;~ According to the present invention there is provided an AC glow discharge heating apparatus comprising a pair of electrodes~opposing each other through a predetermined gap, and means for applying an AC voltage across said pair of electrodes to cause a glow discharge`across said gap and a heated liquid heated with energy that enters heat into said pair of electrodes wherein said pair of electrodes are disposed 30~ to oppose to each other on end surfaces formed into the substantially same shape while being supported only on one portion of said electrodes.

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In a preferred embodiment of the present invention the source of voltage may comprise a source of DC voltage and a hollow anode electrode surrounds the middle portion of a hollow cathode electrode to for:m the predetermined discharge gap therebetween, the ca-thode electrode :Eorming a flow path for the heated liquid.
In ano-ther preferred embodiment of the present inven-tion the source of voltage may comprise a source of ~C
voltage and the pair of electrodes are in the form of hollow cylinders having one end closed and subs-tantially identical in shape to each other, the closed ends of the cylindrical electrodes abutting against each other to form the prede-termined gaF therebetween while flow confiring means is disposed wi-thin each electrode to flow -the liquid in contact relationship with and along the internal surface thereof.
In order to ensure that the glow discharge is prevented from transiting to an arc discharge, the glow discharge heating apparatus may advantageously include an auxiliary ~ source of voltage for applying across the electrodes .

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a high voltage in excess of a discharge breakdown volt~ge across the electrodes upon a discharge voltage across the electrodes approac~ing a glow d:ischarge-hold minimum voltage, to cause a pilot glow discharge therebetween to induce the principal glow discharge.
BRIEF D~SCRIPTION O~ THE DRAWINGS
The present invention will become more readily apparent fro~ the following detailed description taken in conjunction with the accompanying drawings in which:
Figure 1 is a longitudinal sectional view of a glow discharge heating apparatus constructed in accordance with the principles of the prior art;
Figure 2A is a schematic sectional view of a pair o-E
opposite electrode.useful in explaining the glow discharge;
, 15 Figure 2B is a graph illustrating a spatial voltage profile exhibited by the arrangement shown in Figure 2A;
Figure 3 is a fragmental schematic plan view illustrating how a quantity of input heat to a cathode : electrode during a glow discharge is measured;
Figure 4 is a gr~aph illustrating ~he results of the measurement shown in Figure 3 witb the results of a corresponding theoretical calcula~ion;
: Figurç 5 is a graph illustra~ing the relationship between a glow discharge voltage and a gap length thro~lgh : : which a glow:discharge~is caused;
~ Figurç 6 is a graph illustrating the relationship between a volt,age and~a current for the glow discharge;;
Flgure~7 is a:pers:pecti~e~view of a modeled ion ~ ~:
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flux usefu] in expla;ning a quantity of input heat to a cathode c]ectrode resulting from a glow ~ischarge;
Figure 8 is a graph illustrating the current-to-voltage characteristics of the glow discharge;
S Figures 9A and 9B are fragmental schematic plan views of a pair of opposite electrodes useful on explaining ; the principles of the present inventions;
Figure lOA, lOB and lOC are views similar to Figure 9A or 9B but illustrating typically electrode configulations embodying the principles of the present invention; .-: Figure 11 is a longitudinal sectional view of one embodiment according to the glow discharge heating apparatus of the present invention;
, Figure 12 is a current-to-voltage characteristic :~
curve for a glow discharge caused by the arrangement shown in Figure 11; ~
Figures 13 and 14 are graphs useful in explaining : the principles of t~e present invention;
Figure 15 is a longitudinal sectional view of a ~ modification of the arrangement shown in Figure 11;
; : Figures 16 and. 17 are graphs~illustrating the ~ :
: characterlstics of the arraneement shown in Figure 15; .
Figure 18 is a longitudinal sec:tional view of ;Z~ ~ another modiflcation of the present invention;
Pigure 19 is a graph illustrating the characteristic ; ~ ¦ of the arrangement shown in Figure 18;
h ~ Figure 20,, which appears on the same sheet as Fig:. 23, . ~ ~ shows a modification:of the arrangement : : ~ : : ..
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shown in Figure 18 wherein Figure 20A is a cross sectional view and Figures 20B and 20C are side elevational views of the lefthand and rightlland sides respectively;
Figure 21 is a view similar to Figure 18 but illustrating still another modification of the ~resent invention;
Figure 22 is a view similar to Figure 18 but illustrating a modi.fication of the arrangement shown in Figure 21;
Figure 23 is a view similar to Figure 18 but illustrati.ng another modification of the arrangement shown in Figure 21;
Figure 24 is a view similar to Figure 18 but illustrating still another modification of the arrangement shown in Figure 21;
Figure 25 is a gra~h illustrating a leakage current calculated with the arrangement shown in Figure 24;
Figure 26 is a graphical representation of voltage and currcn~ waveforms developed in the arrangement of 2Q Figure 24 filled with a mixture of helium and hydrogen;
Figure 27 is graph illustrating the current-to-: voltage characteristics of glow discharges occurring in the arrangement of Figure 24 filled with mixtures of : helium and hydrogen having different proportions thereof;
Figure 28 is a graph illustrating the theoretical relationship between a glow hold minimum voltage and quantity of input heat to an associated electrode resulting ~ ~¦ from the low disch~rge;

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Figure 29 is a graph illustrating the relationship between an overlapping a-rea for both electrodes and a pressure of a filling gas;
Figure 30, 31 and 32 is graphs illustrating how S the glow hold minimum voltage is changed with a proportion of mixed gases and a dischar~e gap-length;
Figure 33 is a graph illustrating the relationship .~ between the glow hold minimum voltage and a peak discharge current;
Figure 34 is a longitudinal sectional view of a different modification of the present invention including . an auxiliary electrode;
Figures 35, 36 and 37 are fragmental perspective views of different modifications of one of the electrodes shown in Figure 34;
~ Figure 38 is a longitudinal sectional view of ::: modification of Figur~ 34 along with an associated electric : circuit;
Figure 39 is a longitudinal sectional view of another modification of the arrangement shown in Figure 34;
~; Figure 40 is a view similar to Figure 38 but illustrating still ano~her modification of the arrangement :~, shown in Figure 34; ~.
; ~ Figure 41 is view similar to Figure 39 but illustrat-ing a dlfferent modification of the arrangement shown in Figurè 34; ~
~Flgure 42 is a vlew similar to Figure 39 but llustrating a modificatlon of the arrangement shown in : ~
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ll:U~3~ii Figure 41;
Figure 43 is a view similar to Figure 39 but illustrating a modification of the arrangement shown in Figure 40;
Figure 44 is a view similar to Figure 39 but illustrating another modification of the arrangement shown in Figure 34;
Figure 45 .is a view similar to Figure 39 but illustrating a modiication of the arrangement shown in Figure 44;
Figure 46 is a diagram of the fundamental used with control circuit the present invention;
Figure 47 is a graph illustrating a voltage and a current waveform devel~ped in the arrangement shown in : 15 Figure 46; -Figure 48 is a diagram of a control circuit constructed ~:~ in accordance with the principles of the present invention for driving the glow discharge heating apparatus thereof;
Figure 49 is a graph illustrating a voltage and a current waveform developed in the arrangement shown in Figure 48;
: Flgure 50 is a diagram similar to Figure 48 but illustrating a modiflcation of the arrangement shown in ~:
: Figure 48; :
: : Figure 51 is a~graph simllar to Flgure 49 but .-:~lllus~tratlng the arrangement shown in;Figure 50;
Figure 52 is a~diagram of another control circuit : : ~ ~ ..
constructed~ln accordance with the~principles of the ~

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present invent;on and suitable for use wi~h an electrode structure includ;ng an auxiliary electrode;
Figure 53 is a circui~ diagram similar to Figure 52 but illustrating a modifica~ion of the arrangement shown in Figure 52;
Figure 54, wh~ch appears on the same sheet as Fig. 56 and 57, is a graph illustrating voltage wavefor~,s de~eloped at various points in the arrangement shown in Figure 52;
Figures 55 through 5~ are circuit diagrams similar to Figure 52 but illustrating different modifications of the arrangement shown in Figure 52;
Figure 59 is a diagram of still another control circu.it constructed in accordance with the principles of : the present inven.tion;
Figure 60 is a graph illustrating voltage waveforms developed in the arrangement shown in Figure 59;
Figure 61 is a graphical representation of a Laue plot;
. Figurc 62 is a circuit diagram similar to Figure 59 .
but illustrating a modification of the arrangement shown ~ ~ in Figure 59; : :
:~ . Figure 63 is a graph similar to Figure 60 but illustrating:.the arrangemen~ shown in Figure 62;
Figure 64 is a section~al view of an embodiment accord~ing to the three-phase glow discharge hea~ing apparatus: of the present invention and a diagram of a controI circult therefor:; .
Figure 65 is~a graph illustrating various \~aveforms :~ ~ ~:
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developed in the arrangement shown in Figure 64;
Figure 66 is a diagram o:E the detailes of the control circuit shown in Figure 64;
Figure 67 is a wiring diagram of a modification of the arrangement shown in Figure 66;
Figure 68 is a graph similar to Figure 65 but illustrating the arrangement shown in Figure 67;
Figure 69 is a longitudinal sectional view of a modification of the arrangement shown in Figure 44 and a diagram of a control circ~it therefor;
Figure 70 is a longitudinal sectional vi.ew of a modification of the arrangement shown in Figure 69;
Figure 71 is a view similar to Figure 64 but illustrating a modification of the arrangement shown in Figure 64;
Figure 72 is a view similar to Figure 70 but illustrating a modification of the arrangement shown in Figure 69; and .
Figure 73 is a longitudinal sectional view of : 20 another ~odification of the arrangement shown in Figure 69.
Throughout the Figures like reference nurnerals : designate the identical or corresponding components. .
i DESCRIPTION OF THE PREFERRED EMBODIMENTS
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Referring now to Figure 1 of the drawings, there is illustrated a conventional glow discharge-heating apparatus.
The arrangement illustra~ed comprises a holl~w cylindrical c~athode electrode 1, a hollow cylindri.cal anode electrode 2 surrounding coaxially the cathode electrode 1 to form an :' - : .
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~ 5 1 ¦ annular discharge gap 8 therebetwéen with the aid of two ¦ electrically insula~ing spacers 7 in the form of annuli ¦ fixedly disposed between both electrodes l and 2 adjacent to ¦ both end portions of the anode electrode 2, and a cylindrical ¦ enclosure 9 formed o any suitable electrically insulating ¦ ma~erial such as glass and coaxially housing the electrodes ¦ 1 and 2 with the cathode electrode 1 hermetically extending through both ends thereof. A seal fit~ing lO is sealed at the outer periphery to one end, in this case, the lefthand end as viewed in Figure 1 of the enclosure 9 and at the inner periphery to the adjacent portion of the cathode electrode 1 while a corrugated seal fitting 11 is sealed at the outer pheriphery to the other end of the envelope 9 and at the inner periphery to the adjacent ' 15 portion of the cathode electrode 1. The corrugated seal fitting ll is permitted to be axially contracted and ,~
expanded enough to prevent the cathode electrode l from damaging due ~o an axial thermal strains thereof. Thus the envelope 9 and the seal fittings lO and 11 maintain the 20 ~ discharge gap 8 hermetic.
; As shown in Figure 1, the anode electrode 2 includes flared end portions 2g in order,to prevent an electric discharge from concentrating on the end portions of the ~, anode electrode 2.
A positive,terminal 5 connected to the central poTtion of the anode electrode 2 is extended and sealed through the central portion o the cylindrical peripheral wall of the enclosure~ 9 until it lS connected to~a posi~ive ' ~ ~: : ~
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7;151 side of a source of DC voltage 3 having a negative side ¦ connected through a stabilizing res;stor 4 to a negative ¦ terminal 6 that is~ in turn~ connected to one end portion~
¦ in this case~ the righthand end portion as viel~ed in ¦ Figure 1 Of the catl-ode electrode 1, ¦ In the arrangement Of Figure 1~ a DC voltage is applied across the anode and cathode electrodes 1 and 2 ¦ respectively to establish a glow discharge across the l discharge gap 8 thereby to heat the cathode electrode 1, ¦ Under these circumstances, a liquid to be hea~ed such as water is caused to flow through the interior of the cathode electrode 1 tO be directly heated by the heated cathode electrode 1, I Conventional glow discharge heating apparatus such ¦ as shown in Figure 1 have been enabled to instantaneously ¦ heat liquids to be heated, for example, water resulting in ¦ heating 2pparatus simple in construction and s~ill high in I efficiency, However~ since the apparatus have required the ;~ high current, it has been extremely difficult to stably ~20 sustain the giow discharge across the anode and cathode electrodes~. According to circumstances, there has been a fear that the glow di5charge transits to an arc discharge, Further there has been a fear that~ as a result of their heating,~ the electrode5 are axially expanded leading to ~25 ~ ~ the destruction of the heating apparatus. In addition,~
conventional glow disc~harge heating~apparatus have not been provided~with suitable control circuit means for ; ~ e ~ w ~ tl~ th~t~

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it has been difficult to reliably control the glow discharge.
The ~resent invention contemplates to eliminate the disadvantages oE and objections to the prior art practice as above described and characterized by unique means for impartlng a positive resistance to the current-to-voltage characteristic of the glow discharge. It ;las been found that such characteristic is effective for preventing the transit of the glow discharge to an arc discharge.
For a better understanding of the principles of the present invention, the description will now be made in conjunction with the glow discharge, the principles tha. it heats an associated cathode electrode and the current-to-voltage characteristic thereof. I
Figu-re 2A shows a pair of cathode and anode lS electrodes 1 and 2 respectively disposed in spaced opposite relationship and a source of DC voltage 3 including a ;j negative side connected to the cathode electrode 1 and a positive side connec~ed to the anode electrode 2 through a stabillzing resistor 4 whereby a glow discharge occurs within a discharge space formed between both electrodes 1 : and 2. It is well kno~n that the dlscharge space having the glow discharge established therein lS divided into a region of cathode fall a in which positive ions are enriched, a reglon of negative glqw b forming a thin lumunescent ;; layer,~a Faraday dark sp~ace c in which~no light is emitted, ; and a p~sitlve column~dO~consisting of a plasma including electrons and lons, starting with the~side o~ the cathode e}ectrode~

~ 3 5 1 Figure 2B shows a spatial voltage profile in the discharge space with ~he glow discharge established therein.
In Figure 2B, a voltage V is plotted in ordinate against a distance d in abscissa measured from the cathode e]ectrode 1.
From Figure 2B it is seen that the region o-f cathode fall a has a very large potential-gradient because the presence of a space charge until a cathode fall of potential Vc is reached at the end of the region a spaced from the surface of the cathode electrode 1 by a distance of dc. The voltage reaches a glow voltage Vg on the surface of the anode electrode 2.
By visually observing the glow discharge, it is seen that a boundary between the region of cathode fall a and the region of negative glow b are very distinct but a boundary be-tween the region of negative glow b and the Faraday dark space c or between the Faraday dark space and the positive column d~ is not so distinct.
Also the Faraday dark space c and the positive column d are in the so-called plasma stake and relatively small in potential gradient. On the other hand, the region of cathode fall a includes positive ions in the form of a beam. As far as the discharge current is~concernedj it consists essentially of an electron current in each of the Faraday dark space c and positive column do which are in ~2~5 the plasma state and of an ion current~ln the region ~of cathode fall a. The region of negative glow b forms a region of the transltion of one to the other of both currents.
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Two phenomena developed in the region of cathode fall a, that is, (1) the mechanism by which the glow discharge is sustained and (2~ a phenomenon that the cathode electrode is heated with the glow discharge as well as (3) the current-to-voltage characteristic of the glow discharge are pertinent to the principles of the present invention and therefore will now be described.
~1) Mechanism of Sustaining Glow Discharge Positive ions present in the region of cathode fall a collide against the surface of the cathode electrode whereupon the cathode electrode 1 emits electrons by means of the action of emitting secondary electrons called the Yi action. The electrons emitted from the cathode electrode (1~ collide agains~ neutral atoms or molecules during their movement toward the anode electrode which is accompanied by an ionizing action called the ~ action with some probability. Electrons and posltive ions caused by the ionization and co]lision are acc~lerated towa~d the anode and cathode electrodes respectively by means of the action of an electrlc fleld involved. It is noted that the posltive ions ,accelerated with t,he electric ~ield contributes to the yl action. ~
Here ~the sustalnment of the glow discharge will be somewhat quantitatively described. For example, it is said 2;5~ that,~wlth the cathode electrode l~formed of~nickel, the~
; Yi is approximately equal to 0.01 for slow helium ions ~having l~Kev or less.~ That is~ about 100 ions collide agalnst the~cathode elect~rode l'~to emit a single electron ~ ..
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therefrom. .
Also a degree of ionization ~ is a function of ~he type and pressure of a gas confined in the discharge space and a potential gradient developed therein. Electron-ion pairs formed at a distance x from the cathode electrode l :
are proportional to e~x where e designates the base of Napierian logarithms and therefore increase exponen~ially with the distance x. Accordingly, the glow di.scharge is sustained with a distance and a voltage requi.red for about ~lO lO0 electron-ion pairs to be formed in the course of movement of a single electrode toward the anode electrode 2. This distance is designated by the distance dc shown in Figure 2B and this voltage substantially corresponds to the voltage Vc. In other words, the glow discharge can be sustained even when the anode electrode 2 has been displaced ` to its position subs~an~ially shcwn by dc in Figure 2A.
.~ This is substantially applicable to electrodes formed of nickel, copper, iron, stainless steel or the like and operatively associated with a gas selected from t~Le group consisting of helium, neon, argon, hydrogen, . . .
nitrogen etc.
A more detaile~analysis of the phenomena developed ~ in the ViCiDity of the cathode electrode l teaches that a -: ~ curren~ density J on the surface.~o~ the cathode electrode l ..
:25 is expressed by : : ~ : 2 ~:
:~ . j+ j - j~ = KlP ~ :
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where i~ and i designate densities of positive ions and electrons respectively, P a pressure of a discharge gas, and Kl designates a constant determined by both the type of a cathode material and that of the discharge gas.
S Also the region of cathocle fall a has a thickness dc as defined by .

dcP ~2 (2) where K2 designa~es a constant dependent upon both the type of the cathode material and that of the discharge gas.
:~ Within the region of normal glow, the cathode fall of :~ potential Vc is determined by both the type of the cathode material and that of the discharge gas but scarcely dapends lS ~ upon both a discharge current and the pressure of the . .
discharge gas.
. . The following Table I lists values:of the constants ~:
Kl and Kz and the cathode fall o-f potential Vc measured within the region of~ normal glow with different combina-~20: tions of cathode materials and discharge gases with a glow current not higher than 1 amperes and wlth the dischar~e gases maintalned under the pres~sure of 50 Torrs or more~.
The measured.Kl ancl K2 values are expressed ln 10 6 ~ ~-ampere~per~cm~TorrZ~and ~in cm Torr and the voltage Vc is .~ 2~5~ :~expressed:ln volts~. ~Also the current density on the ~ :
surface o~ the~cathode electrode has been determined by measurlng~an~area of~a~negatlve g~low b. Probably, the ¦ ne ti~ ~low 15 very ~hin ~o tha~ s ob~Grved like a~

