EP3022780A1

EP3022780A1 - Thermoelectric generator

Info

Publication number: EP3022780A1
Application number: EP14767042.6A
Authority: EP
Inventors: Sébastien VESIN; Joël DUFOURCQ
Original assignee: Hotblock Onboard; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Hotblock Onboard; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2013-07-17
Filing date: 2014-07-15
Publication date: 2016-05-25
Also published as: FR3008829A1; US20160163946A1; WO2015007960A1

Abstract

The invention relates to a thermoelectric device (1) comprising a first conduit (10) sealingly housed in a second conduit (12). The first (10) and second (12) conduits extend along a longitudinal axis (11). In addition, the device (1) comprises a thermocouple (20) extending along a transverse axis (13). The thermocouple (20) is disposed between the first (10) and second (12) conduits that are formed such that the thermocouple (20) undergoes compressive stress (σ_c) along the transverse axis (13).

Description

Thermoelectric generator

Technical field of the invention

The invention relates to a thermoelectric device for generating an electric current, in particular by exploiting exhaust gases discharged by a combustion engine.

The invention also relates to a method of manufacturing such a thermoelectric device.

State of the art

A conventional architecture of a thermoelectric generator uses thermoelectric modules subjected to a temperature gradient between two of their opposite faces. Such thermoelectric modules generally comprise thermocouples electrically connected in series and thermally in parallel. Each thermocouple is formed by two studs connected to one another at one end by an electrical connection element. The studs forming a thermocouple are based on different thermoelectric materials intended to generate an electric current when they are subjected to a temperature gradient. The thermocouples are electrically connected in series by electrical connection elements which are generally metallic elements. Moreover, the temperature gradient is created by having two heat sources at the opposite faces of the thermoelectric modules, a first so-called cold source and a second so-called hot source. Each of the two sources may comprise a conduit in which a fluid circulates, the fluid associated with the cold source having a temperature lower than that of the fluid associated with the hot source. Such devices can be used cleverly in heat exchangers to produce electricity. In particular, this type of device can be associated with a combustion engine, by converting the heat coming from the exhaust gases of the engine. However, these thermoelectric generators can suffer from the appearance of thermal resistances between the thermoelectric modules and the sources of heat. Indeed, according to certain operating conditions, the thermoelectric modules can be subject, cyclically, to significant thermal gradients, especially when the hot source is generated by heat from the exhaust gas.

The difference between the thermal expansion coefficients of the materials of the thermoelectric modules and the materials forming the heat sources, is at the origin of strong stresses and mechanical deformations, generated by the numerous thermal cycles during the operation of the thermoelectric generator. These thermomechanical deformations can alter the quality of the thermal contacts between the heat sources and the thermoelectric modules, which can have adverse consequences on the thermic and electrical performances of the thermoelectric generator, but also on its thermomechanical reliability and its longevity. The object of the invention

In the field of electric power generation, there is a need to realize a thermoelectric generator taking advantage of its thermal environment while being reliable, efficient, and easy to manufacture.

This need is satisfied by providing a thermoelectric generator comprising:

- A calender extending along a longitudinal axis and provided with two plates each having a through orifice, and respectively disposed at two ends of the calender opposite along the longitudinal axis;

- two additional plates each having a circulation orifice, and arranged so that the shell is interposed between the two additional plates;

a first duct disposed in a second duct, the first and second ducts being disposed in the calender and extending along a longitudinal axis and each having two opposite ends along the longitudinal axis;

a thermocouple interposed between the first and second conduits.

The first conduit of said generator is sealingly assembled on the two additional plates so that each of the ends of the first conduit communicates with the circulation orifice formed in one of the additional plates. In addition, the second duct is assembled on the two plates so that each of the ends of the second duct communicates with the orifice of one of the plates and that the second set duct and calender is sealed.

According to a first embodiment, one of the two plates of the shell is sealed with one of the two additional plates so as to define an inter-plate space communicating with a sealed internal space delimited by the second conduit via minus the orifice formed in the shell of the shell. According to this embodiment, the device also comprises an outlet pipe formed in one of the interconnected plates, and communicating with the inter-plate space.

Preferably, the device comprises means for evacuating the inter-plate space and the internal space via the outlet pipe. Advantageously, the inter-plate space and the internal space comprises an inert gas.

According to another embodiment, the thermocouple extends along a transverse axis, and the first and second conduits are shaped so that the thermocouple undergoes compressive stress, along the transverse axis, between said first and second ducts.

Advantageously, the distance d between the first and second conduits at the cross section of the thermocouple is less than the transverse dimension d2 of the thermocouple, the distance d1 and the dimension d2 being measured at the same temperature.

According to one embodiment, the thermoelectric generator comprises means for circulating a first fluid at a first temperature in the first conduit, and a second fluid covering the second conduit, the second fluid being at a second temperature below the first temperature. first temperature.

Advantageously, the fluid circulation means are configured to circulate a pressurized fluid in the first conduit and / or in the second conduit.

There is also provided a method for producing this type of thermoelectric generator comprising the following steps: - Provide the first and second ducts, the first duct being configured to be housed in the second duct and extend along the longitudinal axis of the second duct;

- Predict the thermocouple extending along the transverse axis;

assembling the first and second ducts so that the temperature of the first duct and / or the thermocouple is lower than the temperature of the second duct during assembly of the first and second ducts and the thermocouple to form the thermoelectric device so that the thermocouple undergoes compressive stress, along the transverse axis, between the first and second ducts.

According to a particular mode of implementation, the method of producing this type of thermoelectric generator comprises the following steps:

providing first and second half-ducts extending along the longitudinal axis and configured to form the second duct by assembling the first and second half-ducts;

placing the first and second half-ducts facing each other so that the first duct is housed between the two half-ducts and the thermocouple is interposed between the first half-duct and the first duct;

pressing the first and second half-ducts towards each other so as to impose on the thermocouple a compressive stress, along the transverse axis, between the first half-duct and the first duct;

- Secure the first and second half-ducts to form the second duct, the thermocouple being maintained in compression, along the transverse axis, between the first and second ducts.

