Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K17/00—Measuring quantity of heat
  • G01K17/06—Measuring quantity of heat conveyed by flowing media, e.g. in heating systems e.g. the quantity of heat in a transporting medium, delivered to or consumed in an expenditure device
  • G01K17/08—Measuring quantity of heat conveyed by flowing media, e.g. in heating systems e.g. the quantity of heat in a transporting medium, delivered to or consumed in an expenditure device based upon measurement of temperature difference or of a temperature
  • G01K17/20—Measuring quantity of heat conveyed by flowing media, e.g. in heating systems e.g. the quantity of heat in a transporting medium, delivered to or consumed in an expenditure device based upon measurement of temperature difference or of a temperature across a radiating surface, combined with ascertainment of the heat-transmission coefficient
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
  • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
  • G01F1/688—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
  • G01F1/6888—Thermoelectric elements, e.g. thermocouples, thermopiles
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
  • G01J5/12—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using thermoelectric elements, e.g. thermocouples

Definitions

• the present invention relates to a heat flux comparator comprising an activation circuit, more particularly suitable for measuring variations in heat flux in various applications, such as the detection of flow of a fluid.
• thermal detection devices In contrast to devices for measuring the temperature of an external environment, known thermal detection devices allow the detection of thermal fluxes without any variation in temperature. Such a device is called a heat flux comparator. French patent application No. 01 15310 describes such a device which allows the comparison of instantaneous heat fluxes coming from two external environments with which the two faces of the device are respectively brought into contact.
• Such a heat flux comparator nevertheless requires that heat fluxes be exchanged between one of the external media and the comparator.
• the external environment (s) are permanently at the same temperature as the comparator, no heat flux is exchanged and the comparator does not provide any detection signal.
• Such conditions are for example achieved when one of the external media is a fluid in motion relative to the comparator, and the speed of the fluid varies without the temperature of the fluid being modified.
• the comparator of the French patent application n ° 01 15310 is then inoperative to detect a variation in the flow speed of the fluid medium.
• thermal detectors are also known, which include an activation circuit and make it possible to detect variations in an external medium such as a change in a flow speed.
• European patent application 0 446 546 describes such a detector, but its sensitivity is particularly low. In addition, its operation does not allow detection when the activation circuit is electrically supplied. Activation periods and measurement periods must then be alternated, this which generates a complicated operating mode and requires complex control means.
• the object of the present invention is to provide a very sensitive and easy to use heat flux comparator.
• the invention relates to a heat flux comparator having at least a first substantially planar inlet face and capable of exchanging heat flows with a first external medium with which said first inlet face is brought into contact.
• the comparator includes:
• thermoelectric detection circuit having a determined longitudinal direction situated in a plane substantially parallel to the first input face, comprising at least a first strip of a first metallic material having a determined thermal conductivity, a determined electrical conductivity and a power thermoelectric determined, having at least two faces, and being partially covered on one of its faces by first disjointed metallic plates of a second metallic material which has a thermal conductivity and an electrical conductivity respectively higher than the thermal conductivity and the electrical conductivity of the first metallic material and which has a thermoelectric power different from the thermoelectric power of the first metallic material;
• thermoelectric activation circuit comprising at least a second strip of a third metallic material having a determined thermal conductivity, a determined electrical conductivity and a determined thermoelectric power, having at least two faces, and being partially covered on one of its faces by second disjointed metal plates of a fourth metallic material which has a thermal conductivity and an electrical conductivity respectively higher than the thermal conductivity and the electrical conductivity of the third material metallic and which has a thermoelectric power different from the thermoelectric power of the third metallic material;
• An electric current generator having two terminals respectively connected to two longitudinal ends of said second strip so as to supply said second strip with a continuous supply electric current
• thermoelectric detection circuit disposed between the thermoelectric detection circuit and the therr ⁇ oelectric activation circuit, the insulating material of said first layer of insulating material having a thermal conductivity lower than the respective thermal conductivities of the first, second, third and fourth materials metallic;
• first and second ribbons are parallel and superimposed in a direction perpendicular to the first entry face, and are respectively covered with first and second plates arranged substantially at right angles to each other in said perpendicular direction, or arranged in a manner that the first plates of said portion of the first ribbon are substantially in line with separation intervals between second plates of said portion of the second successive ribbon in the longitudinal direction.
