US20160305304A1

US20160305304A1 - Thermoelectric module, thermoelectric device, heat exchanger and egr loop

Info

Publication number: US20160305304A1
Application number: US14/917,833
Authority: US
Inventors: Kamel Azzouz; Georges De Pelsemaeker; Cedric De Vaulx
Original assignee: Valeo Systemes Thermiques SAS
Current assignee: Valeo Systemes Thermiques SAS
Priority date: 2013-09-10
Filing date: 2014-09-09
Publication date: 2016-10-20
Also published as: WO2015036408A1; EP3052798A1; FR3010505A1; FR3010505B1; CN105705762A; EP3052798B1

Abstract

The invention relates to a thermoelectric module (1), comprising at least one thermoelectric element (3) allowing the generation of an electric current from a temperature gradient applied between two of its active faces (4 a, 4 p), a first so-called hot circuit (2) able to allow the flow of a first fluid in a heat exchange relationship with one of said active faces and a sheath (8) surrounding said thermoelectric elements (3) and said hot circuit (2) such that the sheath (8) is arranged to establish thermal contact between a so-called cold liquid with a temperature lower than that of the first fluid, and the other of said active faces and to hermetically separate said cold liquid on the one hand and said thermoelectric element(s) (3) and said hot circuit (2) on the other hand. The invention also relates to a thermoelectric device comprising at least one module as described and a heat exchanger comprising such a device.

Description

The present invention relates to a thermoelectric module, a thermoelectric device comprising such a module, a heat exchanger comprising such a device and an EGR (exhaust gas recirculation) loop comprising such an exchanger.
Thermoelectric modules have already been proposed that use so-called thermoelectric elements, making it possible to generate an electric current in the presence of a temperature gradient between two of their opposite faces by the phenomenon known as the Seebeck effect. These devices comprise a stack of first tubes, intended for the circulation of the exhaust gases from an engine, and of second tubes, intended for the circulation of a heat transfer fluid of a cooling circuit. The thermoelectric elements are sandwiched between the tubes so as to be subjected to a temperature gradient originating from the temperature difference between the hot exhaust gases and the cold coolant.
These stacks of first tubes, of thermoelectric elements and of second tubes do however have a complex structure and requires a precise and complicated assembly to ensure a good contact between the tubes and the thermoelectric elements.
The invention aims to improve the situation. For that, it relates to a thermoelectric module, comprising at least one thermoelectric element making it possible to generate an electric current from a temperature gradient applied between two of its active faces, a first so-called hot circuit, suitable for allowing the circulation of a first fluid in heat exchange relation with one of said active faces and a cladding surrounding said thermoelectric element or elements and said hot circuit such that the cladding is arranged to establish a thermal contact between a so-called cold liquid, of a temperature lower than that of the first fluid, and the other of said active faces and hermetically separate, on the one hand, said cold liquid and, on the other hand, said thermoelectric element or elements and said hot circuit.
Thus, by virtue of the invention, it is possible to use, as cold fluid, a liquid without the latter circulating in a complex cold tube stack. There is thus a wide degree of freedom in designing the thermoelectric devices intended to accommodate said modules.
According to different embodiments of the invention, which will be able to be taken together or separately:

- the thermoelectric element is of annular form such that it comprises an inner face, corresponding to the active face in heat exchange relation with the hot circuit, and an outer face, corresponding to the other of said active faces;
- the thermoelectric element is of flattened cross section;
- the cladding is electrically insulating;
- the thermoelectric module comprises separators electrically insulating two neighboring thermoelectric elements at one of their active faces;
- the cladding comprises said separators;
- the cladding is heat-shrinkable;
- the first circuit comprises at least one tube passing through said thermoelectric elements.

The invention relates also to a thermoelectric device comprising a casing and at least one thermoelectric module as described previously, said module being inserted into the casing and said casing comprising a first zone in which said cold liquid is intended to be in contact with said cladding.
Advantageously, said casing defines, at least partly, a second circuit in which said cold liquid is intended to circulate.
The invention relates also to a heat exchanger comprising a thermoelectric device as described previously, said casing comprising a second zone in which the hot circuit is configured to be directly in contact with the cold liquid.
There is thus assured, using just one and the same exchanger, on the one hand a heat exchange function making it possible to cool the hot field and to reheat the cold liquid, and, on the other hand, a function of input from the hot and cold sources necessary to the operation of the thermoelectric elements.
That being the case, the invention relates also to such a heat exchanger, configured to be positioned in an exhaust gas recirculation circuit, without said thermoelectric modules comprising the abovementioned cladding. It will be sufficient for them to be configured to make it possible to create a temperature gradient between said active faces of said thermoelectric element or elements from said hot circuit, passed through by said recirculated exhaust gases, and a cold circuit passed through by a cold liquid, notably a cold circuit comprising tubes.
According to different embodiments of the invention, which will be able to be taken together or separately:

