JPH068498Y2 - Ceramic electromagnetic flowmeter - Google Patents

Description

[Detailed Description of the Invention] <Industrial field of application> The present invention has a ceramic measuring tube, and in a ceramic electromagnetic flowmeter for measuring the flow velocity of a high-temperature fluid, the electrical components in contact with the outer surface of the measuring tube should be protected from high temperature The present invention relates to a ceramic electromagnetic flowmeter to be protected.

<Prior Art> FIG. 3 is an explanatory view of a configuration of a conventional example which is generally used in the past.

In the figure, 1 is a cylindrical measuring tube made of ceramics. In this case, the measuring tube 1 is made of alumina (Al ₂ O ₃ ). Reference numerals 21 and 22 denote columnar cermet electrode portions which are arranged so as to face the measurement tube 1 and which are formed by mixing conductive powder and firing the mixture together with the measurement tube 1.

<Problems to be Solved by the Invention> In such a ceramics electromagnetic flowmeter, since the electric parts such as the magnetic circuit are attached to the measuring tube 1 from the outer peripheral side, the measured fluid temperature is changed from the service life of the electric parts. , I can't make it too high.

For example, hot water at 90 ° C. is passed through an alumina cylindrical tube (λ = 18 Kcal / m ² hr ° C.) having an inner diameter r ₁ 24 mm and an outer diameter r ₂ 40 mm (α ₁ = 4000 Kcal / m ² hr ° C. = 1 m).
/ Velocity), the outer surface is in contact with the atmosphere (α
₂ = 7.5 Kcal / m ² hr ° C.).

α ₁ , α ₂ : Heat transfer coefficient If the surface temperature of the measuring tube 1 is t, heat flow rate ql = {2π (90−t)} / [{1 / (400
0 × 0.012)} + (1/18) 1n (0.020 /
0.012)] = {2π (t-20)} / {1 / (7.
5 × 0.02)} (2π / 0.049) (90−t) = (2π / 6.6
7) (t-20) 0.049t-0.049x20 = 6.67x90-
At 6.67t 6.719t = 601.28t = 89.5 ° C., the temperature of the outer surface in the steady state does not change much from the fluid temperature.

For this reason, the fluid temperature is naturally limited due to the life of the electrical components related to the measuring tube 1.

The present invention solves this problem.

An object of the present invention is to provide a ceramics electromagnetic flowmeter with improved performance capable of expanding the measurable range on the high temperature side.

<Means for Solving the Problems> In order to achieve this object, the present invention provides a ceramics electromagnetic flowmeter equipped with a ceramics measuring tube through which a measuring fluid flows, wherein the measuring tube is heated from the inner circumference to the outer circumference. The ceramic electromagnetic flowmeter is characterized in that it is formed by mixing an insulating ceramic powder having a low thermal conductivity with an insulating ceramic powder having a high thermal conductivity so as to have a low conductivity.

<Operation> In the above configuration, since the measurement tube is configured to decrease the thermal conductivity from the inner circumference toward the outer circumference,
The temperature of the outer peripheral surface of the measuring pipe can be made lower than the temperature of the measuring fluid.

Further, it is possible to effectively mitigate the temperature rise even in an unsteady state other than the steady state, for example, a rapid change of the measurement fluid due to thermal shock.

Hereinafter, detailed description will be given based on examples.

<Embodiment> FIG. 1 is an explanatory view of a main part configuration of an embodiment of the present invention.

In the figure, the same symbols as in FIG. 3 represent the same functions.

Reference numeral 3 is a measuring tube formed by mixing an insulating ceramic powder having a low thermal conductivity with an insulating ceramic powder having a high thermal conductivity so that the thermal conductivity decreases from the inner circumference to the outer circumference.

Reference numerals 31, 32, and 33 indicate portions in which the thermal conductivity is gradually changed so that the thermal conductivity decreases toward the outer peripheral direction.

In this case, the 31st part is made of silicon nitride (Si ₃ N
It is made of ₄ ).

The 32 and 33 parts have considerably lower thermal conductivity, but the ratio of zirconia (ZrO ₂ ) which is superior in strength is set to, for example, 50% and 100%.