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luminescent -film attached to the cathode electrode.
Iable I
r~lEASURED VALUES OF Kl, K2 and Vc . .................... _ . _ . ..
\ Gas He Ne Ar H
Cathode ~~~ _ 2 _ ~ --Kl 6.0 8.3 27 24 .
Cu K2 3-0 3.0 0.8 2.0 Vc 150 150 180 290 . . . _ - - -''--I
Kl 8.0 20 32 32 ; Ni 2 3 0 4 0 3 0 Vc 101 1~0 185 254 _ . ._ ..
Kl 4.4 4.7 17 30 Mo K2 4 0 3.0 0.8 3.0 Vc 180 175 190 290 . .
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Kl 7.6 8.0 22 30 : ¦ SUS 5~7 0.8 .~ :
`~ l Vc - 119 150 180 232 '::
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~2) lleating of Cathode Electrode As above described, positive ions present in the :
: reg;on of cathode fall a colllde against the cathode ~ ..
electrode to cause ~he ~i action. At that time, the posi- :.
tive lons have surplus kinetic energy that IS, In turn spent to~heat the cathode electrode 1. Regarding quantities:
of inp~ut and~output~heat of the cathode: electrodes, there are,:in addition to collision with the positive ions,; heat ~ ::
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conduction from the plasma portions~ exothermic and endothermic effects caused from chemical reactions effected on the surface o-f the cathode electrode 1 due to the glow discharge, cooling ef~ects caused from the sputtering on the cathode electrode and the evaporation of the cathode material etc. I-lowever, an extent to which a quantity of heat enters the cathode electrode has not been elucidated until the present.
In order to determine a quantity o input heat to the cathode electrode due to the glow discharge formed between that electrode and an anode electrode, experiments ~ere conducted with a test device schematically shown in Figure 3. As shown in Figure 3, a cathode electrode 1 in the form of a very long circular rod having a radius r of 1.8 mm was disposed to be thermally isolated from the surrounding and opposite to a similar anode electrode 2 to form therebctween a gap having a length d of 4 mm.
Both electrodes were formed of copper and connected across ¦~ a DC source 3 through a stabilizing resistor 4. Thus a glow discharge g is established across both electrodes l and 2 in the atmosphere. Under these circumstance, a radiation ther~.ometer M was used to~contlnuously measure a temperature at a point~on the outer surface of the cathode i -electrode l spaced way from the discharge surace thereof ~ as ~ by a distance ZO of 3 mm.
The results of the experimen~s are shown in Figure 4 ; wherein the temperature in Centigrade is in ordinate against ~ time in seconds in abscissa with a glow current taken as ~ ~ : ~
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the parameter. In Figure 4, each vertical se~'nent designates a range in which measured values of the temperature are dispersed and solid curve describes calculated values of the tem~erature as will be described hereinafter. The reference numerals 111, 112, 113 and 114 mean the tempera-tures measured and calculated with glow currents of 4~0, 250, 200 and lS0 milliamperes respectively.
From Figure 4 it has been confirmed that the glow discharge ~ransits to an arc discharge upon the measured temperature approaching 1000C. This will be because an oxide film is formed on the sur-face of the cathode electrode at such a temperature.
It is now assumed that in Figure 3, the cathode electrode l with a radius r has the longitudinal axis lying lS on a z axis and the discharge surface passing through the origin for the z axis and that a quantity of input heat to the cathode electrode l is constant per unit area and per unit time. Under the assumed condition, by solving a partial differential equation for conduction of heat referred to the z axis alone and taking account of a radiation loss may be expressed by -a T = K 2 a~ - ~ (T - Toj -~2S~ where ~ designates a thermal~diffusibility defined by the square root of the :quotient of a thermal conductivity k of~
the cathode electrode divided by the product of a density ¦ P and ~ at cayacity tbere~[ and a lS a constaDt on the ¦

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assumption that the radiation loss is a linear function of a temperature T. By solving the partial equation under the boundary conditions s aZ IZ=O ~Ir and a Z lz = co where ~ designates a coefficient of heat input and the :~ initial condition T(z,o) = To where To designates room temperature, a solution results in T(z,t) = To + ~ - ~ ~ e ~20 ~ ~ K -I ,.
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where~I: glow current.
; ~ : ~ln the:expression ~3? F~yl) and P(yz) are error functions ~ I expressed by :~

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~ y2 F(y ) = -1 ¦ e 2 d and ~ 2 F(Y2) = I ¦ ~ 2 dy ; respectively where Yl and Y2 are expressed by ' 10 ~ Y1 = 2~t^z and y = 2~t+z K~ IC~

; respectively. Also a is defined by .:
' 15 : 2~a(Ta3+ToTaZ+To2Ta~To3~
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where designates an:emissivity, a a Stefan-Boltzmann :~
~20~ ~ constant~and Ta designates the mean value of room tempera-ture and a temperature of the cathode electrode. ~ : .
The expression (3):was used to calculate the tlme dependency of the temperature rise on the measured point as : shown in~Figure 3. The~results of the calculations are 2~ ~ indicated~by the solid:curves~shown in ~igure:4.~ : :~
; ~ :From~Plgure 4 it~is séen that the measured values~ ~:
; ~of the~temperature fal~rly wel:l colnc:ide~ wi~th the calculated : ~values the~reo~f, ~ :
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Figure S illustrates a glow discharge voltage V in volts plotted in ordinate against a length of a discharge gap in millimeters in abscissa. The voltage V was measured with the electrodes formed of copper and disposed in the atmosphere. Curves labelled 115, 116, 117 and 118 depict glow currents of 10, 50, 100 and 400 milliamperes respec-tively.
In Figure 4 it is to be noted that the curves have been drawn by equalling the cathode drop of potential Vc in the atmosphere to a voltage of 285 volts estimated with a null gap length from curves shown in Figure 5.
Also the coefficient of heat input ~ has been determined to cause the calculated valves of the temperature to coincide with the measured values ~hereof shown in -lS Figure 4. The coefficient ~ has been of 1.4.
Further it is considered that a quantity of heat corresponding to 0.4 iVc per unit area per unit time will result from one portion of heat generated in that portion ; of the glow discharge formed of both the Faraday dark 2~ space c and the positive column d except for the region of cathode fall a having a thickness dc approximately equal to ~ x 10 centlmeter.
Pigure 6 illustrates a glow voltage Vg in volts plotted in ordinate against a gIow current I in milliamperes in abscissa. Curve labelled 119 describes the glow current-to-voltage characteristic exhibited by the arrange-ment of Flgure 2. Dotted curve 120 S]IOwS the total power consumed by the glow discharge and expressed by IVg while :
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broken curve 121 illustrates an electric power entering the cathode electrode and calculated as 1.4 IVg. Both the glow voltage and powers in watts are plotted in ordinate against the same glow current in absussa.
From Figure 6 it is seen that at least 80 % of the total consumed power enters the cathode electrode and that the higher the glow current I the greater the proport;on of the power entering the cathode electrode to the total consumed power will be.
Also it is seen that a quantity of input heat q to the cathode electrode 1 per unit area per unit time is give by q= iVC = jVg provided that the spaclng d between the cathode and anode electrodes 1 and 2 respectively substantially approximates the thlckness of the region of cathode fall a ~see Figure 2), that is to say, the glow discharge includes no plasma portion. From this it is seen that the smaller the spacing d between the cathode and anode electrodes the larger the proportion of the power entering the cathode electrode to the total consumed power will be.
Figure 7 shows a model for a positive ion flux striking~agalnst the;unit area of the surface o-f the ; ~ cathode electrode per unit time. In Figure 7, a square prism has a square bottom including each side of 1 ~centi-meter and~contacting the surface of the cathode electrode , :~ : :
. :

' : :
' ~ : ~
; ' ~ :

~ 3 ~ 1 1 and a height corresponding to th'e velocity Vi cm/sec of ions multiplied by one second. Within the prism, positive ions designated by the symbol "cross in circle" are moved as shown at the arrow to strike collide wi~h the cathode electrode 1. Thus the square prism designates a positive ion flux colliding against the c:athode electrode per unit area per unit time and electricaLl energy of the i,on flux results in the quantity of input heat q to the cathode electrode. Since the number of the positive ions is expressed by j/e where a designates the elementary electric charge and since each ion has electrical energy of eVc, the quantity of input heat q is expressed by q = eVc~ Vc in watts/cm2.
Thus the model for the positive ion flux also explains that the quantity of input heat to the cathode electrode is expressed by jVc per unit area per unit time.
From the foregoing it will be understood that the , ~ glow discharge established across the cathode and anode electrodes causes the quantity of heat expressed by ~iVc to enter the cathode electrode per unit area per unit time.
Also by decre,asing the spacing between both electrodes to increase the glow current through the spacing, the 25~ guantitylof input heat to the cathode electrode per unit area per unit time~can approximates the product of the current density on the surface of the cathode electrode multiplied by the glow voltage or J Vg.
: :
~ ~ : ~ : ~ : -~ - 26 - ~

i ' ~ L

Therefore the glow discharge without the positive column can be utilized as a heat source hav;ng a high efficiency because almost all heat due to the glow discharge enters the cathode electrode and also as a heat source S having a power density variable at will by changing a gas pressure within the spacing between both electrodes because the current density on the surface of the cathode electrode is proportional to the square of the gas pressure.

(3) Current~to-Voltage Characteristic of Glow Discharge The current-to-voltage characteristic of the-glow - discharge will now be described and then the principles of the present invention will be described in detail.
Figure 8 shows the relationship between a current and a voltage for the glow discharge. In Figure 8 the axis of abscissas represents a current and the axis of ordinates represents a voltage.
: A DC voltage is applied across a cathode and an ~ anode elec~rode 1 and 2 respectively (see Figure 9A) to ; 20~ render the anode electrode 2 positive with respect to ~he cathode electrode I thereby to cause to a glow discharge thereacross. When a current flowing through both electrodes ~; is increased, a negative glow region b included in the glow ~=
discharge spreads in area on the surface of the ca~hode ~ electrode 1 (see Figures 9A and 9B). This results in a change in current-to-voltage characteristic as shown at solld line N in Figure 8.
However, when the current lS qulte low, the :; ~ :

, ., : . ~ .
;

:'' ,~ ~ . :; :

31~'73S~

current-to-voltage characteristic droops as shown by a characteristic portion Nl in Figure 8. A region in which the drooping characteristic Nl appears i.s called a region of subnormal glow e.
In a region following the region of subnormal glow e an increase in current causes the voltage to be kept substantially constant as shown by a characteristic porti.on N2 in Figure 8 as long as that the surface of the cathode electrode 1 having the negative glow b caused thereon is smaller in area than the entire surface thereof opposite to the anode electrode 2 as shown in Figure 9A. A region in which the characteristic portion N2 is developed is called a region of normal glow .
A further increase in current causes an increase in voltage because the negative glow b has covered the entire ~: area of the surface of the cathode electrode 1 opposite to .
the anode electrode 2 as shown ln Figure 9B whereby the negative glow increases in current density. The resulting : I-V characteristic is upturned with an increase in current ~20 as shown by a characteristic portion N3 in Figure 8. The :: characteristic portion N3 is called a positive resistance~
characteristic and a region in which the positive resistance characteristic N3 appers is called a region of abnormal glow. In that region ~of abnormal glow q the entire area .~25~ :; of the surface of the cathode elect.rode 1 is covered with the negatlve glow b tsee Figure 9B) with the resul~ that the current is apt to concentrate~at the edge portion or : ~ :
::~the llke of the cathode electrode 1 and therefore the glow :: ~ -' ~ : ~ "
~ ; ; ~ 28 - .:

: ~ : :.. ,.;~. :'~' ~ 3 5'~

discharge is easily changed to an arc discharge. As a result, it is difficult to maintain the glow discharge in its stable state. The arc discharge appears in a region h as shown in Figure 8.
With no impedance connected between the cathode and anode electrodes 1 and 2 respectively and an electric source for supplyîng ~n electric power across both electrodes, the source side has the current-to-voltage characteristic of the constant current type such as shown at horizontal broken line P in Figure 8. This is because even an increase in current does not cause a voltage drop across an impedance.
Under these circumstance, the glow discharge has its operating point coinciding with a point Pl where the lS characteristic P o-f the source side intersects the charac-teristic N of the glow discharge. However, this operating point Pl lS located in the region of abnormal glow g, which is apt to transit to a region of arc discharge h, as above described. Accordingly it is difficult to maintain the ~20 glow discharge stable in the region of abnormal glow g. .
; ~ Further it is to be noted that the ~lat character-istic P o~ tlle source side can not stably cross the flat characteristic portion N2 of the glow discharge in the 2~:
region of normal glow f.
~25 ~ On the~other hand, wlth a resistance R as the impedance connected to the source, an increase in current I
causes~an increase in voltage drop IR across the resistance. `
Thus~ the source side~h~s ~he current-t~-voltage <-aracteristlc ~ ~ I

. . . . .. .. ... . .. . . .

~ 3~ ~

such as shown at dotted straight iine Q in Figure 8 and the glow discharge has its operating point designated by an intersection Ql of the characteristics Q and N. This operating point is located in the region of normal glow f resulting in the stable glow discharge.
Where electrical energy participating in the glow discharge is converted to thermal energy with a very high efficiency, the connection of an impedance to the source as above described forms one of factors of decreasing an efficiency utilization of electrical energy. For example, the use of a resistor causes a Joules loss and the use of reactor causes a Joules loss of a winding involved and an eddy current loss and a hystersis loss of an iron core involved. Since such energy losses scatter as thermal lS energy, it is possible to recover the thermal energy.
This, of course, deprives the resulting heating device of its convenience and compactness.
From the foregoing it is seen that whether or not an impedance is connected to an electric source retains the abovementioned disadvantages as long as the glow discharge has the current-to-voltage characteristic in the form of a curve such as shown at N in Figure 8.
In order that ~he glow discharge can be maintained --stable even with the flat current-to-voltage characteristic of an associated source side such as shown by straight line P in Pigure 8 and without an impedance connected to the source, the pr~esent invention includes unique means for . ~ .... .
~ ~ mparting~ a po~sitlve reslstance to the current-to-voltage ~ : : :: ':
~ - 30 -~

'~ ~ ' . , . . ~ .

~ 3~i ~

characteristic of the glow discharge in a different manner as compared with conventional abnormal glows.
First it is seen in Figure lOA that surface of a cathode electrode 1 opposite to an anode electrode 2 has an area made sufficiently larger than that of the anode electrode 2 so as not to impede the spread of a negative glow A b. In other words, the opposite surface area of the anode electrode 2 is limited to a small magnitude with respect to the cathode electrode. Thus a peripheral edge root bl of the negative glow _ lying on the opposite surface of the cathode electrode 1 has a distance to the anode electrode 2 is gradually increased as the negative glow b spreads due to an increase in glow discharge current and therefore a voltage across both electrodes 1 and 2 is gradually raised. Under these circumstances, the glow discharge has the current-to-voltage characteristic such that the voltage increases with the cUrFent as shown at broken curve T in Figure 8.
That is, the characteristic is of the positive resistance type~
In this connectlon, it is to be noted that the positive resistance characteristic developed in the region ;; of abnormal glow ~ in the prior art practice as shown atcurve N3 in Figure 8~is cause from the fact that the ;25 ~ ~ negative glow b has spread over the surface of the cathode eIectrode and~can not any more spread (see Figure 9B).
Accordingly, such positive resistance characteristic is quite ditferent from~th~t accordi~ng~to the princlple~s of ~ ~,-~ ~ - 31 -~ ::
::: :
~ ; : ' . .

~ -`

the prescn~ inven~;on. As above described, the ncgative glow of the present invention is permitted to sufficiently spread as an increase in current because the active surface area of the cathode electrode 1 opposite to the anode S electrode 2 is sufficiently larger than that of the anode electrode with the result that there is no probleln that the glow discharge is transits to an arc discharge due to the impossibility of spreading the ne~ative glow.
From the -foregoing it is seen that the characteristic T of the present invention as shown in Figure 8 is developed in the region of normal glow but not in the region of abnormal glow althou~h it has a positive resistance.
In the present invention, even Wit]l an associated electric source having no impedance connected thereto, therefore the characteristic T thereof intersects the characteristic of an associated source side at a point Tl (see Figure 8) where the glow discharge is stablized. It is to be noted that the poin~ Tl lies in the region of the normal glow unlike the characteristic N3 of the prior art practice so that the present invention does not encounter the problems that the glow discharge transits to an are discharge and so on. -In order to impart a positive resistance to the c~rrent-to-voltage characteristic o~ the glow discharge by further increasing the distance between the peripheral edge bl of the negative glow b on a cathode electrode 1 and an associated anode eIectrode 2, the cathode electrode 1 can be made cylindrical and opposite to the anode electrode ' ,-: ; ~ : ' ' ~ ~: - 32 -~ : ' ; . ~ . ~ . - . .- . , .

~ 3S ~

2 as shown in Figure lOB. In the arrangement of Figure lOB, the peripheral glow edge bl is located on the peripheral wall surface of the cylindrical cathode electrode l at some distance from the end surface thereof. Thus, the glow e~ge ~1 is far spaced away from the anode electrode 2 as compared ~ith the arrangement of Figure lOA, resulting in a satisfactory pos;tive resistance characteristic.
When an AC voltage is applied across the cathode and ~` anode electrodes, either of the electrode becomes alterna~ely a positive electrode so tha~ a glow discharge is caused on the opposite surfaces of both electrodes. With an AC
voltage used, it is desirable that the cathode and anode electrodes are in the form of identical cylinders and oppose to each other as shown in Figure lOC. From Figure lOC it is seen that the peripheral edge bl of the negative glow b on either electrode 1 or 2 is far spaced away from the mating electrode 2 or 1 as in the arrangement of Figure lOB.
From the foregolng it is summarized that the principles of the present invention are to cause an area ~20 with which a pair of cathode and anode electrodes are opposite to each other to be smaller than that area of the electrode~wlth which a;negative glow lS caused.
Referring now to Figure lI~ there is illustrated ; ~ - -one embodiment according to the glow discharge heating ~25~ ~ apparatus emb~odying the principles of the present inventlon ~as above described. The arrangement illustrated comprises ~an ~electrically insulatlng~enclosure 9 in~the form of a ~
hollow cylinder formed of glass, a cathoae electrode l in~the ~ :

~ ~ 33~-~ :

3l~35~

form of a hollow cylinder with both open ends coaxially extending through the enclosure 9 and an anode electrode 2 in the form of a hollow cylinder with both open flare ends disposed coaxially with the cathode electrode 1 withing S the enclosure 9 to form an annular glow discharge gap 8 therebetween. ~he cathode electrode 1 is extended and sealed through both ends of the enclosure 9 by means of seal fitting 10 and 11 respectively. Thus the enclosure 9 along with the cathode electrode 1 defines an annular space 81 which includes the glow discharge gap 8 and is filled with an electrically dischargeable gas selected from the group consisting of rare gases such as helium, mixtures thereof, for example, a mixture of neon and argon, a mixture of helium and hydrogen etc.
An annular anode terminal 5 is fixedly secured at the inner periphery to the central portion of the outer cylindrical surface of the anode electrode 2 and has a protrusion extended and sealed through the enclosure 9 by having the outer periphery fixed to a seal fitting sealed to adjacent ends of two similar enclosure portions forming~the ~ :
enclosure 9. The anode terminal 5 is connected to a positlve side of a source of DC voltage 3 lncluding a negative side connected by a stabillzer 4 to a cathode ~ ~ ;
terminal 6 that is connected to that portion of the cathode `
;~25~ electrode 1 dispose~ o,utside of the enclosure 9, in this ~
~ case,~adjacent~to tilë~seal flttin~ 11. The stabilizer 4~may : .. , .. - .
~be a small capacity reactor or a resistor. If desired, the s-ab~liz~r m-y be omitted. ~ ~;
~ ~
.' .

: ~ ' 1~ 3S~ ~
., In order to facilitate the description of the present invention, the symbol ~S-It designates the entire area of that portion of the cathode electrode 1 on which a glow discharge can be caused while the symbol "S~" designates an area of that portion of the anode electrode 2 opposing to the cathode electrode 1 and actually used for the glow dis-charge. Therefore an area labelled S~ is called an "anode area effective for discharge" or an "effective anode area".
According to the principles of the present invention as above described, the anode area S-~ effec~ive for discharge is made smaller than the cathode discharge area S-.
The operation of the arrangement as shown in Figure 11 will now be described. A DC voltage from the source 3 is applied across the anode and cathode electrodes 2 and 1 respectively through the stabilizer 4 to establish a stable glow discharge in the annular discharge gas 8 thereby to heat the cathode electrode 1. Under these circumstances, ;~ a fluid to be heated, for example, water flows into the interior of the cathode electrode 1 as shown at the arrow A
~0 in Figure 11 to absorb heat rom the cathode electrode 1 to~
~e heated. Then the heated fluid flows out from the cathode ~lectrode 1 as shown ~at the arrow B in Figure 1.
Dur:ing the glow discharge, a current and a voltage thereof is illustrated by a characteristic curve shown in Figure~lZ whereln the~glow discharge current Ig ~in amperes ~is plot~ed in abscissa~agai~nst the glow discharge voltàge ~Vg~in;volts~in ~rdinate. ~The glow dlschargc voltage Vg may ;
be ppl~X ma~ely~ expressed by ~ ~ ¦

~ 35 ~ ;

; :~ ; : :

~ 7 3 ~ ~ .

Vg = VO -~ IgR

where VO designates a glow discharge-llold minimum voltage as will be described hereinafter and R des;gnates a slope of the characteristic curve. The slope of the characteristic curve as shown in Figure 12 is called a "positive resistance R".
Referring back to Figure 11, L designates an axial length of the anode electrode 12 and has been differently changed to vary the efEective anode area S+ thereby to obtain the relationship between a ratio of the effective anode area S+ to the cathode discharge area S- and the positive resistance R as shown in Figure 13.
In Figure 13, the positive resistance R in ohms is ~lotted in ordinate against the ratio between both area S+/S- in abscissa. Curves labelled 122, 123 and 124 have been plotted with data measured by filling the interior of the enclosure;9 or the annular space 81 with a gaseous mixture Including 70% by volume of helium and 30% by volume ~20 of hydrogen under pressures of 100, 150 and 200 Toors ~ respectiveIy. The gap~between both~electrodes 1 and 2 has ;~ ~ keen maintained at a magnitude of 1 mm. Also the vertical segment has the same meaning as that shown in Figure 4.
From Figure 13 it is seen that the positive resist-~25~ ance R at¦the latio of S+/S- of 0.2 increases to four or four times that at the ratio o 1.
The tendency~oE the pos~itive resistance characteristic ; ~as shown in Figure 13 can be observed wlth the spacing o .

