HEAT EXCHANGE UNIT

Abstract

A heat exchange unit is constituted of a thermoelectric module and a heat exchanger. The thermoelectric module includes an upper electrode, a lower electrode, and a plurality of thermoelectric elements interposed between the upper electrode and the lower electrode, wherein the heat exchanger composed of aluminum or aluminum alloy having high thermal conductivity is attached to the upper electrode and/or the lower electrode via an insulating layer. The surface roughness of the heat exchanger adjoined to the insulating layer is controlled to be less than 4.7 μm and greater than 0.1 μm. This prevents cracks and fractures from being formed in the insulating layer, which is thus improved in adhesion with the heat exchanger. Thus, it is possible to demonstrate high heat-absorption/dissipation performance and high reliability in the heat exchange unit due to a reduced thermal resistance between the thermoelectric module and the heat exchanger.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to heat exchange units including thermoelectric modules in which thermoelectric elements of different types are alternately aligned and electrically connected in series between heat-absorption electrodes and heat-dissipation electrodes.

The present application claims priority on Japanese Patent Application No. 2009-18498, the content of which is incorporated herein by reference.

2. Description of the Related Art

Conventionally, thermoelectric modules have been developed and designed such that thermoelectric elements composed of P-type semiconductors and N-type semiconductors are alternately aligned and connected in series and are held between heat-absorption electrodes and heat-dissipation electrodes via metals such as soldering metals. Various documents disclose heat exchange units in which heat exchangers join to heat-absorption electrodes or heat-dissipation electrodes of thermoelectric modules so as to improve the heat-dissipation efficiency.

• • Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-332642
  • Patent Document 2: Japanese Unexamined Patent Application Publication No. 2006-234362

Patent Document 1 discloses a thermoelectric transducer unit, namely a heat exchange unit 40 shown in FIG. 14. In the heat exchange unit 40, an insulating layer 42 composed of alumite (or anodized aluminum) is formed on a heat exchange member (a heatsink) 41 composed of an aluminum plate; a metal plating layer 43 is integrally formed on the insulating layer 42 with the same alignment pattern as a metal electrode 44; and the metal electrode 44 is bonded onto the metal plating layer 43. P-type thermoelectric elements 45a and N-type thermoelectric elements 45b are alternately aligned and electrically connected in series between the “lower” metal electrode 44 and an “upper” metal electrode 46. A thermoelectric module 40a is constituted of the thermoelectric elements 45a and 45b as well as the lower metal electrode 44 and the upper metal electrode 46.

Patent Document 2 discloses a heat exchanger, namely a heat exchange unit 50 shown in FIG. 15. The heat exchange unit 50 includes a thermoelectric transducer module (or a thermoelectric module) 50a interposed between a heat-dissipation member (or a heatsink) 51 and a heat-absorption member (or a heatsink) 52, in which a plurality of thermoelectric elements 55 is interposed between a heat-dissipation electrode 53 and a heat-absorption electrode 54. Herein, a resin 56a, a metal foil 56b, and a solder 56c are interposed between the heat-dissipation member 51 and the heat-dissipation electrode 53, while a resin 57a and a grease 57b are interposed between the heat-absorption member 52 and the heat-absorption electrode 54. The resin 56a is deposited on the surface of the heat-dissipation member 51, while the resin 57a is deposited on the surface of the heat-absorption member 52. During the deposition, the resins 56a and 57a are softened to partially infiltrate into cavities and flaws formed on the surfaces of the heat-dissipation member 51 and heat-absorption member 52 and are then hardened.

Recently, fillers composed of alumina powder and aluminum nitride have been used and uniformly dispersed into insulating resin layers (originally having poor thermal conductivity) so as to improve thermal conductivity. The heat exchange unit 40 disclosed in Patent Document 1 is not designed in consideration of the surface roughness of the heat exchanger 41, the thickness of the insulating layer 42, and fillers added to the insulating layer 42 (serving as the insulating resin layer). Even when the heat exchanger 41 is composed of an aluminum alloy whose surface is subjected to anodic oxide coating, it is difficult to improve the adhesion between the heat exchanger 41 and the insulating layer 42 and to reduce the thermal resistance therebetween.

The surfaces of the heat-dissipation member 51 and the heat-absorption member 52 are roughened so that the resins 56a and 57a may easily infiltrate into cavities and flaws, wherein cracks and fractures may occur in the insulating resin layer into which fillers are dispersed to improve the thermal conductivity. This is because the dispersion of “hard” fillers leads to the formation of small cracks and fractures in the insulating resin layer due to pressurization during thermocompression bonding. This drawback recurs even when the insulating resin layer is hardened by applying a varnish resin.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a heat exchange unit in which a heat exchanger is controlled in terms of surface roughness so as prevent cracks and fractures from being formed in an insulating resin layer, thus improving the adhesion between the heat exchanger and the insulating resin layer. The heat exchange unit has high reliability due to a reduced thermal resistance between the heat exchanger and the insulating resin layer.

A heat exchange unit is constituted of a heat exchanger and a thermoelectric module including an upper electrode, a lower electrode, and a plurality of thermoelectric elements. The thermoelectric elements are interposed between and electrically connected in series between the upper electrode and the lower electrode. The heat exchanger is attached to the surface of the upper electrode and/or the surface of the lower electrode via an insulating layer. The surface roughness of the heat exchanger adjoined to the insulating layer is controlled to be less than 4.7 μm. Herein, the surface roughness Ra is estimated according to the Japanese Industrial Standard, namely JIS B0601, for example.

According to the measurement results on the testing examples of heat exchange units, it is possible to prevent cracks and fractures from being formed at the interface between the insulating layer and the heat exchanger with the surface roughness Ra equal to or less than 4.7 μm (where Ra≦4.7 μm) and with the surface roughness Ra equal to or greater than 0.1 μm (where Ra≧0.1 μm), and it is possible to uniformly form the insulating layer with the prescribed thickness. Even when the thickness of the insulating layer is less than 100 μm, it is possible to prevent cracks and fractures from being formed in the insulating layer. This makes it possible to further reduce the thickness of the insulating layer and to thereby reduce the thermal resistance, thus improving the heat-absorption/dissipation performance.

Considering the manufacturability and the manufacturing cost, it is preferable that the heat exchanger be composed of aluminum or an aluminum alloy having high thermal conductivity. It is preferable that the insulating layer be composed of a single insulating resin layer having high thermal conductivity or a composite layer in which the insulating resin layer is laminated on an alumite layer. It is preferable that fillers be dispersed into insulating resins or varnished insulating resins for use in the insulating layer. It is preferable that fillers be composed of alumina powder, aluminum nitride powder, magnesium oxide powder, or silicon carbide powder. It is preferable that insulating resins be selected from among polyimide resins or epoxy resins. In this connection, insulating resins are formed in sheet-like shapes via crimping, or they are varnished and solidified.

Due to the optimized surface roughness of the heat exchanger, it is possible to prevent cracks and fractures from being formed in the insulating layer, it is possible to improve the adhesion between the heat exchanger and the insulating layer, and it is possible to reduce the thermal resistance and to thereby improve the heat-absorption/dissipation performance and the reliability in the heat exchange unit.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, aspects, and embodiments of the present invention will be described in more detail with reference to the following drawings.

FIG. 1A is a longitudinal sectional view showing a first heat exchanger adjoined to a lower electrode via an insulating layer.

FIG. 1B is a longitudinal sectional view in which a plurality of thermoelectric elements is aligned and bonded onto the lower electrode of the first heat exchanger.

FIG. 1C is a longitudinal sectional view in which a second heat exchanger adjoined to an upper electrode via an insulating layer is combined with the first heat exchanger shown in FIG. 1B and in which the thermoelectric elements are interposed between the lower electrode of the first heat exchanger and the upper electrode of the second heat exchanger so as to form a heat exchange unit including a thermoelectric module according to a first embodiment of the present invention.

FIG. 2A is a plan view showing an alignment pattern of the lower electrode.

FIG. 2B is a plan view showing an alignment pattern of the upper electrode.

FIG. 3 is an illustration showing a heat insulating box used for measuring the maximum heat-absorption value Qmax with respect to the heat exchange unit of the first embodiment.

FIG. 4 is an illustration showing the method for measuring the withstand voltage WS of the heat exchange unit of the first embodiment.

FIG. 5 is a graph showing the measurement results of the withstand voltage WS relative to the surface roughness Ra with respect to testing examples of the heat exchange unit of the first embodiment.

FIG. 6A is a side view showing that a lower electrode is formed on the surface of a water-cooled first heat exchanger via an insulating layer in a heat exchange unit according to a second embodiment of the present invention.

FIG. 6B is a side view showing that an upper electrode is attached to the upper ends of thermoelectric elements which are aligned on the lower electrode of the first heat exchanger shown in FIG. 6A.

FIG. 6C is a side view showing that a water-cooled second heat exchanger adjoins to the upper electrode via an insulating layer.

FIG. 7A is a plan view showing an alignment pattern of the lower electrode.

FIG. 7B is a plan view showing an alignment pattern of the upper electrode.

FIG. 8 is an illustration showing a vacuum chamber used for measuring the maximum heat-absorption value Qmax with respect to the heat exchange unit of the second embodiment.

FIG. 9 is a graph showing the measurement results of the withstand voltage WS relative to the surface roughness Ra with respect to testing examples of the heat exchange unit of the second embodiment.

FIG. 10A is a side view showing that a first lower electrode and a first upper electrode are formed on the surface and the backside of a water-cooled first heat exchanger via insulating layers in a heat exchange unit according to a third embodiment of the present invention.

FIG. 10B is a side view showing that a second upper electrode is attached to the upper ends of first thermoelectric elements which are aligned on the first lower electrode while a second lower electrode is attached to the lower ends of second thermoelectric elements which are aligned below the first upper electrode.

FIG. 10C is a side view showing that a water-cooled second heat exchanger adjoins to the second upper electrode via an insulating layer while a water-cooled third heat exchanger adjoins to the second lower electrode.

FIG. 11A is a plan view showing an alignment pattern of the first lower electrode and the first upper electrode.

FIG. 11B is a plan view showing an alignment pattern of the second lower electrode and the second upper electrode.

FIG. 12 is an illustration showing a vacuum chamber used for measuring the maximum heat-absorption value Qmax with respect to the heat exchange unit of the third embodiment.

FIG. 13 is a graph showing the measurement results of the withstand voltage WS relative to the surface roughness Ra with respect to testing examples of the heat exchange unit of the third embodiment.

FIG. 14 is a longitudinal sectional view of an example of a heat exchange unit.

FIG. 15 is a longitudinal sectional view of another example of a heat exchange unit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in further detail by way of examples with reference to the accompanying drawings.

1. First Embodiment

A heat exchange unit 10 according to a first embodiment of the present invention will be described with reference to FIGS. 1A to 1C. As shown in FIG. 1C, the heat exchange unit 10 is constituted of a first heat exchanger (serving as a heat-dissipation or heat-absorption air-cooled heatsink) 11, an insulating layer 12 formed on the surface of the first heat exchanger 11, a lower electrode (serving as a heat-dissipation or heat-absorption electrode) 13 disposed on the insulating layer 12, a plurality of thermoelectric elements 14 bonded onto the lower electrode 13, an upper electrode (serving as a heat-dissipation or heat-absorption electrode) 15 bonded onto the thermoelectric elements 14, a second heat exchanger (serving as a heat-dissipation or heat-absorption air-cooled heatsink) 16, and an insulating layer 17 formed on the surface of the second heat exchanger 16. A pair of terminals connected to a pair of leads (both not shown) is formed on one end of the lower electrode 13.