Advantageously, the first and second ducts respectively comprise first and second substantially plane and parallel surfaces arranged facing each other so that the thermocouple is interposed between said first and second surfaces. Preferably, an interface strip based on an electrically insulating material is interposed between the thermocouple and the first conduit, and / or between the thermocouple and the second conduit. There is further provided a method of generating an electric current by the device made comprising the following steps:

circulating a first fluid having a first temperature in the first conduit;

circulating a second fluid having a second temperature lower than the first temperature, around the second conduit.

According to a preferred embodiment of generating an electric current, the device is configured so that exhaust gases discharged by a heat engine flow either in the first conduit or around the second conduit.

BRIEF DESCRIPTION OF THE DRAWINGS Other advantages and features will emerge more clearly from the following description of particular embodiments of the invention given as non-restrictive examples and represented in the accompanying drawings, in which: FIGS. 3 and 4 schematically illustrate, in cross-section, a thermoelectric device according to different embodiments of the invention;

- Figure 2 illustrates schematically, in longitudinal section, the device of Figure 1;

- Figures 5 to 7 illustrate schematically, in cross section, different steps of a method of manufacturing a thermoelectric device according to one embodiment of the invention; - Figure 8 schematically illustrates an exploded view of a thermoelectric device comprising a calender according to one embodiment of the invention;

- Figure 9 schematically illustrates, in longitudinal section, a thermoelectric device comprising a calender according to one embodiment of the invention.

Description of preferred embodiments

To allow a thermoelectric generator improved operation, it is preferable to take special care to the thermal and electrical connections arranged within the generator. It is therefore advantageous to take care of the quality of the contacts between the heat sources and the thermoelectric module of the generator. In order to produce such a thermoelectric generator, an advantageous arrangement and assembly of certain elements forming the thermoelectric generator is envisaged.

According to an embodiment illustrated in FIG. 1, a thermoelectric device 1 comprises first 10 and second 12 ducts extending along a longitudinal axis 11. The first duct 10 is disposed in the second duct 12. In other words, the first and second ducts 10 and 12 are arranged so that they extend along the longitudinal axis 11, for example in a parallel manner and advantageously in a coaxial manner.

In addition, the thermoelectric device 1 comprises a thermocouple 20 extending preferably along a transverse axis 13, perpendicular or substantially perpendicular to the longitudinal axis 11. The thermocouple 20 is interposed between the first 10 and second 12 ducts. Preferably, the ducts 10 and 12 are shaped so that the thermocouple 20 undergoes a compression stress o _c , along the axis 13. The compressive stress o _c is a clamping stress which is permanently applied to the thermocouple 20, between the first 10 and second 12 ducts, and it is preferably between 0.2 and 10 MPa, advantageously between 0, 5 and 4 MPa.

Preferably, the thermoelectric device 1 also comprises an additional thermocouple 21 also disposed between the first 10 and second 12 ducts. The thermocouple 20 and the additional thermocouple 21 are, for example, arranged on either side along the transverse axis 13, of the first duct 10. According to this preferred configuration, the thermoelectric device 1 comprises a stack, along the transverse axis 13, comprising the thermocouple 20 disposed on the first conduit 10, itself arranged on the additional thermocouple 21. This stack is disposed inside the second conduit 12, so that the thermocouples 20 and 21 are interposed between the first 10 and second 12 ducts. In other words, the first duct 10 is kept at a distance from the second duct 12 by means of the thermocouples 20 and 21.

Thereafter, a thermocouple is defined as being an element comprising two pads electrically connected to each other, preferably at one of their ends, by an electrically conductive, and preferably thermally conductive connection element. The pads of the same thermocouple are formed in two materials of different thermoelectric natures. By materials of different thermoelectric natures, we mean materials of different chemical compositions, able to transform when electrically connected, thermal energy into electrical energy and / or vice versa. For example, it is possible to use the same semiconductor material having different types of doping. As illustrated in FIG. 2, the thermoelectric device 1 comprises, advantageously, several thermocouples electrically connected to each other in series by connection elements 203, to form a first thermoelectric module 25 interposed between the first 10 and second 12 ducts. The module 25 preferably comprises identical thermocouples 20, which also undergo compression stresses a _c between the first 10 and second 12 ducts.

Terminating electrical connectors 204 and 205 are located at the ends of the series of thermocouples 20 of the module 25 to provide the electrical connections of the thermoelectric module 25. The connectors 204 and 205 may be used in particular to recover the electrical current generated by the module 25. or to connect the module 25 with other thermoelectric modules.

Preferably, the thermoelectric device 1 also comprises an additional thermoelectric module 26, comprising the additional thermocouple 21, also disposed between the first 10 and second 12 ducts. In a preferred configuration, the thermoelectric device 1 comprises a stack, along the transverse axis 3, comprising the thermoelectric module 25 disposed on the first conduit 10, itself arranged on the additional module 26. This stack is disposed inside the second conduit 12, so that the modules 25 and 26 are interposed between the first 10 and second 12 ducts.

In the same way as for the module 25, the module 26 preferably comprises a plurality of thermocouples 21 connected together in series by connection elements 213, and electrical termination connectors 214 and 215. The number of thermocouples forming the modules 25 and 26 can be evaluated according to the optimal compromise between the geometry of the thermocouples, their distributions and the electrical power produced from the thermal power therethrough. The thermoelectric device 1 is configured to generate electrical power from a heat transfer between the thermocouple 20 and two heat sources generating a thermal gradient. The thermocouple 20 (21) comprises two pads 201 (211) based on different thermoelectric materials interconnected by an electrically conductive element 202 (212). The two pads 201 (211) may be based on a semiconductor material, such as silicon or silicon-germanium alloy, respectively doped P and N. The pads 201 (211) may also be based on semi -metals (Bi, Sb, etc.). In fact, those skilled in the art are able to choose the type of material of the thermocouple pads (21) depending on the environment of use of the thermoelectric device.

