WO2001063666A1

WO2001063666A1 - Apparatus for heat transport away from heated elements and a method for manufacturing the apparatus

Info

Publication number: WO2001063666A1
Application number: PCT/SE2001/000387
Authority: WO
Inventors: Göran LINDER; Jari Tuomela
Original assignee: Teracom Ab
Priority date: 2000-02-23
Filing date: 2001-02-22
Publication date: 2001-08-30
Also published as: SE0000587D0; AU2001236288A1; SE0000587L

Abstract

An apparatus is provided for transporting away heat from heated elements. The ap-paratus comprises a block (9; 18; 27) of a material having good thermal conductivity on to which the elements are provided in thermal contact. Channels (7,8; 17; 25) are provided in the block. A liquid, for example water, is forced to flow through the channels. Path means (10, 11; 15, 16; 28, 29) in the channels provide a spiral path for the liquid. Whirl means (7,8; 17; 25) in the liquid path provide turbulence to the streaming water. The channels could be made by tubes having corrugated thin walls and made by a non-corrosive material against the streaming liquid, such as steel, preferably acid proof stainless steel. The tubes could be cast, or fastened in some other way, in a material having good thermal conductivity, for example aluminium. A method for producing the apparatus is also disclosed.

Description

Apparatus for heat transport away from heated elements and a method for manufacturing the apparatus

This invention relates essentially to an apparatus for transporting away heat from heated elements as stated in the preamble in Claim 1 , and a method for manufacturing the apparatus.

BACKGROUND

Electrical components most often generate heat when in operation. When the electrical components are power components, or there are many components within a small space, this heat is frequently transported away by so called cold plates, which are cooled with streaming water streaming in channels through them. Cooling with water is thus very often used at power amplifiers provided with semiconductor ele- ments, HF-combiners, semiconductor diodes, and dummy loads for digital transmitters for DTTV (DTTV = Digital Terrestrial Television), for example. However, the usefulness of the invention is not limited to such an application. Some other possible applications for it could be to cool heat-producing components enclosed in a housing and also other kinds of technical regions where a high cooling effect has to be combined with a good corrosion resistance.

RELATED ART

Modern DTTV transmitters have power amplifiers comprising semiconductor ele- ments only. They should be cooled to a temperature as low as possible in order to obtain a long working life. The delivered power dissipation from each transmitter is in the order of 15 kW. It is appropriate to use cooling with water in stead of air, because cooling with water demands less space and operates more silently than cooling with air. Most frequently, up to now, the components to be cooled have been mounted in mechanical thermal contact with a metal plate having internal water channels. Water in a continuous flow has been pumped through the cold plates. It absorbs heat from the components. The water is then led to a cooling structure, most often placed out- doors. This cooling construction could be a conventional fan cooler. It is also possible to have collector tubes mounted down into and up through bore holes in the bedrock, through which the water is pumped.

A common type of prior art cold plate on the market is made by aluminium. In order to create a high capacity of the cooling of semiconductor elements screwed on the cold plates the water channels are provided with milled pins, which provide an extended surface towards the streaming water. The space between the pins is small, ca. 1 mm.

From the thermal point of view, aluminium is an appropriate material with a good thermal conductivity and thermal diffusivity. Aluminium has also a low density, which is advantageous since the cold plates often are mounted on extensible units, which ought to be disconnected from the transmitter to be carried away to a workbench by a single person.

In EP 0 903 971 Al a cold plate of metal is provided on its internal surface with a series of selectively arranged dissipation fins. The plate is sealed by a lid, which by means of several longitudinal baffles create a number of internal ducts, in which a cooling liquid circulates. The fins are provided in "bunches" on the internal surface of the plate only at the points where the electronic components to cool are mounted on the external surface. Nothing is mentioned about what kind of metal the cold plate is made of.

In EP 0715352 Al a substrate having a high cooling efficiency is disclosed. The substrate, which has a high heat-dissipating property, has a high thermal conductivity layer in which a cooling medium flow path is arranged. The material in the sub- strate is for example poly-crystal Si. The high thermal conductivity layer is for example diamond.