A thermoelectric module M (see FIG. 3) is constituted of the thermoelectric elements 14 which are electrically connected in series between the lower electrode 13 and the upper electrode 15 via a joining metal such as a solder.

The first heat exchanger 11 and the second heat exchanger 16 are each composed of aluminum or an aluminum alloy having high thermal conductivity, wherein the surface of the first heat exchanger 11 (adjoined to the insulating layer 12) and the surface of the second heat exchanger 16 (adjoined to the insulating layer 17) are each finished with a surface roughness Ra of 5 μm or less. In addition, numerous fins 11a protrude downwardly from the first heat exchanger 11, while numerous fins 16a protrude upwardly from the second heat exchanger 16.

The insulating layers 12 and 17 are each composed of a polyimide resin, an epoxy resin, or an alumite with a thickness of 10 μm through 100 μm. It is preferable to disperse fillers composed of alumina (Al₂O₃), aluminum nitride (AlN), magnesium oxide (MgO), or silicon carbide (SiC) with an average particle diameter of 15 μm or less into the insulating layers 12 and 17 composed of a polyimide resin or an epoxy resin, thus improving the thermal conductivity. In addition, it is preferable to laminate a polyimide resin or an epoxy resin dispersed with fillers on the insulating layers 12 and 17 composed of alumite.

The upper electrode 15 serves as a heat-absorption electrode when the lower electrode 13 serves as a heat-dissipation electrode, or the upper electrode 15 serves as the heat-dissipation electrode when the lower electrode 13 serves as the heat-absorption electrode. The lower electrode 13 and the upper electrode 15 are each composed of a copper film or a copper alloy film with a thickness of 70 μm through 200 μm. The lower electrode 13 has an alignment pattern shown in FIG. 2A, while the upper electrode 15 has an alignment pattern shown in FIG. 2B. Each segment of the lower electrode 13 is formed in a rectangular shape with a long length of 3 mm and a short length of 1.8 mm. Similarly, each segment of the upper electrode 15 is formed in a rectangular shape with a long length of 3 mm and a short length of 1.8 mm.

The thermoelectric elements 14 composed of P-type semiconductors and N-type semiconductors are electrically connected in series between the lower electrode 13 and the upper electrode 15 in such a way that P-type semiconductors and N-type semiconductors are alternately aligned. The thermoelectric elements 14 are soldered to the lower electrode 13 and the upper electrode 15 via a SnSb alloy, an AuSn alloy, or a SnAgCu alloy. Nickel plating is applied to the distal ends of the thermoelectric elements 14 so that the thermoelectric elements 14 can be easily soldered to the lower electrode 13 and the upper electrode 15.

It is preferable that the thermoelectric elements 14 be composed of sintered thermoelectric materials of Bi—Te having high thermoelectric performance at room temperature. Specifically, it is preferable to use P-type semiconductors composed of ternary compounds of Bi—Sb—Te and N-type semiconductors composed of quaternary compounds of Bi—Sb—Te—Se. In the present embodiment, P-type semiconductors are composed of Bi_0.5Sb_1.5Te₃, while N-type semiconductors are composed of Bi_1.9Sb_0.1Te_2.6Se_0.4, wherein these semiconductors are subjected to liquid quenching so as to produce foil powder, which is then subjected to hot pressing so as to form bulks, which are then cut into pieces each having prescribed dimensions of 1.35-mm length, 1.35-mm width, and 1.5-mm height.

(a) Production of Heat Exchange Unit 10

The heat exchange unit 10 is produced by way of the following procedure.

First, the first heat exchanger 11 (serving as a heat-dissipation air-cooled heatsink) is prepared such that the insulating layer 12 having an adhesive property is formed on one face thereof while the fins 11a are formed on the opposite face thereof. Similarly, the second heat exchanger 16 (serving as a heat-absorption air-cooled heatsink) is prepared such that the insulating layer 17 having an adhesive property is formed on one face thereof while the fins 16a are formed on the opposite face thereof. In addition, the lower electrode 13 (serving as a heat-dissipation electrode) and the upper electrode 15 (serving as a heat-absorption electrode) are prepared in advance. Furthermore, the thermoelectric elements 14 composed of P-type semiconductors and N-type semiconductors are prepared in advance.

The first heat exchanger 11 and the second heat exchanger 16 are each composed of aluminum or an aluminum alloy having high thermal conductivity. The surface of the first heat exchanger 11 (adjoined to the insulating layer 12) and the surface of the second heat exchanger 16 (adjoined to the insulating layer 17) are each finished with the surface roughness Ra of 5 μm or less. The insulating layers 12 and 17 are formed by dispersing fillers of powder composed of Al₂O₃, AlN, MgO, or SiC into polyimide resin layers or epoxy resin layers having adhesive properties. Alternatively, they are formed using composite layers in which filler-dispersed polyimide resin layers or epoxy layers are formed on alumite layers. Herein, the insulating layers 12 and 17 are formed by crimping sheet-shaped materials. Alternatively, varnish is applied to sheet-shaped materials, which are then solidified so as to form the insulating layers 12 and 17. The lower electrode 13 and the upper electrode 15 are each composed of a copper film or a copper alloy film and are each shaped in the prescribed electrode pattern with the prescribed thickness of 70 μm through 200 μm. Nickel plating is applied to the distal ends (or opposite ends in the longitudinal direction) of P-type and N-type semiconductors.

The lower electrode 13 composed of a copper film or a copper alloy film having the prescribed electrode pattern shown in FIG. 2A is bonded onto the insulating layer 12 of the first heat exchanger 11. Subsequently, the thermoelectric elements 14 composed of P-type and N-type semiconductors are alternately aligned on the lower electrode 13 as shown in FIG. 1B, wherein the lower ends of the thermoelectric elements 14 are attached onto the lower electrode 13 via a solder alloy (e.g. a SnSb alloy, an AuSn alloy, and a SnAgCu alloy). In addition, the upper electrode 15 composed of a copper film or a copper alloy film having the prescribed electrode pattern shown in FIG. 2B is disposed on the upper ends of the thermoelectric elements 14.

Thereafter, the upper electrode 15 is attached onto the upper ends of the thermoelectric elements 14 via a solder alloy (e.g. a SnSb alloy, an AuSn alloy, and a SnAgCu alloy). Thus, the thermoelectric elements 14 composed of P-type and N-type semiconductors are alternately aligned and electrically connected in series between the lower electrode 13 and the upper electrode 15.

Lastly, as shown in FIG. 1C, the insulating layer 17 of the second heat exchanger 16 is brought into contact with the upper electrode 15; then, the upper electrode 15 is attached to the insulating layer 17. This completes the production of the heat exchange unit 10 of the first embodiment.

(b) Usage of Heat Exchange Unit 10

The heat exchange unit 10 of the first embodiment can be used to control the temperature of a gaseous matter. That is, the heat exchange unit 10 is arranged such that the fins 16a of the second heat exchanger 16 (serving as the heat-absorption air-cooled heatsink) is brought into a gaseous matter subjected to temperature control. In this state, electricity is applied to the thermoelectric module M in which the thermoelectric elements 14 are electrically connected in series between the “heat-dissipating” lower electrode 13 and the “heat-absorbing” upper electrode 15, so that the upper electrode 15 is cooled to absorb heat from the gaseous matter subjected to temperature control by way of the fins 16a of the second heat exchanger 16. In this connection, heat is generated in the lower electrode 13 being heated but is dissipated via the fins 11a of the first heat exchanger 11.

(c) Measurement of Maximum Heat-Absorption Value Qmax

Using the heat exchange unit 10 of the first embodiment, it is possible to measure the maximum heat-absorption (or endothermic) value Qmax constituting a performance evaluation benchmark by way of the following procedure. Testing examples A1 through A3, B1 through B4, and C1 through C3 are produced based on the heat exchange unit 10. As shown in FIG. 3, a heat insulating box X is used to install the heat exchange unit 10 (i.e. testing examples of heat exchange units A1-A3, B1-B4, and C1-C3) at the opening thereof.

The heat exchange unit 10 is installed in the heat insulating box X in such a way that the fins 16a of the second heat exchanger 16 (serving as a heat absorber) are disposed inside the heat insulating box X while the fins 11a of the first heat exchanger 11 (serving as a heat dissipater) are disposed outside the heat insulating box X, wherein heat is transmitted from the inside to the outside of the heat insulating box X. A heater H serving as a virtual heat source producing a prescribed heating value is arranged inside the heat insulating box X.

The heat exchange unit 10 is driven so as to measure a maximum heating value (W), at which the interior temperature of the heat insulating box X agrees with the exterior temperature, as the maximum heat-absorption value Qmax. Measurement results show that the heat exchange unit A1 indicates that Qmax=113 W, the heat exchange unit A2 indicates that Qmax=114 W, and heat exchange unit A3 indicates that Qmax=113 W. In addition, the heat exchange unit B1 indicates that Qmax=116 W, the heat exchange unit B2 indicates that Qmax=115 W, the heat exchange unit B3 indicates that Qmax=114 W, and the heat exchange unit B4 indicates that Qmax=115 W. Furthermore, the heat exchange unit C1 indicates that Qmax=110 W, the heat exchange unit C2 indicates that Qmax=111 W, and heat exchange unit C3 indicates that Qmax=110 W.

In the above, the heat exchange unit A1 is produced such that fillers composed of alumina (Al₂O₃) powder are dispersed in polyimide resin sheets, thus forming the insulating layers 12 and 17 with a 15-μm thickness. The heat exchange unit A2 is produced such that fillers composed of alumina (Al₂O₃) powder are dispersed in varnished polyimide resins, thus forming the insulating layers 12 and 17 with a 15-μm thickness. The heat exchange unit A3 is produced such that fillers composed of alumina (Al₂O₃) powder are dispersed in epoxy resin sheets, thus forming the insulating layers 12 and 17 with a 20-μm thickness.

In addition, the heat exchange unit B1 is produced such that fillers composed of aluminum nitride (AlN) powder are dispersed in epoxy resin sheets, thus forming the insulating layers 12 and 17 with a 20-μm thickness. The heat exchange unit B2 is produced such that fillers composed of alumina (Al₂O₃) powder are dispersed in varnished epoxy resins, thus forming the insulating layers 12 and 17 with a 20-μm thickness. The heat exchange unit B3 is produced such that fillers composed of magnesium oxide (MgO) powder are dispersed in varnished epoxy resins, thus forming the insulating layers 12 and 17 with a 20-μm thickness. The heat exchange unit B4 is produced such that fillers composed of silicon carbide (SiC) powder are dispersed in varnished epoxy resins, thus forming the insulating layers 12 and 17 with a 20-μm thickness.

Furthermore, the heat exchange unit C1 is produced such that fillers composed of alumina (Al2O3) powder are dispersed in polyimide resin sheets on 10-μm-thick alumite layers, thus forming the insulating layers 12 and 17 with a 100-μm thickness. The heat exchange unit C2 is produced such that fillers composed of alumina (Al2O3) powder are dispersed in epoxy resin sheets on 10-μm-thick alumite layers, thus forming the insulating layers 12 and 17 with a 50-μm thickness. The heat exchange unit C3 is produced such that fillers composed of alumina (Al2O3) powder are dispersed in varnished epoxy resins on 10-μm-thick alumite layers, thus forming the insulating layers 12 and 17 with a 50-μm thickness.