In this way, the thermal conductivity λ _{31 of} silicon nitride (Si ₃ N ₄ )
= 0.02 cal / cmsec ° C. = 7.2 Kcal / m ² h
Thermal conductivity of r ° C. and zirconia (ZrO ₂ ) λ ₃₃ =
0.006cal / cmsec ° C = 2.16Kcal / m ²
hr ° C, and assuming that the linear rule holds for the mixed part, 3
Thermal conductivity of 2 parts (Si ₃ N ₄ 50% ZrO ₂ 50%) λ ₃₂ =
4.7 Kcal / m ² hr ° C., in measuring tube 3, measuring tube 3 when the measuring fluid is 90 ° C.
When the temperature of the outer circumference of is measured, the radius of the measuring tube 3 and the portions 31, 32, 33 is r ₁ = 0.1
m, r ₃₁ = 0.012 m, r ₃₂ = 0.013 m, r ₃₃ =
It will be 0.0135 m.

Assuming that the surface temperature t of the measuring pipe 3 is heat flow rate ql = {2π (90−t)} / [{1 / (400
0 × 0.012)} + (1 / 7.2) 1n (0.013
/0.012) + (1 / 4.7) 1n (0.0135 /
0.013) + (1 / 2.16) 1n (0.1 / 0.0
135)] = {2π (t-20)} / {1 / (7.5 ×
0.02)} (2π / 0.967) (90−t) = (2π / 6.6
7) (t-20) 0.967t-0.967x20 = 6.67x90-
6.67t 7.637t = 619.64 t = 81.1 ° C, which is about 10 ° C lower than the conventional surface temperature.

In the above configuration, since the measurement tube is configured to decrease the thermal conductivity from the inner circumference toward the outer circumference,
The temperature of the outer peripheral surface of the measuring pipe can be made lower than the temperature of the measuring fluid.

Further, it is possible to effectively mitigate the temperature rise even in an unsteady state other than the steady state, for example, a rapid change of the measurement fluid due to thermal shock.

As a result, the temperature of the surface of the measuring tube 3 can be made lower than the fluid temperature, and the reliability of electrical components and the like can be improved.

FIG. 2 is an explanatory view of the essential structure of another embodiment of the present invention.

In this embodiment, 33 parts having the lowest thermal conductivity are provided midway from the inner circumference to the outer circumference of the measuring tube 3.

<Effects of the Invention> As described above, the present invention provides a ceramics electromagnetic flowmeter having a ceramics measuring tube through which a measuring fluid flows, so that the measuring tube has a low thermal conductivity from the inner circumference to the outer circumference. A ceramic electromagnetic flowmeter was constructed by mixing an insulating ceramic powder having low thermal conductivity with an insulating ceramic powder having high thermal conductivity.

That is, since the thermal conductivity of the measuring pipe is reduced from the inner circumference toward the outer circumference, the temperature of the outer circumferential surface of the measuring pipe can be lower than the temperature of the measuring fluid.

Further, it is possible to effectively mitigate the temperature rise even in an unsteady state other than the steady state, for example, a rapid change of the measurement fluid due to thermal shock.

As a result, the temperature of the surface of the measuring tube can be made lower than the fluid temperature, and the reliability of electrical components and the like can be improved.

Therefore, according to the present invention, it is possible to realize a ceramics electromagnetic flowmeter with improved performance capable of expanding the measurable range on the high temperature side.

[Brief description of drawings]

FIG. 1 is an explanatory view of a main part configuration of an embodiment of the present invention, FIG. 2 is an explanatory view of a main part configuration of another embodiment of the present invention, and FIG. 3 is a structure of a conventional example which is generally used conventionally. FIG. 21, 22 ... Electrode part, 3 ... Measuring tube, 31, 32, 3
3 ... part.

Claims (1)

[Scope of utility model registration request] 1. A ceramic electromagnetic flowmeter comprising a ceramic measuring tube through which a measuring fluid flows, the insulating ceramic powder having low thermal conductivity such that the measuring tube has a low thermal conductivity from the inner circumference to the outer circumference. A ceramics electromagnetic flowmeter, characterized by being formed by mixing an insulating ceramics powder having high thermal conductivity with.