In DE 43 01 866 Al describes a cold plate, which comprises channels having a whirl stream body having a screw cylinder and a screw thread with squared section wound around the screw cylinder. Thereby, turbulence is created inside the path means. However, the path means has a smooth and narrow external surface turned towards the cold body of the cold plate. This means that there is an interface between the cooling channels and the cold body providing a rather small surface be- tween the cooling liquid and the cooling body, giving a rather inconsiderable cooling effect from the cooling channels.

PROBLEMS WITH THE PRIOR ART

The cooling properties of the prior art cold plates are not good enough and need be improved.

A passive oxide layer is normally formed on aluminium surfaces. This layer protects the surface against corrosion but this has not been functioning for channels in cold plates of aluminium when in operation. After a few months operation corrosion has been obtained which obstructs the channels, and the components have therefore not been adequately cooled and have therefore been too hot. Use of de-ionizated water having an additive of corrosion protecting substance has not been enough to avoid this problem. It is to be noted that there is a demand for a long lifetime without in- terruption for the cold plate. Also, whirling of the conducted liquid in the channels could cause a still lesser lifetime of this kind of coldplate.

OBJECTS OF THE INVENTION

An object of the invention is to provide an apparatus for achieving an effective cooling of heated components by means of liquid. Another object of the invention is to provide an apparatus for providing different cooling for different components.

Still another object of the invention is to provide an apparatus for cooling heated components by means of liquid, preferably water, flowing in channels without any noticeable corrosion of the inside of the channels, i.e. to provide a cold plate with a long lifetime.

Yet another object of the invention is to provide an apparatus for cooling heated components, in which the excellent thermal conductivity and low density properties of aluminium can be used without having the in-advantageous feature of corrosion of the water channels.

An object of the invention is also to provide a method for manufacture an effective apparatus for cooling heated components by means of a liquid.

INVENTION

The invention relates to an apparatus for transporting away heat from heated elements, comprising a block of a material having good thermal conductivity on to which the elements are provided in thermal contact, and channels in the block, through which a liquid flows. The invention is characterized by the following combination: path means in the channels providing a spiral path for the liquid; and whirl means in the liquid path providing both an extended outer surface of the channel and turbulence to the streaming water.

The path means comprises preferably core bar means in the centre of the channels and means for conveying the liquid in spiral around the core bar means. The means for conveying the liquid could be cord means wound in spiral around the core bar means, or threads on the core bar means, or be provided by providing the core bar with a polygonal section and turned in spiral around its axis. Preferably, the extended surface of the channels could be corrugated to provide the whirl means for the liquid flowing along the channel. The rising gradient of the cord means and/or the rising gradient of the channel walls could be varying in relation to the heat to be transported from components to be cooled.

Each channel could be a tube having thin walls, which is fastened in the block. The channel or channels are cast or sintered or compacted by powder in the block. The tube is made by a material non-corrosive against the liquid. For example, the material is steel, preferably acid proof stainless steel. The material of the block should be a good thermally conducting material, such as aluminium. The path means in the channels could be made by a material non-corrosive against the liquid, and the material is preferably steel, preferably acid proof stainless steel. The channels could be provided by forming a half channel in each of two aluminium blocks, providing an overlay in each half channel, and then firmly join the blocks having the half channels turned towards each other. The overlay could be made by an inert material, such as gold or silver.

The invention relates also to a method of manufacturing an apparatus for transporting away heat from heated elements, comprising a block of a material having good thermal conductivity on to which the elements are provided in thermal contact, and channels in the block through which a liquid flows. The method is characterized by a) providing a corrugated tube of a non-corrosive material against the liquid and having thin walls; b) placing a core bar means having means for conveying the liquid in spiral around the core bar means in the centre of the tube; c) providing the tubes in the block in close contact with the material having good thermal conductivity. Casting or sintering or compacting by powder the tubes of non-corrosive material in the material having good thermal conductivity could be done to bring them in close contact with it. The steps a) and c) above could be provided by forming a half channel in a surface of each of two aluminium blocks and providing an overlay in each half channel, thereafter placing the core bar means in one of the half channels; and then firmly joining the blocks having the half channels turned towards each other. The overlay could be electrochemically provided by an inert material, such as gold or silver.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention and for further objects and advantages thereof, reference is now made to the following description of examples of embodiments thereof - as shown in the accompanying drawings, in which:

