HEAT EXCHANGER

Abstract

A method for operating a heat exchanger comprising a top side, a bottom side, and a thermoelectric device including thermoelectrically active elements which are electrically energizable for generating a heat flow between the top side and the bottom side, the method may comprise electrically energizing the thermoelectric device with an electric alternating current.

Claims

1. A method for operating a heat exchanger comprising a top side, a bottom side, and a thermoelectric device including thermoelectrically active elements which are designed electrically energizable for generating a heat flow between the top side and the bottom side, the method comprising: electrically energizing the thermoelectric device with an electric alternating current; wherein an average first period, in which the electric energization of the thermoelectrically active elements takes place in such a manner that heat is transported from the top side to the bottom side, is shorter than an average second period, in which the electric energization of the thermoelectrically active elements takes place in such a manner that heat is transported from the bottom side to the top side; or/and that and wherein an average first current, in which the electric energization of the thermoelectrically active elements takes place in such a manner that heat is transported from the top side to the bottom side, is lower than an average second current, in which the electric energization of the thermoelectrically active elements takes place in such a manner that heat is transported from the bottom side to the top side.

2. The method according to claim 1, wherein the electric energization includes a zero value for the electric alternating current.

3. The method according to claim 1, wherein the average first period and the average second period or the average first current and the average second current are fixed so that heat quantity transported during a cycle of the electric alternating current from the bottom side to the top side corresponds to heat quantity transported from the top side to the bottom side plus heat quantity generated by the thermoelectrically active elements through dissipation and transported to the bottom side.

4. The method according to claim 1, wherein the average first period and the average second period or the average first current and the average second current are fixed so that a temperature of the top side with respect to time converges against a defined temperature limit value; and/or the average first period and the average second period or the average first current and the average second current are fixed so that a temperature of the bottom side remains substantially constant.

5. The method according to claim 1, wherein the electric alternating current is generated with a predetermined cycle ratio so that the average second period amounts to at least 1.5 times the average first period.

6. The method according to claim 5, wherein the cycle ratio is taken from a predetermined characteristic map.

7. The method according to claim 1, wherein an alternating current frequency[[ (f)]] of the electric alternating current[[ (I)]] amounts to at least 1 Hz.

8. A heat exchanger for controlling temperature of a vehicle seat, comprising: a thermoelectric device including multiple electrically energizable thermoelectrically active elements which, spaced apart from one another, are arranged on a top side and a bottom side of the heat exchanger; a fluid path provided on the bottom side and thermally connected to the same for being flowed through by a fluid; and a control/regulating device configured to carry out the method according to claim 1.

9. The heat exchanger according to claim 8, wherein the heat exchanger comprises an electric power source for generating an electric current in the thermoelectrically active elements of the thermoelectric device or is designed so as to be electrically connectable to such an electric power source.

10. The heat exchanger according to claim 8, wherein in the fluid path a heat transferring structure for transferring heat between the fluid flowing through the fluid path and the thermoelectrically active elements is arranged.

11. The heat exchanger according to claim 8, wherein the thermoelectric device is configured so that upon electric energization of the thermoelectrically active elements in a first electric current direction heat is transported from the top side to the bottom side and upon electric energization of the thermoelectrically active elements in a second electrical current direction opposite the first electric current direction heat is transported from the bottom side to the top side.

12. The heat exchanger according to claim 8, wherein the thermoelectric device includes multiple electric conductor bridges for electrically interconnecting the thermoelectrically active elements; and wherein a respective conductor bridge is thermally connected either to a warm side or to a cold side of installation.

13. The heat exchanger according to claim 12, wherein the electric conductor bridges comprise first conductor bridges facing the bottom side, which form the cold side or the warm side of the thermoelectric device and second conductor bridges facing the top side, which form the warm side or the cold side of the thermoelectric device.

14. The heat exchanger according to claim 13, wherein during an operation of the heat exchanger, the first conductor bridges form the cold side.