The pads 201 (211) may have any geometric shape, for example a parallelepipedal or cylindrical shape. Each pad 201 (211) extends along the transverse axis 13 so that it is disposed between the first 10 and second 12 ducts. In addition, each pad 201 (211) has opposite first and second ends along the transverse axis 13. The first end is disposed between the first duct 10 and the second end, which is itself arranged between the second duct 12 and the first end. Each pad 201 (211) of the thermocouple 20 (21) has at its one end connection elements 203 (2 3), or electrical termination connectors 204 (214) and 205 (215) forming a first end of the thermocouple 20 ( 21).

In addition, the pads 201 (211) of the thermocouple 20 (21) are connected together, preferably at the second end by the electrically conductive element 202 (212) generally formed by a metal element. The element 202 (212) then forms the second end of the thermocouple (21), opposite the first end, along the transverse axis 13. The heat sources of the thermoelectric device 1 are provided with first 10 and second 12 ducts, and are configured to create a thermal gradient between the opposite ends of the thermocouple 20. The first duct 10 is advantageously a sealed duct, configured to allow the circulation of a first fluid.

The first duct 10 preferably comprises internal fins to improve the heat exchange between the first fluid and the inner walls of the first duct 10. The second duct 12 is advantageously a sealed duct configured to be embedded in a second fluid, so as to that the first conduit 10 is devoid of any contact with the second fluid, or to limit the contact between the two fluids. The first 10 and second 12 conduits are, in particular, stainless steel, and they can be formed by any known means, for example by profiling, welding and / or brazing.

In order to facilitate the heat transfer between the heat sources and the thermocouple 20, the first and second ends of the thermocouple 20 are preferably in direct contact with the first 10 and second 12 ducts, respectively. Furthermore, to allow the thermoelectric device 1 to generate electrical energy, the contacts between the conduits 10 and 12, and the thermocouple 20 must avoid the creation of a short circuit within the thermocouple 20 or the thermoelectric module 25 while facilitating the heat transfers. Thus, the portions of the conduits 10 and 12 and / or the thermocouple 20 constituting these contacts are based on an electrically insulating and thermally conductive material.

Preferably, the contacts between the thermocouple 20 and the heat sources comprise a layer based on an electrically insulating material. This layer may be based on silicon oxide, or based on a ceramic-type material. As an example based on aluminas

(AI2O3) having been hard anodized, Ceramaze ^® , Keronite ^® , or based on aluminas with or without titanium dioxide. The layer may also be based on a glass-ceramic type material such as chromium oxide. Furthermore, the parts in contact may undergo, depending on the compatibility of the materials used, an anodizing step, or comprise a coating DLC (DLC for the abbreviation of "Diamond-Like Carbon").

Advantageously, the thermoelectric device 1 comprises an interface lamella 16, commonly called a substrate, interposed between the second conduit 12 and the electrically conductive element 202, ie the second end of the thermocouple 20. The lamella 16 may be based on AIN and it is in direct contact with the thermocouple 20 and / or the second conduit 12.

Preferably, the thermoelectric device 1 also comprises the same type of interface plate 16 interposed between the first conduit 10 and the first end of the thermocouple 20. This type of interface plate 16 advantageously allows the thermocouple 20 to be protected against appearance of a short circuit. In addition, the interface strip 16 may also fulfill a mechanical buffer function to homogenize the clamping stresses applied to the thermocouple 20 by the ducts 10 and 12 during assembly, and possibly during the operation of the thermoelectric device 1. in addition, this type of interface plate 16 advantageously allows thermal homogenization between the ends of the thermocouple 20 and the first 10 and second 12 ducts.

The thermoelectric device 1 described above makes it possible to arrange the thermocouple 20 between two heat exchange walls formed by the conduits 10 and 12. The thermocouple 20 undergoes a compressive stress Oc applied by the first 10 and second 12 ducts, making it possible to advantageously to ensure a permanent clamping constraint, along the transverse axis 13. This clamping constraint makes it possible to avoid or at least to minimize the effect of the thermomechanical deformations of the conduits 10 and 12, and / or of the thermocouple 20 on the alteration of the contact zones between these elements. The compressive stress a _c thus makes it possible to maintain good quality contacts between the heat sources, and the thermocouple 20, which avoids the creation of thermal resistances, in the thermal transfer zones. The thermal resistances are then minimized and the heat transfer improved. As a result, the compressive stress o _c advantageously makes it possible to improve the conversion of the thermal energy passing through the thermocouple into electrical energy.

In addition, the compression stress σ ₀ advantageously makes it possible to limit the shear stresses which are detrimental to the thermoelectric pads 201 of the thermocouple 20.

As illustrated in FIG. 3, the distance d1 separating the first 10 and second 12 ducts at the cross section of the thermocouple 20 is smaller than the transverse dimension d2 of the thermocouple 20. The distance d1 and the dimension d2 are measured at a distance of same temperature Tmes. In fact, the first 10 and second conduit 12 define a space E20 configured to house the thermocouple 20, and the distance d1 corresponds to the transverse dimension of this space E20. Under identical thermal and mechanical conditions, the transverse dimension d2 of the thermocouple 20 is larger than the transverse dimension d1 of the space E20.