:
36~-:, ~
I ;~

~ '7~ ~
I
5 mm betwcen the both electrodes 1 and 2 filled with the dischargeable gas including neon, helium, a mixture of neon and argon, or a mixture of heliurn and at most 30% by volume of hydrogen under a pressure of 200 ~orrs or less.
Also experiments have been conducted with the DC
source 3 having varied regulations of the source voltage.
The results of the experlments are shown in Figure 14 wherein the axis o-E ordinates represents a regulation of source voltage in percent and the axis of abscissas represents a ratio of the actual discharge current I to a rated discharge current Io in percent. Straight lines labelled 125 and 126 describe the regulations of source voltage with the positive resistance R having value of 1 and 3 ohms respectively.
From Figure 14 it is seen that a variation of 15%
in source voltage gives a current regulation or a ratio of the actual current I to the rated discharge current Io multipled by one hundred in percent ~42% and ~14% with positive res~istance R of 1 and 3 ohms respectively. Thus the positive resistance R of 3 ohms renders the glow discharge relatively stable.
~ Further by rendering the positive value R higher, it is po~sslble to control a maximum current for supplying a predetermined~electric~power to a small msgnitude which is, in turn, advantageous in that the glow discharge apparatus is made compact. ~ ~
The measure as nbove descrlbed is also applied~to constructions in which the AC voltage is applied across the electrodes l~and 2 to cause the glow discharge thereacross ; ~ ~ ", ~ ~ 37 ~ : ~

~ 3~
,.
.,, only when the electrode 1 acts as a cathode electrode.
From the foregoing it is seen that the arrangement o Figure 11 eliminates the disadvantages of conventional glow discharge heating apparatus that the positive resistance for the glow discharge is low, the glow discharge is moved about on the electrode, the discharge current much changes with a variation in source voltage resul~ing in the necessity of connecting a stabilizer or like to the source and so on. Those disadvantages have been caused -from the cathode area substantially equalling the anode area.
Figure 15 shows a modification of the present invention operatively associated with an AC source. The arrangement illustrated comprises an inner electrode 1 in the form of a hollow cylinder having one end closed, an cuter electrode 2 in the form of a hollow cylinder having cne end open and disposed coaxially with the inner electrode 1 so that the closed end portion o~ the innsr electrode 1 is inserted into the opened end portion of the outer electrode ~' ~ 2 to form an annular discharge gap 8 therebetween.
The inner electrode 1 is coaxially disposed within a tubular glass enclosure 9 to extend beyond both open en~s ~;~ thereof an~d the open er.d portion of the electrode 1 is rigidly fitted into an annular supporting disc 13 of any ~-suitable metallic material including an outer periphery ~25 ~ connected to the adjacent end of the enclosure 9 through the seal fitting ll. The outer electrode 2 has the open end '':
~¦ ~ portion extendlng into,the enclosure 9 and supported to another annular supportin~ disc 14~o the same`material as : : ' '~ ~ ` : ::
~: ~ : : ~ :
: .

1 ~
~ .

)73~
..
` .
the disc 13 similarly connected to the other end of the enclosure 9 through another sela fitting 10. In this way the enclosure 9 defines a hermetic space 81 with the supporting discs 13 and 14, the seal fittings 10 and 11, the inner electrode 1 and the outer electrode 2 having the other end closed.
Then a pair of terminals 5 and 6 is attached 1:o t]le supporting discs 13 and 14 to connect both electrodes 1 and 2 to an AC source 3~ therethrollgh.
; lO An inflow tube 15 is coaxially disposed within the inner hollow electrode 1 to form an annular passageway therebetween. Ihe tube 15 is maintained in place through a closing member 16 rigidly fitted into the open end of the inner electrode 1 and having the tube 15 extending there-through. The inner electrode 1 is provided on the open end portion with an outlet duct 17.
~n the other hand, the outer electrode 2 is double walled and provided on the closed end portion of the outer wall with an inlet duct 18 and that portion thereof adjacent to the supporting disc 14 with an outlet duct 19 communicat-ing with the inlet duct 18 through an annular space defined ~y the inner and outer walls of the electrode 2. A liquid to be heated~,~for example, water enters the inlet duct 18 as shown at the arrow A in Figure 15 and thence to the annular;space due to the double-walled structure of the outer --electrode 2 after which it leave the outlet duct 19. Also water enters the inflow tube 15 as shown at the arrow C in Flgure 15 and thence the annular space be~ween the inflow ': : ~ : , .' ~ , : ' "
~ - 39 -: ~ :
, , ~ '':' ~ 3~

¦ tube 15 and the inner electrode 1. Then the water flows out from the outlet duct 17 as shown at the arrow D in ¦ Figure 15.
¦ It will readily be understood that the space 81 is ¦ filled with an easy dischargeable gas as above described in conjunction with Figure 11.
l In operation an AC voltage across the source 31 is ¦ applied across both electrodes 1 and 2 to cause a glow I cischarge mainly in the annular discharge gap 8.
¦ As above described, the inner electrode 1 is inserted into the outer electrode ~ to overlap the latter.
This ensures that an area of that portion o-f one of the electrodes opposite to the other electrode is smaller than ¦ an electrode area with which a glow discharge can occur ¦ between the electrodes 1 and 2. This means that an anode ¦ area on the side of that electrode acting as an anode for I the glow discharge is always limited. For example, with the ¦ dischargeable gas maintained under a pressure of about 200 : ¦ Torrs and with the gap between both electrodes having a ¦ length not exceeding 5 millimeters, the limitation of the I ¦ anode area results in an indirect limitation of an associated ¦ negative glow reglon and therefore an increase in positive resistance for the glow discharge. That is, the current-to-¦ voltage characteristic of the glow discharge such as shown ~ ¦ at curve Tl in Figure 8 has a larger slope whereby the AC
~; ¦ glow discharge can be maintained stable. Accordingly, a ¦ stable glow discharge can be sustained even with a high current under a high pressure without the glow discharge ,, ~ , - :, . .

110'~'3~ 1 changed to an arc discharge.
Under these circumstances, a either of the inner and outer electrodes l and 2 respectively is heated when it acts as the cathode electrode resulting in hea~ g of both electrodes. Thus the fluid such as water flowing in contact with the elec~rodes is instantaneously heated and the heated fluid leaves the outlet ducts 17 and 19.
Figure 16 is a characteristic curve i]lustrating the relationship between the area of one of the electrodes overlapping the other electrode and the positive resistance exhibited by the glow discharge. In Figure 16 the positive resistance R in ohms is plotted in ordinate against a ratio of the overlapping area to the entire area of the electrode acting as the cathode in abscessa. Curves labelled 127, 128 and 129 have been plotted with the discharge gap 8 having a length not exceeding 5 mm and iilled with a mixture of helium and hydrogen under pressures of 100, 150 and 200 Torrs respectively. The vertical segment has the same meaning as that shown in Figure 4.
From Figure 16 it is seen that the smaller the overlapping area for both electrodes 1 and 2 the higher the positive resistance wlll be.
; In the~arrangement of Figure 15, the inner and outer electrodes 1 and 2 respectively are disposed in coaxial ~25 ~ relationship but different in shape from each other. There-fore the curren~o-voltage characteristic of the glow discliarge is different between the half-cycle of the source 31; hav;ng the lnner electra~de l acting as a cathode and that ~': : ' .':

; ~ 41 - ;
~ : :
- ~ ~ :, :, , - ~ .

ll`U~3Sl having the outer electrode acting as an anode as shown in ¦ Figure 17. In Figure 17, the axis of ordinates represents ¦ a discharge voltage V and the axis of abscissas represents ¦ a discharge current I. When the inner electrode 1 acts as ¦ the cathode, the discharge current I is forwardly and ¦ rearwardly changed along a straight line 130 shown in l Figure 17 and has a maximum value of Il. In the next ¦ succeeding half-cycle the outer electrode 2 takes over the ¦ cathode and the current is forwardly and rearwardly changed ¦ along a straight line 131 shown in Figure 17. In the latter ¦ case, the current has the absolute maximum value I2 different from that of the current I2 flowing in the just preceding half cycle of the source 31. Both straight lines have the I same absolute values of a voltage VO at a null current.
¦ Thus the resulting characteristic become unsym~.etric to -~ ¦ permit a ~ero-phase sequence component o-f a current to flow ¦ through the AC source 31. This is objectionable to the source 31. Further the inner electrode 1 is free at one end but the outer electrode 2 includes no free end. This resul~s ~20 I in the occurrence of thermal strains in the outer electrode 2 during the glow discharge.
These objections can be eleminated by still another modification~of the present lnvention shown in Flgure 18.
I In the ar;rangement illustrated, a first electrode l in the ~2~5 ~ form of a hoIlow cyllnder havlng one end closed with a -flat ~d~isc opposes to a second electrode 2 1dentical to the first electrode to form a discharge gap 8 having a predetermined ~-spaclng~or gap length o~f d between the opposite closed end :: ~ : :
~ ;

~lc~l surfaces.
A Elow confining tube 20 or 21 of the double wall type inserted into the second or first electrode 2 or 1 respectively includes a central tubular yortion extending on the longitudinal axis of the mating electrode, a radially extended end wall to form :a predetermined gap betwecn the same and the internal closed end surface of the electrode and a peripheral wall extending in parallel to the internal peripheral surface of the latter to form also a predetermined annular gap therebetween. Each electrode 1 or 2 is provided on the open end portion with an outlet duct 18 or 17 communicating with the flow path formed therein w1lile annular blind cover disc 23 or 22 is rigidly inserted into the annular gap between the peripheral surface of the electrode l or 2 znd the outerwall of the tube 21 or 20 at the open end. The ; ~urpose of the -flow confining tubes 20 or 21 is to cause a fluïd to be he~ted to enter first the central tubular portion as shown at the arrow A or C in Figure 18 and flow along the internal surface of the mating electrodes at an increased cpeed to enhance the heat transfer between the fluid and the electrode and also to enable the -Eluid to be instantaneously heated. The heated fluid then flows out from tlle outlet duct 18 or 17 as shown at the arrow B or~D in Figure 18.
Then the first and second electrodes 1 and 2 25 ~ respectively are sungly fitted into individual supporting rings 14 and 13 which are hermetically connected to both ends of circular enclosure 9 through annular seal fittings 10 and lI. In this way both electrodes 1 and 2 are supported :`: ;: :

- 43~ -..
:
~ ~ ~ :

.

~ 1L1~7~51 ..
., .
in cantilever manner to the supporting members 14 and 13 and the substantiall portions thereof are coaxially disposed within the enclosure 9 to form the space 81 that is then filled with a dischargeable gas such as previously described.
As in the arrangement shown in Figure 11 or lS, the AC source 31 is connected across the electrodes 1 and 2 through the terminals 6 and 5 connected thereto respectively.
In the arrangement of Figure 18 it is noted that those portions of both electrodes 1 and 2 superposing each cther as designated by the reference character 1 is made smaller in area than that portion of each electrode on ~hich the glow discharge occurs. In the example illustrated : the glow discharge occurs on each of the electrodes 1 and 2 throughout the surface.
lS The arrangement o~ Figure 18 is characterized in that the electrodes 1 and 2 ~ormed to be symmetric abut a-gainst each other with the predetermined gap 8 formed therebetween. This results in the symmetric glow discharge characteristic as shown in Figure 19. In Figure 19 similar ao to Figure 17, the characteristics 132 and 133 are substantially symmetric and have respective discharge currents Il and I2 equal in the absolute value to ,each other.
Also, as the el~ectrodes 1 and 2 supported in contilever manner to the annular supporting discs 14 and 13 25~ respectlvely, the elect~rodes are prevented from breaking ; ~ due to,thermal stains.
~It will readily be understood that the gap 8 betwoen ; ~ both electrodes l and 2 should be dimensloned so that the ;`;
' ~ : ~ ~

~ ' . ' : : ;~

electrodes are prevcnted from contacting each other due to termal expansions thereof in operation.
As in the arrangement of Figure 15, an AC voltage across the source 3] is applied across the electrodes 1 and 2 to cause a glow discharge between the opposite surfaces thereof while a fluid to be heated enters the interiors of the electrodes 1 and 2 as shown at the arrows A and C
in Figure 18. Then the fluid flows through spacing formed between each electrode and the flow confining tube 21 or 22 to be heated with heat generated on the electrode 1 or 2 due to the glow discharge. Thereafter the heated fluid flows out from each outlet duct 19 or 17.
Figure 20 illustrates a modification of the arrange-ment shown in Figure 18. As shown in vertical section in ~15 Figure 20A, the electrodes 1 and 2 of the identical structure opposes to and somewhat offset each o~her to form a predetermined discharge gap 8 therebetween. As seen in side elevational views of Figures 20B and 20C, the electrodes 1 and 2 are in the form of rectangular boxes and therefore ~20 discharge surfaces thereof are rectangular and flat. Then ~ each electrode is provided on the rear surface with a pair ; of inlet and outlet tubes.
In~other respects9 the arrangement is substantially ~-identical to that shown in Figure 18. The electrodes 1 and 2 include the discharge surfaces identical in shape to each other and are oE the cantilever type so that the arrangement ~; exhibits the same results as that shown in Figure 18.
the ~rrangements of the presen~ invention shown : :
:

~ 73rj ~

in Figures 15, 18 and 20 the electrode material and impurities such as metallic oxides included in the electrodes might be scattered in the discharge gap during the glow l discharge and sticked to that surface portions of the S ¦ enclosure 9 facing the electrodes 1 and 2. This sticking of such metallic materials to the enclosure might lead to not only a danger that the seal fitting 10 and 11 are short-circuit with each other through the sticked ~aterials but Glso to a fear that, if the scattered impurities again adhere to the electrodes that the glow discharge will have transited to an arc discharge.
~he present invention also contemplates to eliminate ~he danger and fear as above described, by the provision ~f the arrange~ent shown in Figure 21. The arrangement illustrated is different from that shown in Figure 18 only in that in Figure 21 a pair of annular shields 24 and 25 ~ne for each electrode are disposed to surround the mating electrodes and face at least the internal surface portions of the enclosure 9 by having flare ends thereof fixedly 2~0~ secured to the Internal surface portions of the enclosure 9 respectively. Each shield 24 or 25 lncludes the substan-tial portion parallel to the asso~ciated electrode and ; ending short o~ the adjacent annular supporting disc 13 or 14. The shields 24 and 25 may be of an electrically ~25~ in~sulating or conductive material.
In operation;when the electrode material and the ~
~impuritles~ are emitté~d from the electrode~l or 2 and scattered ~in the discharge gap, they are stl~ck~ed~to that~surface of ~

~ :
~ ~ 46 ~ ;

: ~ .

I each shield 2~ or 25 facing the associated electrode and ¦ prevented from adhering to that inner surface portion of ¦ the enclosure 9 covered with the shield 24 or 25. Also ¦ the shield is effective for preventing the scattered ¦ electrode material and impurities from again adhering to the associated electrode.
The arrangement illustrated in Figure 22 is different from that shown in Figure 21 only in that in l Figure 22 a pair of annular electrodes 26 and 27 are buried ¦ in the annular shields 24 and 25 formed of an electrically insulating material respectively. Then a suitable voltage ¦ is applied to the annular electrode 26 and 27 whereby the scattered metallic materials are apt to adhere to the l shields 24 and 25.
¦ Figure 23 shows another modification of the arrange-ment illustrated in Figure 21. In Figure 23 the electrodes l and 2 are in the form of hollow flat discs and disposed in opposite relationship to form the discharge gap 8 having a predetermined gap length of d therebetween.
~20 The seal fitting lO in the form of a short hollow cylinder has one end fixedly secured to the peripheral portion of that surface of the electrode 1 remote from tlle elec~rode 2 and the other end in the form of a flange to an enclosure portion 91 in the form of an annulus. Then an annular shield disc 28 of electrically insulaJcing material is located between the annular enclosure portion 91 and the peripheral portion of the electrocle 1 by having a ~ittlng perpendicular to the same and connected to the outer :~ :

~ ~ , -; 47 - - ~

~ ' ; :
:-:

~ 735~

peripheral surface of the seal fitting lQ. ~he sealing fitting 11, an enclosure portion 92 and a shield 29 identieal to the components 10, 91 and 28 respectively are operatively coupled in the same manner to the electrode 2.
A toroidal metallic enclosure portion 93 of double L-shaped cross section is hermetically connected tc the annular enclosure portions 91 and 92 to form a hermetically closed space 81 in the form of a toroid.
As shown in Figure 23, a feed water tube 18 and a drain tube 19 project in spaced relationship from that surface of the electrode 1 remote from the electrode 2 and a pair of deflector or baf-fle plates 30 and 32 are disposed in the interior of the electrode 1 so as to direct a liquid to be heated toward the peripheral portion thereof and enter ~15 the fluid into the dra;n tube 19 after it has flowed along the heated surface of the electrode 1 to be heated. Also a feed water tube 18' and a drain tube 17 similarly project from the electrode 2 and a pair of baffle plates 33 and 34 are similarly disposed within the hollow electrode 2.
If desired, the shield 28 and 29 may be formed of any suitable me~allic materlal. In the latter case, the shields 28 and 29 are suitably insulated from the associated electrodes 1 and 2 respectively.
Further the present invention contemplates to prevent ~:25 the occurrence of electric shock-accidents through the heated llquid su~ch as water. ~
The arrangement illustrated~in Figure 24 is substan-all~ similar ~ tl-at shown In Figure 22 except for 'he ~- 48 - ~

~ : ~ :
: : ~

. ~ 3~i~
I
provision of means for preventing the user ~from receiving electric shocks. As shown in Figure 24, the con~rol tubular portion of the flow confining tube 20 or 21 is connected to an electrically insulating tube 37 or 38 that is, in turn, connected to metallic inflow tube 41 or ~2. .
The outlet of the flow confining tube 20 or 21 is connected to connecting tube 35 or 36 subse~uently connected to an electrically insulating tube 39 or 40 that is, in turn, connected to a metallic outflow tube 43 or 44.
The metallic tubes 41 and 43 are electrically connected together to ground as do the metallic ~ube 42 and 44.
:: It has been found that an end-to-end distance lp between the central tubular portion of the flow confining lS tube and the inflow tube or between the connecting tube and the outflow tube, that is to say, a length of the insulating portion should be equal to or less than a predetermined magnitude dependent upon a voltage applied across the electrodes, a resistivity of the particular liquid to be ..
heated, a cross sect~onal area of the tube etc. ....
-~ The arrangement of Figure 24 is operated as follows:
A switch 45 is closed to apply an AC voltage rom the source ~ 31 across the~electrodes l and Z. This causes the flow - :~ confining tubes 20 and 21, and the connecting tubes 35 and 25~ 3S to be put at a certaln potential re~lative to the ground potential. For example, in glow discharge heating apparatus having a dlscharge input of about 8 kilowatts, the AC source ~31 is required to supply to the heating apparatus an AC

:~ ~ ~
; - 49 -::: : : , .

: :' : , ':
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voltage having tl-e effective valué of 200 volts so that the tubes 20, 21, 35 alld 36 are put at a voltage havillg the effective value of 200 volts.
On the othcr hand, thc mctallic inflow tubcs 41 and 42 and the Inctallic outrlow tubes 43 and 44 are connected to ground so that the particular liquid ~Flowing into or out from the extremities thereof is put at a null potential. This cnsures that elcctric shock acci~ents are prevented from occurring througll the l;quid.
~lore specifica]ly, the source voltage is applied across the electrodes 1 and 2 to cause a glow discharge therebetween. Ileat generated during the glow discharge heats the liquid. When the heated liquid flow within the apparatus~ the same reaches any of the tubes 41, 42, 43 and 44 where it is put at the ground potential. This ensures that the user is maintained safe.
Under these circumstances the electrodes 1 and 2 rapidly transfers heat to the liquid flowing within the interiors tllereof to prevent the elec~rodes 1 and 2 from ~20 effecting an abnormal temperature rise whereby the stable glow disc]large is sustained.
llowever, as a potential difference having the ~; effective value of 20D volts occurs between the infiow and outflow tubes 41, 42 and 43, 44 and the confining and connecting tubes 20,: al and 357 36, the insulating tubes 37, 38, 39 and 40 must ~ave a dielectric s~rength withstanding a volta~e having the effect~ve evalue of Z00 volts. In this connection, it is required to consider a leakage ; :
: ~
:: : :
: ~ :
'.

