AU2005228057B2 - A heat exchanger - Google Patents

Description

WO 2005/096377 PCT/AU2005/000475 1 A HEAT EXCHANGER TECHNICAL FIELD This invention relates to heat exchangers and more particularly to a heat exchanger suitable for use with computer central processing units and/or 5 thermo-electric modules. BACKGROUND ART A prior art multi-channelled heat exchanger described in Australian patent specification No. 779,519. For the sake of convenience, the invention will be described in relation to the use of a heat exchanger with a computer 10 central processing unit. The performance of a computer central processing unit can be improved by removing heat and thus there is a need for a heat exchanger adapted for use with a computer central processing unit. SUMMARY OF THE INVENTION 15 According to one aspect of the invention there is provided a heat exchanger comprising: (i) a conductive base, (ii) an array of heat exchanger fins on the base defining a plurality of channels through which coolant liquid may flow, 20 (iii) a sealing sheet or pad overlying the surface of the fins remote from the base, and (iv) a non-conductive cover sealingly engaged with the base and enclosing the heat exchange channels, the cover having an inlet leading to the channels and at least one outlet leading from the 25 heat exchange channels. According to another aspect of the invention there is provided a heat exchanger comprising:- WO 2005/096377 PCT/AU2005/000475 2 (i) a conductive base, (ii) an array of heat exchanger fins on the base defining a plurality of channels through which coolant liquid may flow, and (iii) a conductive cover sealingly engaged with the base and 5 enclosing the heat exchange channels, the cover having an inlet leading to the channels and at least one outlet leading from the heat exchange channels. In one form of the invention, the conductive cover has a central inlet which directs the coldest liquid directly to the metal fins adjacent to the source 10 of heat from a CPU die. A central inlet, will most likely be preferred if only a heat exchanger is applied to the CPU. If a thermoelectric module is used in conjunction with the heat exchanger then the preferred form will be with inlet and outlet at either end of the heat exchanger. BRIEF DESCRIPTION OF THE DRAWINGS 15 Fig. 1 is a partially cut away perspective view of a heat exchanger according to one embodiment of the invention, Fig. 2 is an exploded view of the heat exchanger shown in Fig. 1, Fig. 3 is a plan view of the heat exchanger shown in Fig. 1, Fig. 4 is a cross-sectional view of the heat exchanger taken along lines 20 A-A of Fig. 3, Fig. 5 is an enlarged view of portion C of Fig. 4, Fig. 6 is a cross-sectional view of the heat exchanger taken along lines D-D of Fig. 3, Fig. 7 is an enlarged view of portion F of Fig. 6, 25 Fig. 8 is a perspective view of a heat exchanger according to another embodiment of the invention, Fig. 9 is a plan view of the cover shown in Fig. 8, WO 2005/096377 PCT/AU2005/000475 3 Fig. 10 is a cross-sectional view of the cover shown in Fig. 8 taken along lines A-A of Fig. 9, Fig. 11 is a cross-sectional view of the cover shown in Fig. 8 taken along lines B-B, and 5 Fig. 12 is a graph of thermal resistance (C/W) and pressure drop (kPa) against flow rate (L/min) for a heat exchanger according to one embodiment of the invention. MODES FOR CARRYING OUT THE INVENTION The heat exchanger 10 shown in Figs. 1 to 7 consists of a copper base 10 or tray 11 which seats in a plastic bottom flange 12 and supports an array of copper fins 13 which define heat exchanger channels. A rubber sealing member in the form of a sheet or pad 14 overlies the fins 13 and a plastic cover 15 is sealingly engaged with the base flange 12 with O-ring 16 therebetween. The fins 13 are made from a continuous sheet of copper, folded in a 15 concertina fashion. The top and bottom surfaces of the channels are sealed by virtue of the compression of the fins against each other. The fins 13 are soldered to the copper base and sealed with the rubber pad 14 at the top to prevent liquid bypass between the top of the fins and the plastic cover. The heat exchanger channels defined by the array of fins 13 extend 20 from an inlet side 20 to an outlet side 21 of the heat exchanger 10. The cover 15 has an inlet 22 leading to the inlet side 20 and an outlet 23 leading from the outlet side 21. As can be seen in Figs. 5 and 7, the cover or manifold top 15 has a peripheral flange 24 which terminates in an inwardly directed flange 25 to 25 define therebetween a channel 26 in which the O-ring 16 is seated. The flange 24 has a stepped recess 27 on its inner face 28 which receives a similarly shaped lip 29 of the bottom flange 12. In one embodiment of the invention, the WO 2005/096377 PCT/AU2005/000475 4 heat exchanger 10 is placed directly onto the computer central processing unit and then clamped in place. Water is pumped through the heat exchanger to remove heat from the computer central processing unit and piped to a remote radiator where the heat is dissipated to atmosphere. 5 In another embodiment of the invention, the heat exchanger 10 is mounted onto a thermo electric module 40 which is placed into contact with the computer central processing unit or other heat source or cold sink. The thermo electric module actively removes heat from the computer central processing unit and transfers it to water flowing through the heat exchanger mounted on 10 the hot side of the thermo electric module. As before, water is piped to a remote radiator which dissipates the heat to atmosphere. The heat exchanger of the embodiment shown in Figs. 8 to 11 has a cover or manifold top 30 made of copper and has a central inlet 31 and two outlets 32 and 33 on either side of the inlet 31. The use of the copper cover 30 15 allows a soldered joint to be used in place of the O-ring 16 of the embodiment of Fig. 1. Thus, the base 34 is soldered to the cover 30 and obviates the need for the flange 12 of the Fig. 1 embodiment and rubber pad 14 and o-ring 16. As shown in Fig. 11, the copper fins 13 have a V-shaped cut 35 across them to assist the entry of fluid. This jet impingement feature directs the 20 coldest liquid directly to the metal fins adjacent to the source of heat from the CPU die thereby enhancing cooling performance. The thermo-electric heat exchangers shown in the drawings have a remarkably low thermal resistance at very modest pumping power. A thermal resistance of only 0.01 C/W with a pumping power requirement of 2.2 watts for 25 2 litres per minute flow rate on a 40mm x 40mm face area has been achieved. Optimized microchannels have enabled these low thermal resistances to be achieved and the benefit can be demonstrated by considering the effect on WO 2005/096377 PCT/AU2005/000475 5 a high heat pumping thermo-electric module. If the module is cooling at 100W capacity with a coefficient of performance (COP) of 1.0 then the heat passing through the cold side is 100W and the heat passing through the hot side is 200W. Heat exchangers on the cold side and hot side pose thermal resistance 5 to heat flow, i.e. there is a temperature difference required to force the heat across the interface. Typical forced convection air flow heat exchangers for thermo-electric modules have a thermal resistance of 0.1 C/W compared to 0.01 0 C/W heat exchanger of the invention. The table below shows the effect on the dT a thermo-electric module 10 can achieve with a heat exchanger of the invention compared to typical heat exchangers, assuming a 100W coldside. dT (0C) TR = 0.01*C/W TR = 0.1 0 C/W Coldside 100W 10C 10 C Hotside 200W 20C 200C Parasitic dT (sum of coldside & hotside) 30C 300C The best thermo-electric modules have a maximum dT of 750C so a 15 300C loss across the heat exchanger interfaces leaves only 450C of effective temperature differential. Compare this to the 30C temperature differential with heat exchangers of the invention where the module is left with 720C of effective temperature differential. According to another embodiment of the invention, the base is made 20 from pure silver and the cover is made from polycarbonate. The cooling performance of one specific embodiment of the invention is as follows:- WO 2005/096377 PCT/AU2005/000475 6 CPU Thermal Resistance 0.08 OC/W Total Thermal Resistance 0.01 C/W Heat transfer area 16 cm 2 Fig. 12 is a graph of the thermal resistance (C/W) and pressure drop (kPa) against flow rate (L/min) for a heat exchanger according to the invention. Various modifications may be made in details and design and 5 construction of the heat exchanger without departing from the scope and ambit of the invention.