The realization of the thermoelectric device 1 can be carried out according to several modes, in particular by exploiting the difference of the thermomechanical deformations of the conduits 10 and 12, and the thermocouple 20. Thus, and by way of example, the temperatures of the thermocouple 20, and conduits 10 and 12 may be adjusted during the embodiment of the device 1, so that the thermocouple 20 can be arranged in the space E20. When returning to a thermal equilibrium, in other words, the ducts 10 and 12, and the thermocouple 20 are for example at the same temperature, the thermocouple 20 then undergoes a compressive stress, along the transverse axis 13, applied between the first 10 and second 2 ducts. The materials of the conduits 10 and 12 are chosen so that they are sufficiently rigid to subject the thermocouple 20 to said thermal equilibrium compression stress.

In the particular embodiment that follows, the thermoelectric device 1 comprises means (not shown in the figures) for circulating fluids within the device 1. These means are configured to circulate a first fluid at a first temperature T1 in the first conduit 10. The circulation means are also configured to circulate a second fluid covering the second conduit 12, the second fluid being at a second temperature T2 preferably lower than the first temperature T1. Furthermore, the fluid circulation means can be configured to circulate a pressurized fluid in the conduit 10 and / or the conduit 12, thereby increasing the compression stress o _c applied to the thermocouple 20.

Advantageously, the first temperature T1 is chosen so that the first duct expands, and / or the second temperature T2 is chosen so that the second duct 12 contracts. The thermomechanical deformations of the ducts 0 and 12 produced by the choice of the first T1 and second T2 temperatures, further reduce the transverse dimension of the space E20, thereby accentuating the compression stress o _c experienced by the thermocouple 20. As a result, quality thermal contact between the thermocouple 20 and the ducts 10 and 12, can be guaranteed. The circulation means of the first and second fluids may comprise, for example, a pump configured to circulate a cooling liquid in a calender comprising the second conduit 12. In addition, the circulation means may comprise a set of ducts configured to convey and circulate exhaust gas, discharged by a combustion engine, into the first duct 10. The temperatures of the exhaust gas, and the liquid of cooling are different and can generate a large thermal gradient at the ends of the thermocouple 20, along the transverse axis 13.

From an electrical reliability point of view, the metallic connections of conventional thermoelectric generators can suffer from an oxidation problem, especially when subjected to high temperatures, which is often the case for this type of thermoelectric device. Moreover, this oxidation is accentuated when these metal connections are arranged in an atmosphere with corrosive residues such as an atmosphere comprising exhaust gases from a combustion engine.

According to a preferred embodiment, the first 10 and second 12 ducts delimit an internal space E ₁₂ sealed. Advantageously, the thermoelectric device 1 comprises means for evacuating the internal space E12. Furthermore, the thermoelectric device 1 may advantageously comprise means for chambering the internal space E12 with an inert gas such as argon, helium or nitrogen.

The evacuation or under an inert gas of the internal space E12, advantageously protects against oxidation, the elements forming the thermocouple 20, in particular the electrically conductive element 202, the connection elements 203 or the connectors of 204 and 205, which are generally based on easily oxidizable metal materials. Furthermore, when the thermoelectric device 1 is configured to operate in an environment with exhaust gases, a corrosive environment, the risk of oxidation of the elements of the thermoelectric device 1 is higher. This preferred embodiment also makes it possible to protect the outer walls of the first duct 10 and the internal walls of the second duct 12 against oxidation, thus improving the reliability of the device 1 from a thermal and electrical point of view.

The method of manufacturing a thermoelectric device as defined above comprises the following steps:

- Provide the first 10 and second 12 ducts, the first duct 10 being configured to be housed in the second duct 12 and extend along the longitudinal axis 11 of the second duct 12;

- provide the thermocouple 20 extending along the transverse axis 13.

In addition, the manufacturing method comprises a step where the first and second ducts 10 and 12 are assembled so that the thermocouple 20 undergoes a compressive stress o _c , along the transverse axis 13, between the first 10 and second 12 ducts. During assembly, the thermocouple 20 is interposed between the ducts 10 and 12 and is subjected to the compression stress a _c applied by the ducts 10 and 12.

Preferably, the compression stress a _c is a permanent clamping constraint, along the transverse axis 13. Clamping stress means a constraint for freezing and immobilizing the thermocouple 20 with respect to the ducts 10 and 12, in particular along the transverse axis 13. Thus, the shear stresses within the thermocouple 20, are limited. Mitigating the effect of this type of constraint, advantageously makes it possible to limit the deterioration and the risk of breakage of the thermoelectric pads of the thermocouple 20. The application of a compressive stress o _c during the assembly of the elements of the thermoelectric device 1 can be performed by any means known in the field of assembly of mechanical parts. As for example, the thermoelectric device 1 may comprise clamping means configured to reduce the dimension, along the transverse axis 13, of the second conduit 12. The thermoelectric device 1 may comprise, thus, clamping elements such as a ring in the case of assembly, the clamping ring can be mounted so as to enclose the second conduit 12, a portion of the wall of which is thus interposed between a wall of the Then, the ring is tightened so as to apply the compressive stress o _c to the thermocouple 20 between the first 10 and second conduit 12.

In fact, the clamping means make it possible to press the opposite walls, along the transverse axis 13, of the second duct 12 towards each other. Furthermore, the first duct 10 and the thermocouple 20 are disposed inside the second duct 12, so that the thermocouple 20 is interposed, along the transverse axis 13, between the first duct 10 and the second duct 12. conduits 10 and 12 and the thermocouple 20 are arranged so that the clamping means can press the first conduit 10 to the second conduit 12 so that the thermocouple 20 undergoes compression stress o _c .

In the thermoelectric device 1, the ducts 10 and 12 are configured to form the heat sources associated with the thermocouple 20. In order to obtain an efficient thermal behavior, the heat sources are preferably thermally isolated from each other, or far removed from each other as much as possible. As illustrated in FIG. 4, the first duct 10 has a first wall separated from the second duct 12 by the thermocouple 20, and second wall opposite the first wall, along the transverse axis 13. For thermal and mechanical considerations, a shim 40 preferably based on a non-compressible and thermally insulating material, is interposed between the second wall of the first duct 10 and the second conduit 12.