15. The heat exchanger according to claim 14, wherein the thermoelectric device includes a thermoelectric fabric or is formed as thermoelectric fabric, wherein the thermoelectric fabric includes: a plurality of first threads which are alternately formed by p-doped and n-doped thread portions and electrically conductive first and second thread portions arranged in between, wherein the first thread portions of the fabric form the first conductor bridges and the second thread portions form the second conductor bridges of the heat exchanger; and a plurality of second threads which are preferentially formed so as to be electrically insulating; wherein the first threads form weft threads and the second threads form warp threads of the fabric, or vice versa.

16. A vehicle seat, comprising the heat exchanger according to claim 8; wherein the top side of the heat exchanger is thermally connected to a seating surface of the vehicle seat.

17. The method according to claim 1, wherein the electric alternating current is generated with a predetermined cycle ratio so that the average second period amounts to approximately 2 to 10 times the average first period.

18. The method according to claim 1, wherein an alternating current frequency of the electric alternating current amounts to at least 10 Hz.

19. The heat exchanger according to claim 14, wherein during the operation of the heat exchanger, the second conductor bridges form the warm side.

20. The heat exchanger according to claim 8, wherein the thermoelectric device includes a thermoelectric fabric.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] It shows, in each case schematically:

[0034] FIG. 1 an example of a heat exchanger according to the invention with electrically energized thermoelectric elements of the heat exchanger in a first electric current direction,

[0035] FIG. 2 the heat exchanger of FIG. 1 with electrically energized thermoelectric elements in a second electric current direction opposite to the first electric current direction,

[0036] FIG. 3a a first current-time diagram for illustrating the electric energization of the thermoelectric elements with an electric alternating current,

[0037] FIG. 3b a second current-time diagram for illustrating the electric energization of the thermoelectric elements with an electric alternating current,

[0038] FIG. 4 a temperature-time diagram which illustrates the temperature development over time on the top side and bottom side of the heat exchanger with electrically energized thermoelectric elements in accordance with the method according to the invention,

[0039] FIG. 5 a special technical configuration of the heat exchanger of FIGS. 1 and 2, in which the thermoelectric device with the thermoelectric elements is formed by a thermoelectric fabric.

DETAILED DESCRIPTION

[0040] FIG. 1 illustrates an example of a heat exchanger 1 according to the invention for temperature controlling a vehicle seat. The heat exchanger 1 comprises a thermoelectric device 2 which includes multiple electrically energizable thermoelectrically active elements 3. The elements 3, electrically connected in series, can be wired to one another by means of electrically conductive conductor bridges 10 and be alternately formed by a semi-conductor of a p-doped and n-doped material. Possible semi-conductor materials are for example bismuth as well as tellurium or bismuth telluride.

[0041] According to FIG. 1, the elements 3 are arranged spaced apart from one another between a top side 4 and a bottom side 5 of the heat exchanger 1. The terms “top side” and “bottom side” relate to a preferred usage position of the heat exchanger 1, in particular when the same is integrated in the said vehicle seed: in this case the top side 4 faces the seating surface of the vehicle seat. When the heat exchanger 1 is integrated in other components this takes place in such a manner that the top side 4 faces the surface to be temperature controlled. The elements 3 can be arranged between a top side substrate 14 and a bottom side substrate 15. The two substrates 14, 15 are preferably designed so as to be electrically insulating and particularly preferably consist of a material with high thermal conductivity.

[0042] Furthermore, the heat exchanger 1 comprises a fluid path 6 that is thermally connected to the bottom side 5 and arranged on the bottom side 5 for being flowed through by a fluid F. The fluid path 6 can be designed as fluid channel and for this purpose be delimited for example by a suitable tubular body 16. Apart from this, a control/regulating device 7 is provided which is equipped/configured for carrying out the method. An electric alternating power source 8 with a first and a second connection 8a, 8b serves for generating the electric current I in the thermoelectric device 2. For this purpose, the power source 8 is designed so as to be controllable by the control/regulating device 7 and the two connections 8a, 8b are electrically connected to the thermoelectrically active elements 3.

