Thermoelectric Device with Flexible Heatsink

Abstract

A thermoelectric device suitable for power generation by the Seebeck effect or heating and cooling by the Peltier effect includes a flexible thermoelectric layer with a flexible heatsink layer. A thermally conductive layer can optionally be included on the side of the thermoelectric layer opposite the flexible heatsink layer. Because of its flexibility and durability, the thermoelectric device can be utilized for products such as a thermoelectric generator or cooling/heating system for consumer products, such as a bedding, clothing, hats, seat cushions, and personal portable devices.

Claims

1. A thermoelectric (TE) device comprising: a thermoelectric layer including one or more thermoelectric modules embedded in a flexible substrate, said thermoelectric layer having a first and second side; and a flexible heatsink layer bonded to the first side of the thermoelectric layer or integrally formed with the thermoelectric layer on the first side of the thermoelectric layer.

2. The TE device of claim 1 wherein the one or more thermoelectric modules in the thermoelectric layer includes a plurality of thermoelectric modules.

3. The TE device of claim 1 wherein the flexible heatsink layer is comprised of a flexible material, a thermally conductive material, and a heat storage material.

4. The TE device of claim 3 wherein the thermally conductive material is a carbon material.

5. The TE device of claim 4 wherein the carbon material is selected from the group consisting of graphite powder, carbon nanotube, and graphene flake.

6. The TE device of claim 3 wherein the heat storage material is a phase change material.

7. The TE device of claim 6 wherein the phase change material is selected from the group consisting of paraffin waxes, polyethyleneglycols, fatty acids and derivatives, polyalcohols and derivatives, and inorganic salt hydrates and other salts.

8. The TE device of claim 6 wherein the phase change material is microcapsulated.

9. The TE device of claim 3 wherein the flexible material is selected from the group consisting of a silicone rubber, an elastomer, a polyurethane, and a polyolefin.

10. The TE device of claim 1 further comprising a thermally conductive layer either bonded to the second side of the thermoelectric layer or integrally formed on the second side of the thermoelectric layer.

11. The TE device of claim 10 wherein the thermally conductive layer is selected from the group consisting of conductive silicone films, graphite films, carbon nanotube films, graphene films, and conductive polymer films.

12. The TE device of claim 10 configured as a wearable Peltier device.

13. The TE device of claim 12 wherein a wearable Peltier device is configured for positioning the thermally conductive layer on a portion of skin of a user.

14. The TE device of claim 10 configured as a wearable thermoelectric generator.

15. The TE device of claim 14 wherein the wearable thermoelectric generator is configured for positioning the thermally conductive layer on a portion of skin of a user.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0021] FIG. 1 is a schematic end view and side-view of a TE device with a flexible heatsink and a thermally conductive layer.

[0022] FIG. 2 is a top-view structure of the TE layer.

[0023] FIG. 3 illustrates two examples of the wearable TE device.

[0024] FIG. 4 is a graph showing the short-term cooling performance of the TE device with and without the flexible heatsink.

[0025] FIG. 5 illustrated the long-term cooling performance of the TE device with the flexible heatsink.

DETAILED DESCRIPTION

[0026] FIG. 1 shows that the flexible TE device comprises a TE layer 1, a flexible heatsink layer 2, and an optional thermally conductive layer 3. Each layer can be produced simultaneously, or individual layers can be bonded together after fabrication. Simultaneous formation and/or bonding separate layers together achieves good thermal contact and mechanical durability. To achieve good contacts between each layer, in one embodiment, thermally conductive adhesives or tapes may be used. In one embodiment, the TE layer 1 and the flexible heatsink 2 can be made using the same flexible materials to help to guarantee good contact and bonding.

[0027] Referring to FIG. 2, the flexible TE layer 1 can be made of multiple, small-size commercial TE (Peltier) modules 4 embedded in flexible material which functions as a flexible supporting unit 5. The flexible material may be PDMS or Ecoflex® or another suitable material. The size of TE module 4 can vary depending on the final application. A preferred dimension of the TE module 4 is 15 mm×15 mm×5 mm or smaller. The TE layer 1 can be altered and be embodied in other variations.

[0028] Referring back to FIG. 2, in some embodiments, the flexible heatsink 2 is an important part for real-world applications, as it preferably has or satisfies multiple properties including flexibility, durability, low weight, high thermal conductivity, and large heat capacity. In one embodiment, the flexible heatsink 2 can be manufactured as a multi-component composite material comprising a flexible material, a thermally conductive material, and a heat storage material. For example, in some embodiments, the flexible material may be PMDS or Ecoflex® silicone. This flexible material can be utilized as a basic matrix and can be mixed with heat storage materials such as phase-change materials, which include but are not limited to EnFinit® PCM 28 CPS powder. The high thermally conductive materials include but are not limited to carbon materials such as graphite powder, carbon nanotube, or graphene flake. These carbon materials can be added to improve the heatsink performance. It should be noted that embodiments of the invention are not limited to the above materials. In some cases, component materials can be replaced with other desirable materials for specific applications.