Advantageously, the production method provides an additional thermocouple 21, preferably symmetrical to the thermocouple 20 relative to the first conduit 10. The additional thermocouple 21 is disposed between the second wall of the first conduit 10, and the second conduit 12. The means Thus, this advantageous arrangement allows both the thermocouple 20 and the additional thermocouple 21 to be applied compressively. This advantageous arrangement makes it possible both to separate the heat sources (the ducts 10 and 12). from one another, and provide a second source of electrical generation (the additional thermocouple 21) for better exploitation of the thermal gradient provided by the heat sources.

According to a particular embodiment, an interface strip 16 based on an electrically insulating material is interposed between the thermocouple 20 and the first conduit 10, and / or between the thermocouple 20 and the second conduit 12. The lamella d The interface 16 may be based on AIN, and it is arranged to be in direct contact with the thermocouple 20, and / or the conduits 10 and 12. The lamella 16 advantageously avoids the occurrence of a short circuit within the thermocouple 20 and to homogenize the compressive stresses applied to the thermocouple 20 by the first 10 and second 20 conduits.

According to a particular mode of implementation, the production method comprises an assembly step in which the assembly temperature Ta1 of the first conduit 10 and / or the thermocouple 20 is less than the assembly temperature Ta2 of the second conduit 12 When of this assembly step, the thermocouple 20 is arranged to be in contact with the two heat sources. By contact with a heat source, it is meant that the thermocouple 20 is in direct contact, either with the conduit associated with said heat source (10 or 12), or with the interface plate 16 which is itself in direct contact. with said conduit (10 or 12).

Preferably, the assembly temperature Ta1 of the first duct 10 and / or the thermocouple 20 is chosen to be lower, and advantageously much lower, than the temperature of the heat source comprising the first duct 10 when the thermoelectric device 1 is operational and generates electrical energy. In the same manner, the assembly temperature Ta2 of the second duct 12 is chosen to be greater, and advantageously much greater, than the temperature of the heat source comprising the second duct 12 when the thermoelectric device 1 is operational and generates an electrical energy.

The assembly step described above, advantageously generates thermomechanical deformations of the ducts 10 and 12 which allow an increase or an application of the compression stress o _c experienced by the thermocouple 20. Indeed, after the step of assembly, and when the thermoelectric device 1 is subjected to the temperature gradient created by the heat sources, the first conduit 10 expands, while the second conduit 12 contracts, further compressing the thermocouple 20 interposed between the two conduits 10 and 12 .

According to a preferred embodiment illustrated in FIGS. 5 to 7, the method of manufacturing the thermoelectric device 1 uses the assembly of two half-ducts to form the second duct 12. In fact, first and second 14s are provided. half ducts extending along the longitudinal axis 11. The two half-ducts 14 and 15 are configured to form, in a sealed manner, the second conduit 12 when assembled. The two half-ducts 14 and 15 may, for example, have complementary concave shapes configured to form the shape of the second duct 12.

The first 14 and second 15 half-ducts are then arranged opposite, by arranging the first duct 10 and the thermocouple 20 between the first 14 and second 15 half-ducts. In addition, the facing of the half-pipes 14 and 15 is carried out so that the thermocouple 20 is interposed between the first half-pipe 14 and the first pipe 10.

Then, the first 14 and second 15 half-ducts are pressed towards each other by applying a pressure P to the two half-ducts 14 and 15. This step makes it possible to transfer the pressure P exerted between the first 14 and second Thus, this step is performed to impose on the thermocouple 20 a compression stress, along the transverse axis 13, between the first half-pipe 14 and the first pipe 10. In order to maintain the stress of compression imposed on the thermocouple 20, the first and second half-ducts 14 and 15 are subsequently secured to form the second duct 12. The first duct 10 defines an internal space Em, and the assembled duct 12 defines an internal space E12 completely independent and sealed with respect to the internal space E-10 of the first duct 10.

The two half-ducts 14 and 15 are secured in a sealed manner, in particular by longitudinal seam welds S _c , or any other known means. Longitudinal seam welding means, a longitudinal joint overlap for joining the two half-pipes 14 and 5 while ensuring the continuity of the material, and thus the sealing of the second conduit 12 formed. This joining is carried out so that the thermocouple 20 is maintained in compression, along the transverse axis 13, between the first duct 10 and the first half-duct 14, ie the second duct 12. According to a preferred embodiment, the first and second ducts 10, 12 respectively comprise first 101 and second 121 facing surfaces so that the thermocouple 20 is interposed between said first 101 and second 121 surfaces. The first 101 and second 121 surfaces may have a convex shape. The thermocouple 20 is then interposed between the convex surfaces 101 and 121 which provide a spring effect, during the transfer of the pressure P to the thermocouple 20. This advantageously makes it possible to homogenize the stress applied to the thermocouple 20. Advantageously, the first and second 121 surfaces are substantially planar and parallel. The particular shape of the first and second ducts 10 and 12 advantageously facilitates the assembly of the thermocouple 20 and its arrangement between these two ducts. It also makes it possible to obtain a better distribution of the clamping stress and a reduction of the contact thermal resistance.

In addition, the arrangement of the thermocouple 20 between the planar surfaces advantageously makes it possible to easily and effectively transfer the pressure P applied to the two half-ducts 14 and 15 to the thermocouple 20 disposed between the two ducts 10 and 12. Thus, the thermocouple 20 undergoes compression stress o _c applied by the first and second ducts 10 and 12.

