DE102012209619A1 - Thermoelectric element for converting energy between thermal energy and electrical energy and a method for disassembling the thermoelectric element - Google Patents

Abstract

The invention provides a thermoelectric element for converting energy between thermal energy and electrical energy, comprising: a first thermoelectric leg (10), a second thermoelectric leg (20), the first thermoelectric leg (10) having a first magnetic region (10a) and the second thermoelectric leg (20) has a second magnetic region (20a) and a first magnetic track device (30) which is magnetically frictionally connected to the first and second magnetic regions (10a; 20a). Furthermore, the invention provides a method for disassembling the thermoelectric element.

Description

The invention relates to a thermoelectric element (also called thermocouple) for the conversion of energy between thermal energy and electrical energy and a method for disassembly of the thermoelectric element.

State of the art

2 is a schematic representation of the structure of an exemplary thermoelectric element, and 3 is a schematic representation of the structure of an exemplary thermoelectric module with series-connected thermoelectric elements.

Such thermoelectric elements or thermoelectric modules composed thereof are made of individual thermoelectric legs 10 . 20 built, as for example in the AT 410 492 B is described. In this case, the structure provides for alternating the legs of the p-type (conduction mechanism by defect electrons) and n-type (conduction mechanism by electrons).

4a ) is a schematic representation of the frictional structure of an exemplary thermoelectric element, and 4b ) is a schematic representation of the cohesive structure of another exemplary thermoelectric element.

There are essentially two types of modular construction. The difference between these two types of modules lies in the thermal and electrical connection of the individual components. This can be frictionally F, as in 4a ), or materially S, as in 4b ) shown. In addition, combinations of the two aforementioned modular types are possible. Due to the large number of series-connected thermoelectric legs 10 . 20 , as in 3 In the case of a material-locking construction of the module, the risk of a module failure increases because the material-locking construction reduces the mechanical load on the thermoelectric legs 10 . 20 and the joints is at least an order of magnitude higher than in non-positive construction. Already a single interruption of the current flow, for example by a crack in a thermoelectric leg or by a detached connection point, causes the module to fail. Modules according to the current state of the art can not be repaired in the event of a defect due to their cohesive structure but can only be replaced. In addition, the valuable metals contained in the module can be recycled only with great effort. For recycling, the module must be restored to its original components.

State of the art is also the cohesive connection between the thermoelectric legs 10 . 20 and the conductor track devices 30 . 50 . 60 , These cohesive connections are susceptible to cracking or, due to differences in the coefficient of thermal expansion, can disrupt the thermoelectric material, in particular under thermocycling. In addition, in material-locking connection thermal process steps are necessary, which are carried out at temperatures that are well above the maximum operating temperature of the module. For example, in thermoelectric materials such as skutterudites, these thermal process steps require the individual legs to be coated prior to vacuum brazing to avoid sublimation of antimony from the material. When frictional structure very high forces are necessary to hold a module reliably in the composite and thus to ensure good thermal and electrical contacts. These forces can be up to 1000 N per module.

Disclosure of the invention

The present invention provides a thermoelectric element for converting energy between thermal energy and electrical energy, comprising: a first thermoelectric leg, a second thermoelectric leg, wherein the first thermoelectric leg has a first magnetic region and the second thermoelectric leg has a second Magnetic region, and a first magnetic conductor device, which is connected to the first and the second magnetic region magnetic force-locking. Magnetic-positive means that the adhesion is caused by the magnetic attraction.

The present invention also provides a method of disassembling a thermoelectric element.

Preferred developments are the subject of the respective subclaims.

Advantages of the invention

In the device according to the invention, soft and hard magnetic materials can be used to construct a thermoelectric module. As a result, a frictionally constructed module can be advantageously realized, which retains its frictional structure even without external force or requires only very small external forces to function reliably. As a result, in contrast to the purely non-positive modular design, the housing, which receives the contact force for the modules, be much less solid or even designed as in the cohesive modular design.