- the first zone and the second zone are positioned in series in the direction of circulation of the hot fluid;
- the first circuit is configured such that the first zone is situated upstream of the second zone in the direction of circulation of the hot fluid;
- the exchanger is configured such that the cold liquid is intended to run parallel through the first zone and the second zone;
- the exchanger comprises a partition separating the first zone from the second zone such that the cold liquid circulating in the first zone and the cold liquid circulating in the second zone are separated;
- the first cone and the second zone are situated in series in the direction of circulation of the cold liquid;
- the first zone represents 40% to 90% of a volume defined by the interior of the casing, the second zone representing the remaining portion of said volume;
- the first zone represents 50% of a volume defined by the inferior of the casing, the second zone representing 50% of this volume;
- the first zone represents 80% of a volume defined by the interior of the casing, the second zone representing 20% of this volume;
- the hot fluid comprises EGR gases.

The invention relates also to an EGR gas recirculation circuit of a motor vehicle comprising a thermoelectric device or a heat exchanger as described previously.
In effect, with the dimension of the exchanger being reduced, it is possible to incorporate it in an exhaust gas recirculation duct of the motor vehicle.

The invention will be better understood in light of the following description which is given by way of indication and which is in no way intended to limit it, accompanied by the attached drawings in which;

FIG. 1 schematically represents, in exploded perspective, a thermoelectric module according to the invention;

FIG. 2 schematically illustrates, in cross section, the thermoelectric module of FIG. 1;

FIG. 3 represents, in exploded perspective, a thermoelectric device comprising said module;

FIG. 4 schematically illustrates, in transverse cross section, a heat exchanger according to the invention comprising the thermoelectric device of the invention;

FIG. 5 schematically illustrates, in lateral cross section, a part of the heat exchanger illustrated in FIG. 4.