[0043] In the fluid path 6, a heat-transferring structure 9 for the more efficient transfer of heat between the fluid F flowing through the fluid path 6 and the thermoelectrically active elements 3 can be arranged.

[0044] In the example of the figures, the fluid paths 6 extend along a first extension direction E1. The first extension direction E1 is a main flow direction of the fluid F through the fluid path 6 or through the fluid channel.

[0045] Practically, the top side 4 and the bottom side 5 are situated along a second extension direction E2 of the heat exchanger 1, which extends orthogonally to the first extension direction E1, opposite to one another.

[0046] The thermoelectric device 2 includes—as already mentioned—multiple electrical conductor bridges 10 for electrically interconnecting the thermoelectrically active elements 3. These electrical conductor bridges 10 are composed of first conductor bridges 10a facing—with respect to the second extension direction E2—the bottom side 5 and second conductor bridges 10b facing the top side 4. The first conductor bridges 10a can be arranged on the bottom side substrate 15. The second conductor bridges 10b can be arranged on the top side substrate 14. The first conductor bridges 10a form a cold side 11 of the thermoelectric device 2. The second conductor bridges 10b form a warm side 12 of the thermoelectric insulation 2.

[0047] In the example of FIG. 1, the electric energization of the thermoelectrically active elements 3 takes place in such a manner that heat (see arrows W) is transported from the top side 4 to the bottom side 5 of the heat exchanger 1. In this way, the top side 4 is cooled through the heat discharge.

[0048] Compared with this, FIG. 2 shows a scenario in which the thermoelectrically active elements 3 are electrically energized in such a manner that heat is transported from the bottom side 5 to the top side 4 of the heat exchanger 1. In this way, the top side 4 is heated through the supply of heat.

[0049] When carrying out the method according to the invention, the thermoelectric elements 3 of the thermoelectric device 2 are energized with an electric alternating current I(t) so that an average first period tm.sub.1, in which the electric energization of the thermoelectrically active elements 3 takes place in such a manner that heat W is transported form the top side 4 to the bottom side 5, is shorter than an average second period tm2, in which the electric energization of the thermoelectrically active elements 3 takes place in such a manner that heat W is transported from the bottom side 5 to the top side 4.

[0050] The average first period tm.sub.1 and the average second period tm2 are preferably fixed so that the heat quantity transported during a cycle T of the electric alternating current I(t) from the bottom side 5 to the top side 4 substantially corresponds to the heat quantity transported from the top side 4 to the bottom side 5 plus the heat quantity (Joule heat) generated by the thermoelectrically active elements 3 through dissipation.

[0051] Such a cycling of the electric alternating current I(t) that is substantial for the invention is exemplarily reproduced in the current-time (I-t) diagram of FIG. 3a. It is noticeable that the alternating current I(t) follows a rectangular time profile with alternately positive and negative current values +I.sub.0 or −I.sub.0. Within a respective cycle T the period t2, in which the electric alternating current I(t) assumes the negative current value −I.sub.0 is three times that of the period t1, in which the electric alternating current I(t) assumes the positive value I.sub.0. This constitutes a technically easily realisable possibility of achieving the required different average periods tm.sub.1, tm.sub.2. For the average second period tm.sub.2 a three-fold value of the first average period tm.sub.1 materialises. The electric alternating current I(t) is thus generated in the exemplary scenario with a predetermined cycle ratio of 1:3. Different cycle ratios are also conceivable in variants of the example. The rectangular current course exemplarily shown in FIG. 3a can also be replaced with other suitable current courses—for example ramp-shaped triangular or sinusoidal. The desired heating of the top side 4 with substantially constant temperature T.sub.U of the bottom side 5 at the same time is ensured in that a cycle ratio of at least 1:15, preferably between 1:2 and 1:10 is selected. The cycle ratio to be preferably selected can be taken from a predetermined characteristic map stored in the control/regulating device 7. Practically, the alternating current frequency f of the electric alternating current I amounts to at least 1 Hz, preferably at least 10 Hz. Thus, a cycle T of the alternating current I defined by the sum of first- and second-period t1, t2 amounts to maximally 1 s, preferably maximally 1/10 s.