According to a preferred development, wherein the first thermoelectric leg has a third magnetic region and the second thermoelectric leg has a fourth magnetic region; and wherein a second magnetic track device is provided, which is magnetically-positively connected to the third magnetic region and wherein a third magnetic track device is provided, which is magnetically-positively connected to the fourth magnetic region, there is a further advantage of the module structure according to the invention under use of magnetic forces in that for the module structure and the connection technology no process steps are necessary, in which the material is exposed to higher temperatures than the later operating temperatures. This ensures a longer service life of the thermoelectric legs and in particular the coating on the legs.

According to a preferred development, between the first magnetic region and the first magnetic conductor device and the second magnetic region and the first magnetic conductor device additionally at least partially a first electrical conductive layer is provided, there is the advantage of a better electrical coupling of the thermoelectric legs to the magnetic conductor tracks ,

According to a preferred refinement, wherein at least partially a second electrical conduction layer is additionally provided between the third magnetic region and the second magnetic conduction device, there is the advantage of an even better electrical coupling of the thermoelectric legs to the magnetic conductor path devices.

According to a preferred development, wherein at least partially a third electrical conduction layer is provided between the fourth magnetic region and the third magnetic conduction device, there is the advantage of an even better electrical coupling of the thermoelectric legs to the magnetic trace devices.

According to a preferred development, wherein the first magnetic track device has a first recess for receiving the first magnetic area and a second recess for receiving the second magnetic area, the advantage of the far-reaching robustness of the structure against all types of shocks, the shear forces on the individual Can exercise components.

According to a preferred development, wherein the second magnetic strip conductor device has a third recess for receiving the third magnetic area and / or wherein the third magnetic strip line device has a fourth recess for receiving the fourth magnetic area, the advantage of the far-reaching robustness of the construction also results all kinds of vibrations that can exert shear forces on the individual components.

According to a preferred development, wherein the first magnetic strip conductor device is connected in a magnetically non-positively connected manner to a first magnetic heat distribution device via a first electrical insulation layer lying therebetween, a further advantage of the non-positive construction according to the invention results from the extensive mechanical decoupling of the components of the module. This means that the frictional connection of the thermoelectric legs, the conductor track devices and the heat distribution devices takes place completely or predominantly by magnetic forces.

Thereby, the advantages of cohesive construction (good thermal and electrical contacts, lightweight housing, easier installation) and the frictional structure (no critical transmission of mechanical loads by different thermal expansion coefficients of the components, very easy dismantling for recycling / recycling) in the Uniting principle according to the invention.

According to a preferred development, wherein the second and the third magnetic strip conductor device are connected in a magnetically non-positively connected manner to a second magnetic heat distribution device via a second electrical insulation layer lying therebetween, the latter advantage likewise results.

By the invention, the production of thermoelectric modules on the principle of frictional connection is greatly simplified, since there are already holding forces between the individual components during construction by the magnetism and not only when the complete structure for the frictional connection is mechanically compressed. When using magnetic or magnetizable materials for the heat exchanger and a connection of the modules to the heat exchanger via the magnetic forces can be realized.

Another advantage of the method and the element according to the invention is the ability to repair a defective module can. Since the components of the module are fixed only by magnetic forces, a defective module can be dismantled with little effort and the defective components are replaced. This simple dismantling of the module also allows the modules with very little effort to disassemble into their individual components and thus sort of a recycling to perform. In addition, the components of the module can also be used directly for the construction of new modules.

Further features and advantages of embodiments of the invention will become apparent from the following description with reference to the accompanying drawings.

Brief description of the drawings

Show it:

1 a schematic representation of a thermoelectric element for the conversion of energy between thermal energy and electrical energy according to an embodiment of the invention;

2 a schematic representation of the structure of an exemplary thermoelectric element;

3 a schematic representation of the structure of an exemplary thermoelectric module with series-connected thermoelectric elements;

4a) a schematic representation of the frictional structure of an exemplary thermoelectric element; and

4b) a schematic representation of the cohesive structure of another exemplary thermoelectric element.