FIG 1 shows a first embodiment a liquid channel, in duplicate, in an apparatus according to the invention, i.e. in a side view and a partly sectional view at the inlet or outlet of the channel;

FIG 2 shows a second embodiment of a channel for liquid in a block; FIG 3 shows a third embodiment of a channel for liquid in a block; FIG 4 illustrates a method to provide the channels in a block; and FIG 5 illustrates a fourth embodiment of a channel for liquid in a block; FIG 6 illustrates a fifth embodiment of a channel for liquid in a block.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to FIG 1 , a water supply tube 1 supplies a liquid, for example water, to several parallel inlet channels, of which only two, 3 and 4, are illustrated. The upper one 3 in FIG 1 is a side view and the lower one 4 is shown having its outer wall in section and its connection to the tube 1 also shown in section.

Each outer tube part 5 and 6 for the inlets 3 and 4, respectively, for connection to the supply tube 1 has a smooth configuration and is inserted in an opening in and sealed tightened to it. A corrugated channel 7 and 8 is connected to the tube parts 5 and 6, respectively. A corrugation provides an extended surface of the channel walls towards the liquid.

The channels 7 and 8 could be provided in a material 9 having very good thermal conducting properties. This material could be a heat dissipating substrate, and then the channels 7 and 8 could be cast, or fastened in some other way, such as sintering or compacting of powder, directly in such a material. However, in order to get the corrugated surface of the channel, the channel could preferably first be provided as a tube having a thin corrugated wall, which then is cast in the substrate or fastened in some other way.

An essential feature is that the liquid molecules are whirling in a corrugated channel inside the cold plate. The material of the tube should be non-corrosive to the streaming water forced through it. Thus other ways to provide whirling than a corrugated channel could be provided, such as lugs on the channel walls and/or the core bar and/or the cord.

However, if aluminium is chosen as the material 9, then, in accordance with an aspect of the invention, the corrugated channels could be tubes of a non-coπosive material, such as steel, preferably acid proof stainless steel, for example the stainless alloy 316L. The steel tubes 7, 8 do then have to have very thin walls, since this material is a bad thermal conductor in relation to aluminium. The steel tubes are provided in a firm thermal contact with the aluminium, preferably cast, but also sintered or compacted by powder or fastened in some other way, in an aluminium block 9, since aluminium is a very good thermal conductor. Another way, shown in FIG 4, to create a firm thermal contact with a corrugated channel of non-corrosive material could be to form press, or cut or mill, a half channel 32, 33 in two aluminium blocks 30, 31, respectively, and create an overlay 34, 35, respectively, with the non-corrosive material in each half channel. The surface of the half channels could for example then be lined electrochemically with for example gold, silver or some other inert material. The two aluminium blocks with the half-channels are then firmly joined turned towards each other, after that the core bar with its winded cord has been placed in one of the half channels.

A core bar 10 having a smaller diameter than the channel 7, 8 is inserted in the centre of each channel 7, 8. A cord 11 of stainless steel, for example of the same alloy as the bar 10, is wired around the bar 10 as a means for conveying the liquid in spiral around the core bar. At the inlet the bar 10 is provided through the tube 1 and tightened held by the tube wall. Instead, its end could be held by a screw joint or the like provided through the tube 1 wall.

The wired cord 11 fills the space between the core bar 10 and the corrugated wall of the channels 7, 8. When the channel is made of a stainless tube to be cast in the material 9, the tube is form stable in all directions as soon as it has been provided with the core bar 10 and the cord 11 as a means for conveying the liquid in spiral around the core bar. This form stable tube is then cast in aluminium to form the cold plate. The core bar and the cord could be made by any material being form stable and non-corrosive to the streaming liquid. However, it is best to have the tube and the elements in it in the same material. Therefore, the best choice of material for the core bar and the cord is acid proof stainless steel.