[0029] In one embodiment, to guarantee constant material properties of the TE device layer 1 and the flexible heat sink 2, liquid-curable flexible materials such as PDMS or Ecoflex® silicone are preferred. They can be used to create a specific shape of a heatsink, such as circular, rectangular, fin-shaped geometries. Any other flexible materials may also be utilized as a matrix for a TE device in accordance with the practice of various embodiments of the invention. These materials can be any material with sufficient flexibility to allow for bending of the finished TE device. In some embodiments, a flexible matrix can be sufficiently flexible to form a bend of at least 10 degrees, a bend of at least 30 degrees, a bend of at least 45 degrees, a bend of at least 70 degrees, or a bend of at least 90 degrees (e.g. 120 or 180 degrees). Such flexibility likewise will preferably apply to the finished flexible TE device.

[0030] To fabricate a homogeneous product, a mechanical mixer or homogenizer can be utilized to mix each component. In some embodiments, the mechanical flexibility, durability, and thermal conductivity of the heatsink 2 can be adjusted by changing one or more or each component of the composition. For example, an increase of the flexible material in the composition will improve its mechanical durability and flexibility of layer, and an increase of the heat storage material or the thermally conductive material in the composition can improve the heat capacity or thermal conductivity of the heatsink 2, respectively.

[0031] With reference back to FIG. 1, thermally conductive layer 3 can be provided for the efficient spread of heating or cooling through the entire surface (i.e., the top surface 6, which may be a skin contacting surface for a wearable, etc.). Examples, of thermally conductive materials suitable for layer 3 include but are not limited to conductive silicone, graphite, carbon nanotube, or graphene films. If the thermally conductive layer 3 is not included in the TE device, the top surface would be the TE layer 1 itself.

[0032] In order to increase or decrease the targeting cooling or heating performance of the present TE device, in some embodiments, the degree of applied current to TE device can be adjustable. For example, by both the adoption of a higher-performing TE module and an increase in applied current, the degree of cooling or heating can be enhanced. The heating or cooling mode can also be switched through changing the direction of current.

[0033] In addition, embodiments of the invention are not limited to cooling or heating applications but can also be used to generate electricity directly via Seebeck effect, thereby also enabling this device design to be used as a wearable TE device, for example. For the electrical generation mode, a thermally conductive layer 3 preferably faces the heat source, i.e., referring to FIG. 3, the top surface 6 contacts the heat source (e.g., person's skin, etc.), and the flexible heatsink layer 2 preferably faces the opposite direction to dissipate heat. Because the generation power by the TE layer 1 gradually decreases when the temperature gradient between the top and bottom side of TE layer 1 decreases, a thermally conductive layer and flexible heatsink are required to maintain the consistent working performance of TE device during long-term uses.

[0034] FIG. 3 shows some examples of wearable TE devices with a flexible heatsink and a thermally conductive layer 6. In particular, if cooling (or heating) for person's head (or other body part) is desired, a headband (or hat, or helmet, etc.) could have TE device with the thermally conductive layer adjacent the user's forehead (or other body part) for selective heating or cooling using the Peltier effect. In another embodiment, if energy harvesting is desired by the Seebeck effect, the TE device could be made as part of a wearable that attaches to a body part. For example, a wristband might be affixed to the user's arm (or other body part) which has a TE device having a thermally conductive layer 6 facing the user's skin. While wearing, the TE device can harvest energy from the user's body heat. The present TE device is not limited to headband or wristband types of wearable device, but can also be similarly utilized for consumer products, such as a bedding, clothing, hats, seat cushions, personal portable devices, etc.

Example 1

[0035] A prototype flexible TE device was prepared by combining a TE layer and a heatsink layer. To make the TE layer, a commercial TE (Peltier) module (15 mm×15 mm×5 mm) was embedded in Ecoflex® silicone rubber. The heatsink layer was made by blending Ecoflex® silicone rubber (55 wt %), graphite powder (30 wt %), and EnFinit® PCM 28 CPS powder (15 wt %). 0.75 Voltage was applied to the TE device and the temperature of the cold surface of the device was measured with time. For comparison, the temperature of the same TE layer without the heatsink was measured.

[0036] FIG. 4 shows the short-term cooling performance of the TE layer with and without the heatsink. Without the heatsink, the TE layer could not keep cooling more than 60 seconds, whereas the TE layer with heatsink kept cooling below the initial temperature by around 4° C. for over 300 seconds.

[0037] FIG. 5 shows the long-term cooling performance of the TE layer with the heatsink. It is shown that around 3° C. cooling was kept during 5 hours of testing.