Embodiments of the invention

In the figures, like reference numerals designate the same or functionally identical elements.

1 FIG. 4 is a schematic representation of a thermoelectric element for converting energy between thermal energy and electrical energy according to an embodiment of the invention. FIG.

In 1 denotes reference numeral 10 a first thermoelectric leg and reference numerals 20 a second thermoelectric leg connected to the first thermoelectric leg 10 via a first magnetic conductor device 30 connected is. reference numeral 50 denotes a second magnetic track device which is connected to the thermoelectric leg 10 is connected, and reference numerals 60 denotes a third magnetic track device which is connected to the thermoelectric leg 20 connected is. reference numeral 100 and 300 Denote a first and second electrical insulation layer. reference numeral 200 and 400 Denote a first and second magnetic heat distribution device. Reference numerals L1, L2, L3 denote first, second and third electrical conduction layers, and reference symbols V1, V2, V3, V4 denote first, second, third and fourth recesses for receiving first and second magnetic regions 10a . 10b of the first thermoelectric leg 10 and a first and second magnetic region 20a . 20b of the second thermoelectric leg 20 ,

The core of the embodiment is the use of soft and hard magnetic materials for the construction of a thermoelectric element by adhesion. These are the two thermoelectric legs 10 . 20 coated with a soft or hard magnetic material. As a material for the magnetic track devices 30 . 50 . 60 a hard magnetic connection is chosen. In addition, for the electrical insulation layers 100 . 300 a magnetic plate can be used, which is coated electrically insulating. Thereby, the magnetic force can be increased, with which the magnetic conductor tracks 30 . 50 . 60 on the two thermoelectric legs 10 . 20 be liable. In particular, the following components, as in 1 represented, made of soft or hard magnetic material: the coating of the contact surfaces of the thermoelectric legs 10 . 20 ie the magnetic areas 10a . 10b . 20a . 20b , the conductor tracks 30 . 50 . 60 and optionally the heat spreaders 200 . 400 ,

Such thermoelectric elements and thermoelectric modules composed thereof are exposed to very high temperatures when used in the exhaust system of a car. Therefore, in the selection of soft or hard magnetic materials, the height of the Curie temperature of importance. The following materials have a high Curie temperature and are therefore particularly suitable as magnetic materials for the hot side of the structure of the invention. Examples of particularly suitable hard magnetic and semi-hard magnetic materials are summarized in Table 1 below. For comparison, copper electrical resistivity: 0.0178 Ωmm ² / m, thermal conductivity of exhaust stainless steel 1.4313 (= X3CrNiMo13-4 = C max: 0.05, Cr: 12.00-14.00, Ni: 3.50 Mo: 0.30-0.70, N: at least 0.02 (in% by mass): 25 W / mK elements Markentnamen Curie temperature in ° C thermal expansion coefficient Special electr. Resistance in Ωmm ² / m Thermal conductivity in W / mK Coercive force Hc in kA / m Energy product BH in kJ / m3 FeCrCo CROVAC 16/550 (vacuum melt) Arnokrome ^TM 3 (Arnold) 640 10 0.7 20.5 53-61 37 AINiCo Aleast VIII (Cibas) 850 11-13 0.5 60 113-122 36.5 to 44 CoFeV Magnetoflex 93 (Vacuumsch melze) 700 11 0.65 30 30-35 20 Table 1

Table 2 below shows a list of suitable soft magnetic elements. Surname Curie temperature in ° C thermal expansion coefficient Special electr. Resistance in Ωmm ² / m Thermal conductivity in W / mK nickel 360 13.0 0.0693 90.7 cobalt 1121 12.7 0.0624 100 iron 768 12.2 0.10-0.15 80.2 Table 2