~" .~ : , - - .

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current f~owing to ground thro~lgh the liqtlid, in ad(]ition to the sllrface status of thc insulating tubes.
In the arrangement of ~igure 24 applied to a water warmer operated with the so~rce voltage of 200 volts, the same is obliga-ted to be provided Wit]l a leakage breaker.
Leakage breakers are responsive to the leakage current in excess of the predetermined magnitl1de flowing through the inflow and outflow tubcs 41, 42 and 43, 44 to ground to be continuously operated to prevent the source voltage from being appliccl across the electrodes 1 and 2. Accordingly, it is required to impart to the lellgth Qp of the insulating portion a value suf-ficient to limit the leakage current to a certain value or less. `
Assuming tllat each of the insulating tubes 37, 38, 39 and 40 has a cross sectional area of flow path designated by S and a ligned ~o be heated such as water has a resistivity designated by p, the insulating portion presents a resistance Q before the liquid ex~ressed by . ~ ~ Q ' ~20 RQ, P S ~4) Also assumlng that each of the insulating tubes 37, 38, 39 and 40 has a surface resistance sufficiently large as compared with the resistance of the llcluid, the leakage curFent I Q~ may be expre9sed by ~

ll = RQ - VQ-pS- ~ Qp Q (5) ::
: : ~ :
:~ 51 : : ~ ~

~735~

wl~ere VQ ~lcsignates a voltage across the liclllid located in the insulating portion having the length Or Qp. ~ccordingly, the leakage current I~ is inverscly proportional to the length Qp with the voltage V~, the cross sectional area S and the S resistivity p remaining unchanged.
Figure 25 a graph illustrating the relationship between the length Q~ of thc insulating portion and the leakage current IQ on the basis of the above two exprcssions

(4) and (S) and with VQ - 200 volts, S = 0.636 square centimeters (which results from the insulating tubes 37, 38, 39 an(l 40 having the inside diameter of 9 millimcters) and p = 1300 ohms-centimeter. The resistivity of 1300 ohms-centimeter is a minimum value of a resistivity of usable water as determined by the IEC standards. In Figure 25 the leaXage current IQ in milliamperes is plotted in ordinate against the length Qp of the insulating portion in centi-meters in abscissa.
Assuming that the particular water warmer is provided with a highly sensitive leakage breaker having a rated sensible current of 15 milliamperes, the breaker has a rated inoperative current of 7.5 milliamperes. In order to preve~nt tllis leakage breaker from being continuously operated due to a leakage current ~lowing through the .
insulating portion, the length Q~ of the latter is necessarily ~5~ of at least 13 centimeters with used water having a resist-ivity of 1,300 ohms centimeter as will be seen from the curve of Figure 25. The expression (5~ indicates that the leneth Q~ changes wlth the leakage current1 voltage, the `: : . .
:; : ~ : ~ : :

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: : ' ::
~ ,.,,., . : :... ,., ., ~735~

cross sectional area of the flow path and resistivity of the liquid. Ilowevcr, a length of the particular insulating portion can be estimated as above described and in accordance with the rating of a given leakage breaker, the source voltage, a resistivity of the particular licluid and the cross sectional area of the flow path.
In the arrangement of Fi.gure 24, the flow path of the heated liquid has been provi.dect with the insulating tubes having the required length while each of the insulating tubes has been connected at the extremity to the metallic inflow or outflow tube that is connected ~o ground. Accord-; ingly, it is ensured that the any.electric shock accident can be prevented from occurring through a liquid involved and still one can eliminate the insulating treatment that electrode components are coated with an electrically insulating material. This results in simplified inexpen-sive apparatus and also the heat transfer~from the electrode components to the l1quid being rapidly effected. ~herefore ~: ; the arrangement of Figure 24 is extremely advantageous in ~ 20 ~ both the heat effeciency and the stabilit:y of operation. ~:
; ~ ~ Also glow d1scharge heat1ng apparatus such as shown :
in Figure 24 can be util1zed to instantaneously heat a l1quid,~for example, water by flowing the water in a flow .
rate of from 1 to 10 ;litres per minute t}lrough the interior 25 ~ of the electrodes the~reby to transfer thermal energy :
::: in jected 1nto the electrodes~to :the water. Under these circums~tances, water~at room~temperature~nlust be heated to e~pe~a e ~of abo~ 80'C ~A~ su s ~n ~the nec~ssity ~ ;
' ' :

11~'735~L

of injccting tilcrmal energy of at least 5 kilowatts into the e]ectrodes. Ih;s means that9 with a powcr source of AC 200 volts Ised, -the efrective current Or at leclst 25 ampercs must rlOw throu~h the c:lectrodes. If a discharge current becomes hi~h and also if the discharge gap is filled with a gas under an increasing pressure then it is dif~icult to sustain the flow discharge. For exarnple, the glow dis-charge transi-ts to an arc discharge.
It has been found that the stable m~intenance oE the glow clischarge is affected by the type of gas filling the discharge space. ~lso it has been experimentally confirmed that, by filling tlle discharge space with a mixture of at least helium and hydrogen, the glow discharge can be sustained without the transit to an arc discharge, even Witll an electric power required for heating the p~rticular liquid, that is to say, a discharge current as high as possible.
This will now be described in conjunction with Figure 24. Various experiments were been conducted with the discharge space 81 filled Wit]l an inert gas heavier than argon under a pressure ranuing from 50 to 200 Torrs. The result of experiments indicates that the glow discharge is difficult to spread and that an increase in glow current causes a contraction oE a positive column included in the glow discharge to move the glow discharge about on the electrodes 1 and 2. Thus the glow disch~arge is put -;~ in it~ unstabLe state so that it lS apt tG transit to an arc~ discharge The mean value of the glow current in excess of .' .
' :~ ~ ~ : : : .. :
: 5 ~
~: ~ , : , ~ ' .

~ ~: , - , . .

1 13735:1

5 aml)eres has caused the glow discharge to transit to an arc discharge.
l~ith neon used, relatively stable glow discharge has occurred under a gas pressure not higher than 70 'I'orrs.
Under a gas pressure of lO0 Torrs, however, the glow discharge has been relativily stable at the deerctive current up to about 20 amperes. Upon the effective current exceeding 20 ampere, the positive column has becn contracted. This might cause the glow discllarge to transit to an arc discharge.
Further, when an inert gas used has been heavier than neon, the scatter from the elcctrodes l and 2 has increased in amounts with the result that the electrodes 1 and 2 are violently consumed while insulating materials such as glass f~rming the enclosure 9 is sharply deteriorated in electrical insulation because metallic materials scattered from the elcctrodes 1 and 2 are sticked thereto. As a ' result, the useful life of the glow discharge heating appara-tus has been much reduced.
From thc foregoing it is sulllmerizoa that, with the .
arrangement of Figure 24 used as a heating apparatus for instantaneously heating water, it is required to sustain stably the g~low discharge under a relatively high pressure of 50 Torrs or more and still at a high current exceding 25 amperes at an AC voltage of 200 volts. ~ ' 25 ~ Also rrom the foregoing it has been found that it is des~irable to flll the dischdrge space 81 with a chemically ~stable, iight~ inert gas and suitabIe examples of the inert ;gas involve~ helium and hydrogen.
~ :

~ ~ 55 ~ ~
: ~ :
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11073~1 In the arrangement of Figure 24, however, it has been seen that, with helium fil]ing the discharge space 81, the flow dischargc s~reads througho~t the surface of the electro~es 1 and 2 at low current because of a small currerlt S density and that electri.cal energy o~ the glow discharge entering the electrodes l and 2 amounts only to about 2 Killo~atts. Also in a glow clischarge caused in an atmosphere of helium, its positi~e cloumn has been contracted upon a pressure of helium increasing to 150 Torrs to increase a current density for the glow discharge. Thus the glow discharge has been moved about on the electrodes and become unstable. Ihe glow discharge has often transit to an arc discharge.
On the other hand, a glow discharge in an atmosphere lS of hydrogen has made a discharge hold minumum voltage Vo equal to at least 240 volts as shown in Figures 30, 31 and 32 which will be described hereina~ter. Therefore, it has been difficult to cause a glow discharge having an electric power of S kilowatts or more by using an AC source with 200 volts.
It has been found that, in ord:er to manufacture glow discharge heating apparatus requiring at least S kilowatts with an AC~voltage o~ 200 volts, it is optimum to employ a mixture of helium (Ile~ and hydrogen (~l2) as a filling gas.
; ~Whe;n the arrangement of Figure 24 1s filled wlth a mixture of helium and hydrogen under a pressure of 100 Torrs~, and applied~wlth an AC volta~e of 60 hertzs having a waveform E shown i~n Flgure 26, a glow current~flowing ~ , : . : ~ ::

~ 7 3~ 1 therethrough is changed in accordance with a proportion of hydrogen to helium as shown at current waveforms F, G, H
and I in Figure 26. Eigure 26 shows the voltage and current waveforms in one cycle of the source volta~e. l'he current waveforms F, G, 11 and I have bcen plo~ted with gaseous mixture including 5, 10 30 and 50 % by volume of hydrogen and the balance, helium respectively.
Also the glow discharge exhibits the current-to-voltage characteristic dependellt upon ~he proportion of the hydrogen to the helium as shown in Figure 27 wherein a voltage in volts is plo~ted in ordinate against a current I
in amperes in abscissa and like reference characters have been employed to identify the helium-hydroge mixtures identical to those designated in Figure 26. As shown in Figure 27, each of the current-to-voltage characteristics is substantially rectilinear. By calculating both values of glow voltages S, T, U and W through the extrapolation and slopes of respective characteristic curves, the glow voltage Vg may be a~proximately expressed by Vg = V0 ~ RI
: ' ., where V0 designates a glow discharge hold minimum voltage designated by S, T, U or W, and R designates the slope of 25~ ~ the characteristlc ca~led the positive character1stic R.
As well known9 the voltage V0 is~expressed by V0 = Em sln ~t~
where, Em designates the peak value~ tllereof and~ designates ~ -an angular~frequency of the source voltage. To calculate a : ~
~; : ~ ~ : :; ' :
~ :: ~ ~

: ~ , l ~ 3 5 ~

discharge power P form the above expression for VO referring to Figure 26 givcs IR ¦ (F.m sin wt - Vo) Em sin wt dt = -rER~ { ]-Tr.m Em sin lVE
' 10 Vw cos(sin l VEm) }

lS where ~ designates a period of the source voltage. The discharge voltage is thermal energy entering the electrodes 1 and 2 due to the glow discharge.
Assuming that the source voltage has its fre~uency of 60 her:tzs and 200 volts or the peak value of Em = J~ 200 ~ 280 volts7 its period Is of 16.67 milli-seconds and its angular -Erequency is of 377 radius per second. By using those figures in the expression for the discharge power, the glow discharge hold minimum voltage VO relates to the positive characteristic R as shown in 25 ~ Flgure~28 wherein the positlve resistance R in ohms is plotted in ordinate a~alnst the glow hold minimum voltage VO in volts in abscissa with the ~arameter being the discharge power or thermal energy P.
: ~ ~ :

; ~ ; ~ ~,.. ,~ .'- ' ~ ~ - 5~ -~ :: : ~
~: : : ~:

i~L073~1 From the Figure 28 it is seen that, in order to provide thc the]mal energy not ]ess than 5 kilowatts, the VO and R may lie in a h.ltched region as shown in Figure 28 defined hy a line for thc l~ower of 5 kilowatts, alld both coordinate axes.
Also the glow hold minimum voltage VO is determined by a pressure of a filling gas and the gap length d between the electrodes 1 and 2 wllilc the positive character-istic R is determined by the configuration of the electroclcs of the overlapping area SO for both electrodes 1 and 2 and the pressure of the filling gas.
By cl~angillg a relative diameter M of one to the other of the electrodes 1 and 2 to vary ~he overlapping area SO therefor and also by cllanging the pressure of the filling gas, the positive characteristic R is varied as shcwn in Figure 29 wherein the overlapping area SO in square centimeters is plotted in ordinate against the pressure of the filling gas in 'rorrs in abscissa with the positive characteristic R varlously cllanged. In Figure 29 solid line indicates measured values and dotted line indicates values estlmated from the associated measured values.
; From Figure 29 it is seen that, under a gas pressure less than 50 lorrs, a currellt dens~ity for the glow discharge is low and the supply o~ a discharge power or a heat input in excess of 5 kllo~atts to the electrodes requires an increase in owerlapping area S. This has encountered the problem in the portability because the~electrode area must increases, ~ ~
: ~ :
: :' :~ : :
~ : ~; ' 11~735:1 ~n the otller hand, a gas prcssure in c~cess of 150 Torrs ca-l~cs t]lc discharge input to tlle clcctTo(3es to increasc to at least 5 kilowatts, resultin~ in a glow current of at least 25 anlp~res. ~Jn(3er these circulllstances a positive column involved is contracted and the particular glow discharge is moved about on the clcctrodes. rhis might sometimes cause thc ~low discllarge to transit to an arc discharge .
l~itll the gas pressure furtller increased to 200 Torrs ]0 or hi~het, a l-os;tive column involvcd is contracted at a glo~Y currellt of at least 5 ampercs until the transit to an arc discharge occurs.
~s an example~ it is assuTned that the glow hold minimum voltage VO is imposs;ble to decrease to 176 volts or less. Under the assumed con~ition~ it is seen from ~igure 28 that, in order to manufacture glow discharge heating ap~aratus llaving a discharge input of at least 5 kilowatts, the prcssure of the particular filling gas, the overl.~}~in~ arca ~O al)d the l~ositivc charactcristic l~
~ Z0 must lie ;n the hatched portion sho~n in Figure 29 as being ; defined ~y a pair of vertical broken lines passing through the abscissas of 50 and 150 Torrs respectively and curve labelled R = 2Q ~ -In adclition, by changing both the proportion of 25 ~ hydrogen to helium and the gap length d between the electrodes l and 2, the glCJ~V hold minimum volt~ge VO is varled as ~
shown in rigures 30, 31 and 32 wherein the axis of ordinates re~resents the pro~ortion of hydrogen to helium in percent ,~ ~ :: : -, : "~

~ : ~ - : : : : . , ~ : : :

~ ; ; ~`~'~ ~., ~:' ~ ~ . .;., . .,.~, . . ~ ., ",. , : ' ~lU~35~

and t~)e ~IXiS o~ ~lbscissas rcprcsents the gap len~th d in millimeters. The ]~elium-]lydrogen Inixture is maintained under l~ressures Or 50, l0~ and l50 lorrs in Tigurcs 30, 31 and 32 rcsl)ce~ively. In tl~ese l:igl]res curvcs ~re lilbcll~d measured values o-f the glow hold minimum voltage V~ and for pure hydrogen the measured voltages VO are denoted aside correspondillg dots.
Also the gap lcngth d less than about 0.5 millirneter between both electrodes 1 ancl (2) has resul~ed in a danger that bot]~ electrodes may contact ~nd sllortcircuit each other due to a pressulc difference betwccn a pressure of the particular heated liquid within ei-ther oE the electrodes and that of a filling gas involved. On the other hand, an excessively large gap length d between both electrodes cause a positive column to constract to move the resulting discharge about Gn the electrodes until the discharge sometimes ~ransits to an arc discllarge. This might result in a cause for damaging the e]ectrodes 1 and 2. It has been seen that the contraction of the positive column occurs with the gap length d of at least 9, 6 and 3 millimeters :
under the gas pressures of 50, 100 and 150 Torrs respectively.
With the p2 oportion of hydrogen to helium decreased to 2.5% or less, the resulting glow discharge resembles that occurring in an atmosphere of pure helium. This has 25~ made it difficult to increase the discharge input to at least :
~;5 kilowatts. Also as Figure 29 descri~bes that it is difficult ~to decrease the pos~itlve chara~cte~ristlc~R to at most 1,~0.5 and 0.3 ohms under gas pressures of 50, 100 and 150 Torrs : ~ ~ : .' : ~
~ ~ 61 -: ~

11~073~

rcspectively, it i)as becn difficult to incrcase t]~c d-ischarge input to at least 5 kilowatts at the glow hold minimurn VOlt;lgCs Vo Or ~It ]cast 2]0, 2~0 alld 24n volts under the gas prcssules of 50, lO() and 15() rorrs respectively as will readily be urlc1erstood rrorn t]-e graph shown in ~igure 28.
Further an increase in glow hold minimum voltage VO causes an increase in peak vialue of tlle glow curr~nt as shown in Figure 33 w]lelein the pcak curre1lt ror the glow ~ischarge in aml~eres is plotted in ordi1late agaillst the ~low hold millimuin voltage VO in volts in abscjssa. 1`his has rcsulted in the disadv.1lltagc that the rcsl1lti1lg appaiat1Js sl~ould be made larger.
~rom the foregoing it will readily be understood that the proportion of hydrogen to helium and gap length - lS d between the electrodcs l and 2 are desirably located in dotted closed areas S]lOWII in Figure 30, 31 and 32. ~lore syecifically, the ~roportion of~hy-lrogen is not less than 2.5% and the gap lcngth d is not less than 0.5 millimeter while the voltage VO has values of 2l0, Z~0 and 240 volts dependent upon the pressure of the filling gas.
While the present invention has been described in conjunction Wit]l an AC source havjng a voltage of 200 volts it is to~be understood that It is cqually applicable to AC
sources having the voltage higher than that of 200 volts, ~or ~25~ example, the voltage of 400 volts. In the la~ter case, the .
glow corrent~may be low by using a heliu~m-hydrogen mlxture including not less than 50% by volume of hydrogen which is effective for increasiJ1g the glow ]lold minimum voltage VO
:~ ; .
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. ~73~ .

s}-own at any of the points S, 1', U and W illustrated in Figure 27. 'I'his provides a stahle glow discharge while being able to decrease the surface area of the e]ectrodes 1 and 2. In addition, wiring leads may be fine. Therefore the rcsulting ap~aratus can be made coMpact.
Examples of the electrode material rnay involve copper, aluminum, nickel, pure ion, molybdenum, stainless steel, Kovar (Trade mark) etc. used with vacuum tubes or voltage regulator tubes. I-lowever, copper is not suitable for use in the present invention because the copper has a high current density for the glow disch~rge to enhance the sputtering thereby to deteriorate seversely the insulation of associated insulators. Also aluminum is not suitable for used in the present invention because a glow discharge involved transits to an arc discharge with a current as low as one ampere. Therefore suitable examples of the electrode material involve nickel, pure iron, molybdenum, stainless steel and Kovar ~Trade mark~. 'I'he electrode used with the present invention has been formed of sheet nickel or stainless steel one millimeter thick.
From the foregoing it is seen that the filling of ~; ~ the discharge space 8 w~th a mixture including at least ' helium and hydrogen can eliminate che transit of the glow to .
an arc discharge and ~he sputtering with a hlgh discharge ~ current. This gives the result th~t a st~ble glow discharge can be sustained. The reason -for which the glow discharge can be prevented from transiting to an arc dlscharge is to remove oxides OA ~he surface of tbe~elec~lodcs by the hydrogen ~: : : ~
~ . - 63 -; ; :

., , .