(d) Measurement of Withstand Voltage WS

Heat exchange units A11 through A19, A21 through A29, and A31 through A39 are produced based on the heat exchange units A1, A2, and A3 by varying the surface roughness Ra on the surface of the first heat exchanger 11 adjoined to the insulating layer 12 and on the surface of the second heat exchanger 16 adjoined to the insulating layer 17. Withstand voltages WS are measured with respect to the heat exchange units A11-A19, A21-A29, and A31-A39 using different values of the surface roughness Ra.

Specifically, the surface roughness Ra (on the surface of the first heat exchanger 11 adjoined to the insulating layer 12 and on the surface of the second heat exchanger 16 adjoined to the insulating layer 17) is changed with respect to the heat exchange unit A1 so that the heat exchange unit A11 has the surface roughness of 0.3 μm, the heat exchange unit A12 has the surface roughness of 0.5 μm, the heat exchange unit A13 has the surface roughness of 1.0 μm, the heat exchange unit A14 has the surface roughness of 1.6 μm, the heat exchange unit A15 has the surface roughness of 2.2 μm, the heat exchange unit A16 has the surface roughness of 3.2 μm, the heat exchange unit A11 has the surface roughness of 4.4 μm, the heat exchange unit A18 has the surface roughness of 4.7 μm, and the heat exchange unit A19 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit A1a having the surface roughness of 0.07 μm and a heat exchange unit A1b having the surface roughness of 0.1 μm are produced based on the heat exchange unit A1 and are measured in the withstand voltage WS. The measurement results are shown in Table 1-1, wherein the insulating layer 12 (17) is a 15-μm-thick polyimide sheet, and fillers are composed of alumina (Al₂O₃).

TABLE 1-1
Type	A1a	A1b	A11	A12	A13	A14	A15	A16	A17	A18	A19
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.2	3.2	4.4	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	1.75	1.75	1.75	0.25
(kV)
Qmax	98	113	113	113	113	113	113	113	113	113	113
(W)

In addition, the surface roughness Ra is changed with respect to the heat exchange unit A2 so that the heat exchange unit A21 has the surface roughness of 0.3 μm, the heat exchange unit A22 has the surface roughness of 0.5 μm, the heat exchange unit A23 has the surface roughness of 1.0 μm, the heat exchange unit A24 has the surface roughness of 1.3 μm, the heat exchange unit A25 has the surface roughness of 2.4 μm, the heat exchange unit A26 has the surface roughness of 3.2 μm, the heat exchange unit A27 has the surface roughness of 4.3 μm, the heat exchange unit A28 has the surface roughness of 4.7 μm, and the heat exchange unit A29 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit A2a having the surface roughness of 0.07 μm and a heat exchange unit A1b having the surface roughness of 0.1 μm are produced based on the heat exchange unit A2 and are measured in the withstand voltage WS. The measurement results are shown in Table 1-2, wherein the insulating layer 12 (17) is a 15-μm-thick polyimide varnish, and fillers are composed of alumina (Al₂O₃).

TABLE 1-2
Type	A2a	A2b	A21	A22	A23	A24	A25	A26	A27	A28	A29
Ra	0.07	0.1	0.3	0.5	1.0	1.3	2.4	3.2	4.3	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	1.75	1.75	1.75	0.25
(kV)
Qmax	96	114	114	114	114	114	114	114	114	114	114
(W)

Furthermore, the surface roughness Ra is changed with respect to the heat exchange unit A3 so that the heat exchange unit A31 has the surface roughness of 0.3 μm, the heat exchange unit A32 has the surface roughness of 0.5 μm, the heat exchange unit A33 has the surface roughness of 1.0 μm, the heat exchange unit A34 has the surface roughness of 1.6 μm, the heat exchange unit A35 has the surface roughness of 2.2 μm, the heat exchange unit A36 has the surface roughness of 3.2 μm, the heat exchange unit A37 has the surface roughness of 4.4 μm, the heat exchange unit A38 has the surface roughness of 4.7 μm, and the heat exchange unit A39 has the surface roughness of 5.0 μm. Additionally, a heat exchange unit A3a having the surface roughness of 0.07 μm and a heat exchange unit A3b having the surface roughness of 0.1 μm are produced based on the heat exchange unit A3 and are measured in the withstand voltage WS. The measurement results are shown in Table 1-3, wherein the insulating layer 12 (17) is a 20-μm-thick epoxy sheet, and fillers are composed of alumina (Al₂O₃).

TABLE 1-3
Type	A3a	A3b	A31	A32	A33	A34	A35	A36	A37	A38	A39
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.2	3.2	4.4	4.7	5.0
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	0.25
(kV)
Qmax	96	113	113	113	113	113	113	113	113	113	113
(W)

As shown in FIG. 4, the measurement of the withstand voltage WS is performed using the heat exchanger 11 (16) adjoined to the insulating layer 12 (17) on which the electrode 13 (15) is formed with the prescribed pattern, wherein a plurality of probes P is disposed at the prescribed positions of the electrode 13 (15) and is then brought into contact with the electrode 13 (15). A prescribed voltage V is applied to the probes P for five seconds so as to measure the withstand voltage WS when the leak voltage exceeds 5 mA.

The measurement results regarding the heat exchange units A11-A19, A21-A29, and A31-A39 in Tables 1-1, 1-2, and 1-3 are plotted on a graph of FIG. 5 whose horizontal axis represents the surface roughness Ra (μm) and whose vertical axis represents the withstand voltage WS (kV), thus drawing measurement curves (or broken lines) A1, A2, and A3. The above measurement results shown in FIG. 5 and Tables 1-1 through 1-3 clearly show that the withstand voltage WS is good as long as the surface roughness Ra is less than 4.7 μm, but it rapidly decreases when the surface roughness Ra exceeds 4.7 μm. Thus, it is preferable that the surface roughness Ra of the heat exchanger 11 (16) be less than 4.7 μm.

Next, heat exchange units B11 through B19, B21 through B29, B31 through B39, and B41 through B49 are produced based on the heat exchange units B1, B2, B3, and B4 by varying the surface roughness Ra on the surface of the first heat exchanger 11 adjoined to the insulating layer 12 and on the surface of the second heat exchanger 16 adjoined to the insulating layer 17. Withstand voltages WS are measured with respect to the heat exchange units B11-B19, B21-B29, B31-B39, and B41-B49 using different values of the surface roughness Ra.

Specifically, the surface roughness Ra (on the surface of the first heat exchanger 11 adjoined to the insulating layer 12 and on the surface of the second heat exchanger 16 adjoined to the insulating layer 17) is changed with respect to the heat exchange unit B1 so that the heat exchange unit B11 has the surface roughness of 0.3 μm, the heat exchange unit B12 has the surface roughness of 0.5 μm, the heat exchange unit B13 has the surface roughness of 1.0 μm, the heat exchange unit B14 has the surface roughness of 1.6 μm, the heat exchange unit B15 has the surface roughness of 2.2 μm, the heat exchange unit B16 has the surface roughness of 3.2 μm, the heat exchange unit B17 has the surface roughness of 4.4 μM, the heat exchange unit B18 has the surface roughness of 4.7 μm, and the heat exchange unit B19 has the surface roughness of 5.2 μm. Additionally, a heat exchange unit B1a having the surface roughness of 0.07 μm and a heat exchange unit B1b having the surface roughness of 0.1 μm are produced based on the heat exchange unit B1 and are measured in the withstand voltage WS. The measurement results are shown in Table 2-1, wherein the insulating layer 12 (17) is a 20-μm-thick epoxy sheet, and fillers are composed of aluminum nitride (AlN).

TABLE 2-1
Type	B1a	B1b	B11	B12	B13	B14	B15	B16	B17	B18	B19
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.2	3.2	4.4	4.7	5.2
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	2.0	0.25
(kV)
Qmax	96	116	116	116	116	116	116	116	116	116	116
(W)

In addition, the surface roughness Ra is changed with respect to the heat exchange unit B2 so that the heat exchange unit B21 has the surface roughness of 0.3 μm, the heat exchange unit B22 has the surface roughness of 0.5 μm, the heat exchange unit B23 has the surface roughness of 1.0 μm, the heat exchange unit B24 has the surface roughness of 1.6 μm, the heat exchange unit B25 has the surface roughness of 2.1 μm, the heat exchange unit B26 has the surface roughness of 3.3 μm, the heat exchange unit B27 has the surface roughness of 4.4 μm, the heat exchange unit B28 has the surface roughness of 4.7 μm, and the heat exchange unit B29 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit B2a having the surface roughness of 0.07 μm and a heat exchange unit B2b having the surface roughness of 0.1 μm are produced based on the heat exchange unit B2 and are measured in the withstand voltage WS. The measurement results are shown in Table 2-2, wherein the insulating layer 12 (17) is a 20-μm-thick epoxy varnish, and fillers are composed of alumina (Al₂O₃).

TABLE 2-2
Type	B2a	B2b	B21	B22	B23	B24	B25	B26	B27	B28	B29
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.1	3.3	4.4	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	1.75	1.75	1.75	0.5
(kV)
Qmax	96	115	115	115	115	115	115	115	115	115	115
(W)

Furthermore, the surface roughness Ra is changed with respect to the heat exchange unit B3 so that the heat exchange unit B31 has the surface roughness of 0.3 μm, the heat exchange unit B32 has the surface roughness of 0.5 μm, the heat exchange unit B33 has the surface roughness of 1.0 μm, the heat exchange unit B34 has the surface roughness of 1.6 μm, the heat exchange unit B35 has the surface roughness of 2.2 μm, the heat exchange unit B36 has the surface roughness of 3.3 μm, the heat exchange unit B37 has the surface roughness of 4.5 μm, the heat exchange unit B38 has the surface roughness of 4.7 μm, and the heat exchange unit B39 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit B3a having the surface roughness of 0.07 μm and a heat exchange unit B3b having the surface roughness of 0.1 μm are produced based on the heat exchange unit B3 and are measured in the withstand voltage WS. The measurement results are shown in Table 2-3, wherein the insulating layer 12 (17) is a 20-μm-thick epoxy varnish, and fillers are composed of magnesium oxide (MgO).

TABLE 2-3
Type	B3a	B3b	B31	B32	B33	B34	B35	B36	B37	B38	B39
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.2	3.3	4.5	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	1.75	1.75	1.75	0.25
(kV)
Qmax	98	114	114	114	114	114	114	114	114	114	114
(W)

Moreover, the surface roughness Ra is changed with respect to the heat exchange unit B4 so that the heat exchange unit B41 has the surface roughness of 0.3 μm, the heat exchange unit B42 has the surface roughness of 0.5 μm, the heat exchange unit B43 has the surface roughness of 1.0 μm, the heat exchange unit B44 has the surface roughness of 1.6 μm, the heat exchange unit B45 has the surface roughness of 2.2 μm, the heat exchange unit B46 has the surface roughness of 3.4 μm, the heat exchange unit B47 has the surface roughness of 4.5 μm, the heat exchange unit B48 has the surface roughness of 4.7 μm, and the heat exchange unit B49 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit B4a having the surface roughness of 0.07 μm and a heat exchange unit B4b having the surface roughness of 0.1 μm are produced based on the heat exchange unit. B4 and are measured in the withstand voltage WS. The measurement results are shown in Table 2-4, wherein the insulating layer 12 (17) is a 20-μm-thick epoxy varnish, and fillers are composed of silicon carbide (SiC).