For the construction of such a thermoelectric element via magnetic forces are the contact surfaces, ie the magnetic regions 10a . 10b . 20a . 20b , on the thermoelectric legs 10 . 20 particularly important. The contact surfaces can be made of a soft magnetic or semi-hard or a hard magnetic material. Particularly suitable are semi-hard or hard magnetic Materials whose coefficient of thermal expansion is as close as possible to the thermal expansion coefficient of the thermoelectric material. The following Table 3 shows thermal expansion coefficients of some thermoelectric materials. Thermal expansion coefficient in K ^-1 skutterudites Half-Heusler n-type 11-13 10-12 p-type 9-11 8-10 Table 3

The connection of the contact surface, ie the magnetic regions 10a . 10b . 20a . 20b , to the thermoelectric legs 10 . 20 must be such that it can withstand a multiple of the forces that can be transmitted by the magnetic forces. Since these forces are comparatively low, numerous methods are suitable for the connection of the contact surface. Particularly advantageous is the connection, if in the production of the thermoelectric material for the later thermoelectric leg 10 . 20 The magnetic material of the contact surfaces is already sintered as the lower and upper contact surface in the powder compact. Preferred methods for sintering are high-current assisted sintering (eg SPS) or hot pressing, both of which achieve a very good material connection between the thermoelectric and the magnetic material.

In order to achieve sufficiently high magnetic forces, the contact layer of the magnetic regions should 10a . 10b . 20a . 20b on the thermoelectric leg 10 . 20 have a thickness that can be in the range of 0.1 mm-5 mm. Particularly suitable is a thickness> 1 mm, since material is removed from the contact surface during later dimensional grinding.

In addition, it is very advantageous if both for the contact surfaces in the interconnect devices 30 . 50 . 60 as well as for the conductor track devices in the connection to the heat distribution devices 200 . 400 the appropriate recesses V1, V2, V3, V4 are provided, as in 1 is shown by way of example. These recesses V1, V2, V3, V4 prevent the thermoelectric element or module from becoming inoperative due to supercritical vibration forces or shearing movements. Particularly advantageous depths for these recesses V1, V2, V3, V4 are 10 μm-1 mm. A preferred design for the contact surfaces provides that they are lapped and the contact surfaces are plane-parallel without air gap in contact.

In a real thermoelectric element or module certain requirements, in particular to the parallelism, to meet only with great effort. Therefore, alternative measures to improve the thermal or electrical connection between the corresponding components are necessary. Particularly preferred are the use of very thin graphite foils or of liquid metal or metal with a low melting point to fill the capillary gap in the contact surface. As a result, the production-related defects in the surface condition of the contact points between the components are optimally balanced and the thermal or electrical resistance is reduced.

The magnetic alloys used for the conductor tracks 30 . 50 . 60 are used, are electrically rather bad conductors. The present embodiment therefore includes printed conductor devices 30 . 50 . 60 magnetic alloy, which are additionally coated with a good conductive conductive layer L1, L2, L3 on the side, in contact with the thermoelectric legs 10 . 20 stands. The advantage is that thereby an electrical conductor with very low electrical resistance in direct contact with the thermoelectric legs 10 . 20 stands and thereby the electrical losses are minimized.

As a metal for the coating of the conductor track devices 30 . 50 . 60 Cobalt or a nickel-cobalt alloy is particularly advantageous because they still have their ferromagnetic properties even at high temperatures and so even at high temperatures, the magnetic forces are transmitted through the electrical conductive layer L1, L2, L3 almost lossless.

Due to the very good corrosion resistance of certain magnetic alloys such as AINiCo, the reinforcing magnet of the heat spreader device 200 . 400 Also come directly as a heat exchanger with the exhaust gas in the exhaust system in contact.