~ 35~ ~

included in the filling gaseous rnixture.
The ~se of the helium-hydrogen mixture is also advantageous in that, only by changing the proportion of the hydrogen to the helium, the glow hold minimum voltage can be selected at will to control the discharge input to both electrodes involved as desired.
Figure 34 shows still another modirication of the present invention. The arrangement illustrated is different from that shown in Fi~ure 24 only in that in l~igllre 34 the opposite surfaces of the elcctrodes 1 and 2 are corrugated to increase the surface areas of the elect-rodes and an auxiliary electrode 46 is operatively associated with the ~ap 8 formed between the electrodes 1 and 2 as will be subsequently described.
In glow discharge heating apparatus having the discharge lnput of 5 kilowatts, for example, the diameter M of the electrodes 1 and 2 is re~uired to be of at least B0 millimeters and also that of the insulating enclosure 9 is necessarily of at least 100 millimeters. In other words~
the larger~the diameter of the electrodes the larger the enclosure 9 and therefore the seal Elttings 10 and 11 will `~ be. This is attended with the disadvantages that the compo-; ~ nents become excessively expensive and also a manufacturing ..
`~ cost l S increased.
2~5~ In addition, the opposite surfaces of the electrodes l~and 2 are can be forced toward each other to be crowned in response to a difference between a pressure within discharge space 81 and a pressure of a heated liquid withln : ~ ~ ~ ' , , ~ - 6~ -;~~ - ' :~ :~
: ~ ~ .~ ' ~ 'J I 3~

each electrode so that the bending o:E the electrodes increases to be proportional to the -fourtl1 power of the radium M/2 thereof. Accordingly, ~n increase in diameter o-f the electrodes may causes thc electrodes l and 2 to contact and short circuit cach other due to the crowning thereof.
To avoid this objection, the o~osite surfaces of the electrodes l and 2 have a diametric section of corru~ted shape to ir.crease areas of the op1~osite electrode sur~aces with the diameter of the electrodes remaining unchanged.
In the arrangement of Figure 34 each electrode l or 2 has the diameter M oI 52 millimeters an~ the area of 80 square centimeters of that surface t11ereof opposite to the other electrode 2 or l.
As shown in Figure 34, the auxiliary electrode 46 is lS extended and sealed through the insulating enclosure 9 so as to center the gap 8 formed between the opposite corrugated ; surfaces of the electrodes l an~d 2 and to be substantially contacted at the free end by the adjacent portion of the edge of the gap 8.
T11en the Ac source 31~is connected at one end to the ;` electrode terminal 5 tl1rough a normally open switch 45 and at tlle other end di~rectly to the electrode terminal 6. The auxiliary electrode 46 is connected to the electrode terminals :: ~ :

6 and~5 through respective resistors 47 and 48 and also by 25~ a res1stor;49 to one output of an~auxlliary source circuit 50.
;~The~aux~ ary:source~circuit 50 1ncludcs the other output connected to the electrode terminal 5 and ti1erefore the switch 45~and~ls also~connected to~the sw~1tch 45 through ~ ~
~ :: : '. - ;
~ : ~
65 ~
: : ~ : : ,,.~,, ~ 3s a another normally open switch 5l and to t1 ~ other end of the AC source 31. The operation of the abovementioned circuit configuration will be described hereina-Eter.
With the ~uxiliary elect:rode 46 operatively associated with the discharge gap 8 as in the arrangement of Figure 34, the electrodes 1 and 2 are called hereinafter the "main electrodes" to be distinguished from the auxiliary electrode 46.
In the arrangement of Figure 34 a glow discharge is fired between the main electrodes 1 and 2 after which the glow discharge is smoothly spread on the corrugated surfaces la and lb respectively of the main electrodes 1 and 2. Under : these circumstances, a high current can enter the opposite . corrugated surfaces of the main electrodes 1 and 2 as ~ 15 compared with pairs of discharge electrodes including t~he opposite flat surfaces. Therefore, the discharge input to the electrodes increased while the voltage across the main electrodes~remains unchanged.
~ : ~ : -As a result, the~corrugated surface of the main electrodes permits a decrease ln diameter thereof attended -with a~ reduction~in diameter of each of the insulating ~
enclosure 9 and the~seal fittings 10 and 11. Accordingly a :
~manufac~turlng cost can~be decreased~. ~Also the corrugated ~ :
surface;of the main electrode is efective for preventing 25~ the;crowning of the~opposite surfaces thereof. ~ : -- :
The opposite surface la of the main electrode I :
shown In~Flgure 35~lncludes a ~lurall~ty of grooves of rec~angular`~cross section .o^centrlc-lly dl~p~sed at subs- n-~

66~

:

~ 73~ il tially equal intervals thereon.
Figure 36 shows a plurality of parallel grooves disposed at predetermined intervals on the discharge surface la of the main electrode 1.
S The discharge surface la of the main electrode 1 shown in Figure 37 includes a plurality of cylindrical depressions disposed in a predeterrlined pattern thereon.
In the arrangement shown in Figure 38, a pair of flow confining blocks generally designated by the reference numeral 200 and 210 respectively are of the same counstance-tion and disposed in place within the main electrodes 2 and 1 to form heating spaces or flow paths 2A and lA for a heated liquid therein respectively. The flow confining block 200 is formed of an electrically insulating material such as a synthetic resinous material and includes a feed : water tube 201 and a drain tube 2r)2 formed in parallel relationship on the exposed end surface thereof to be integral therewith and through openings 201a and 202a connected to t]le tubes 201 and 202 respectively. Then openings 201a and 202a open on that end surface thereof facing the inside of ehe gap forming surface of the main electrode 2 and a peripheral surface thereof respectively.
The tube Z01 and the opening 20a interconnected serves as a -feed water tube opening in the flow~path ZA while the tube 202 and the opening Z02a interconnected serves as a drain tube~also openin~ in the flow path 2A.
The~f:low confining block 210~ 1nc1udes a feed water~
and~a~dra1n tube identical to those a~s above descrlbed in ;
: ~
~ ; : : '-~ ~ 67 - ~
~ ', 11~3 ~'3~

conjunction with the flow confiri.ng block 200 and designated by like reference numeral identifying the corresponding components of the confining block 200 and added with the numeral 10. For example, the reference numeral 211 designates a feed water tube.
The flow confining blocks 200 and 210 have the exposed end portions screw threaded through the blind cover plate 22 and 23 fixed to the open end portions o-f the main electrodes 2 and 1 to be flush with the open ends thereof respectively.
In other respects, the arrangement is substantially identical to that sho~n in Figure 34 except for the omission of the insulating tubes 37, :38, 39 and 40 shown in Figure .:
.- . 34. ,' In the arrangement of Figure 38, t,he flow confining blocks 200 and 210 can be removed from the blind cover .. ..
plates 22 and 23 respectively fo~r tlle purpose of inspecting : or cleaning the internal surfaces of the main electrodes 2 and 1. Therefore the heating efficiency can be always "
maintained high. ' :~ Figure 39 shows modification of the arrangement shown ln Flgure 15 wherein the user is accessible to the ,, heat transfer surfaces of the main electrodes as in the ., ; arrangement~of Figure 38 and an auxiliary electrode 46 is operatlvely as:sociated with the discharge gap 8. As shown in ::~ Figure 39 a flow confining tube 200 in the form of a hollow ~ cylinder~:having both ends open is coaxially disposed within :~ the maln~electrode l to form a flow path for a heated :liquid therebetween. The cylindrical tube 200 is screw 68 ~
:: :

;~ ' ', ' '' ' ' ' . .

73~

thr~aded thl-o~lgll a scr~w melnl)er 200a rigidly ritted into the o~en end of the main electro~le l.
~imilarly a1l0tllcr ~[]ow ~onfining tube 210 in the form of a hollol~ cylindcr having one end closed i~ de~achably connected to t]lC main electrode 2 at the outwar(lly folded end through a screw member 210_ formed internally with the tube 210 to form an annular f~ol~ ~ath for tile heated liquid therebetween.
T]le -rlow confining tuhes 20~ and 210 are of an electrically insulatillg material such as a synthetic resinous material.
As in the arrangeTnent of Figure 38, the flow confining blocks 200 and 210 can reaidly be removed from the main electrodes 1 and 2 respectively for purposes of inspection and cleaning.
In otller respects, the arrangement is substantially similar to that shown in Figure 1~ excepting that electric shock preventing means such as above described in conjunc-tion with Figure 24 are provided on tlle feed water and drain ~;~20 tubes 41, 42 and 43, 44 and the auxiliary electrode 46 is operatively coupled to the gap ~ formed between the main ~` opposite electrodes l and 2.
Figure 40 shows a different modification of the ;~ present invention enabled to decrease the dimension of the ~, 25 electrically insulating enclosure and still increase the ~dlameter of the main electrodes. In the arrangement llustrated a~air of n-ain electrodes l and 2 identical~to ~each other~are horizontally~disposed In opposlte relationship : :' ~
~; ,~
:

~ 7~

to form a discharge gap 8 ~herebe~ween. Each of the main electro~es 1 or 2 is in the form of a hollo~J cylinder having one end closed and the other end portion lB ~r 2B reduced in diameter. The closed flat ends of both main electrodes 1 and 2 form therebetween the gap 8 having a width or a gap length of d and a diameter of M.
~ach electrode 1 or 2 incllIdes a shoulder connected to an electrically insulating enclosure 9a or 9b in the form of a narrow annulus througIl a first annular seal fitting lOa or lla. Thus the enclosures 9a or 9b eIIcircles the reduced diameter end portion lB or 2B of the main electrode 1 or 2.
Then a cylindrical metallic shell 9c or 9d encircles in spaced relat;onship the adjacent main electrode 1 or 2 and , includes a radially inward directed Clange connected at one end to the enclosure 9a or 9 through a second annular seal fitting 10_ or llb. Both shells 9c and 9d have the other end.s abuttin~ against and fixed ~ogetIler as by welding.
Thus the shells 9c and 9d and the main electrodes 1 and 2 form therebetween an annular dIscharge space 81 including~the 20~ gap 8 with tlie enclosures 9a and 9_, the seal fittings lOa, lOb, ~la and 11_. ~
The lI~nd coveI,~la~e 22 or 23 Is rigIdly fitted into the open end of the main electrode 1 or 2. A feed .;, ~ ; :
water tube 41 or 42 is extended a~nd sealed through the ;~25~ blind c'over pl;ate 22~ or 23 and has an outlet opening ~ ' substantially ~flush with the internal surface of the cover : ~ :
~;pl~ate 22 or 2~.~ Als;o a draIn tube 43 or 44 is extended and~
~se~Ied through~the~bIInd,cover plate 22~F~23~and~has~an end : .
~ 70 -~

~ .

portion bcnt into an L in order to fill a heating space lA
or 2~ formed of t]-e interior of the main electrode 1 or 2 with a li~uid to be h~ated The en~ of the ].-shape tube 43 or 44 faces the upl-ermost portion of -the internal surface of the main electrode 1 or 2 witl- a distancc QO maintained therebetween.
Further, the auxiliary electrocle 46 and an associated electric circuit are provided in the same manner as above described in conj~lnction with Figure 34 The main electrodes 1 and 2 may be of any desired shape other than the cylindrical sh.lpe as above described.
As the main electrodes 1 and 2 are of the same structtlrc, thc operatiotl wil] TlOW be described in conjunction of one of the electrodes, for example, the elec-trode 1.
A liquid to be heated entcrs the heating space lA
through the feed water tube 42 as sllown at the arrow A in Figure 40 until its liquid surface reaches a level at which the drain tube 44 opens while the liquid is heated by the main electrode 1. ~hereafter the heated liquid is 20~ exhausted from the space lA through the drain tube 44 as shown at the arrow B in Figure 40. The outflow af the liquid causes a pressure loss across the drain tube 44 permitting the heated llquid charged in the hea~ing space lA to have a pressure~higher than the atmospheric pressure. In keeplng ~with this increase in pressure, the surface of ~he liquld within the heating space lA is forced to be gradually raised beyond the open cnd of the clraln tube 44 resulting a decreas~ ln~vol~me of a cavity exist~ng in the heating ~ - 71 -~ ~ : ~ : :
:: .
. , ~
. - . . . . :, - ~ ~ - .. : . . .

space lA.
In this case, the smaller the diameter of the drain tube 44 will be which is ~ccompanied by an increase in speed of the liquid flowing thro~lgh the drain tube 44. As a result, the open end of the drain tube 44 is less in pressure than the cavity within the heating space lA. This causes an increase in rate at which the drain tube 44 sucks up air leEt within the heatin~ space lA.
It has been experimen-tally proved that the distance Q exceeding 10 millimeters causes the air phase in the heating space lA to be too far spaced from that ~ortion of the liquid just flowing throu~h the open end of the drain tube 44. Therefore the heating space lA has been difEicult to be sufficultly deaerated. This means that the distance QO is pre-Eerably of at most 10 millimeters.
In olher words, the distance QO is so ~limensioned that, even though steam bubbles would be evolved from the liquid bein~ heated within either of tlle heatin~ spaces lA
and 2A and reach the upperr~ost portion of thereof, they can ~20 be rapidly exhausted through the drain tube 43 or 44.
After the air has been fully removed frorn either of the heatlng spaces lA and ZA as abnve desdribed, both spaces~is entlrely filled with ti~e heated li~uid without the steam bubbles accumul~ated to forni a cavity therein.
25~ Otherwlse a cavity not fllled wlth the heated llquid is formed within~either of the main clectrodes l and 2 and ~th~refore that portion thereof contacted by and located ; ~ adjacent to~the cavity excessively rises in temperature ~ .'-.~

resulting in its ~ailure.
The arrangement of Figure 10 is urther advantageous in that the insultaing enclosures decrease in diameter and therefore are easily manufactured with low cost and mechanically strong because the enclosures surround the reduced dia~eter portions of the main electrodes ~hich are encircled by the metallic shells interconnected into a unitary structure to permit a region occupied by the insulating enclosures to be extremely decreased. Purther the main electrodes are insula~ed from the shells through the insulating enclosures respectively. Accordingly, the resulting apparatus is easy to be manufactllred, inexpensive and robust while having a long useful life.
In the arrangement shown in Figure 41, the insulating :
enclosure 9 in the form of a hollow cylinder having both ends open includes a pair of upper and lower apertured cover plates 13 and 14 respectively connected to both open ends thereof through annular seal fittings 10 and 11 respectively. A pair~of hollow main electrodes 1 and 2 ;~ 20 having one end open are ver~ically disposed in opposite ; parallel relationship within the enclosure 9 to be staggered longitudinally of the enclosure and orm a discharge gap 8 ~ ~ : :
in a discharge space 81 defined by the enclosure 9, the seal fi~tings 10, ll and the cover plates 13 and 14. The ; ~;main electrodes 1 and 2 have the other open ends flxedly ~fitted~into apertures on the upper~and lower cover p ates~
` ; 13 and 14 to be~flush~with the oi~ter surfaces thereof ~respective~ly.

;~ ;' ~ ~ 3 ~ ~

~ 3~
¦ The main electrodes l and 2 have the open cnds closed ¦ w;th blind cover plate 23 and 22 having central openings ¦ respectively. Tllen a L-sha~d tube 44 or 41 has one leg ¦ conllecte~l to the central opening on the blind cover plate ~ 23 or 22 and the other leg horizontally extendcd to form an ¦ outflow or an inflow tube.
¦ A ~eed water tube 42 extends in sealing relationship ¦ through the one leg of the outflow tube 44 and into a heating space lA within the main electrode 1 from above the ¦ upper plate 1~. Similarly, the drain tube 43 extends through ¦ the inflow tube 14 and into a heating space 2A within the main electrode 2 from below the lower plate 14.
I As in the arrangement o~ Figure 40, the drain tube ¦ 43 has its open end facing the inside of the closed end of ¦ the main electrode 2 through ~ spacing QO not greater than ¦ 10 millimeters.
¦ As shwon in Fi~gure 41, the inflow tube 41 has the end opening in the heating spacè 2A below the inlet o~ the drain tube 4~ while the feed liquid tube 42 has the end ~; Z~ ¦ opening in tlle heating space lA below the inlet of the drain ¦ tube 44. Therefore the 'neating spaces 1~ and 2A can be entirely filled with the heated li~uid as in the arrangement ¦ of Figure 40-Further an auxillary electrode~46 is operatively c ¦ associnted Wlt}l the discharge gap 8 formed;between the main op~osite electrodes l~and 2. If desired, both main electrodes ~may be concentrically~disposed. ~
~; ~ l ~ he arrana~rent sh~n ln l;3~re 4Z, a ~eamless ~ ¦

: . , ~

~ 35~

metallic tube is closcly wound into a helix 41a or 42_ having the outside cliameter suhstantially equal to the inside diameter of the main electrode 2 or 1. The helix 41a or 42a includes one end portion 43 or 42 extend;ng through the central hollow portion thcreof and the other end portion 41 or 44 bent into an L-sha~e. Both helices 41a and 42_ are inserted into the main electrodes 2 and 1 -to be brazed or welded to the intcrnal surfaces tllereoi res~ectively for the purpose oE improving the heat transfer -Erom the mating main electrodes thereto. A liquid to be heated enters the helix 41a or 42a through the end portion 41 or 42 and leaves the end portion 43 or 44.
In other respects, the arrangement is identical to that shown in Figure 41.
Each of the m~in electrodes 1 or 2 can be prevented -from corroding starting with those ~ortions t}lereof brazed or welded to the hellx 42a or 41a because the brazed or welded portions are not directly cont~acted by the heated liquid ~l~owing through the helix. Since the heated~liquid flows at a high s~eed tllrough the helix 41a or 42a, the ~ ~ -~
nuclear~ebullition can be ~revented and also a pressure loss in the helix IS increased to prevent steam~bubbles from staying~in the helix. This results~in the;smooth heat transfer from the main eiectrode to the heated llquid Elowing through~thc nla~ting llC~iX. ~ l`hus thc main electrodes are ~prevent;ed~ from~cxc~ess~vely rising in surrace tem]~erature ~ ~
thereby to~sustain~stably the glow~dlschar~e~ ~ -The Drr~angement~shown in ~l~gure~43 1s substantially ; ~ 75 ~ ~
: :~ , ~'3~

similar tQ that illustrated in ~igure 40 exceptirlg that, in addition to disposing the main electrodes 1 and 2 vertically, they are in the form of square hollow prisms and a tube is closely wound in helix compleMentary in shape to the interior of the associa-ted main electrode and fixed thereto.
Each of the arrangements shown in Figures 42 and 43 is characterized in that tube means formed of a good thermally conductive material contacts the internal sur-face of the mating main electrode to be thermally integral therewith and the heated liquid -flows through the tube means. This results in the allevia~ion of limitations as to the configura-tion of the main electrode while ~acilitating the manufacturing of the apparatus and prolonging the useful life.
In the arrangement shown in Figure 44 either of the ; 15 blind cover plates 22 and 23 is provlde~ on that portion diametrically opposite to the nQrmal outlet with an exhaust port that is, in turn, closed wit]l a plug 221 or 231 for . .
example through a screw meahcnism. Further an auxiliary electrode 46 is operatively coupled to the ga~ formed between the main opposite electrodes l and 2 as above described in conjunction with Figure 34.
In other respects, the, arrangement is substantially identical t o that shown in Flgare 24. ..
; i ~ The~arrangement shown in Figu~e 45 includes the ~25~ U-shaped flow path or heating space lA or ZA~within the main ~electrode l or 2 and~a~connecting tube 361 or 351 connected ;
to the heating space IA or lB~ on the inlet side. ~hen the ¦~ connec~n~ ~abe ~61 ~r 351 ] s rTov~d~d w~th an exhaust : ; ~ : :
76 ~

~ ~ 11 11~73~1 port closed with a detachable plu~ 231 or 221.
In other respccts the arran~ement is substantially idcntical to that shown in Figure 44.
When each of the arrangc]ncnts shown in Figllres 44 S and 45 is desired to be out of scrvice for a long time, the plugs 221 and 231 can be removed from the associated exhaust ports to drain the liquid out from interior of the main electrodes for the pur~ose of prcvcnting the liquid within the main electrode from spoiling or freezing. Also the useful life can be prolonged.
l~hile the main electrodes have been described as being in the form of hollow cylinders having the same shape and disposed in opposite relationship it is to be understood that the main electrode may be of any other desired shape.
For example, the main electrodes may be in the form of hcllow cylinders dis~osed in coaxial relationship. It is essential that, in order to cmpty the interior of the main electrodes, the exhaust port must be provided on the lower portions thereof.
While some of the abovementioned Figures, for example, Figure 34 illustrate the control circuit for controlling the ~low discharges Figllre 46 shows the fundamental circuit configuration of a control circuit for controlling any of ~he arrangements as above descrihed including no auxiliary electrode. In Figure 46, the arrangement generally designated by the reference numeral 100 comprise~ a pair of first and second electrodes 1 and 2 res~ectively disposed in opposite relations~ip to form therebetwcen a gap havin~ a ~ 7 3 ~ ~