[0052] FIG. 3b shows a variant of the example of FIG. 3a. In the example of the FIG. 3b, an average first current Im.sub.1, in which the electric energization of the thermoelectrically active elements 3 takes place in such a manner that heat W is transported from the top side 4 to the bottom side 5 is smaller than an average second current Im2, in which the electric energization of the thermoelectrically active elements 3 takes place in such a manner that heat is transported from the bottom side to the top side. Analogously to the example of FIG. 3a, heat W is thus also transported as a result from the bottom side 4 to the top side 4. It is noticeable that the alternating current I(t) in the example of FIG. 3b has a rectangular profile with alternately positive and negative current values +I.sub.1 or −I.sub.2. In this case 1 Im.sub.1 1=I.sub.1 and 1 Im.sub.2 1=I.sub.2 applies. The amount of the positive current value I.sub.1 is lower than the amount of the second current value I.sub.2, i.e. 1 Im.sub.1 1<1 Im.sub.2 1.

[0053] Instead of a rectangular current profile, a sinusoidal current profile can also be selected for the alternating current I(t) for example, which in FIG. 3b is complementarily shown in dashed representation. The two current values +I.sub.1 and −I.sub.2 correspond to the maximum or minimum value of the sine curve. The average first current Im.sub.1 is thus obtained by averaging the current value I(t) over the first positive half wave of the sine curve. The average second current Im2 is accordingly obtained by averaging the current value I(t) over the second negative half wave of the sine curve.

[0054] In contrast with the example of FIG. 3a, the period t1 with positive current value in the example of FIG. 3b is identical to the period t2 with negative current value.

[0055] It is expressly emphasised that the exemplary scenarios explained by way of the FIGS. 3a and 3b can also be combined with one another.

[0056] The average first period tm.sub.1 and the average second period tm2 are fixed for carrying out the method both in the example of FIG. 3a so that a temperature T.sub.O of the top side 4 converges against a defined temperature limit value T.sub.G and a temperature of the bottom side T.sub.U remains substantially constant. This scenario is reproduced in the temperature-time (T-t-) diagram of FIG. 4. The same applies to the current values I.sub.1, I.sub.2 in the example of FIG. 3b. The absolute value of the temperature limit value T.sub.G can be adapted by changing the current I(t) to the respective requirements.

[0057] In a variant which is not shown, the current I.sub.0 or I.sub.1, I.sub.2 can also be a zero value at times which corresponds to an interruption of the electric energization of the thermoelectrically active elements 3.

[0058] FIG. 5 shows a preferred configuration variant of the heat exchanger. In the example of FIG. 5, the thermoelectric insulation 2 is formed as thermoelectric fabric 13. The terms “fabric” and “threads” refer primarily to the arrangement of the multiple flexible longitudinal components of which the “fabric” is composed. These are arranged similarly to the “threads” in a classic textile fabric, which is why for illustration the terms weft, threads and warp threads as well as fabric are used here.

[0059] As is evident from FIG. 5, the term “thread” also includes flexible band-like structures or longitudinal block-like structures here. The fabric 13 can include a plurality of first threads which are alternately formed by p-doped and n-doped thread portions and electrically conductive first and second thread portions arranged in between. Here, the first thread portions of the fabric 13 form the first conductor bridges 10a and the second thread portions of the fabric 13 form the second conductor bridges 10b of the installation 2.

[0060] Furthermore, the fabric 13 comprises a plurality of second threads which are preferentially formed so as to be electrically insulating. In the case of the fabric 13, the first threads form the weft threads and the second threads the warp threads or vice versa. The heat exchanger 1 with the thermoelectric fabric 13 shown in FIG. 5 is particularly suitable for integration in a vehicle seat. The top side 4 of the fabric 13 is then practically arranged in the region of a seating surface of the vehicle seat assigned to the top side 4. When carrying out the method according to the invention, heat is transported “nett” from the bottom side 5 to the top side 4 and the seating surface thus heated.