The invention relates to a thermoelectric module 1 as represented in FIGS. 1 and 2. Such a module 1 comprises a first so-called hot circuit 2, suitable for allowing the circulation of a first fluid, notably exhaust gases from an engine. The first circuit 2 here comprises a tube 5.
The module 1 also comprises a plurality of thermoelectric elements 3 capable of generating an electric current under the action of a temperature gradient exerted between two of their active faces 4 a, 4 b, Such thermoelectric elements 3 operate, according to the Seebeck effect, by making it possible to create an electric current in a load connected between said faces 4 a, 4 b subjected to the temperature gradient. As is known to those skilled in the art, such elements consist, for example, of bismuth and tellurium (Bi₂Te₃).
The thermoelectric elements 3 are, for a first part, elements 3P of a first type, called Pf making it possible to establish an electric potential difference in one direction, called positive, when they are subjected to a given temperature gradient, and, for the other part, elements 3N of a second type, called making it possible to create an electric potential difference in an opposite direction, called negative, when they are subjected to the same temperature gradient. Said thermoelectric elements 3 are, for example, grouped in pairs, each pair being formed by one said P-type thermoelectric element and one said N-type thermoelectric element.
The thermoelectric elements 3 are here of annular form and are notably of flattened cross section. The active faces 4 a, 4 b are therefore situated on the inner and outer periphery of the annular form such that the thermoelectric elements 3 has an inner active face 4 a and an outer active face 4 b. That thus makes it possible to have the first circuit 2 at least partly inside the thermoelectric elements 3 in contact with the inner active face 4 a.
The module 1 also comprises at least one internal ring 6 arranged between the first circuit 2 and the thermoelectric elements 3, that is to say in contact with the inner face 4 a of the thermoelectric elements 3. The internal ring 6 is electrically and thermally conductive and links together two thermoelectric elements 3 of a same pair.
The module 1 further comprises at least one external ring 7 in contact with the outer active face 4 b of the thermoelectric elements 3, The external ring 7 is electrically and thermally conductive and links together two thermoelectric elements 3 of two neighboring pairs.
Said module 1 is thus configured to allow a circulation of current between the inner active faces 4 a of the thermoelectric elements 3 of a same pair by virtue of the internal rings 6 and a circulation of current between the outer active faces 4 b of two neighboring thermoelectric elements 3 belonging to two different pairs by virtue of the external rings 7. In this way, a circulation of current is established in series from one thermoelectric element to another, by alternating the P-type and N-type thermoelectric elements.
The module 1 of the invention further comprises a hermetic cladding 8, here surrounding the thermoelectric elements 3 and the first circuit 2 such that they are situated inside the cladding 8. The cladding 8 is thus arranged on the side of the outer active face 4 b of the thermoelectric elements. It is here in contact with the external rings 7.
This cladding 8 hermetically separates the thermoelectric elements 3 and the first circuit 2 from the outside of the module 1, that is to say that it prevents any contact of a fluid outside the module 1 with the thermoelectric elements 3 and the first circuit 2 situated inside the cladding, as well as, here, with the internal 6 and external 7 rings. In other words, the assembly is encapsulated in the cladding 8 which jackets it.
The cladding 8 is also thermally conductive. It can thus be positioned in contact with a coolant, called cold liquid, in order to provide the thermoelectric elements 3, notably via the external rings 7, with the cold source necessary to provide the temperature gradient that the thermoelectric elements need to generate electricity without the liquid entering into contact with the internal rings 6, the external rings 7, the thermoelectric elements 3 and the first circuit 2.
The cladding 8 is also electrically insulating. It thus makes it possible to electrically insulate the external ring 7 and the thermoelectric elements 3 from the outside of the module 1 and in particular from the cold liquid intended to be in contact with the cladding 8.
The module 1 of the invention will also be able to comprise separators 9 arranged between the neighboring thermoelectric elements 3 so as to electrically insulate them from, one another at one of their active faces 4 a, 4 b. Thus, the separators electrically insulate the outer faces 4 b of the thermoelectric elements 3 of a same pair and the inner faces 4 a of the neighboring thermoelectric elements 3 of two different pairs. The separators 9 further help to promote the seal-tightness of the module provided by the cladding 8 as seen previously.
In a particular embodiment of the invention, and as illustrated in FIGS. 1 and 2, it is the cladding 8 which comprises these separators 9 such that the cladding 8 extends between said thermoelectric elements. They are for example made in a single piece with the cladding 8. This notably facilitates the manufacturing and the assembly of the module 1,
The cladding 8 is advantageously heat-shrinkable such that the tight fitting of the cladding 8 on the rest of the module is facilitated,
As explained previously, the invention relates also to a thermoelectric device 10 as illustrated in FIG. 3. This device 10 comprises at least one module 1 as described previously and in particular a plurality of modules 1. The device 10 also comprises a casing 11 defining a volume and inside which are inserted the modules 1. The modules 1 are here stacked one on top of the other and arranged in two rows side by side.
The device 10 is configured to have the cold liquid circulate in contact with said thermoelectric modules 1. Here it is the casing 11 which defines a second circuit inside which the cold liquid circulates by passing between said modules 1.
The device 10 comprises a first zone in which the cold liquid is intended to be in contact with the cladding of the modules 1.
The device 10 also comprises a collecting box 15 situated at a second longitudinal end 16 of the modules 1. Thus, the hot fluid can circulate from a first longitudinal end 17 of a first group of modules 1 to the collecting box 15, which then directs it to a second group of modules 1 into which it enters by the second longitudinal end 16. The hot fluid then circulates in the opposite direction until it exits from the second group of modules 1 then from the device 10 at the same first longitudinal end 17 of the modules 1 by which it entered.
The invention relates also to a heat exchanger 20, comprising such a device 10, The exchanger then comprises, as illustrated in FIGS. 4 and 5, a second zone 32, situated inside said casing 11 and in which the first circuit 2 and the cold liquid are directly in contact.
In these exemplary embodiments, the first zone 31 and the second zone 32 are positioned in series according to the first circuit 2, that is to say in the direction of circulation of the hot fluid. Thus, the hot fluid enters into the exchanger 20 in the first zone 31, passes through the first circuit 2 in the modules 1 and continues to pass through the first circuit 2 by exiting from the modules 2 and therefore by entering into the second zone 32 before exiting from the exchanger 20.
It can be noted that the first circuit 2 is, here, continuous over the entire path of the hot fluid notably between the first and second zones 31, 32, that is to say that the tubes 5 are continuous. Thus, the first zone 31 allows the modules 1 to generate electricity by virtue of the temperature gradient created by the hot fluid and the cold liquid. The hot fluid is then insulated from the cold liquid by the internal ring, the thermoelectric elements 3, the external ring and the cladding 8. It therefore changes temperature only very little when it passes through the modules 1 which guarantee the electrical generating efficiency of the modules 1.
On the other hand, when the hot fluid is in the second zone 32, the second circuit is directly in contact with the cold liquid. The heat exchange between the two fluids is therefore much greater and the cooling of hot fluid will then be able to be performed.
It can be noted that the invention makes it possible to allow the zones 31, 32 to spread in the exchanger 20 as a function of the electrical and thermal efficiency that is desired. Thus, to increase the production of electricity, the size of the first zone 31 is increased whereas, to increase the cooling of the hot fluid, the dimensions of the second zone 32 are increased. FIG. 4 illustrates an example in which 50% of the internal volume defined by the casing 11 is occupied by the first zone 31 and 50% by the second zone 32. In the exemplary embodiment of FIG. 5, 80% of the internal volume is occupied by the first zone 31 and 20% by the second zone 32.
The liquid can pass, for example, parallel through the first and second zones 31, 32 as illustrated in FIG. 4. The exchanger here comprises a partition 21 separating the cold liquid in contact with the first circuit 2 in the second zone 32 from the cold liquid in contact with the modules 1 in the first zone 31. The cold liquid in contact with the modules 1 exchanges only very little heat with the first circuit 2 which guarantees the efficiency of the thermo-generating elements.
According to an alternative, the first zone and the second zone are situated in series in the direction of circulation of the liquid. The cold liquid firstly adds the cold source to the modules 1 without exchanging much heat with the first circuit 2 then directly exchanges heat with the first circuit 2 in order to cool the hot fluid, or vice versa to favor the heat exchange, the temperature gradient for the thermoelectric function then remaining sufficient given the high heat capacity of the cold fluid, the latter being liquid.