By way of example, the half-ducts 14 and 15 may advantageously have a U-shaped cross-section (FIG. 5). Thus, each half-pipe 14 and 15 has two lateral surfaces connected by a central surface. During assembly, the thermocouple 20 can be placed on the central surface 121 of the first half-pipe 14 (Figure 6). Furthermore, the first conduit 10 has, preferably, a parallelepipedal shape so that it has a flat surface 101. The first conduit 10 is then placed on the thermocouple 20 so that the flat surface 101 is parallel to the central surface 121 of the first half-conduit 14. In other words, the thermocouple 20 is interposed between the central surface 121 and the flat surface 101 (Figure 6). To form the second duct 12, the second half-duct 15 is, in a first step, arranged facing the first half-duct 14, more particularly facing the stack comprising, successively, the first half-duct 14, the thermocouple 20 and the first conduit 10 (Figure 7). The second duct 12 thus forms the internal space E12, totally independent of the internal space E10 of the first duct 10.

Moreover, for thermal and / or mechanical considerations, a shim 40 may be interposed between the first duct 10 and the second duct 12 (FIG. 4). The shim 40 and the thermocouple 20 being disposed on either side, along the transverse axis 13, of the first conduit 10. The shim 40 is preferably based on a non-compressible and thermally insulating material. The wedge thus makes it possible to efficiently transfer the pressure applied to the two half-ducts 14 and 15 to the thermocouple 20. In addition, the wedge 40 also makes it possible to thermally isolate the heat sources of the thermoelectric device 1.

Advantageously, the shim is formed by an additional thermocouple 21 (FIG. 7). From an electrical point of view, this arrangement advantageously makes it possible to provide a second source of electrical generation for better exploitation of the thermal gradient created by the first 10 and second 12 ducts. From a thermal point of view, this arrangement also makes it possible to keep the ducts 10 and 12 away from each other, to minimize the mutual thermal influence of the two heat sources of the thermoelectric device 1.

According to a preferred implementation, provision is made for the use of a calender comprising a bundle of ducts of the same type as the second duct 12. By calender means a cavity preferably having a cylindrical shape delimited by a hollow body. A calender allows a flow of a given fluid around a duct, or a bundle of ducts, housed in the calender, thus forming one of the two heat sources of the thermoelectric device.

As illustrated in FIGS. 8 and 9, the method provides for the use of a calender 30, extending along a longitudinal axis 11 '. Preferably the longitudinal axis 11 'of the shell is parallel to the longitudinal axis 11 of the pipes 10 and 12. The shell 30 is provided with two plates 31 and 32 respectively disposed at the two ends of the shell 30, opposite along the axis longitudinal 11 '.

The calender 30 and the second duct 12, or the bundle of the ducts 12, define a calender volume V30, totally independent of the internal space E12 of each duct 12. Furthermore, the calender 30 can comprise an inlet and an outlet, configured to circulate a fluid, preferentially coolant, in the cavity of the shell 30 around the second conduit 12. The fluid flowing in the shell 30 is in contact with the outer walls of the second pipe 12, or the bundle of pipes 12.

Preferably, the shell 30 has a cylindrical shape, the two plates 31 and 32 constitute the bases. In addition, the plates 31 and 32 each comprise at least one through orifice. In FIG. 8, the plate 31 has the orifice 31 and the plate 32 has the orifice 321. The orifices 311 and 321 are pierced in the plates 31 and 32 so as to receive the second duct 12. In fact, the second duct 12 has two longitudinal ends 122 and 123, in other words, opposite ends along the longitudinal axis 11 conduits 10 and 12. Each end communicates with the orifice (311 or 321) formed in one of said plates (31 or 32). Furthermore, the second conduit assembly 12 and calender 30 is secured in a sealed manner.

Preferably, the duct 12 is arranged to be substantially parallel to the longitudinal axis 11 'of the calender. Furthermore, the duct 12 may also be arranged in the shell 30, between the plates 31 and 32, in any direction, for example inclined or curved.

By way of example, each of the ends (122 or 123) is configured to be engaged in the orifice (311 or 321) of one of the two plates 31 and 32. The ends of the second duct 12 are then secured in a leaktight manner. the plates 31 and 32 of the calender 30, in particular by stirring, welding, or any other known means. Thus, the second duct 12 is disposed between the plates 31 and 32 of the calender 30. The internal space Ei ₂ sealed of the second duct 12, is accessible only via the two orifices 311 and 321 respectively formed in the plates 31 and 32, which are commonly called "tube plates" of the calender 30. In addition, this internal space E ₁₂ is totally independent of the volume V30 of the calender 30. In the same way as for a single second duct 12, a duct bundle 12, Preferably, these two plates 31 and 32 are advantageously identical. Advantageously, the method also uses a bundle of conduits of the same type as the first conduit 10. According to a particular mode of implementation, provision is made for the use two additional plates. As illustrated in FIG. 8, two additional plates 33 and 34 are provided, each comprising at least one through-hole 331 and 341. The circulation holes 331 and 341 are pierced in the additional plates 33 and 34 so as to receive the first duct 10. Furthermore, the calender 30 is interposed between the two additional plates 33 and 34. The first duct 10, having two opposite longitudinal ends 102 and 103, is disposed between the two additional plates 33 and 34. Each of the ends 102 and 103 of the first conduit 10 communicates with the circulation port 331 and 341 formed in one of said additional plates 33 and 34.

By way of example, each of the ends 102 and 103 of the first duct 10 are engaged in the orifices 331 and 341 respectively of the two additional plates 33 and 34. These ends are then sealed to the additional plates 33 and 34 by any means. known. The first duct 10, housed in the second duct 12, thus passes through the calender 30 without any interaction between the internal space E- | ₀ of the first duct 10 and the environment of the volume V30 of the calender 30.