TABLE 2-4
Type	B4a	B4b	B41	B42	B43	B44	B45	B46	B47	B48	B49
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.2	3.4	4.5	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	1.75	1.75	1.75	0.25
(kV)
Qmax	98	115	115	115	115	115	115	115	115	115	115
(W)

The measurement results regarding the heat exchange units B11-B19, B21-B29, B31-B39, and B41-B49 in Tables 2-1, 2-2, 2-3, and 2-4 are plotted on the graph of FIG. 5, thus drawing measurement curves (or broken lines) B1, B2, B3, and B4. The above measurement results shown in FIG. 5 and Tables 2-1 through 2-4 clearly show that the withstand voltage WS is good as long as the surface roughness Ra is less than 4.7 μm, but it rapidly decreases when the surface roughness Ra exceeds 4.7 μm. Thus, it is preferable that the surface roughness Ra of the heat exchanger 11 (16) be less than 4.7 μm.

Next, heat exchange units C11 through C19, C21 through C29, and C31 through C39 are produced based on the heat exchange units C1, C2, and C3 by varying the surface roughness Ra on the surface of the first heat exchanger 11 adjoined to the insulating layer 12 and on the surface of the second heat exchanger 16 adjoined to the insulating layer 17. Withstand voltages WS are measured with respect to the heat exchange units C11-C19, C21-C29, and C31-C39 using different values of the surface roughness Ra.

Specifically, the surface roughness Ra (on the surface of the first heat exchanger 11 adjoined to the insulating layer 12 and on the surface of the second heat exchanger 16 adjoined to the insulating layer 17) is changed with respect to the heat exchange unit C1 so that the heat exchange unit C11 has the surface roughness of 0.3 μm, the heat exchange unit C12 has the surface roughness of 0.5 μm, the heat exchange unit C13 has the surface roughness of 1.0 μm, the heat exchange unit C14 has the surface roughness of 1.5 μm, the heat exchange unit C15 has the surface roughness of 2.2 μm, the heat exchange unit C16 has the surface roughness of 3.2 μm, the heat exchange unit C17 has the surface roughness of 4.4 μm, the heat exchange unit C18 has the surface roughness of 4.7 μm, and the heat exchange unit C19 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit C1a having the surface roughness of 0.06 μm and a heat exchange unit C1b having the surface roughness of 0.1 μm are produced based on the heat exchange unit C1 and are measured in the withstand voltage WS. The measurement results are shown in Table 3-1, wherein the insulating layer 12 (17) is a 100-μm-thick polyimide sheet plus a 10-μm-thick alumite layer, and fillers are composed of alumina (Al₂O₃).

TABLE 3-1
Type	C1a	C1b	C11	C12	C13	C14	C15	C16	C17	C18	C19
Ra	0.06	0.1	0.3	0.5	1.0	1.5	2.2	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.25	2.25	0.5
(kV)
Qmax	92	110	110	110	110	110	110	110	110	110	110
(W)

In addition, the surface roughness Ra is changed with respect to the heat exchange unit C2 so that the heat exchange unit C21 has the surface roughness of 0.3 μm, the heat exchange unit C22 has the surface roughness of 0.5 μm, the heat exchange unit C23 has the surface roughness of 1.0 μm, the heat exchange unit C24 has the surface roughness of 1.5 μm, the heat exchange unit C25 has the surface roughness of 2.2 μm, the heat exchange unit C26 has the surface roughness of 3.2 μm, the heat exchange unit C27 has the surface roughness of 4.4 μm, the heat exchange unit C28 has the surface roughness of 4.7 μm, and the heat exchange unit C29 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit C2a having the surface roughness of 0.06 μm and a heat exchange unit C2b having the surface roughness of 0.1 μm are produced based on the heat exchange unit C2 and are measured in the withstand voltage WS. The measurement results are shown in Table 3-2, wherein the insulating layer 12 (17) is a 50-μm-thick epoxy sheet plus a 10-μm-thick alumite layer, and fillers are composed of alumina (Al₂O₃).

TABLE 3-2
Type	C2a	C2b	C21	C22	C23	C24	C25	C26	C27	C28	C29
Ra	0.06	0.1	0.3	0.5	1.0	1.5	2.2	3.2	4.4	4.7	5.1
(μm)
WS (kV)	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.25	2.25	0.5
Qmas (W)	90	111	111	111	111	111	111	111	111	111	111

Furthermore, the surface roughness Ra is changed with respect to the heat exchange unit C3 so that the heat exchange unit C31 has the surface roughness of 0.3 μm, the heat exchange unit C32 has the surface roughness of 0.5 μm, the heat exchange unit C33 has the surface roughness of 1.0 μm, the heat exchange unit C34 has the surface roughness of 1.6 μm, the heat exchange unit C35 has the surface roughness of 2.2 μm, the heat exchange unit C36 has the surface roughness of 3.2 μm, the heat exchange unit C37 has the surface roughness of 4.4 μm, the heat exchange unit C38 has the surface roughness of 4.7 μm, and the heat exchange unit C39 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit C3a having the surface roughness of 0.06 μm and a heat exchange unit C3b having the surface roughness of 0.1 μm are produced based on the heat exchange unit C3 and are measured in the withstand voltage WS. The measurement results are shown in Table 3-3, wherein the insulating layer 12 (17) is a 50-μm-thick epoxy varnish plus a 10-μm-thick alumite layer, and fillers are composed of alumina (Al₂O₃).

TABLE 3-3
Type	C3a	C3b	C31	C32	C33	C34	C35	C36	C37	C38	C39
Ra	0.06	0.1	0.3	0.5	1.0	1.6	2.2	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.5	2.25	0.75
(kV)
Qmax	96	110	110	110	110	110	110	110	110	110	110
(W)

The measurement results regarding the heat exchange units C11-C19, C21-C29, and C31-C39 in Tables 3-1, 3-2, and 3-3 are plotted on the graph of FIG. 5, thus drawing measurement curves (or broken lines) C1, C2, and C3. The above measurement results shown in FIG. 5 and Tables 3-1 through 3-3 clearly show that the withstand voltage WS is good as long as the surface roughness Ra is less than 4.7 μm, but it rapidly decreases when the surface roughness Ra exceeds 4.7 μm. Thus, it is preferable that the surface roughness Ra of the heat exchanger 11 (16) be less than 4.7 μm.

2. Second Embodiment

The first embodiment is directed to the heat exchange unit 10 constituted of the first heat exchanger 11 and the second heat exchanger 16 each serving as air-cooled heatsinks, which is not a restriction; hence, it is possible to employ a water-cooled heatsink. A second embodiment is designed to use water-cooled heatsinks as first and second heat exchangers.

A heat exchange unit 20 according to a second embodiment of the present invention will be described with reference to FIGS. 6A to 6C. As shown in FIG. 6C, the heat exchange unit 20 is constituted of a first heat exchanger (serving as a heat-dissipation or heat-absorption water-cooled heatsink) 21, an insulating layer 22 formed on the surface of the first heat exchanger 21, a lower electrode (serving as a heat-dissipation or heat-absorption electrode) 23 disposed on the insulating layer 22, a plurality of thermoelectric elements 24 bonded onto the lower electrode 23, an upper electrode (serving as a heat-dissipation or heat-absorption electrode) 25 bonded onto the thermoelectric elements 24, a second heat exchanger (serving as a heat-dissipation or heat-absorption water-cooled heatsink) 26, and an insulating layer 27 formed on the surface of the second heat exchanger 26. A pair of terminals connected to a pair of leads (both not shown) is formed on one end of the lower electrode 23.

A thermoelectric module M (see FIG. 8) is constituted of the thermoelectric elements 24 which are electrically connected in series between the lower electrode 23 and the upper electrode 25 via a joining metal such as a solder.

The first heat exchanger 21 and the second heat exchanger 26 are each composed of aluminum or an aluminum alloy having high thermal conductivity, wherein the surface of the first heat exchanger 21 (adjoined to the insulating layer 22) and the surface of the second heat exchanger 26 (adjoined to the insulating layer 27) are each finished with the surface roughness Ra of 5 μm or less. In addition, a plurality of channels 21a (allowing a cooling medium, i.e. water, to flow therethrough in the prescribed direction, i.e. from the right to the left) is formed in the first heat exchanger 21, while a plurality of channels 26a is formed in the second heat exchanger 26. As shown in FIG. 7A, a plurality of mounting holes 21b is formed on the surface of the first heat exchanger 21 so that the lower electrode 23 and the upper electrode 25 cannot be aligned thereon. As shown in FIG. 7B, a plurality of mounting holes 26b is formed on the surface of the second heat exchanger 26 so that the lower electrode 23 and the upper electrode 25 cannot be aligned thereon.

The insulating layers 22 and 27 are each composed of a polyimide resin, an epoxy resin, or an alumite with a thickness of 10 μm through 100 μm. It is preferable to disperse fillers composed of alumina (Al₂O₃), aluminum nitride (AlN), magnesium oxide (MgO), or silicon carbide (SiC) with an average particle diameter of 15 μm or less into the insulating layers 22 and 27 composed of a polyimide resin or an epoxy resin, thus improving the thermal conductivity. In addition, it is preferable to laminate a polyimide resin or an epoxy resin dispersed with fillers on the insulating layers 22 and 27 composed of alumite.

The upper electrode 25 serves as a heat-absorption electrode when the lower electrode 23 serves as a heat-dissipation electrode, or the upper electrode 25 serves as the heat-dissipation electrode when the lower electrode 23 serves as the heat-absorption electrode. The lower electrode 23 and the upper electrode 25 are each composed of a copper film or a copper alloy film with a thickness of 70 μm through 200 μm. The lower electrode 23 has an alignment pattern shown in FIG. 7A, while the upper electrode 25 has an alignment pattern shown in FIG. 7B. Each segment of the lower electrode 23 is formed in a rectangular shape with a long length of 3 mm and a short length of 1.8 mm. Similarly, each segment of the upper electrode 25 is formed in a rectangular shape with a long length of 3 mm and a short length of 1.8 mm.

The thermoelectric elements 24 composed of P-type semiconductors and N-type semiconductors are electrically connected in series between the lower electrode 23 and the upper electrode 25 in such a way that P-type semiconductors and N-type semiconductors are alternately aligned. The thermoelectric elements 24 are soldered to the lower electrode 23 and the upper electrode 25 via a SnSb alloy, an AuSn alloy, or a SnAgCu alloy. Nickel plating is applied to the distal ends of the thermoelectric elements 24 so that the thermoelectric elements 24 can be easily soldered to the lower electrode 23 and the upper electrode 25.

It is preferable that the thermoelectric elements 24 be composed of sintered thermoelectric materials of Bi—Te having high thermoelectric performance at room temperature. Specifically, it is preferable to use P-type semiconductors composed of ternary compounds of Bi—Sb—Te and N-type semiconductors composed of quaternary compounds of Bi—Sb—Te—Se. In the present embodiment, P-type semiconductors are composed of Bi_0.5Sb_1.5Te₃, while N-type semiconductors are composed of Bi_1.9Sb_0.1Te_2.6Se_0.4, wherein these semiconductors are subjected to liquid quenching so as to produce foil powder, which is then subjected to hot pressing so as to form bulks, which are then cut into pieces each having prescribed dimensions of 1.35-mm length, 1.35-mm width, and 1.5-mm height.

(a) Production of Heat Exchange Unit 20

The heat exchange unit 20 is produced by way of the following procedure.

First, the first heat exchanger 21 (serving as a heat-dissipation water-cooled heatsink) is prepared such that the insulating layer 22 having an adhesive property is formed on the surface thereof, and a plurality of channels 21a is formed inside thereof to allow a cooling medium (i.e. water) to run therethrough. Similarly, the second heat exchanger 26 (serving as a heat-absorption water-cooled heatsink) is prepared such that the insulating layer 27 having an adhesive property is formed on the surface thereof, and a plurality of channels 26a is formed inside thereof to allow a cooling medium (i.e. water) to run therethrough. In addition, the lower electrode 23 (serving as a heat-dissipation electrode) and the upper electrode 25 (serving as a heat-absorption electrode) are prepared in advance. Furthermore, the thermoelectric elements 24 composed of P-type semiconductors and N-type semiconductors are prepared in advance.