¦ gap length or a ~idth d and each including an inflow and ¦ an outflow tube. Water enters thc interior of either ¦ electrodes 1 and 2 througll the inflow tube to be l-eated ¦ and heated watcr lcaves it thro-l~h the outflow tube.
¦ The source of AC voltage 31 is connected across the ¦ electrodes 1 and 2 through a biclirectional triode thyris~or ¦ 60 with the first electrode 1 connected to ground. Ihe bidirectional triode tl~yristor is called hereinafter a ~ "Triac" (grade mark). The source 30 is also connected ¦ across a gate circuit 61 tllrough a normally open switch 62.
Then the gate circuit is. connected across one electrode and a gate elec~rode of the Triac 60. The switch 62 is closed to fire a glow discharge between the electrodes 1 and 2 there-: I by to heat a liquid, for example, water flowing through the ¦ interior of each electrode.
¦ The operation of the control circult shown in .
¦ Figure 46 will now be described with reference to Figure 47 wherein there are illustrated a voltage waveform V supplied ¦ from the source 31 and having a peak value Em and a current ; I waveform V of the glow~discharge. As shown in Figure 47, the voltage waveform V~in the positive half-cycle of the :., ~
source gradually Increases from lts null point until tlme point tl lS reached. At that time voltage reaches a value of a discharge breakdown voltage~5 to fire a glow discharae Z~5~ between~the electrodes 1 and 2. At that time point tl a ;glow curre~nt Ilabruptly flows through the~electrodes 1 andl Z.~ The~glow current I~corresponds to~a voltage drop expressed ~by Vf - VO where VO desig~nates a glow hold minimum voltage and may be expressed by I = ~V~ - Vo)/R where R design~ltes a discharge resistance corresponding to a slope of a current-to-voltage characteristic curve for a glo~ discharge as above described in conjunction with Figure 8.
The at time point t2 the voltage V is equal to the glow hold minimum voltage VO after which the glow discharge is extinguished because the volta~e is less than the voltage VO.
Therea-fter the sourc3 31 enters the next succeeding negative half-cycle of the source in which the process as above described is repeated to cause a glow discharge between the electrodes 1 and 2. In the arr~ngement shcwn in Figure 46 the application of the AC voltage causes the electrodes 1 and 2 to act alternately as a cathode and an anode electrode ; 15 respectively to be heated because the glow discharge heats that electrode acting as the cathode as above described.
From the foregoing it will ~ seen that, the firing of the glow discharge at time point tjL causes an instantaneous ~ ~ increase in glow current so that the glow discharge can not spread following ~his increase in glow current. This results in the tendency to locally concentrate the glow current nn the electrode to translt the glow discharge to an arc discharge. T~e arc charge has a fear that it melts the electrode which, in turn, reduces the useful life~of the 2~5 heatlng apparatus.
Also~the glow current is initiated to flow through the elect~rodes :L and Z only upon the source vol~age across both elecllodes reac'ing the discllarge breakd~wn voltage V~

: ~

; ~ :

~ 73~ ~

while Vf > VO hilds. Therefore it is impossible to utilize a time interval during which the source voltage is not less than the giow hold minimum voltages VO as a co~duction ti.me resulting in a poor effici.ency oi utilization of the source ~oltage.
Figure 48 shows a contro]. circuit for controlling the glow disch~rge heating apparatus of the present invention constructed in accordance with the principles thereof. The arrangement illustrated comprises an auxiliary source circuit 61 connected across the source of AC voltage 31 that supp].ies hC voltage of 200 volts at the commercial frequency. The circuit 61 includes a normally open switch 62, a step-up . transformer 63 having a primary winding connected across the : source 31 through the switch 62 and a secondary winding ~lS having one end connected to the electrode 2 through a ~: current limiting resis~or 64 and the other end connected to theelectrode 1 and also to ground.
As in the arrangement of Figure 46, the source 31 is ~ connected to the electrode 2 1hrough the Triac 60. The :~2~D resistor 64~is connect~ed across~a primar~y winding of an electrically insulating transformer 65 including a secondary ~winding~connected across~a pair of AC~inputs of a recti.-E.ier :
~bridge 66. The rectlfier bridge 66 include a pair of DC .
outputs one of which lS connected to the junction~of the :~
~25~ ~source 31;and the Triac 60 through a reslstor 67 and the ~ther:~of~wh~ich i~s conne~cted to the remalnlng terminal or a~
~;g:ate termi;n~al~or the:Triac 60. :
The ster-up trans~ormer 63; is deslgn~ed and ~ : ~ :

;:
`

~ ~' ~ : 1~ ' constrllcted so that the disch~rge br~akdown voltage Vf is applied across the electrodes 1 a3ld 2 berore time point where an instantaneous voltage -from the source 31 reaches the ~low discharge minimum voltage VO.
The operation of the arrangement shown in Figure 48 will now be described with reference to Figure 49 similar to Figure 47. In Figure 49 wherein ]ilce re~erence characters designates the compollents corresponding to those shown in Figure 47, the switch 62 is closed at time point A to perrn;t the source to apply the source voltage across the primary winding of the transformer 63. At a point B, a secondary or an output voltage rom the transformer 63 reaches the discharge breakdown voltage Vf whereupon the gap between the electrodes l and 2 is brolcen down to start an electric discharge therebetween. At that time the output voltage drops to the glow hcld minimum voltage VO (see point C, Figure 49) for a glow discharge by means of the current limiting resistor 64. This causes a current i on the order of 0.1 ampere to flow through the electrodes 1 and 2 resulting ~0 in a glow discharge occurring across the electrodes l and 2.
That glow discharge is called a "pilot glow discharge".
The current for the pilot glow discharge causes a voltage drop across the current limiting resistor ~4 that, in turn~ induces a secondary voltage across the transformer 65. The secondclry voltage from the transformer 65 is applied to the gat~e electrode of the Triac 60 a~ter having been full-wave recti-fied by the rectifier bridge 67 to put the Triac 60 in i conducting state ~herefore the source voltage is :
: ~
: ~ ,, ~ 735~
., applied across the electrodes 1 and 2. Ur.der these circumstance, if the pilot glow discharge has not occurred across the electrodes l and 2 then the p:ilot glow current i coes not flow through the electrodes 1 and 2 and no voltage is induced across the insulating transformer 65 with the Tesult that the Triac 60 is maintained non-conducting.
This ensures that the application o-~ the high AC voltage across the electrodes l and 2 does not results in the cccurrellce of an arc discharge therebetween unless the pilot glow discharge preliminarily occur across ~he electrodes 1 and 2.
When the source voltage is applied across the electrodes 1 and 2 throllgh the now conducting Triac 60 and : reaches the glow hold minimum voltage V0, the principal glow discharge is fired across the electrodes 1 and 2.
That is, a current I for the principal glow discharge flows through the electrodes 1 and 2. That principal glow discharge : current I is extinguished after the source voltage V has :~ again reached the glow hold minimum voltage V0 at point E
or time point t2 and therefore the principal glow discharge ,. is extinguished. Ilowever it is noted that at point E the voltage V0 from the step-up transformer 63~is applied across ~: the electrodes l and 2 through the resistor 64 with the result that the pilot glow discharge is still established.
: Then at point F, the outpu~ voltage from the step-up transformeT :63 hecomes also less tllan the voltage V0 to cease the pllot~glow dlscharge. ~
;: Then the source 31 enters the next succeeding negative :~ : : :~
:: : ~: ~ :
~ - 82 -: :; ~ : :
.

~ 3 ~

half-cycle in which the process as above described is rcpeated.
The concept of the ernbodiment of the present invention as shown in Figure ~8 is to apply preliminarily a high ~-oltage across the electrodes by means of the auxiliary cource circuit to cause the preliminary or pilot glow cischarge thereacross and to smoothly derive the principal glow discharge from the pilot glow discharge. T~erefore the arrangement O r Figure 48 is effective for preventing the principal glow discharge current from abruptly increasing resulting an arc discharge as in the arrangement of Figure 46. Further the efficiency of utilization of the source is increased.
The arrangement shcwn in Figure 50 comprises a reactor 68 connected between the source 31 and the electrode 2 and an AC pulse generator 69 connected across the source 31 through the normally open switch 62. The pulse generator ~9 includes one output connected by the current lirniting ;~ resistor 64 to the junction of the reactor 68 and the -~ electrode 2 and the other output connected to the electrode Iz 1 and therefore to ground. ~ -The gap formed between the electrodes 1 and 2 is so dimensioned that the peak voltage Em from the source 31 is prevented from effecting t;lle discharge breakdown of the gap.
As shown in Figure 51 wherein a voltage and a current ~25~ waveform V and I respectively and a pulse waveform P are illustrated the AC~ pulse generator 69 generates an AC
:
~; pulse voltage P suf-ficient to reach the discharge breakdown : :
voltage Vf at time point tl where the voltage from the ~ : :
- ~ ~
~ ~ ~ - 83 -~ :

: : .

3 ~ ~

source 31 approximately reaches the glow hold minimum voltage VO The pulse vol-tage P first effects the discharge break-~own of the gap between the electrodes 1 and 2 followed by a flow of the principal glow current I through the electrodes.
As in the arrangement of Figure 46, the current I
becomes null at time point t2to extinguish the glow discharge after which the process as above described is repeated in the next succeeding negative half-cycle.
It is noted that the reactor 68 is designed and constructed so that it present a high impedance to the pulse waveform P but a low impedance to the commercial ; frequency of the source 31.
Thus the arrangement of Figure 50 ensures that, ~ihen the source voltage V is close to the glow hold minimum voltage VO~ the principal glow discharge is initiated between the electrodes 1 and 2 and then the principal glow curr~nt I is smoothly increased without the transit to an arc discharge.
~ Figure 52 shows a modification of the present invention wherein the pilot glow discharge occurs between the auxiliary electrode and either of~the main electrodes prior to the principal glow discharge as above described, for example, in conjunctlon with Figure 34. In Figure 52, the main and auxiliary~electrodes 1, 2 and 46 respective~y are schematically ~25~ shown and may have any of their structures shown in Figure 34 and Figures ~8 through 45.
; ~The ar~rangement illustrated comprises the AC source :
31~and an auxlllary source shown~as comprising a step-up ; ~ 84 : :
-: : , ~ : ;

~ 7 3 ~ 1 ¦ ~rallsformer 70 including a primary winding connected across ¦ the source 31 through the normally open switch Sl and a ¦ center-tapped secondary winding. The dot convention is ¦ used to identify the polarity of the instantaneous voltage ¦ across the associated winding. The secondary winding ¦ includes center tap connected to the auxiliary electrode 46 ¦ through a current limiting resistor 71 and a normally open ¦ switch 72, and a pair of end terminals connected to the main ¦ electrodes 1 and 2 through indiv:idual semiconductor rectifier ¦ diodes 73 and 74 with anode electrodes thereof connected to ¦ the main electrodes respectively. The gap formed between ¦ the electrodes l and 2 has a distance or a gap length d ¦ g ~ Em > VO~ where Vf~ Em and V have been ¦ previously defined.
lS ¦ The switch 51 is closed to apply the AC voltage V
from the AC source 31 across the electrodes ]. and 2 while the switch 72 is closed to apply a high voltage wa~eform ~; ¦ from the step-up trans~ormer 70 to the auxiliary electrode ¦ 46. Under these circumstances, when a potential at the main l electrode l i5 higher than that at ~he main electrode 2, the ¦ diodes 73 and 74 are turned off and on respectively to cause a pilot glow discharge between the auxiliary electrode 46 ¦ acting as an anode and the main electrode 2 acting as a ¦ cathode. On the contrary, when the main electrode 2 is ~25~ higher in potential than the maln electrode 1, the diodes 73 and 74 are turned on and off respectively to cause a pilot glow discharge between the auxiliary electrode 46 acting.as anode and the maln electrode 1 as the cathode.
:
~~ : ~ ~ ~: :
' ; ~ ~ - 85 : ~ :
:~ :

.
: ~ , , .

~ 73~
I
¦ In addition, as the auxiliary electrode 46 has ~ppl;ed ¦ thereto the voltage from the center tap on the secondary ¦ transformer 70 winding, the voltage applied across the ¦ auxiliary electrode 46 and the main electrode 1 to cause ¦ the pilot glow discharge therebetween is quite identical to ¦ that applied across the auxiliary electrode 46 and Inain ¦ electrode 2 to cause the pilot discharge therebetween.
¦ Therefore, the transit of the pilot glow discharge due to ¦ the auxiliary electrode to the principal glow discharge ¦ between the main electrodes 1 and 2 are equally effected between each of the positive half-cycles and the negative ¦ half-cycle of the source 31.
Further the occurrence of the pilot glow discharge l completes a closed circuit including the diode 73 or 74, ¦ the associated half of the secondary transformer 70 winding, ¦ the resistor 71, the closed switch 72 and the pilot glow ~ ¦ discharge between the auxiliary electrode 46 and the main I I electrode 1 or 2. This prevents the current for the pilot ¦ glow discharge~ from entering a circuit wlth the source 31.
:~20 ¦ The opening of the~wltch 72 ceases the pilot glow discharge from occurring between the auxiliary electrode 46 and either of the main electrodes 1 and 2. ~hus the ¦ principal glow dischalges are not fired in the next succeeding cycle of the source and the cycles following the latter with 2s~ ¦ the result that the heating operation is not performed. In other words, the QN-OF~F control of~the principal glow discharge can be conducted by turning the pilot discharge~on and off.
, ~: I : . ~
It 15 noted that the pllot gl~ow~dlscharge always ~ ;

- 86 - `
~ ~ ~ ~ :
: ~ , . . : , . .. ~ . ~ . . . . , - :

~ '3~

occurs between the auxiliary electrode 46 acting clS the anode and either of the main electrodes 1 and 2 acting as the cathode so that the auxiliary electrode 46 is not heated.
This results in the elimination of the necessity of cooling the auxiliary e~ectrode.
From the foregoing it is seen that, the arrangement when effecting the ON-OFF contro:L of the heating apparatus proper of Figure 52 ensures the ~ransit of the glo'w discllarge by turning the pilot g:Low discharge on and of-~.
The arrangement illustrated in Figure 53 is different from that shown in Figure 52 only in that in Figure 53 a zero-voltage firing circuit is provided to prevent the glow current from bruptly increasing. In Figure 53 a`~pair of serially connected resistors 75 and 76 are connected`~across the AC source 31 through the normally open switch 5l~to form a voltage divider, and the junction A of both resistGr is connected to a resistor 77 subsequently connected to a bas~`,resistor 78 that i5 connected to a~base source VBB. The resi~stor 76 is connected to ground. The ~20 junction B of the resi~stors 77 and 78 is connected to a base e1ectrode of an NPN' transistor 79 including an emitter electrode connected to~thè res1stor 76 and a collector electrode connected to a DC source Vcc through a collector resistor 80. ~The transistor /79 has connected across the 25~ emitter and base e,lectrodes a semiconductor diode 81 serving to~prevent a high reverse volt~age from being applied across those electrodes and also connected across the collector :~ ; and emitter el~ctrodes~ d~1f~erent1at1ng~ c1rcu~1t 1ncludin~ a : : `

~ ~ :87~-~ .'

7 3~ ~

¦ capacitor 82 and a resistor 83. The junction of ~hat ¦ collector electrode and the capacitor is designated by the ¦ reference character C and the junction of tlle capacitor 82 ¦ and the resistor 78 is designated by the reference character ¦ D only for purposes of illustratlon.
The junction D is connected to one AC input to a rectifier bridge 84 including the other AC input connected to the resistor 83. The rectifier bridge 84 incl~des a l ~air of DC outputs connected across a resistor 85 that is ¦ connected at one end to a gate electrode of a Triac 87 ~hrough a normally open switch 86 and at the other end to the primary winding of the transformer 70. The Triac 87 is connected across AC source through the primary transformer I 70 winding and the switch 51 and has connected thereacross ¦ a series combination of a capacitor 88 and a resistor 89 - ¦ serving as an absorber.
:~ I The components 75 through 89 as above described ¦ form a zero-voltage firing circuit generally designated by ¦ the reference numeral 90.
2~0~ ¦ Wlth the switch 51 closed, an AC voltage developed at the point A is similar to the source voltage and sinusoidal as shown at waveform A in Figure 54. The AC
sinusoidal vo~tage passes through its ze~ro voltage points at time points to, tl and t2 in each cycle of the source 31.
~Assuming that the source VBB is at a null potential~, a voltage developed at the point B i~s sinusoidal between time polnts~tO and tl or in the positive ~half-cycle o the source and remalns null beeveen ~i e polnt tl~and t~ or In the ~ 7~

negative half-cycle thereof by means of the action of the diode 81 as shown at wave-form B in Figure 54. Since the transistor 79 is turned on only in response to a voltage applied to the base electrode to render the latter positive S with respect to the emi~ter electrode, the same is in its ON state between time points to and tl and in its OFF
state between time points tl and t2. Accordingly, a voltage developed at the point C is null when the transistor 79 is in its ON state and equal to a voltage across the source Vcc also designated by Vcc l~hen it is in its OFF
state as shown at waveform C in Figure 54.
The voltage at the point C is differentiated by the differentiating circuit 82, 83 to produce alternately a negative and a positive pulse at the point D as shown at.
. lS waveform D in Figure 54. Those pulse are rectified by the rectifier bridge 84 to form positive pulses which appear at a point E connected to the switch 84 at time points to, tl and t2 as shown at waveform E on Figure 54.
~:;; With the switch 86 closed, the pulses shown at ~: waveform E in Figure 54 are successively applied to the -~ gate electrode of the Tr.iac 87. In other words, gate pulses are necessarily developed at the gate electrode of the Triac 87 at the zero passage~points of the source voltage or at tlme points to, ~ and _2 Thus it is seen that, 25~ ~ even though the switch:86 has been closed at any time point, the Trlac 87 is brought into lts ON state starting with the zero passage po.int of the~source voltage. As a result,~ a ;~pilot~vol.tage from the~transformer 70 lS applled to the ~ : ~ :.

~ : ~ 89 - :
:'' : ~ , ., -¦, al~xiliary electrode 46 starting with the ~ero p.ls~age point ¦ of the source voltage or time point to, tl or t2 ~ith the result that the principal glow current is ~rcventcd from sharply increased. I`his means that 8 liquid -rlOwi,lg in heat transfer relationship along the internal surface of cach electrode 1 or 2 is smoothly heated.
The arrangement of Figure 53 is advantageous in that a principal glow current is preven-ted from sharply ~ rising at a firing time pOillt and the glow discharge is ¦ prevented from transiting to an arc discharge due to the local concentration of the current while ef-ficiency of utili-zation of the source voltage is high.
If desired, the zero voltage firing circuit 90 may ¦I be formed of solid state relays.
l¦ In the arrangements shown in Figures 52 and 53 the ¦. auxiliary source circuit including the step-up transformer ¦l is formed of components having stray capaci~ances between one another and with respect to ground with the switch 72 t put in its open position. This results in a fear that a ¦ potential at the auxiliary electrodes 46 would be raised due to those stray capacitances until a voltage across the auxiliary electrode 46 and either of the main electrodes 1 and 2 e~xceeds the discharge breakdown voltage across the ; associated~gap.~ This results in the undesirable occurrence ~25~ of a glow discharge between the main electrodes 1 and 2 which dlsables the pr~incipal~g~low~discharge to be controlled with the pllot~g~low dischargè.
In order to avoid~thls ob~ectlon, the arrangement : ~ :
~ : :
~90' ~ : .,-.~.. ,:-' :

73~;~

illustra~ed in Figure 55 incl~des a pair of d~mmy resistors ~3 and 94 connected between the diode 73 and the resistor 71 and bet~een the diode 74 and the resistor 71 respectively.
rhe resistors 9~ .lnd 94 are effective for determining the potential at the aux;liary electrode 46 so as to prevent the voltage across the auxiliary electrodes 46 and either of the main electrodes 1 and 2 from exceeding the discharge breakdown voltage across the gap as above describéd.
In other respects, the arrangement is idcntical to 1~ that shown in Figure 53 except for the omission of the switch 2.
The auxiliary electrode 46 is normally positioned to be equidistant from both main electrodes 1 and 2 and ~herefore the resistors 93 and 94 are equal in magnitude of resistance to each other in order to equal the voltage across the auxiliary electrode 46 and the main electrode 1 to that across the electrodes 46 and 2 with the switch 62 put in its open position. Even under these circumstances, it is to be understood that the gap length bct~een the auxiliary electrode 46 and either of the main electrodes 1 and 2, and the type and pressure af a dischargeable gas should be preliminarily determined so as to prevent the occurrence of a discharge breakdown between the auxlliary electrode 46 and either of the main eIectrodes l and 2 with the switch 62 put ~25~ in its apen position. - ~
The~arrangement~illustrated in Figure 56 lS dlfferent from~that shawn~in Figure 55 only in~that in Figure 56 a ~: ~Trlac l~S substltuted far the switch 6Z In arder ta permit~ ~:

1 ; ~ 91 ~ ~

~ ,~

¦ the ON-OFF oper~tion to be re~eatedly ~erformed with a high freq~ency. As sho~n in ~igllre 56, a Iriac or a bidirectional triode thyristor 95 is located in place of the switch 62 ¦ shown in Figure 55. The Triac 95 includes a gate circuit ¦ 95 connected to a gate electrode thereof to deliver trigger ¦ signals to the gate electrode to turn the Triac 95 on and off . I and a series combination of a capacitor 97 and a resistor 98 .. ¦ serving as an absorber.
l If desired, the Triac 95 may be included in the zero ¦ voltage firing circuit 90.
When the pilot glow discharge has the discharge ¦ breakdown characteristic with a fairly long time delay, the pilot glow discharge may be fired at time point where the I source voltage approaches its peak value provided that the Triac 95 has flowing therethrough a current an excess of :~ its holding current. This is attended with the occurrence of the principal glow discharge having a sharply rising current. A current -for this glow discharge may sharply rise. In this case, a negative glow included in the .~:20 ~ principal discharge can not spread following an increase in : :
current to locally concentrate the current resulting in a danger that the glow~dl~scharge transits to an arc discharge.
In order to avoid thls danger, it is necessary to determine magnitudes of resistances 93 and 94`and an impedance on the ~25~ ~ primary slde of the step-up transformer 70 enough to prevents a ~flow of current through the Triac 95 inexcess of its :
holding~current. ~ ~ .-n h~rrang-mcn. l]llsira~d in Flgur- 57 an ~ 92 - :

.. . . ,, , ~ . . . . . ... .. . ..