Claims

1. A thermoelectric module , comprising:

at least one thermoelectric element for generating an electric current from a temperature gradient applied between two of its active faces

a first hot circuit for allowing the circulation of a first fluid in heat exchange relation with one of said active faces and a cladding surrounding said thermoelectric element or elements and said hot circuit, such that the cladding is arranged to establish a thermal contact between a cold liquid, of a temperature lower than that of the first fluid, and another of said active faces, and hermetically separate said cold liquid and said thermoelectric element or elements and said hot circuit.

2. The thermoelectric module as claimed in claim 1, in which the thermoelectric element is of annular form such that it comprises an inner face, corresponding to the active face in heat exchange relation with the hot circuit, and an outer face, corresponding to the other of said active faces.

3. The thermoelectric module as claimed in claim 2, in which the thermoelectric element is of flattened cross section.

4. The thermoelectric module as claimed in claim 1, in which the cladding is electrically insulating.

5. The thermoelectric module as claimed in claim 1, in which the thermoelectric module comprises separators electrically insulating two neighboring thermoelectric elements at one of their active faces.

6. The thermoelectric module as claimed in claim 5, in which the cladding comprises said separators.

7. The thermoelectric module as claimed in claim 1, in which the cladding is heat-shrinkable.

8. A thermoelectric device comprising;

a casing; and

at least one thermoelectric module as claimed in claim 1,

said module being inserted into the casing and said casing comprising a first zone in which said cold liquid is intended to be in contact with said cladding.

9. The thermoelectric device as claimed in claim 8, in which said casing defines at least partly, a second circuit in which said cold liquid is intended to circulate.

10. A heat exchanger, comprising a thermoelectric device as claimed in claim 8, said easing comprising a second zone which the hot circuit is configured to be directly in contact with the cold liquid.

11. The heat exchanger as claimed in claim 10, in which the first zone and the second zone are positioned in series in the direction of circulation of the hot fluid.

12. The heat exchanger as claimed in claim 11, in which the first circuit is configured such that the first zone is situated upstream of the second zone in the direction of circulation of the hot fluid.

13. The heat exchanger as claimed in claim 10, in which the exchanger is configured such that the cold liquid is intended to run parallel through the first zone and the second zone.

14. The heal exchanger as claimed in claim 13, in which the exchanger comprises a partition separating the first zone from the second zone such that the cold liquid circulating in the first zone 0 and the cold liquid circulating in the second zone are separated.

15. The heat exchanger as claimed in claim 10, in which the first zone and the second zone are situated in series in the direction of circulation of the cold liquid.

16. The heat exchanger as claimed in 10, in which the first zone represents 40% to 90% of a volume defined by the interior of the casing, the second zone representing the remaining portion of said volume.

17. The heat exchanger as claimed in claim 10, in which the hot fluid comprises EGR gases.

18. An EGR gas recirculation circuit of a motor vehicle comprising a thermoelectric device as claimed in claim 8.

19. An EGR gas recirculation circuit of a motor vehicle comprising a heat exchanger as claimed in claim 10.