The first heat exchanger 21 and the second heat exchanger 26 are each composed of aluminum or an aluminum alloy having high thermal conductivity. The surface of the first heat exchanger 21 (adjoined to the insulating layer 22) and the surface of the second heat exchanger 26 (adjoined to the insulating layer 27) are each finished with the surface roughness Ra of 5 μm or less. The insulating layers 22 and 27 are formed by dispersing fillers composed of Al₂O₃, AlN, MgO, or SiC into polyimide resin layers or epoxy resin layers having adhesive properties. Alternatively, they are formed using composite layers in which filler-dispersed polyimide resin layers or epoxy layers are formed on alumite layers. Herein, the insulating layers 22 and 27 are formed by crimping sheet-shaped materials. Alternatively, varnish is applied to sheet-shaped materials, which are then solidified so as to form the insulating layers 22 and 27. The lower electrode 23 and the upper electrode 25 are each composed of a copper film or a copper alloy film and are each shaped in the prescribed electrode pattern with the prescribed thickness of 70 μm through 200 μm. Nickel plating is applied to the distal ends (or opposite ends in the longitudinal direction) of P-type and N-type semiconductors.

As shown in FIG. 6A, the lower electrode 23 composed of a copper film or a copper alloy film having the prescribed electrode pattern shown in FIG. 7A is bonded onto the insulating layer 22 of the first heat exchanger 21. Subsequently, the thermoelectric elements 24 composed of P-type and N-type semiconductors are alternately aligned on the lower electrode 23 as shown in FIG. 6B, wherein the lower ends of the thermoelectric elements 24 are attached onto the lower electrode 23 via a solder alloy (e.g. a SnSb alloy, an AuSn alloy, and a SnAgCu alloy). In addition, the upper electrode 25 composed of a copper film or a copper alloy film having the prescribed electrode pattern shown in FIG. 7B is disposed on the upper ends of the thermoelectric elements 24.

Thereafter, the upper electrode 25 is attached onto the upper ends of the thermoelectric elements 24 via a solder alloy (e.g. a SnSb alloy, an AuSn alloy, and a SnAgCu alloy). Thus, the thermoelectric elements 24 composed of P-type and N-type semiconductors are alternately aligned and electrically connected in series between the lower electrode 23 and the upper electrode 25.

Lastly, as shown in FIG. 6C, the insulating layer 27 of the second heat exchanger 26 is brought into contact with the upper electrode 25; then, the upper electrode 25 is attached to the insulating layer 27. This completes the production of the heat exchange unit 20 of the second embodiment.

(b) Usage of Heat Exchange Unit 20

The heat exchange unit 20 of the second embodiment can be used to control the temperature of a prescribed object (i.e. a subject that needs to be controlled in temperature, not shown). For example, hot water that is warmed by absorbing heat from the prescribed object is supplied to the inlet of the channel 26a of the “heat-absorbing” second heat exchanger 26, while the outlet of the channel 26a is connected to the prescribed object. In addition, cold water is supplied to the inlet of the channel 21a of the first heat exchanger 21, while the outlet of the channel 21a is used as a drain. In this state, electricity is applied to the thermoelectric module M in which the thermoelectric elements 24 are electrically connected in series between the “heat-dissipating” lower electrode 23 and the “heat-absorbing” upper electrode 25, whereby the upper electrode 25 is cooled so as to absorb heat from hot water supplied to the prescribed object via the “heat-absorbing” second heat exchanger 26, while the “heat-dissipating” lower electrode 23 is heated so that the heat thereof is dissipated via cold water flowing through the channel 21a of the “heat-dissipating” first heat exchanger 21.

(c) Measurement of Maximum Heat-Absorption Value Qmax

Using the heat exchange unit 20 of the second embodiment, it is possible to measure the maximum heat-absorption (or endothermic) value Qmax constituting a performance evaluation benchmark by way of the following procedure. Testing examples D1 through D3, and E1 through E2 are produced based on the heat exchange unit 20. As shown in FIG. 8, a vacuum chamber Y is used to install the heat exchange unit 20 (i.e. testing examples of heat exchange units D1-D3, E1, and E2) therein. Then, a pipe of hot water (not shown) is connected to the inlet of the channel 26a of the second heat exchanger 26, while a pipe of a drain (not shown) is connected to the outlet of the channel 26a.

In addition, a pipe of cold water (not shown) is connected to the inlet of the channel 21a of the first heat exchanger 21, while a pipe of a drain (not shown) is connected to the outlet of the channel 21a.

The heat exchange unit 20 is driven so as to measure the inlet temperature and the outlet temperature of the channel 21a as well as the inlet temperature and the outlet temperature of the channel 26a for ten minutes, wherein measurement is performed by increasing the inlet temperature so as to measure the average value of the outlet temperature, thus estimating the maximum heat-absorption value Qmax. Measurement results show that the heat exchange unit D1 indicates that Qmax=218 W, the heat exchange unit D2 indicates that Qmax=222 W, and heat exchange unit D3 indicates that Qmax=220 W. In addition, the heat exchange unit E1 indicates that Qmax=225 W, and the heat exchange unit E2 indicates that Qmax=224 W.

In the above, the heat exchange unit D1 is produced such that fillers composed of alumina (Al₂O₃) powder are dispersed in polyimide resin sheets on 5-μm-thick alumite layers, thus forming the insulating layers 22 and 27 with a 30-μm thickness. The heat exchange unit D2 is produced such that fillers composed of alumina (Al₂O₃) powder are dispersed in epoxy resin sheets on 5-μm-thick alumite layers, thus forming the insulating layers 22 and 27 with a 20-μm thickness. The heat exchange unit D3 is produced such that fillers composed of alumina (Al₂O₃) powder are dispersed in varnished epoxy resins on 5-μm-thick alumite layers, thus forming the insulating layers 22 and 27 with a 20-μm thickness.

In addition, the heat exchange unit E1 is produced such that fillers composed of magnesium oxide (MgO) powder are dispersed in epoxy resin sheets, thus forming the insulating layers 22 and 27 with a 20-μm thickness. The heat exchange unit E2 is produced such that fillers composed of silicon carbide (SiC) powder are dispersed in epoxy resin sheets, thus forming the insulating layers 22 and 27 with a 20-μm thickness.

(d) Measurement of Withstand Voltage WS

Heat exchange units D11 through D19, D21 through D29, and D31 through D39 are produced based on the heat exchange units D1, D2, and D3 by varying the surface roughness Ra on the surface of the first heat exchanger 21 adjoined to the insulating layer 22 and on the surface of the second heat exchanger 26 adjoined to the insulating layer 27. Withstand voltages WS are measured with respect to the heat exchange units D11-D19, D21-D29, and D31-D39 using different values of the surface roughness Ra.

Specifically, the surface roughness Ra (on the surface of the first heat exchanger 21 adjoined to the insulating layer 22 and on the surface of the second heat exchanger 26 adjoined to the insulating layer 27) is changed with respect to the heat exchange unit D1 so that the heat exchange unit D11 has the surface roughness of 0.3 μm, the heat exchange unit D12 has the surface roughness of 0.5 μm, the heat exchange unit D13 has the surface roughness of 1.0 μm, the heat exchange unit D14 has the surface roughness of 1.6 μm, the heat exchange unit D15 has the surface roughness of 2.1 μm, the heat exchange unit D16 has the surface roughness of 3.2 μm, the heat exchange unit D17 has the surface roughness of 4.4 μm, the heat exchange unit D18 has the surface roughness of 4.7 μm, and the heat exchange unit D19 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit D1a having the surface roughness of 0.06 μm and a heat exchange unit D1b having the surface roughness of 0.1 μm are produced based on the heat exchange unit D1 and are measured in the withstand voltage WS. The measurement results are shown in Table 4-1, wherein the insulating layer 22 (27) is a 30-μm-thick polyimide sheet plus a 5-μm-thick alumite layer, and fillers are composed of alumina (Al₂O₃).

TABLE 4-1
Type	D1a	D1b	D11	D12	D13	D14	D15	D16	D17	D18	D19
Ra	0.06	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.0	2.0	2.0	1.75	1.75	0.5
(kV)
Qmax	189	218	218	218	218	218	218	218	218	218	218
(W)

In addition, the surface roughness Ra is changed with respect to the heat exchange unit D2 so that the heat exchange unit D21 has the surface roughness of 0.3 μm, the heat exchange unit D22 has the surface roughness of 0.5 μm, the heat exchange unit D23 has the surface roughness of 1.0 μm, the heat exchange unit D24 has the surface roughness of 1.6 μm, the heat exchange unit D25 has the surface roughness of 2.1 μm, the heat exchange unit D26 has the surface roughness of 3.2 μm, the heat exchange unit D27 has the surface roughness of 4.4 μm, the heat exchange unit D28 has the surface roughness of 4.7 μm, and the heat exchange unit D29 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit D2a having the surface roughness of 0.06 μm and a heat exchange unit D2b having the surface roughness of 0.1 μm are produced based on the heat exchange unit D2 and are measured in the withstand voltage WS. The measurement results are shown in Table 4-2, wherein the insulating layer 22 (27) is a 20-μm-thick epoxy sheet plus 5-μm-thick alumite layer, and fillers are composed of alumina (Al₂O₃).

TABLE 4-2
Type	D2a	D2b	D21	D22	D23	D24	D25	D26	D27	D28	D29
Ra	0.06	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.5	2.0	2.0	1.75	1.75	0.5
(kV)
Qmax	188	222	222	222	222	222	222	222	222	222	222
(W)

Furthermore, the surface roughness Ra is changed with respect to the heat exchange unit D3 so that the heat exchange unit D31 has the surface roughness of 0.3 μm, the heat exchange unit D32 has the surface roughness of 0.5 μm, the heat exchange unit D33 has the surface roughness of 1.0 μm, the heat exchange unit D34 has the surface roughness of 1.6 μm, the heat exchange unit D35 has the surface roughness of 2.1 μm, the heat exchange unit D36 has the surface roughness of 3.2 μm, the heat exchange unit D37 has the surface roughness of 4.4 μm, the heat exchange unit D38 has the surface roughness of 4.7 μm, and the heat exchange unit D39 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit D3a having the surface roughness of 0.06 μm and a heat exchange unit D3b having the surface roughness of 0.1 μm are produced based on the heat exchange unit D3 and are measured in the withstand voltage WS. The measurement results are shown in Table 4-3, wherein the insulating layer 22 (27) is a 20-μm-thick epoxy varnish plus a 5-μm-thick alumite layer, and fillers are composed of alumina (Al₂O₃).

TABLE 4-3
Type	D3a	D3b	D31	D32	D33	D34	D35	D36	D37	D38	D39
Ra	0.06	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.5	2.0	2.0	1.75	1.75	0.25
(kV)
Qmax	192	220	220	220	220	220	220	220	220	220	220
(W)

The measurement results regarding the heat exchange units D11-D19, D21-D29, and D31-D39 in Tables 4-1, 4-2, and 4-3 are plotted on a graph of FIG. 9 whose horizontal axis represents the surface roughness Ra (μm) and whose vertical axis represents the withstand voltage WS (kV), thus drawing measurement curves (or broken lines) D1, D2, and D3. The above measurement results shown in FIG. 9 and Tables 4-1 through 4-3 clearly show that the withstand voltage WS is good as long as the surface roughness Ra is less than 4.7 μm, but it rapidly decreases when the surface roughness Ra exceeds 4.7 μm. Thus, it is preferable that the surface roughness Ra of the heat exchanger 21 (26) be less than 4.7 μm.