1 ~ 7~qjl electronic switch 98 such as a thyristor with a trigger circuit ~9 is connected between the resistor 71 ~nd the junction of dummy re.~istors 93 and 44 as shown in Figure 57.
IYllen a volt~ge drop across the serially connected resistors 93 and 94 decrease to some extent, and when the electronic switch 98 is put in its ON state by the trigger circuit 99, a current flowing through the electronic switch 98 may exceed its holding current even :in the absence of a pilot glow discharge. Under these circumstances~ i~ the pilot glow discharge has the discharge breakdown characteristic with a long time delay, there is a danger that the resulting glow discharge transits to an arc discharge as above described. In order to avoi-l this danger, the resistors 93 and 94 are required to high somewhat in resistance.
lS Alternatively the electronic switch 98 with its trigger circuit 99 may be connected between the junction of ~-` the dummy resistors 93 and 94 and the auxiliary electrode 46 as shown in Figure 58. In these case, the resistors 93 and 94 are no~ particularly subjected to limitations as to Z0~ their resistances unless a ~oltage across the auxiliary elec~rode~46 and either of the main electrodes 1 and 2 is reduced. ~ ~
The arrangements shown in Figures 55 through 58 ensure that the princ~ipal glow d1scharge is controlled with 25 ~ the pilot glow~discharge. This is because, the dummy res~stors prevent the potential at the aoxiliary electrode from floating by means of stray capacitances as abo~e described ln conjunctlon with Figures 52~and 53 and the : : ' ~'' : ~ :

~; ~ I ~ :

lll like in the absence of the voltage appl.ied to the auxiliary I electrode.
¦ The arrangement illustrated in Figure 59 comprises ~ ¦ an electrically isolating transormer 141 including a ~¦ primary winding connected across the AC source 31 and a ¦¦ secondary winding connected across a series combination of a rectifying dic.-le 142, a current :Limiting resistor 143 and capacitor 144, and an NPN transistor 149 including an I emitter electrode connected to one side of the capacitor 144 and a collector electrode connected to the other side of the capacitor 144 through a semiconductor diode 146 for absorbing back pulses. The transistor 145 includes a base electrode connected to a gate circuit 149 also connected to ¦¦ the emitter electrode thereof to turn the transistor 145 on ~ :
lS ¦¦ and off.
The components 141 through 146 form a high voltage pulse generator circuit generally designated by the reference numeral 140 with a step-up pulse transformer 147 which ~ includes a primary winding connected across the diode 146 .~2~0 ¦1 and a secondary: winding connected to a semiconductor diode 148 for shaping a pulse waveform. : . :
As~ln the arrangement of Figure 57, the diode 148 is connected to the resistor 71 subseguently connected to the auxiliary~electrode 46 through the thyristor 98 ~hich is ~1~25 ~ ~ ¦ turned~on and~o:ff by a trlgger clircu~t 99. Further ~he ¦ serlally connec~ted dummy resistors 93 and 94 are connected : I across~the main electrodes 1 and~2 also through the switch SI ~cross tl;e AC sourc~ wi~b ~h~ unctlon of bcth resistors~

I ~

: ~ : .
:~
~ ' ' . ' ! . . .

; . , connected to the auxiliary electrode 46.
I The operation of the ~rrangement shown in Figure 59 ¦ ~ill now be described with reference to Figure 60 wherein I there are illustrated a voltage waveform V across the main I electrodes 1 and 2 and a no-load voltage waveform VN at I the auxiliary electrode 46. With the main electrode 1 ¦, disposed oppositely to the main electrode 2 to form there-between a predetermined gap fulfilling the relationship I that the discharge breakdown voltage Vf ~or the gap is ' higher than the peak value Em of the source volta~e under the predetermined discharge conditions, the switch 51 is closed to apply the AC voltage across both electrodes 1 and ,I from the source 31. Also the source 31 charges the capacitor ¦
1 144 with the polarity illustrated through the transformer 141, ll the diode 14Z and the resistor 143. Then gate and trigger circuits 149 and 99 respectively apply simultaneously ¦ respective gate signals to the transistor 145 and the ¦ thyristor 99 to turn them on. The turn-on of the transistor 149 causes the charged capacltor 144 to discharge through the 20~ primary winding of the pulse transformer 147 and the now conducting traDsistor 145. As a result, a pulse voltage stepped up by the pulse transformer 147 is supplied from the secondary winding thereof through the diode 148, the resisto~
71 and the now conducti~ng thyrlstor~98 to the auxiliary-~;25~ electr`ode 46. It is noted that the circuits 149 and 99 generate;the respective pulses before the voltage acrass the main electrode 1 and 2 reaches the disc~harge breakdown ~
voltage VO.~ A~s shown~in Flgure 60,1the CilCUits 149 and ~ ~ ;

~ ~ ~9~

73~ ~ ~

. , 99 generate the pulses at tirne point t2 before time point to ~here the source voltage reaches the discharge breakdown voltage VO in each positive half cycle thereof and the pulses terminates short after .ime point to. That is, each pulse has a predetermined pulse width a little longer than a time interval between time points t2 and to. Each pulse is shown at waveform VN in Figure 60 as being super~osed on that portion of the source voltage divided by the resistors 93 and 94, assuming that both resistors are equal in magnitude of resistance to each other. In the next succeeding negative cycle of the source voltage the pulse ls similarly developed at time point t3 be-fore time point tl where the voltage across the main electrodes l and 2 reaches the negative value -VO of the discharge breakdown IS ; voltage and terminates short after time point tl to have the same pulse width as that appearing in the positive half-cycle of the source voltage.
In the arrangement of Figure S9 it is required to cause a pilot glow discharge before time point to or ~1 by Z0 1l applying the pulse waveform VN to the auxiliary electrode 46 as above described. ~lso it is required to select the pulse width so as to effect surely the discharge breakdown of the gap between the atlxiliary~electrode and either of the main~ele~ctrodes 1 and withln the duratlon of the ; ; associ~ated pulse. ~ ~ ;
; 1~ ID general a time delay~ is~caused after the voltage ` has been applled across~discharge~gaps and un~til the ;
discharge breakclown is accomplished therebetween. It is well 96~-~7~

known that this t;me delay is equal to ~he sum of a time interval between the application of the voltage across discharge gap and the appearance of a first electron resultillg in the initiation of development of the electron avalanche and another time interval be-tween the initiation of development of an electron avalanche and the completion of a stead-state discharge. The first mentional time ¦ interval is called a statistic delay and the latt~r is l called a formation delay. The statistic delay is over-poweringly long.
Assumlng that a voltage applied across the particular discllarge gaP has the peak value hig]ler that a voltage effecting the DC breakdown of the discharge gap, steped voltages are applied across the discharge gap nO times.
Assuming that, among them the n applications of the voltage has time delays not shorter than T and (n ~ ~n) applications thereof has time delays not shorter than (T + ~T), ;~ ~ :
~ ~ ~n = -An~T
~ZO ~ , ~' ; I kolds where A deslgnates a constant. lhus n~= nOe ~ ~ .=
: ~ .' ~25~ is fulfllled~by the statistic delay. The above expression may be pl~otted~lnto a straight line with t~he axes o ordinates~;and abscissas: repr~esentlng the~n~and~T respectivel~y ;~in a ~semiloga~rithmic scal~e.~A;graphic representation thus - . ~

~ 7~L

plotted is called a La~ie plot.
Figure 61 shows on example of the l,aue plot. In ~igure 61 an extremity of an auxiliary electrode having a ¦ diameter of 3 millimeters is located at an edge of a gap ¦ of 3 millimeters formed between a pair of main opposite electrodes to form a spacing of about 1 millimeter between the extremity of the auxiliary electrode and either of the main electrodes. The gap was filled with a discharge gap ormed of a mixture including 89% by volume of helium and ll% by volume of hydrogen under a pressure of lO0 Torrs.
In Figure 61 the reference numerals 150, lSl, 152 and 153 depict the source voltages having the peak values oE 600 ~00, 1000 and 1200 volts respectively. From a stepped urve 152, for example, it is seen that for the peak source lS value of lO00 volts the time interval between the t2 and to or between the t3 and tl ~see Figure 60) must be of at least 250 microseconds. Also the auxiliary source for the pilot glow discharge should have a current capacity of at least about 10 milliamperes in order to transit smoothly the pilot glow discharge to the principal glow discharge.
~; By taking account of a time delay with which the discharge gap is brown down with the pulse--voltage of the voltage wave~orm NN shown in ~igure 60, the waveform UN is givcn a pulse width or a duration defined by the time intervals ~25 ranging from time point t2 or t3 to time point to or tl respectively while the current capacity of the auxiliary source is determined as required for transiting the pilot glow dîscharge to the prlncipal glow discharge and the ~ ~ : :
:~ ~ : 9 ~ ~ ': : ~ :
: ~ ~ ' :: ~
~ ~ ~ :
;, . . .: .

~ 73~

pulse voltage delays rapidly at and after time point to or tl.
This measure ensures that the pilot glow discharge is always caused prior to time point to or tl and the principal discharge current surely rises al: time point to or tl.
After the principal glow discharge has been caused between the main electrodes 1 and 2, discharge energy from the principal glow discharge as t:hermal energy alternately enters the main e]ectrodes 1 and 2 with result that a liquid flowing in contact relationship through either oE the main electrodes is instantaneously heated.
The arrangement of Figure 59 is advantageous in that the principal discharge current smooth]y rises to cause the deve~lopmentof a negative glow involved to satisfactorily follow up a change in discharge current thereby to prevent the local concentration of the current without the glow discharge transiting to an arc discharge while the effic;ency of utilization of the source voltage. This is because the auxiliary electrode is adapted to be applied with a pulse voltase that rises before time point~where a voltage applied 20~ across the main electrodes reaches a glow hold minimum voltage across the main electrodes thereby to fire always the pllot glow discharge before that time point and rapidly falls to its null value at and after said tirne point. Also ` the use of the pulse waveform is effective for decreasing "~2~S the power càpacity of the auxiliary source and therefore ~; reducing a dimension and a cost thereof.
Figure 62 shows a modification of the arrangement shown in~Pigure 59.~ The arrangement illastrated comprises a : ~`~ 99 '; ~
::~: `:: ::: :: ::~ :
:~
''' ~ ': '~

~ 73~

pair of electrically isolating transformers 1~1 and 155 including a common iron core and a common primary winding connected across the AC source 31 through the nor~ally open switch 51, the high voltage pulse generator circuit 1~0 as zbove described in conjunction w;th Figure 59 connected to the transformer 141, and a current supply circuit generally cesignated by the reference numeral 154 and connected across the transformer 155`.
The current supply circui.t 154 includes a center-t:apped secondary winding of the transformer 155, and a pair of semiconductor diodes 156 and 157~ The diode 156 is connected at the anode electrode to one side of the source 31 through the switch 51 and therefore the main electrode 1 while diode 157 is connected at the anode electrode to the 1 15 Gther side of the source 31 and therefore the main electrode 2 that is, in turn, connected to ground. lhe center tap ; on the secondary transformer 155 winding is connected to the output of the pulse generator circult 140 or the junction of the diode 148 and the current limiting resistor 71.
~20 ¦ In other respects, the arrangemen~ is identical ¦ to that shown in Figure 59. ~The dot convention i5 used to ¦ identify the polarity of the instantaneous voltage developed across the associated transformer winding.
~ The current supply circuit 155 is operative to :~25~ ~¦ full-wave rec~ify an AC voltage induced across the secondary transformer~l55 winding and supply a current due to the full-wave recti-Fied voltage~to the auxlliary electrode 46 through the res.Lstor 71 and the thyristor 98 with the pulse I
` ~ ~ : 1 : :
100 -:
: : ..: ' : :~ I : ~ - -¦ voltage from the pulse generator circuiL 140.
¦ In the arrangement of Figure 62, the discharge gap ¦ hetween the main electrodes 1 and 2 has been dirnensioned ¦ as above described in conjunction with Figure 59 and the ¦ switch 51 is closed to supply the source voltage across the ¦ main electrodes 1 and 2. The source voltage is a comrnercial ¦ ~C voltage having a frequency of 60 hertzs as shown at dotted ¦ waveform V in Figure 63 wherein :its cycle has a d~iration of ¦ i6.7 milliseconds.
¦ The pulse generator circuit 140 generates a high voltage pulse in each of the half-cycles of the source voltage in the same manner as above described in conjunction with Figure 59. A:Eter having shaped by the diode 148, the high volts ~ulse is developed on the resistor 71 and lS superposed on the full-wave rectified voltage from the ;~ current supply circuit 154 also applied to the resistor 71 as shown at voltage waveform VN in Figure 62. Then pulse voltage VN superposed on the voltage from the current supply circuit 154 is supplied to the auxiary electrode 46 through the conduct~ing thyristor 98.
: ~ From Figure 63 it is seen that the vol~age waveform ~'N includes the~full-wave rectlfied component having a relative voltage to the~main electrode 2 equal to a vol~age VOP for~the pilot glow~discharge a~ time point t6 in the 25 ~ positive half-cycle of the source~voltage an also a relative voltage to the maln electrode 1 equal to that voltage VOP
at time point t7 in the negative half-cycle thereof. Time ~points t6~and t,~are~head of~tlme polnts t ~and t :

3~

respectively where the source voltage is equal to the glow hold minimum voltage VO.
With the main electrode 1 higher in potential than the main electrode 2, the diodes 156 is in its OFF state while the diode 157 is in its ON state tending to cause a pilot glow discharge between the auxiliary electrode 46 and the main electrode 2. On the contrary, with the main electrode 1 less in potential than the main electrode 2, the diodes 156 and 157 are turned on and off respectively.
This tends to cause a pilot glow discharge between the auxiliary electrode 46 and the main electrode 1. In each ~ase, the voltage across the auxiliary and main electrode 46 and 1 respectively is equal to that across the auxiliary and main electrode 46 and 2 respectively so that a current for the pilot glow discharge remain unchanged. With the auxiliary electrode 46 equidistant from the main electrodes 1 and 2, the transit of the pilot glow discharge to the principal glow discharge between the main electrodes 1 and 2 is accomplished in the similar manner in both cases.
20~ l The voltage waveform VN also includes a pulse waveform component from the pulse generator circuit 140 rising at time pOillt t2 or t3 behind time point t6 or t2 and fal~ling at time point t4 ahead of time point to or _1.
The pulse waveform com~onent results from a gate pulse P
from either of the gate and~trigger circu~ts 149 and 9g rising and falllng simultaneously with the rise and fall o the associated pulse co~mponent. The pulse waveform component is re.quired t~o have a pulse width su:~ficient to effect the ~ , ' ~ : ':

: ~ - 1 0 ~ - : . ' ; ~ , ~ I

, ~ . . .

~ 73~

discharge breakoown of the gap between the auxiliary electrode 46 and either of the main electrodes 1 and 2. It is to be noted that it is not required to cause time point r.4 or t5 to coincide with time point t2 or t1 respectively as in the arrangement of Figure 59 and that the pulse width may be sufficiently shorter than that reouired for the latter. In addition the discharge breakdown scarcely .equires a current resulting in the pulse generator circuit 140 reducing su-fficiently in power capacity.
The gate pulse from each of the gate and trigger circuits 149 and 99 should have a rise time fulfi~ling the rollowing requirements: The gate pulse Pl should rises at time point t2 or t3 required to be behind time t6 or t7 I respectively while the pilot glow discharge should be caused ¦ not later than time point to or tl. Otherwise the principal ¦ discharge current is too sharply raised to cause the spread of the particular negative glow to follow this rise in ¦ current resulting in a danger that the current is locally concentrated on either of the main e]ectrode to permit the ~20 glow discharge to transit to an arc discharge. Also tlle source voltage can be utilized only with a low efficiency.
Thus time point t4 or t5 should be ahead of time point to or tl respectively.
Wlth the gate pulse Pl generated to fulfill the requirements as above described, the pilo~ glow discharge is always caused ahead of time _0 or tl in the positive or negatlve half-cycle o~ ~the source voltage and the glow li disch ~T cur~ t thlough the mal~ ~lectr~des 1 anl 2 smoothly~

103~-: :

: : : : :
. ~

1 ~7~5~

¦ rises a~ and after time point to or tl in tlle positive or negative half-cycle o-f the source vol~age. Accord;ngly the prillcipal glow disch~rge is established resulting in tl~e l ~nstantaneous heating o-F the particular li~uid contacted ¦ by either of the main electrodes 1 and 2.
l F~rther it is required to make -the peak voltage ¦ value of the sinusoidal component of the voltage waverorm ~/N less than the discharge breakdowll voltage -For ~he gap between the auxiliary electrode 46 and either of the main electrodes 1 and 2 thereby to prevent the pi].ot glow discharge from firing with the sinusoidal component.
~lternatively it is required to impart a high value to each of the resistance 93 or 94 to prevent the voltage waveform .~ ~N from being applied to the auxiliary electrode 46 in the 15 absence of the gate pulse Pl and to prevent a current flowing hrough the thyristor 98 via the resistors 93 and 94 from exceeding the holding current thereo~ when the pilot glow discharge is not fired. Also the diodes 156 and 157 must : have such reverse voltage withstanding charac~eristic that :: 20 both diodes are not broken down with the high voltage pu].ses generated by the pulse generator circuit 14~.
: If desired tl-e pulse generator circuit may utilize a peak transformer.
The arrangement of Figure 62 is advantageous in ;25~ that the pulse generator circuit can reduce in power capacity resulting in the provision of an auxiliary source ~.
circuit easy to be mallufactured and inexpensive. This is .`
because the pulse generator circuit for effecting the ;: ~
:: :
: - 10~ -~ .
~:~:: :; ~ : :
,~

~ 3 5 ~

discharge breakdown of the pilot glow discharge gap is separated from the circuit for supplying current to the main electrodes after this discharge breakdown.
~igure 64 shows a different modi-~ication of the present invention driven by a three-~hase AC source. The arrangement illustrated comprises three main electrodes lU, lV and lW radially disposed by having their longitudinal axes arranged at equal angular intervals of 120 degrees.
The main electrodes are in the ~orm of hollow cylinders having one end closed into a crown shape that, in turn, faces the remainin~ closed ends of the same shape. The main electrode lU, lV and lW include the other end portions rigidly fitted into respective annular supporting members 14U, 14V and 14W interconnected through enclosure portions 9 formed of an elec~rically insulating material such as glass porcelain or the like and seal fittings lOU, lOV and lOW
connected to both adjacent supporting members and the adjacent edges of the enclosure portions 9 to define a hermetic discharge space. The other ends of each electrode lU, lV or lW is closed with a blind cover plate 23U, 23V or 23W having an inf~low tube 42U, 42V or 42W and an outflow tube 44U, 44V
or 44W is extended and sealed therethrough.
Three auxiliary electrodes 46U, 46V and 46W are radially extended and sealed through the enclosure portions 9 25 ~ respectively to be equidistant from the adjacent main electrodes and includes end portlons bent toward the associate main electrodes to form very narrow gaps therebetween. For example~ the auxiliary electrode 46U is radially extended and ~' ~ : ~ -: : , ; ~ - 105 -: : : ,, ~ :
- . : . ., .
. ~. , - . .. . , :. : :
. ~ . ... ..... , : .