Tabelle 4 Table 4 below shows an exemplary embodiment of a structure of a thermoelectric element for modular construction. The names for the individual components are off 1 accepted. On the cold side, neodymium-iron-boron (NdFeB) is used as the magnetic material in this embodiment. NdFeB is currently the most powerful magnetic material. Its maximum operating temperature is around 200 ° C. On the hot side and in direct contact with the thermoelectric leg aluminum-nickel-cobalt is used. Although this material is less powerful than NdFeB, it has an operating temperature of at least 500 ° C, a thermal expansion coefficient which is very good for the thermoelectric materials Skutterudit and Halb-Heusler, and outstanding corrosion resistance.

Table 4

The repair of thighs, elements or modules and the dismantling of thighs, elements thighs or modules for recycling are very simple by the principle of construction on magnetic adhesive forces. In particular, for recycling can be demagnetized by use of very strong external magnetic fields and / or by heating on the Curie temperature of the material of at least one magnetic component, the magnetic components of the element or module and so the elements or modules in a very simple way and Be broken down into their individual components.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• AT 410492 B [0003]

Claims (10)

Thermoelectric element for converting thermal energy into electrical energy, comprising: a first thermoelectric leg ( 10 ); a second thermoelectric leg ( 20 ); wherein the first thermoelectric leg ( 10 ) a first magnetic region ( 10a ) and the second thermoelectric leg ( 20 ) a second magnetic region ( 20a ) having; and a first magnetic conductor device ( 30 ), which with the first and the second magnetic region ( 10a . 20a ) is magnetically-positively connected. Thermoelectric element according to claim 1, wherein the first thermoelectric leg ( 10 ) a third magnetic region ( 10b ) and the second thermoelectric leg ( 20 ) a fourth magnetic region ( 20b ) having; and wherein a second magnetic circuit device ( 50 ) provided with the third magnetic region ( 10b ) is magnetically-positively connected and wherein a third magnetic conductor device ( 60 ) provided with the fourth magnetic region ( 20b ) is magnetically-positively connected. Thermoelectric element according to claim 1 or 2, wherein between the first magnetic region ( 10a ) and the first magnetic track device ( 30 ) and between the second magnetic region ( 20a ) and the first magnetic track device ( 30 ) at least partially a first electrical conductive layer (L1) is provided. Thermoelectric element according to claim 2, wherein between the third magnetic region ( 10b ) and the second magnetic circuit device ( 50 ) at least partially a second electrical conductive layer (L2) is provided. Thermoelectric element according to one of claims 2 to 4, wherein between the fourth magnetic region ( 20b ) and the third magnetic track device ( 60 ) In addition, at least partially, a third electrical conductive layer (L3) is provided. Thermoelectric element according to one of the preceding claims, wherein the first magnetic conductor device ( 30 ) a first recess (V1) for receiving the first magnetic region (V1) 10a ) and a second recess (V2) for receiving the second magnetic region ( 20a ) having. Thermoelectric element according to one of claims 2 to 6, wherein the second magnetic circuit device ( 50 ) a third recess (V3) for receiving the third magnetic region ( 10b ) and / or wherein the third magnetic conductor device ( 60 ) a fourth recess (V4) for receiving the fourth magnetic region (V4) 20b ) having. Thermoelectric element according to one of the preceding claims, wherein the first magnetic conductor device ( 30 ) magnetic force-locking with a first magnetic heat spreader device ( 200 ) via an intervening first electrical insulation layer ( 100 ) connected is. Thermoelectric element according to one of claims 2 to 8, wherein the second and the third magnetic circuit device ( 50 ; 60 ) magnetically frictionally connected to a second magnetic heat distribution device ( 400 ) via an intermediate second electrical insulation layer ( 300 ) are connected. A method of disassembling the thermoelectric element according to any one of claims 1 to 9, comprising the steps of: heating the thermoelectric element to a temperature above a Curie temperature of at least one of its magnetic components ( 10a ; 20a ; 10b ; 20b ; 30 ; 50 ; 60 ; 200 ; 400 ) lies; and / or applying an external magnetic field to the thermoelectric element for demagnetizing at least one of its magnetic components ( 10a ; 20a ; 10b ; 20b ; 30 ; 50 ; 60 ; 200 ; 400 ).

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