Similarly, the surface roughness Ra is changed with respect to the heat exchange unit E1 so that the heat exchange unit E11 has the surface roughness of 0.3 μm, the heat exchange unit E12 has the surface roughness of 0.5 μm, the heat exchange unit E13 has the surface roughness of 1.0 μm, the heat exchange unit E14 has the surface roughness of 1.6 μm, the heat exchange unit E15 has the surface roughness of 2.1 μm, the heat exchange unit E16 has the surface roughness of 3.2 μm, the heat exchange unit E17 has the surface roughness of 4.4 μm, the heat exchange unit E18 has the surface roughness of 4.7 μm, and the heat exchange unit E19 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit E1a having the surface roughness of 0.07 μm and a heat exchange unit E1b having the surface roughness of 0.1 μm are produced based on the heat exchange unit E1 and are measured in the withstand voltage WS. The measurement results are shown in Table 5-1, wherein the insulating layer 22 (27) is a 20-μm-thick epoxy sheet, and fillers are composed of magnesium oxide (MgO).

TABLE 5-1
Type	E1a	E1b	E11	E12	E13	E14	E15	E16	E17	E18	E19
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	1.75	1.75	1.75	0.25
(kV)
Qmax	192	225	225	225	225	225	225	225	225	225	225
(W)

In addition, the surface roughness Ra is changed with respect to the heat exchange unit E2 so that the heat exchange unit E21 has the surface roughness of 0.3 μm, the heat exchange unit E22 has the surface roughness of 0.5 μm, the heat exchange unit E23 has the surface roughness of 1.0 μm, the heat exchange unit E24 has the surface roughness of 1.6 μm, the heat exchange unit E25 has the surface roughness of 2.1 μm, the heat exchange unit E26 has the surface roughness of 3.2 μm, the heat exchange unit E27 has the surface roughness of 4.4 μm, the heat exchange unit E28 has the surface roughness of 4.7 μm, and the heat exchange unit E29 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit E2a having the surface roughness of 0.07 μm and a heat exchange unit E2b having the surface roughness of 0.1 μm are produced based on the heat exchange unit E2 and are measured in the withstand voltage WS. The measurement results are shown in Table 5-2, wherein the insulating layer 22 (27) is a 20-μm-thick epoxy sheet, and fillers are composed of silicon carbide (SiC).

TABLE 5-2
Type	E2a	E2b	E21	E22	E23	E24	E25	E26	E27	E28	E29
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	2.0	1.75	1.75	1.75	0.25
(kV)
Qmax	193	224	224	224	224	224	224	224	224	224	224
(W)

The measurement results regarding the heat exchange units E11-E19 and E21-E29 in Tables 5-1 and 5-2 are plotted on the graph of FIG. 9, thus drawing measurement curves (or broken lines) E1 and E2. The above measurement results shown in FIG. 9 and Tables 5-1 and 5-2 clearly show that the withstand voltage WS is good as long as the surface roughness Ra is less than 4.7 μm, but it rapidly decreases when the surface roughness Ra exceeds 4.7 μm. Thus, it is preferable that the surface roughness Ra of the heat exchanger 21 (26) be less than 4.7 μm.

3. Third Embodiment

The heat exchange unit 10 of the first embodiment and the heat exchange unit 20 of the second embodiment are designed such that the electrodes 13, 15, 23, and 25 are uniformly formed on the surfaces of the heat exchangers 11, 16, 21, and 26; but when prescribed areas on the surfaces of the heat exchangers do not allow for the uniform alignment of the electrodes thereon, it is possible to align the electrodes so as to be kept out of the prescribed areas on the surfaces of the heat exchangers. A third embodiment of the present invention is designed based on this concept.

A heat exchange unit 30 according to the third embodiment of the present invention will be described with reference to FIGS. 10A to 10C. As shown in FIG. 10C, the heat exchange unit 30 is constituted of a first heat exchanger (serving as a heat-dissipation or heat-absorption water-cooled heatsink) 31, insulating layers 32a and 32b formed on the surface and the backside of the first heat exchanger 31, a first lower electrode (serving as a heat-dissipation or heat-absorption electrode) 33a formed on the insulating layer 32a, a first upper electrode (serving as a heat-dissipation or heat-absorption electrode) 33b formed on the insulating layer 32b, a plurality of first thermoelectric elements 34a adjoined to the first lower electrode 33a, a plurality of second thermoelectric elements 34b adjoined to the first upper electrode 33b, a second upper electrode (serving as a heat-dissipation or heat-absorption electrode) 35a adjoined to the upper ends of the first thermoelectric elements 34a, a second lower electrode (serving as a heat-dissipation or heat-absorption electrode) 35b adjoined to the lower ends of the second thermoelectric elements 34b, a second heat exchanger (serving as a heat-dissipation or heat-absorption water-cooled heatsink) 36, an insulating layer 37 formed on the surface of the second heat exchanger 36 above the second upper electrode 35a, a third heat exchanger (serving as a heat-dissipation or heat-absorption heatsink) 38, and an insulating layer 39 formed on the surface of the third heat exchanger 38 below the second lower electrode 35b. A pair of terminals connected to a pair of leads (both not shown) is formed on one end of the first lower electrode 33a.

As shown in FIG. 12, a first thermoelectric module M1 is constituted of the first thermoelectric elements 34a which are electrically connected in series between the first lower electrode 33a and the second upper electrode 35a via a joining metal such as a solder. In addition, a second thermoelectric module M2 is constituted of the second thermoelectric elements 34b which are electrically connected in series between the first upper electrode 33b and the second lower electrode 35b via a joining metal such as a solder.

The heat exchangers 31, 36, and 38 (serving as water-cooled heatsinks) are each composed of aluminum or an aluminum alloy having high thermal conductivity, wherein the surface and backside of the first heat exchanger 31 (adjoined to the insulating layers 32a and 32b), the surface of the second heat exchanger 36 (adjoined to the insulating layer 37), and the surface of the third heat exchanger 38 (adjoined to the insulating layer 39) are each finished with the surface roughness Ra of 5 μm or less. In addition, a plurality of channels 21a (allowing a cooling medium, i.e. water, to flow therethrough in the prescribed direction, i.e. from the right to the left) is formed in the first heat exchanger 31. Similarly, a plurality of channels 36a is formed in the second heat exchanger 36, and a plurality of channels 38a is formed in the third heat exchanger 38. Herein, cavities or recesses are formed on the surfaces of the heat exchangers 31, 36, and 38 subjected to molding (or casting) using instruments. For this reason, bypass areas 31c, 36c, and 38c are formed to prevent the formation of the electrodes 33a, 33b, 35a, and 35b on the surfaces of the heat exchangers 31, 36, and 38 as shown in FIGS. 11A and 11B. In addition, a plurality of mounting holes 31b, 36b, and 38b is formed on the corners of the heat exchangers 31, 36, and 38.

The insulating layers 32a, 32b, 37, and 39 are each composed of a polyimide resin, an epoxy resin, or an alumite with a thickness of 10 μm through 100 μm. It is preferable to disperse fillers composed of alumina (Al₂O₃), aluminum nitride (AlN), magnesium oxide (MgO), or silicon carbide (SiC) with an average particle diameter of 15 μm or less into the insulating layers 32a, 32b, 37, and 39 composed of a polyimide resin or an epoxy resin, thus improving the thermal conductivity. In addition, it is preferable to laminate a polyimide resin or an epoxy resin dispersed with fillers on the insulating layers 32a, 32b, 37, and 39 composed of alumite.

The electrodes 33a, 33b, 35a, and 35b are each composed of a copper film or a copper alloy film with a thickness of 70 μm through 200 μm. Each of the first lower electrode 33a and the first upper electrode 33b has an alignment pattern shown in FIG. 11A, while each of the second upper electrode 35a and the second lower electrode 35b has an alignment pattern shown in FIG. 11B. Each segment of the electrodes 33a, 33b, 35a, and 35b is formed in a rectangular shape with a long length of 3 mm and a short length of 1.8 mm. In addition, the minimum distance t between adjacent segments is shorter than the short length of each rectangular segment (e.g. 1.8 mm).

The first thermoelectric elements 34a composed of P-type semiconductors and N-type semiconductors are electrically connected in series between the first lower electrode 33a and the second upper electrode 35a in such a way that P-type semiconductors and N-type semiconductors are alternately aligned. Similarly, the second thermoelectric elements 34b composed of P-type semiconductors and N-type semiconductors are electrically connected in series between the first upper electrode 33b and the second lower electrode 35b in such a way that P-type semiconductors and N-type semiconductors are alternately aligned. The thermoelectric elements 34a and 34b are soldered to the electrodes 33a, 33b, 35a, and 35b via a SnSb alloy, an AuSn alloy, or a SnAgCu alloy. Nickel plating is applied to the distal ends of the thermoelectric elements 34a and 34b so that the thermoelectric elements 34a and 34b can be easily soldered to the electrodes 33a, 33b, 35a, and 35b.

It is preferable that the thermoelectric elements 34a and 34b be composed of sintered thermoelectric materials of Bi—Te having high thermoelectric performance at room temperature. Specifically, it is preferable to use P-type semiconductors composed of ternary compounds of Bi—Sb—Te and N-type semiconductors composed of quaternary compounds of Bi—Sb—Te—Se. In the present embodiment, P-type semiconductors are composed of Bi_0.5Sb_1.5Te₃, while N-type semiconductors are composed of Bi_1.9Sb_0.1Te_2.6Se_0.4, wherein these semiconductors are subjected to liquid quenching so as to produce foil powder, which is then subjected to hot pressing so as to form bulks, which are then cut into pieces each having prescribed dimensions of 1.35-mm length, 1.35-mm width, and 1.5-mm height.

(a) Production of Heat Exchange Unit 30

The heat exchange unit 30 is produced by way of the following procedure.

First, the first heat exchanger 31 (serving as a heat-absorption water-cooled heatsink) is prepared such that the insulating layers 32a and 32b having adhesive property is formed on the surface and backside thereof, and a plurality of channels 31a is formed inside thereof to allow a cooling medium (i.e. water) to run therethrough. The second heat exchanger 36 (serving as a heat-dissipation water-cooled heatsink) is prepared such that the insulating layer 37 having an adhesive property is formed on the surface thereof, and a plurality of channels 36a is formed inside thereof to allow a cooling medium (i.e. water) to run therethrough. The third heat exchanger 38 (serving as a heat-dissipation water-cooled heatsink) is prepared such that the insulating layer 39 having an adhesive property is formed on the surface thereof, and a plurality of channels 38a is formed inside thereof to allow a cooling medium (i.e. water) to run therethrough. In addition, the first lower electrode 33a, the first upper electrode 33b, the second upper electrode 35a, and the second lower electrode 35b are prepared in advance. Furthermore, the thermoelectric elements 34a and 34b composed of P-type semiconductors and N-type semiconductors are prepared in advance.