5~

sealed through the enclosure portion ~ disposed between the main electrodes lU and lV and includes the end portion bent toward the main electrode lU so as to cause a pilot glow l discharge. Each of the auxiliary electrodes is coated with ¦ the same electrically insulating material as the enclosure ¦ portion 9 except for both the end facing the associated l main electrode and that portion externally protruding from - ¦ the mating enclosure portion 9.
¦ A three-phase source is represented by source ¦ terminals U, V and W which are connected to annular electrode terminals 6U, 6V and 6W fitted onto those portions of the main electrodes lU, lV and lW disposed externally of the l enclosure portions 9 respectively. Each of the auxiliary :: ¦ electrodes is connected to the electrode terminals disposed lS ¦ on the adjacent main electrodes through individual dummy : ¦ resistors. For example, the auxiliary electrode 46U is connected to the electrode terminal 6U of the main cylinder lU through the dummy resistor 47U on the one hand and to the electrode terminal 6V o-f the main electrode lV through the 0 dummy resistor 48U.
The auxiliary eIectrode 46U is also connected by a current llmiting resistor 49U to an auxiliary source circuit S0 also connected ~o the electrode terminal 6U. The .-.
auxiliary source circuit 50 is further connected across the Z~s source terminals U and V :through a normally open switch SlU connected~to the source terminal V.
A~clrcuit identical to that above described is ~ : ~ provided for each of the remaining main electrodes and the ;. ~; : ~ ~ ~
~: ~ :

:
~:;

~. ~ . , , . :

auxiliary electrode operatively associated therewith alld includes the components identical to those above described.
Therefore the identical components are designated by like reference numerals suffixed with the reference character U, V or W i~entifying the mating source terminal or the phase of the three-phase source.
The operation of the arrangement shown in Figure 64 will now be described with reference to Figure 65 wherein there are illustrated volta~e and current waveforms developed at ~arious points in the arrangement of Figure 64 with a voltage Vu applied to the main elec~rode lU being selected as a reference.
While a liquid to be heated is flowing through the interior of each main electrode via the associated inflow tube and leaves the mating outflow tube a three phase voltage is applied to the main electrodes lU, lV and lW through the source terminals U, V and W and all the switches 51U, 51V
;~ and 51W put in their closed position. At time point tl ' ` short before a voltage (see waveform Vv, Figure 65) applied across the main electTodes lU and lV reaches a glow hold minimum voltage V0, a high voltage pulse (see waveform Puo, Figure 65~ from the auxiliary source circuit 50U is applied to the auxiliary electrode 46U to cause a pilot glow discharge across the narrow gap between the auxiliary ~25 elect~rode and main electrodes 46U and lU respectively with '~ ~ the main electrode lU ac~ing as a cathode. This pilot glow ~ ~ di~scharge ls caused with a low current, and upont time ~ : ~ ~ ~ :: :
point~D being~reached, it instantaneously înduces a glow ~: ~ : : . ' ;~ ~ ' ~: ~ :

; ~

~ 7~

¦ discharge hetween the main electrodes :LU and lV ~ith the ¦ electrode lU acting as a cathode. The latter discharge ¦ spreads through the surface of both main electrodes lU and ¦ lV and is sustained after time point D.
¦ Then when a voltage (see waveform VWJ Figure 65) ¦ applied across the main electrodes lU and lW exceeds the ¦ glow hold minimum voltage V0 at time point E, the glow ¦ discharge developed be~ween the main electrodes lU and lV
¦ plays a role of the pilot glow discharge to cause a glow ¦ discharge between the main e]ectrodes lU and lW at and ` ¦ after that time point with the main electrode lU acting as a cathode.
¦ At time point F voltaee across the main electrodes lV and lW is equal to the voltage V0 but no discharge is caused between those main electrodes because of the absence of a pilot glow discharge with the main electrode l~ acting as a cathode. Therefore a high voltage pulse (see wave~orm PvO, Figure 65) from the auxiliary source circuit 50V is applied to the auxiliary electrode 46V at time point t2 - ~2~0 short ahead of time point F to cause a pilot glow discharge between the auxiliary and main electrodes 46V and lV
respectively. That pilot glow discharge similarly causes a glow discharge between the main electrodes lV and lW at and after time poin~ F with the main electrode lV acting as 25~ ~ a cathode. ~
: ~ , ~ ~ :
When time point G is reached, the voltage Vv across the main electrodes lU and lV is eoual ~to the voltage V0 and the glow discharge caused between the~ aiD electrode lV

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acting as the eathode and the main electrode lW plays a role of a pilot glow disc]-arge. This causes a glow discharge betl~een the main electrode IV acting as a cathode and the main electrode lW at and after time point ~.
Similarly, since the voltage Vw across the main electrodes lW and lU exceeds the voltage VO at time point 1-1, a high voltage pulse ~see waveform P~yO, Figure 65) frorn the auxiliary source ~ircuit 50W has been preliminarily applied to the auxiliary electrode 46W at -time point t3 short ahead of time point H to cause a pilot glow discharge between the auxiliary electrode 46W and the ~ain electrode acting as a cathode. The pilot ~lol~ discharge between the auxiliary and main elect~ode 46W and lW respectively transits to a glow discilarge caused between the main electrode lW
acting as a cathode and the main electrode lU at and after time point H.
Then at time point I the voltage Vw across the main electrodes lV and lW exceeds the voltage V~ so that the glow discharge between the main electrodes lW and lU ser~es as a pilot glow discharge to cause a glow discharge between the main electrode lW acting as a cathode and the main electrode lU until one cycle of the source voltage is completed. `
Thereafter the process as above described is ~;~ 25 repeated to cause repeatedly glow discharge between pairs of the main eiectrodes~. When acting as the cathode, the main electrodes successively heat the liquid therein.
From the foregoing it wlll readily be understood ; ~
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1 1?3~ 3 ~ 1 that ~he gate pulses are repeatedly applied to the auxiliary electrodes 46U, 46V and 46W at time points t defined by t = tl ~ nT, t = t2 + rlT and t = t3 + nT
, S
respecti~ely where T designates a period of ~he ~hree-phase source voltage and n indicate any positive integer including zero.
In Figure 65 solid current wav~form IU designates 1~ a glow discharge currents with the main electrode lU
acting the cathode, dotted current waveform IV those with the main electrode iV acting as cathode and broken current waveform lW designates the glow discharge current with the main electrode lW acting as the cathode. The reerence PuO, PvO and PwO designate no-load pulse wave-forms which or change to the actual pulse waveforms Pu~ PV
and PW respectively after the associated pilot glow discharges have been fired.
Also it is noted that Figure 65 illustrates the ~0 waveforms developed during a time interval equal to twice the period T of the source voltage Vv appl~ied across the main elec~rodes lU and lV and that the polarity of ~he .: ~
current waveforms have not been considered.
From the fore~oing it will readily be understood 25~ ~ that the glow~discharge has~a time period equal to three times~that provided by;single-phase sys~em and therefore ~ ~ three-phase apparatus tripple ln ~ower capaclty single-`~ ~phase apparatus.
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- ~373~.31 In the arrangement of Figllre 6~5 the auxiliary electrode is disposed between each pair of adjacent main electrodes for the purpose of controlling thermal energy entering each of ~he main electrodes. ~lowever it is included in the scope of the present invention to replace the auxiliary electrode by a bidirectional triode thyristor serially connected to each of the main electrode to control thermal energy entered thereinto through the ON-OFF
operations of the thyristors.
The arrangement illustrated in Figure 66 is different from that shown in Figure 64 only in that in Figure 66 a combina~ion of a pulse transformer 70U, 70V or 70W and a high voltage pulse generator circuit 140U, 140V
or 140W is substituted for each auxiliary source circuit.
The combination of the pulse trans-~ormer and pulse generator circuit may be identical to the pulse generator circuit 140 shown in Figure 59.
Also the main and auxiliary electrodes are I schematically illustrated in Figure 66 and may be similar to those shown in Figure 64 and the resistors 48U, 48V and 48W are omitted.
1~ Figure 67 shows another modification of the arrange-ment shown in Figure~66. In the arrangement illustrated, the electrically isolating transformer 70 includes a primary 25~; winding Wl connected across the source terminals U and Y
through~the switches 51 and a palr of secondary windings W2 and~W3 connected~respectively across a high voltage pulse generator circuit 140 such as above described in : ~ :
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~73~

conjunction with Figure 59 and a gate circuit 161. The pulse generator circuit 140 includes one output connected to the sourc~ terminal U and the other output connected to anode electrodes o thyristors Su, Sv and Sw through the common current limiting resistor 49. The thyristors Su, Sv and Sw include ca~hode electrodes connected to the auxiliary electrodes 46U, 46V and 46W respectively. The gate circuit 16]. is connected to the thyristors Su, Sv and : SW ~ control the firing thereof.
In other respects, the arrangement is substantially ~; identical to that shown in Figure 66.
Figure 69 illustrates voltage and current waveforms developed at various points in the arrangement shown in Figure 67. From the comparison of Figure 68 with Figure 65 it is seen that voltage and current waveforms shown on the ., upper portion of Figure 68 are substantially similar to those illustrated in Figure 65 and pulse waveforms Po are substi~uted for the pulse;waveforms PU-Puo, PV-Pvo and PW-Pwo shown in Figure 65. Thus like reference characters ~ZO have been employed to ldentify the waveforms corresponding to those i:llustrated in Figure fi5. Thus the arrangement ~:
is substantially identical in operation to that shown in Flgure 66.~
As seen in Figure 6R, the gate circuit 161 applies ~; 25 ~ a gate pulse (~see waveform Gu) across the gate and cathode :electrodes~of the thyristor Su short before the high voltage pulse (see~waveform Po from the pulse generator 140 is supplied to the aux~iliary electrode 46U to bring it in ..

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., its conducting st~te and ~hen the pulse Po is supplied to the auxiliary electrode 46U through the resistor 49 and the now conducting thyristor Su. rhis is true in the case of the remaining pulses P passing through the respective thyristors Sv and SW.
Each of the gate pulses shown at waveforms Gu~ GV
and GW in Figure 68 should have a pulse width sufficient to ensure that a pilot glow discharge is fired between the associated auxiliary and main electrodes such as shown by 46U and lU and transits to the principal glow discharge caused between the mating main electrodes such as shown by lU and lV. That is, the gate pulse should be at least sustained until time point is reac]led where the associated source voltage, for example, the voltage Vv exceeds the glow minimum voltage V0. If the pilot glow discharge causes a current 10wing through the associated thyristor to exceed its holding current then the gate pulse may continue until the pilot glow discharge is fired.
The arrangement of Figure 67 is advantageous over that shown in Figure 66 in that the resulting circuit is simple, small-sized and inexpensive because of the provision of a single high voltage pulse generator circuit.
In the pre-ferred embodiments of the present invention, ~.
the main electrodes~and associated components, such as the flow confinlrng tubes, the connecting tubes, the inflow and outflow~tubep the blind cover plates shown, for example, in Figure 24~are ~ormed o~ metallic material and put in ; ~ contact with a heated liquid that is electrolytic. This : ~ : ~ ., .
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may result in a fear -that those métallic components are corroded with the heated liquid and reduced in useful life.
Particularly the main electrodes and those tubes directly connected thereto have high probabilities of electrolytic corrosion because the source voltage is directly applied across the main electrodes while the inflow and outflow tubes are connected to grouned thereby to permit currents to flow in to the main electrodes and those tubes through the heated electrolytic liquid.
The arrangement shown in Figure 69 includes corrosion preventing electrodes ~or preventing metallic components from corroding as above described. In the arrangement illustrated a corrosion preventing electrode 161 or 162 is electrically insulatingly extended and sealed through that wall portion of the flow confining tube 20 or ~1 facing ~` the inside of the gap forming surface of the main electrode 2 or 1, that is, each of the opposite surfaces of both main electrodes with an electrically insulating holder 163 or 164 hermetically interposed therebetween. The electrode protrudes into the flow path for the heated llquid. The anticorrosive electrode may be formed of platinu~, carbon, triiron tetroxide (Fe3O~) or the like. The a DC source 165 or 166 is connected across the corrosion preventing electrode ~=
161 or 162 and the electrode terminal 5 or 6 thereby to supply to the electrode 161 or 162 a voltage higher than the voltage across the main electrodes. To this end. Each of the DC source 165 or 166 includes a negative side connected to the associated eIectrode te~rminal 5 or 6.
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Then the e~ectrode terminals 5 and 6 are connected to a control circuit identical to that shown in Figure 34.
In other respects, the arrangement is identical to that shown in Figure 24 except for the provision of the auxiliary electrode 46 but the main electrode 1, in this case, made of stainless steel or the like, the flow confining tube 21, the blind cover plate 23, the connecting tube 36, the insulating tubes 38 and 40, the inflow tube 42 and the outflow tube 44 form an assembly prevented from corroding and generally designated by the reference numeral 167. Also, the similar components 2, 20, 22, 35, 37, 39, 41 and 43 form another assembly prevented from corroding and generally designated by the reference numeral 168. The main electrode 2 is also made of stainless steel.
The corrosion of the main electrodes and others is -; called the electrolytic corrosion resulting from a flow of current therethrough via a heated electrolytic liquid that is caused from the dissolution of materials forming the main electrode and others into an electrolyte such as water. In the arrangement of Figure 69, the ~C sources 165 and 166 are adapted to apply to the respective corrosion preventing ;~ ~ electrodes 161 and 162 voltages higher that the voltage applied across the associated main electrodes. Thus the corrosion preventing electrodes 161 and 162 provide the so-called scapegoat electrodes. That is) the material or materials forming the scapegoat electrode is or are dissolved into an electrolyte such as water thereby to prevent the materials forming the assemblies 167 and 168 form dissolving ,~
: ~ : .
~ - 115 -: .
: ~ , . , , , . ~ :' :~LlU73~1 into the heated liquid resulting in no corroslon occurring.
I`he DC sources 165 and 166 may be omitted by for1l)ing the corrosion preventing electrocle of a metallic material less in corrosion potential and more easily ionized than the material of the main electrocle. For example, with the main electrodes 1 and 2 formed ot` stainless steel, magnesiurn, zinc, aluminum, etc. are optimum -for forming ti-e corrosion preventing electrode.
Also the DC source may be repaced by any suitable source :tor supplying a DC voltage.
Figure 70 shows corrosion preventing electrodes Frovided on the arrangement shown in Figure 39. In Figure 70 the corrosion preventing electrodes 161 and 162 are provided on the exposed portion of the feed water tube 20 disposed within the main electrode 2 and on the outer wall of the main electrode l respectively in the same manner as above described in conjunction with Figure 69.
Then the corrosion preventing electrodes 161 and 162 are connected to terminals d and e subsequently connected, for example, to the DC sources 165 and 166 (see Figure 69) respectively. Also terminals a and b connected to the electrode termiDals 5 and 6 respectively are connected across the AC.source 31 shol~m in Figure 69 while a terminal C connected to the auxilialy electrode 46 is connected to ~25 teh auxiliary source circuit 50 also shown in Figure 69.
Figure 71 shows anticorrosive electrodes provided ~ :
on the a~rrangement iliustrated in Pigure 64~ As shown, an ~; antlcorTosivee~lectrode~161U, 161V or 161W is electrically ~ ' ~ 116-:: ~ ~ : :
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~ 73~ .

insulatingly extended and sealed through the feed water tube 42U, ~2V or ~2W operatively couplecl with each main electrode lU, lV or lW with an electrically insulating holder 164U, 164V or 174W interposed therebetween.
~igure 72 shows a separat:e modirication of the present i.nvention wherein a temperature o-f a heated llquid is measured. In the arrangement illustrated, a temperature .,ensor 169 such as a therrn;stor is electrically i3isulatingly extended and sealed through that portion of a flow conEining ..
,ube 20 facing the peripheral wall oE the main electrode 2 with an electrically insulating holder 170 interposed ~herebetween.
The temperature sensor 16g may entirely covered l with a electrically insulating material in accordance lS with the particular electric field established in the vicinity thereof .
In other respects, the arrangement is substantially -dentical to that shown in Figure 24 except for the provision .: of the auxiliary electrode 46.
The electrode terminals 5 and 6 and the auxiliary electrode 46 are connected to a control circuit identical ; to that shown in Figure 57 except For the omission of the zero volt fir.ing circuit 90. The temperature sensor 169 includes an output connected to the trigger circuit 99 for the thyristor 98.
In operation the temperature sensor 169 senses : the temperature of the heated li~uid and feeds a measule temperatur~ signal to the trigger circutt 99.

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More specifically9 with the temperature sensor 169 :formed of a thermistor or a temperature measuring resistor, a resistance theIeof is changed with a tempcrature so that a sigllal representative of a change in resistance is applied to the trigger circui.t 99. Alternatively, with the tempera-ture sensor 169 formed of a thern~ocouple, it responds to t:he temperature of the heated liquid to change in thermo-electromotive force thereof. This change in thermoelectro-motive force is signalled to the tri.gger circuit 99.
If it is desired to control the heated liquid to â predetermined fixed temperature then the actual tempera-ture measured by the temperature sensor 169 is compared ~ith an output therefrom at a predetermined temperature as the reference. With the actual temperature higher than the predetermined temperature, the trigger circuit 99 applies no trigger signal to the thyristor 98. Otherwise, ~ ¦ the trigger circuit 99 delivers the trigger signal to the : ¦ thyristor 98. Then the thyristor 98 is correspondingly : turned on and off to fire and extinguish a pilot glow dis-c.harge ~hereby to effect the ON-OFF control of a glow ~ d:ischarge between the main electrodes 1 and 2.
: Under these circumstances, some time goes until heat from either of the main electrodes 1 and 2 acting as ' the heating surface is transferred to the heated liquid.
This results in a time delay Wit]l which the temperature of the heated llquld is controlled. lherefore, the temperature ~: sensor 169 has~preferably a sensor end loca~ed as near to ~;~ : the heating surface of the assoc~ated maln electrode as ~ ' :

~ : : - 118 -:
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With the temperature of the heated -temperature controlled according to a predetermined program, the Function of effect;ng such control may be incorporated into the trigger circuit 99 and the thyristor 98 is operated in the ON-OFF control mode and in accordance with the ou~put signal from the temperature sensor 169.
Tlle temperature sensor 169 may be used with the ~:ontrol of the glow discharge effected by a control SUC]l as a thyristor connected in series to the particular glow discharge heating apparatus in a circuit wi.th an electric source circuit for the apparatus.
¦ The arrangement illustrated in Figure 73 is different ~ ~`rom that shown in Figure 72 only in that in Figure 73 a :~ bidirectional triode thyristor or a Triac is provided to c.ontrol the glow discharge as in the arrangement of Figure 48. In Figure 73 a thyristor 172 is connected at the anode electrode to one of the DC output terminals of the rectifier brldg~e 66 and at the cathode electrode to tlle ..
~:. Triac 60. The resistor 67 is connected to the Triac 60 at the gate electrode but not to one main electrode thereof.
Then the thyristor 172 has the cathotle and gate electrodes : ~ connected across a trigger circuit 173 subsequently connected ;~ to the temperature sensor 172.
25 ~ In:other respects, the control circuit is substan-tially Ident~cal to that shown in Figure 48.: Mowever the dot convention lS used to Identifv the polarity of the instantaneous voltage across~the~assoclated transfor~er , ~ : ~ : ~ :
; ~: : : ~ : ~ ' :'.
~ 1 1 9 '1~ 3..i winding.
l The electrically isolating transformer 65 is opera-¦ tive to adapt a potential difference developed across the l resistor 64 to a voltage requirecl for the Triac 60 to be ¦ fired.
With the swi.tch 51 put in its closed position, the step-up transformer 70 applies a high AC voltage across t.he electrodes 1 and 2 resulting in the discharge breakdown l cccurring therebetween. This cause a potential di-fference lU ¦ across the current limiting resistor 6~ whereby a potential difference appears across the resistor 67 through the transformer 65 and the rectifier bridge 66. At that time, : the trigger circuit 173 is actuated to put the thyristor 172 in its ON state to cause a tri~ger signal to be applied to the gate electrode of the Triac 60 to turn it on. There-fore the AC source across the source 31 is supplied across ;: the main electrodes l and 2 through the now conducting : thyristor 60 to cause a glow discharge therebetween.
- Under these circumstances~ the temperature sensor ~:~2Q 169 senses a temperature of a heated liquid involved and feeds signal for the sensed temperature to the trigger circuit to:control the glow discharge between the electrodes 1 and 2. :
From the foregoing it is seen that in the arrange-~ ments shown in Figures 72 and 73 tlle temperature of theheated liquld sensed by the temperature sensor is fed to : ~ l the auxlliary source circuit for controiling the glow dis-l charge caused between the main electrod~es resulting in the I : ; :
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IL1~73~i1L

easy, reliable t~mperature control of the heated liquid.
While the present invention has been illustrated and described in conjunction with various preferred embodi-ments thereof it is to be understood that numerous changes and modifications may be resortecl to without departing from the spirit and scope of the present invention. For example, the embodiments of the present invention illustratcd and described in conjunction with the single-phase source may readily be modified to be driven by ~he three-phase source. Similarly, the embodiments illustrated and described in conjunction with the three-phase source may readily be suited for use with polyphase sources having m phases where _ is greater than three (3). In the latter case, an _-phase AC voltages is applied to m main electrodes to cause successively glow discharges between the pairs thereof.
The resulting power capacity is equal to m times that provided by single-phase apparatus leading to inexpensive structures.
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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An AC glow discharge heating apparatus comprising a pair of electrodes opposing each other through a predetermined gap, and means for applying an AC voltage across said pair of electrodes to cause a glow discharge across said gap and a heated liquid heated with energy that enters heat into said pair of electrodes wherein said pair of electrodes are disposed to oppose each other on end surfaces formed into the substantially same shape while being supported only on one portion of said electrodes.