• the comparator of the invention makes it possible to detect variations in the external environment (such as a flow speed) when the latter keeps a constant temperature equal to that of the comparator.
• the activation circuit is supplied by an electric current
• each of the second wafers has a heated end and a cooled end by thermoelectric effect, creating local heat flows exchanged with the outside environment.
• Each of the first wafers of the detection circuit located above a second wafer thus activated or located between two seconds successive plates thus activated, then instantly detects possible variations in these local heat fluxes, due to variations in the external environment, even without appreciable variation in the temperature thereof.
• the structure of the heat flux comparator allows excellent detection sensitivity.
• the comparator further comprises third plates arranged on a face of the second layer of insulating material opposite to the thermoelectric circuits.
• the third plates are each arranged at right, in the perpendicular direction, of a respective longitudinal end of the first plates.
• the third plates create an asymmetry between the two longitudinal ends of each first plate which makes it possible to detect thermal fluxes even in the absence of electric current in the activation circuit.
• the heat flux comparator further comprises a second inlet face, substantially planar and parallel to the first inlet face.
• the heat flux comparator can then exchange heat fluxes with a second external medium brought into contact with the second input face.
• the second input face is disposed on one side of the detection and activation circuits opposite to the first input face, and a third layer of insulating material is disposed between the second input face and the thermoelectric circuits.
• the invention also relates to methods for comparing heat fluxes using a heat flux comparator as described above.
• the activation thermoelectric circuit is supplied with a constant direct electric current, and the electric voltage detected by the detection thermoelectric circuit is identified.
• the value of the electric supply current of the thermoelectric activation circuit is adjusted so as to locate the value of said current which cancels the electric voltage detected by the thermoelectric detection circuit.
• FIG. 1 is a section through an example of heat flux comparator according to the invention.
• FIG. 2 is an exploded perspective view of part of the heat flux comparator of Figure 1;
• FIG. 3 illustrates an example of use of a heat flux comparator according to the invention;
• FIG. 4 is a section through a heat flux comparator according to a preferred embodiment of the invention.
• FIG. 5 is an exploded perspective view of the heat flux comparator of Figure 4.
• FIG. 6 is a section through a heat flux comparator according to a variant of the preferred embodiment of the invention.
• the heat flux comparator comprises a thermoelectric detection circuit formed by the metal strip 1, partially covered with a series of metal plates 2 arranged in a longitudinal direction L of the strip 1.
• the strip 1 can be arranged in meanders juxtaposed in the same plane.
• the direction L is then the local longitudinal direction of the ribbon 1.
• the plates 2 are separated from each other and distributed in a substantially regular manner along the ribbon 1.
• the plates 2 are applied to the ribbon 1 so as to have with him a good electrical contact and a good thermal contact at least at the level of two longitudinal ends of the plates 2 in the direction L.
• the plates 2 may be rectangular in the plane of the tape 1, or of any other shape.
• the ribbon 1 can be made of a resistive alloy known as constantan, or another resistive alloy such as chromel.
• the plates 2 are made of a metallic material such as copper, gold, silver, nickel, aluminum, or an alloy comprising at least some of these metals.
• the materials of the tape 1 and the plates 2 are chosen so as to have different respective thermoelectric powers, and so that the plates 2 have an electrical conductivity and a thermal conductivity greater than those of the tape 1.
• the tape 1 is in constantan and the plates 2 are made of copper.
• thermoelectric circuit consisting of a metal strip 3 and wafers 4 is identical to the detection circuit formed by the strip 1 and the wafers 2.