The heat exchangers 31, 36, and 38 are each composed of aluminum or an aluminum alloy having high thermal conductivity. The surface and backside of the first heat exchanger 31 (adjoined to the insulating layers 32a and 32b), the surface of the second heat exchanger 36 (adjoined to the insulating layer 37), and the surface of the third heat exchanger 38 (adjoined to the insulating layer 39) are each finished with the surface roughness Ra of 5 μm or less. The insulating layers 32a, 32b, 37, and 39 are formed by dispersing fillers composed of Al₂O₃, AlN, MgO, or SiC into polyimide resin layers or epoxy resin layers having adhesive properties. Alternatively, they are formed using composite layers in which filler-dispersed polyimide resin layers or epoxy layers are formed on alumite layers. Herein, the insulating layers 32a, 32b, 37, and 39 are formed by crimping sheet-shaped materials. Alternatively, varnish is applied to sheet-shaped materials, which are then solidified so as to form the insulating layers 32a, 32b, 37, and 39. The electrodes 33a, 33b, 35a, and 35b are each composed of a copper film or a copper alloy film and are each shaped in the prescribed electrode pattern with the prescribed thickness of 70 μm through 200 μm. Nickel plating is applied to the distal ends (or opposite ends in the longitudinal direction) of P-type and N-type semiconductors.

As shown in FIG. 10A, the first lower electrode 33a composed of a copper film or a copper alloy film having the prescribed electrode pattern shown in FIG. 11A is bonded onto the insulating layer 32a of the first heat exchanger 31. The first upper electrode 33b composed of a copper film or a copper alloy film having the prescribed electrode pattern shown in FIG. 11A is bonded onto the insulating layer 32b of the first heat exchanger 31. Subsequently, the thermoelectric elements 34a composed of P-type and N-type semiconductors are alternately aligned on the first lower electrode 33a as shown in FIG. 10B, wherein the lower ends of the thermoelectric elements 34a are attached onto the first lower electrode 33a via a solder alloy (e.g. a SnSb alloy, an AuSn alloy, and a SnAgCu alloy). The second thermoelectric elements 34b composed of P-type and N-type semiconductors are alternately aligned below the first upper electrode 33b, wherein the upper ends of the thermoelectric elements 34b are attached to the first upper electrode 33b via a solder alloy (e.g. a SnSb alloy, an AuSn alloy, and a SnAgCu alloy). The second upper electrode 35a composed of a copper film or a copper alloy film having the prescribed electrode pattern (see FIG. 11B) is disposed on the upper ends of the first thermoelectric elements 34a, while the second lower electrode 35b composed of a copper film or a copper alloy film having the prescribed electrode pattern (see FIG. 11B) is disposed below the lower ends of the second thermoelectric elements 34b.

Thereafter, the second upper electrode 35a is attached to the upper ends of the first thermoelectric elements 34a while the second lower electrode 35b is attached to the lower ends of the second thermoelectric elements 34b via a solder alloy (e.g. a SnSb alloy, an AuSn alloy, and a SnAgCu alloy). Thus, the first thermoelectric elements 34a composed of P-type and N-type semiconductors are alternately aligned and electrically connected in series between the first lower electrode 33a and the second upper electrode 35a, while the second thermoelectric elements 34b composed of P-type and N-type semiconductors are alternately aligned and electrically connected in series between the first upper electrode 33b and the second lower electrode 35b.

Lastly, as shown in FIG. 10C, the insulating layer 37 of the second heat exchanger 36 is brought into contact with the second upper electrode 35a, while the insulating layer 39 of the third heat exchanger 38 is brought into contact with the second lower electrode 35b; thereafter, the second upper electrode 35a is bonded to the insulating layer 37, while the second lower electrode 35b is bonded to the insulating layer 39. This completes the production of the heat exchange unit 30 of the third embodiment.

(b) Usage of Heat Exchange Unit 30

The heat exchange unit 30 of the third embodiment can be used to control the temperature of a prescribed object (i.e. a subject that needs to be controlled in temperature, not shown). For example, hot water that is warmed by absorbing heat from the prescribed object is supplied to the inlet of the channel 31a of the “heat-absorbing” first heat exchanger 31, while the outlet of the channel 31a is connected to the prescribed object. In addition, cold water is supplied to the inlet of the channel 36a of the second heat exchanger 36 and the inlet of the channel 38a of the third heat exchanger 38, while the outlets of the channels 36a and 38a are used as drains.

In the above state, electricity is applied to the first thermoelectric module M1 in which the first thermoelectric elements 34a are electrically connected in series between the “heat-dissipating” second upper electrode 35a and the “heat-absorbing” first lower electrode 33a, whereby the first lower electrode 33a is cooled so as to absorb heat from hot water supplied to the prescribed object via the “heat-absorbing” first heat exchanger 31, while the second upper electrode 35a is heated so that the heat thereof is dissipated via cold water flowing through the channel 36a of the second heat exchanger 36.

Electricity is applied to the second thermoelectric module M2 in which the second thermoelectric elements 34b are electrically connected in series between the “heat-dissipating” second lower electrode 35b and the “heat-absorbing” first upper electrode 33b, whereby the first upper electrode 33b is cooled so as to absorb heat from hot water supplied to the prescribed object via the first heat exchanger 31, while the second lower electrode 35b is heated so that the heat thereof is dissipated via cold water flowing through the channel 38a of the third heat exchanger 38.

(c) Measurement of Maximum Heat-Absorption Value Qmax

Using the heat exchange unit 30 of the third embodiment, it is possible to measure the maximum heat-absorption (or endothermic) value Qmax constituting a performance evaluation benchmark by way of the following procedure. Testing examples F1, F2 and G1 through G4 are produced based on the heat exchange unit 30. As shown in FIG. 12, a vacuum chamber Z is used to install the heat exchange unit 30 (i.e. testing examples of heat exchange units F1, F2, and G1-G4) therein.

A pipe of hot water (not shown) is connected to the inlet of the channel 31a of the first heat exchanger 31, while a pipe of a drain (not shown) is connected to the outlet of the channel 31a. A pipe of cold water (not shown) is connected to the inlet of the channel 36a of the second heat exchanger 36, while a pipe of a drain (not shown) is connected to the outlet of the channel 36a. A pipe of cold water is connected to the inlet of the channel 38a of the third heat exchanger 38, and a pipe of a drain is connected to the outlet of the channel 38a.

The heat exchange unit 30 is driven so as to measure the inlet temperature and the outlet temperature of the channel 31a, the inlet temperature and the outlet temperature of the channel 36a, and the inlet temperature and the outlet temperature of the channel 38a for ten minutes, wherein measurement is performed by increasing the inlet temperature so as to measure the average value of the outlet temperature, thus estimating the maximum heat-absorption value Qmax. Measurement results show that the heat exchange unit F1 indicates that Qmax=435 W, and the heat exchange unit F2 indicates that Qmax=440 W. In addition, the heat exchange unit G1 indicates that Qmax=432 W, the heat exchange unit G2 indicates that Qmax=434 W, the heat exchange unit G3 indicates that Qmax=430 W, and the heat exchange unit G4 indicates that Qmax=430 W.

In the above, the heat exchange unit F1 is produced such that fillers composed of alumina (Al₂O₃) powder are dispersed in polyimide resin sheets, thus forming the insulating layers 32a, 32b, 37, and 39 with a 15-μm thickness. The heat exchange unit F2 is produced such that fillers composed of alumina powder are dispersed in varnished polyimide resins, thus forming the insulating layers 32a, 32b, 37, and 39 with a 20-μm thickness.

The heat exchange unit G1 is produced such that fillers composed of alumina (Al₂O₃) powder and aluminum nitride (A1N) powder are dispersed in epoxy resin sheets on 10-μm-thick alumite layers, thus forming the insulating layers 32a, 32b, 37, and 39 with a 20-μm thickness. The heat exchange unit G2 is produced such that fillers composed of alumina (Al₂O₃) powder and aluminum nitride (AlN) powder are dispersed in varnished epoxy resins on 10-μm-thick alumite layers, thus forming the insulating layers 32a, 32b, 37, and 39 with a 20-μm thickness. The heat exchange unit G3 is produced such that fillers composed of alumina (Al₂O₃) powder and magnesium oxide (MgO) powder are dispersed in epoxy resin sheets on 10-μm-thick alumite layers, thus forming the insulating layers 32a, 32b, 37, and 39 with a 20-μm thickness. The heat exchange unit G4 is produced such that fillers composed of alumina (Al₂O₃) powder and silicon carbide (SiC) powder are dispersed in varnished epoxy resins on 10-μm-thick alumite layers, thus forming the insulating layers 32a, 32b, 37, and 39 with a 20-μm thickness.

(d) Measurement of Withstand Voltage WS

Heat exchange units F11 through F19, and F21 through F29 are produced based on the heat exchange units F1 and F2 by varying the surface roughness Ra on the surface and backside of the first heat exchanger 31 adjoined to the insulating layers 32a and 32b, on the surface of the second heat exchanger 36 adjoined to the insulating layer 37, and on the surface of the third heat exchanger 38 adjoined to the insulating layer 39. Withstand voltages WS are measured with respect to the heat exchange units F11-F19, and F21-F29 using different values of the surface roughness Ra.

Specifically, the surface roughness Ra (on the surface and backside of the first heat exchanger 31 adjoined to the insulating layer 32a and 32b, on the surface of the second heat exchanger 36 adjoined to the insulating layer 37, and on the surface of the third heat exchanger 38 adjoined to the insulating layer 39) is changed with respect to the heat exchange unit F1 so that the heat exchange unit F11 has the surface roughness of 0.3 μm, the heat exchange unit F12 has the surface roughness of 0.5 μm, the heat exchange unit F13 has the surface roughness of 1.0 μm, the heat exchange unit F14 has the surface roughness of 1.6 μm, the heat exchange unit F15 has the surface roughness of 2.2 μm, the heat exchange unit F16 has the surface roughness of 3.2 μm, the heat exchange unit F17 has the surface roughness of 4.4 μm, the heat exchange unit F18 has the surface roughness of 4.7 μm, and the heat exchange unit F19 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit F1a having the surface roughness of 0.08 μm and a heat exchange unit F1b having the surface roughness of 0.1 μm are produced based on the heat exchange unit F1 and are measured in the withstand voltage WS. The measurement results are shown in Table 6-1, wherein the insulating layers 32a, 32b, 37, and 39 are each configured of a 15-μm-thick polyimide sheet, and fillers are composed of alumina (Al₂O₃).

TABLE 6-1
Type	F1a	F1b	F11	F12	F13	F14	F15	F16	F17	F18	F19
Ra	0.08	0.1	0.3	0.5	1.0	1.6	2.2	3.2	4.4	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	1.75	1.75	1.75	1.75	1.75	1.75	0.25
(kV)
Qmax	396	435	435	435	435	435	435	435	435	435	435
(W)

In addition, the surface roughness Ra is changed with respect to the heat exchange unit F2 so that the heat exchange unit F21 has the surface roughness of 0.3 μm, the heat exchange unit F22 has the surface roughness of 0.5 μm, the heat exchange unit F23 has the surface roughness of 1.0 μm, the heat exchange unit F24 has the surface roughness of 1.6 μm, the heat exchange unit F25 has the surface roughness of 2.2 μm, the heat exchange unit F26 has the surface roughness of 3.2 μm, the heat exchange unit F27 has the surface roughness of 4.4 μm, the heat exchange unit F28 has the surface roughness of 4.7 μm, and the heat exchange unit F29 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit F2a having the surface roughness of 0.08 μm and a heat exchange unit F2b having the surface roughness of 0.1 μm are produced based on the heat exchange unit F2 and are measured in the withstand voltage WS. The measurement results are shown in Table 6-2, wherein the insulating layers 32a, 32b, 37, and 39 are each configured of a 20-μm-thick polyimide varnish, and fillers are composed of alumina (Al₂O₃).