Claims (19)

1. A heat exchanger comprising: (i) a conductive base, (ii) an array of heat exchanger fins on the base defining a plurality of channels through which coolant liquid may flow, (iii) a sealing sheet or pad overlying the surface of the fins remote from the base, and (iv) a non-conductive cover sealingly engaged with the base and enclosing the heat exchange channels, the cover having an inlet leading to the channels and at least one outlet leading from the heat exchange channels.

2. A heat exchanger according to claim 1 and further including an "0" ring seal between the cover and the base.

3. A heat exchanger according to claim 1 wherein the base is made of copper.

4. A heat exchanger according to claim 1 wherein the cover is made of a plastics material.

5. A heat exchanger according to claim 1 wherein the fins are formed from a continuous sheet of copper folded in a concertina manner.

6. A heat exchanger according to claim 5 wherein the array of fins is compressed so that the top and bottom of adjacent channels formed between the fins are sealed by virtue of the compression of the fins against each other. WO 2005/096377 PCT/AU2005/000475 8

7. A heat exchanger according to claim 5 wherein the bottom face of the array of fins is soldered to the base.

8. A heat exchanger according to claim 2 wherein the cover has a peripheral flange which terminates in an inwardly directed flange with a channel being defined between the flanges, the channel being adapted to receive the "0" ring.

9. A heat exchanger according to claim 8 wherein the base has a peripheral flange having an outwardly directed lip and the inwardly directed flange of the cover has a similarly shaped lip which is adapted to engage with the lip of the base.

10. A heat exchanger according to claim 1 further including a thermo-electric module in heat transfer relationship with the outside of the base.

11. A heat exchanger comprising: (i) a conductive base, (ii) an array of heat exchanger fins on the base defining a plurality of channels through which coolant liquid may flow, and (iii) a conductive cover sealingly engaged with the base and enclosing the heat exchange channels, the cover having an inlet leading to the channels and at least one outlet leading from the heat exchange channels.

12. A heat exchanger according to claim 11 wherein the cover has a centrally located inlet and an outlet on either side of the inlet. WO 2005/096377 PCT/AU2005/000475 9

13. A heat exchanger according to claim 11 wherein the cover is made of copper.

14. A heat exchanger according to claim 13 wherein the cover is soldered to the base.

15. A heat exchanger according to claim 11 wherein the fins are formed from a continuous sheet of copper folded in a concertina manner.

16. A heat exchanger according to claim 15 wherein the array of fins is compressed so that the top and bottom of adjacent channels formed between the fins are sealed by virtue of the compression of the fins against each other.

17. A heat exchanger according to claim 11 further including a thermo electric module in heat transfer relationship with the outside of the conductive base.

18. A heat exchanger according to claim 1 wherein the base is made of silver.

19. A heat exchanger according to claim 11 wherein the base is made of silver.