• This second thermoelectric circuit is the activation circuit. It is arranged parallel to the detection circuit, in a position offset with respect to the detection circuit in a direction N perpendicular to the plane of the strip 1, so that the plates 2 and the plates 4 are superimposed two by two in the direction N.
• FIG. 2 shows, in a perspective view, the superposition of the detection and activation circuits for a meandering configuration of the strips 1 and 3.
• a layer 5 ( Figure 1) of insulating material is interposed between the detection and activation circuits.
• Another layer 6 of insulating material covers the detection circuit, on a side opposite to the activation circuit.
• Layers 5 and 6 can be made of Kapton® or of alumina fiber fabric, especially for high temperature applications.
• the whole of layer 6, of the detection circuit, of layer 5 and of the activation circuit is tightened in the direction N in order to present good thermal contacts along planes perpendicular to the direction N.
• the free face of layer 6 constitutes an input face E1 of the heat flux comparator. It can be brought into contact with an external medium 100, which can be of any kind, gaseous, liquid or solid.
• the face of the layer 6 constituting the input face E1 can be covered with a thin metallic layer, preferably with a soft metal, so as to improve the thermal contact between the external medium 100 and the comparator.
• the comparator is placed on a support S by its face opposite to the input face E1.
• the layer 6 has a thermal conductivity in the direction N less than the thermal conductivity of the layer 5 in the direction N.
• the detection and activation circuits can be considered to be almost confused with respect to the flows heat exchanged between the comparator and the medium 100, through the input face E1.
• the strip 1 is connected by its two ends to two respective terminals of an electric voltage detector 20, such as, for example, a voltmeter.
• the ribbon 3 is connected by its two ends to two respective terminals of an electric current generator 30, capable of delivering a direct current of adjustable intensity I.
• the current I thus delivered then flows through the ribbon 3.
• E2 represents the contact surface between the comparator and the support S (FIG. 1).
• thermoelectric activation circuit being supplied with a non-zero continuous electric current by the generator 20, it creates local heat fluxes around the longitudinal ends of the plates 4.
• the two longitudinal ends of each plate 4 are respectively heated and cooled by the Peltier effect. , known to a person skilled in the art, produced by the supply current of the activation circuit.
• These local heat flows diffuse in the direction N through the input face E1 and reach the external medium 100.
• the external medium 100 influences these local thermal fluxes according to its intrinsic thermal characteristics.
• an external fluid medium 100 in movement, by its renewal in contact with the inlet face E1 promotes the local heat fluxes generated by the activation circuit.
• the heat flux comparator of the invention makes it possible to detect changes in the thermal characteristics of an external medium, even when the external medium and the comparator have strictly equal temperatures.
• the activation circuit powered by the current I delivered by the current source, in fact makes it possible to overcome the need for spontaneous heat fluxes through the input face of the comparator.
• the ends of the strip 1 connected to the electrical voltage detector 20 each have an electrical polarity identical to that of the end of the strip 3 to which it is superimposed in direction N.
• Figures 4 and 5 show a second embodiment of a heat flux comparator. Elements 1 to 6 described above are repeated identically. In particular, the plates 2 and 4 are arranged in line with each other in the direction N. A layer 7 of insulating material, identical to the layer 6 is placed against the activation circuit, on a side opposite the circuit of detection. The free face of layer 7 constitutes a second input face E2 of the heat flux comparator. The input face E2 is brought into contact with a second external medium 200.
• plates 8 and 10 are respectively arranged on the faces of the layers 6 and 7 of insulating material facing outwards from the comparator.
• Each plate 8 is positioned centrally relative to the first longitudinal end, in the direction L, of a plate 2 of the detection circuit, itself located in line, in the direction L, of a plate 4 of the activation circuit.
• each plate 10 is positioned centrally relative to the second longitudinal end of a plate 2.