TABLE 6-2
Type	F2a	F2b	F21	F22	F23	F24	F25	F26	F27	F28	F29
Ra	0.08	0.1	0.3	0.5	1.0	1.6	2.2	3.2	4.4	4.7	5.1
(μm)
WS	2.0	2.0	2.0	2.0	2.0	2.0	1.75	1.75	1.75	1.75	0.25
(kV)
Qmax	399	440	440	440	440	440	440	440	440	440	440
(W)

The measurement results regarding the heat exchange units F1′-F19, and F21-F29 in Tables 6-1 and 6-2 are plotted on a graph of FIG. 13 whose horizontal axis represents the surface roughness Ra (μm) and whose vertical axis represents the withstand voltage WS (kV), thus drawing measurement curves (or broken lines) F1 and F2. The above measurement results shown in FIG. 13 and Tables 6-1 and 6-2 clearly show that the withstand voltage WS is good as long as the surface roughness Ra is less than 4.7 μm, but it rapidly decreases when the surface roughness Ra exceeds 4.7 μm. Thus, it is preferable that the surface roughness Ra of the heat exchangers 31, 36, and 38 be less than 4.7 μm.

Similarly, heat exchange units G11 through G19, G21 through G29, G31 through G39, and G41 through G49 are produced based on the heat exchange units G1, G2, G3, and G4 by varying the surface roughness Ra on the surface and backside of the first heat exchanger 31 adjoined to the insulating layers 32a and 32b, on the surface of the second heat exchanger 36 adjoined to the insulating layer 37, and on the surface of the third heat exchanger 38 adjoined to the insulating layer 39. Withstand voltages WS are measured with respect to the heat exchange units G11-G19, G21-G29, G31-G39, and G41-G49 using different values of the surface roughness Ra.

Specifically, the surface roughness Ra (on the surface and backside of the first heat exchanger 31 adjoined to the insulating layer 32a and 32b, on the surface of the second heat exchanger 36 adjoined to the insulating layer 37, and on the surface of the third heat exchanger 38 adjoined to the insulating layer 39) is changed with respect to the heat exchange unit G1 so that the heat exchange unit G11 has the surface roughness of 0.3 μm, the heat exchange unit G12 has the surface roughness of 0.5 μm, the heat exchange unit G13 has the surface roughness of 1.0 μm, the heat exchange unit G14 has the surface roughness of 1.6 μm, the heat exchange unit G15 has the surface roughness of 2.1 μm, the heat exchange unit G16 has the surface roughness of 3.2 μm, the heat exchange unit G17 has the surface roughness of 4.4 μm, the heat exchange unit G18 has the surface roughness of 4.7 μm, and the heat exchange unit G19 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit G1a having the surface roughness of 0.07 μm and a heat exchange unit G1b having the surface roughness of 0.1 μm are produced based on the heat exchange unit G1 and are measured in the withstand voltage WS. The measurement results are shown in Table 7-1, wherein the insulating layers 32a, 32b, 37, and 39 are each configured of a 20-μm-thick epoxy sheet plus a 10-μm-alumite layer, and fillers are composed of alumina (Al₂O₃) plus aluminum nitride (AlN).

TABLE 7-1
Type	G1a	G1b	G11	G12	G13	G14	G15	G16	G17	G18	G19
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.0	2.0	1.75	1.75	1.75	0.5
(kV)
Qmax	398	432	432	432	432	432	432	432	432	432	432
(W)

The surface roughness Ra is changed with respect to the heat exchange unit G2 so that the heat exchange unit G21 has the surface roughness of 0.3 μm, the heat exchange unit G22 has the surface roughness of 0.5 μm, the heat exchange unit G23 has the surface roughness of 1.0 μm, the heat exchange unit G24 has the surface roughness of 1.6 μm, the heat exchange unit G25 has the surface roughness of 2.1 μm, the heat exchange unit G26 has the surface roughness of 3.2 μm, the heat exchange unit G27 has the surface roughness of 4.4 μm, the heat exchange unit G28 has the surface roughness of 4.7 μm, and the heat exchange unit G29 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit G2a having the surface roughness of 0.07 μm and a heat exchange unit G2b having the surface roughness of 0.1 μm are produced based on the heat exchange unit G2 and are measured in the withstand voltage WS. The measurement results are shown in Table 7-2, wherein the insulating layers 32a, 32b, 37, and 39 are each configured of a 20-μm-thick epoxy varnish plus a 10-μm-alumite layer, and fillers are composed of alumina (Al₂O₃) plus aluminum nitride (AlN).

TABLE 7-2
Type	G2a	G2b	G21	G22	G23	G24	G25	G26	G27	G28	G29
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.0	2.0	1.75	1.75	1.75	0.5
(kV)
Qmax	403	434	434	434	434	434	434	434	434	434	434
(W)

The surface roughness Ra is changed with respect to the heat exchange unit G3 so that the heat exchange unit G31 has the surface roughness of 0.3 μm, the heat exchange unit G32 has the surface roughness of 0.5 μm, the heat exchange unit G33 has the surface roughness of 1.0 μm, the heat exchange unit G34 has the surface roughness of 1.6 μm, the heat exchange unit G35 has the surface roughness of 2.1 μm, the heat exchange unit G36 has the surface roughness of 3.2 μm, the heat exchange unit G37 has the surface roughness of 4.4 μm, the heat exchange unit G38 has the surface roughness of 4.7 μm, and the heat exchange unit G39 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit G3a having the surface roughness of 0.07 μm and a heat exchange unit G3b having the surface roughness of 0.1 μm are produced based on the heat exchange unit G3 and are measured in the withstand voltage WS. The measurement results are shown in Table 7-3, wherein the insulating layers 32a, 32b, 37, and 39 are each configured of a 20-μm-thick epoxy sheet plus a 10-μm-alumite layer, and fillers are composed of alumina (Al₂O₃) plus magnesium oxide (MgO).

TABLE 7-3
Type	G3a	G3b	G31	G32	G33	G34	G35	G36	G37	G38	G39
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.0	2.0	1.75	1.75	1.75	0.25
(kV)
Qmax	409	430	430	430	430	430	430	430	430	430	430
(W)

The surface roughness Ra is changed with respect to the heat exchange unit G4 so that the heat exchange unit G41 has the surface roughness of 0.3 μm, the heat exchange unit G42 has the surface roughness of 0.5 μm, the heat exchange unit G43 has the surface roughness of 1.0 μm, the heat exchange unit G44 has the surface roughness of 1.6 μm, the heat exchange unit G45 has the surface roughness of 2.1 μm, the heat exchange unit G46 has the surface roughness of 3.2 μm, the heat exchange unit G47 has the surface roughness of 4.4 μm, the heat exchange unit G48 has the surface roughness of 4.7 μm, and the heat exchange unit G49 has the surface roughness of 5.1 μm. Additionally, a heat exchange unit G4a having the surface roughness of 0.07 μm and a heat exchange unit G4b having the surface roughness of 0.1 μm are produced based on the heat exchange unit G4 and are measured in the withstand voltage WS. The measurement results are shown in Table 7-4, wherein the insulating layers 32a, 32b, 37, and 39 are each configured of a 20-μm-thick epoxy varnish plus a 10-μm-alumite layer, and fillers are composed of alumina (Al₂O₃) plus silicon carbide (SiC).

TABLE 7-4
Type	G4a	G4b	G41	G42	G43	G44	G45	G46	G47	G48	G49
Ra	0.07	0.1	0.3	0.5	1.0	1.6	2.1	3.2	4.4	4.7	5.1
(μm)
WS	2.5	2.5	2.5	2.5	2.5	2.0	2.0	1.75	1.75	1.75	0.5
(kV)
Qmax	401	430	430	430	430	430	430	430	430	430	430
(W)

The measurement results regarding the heat exchange units G11-G19, G21-G29, G31-G39, and G41-G49 in Tables 7-1 through 7-4 are plotted on the graph of FIG. 13, thus drawing measurement curves (or broken lines) G1, G2, G3, and G4. The above measurement results shown in FIG. 13 and Tables 7-1 through 7-4 clearly show that the withstand voltage WS is good as long as the surface roughness Ra is less than 4.7 μm, but it rapidly decreases when the surface roughness Ra exceeds 4.7 μm. Thus, it is preferable that the surface roughness Ra of the heat exchangers 31, 36, and 38 be less than 4.7 μm.

According to the additional measurement results regarding the heat exchange units A1a-A3a, A1b-A3b, C1a-C3a, C1b-C3b, D1a-D3a, D1b-D3b, E1a-E2a, E1b-E2b, F1a-F2a, F1b-F2b, G1a-G4a, and G1b-G4b, the maximum heat-absorption value Qmax greatly decreases so as to degrade the heat-absorption/dissipation performance when the surface roughness Ra becomes less than 0.1 μm. This is because, when the surface roughness Ra becomes less than 0.1 μm, the surface of the heat exchanger may serve as a mirror surface, which reduces the interface area formed between the insulating layer and the surface of the heat exchanger so as to increase the thermal resistance at the interface area, which in turn decreases the thermal exchange efficiency. Thus, it is preferable that the surface roughness Ra at the interface between the insulating layer and the heat exchanger be greater than 0.1 μm.

4. Industrial Applications

The above embodiments are configured using synthetic resin materials such as polyimide resins and epoxy resins. Of course, it is possible to use other materials such as aramid resins and BT (Bismaleimide-Traiazine) resins, which demonstrate aforementioned effects as well.

The above embodiments are configured using fillers such as alumina powder, aluminum nitride powder, magnesium oxide powder, and silicon carbide; but this is not a restriction; hence, it is possible to use other filler materials having high thermal conductivity such as carbon powder, silicon carbide powder, and silicon nitride. A single filler material may suffice the above embodiments, but it is possible to use a mixture of two or more filler materials. In addition, fillers can be formed in any shapes such as spherical shapes and spicular shapes, and their combinations.

Lastly, the present invention is not necessarily limited to the above embodiments, which can be further modified in various ways within the scope of the invention as defined in the appended claims.

Claims

1. A heat exchange unit comprising: an upper electrode;a lower electrode;a plurality of thermoelectric elements interposed between the upper electrode and the lower electrode; anda heat exchanger that is attached to the upper electrode or the lower electrode via an insulating layer,wherein the heat exchanger is composed of a metal having high thermal conductivity, and the surface roughness of the heat exchanger adjoined to the insulating layer is less than 4.7 μm.

2. The heat exchange unit according to claim 1, wherein the heat exchanger is composed of aluminum or an aluminum alloy.

3. The heat exchange unit according to claim 1, wherein the insulating layer is composed of an insulating resin layer having high thermal conductivity.

4. The heat exchange unit according to claim 1, wherein the insulating layer is a composite layer in which an insulating resin layer having high thermal conductivity is laminated on an alumite layer.

5. The heat exchange unit according to claim 1, wherein the insulating layer is composed of a polyimide resin or an epoxy resin.

6. The heat exchange unit according to claim 1, wherein the insulating layer is composed of a varnished polyimide resin or a varnished epoxy resin.

7. The heat exchange unit according to claim 1, wherein the insulating layer is composed of an insulating resin dispersed with fillers having high thermal conductivity.

8. The heat exchange unit according to claim 1, wherein the insulating layer is composed of a varnished insulating resin dispersed with fillers having high thermal conductivity.

9. The heat exchange unit according to claim 7, wherein the fillers are composed of alumina powder, aluminum nitride powder, magnesium oxide powder, or silicon carbide powder.

10. The heat exchange unit according to claim 8, wherein the fillers are composed of alumina powder, aluminum nitride powder, magnesium oxide powder, or silicon carbide powder.

11. The heat exchange unit according to claim 1, wherein the surface roughness of the heat exchanger adjoined to the insulating layer is greater than 0.1 μm.