The internal space E-io sealed first conduit 10 is accessible only through the two orifices 331 and 341 respectively formed in the additional plates 33 and 34. The internal space Ei ₀ of the first conduit 10 is completely independent of the volume V30 of the calender 30 and the internal space E ₁₂ of the second duct 12. In the same way as for a single first duct 10, a bundle of ducts 10, preferably identical, can be advantageously assembled between these two additional plates 33 and 34. This particular mode of assembly advantageously makes it possible to access the internal spaces E10 of all the conduits 10 simultaneously via the two additional plates 33 and 34. Thus, the two additional plates 33 and 34 can respectively form an inlet and an outlet of a fluid that can circulate at the same time in the different ducts 10.

This particular mode of implementation, allows to form a heat source comprising the first conduit 10, or a bundle of conduits, configured to circulate a fluid, preferably coolant. This heat source is advantageously independent of the calender 30 and therefore of the heat source comprising the second duct 12. Thus, the production method advantageously makes it possible to produce a thermoelectric device 1 arranged so as to comprise several pairs of first and second ducts. (10 and 12), ie several thermocouples (20, 21) or thermoelectric modules (25, 26) arranged between two different heat sources. This advantageous arrangement thus makes it possible to increase the electrical generation capacity of the thermoelectric device 1.

Advantageously, at one end of the calender 30, along the longitudinal axis 11 ', a plate of the calender 31 or 32 is sealed with an additional plate 33 or 34. This assembly is performed in such a way that the solid plates form an empty space Eip that will be called inter-plate space.

Preferably, the plates are joined together at their peripheries, so that the orifice or the orifices formed in the calender plate (31 or 32) communicate with the inter-plate space Eip, and that they not be blocked by the additional plate (33 or 34). For example, the inter-plate space Eip can be achieved by a counterbore in the thickness of one of the two assembled plates. The joining of the two plates can be obtained by any known means, for example by welding or by the use of a compressed seal 50 by clamping between the secured plates. Thus, this assembly step makes it possible to form an inter-plate space Eip communicating with the internal space E12 of the second conduit, or of the bundle of conduits 12 via the orifice or the orifices of the plate (31 or 32) of the grille 30. The inter-plate space Eip is totally independent of the space of the V30 grille. In addition, the inter-plate space Eip is completely independent of the internal space E10 of the first conduit 10 or the bundle of conduits 10 collected by the additional plate (33 or 34).

Advantageously, an outlet pipe 37 is made in one of the plates between which the inter-plate space Eip is disposed. The outlet pipe 37 is configured to communicate with the inter-plate space Eip. The outlet pipe 37 preferably comprises a valve configured to regulate the opening of the pipe 37, and possibly the flow rate of a fluid inside the internal space E12 of the pipe 12 or the bundle of pipes 12 via the interplate space Eip.

In order to avoid the corrosion problems of the elements of the thermoelectric device 1, in particular the conduits 10 and 12 as well as the elements of the thermocouple 20, the internal volume E12 of the second conduit 12 is advantageously evacuated. In other words, the internal space E12 of the second duct 12, or of the duct bundle 12 is drawn to vacuum via the outlet pipe 37 and the inter-plate space Eip. Moreover, the internal volume E12 of the second duct 12 can also be put under an inert gas: the inter-plate space Eip and the internal space E12 are in an inert atmosphere. In other words, the sealed space E ₁₂ of the second duct 12 or the duct bundle 12 is filled with an inert gas, via the outlet duct 37 and the inter-plate space Eip. By way of example, the inert gas may be based on argon, helium or nitrogen. The use of the thermoelectric device 1 thus produced preferably comprises the circulation of heat transfer fluids respectively in the first duct 10 and around the second duct 12. According to a preferential mode of generating an electric current by the thermoelectric device 1 illustrated in FIG. FIG. 9 circulates a first fluid F1 having a first temperature T1 in the first duct 10. In addition, around the second duct 12, a second fluid F2 is circulated having a second temperature T2, preferably less than the first one. T1 temperature.

In other words, under these conditions, the hot source of the thermoelectric device 1 is represented by the first conduit 10 and the cold source is represented by the second conduit 12. This particular arrangement of the heat sources advantageously makes it possible to accentuate, if not to preserve the compressive stresses applied to the thermocouple 20 by the first 10 and second 12 conduits.

In fact, when the temperature T1 of the fluid F1 is sufficiently high, for example greater than 100 ° C., generally greater than 250 ° C., the first duct 10, which is generally based on a metallic material, has a tendency to expand . Similarly, when the temperature T2 of the second fluid F2 is sufficiently low, for example less than 100 ° C, the second conduit 12 tends to contract. The thermomechanical deformations of the first duct 10 and the second duct 12 thus generated, cause a pressure application, having a direction from the first duct 10 to the second duct 12, to the thermocouple 20. As a result, the circulation of the first fluid F1 having the first temperature T1 and / or the second fluid F2 having the second temperature T2 advantageously contributes to the increase in compression stress initially applied to the thermocouple 20. Advantageously, the thermoelectric device 1 exploits the evacuation of the exhaust gases of a combustion engine. In other words, the exhaust gases are used to contribute to the formation of a heat source within the thermoelectric device 1.

The method for generating an electric current can thus comprise a step during which the exhaust gases of the combustion engine are evacuated so as to flow in the first duct 10. Thus, the evacuation of the exhaust gases can contribute, advantageously, to forming the hot source of the thermoelectric device 1. When a duct, or several ducts 10 are collected by the additional plates 33 and 34, the exhaust gases can be directed towards one of these plates additional. The exhaust gases are introduced through one of the additional plates 33 or 34 and then flow through the conduit (s) 10 to exit through the other additional plate.