• the comparator comprises as many plates 8 and plates 10 as plates 2 or 4, so that it appears to consist of thermal cells juxtaposed in the direction L, each thermal cell comprising a plate 2, a plate 4, a plate 8 and a plate 10 (see FIG. 5).
• the plates 8 and 10 are advantageously identical to each other and can be of different types, in particular:
• the plates 8 and 10 can be radiation reflectors, acting respectively to reflect a part of the incident radiation on the input faces E1 and E2, coming from the external media 100 and 200. They then consist of a material to high electrical conductivity such as aluminum, silver, gold, chromium, copper and alloys comprising at least one of these metals.
• the comparator makes it possible to compare radiative fluxes emitted by flux sources disposed substantially opposite, between which the comparator is placed;
• the plates 8 and 10 can be radiation absorbers, acting respectively to absorb part of the radiation incident on the input faces E1 and E2.
• they can be made of a material with high absorption power, such as a black film, a ceramic or a chromium oxide, possibly combined with another metal.
• a comparator is then identical to that of a comparator with reflecting plates 8 and 10;
• the plates 8 and 10 can constitute thermal bridges between layers of insulating material forming the entry faces E1 and E2 and the layers 6 and 7.
• FIG. 6 represents an example of a heat flux comparator having such a structure.
• Two additional layers of insulating material 9 and 11 are arranged on either side of layers 6 and 7, parallel to the latter and on the side of each opposite to the thermoelectric circuits.
• the layers 9 and 11 are respectively separated from the layers 6 and 7 by the plates 8 and 10.
• the plates 8 and 10 can be made of an epoxy type material or of a metallic material such as copper, aluminum, silver, chromium, nickel and an alloy comprising at least one of these metals.
• a volume of thermal insulation 12 can be arranged between neighboring plates 8 or between neighboring plates 10, in a separation interval between layers 6 and 9 for plates 8, and between layers 7 and 11 for plates 10.
• the volumes 12 can be empty or filled with gas.
• the ends of the ribbon 1 are connected to the terminals of an electric voltage detector 20, and the ribbon 3 is connected to the terminals of a current generator 30 (FIG. 3), which delivers a direct current I in the ribbon 3.
• the voltmeter 20 measures an electric voltage representative of a balance of the thermal fluxes incident on the input faces El and E2 of the comparator, according to an operation identical to that of any known thermal detector.
• a variation in the thermal fluxes incident on the input faces E1 and E2 is detected in the form of a variation in the intensity of the supply current to the activation circuit which is necessary to compensate for the variation in the electric voltage generated in the comparator by said variation in heat fluxes.
• the electrical polarities of the ends of the ribbons 1 and 3 superimposed in the direction N can have identical or opposite electrical polarities, depending on the type of plates 8 and 10.
• the comparator has the structure shown in FIG. 1, supplemented by plates 8, and possibly a layer of insulating material 9, arranged on the layer 6 of as described above.
• such a comparator may also have an operation by reflection or absorption of radiation, or by thermal bridges, with respect to the external medium 100 in contact with the face of input E1.
• the comparator can also possibly be placed on a support (S) by its face opposite to the input face E1.
• S support
• thermoelectric detection circuit and a thermoelectric activation circuit associated in one of the ways described above.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Combustion & Propulsion (AREA)
• Fluid Mechanics (AREA)
• Investigating Or Analyzing Materials Using Thermal Means (AREA)

Applications Claiming Priority (3)

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• 2002
  • 2002-10-18 FR FR0212985A patent/FR2846091B1/fr not_active Expired - Fee Related
• 2003
  • 2003-10-09 EP EP03775480A patent/EP1552257A1/de not_active Ceased
  • 2003-10-09 WO PCT/FR2003/002980 patent/WO2004038352A1/fr not_active Ceased
  • 2003-10-09 AU AU2003283506A patent/AU2003283506A1/en not_active Abandoned

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