Furthermore, the exhaust gases of the combustion engine can also be evacuated so as to circulate around the second duct 12. When several ducts 12 are collected by the plates 31 and 32 of the calender 30, the exhaust gases can be conveyed by an exhaust duct connected to the inlet of the calender 30 so as to circulate around the duct or ducts 12, to be subsequently discharged via the outlet of the calender 30. As a result, the thermoelectric device 1 can be installed in an apparatus comprising a combustion engine, for example a vehicle. In general, this type of apparatus comprises an alternator driven by said motor, to generate electricity. Thus, the thermoelectric device 1, generating an electrical energy from a heat conversion of the exhaust gas, advantageously reduces the fuel consumption of the engine, replacing the alternator permanently or temporarily.

Claims

claims

Thermoelectric device (1) comprising:

A shell (30) extending along a longitudinal axis (11 ') and provided with two plates (31, 32) each having a through orifice (31 1,

321), and disposed respectively at two ends of the calender (30) opposite along the longitudinal axis (1 1 ');

• two additional plates (33, 34) each having a circulation orifice (331, 341), and arranged so that the calender (30) is interposed between the two additional plates (33, 34);

A first duct (10) disposed in a second duct (12), the first (10) and second (12) ducts being arranged in the calender and extending along a longitudinal axis (1 1) and comprising each two ends (102, 103, 122, 123) opposite along the longitudinal axis (11);

A thermocouple (20) interposed between the first (10) and second (12) conduits;

the second duct (12) being assembled on the two plates (31, 32) so that each of the ends (122, 123) of the second duct (12) communicates with the orifice (31 1, 321) of one of the plates (31, 32) and that the second conduit assembly (12) and calender (30) is sealed; and

the first duct (10) being sealingly assembled to the two additional plates (33,34) so that each of the ends (102, 103) of the first duct (10) communicates with the circulation orifice (31 1, 321 ) formed in one of the additional plates (33, 34).

2. Device according to claim 1, characterized in that one of the two plates (31) of the calender (30) is sealed with one of the two additional plates (33) so as to define an inter-plate space (Eip) communicating with an internal space (E12) delimited by the second duct (12) via at least the orifice (31 1) formed in the plate (31) of the shell (30), and in that an outlet duct (37) is formed in one of the secured plates (31 or 33), and communicates with the inter-plate space (Eip).

3. Device according to claim 2, characterized in that it comprises means for evacuating the inter-plate space (Eip) and the internal space

(E12) via the outlet pipe (37).

4. Device according to claim 2, characterized in that the interplate space (Eip) and the internal space (E12) are inert atmosphere.

5. Device according to any one of claims 1 to 4, characterized in that the thermocouple (20) extends along a transverse axis (13), and in that the first (0) and second (12) ) ducts are shaped so that the thermocouple (20) undergoes a compressive stress (o _c ) along the transverse axis (13) between said first (10) and second (12) ducts.

6. Device according to claim 5, characterized in that the distance d1 separating the first (10) and second (12) conduits at the cross section of the thermocouple (20) is less than the transverse dimension d2 of the thermocouple (20). ), the distance d1 and the dimension d2 being measured at the same temperature (Tmes).

7. Device according to any one of claims 1 to 6, characterized in that it comprises means for circulating a first fluid at a first temperature (T1) in the first conduit (10), and a second fluid covering the second conduit (12), the second fluid being at a second temperature (T2) lower than the first temperature (T1).

8. Device according to claim 7, characterized in that the fluid circulation means are configured to circulate a pressurized fluid in the first conduit (10) and / or in the second conduit (12).

9. A method of producing a device according to any one of claims 1 to 8, comprising the following steps:

- providing the first (10) and second (12) conduits, the first conduit (10) being configured to be housed in the second conduit (12) and extend along the longitudinal axis of the second conduit (12);

- providing the thermocouple (20) extending along the transverse axis (13); characterized in that the temperature of the first conduit (10) and / or the thermocouple (20) is lower than the temperature of the second conduit (12) when assembling the first and second conduits (10, 12) and the thermocouple ( 20) to form the thermoelectric device (1) so that the thermocouple (20) undergoes compressive stress, along the transverse axis (3), between the first and second conduits (10, 12).

10. A method of producing a device according to any one of claims 1 to 8, comprising the following steps:

- providing first (14) and second (15) half-pipes extending along the longitudinal axis (1) and configured to form the second conduit (12) by assembling the first and second half-pipes (14, 15);

placing the first and second half-ducts (14, 15) facing each other so that the first duct (10) is housed between the two half-ducts (14, 15) and the thermocouple (20) is interposed between the first half-conduit (14) and the first conduit (10);

pressing the first (14) and second (15) half-pipes towards each other so as to impose on the thermocouple (20) a compressive stress, along the transverse axis (13), between the first half conduit (14) and the first conduit (10);

- securing the first and second half-ducts (14, 15) to form the second duct (12), the thermocouple (20) being held in compression, along the transverse axis (13), between the first (10) and second (12) ducts.

11. Method according to one of claims 9 and 10, characterized in that the first and second ducts (10, 12) respectively comprise first (101) and second (121) substantially flat and parallel surfaces arranged in opposite directions. the thermocouple (20) is interposed between said first (101) and second (121) surfaces.

12. Method according to any one of claims 9 to 11, characterized in that an interface lamella (16) based on an electrically insulating material is interposed between the thermocouple (20) and the first conduit (10). ), and / or between the thermocouple (20) and the second conduit (12).

13. A method of generating an electric current by the device according to any one of claims 1 to 8, characterized in that it comprises the following steps:

circulating a first fluid (F1) having a first temperature (T1) in the first conduit (10);

circulating a second fluid (F2) having a second temperature (T2) lower than the first temperature (T1) around the second conduit (12).

14. A method of generating an electric current by the device according to any one of claims 1 to 8, characterized in that exhaust gases discharged by a heat engine flow in the first conduit (10).

15. A method of generating an electric current by the device according to any one of claims 1 to 8, characterized in that exhaust gases discharged by a heat engine circulate around the second conduit (12).