The water pumped through each of the channels will flow in the space between the channel wall and the core in a rotating movement creating a turbulent, whirling flow across the corrugations of the channel walls. A great share of the water molecules in the water will repeatedly come into contact with the inside of the channel wall to absorb heat therefrom.

The embodiment in FIG 2 illustrates, that the cord 15 wired around the core bar 16 could have a varying rising gradient. This embodiment represents the best mode of the invention.

The section in FIG 2 is turned 90° in relation to the section in FIG 1. The tube 17 is made of very thin stainless steel and cast in a block 18 of aluminium. A component 19 to be cooled is provided in good thermal contact with the block 18. Inside the block, at the vicinity of the component 19, the rising gradient of the cord 15 is lower than the rising gradient of the cord where there is no heat-generating component in the vicinity.

The effect of lowering the rising gradient of the wired cord 15 in those sections of the cold plate, which have an extensive heat delivery from components, is that the rotating water could be forced to absorb heat more efficiently from the whole surface of the corrugated tube, due to an increasing centrifugal power forcing the water in the corrugations of the tube to move forwards in the stream direction in the tube.

In sections having a lower heat supply the rising gradient of the cord could have such a rising gradient that the cord only functions as a fixation means for the core bar within the tube 17. This feature provides the lowest possible fall of pressure per unit of length of the tube, and thus an optimal function could be obtained of the entire cold plate.

The meaning of having a core bar 10 or 16, together with means for conveying the liquid in spiral around it, such as the cord, has two purposes. One purpose is thus to hold the corrugated tube 17 or 7 in a form stable position during the time, it is cast, or fastened in some other way, in the aluminium. Casting is to be prefeπed in order to ensures a good thermal contact between the thin steel tube and the surrounding aluminium block, since a very good thermal contact is provided by the fact that aluminium has a higher thermal expansivity than acid proof steel. When the aluminium charge is cooling down a strong pressure is created towards the surface of the tube.

Another purpose is to provide a turbulent, whirling flow of the water pumped through it. The turbulence causes the water molecules to come into contact with the tube wall. Since the tube wall is very thin the heat transmitted from a heat producing component 19 (in FIG 2) through the aluminium block is easily transmitted across the thin steel wall and absorbed instantly by the molecules in the turbulently moving water. If the tube only should be corrugated and have the core bar without any means to convey the liquid in spiral around the core bar, then some part of the water should be streaming in the centre space between the tube and the core bar. Some part of the water could then be standing in the corrugations of the tube. This gives a worse efficiency than to have a cord wired around the core bar or the like giving a spiral formed path for the water. The corrugations then provide the turbulence of the streaming water, which makes this cold plate so utterly efficient.

FIG 3 shows an embodiment in which the tube has different corrugations along its length. Thus instead of, or as a complement, having a varying rising gradient the corrugation of the tube 25 could be varied. The corrugation could be closer at posi- tions near to a heat producing component 26 placed on the surface of the cold plate 27 and smoother at positions where there is little or no need for heat transport from a printed circuit, for example. If the material of the tube is extendable, the tubes could be provided in the adapted loops before cast. The tubes could then be adequately stretched and compressed. Thereafter, they are cast in the material having good heat transportation features, such as aluminium. It is to be noted that varying rising gradients or varying corrugation along the water paths in a cold plate are preferably used in cases where the cold plate and the printed circuit or the like are to be made together in numerous series. Then it is economical to make the effort to adapt the heat transport to the circuits to be cooled.

FIG 5 illustrates that the core bar 41 itself provided in the block 42 could provide the rotation of the liquid by being provided with spiral threads 43 or the like along its length. The threads have a rising gradient adapted to the corrugation 44 of the channel.

It is also possible, as illustrated in FIG 6, to have a core bar 45 having a polygonal section and being screwed along its length. This will provide several, parallel channels inside the corrugated channel with whirling liquid.

Although the invention is described with respect to exemplary embodiments it should be understood that modifications can be made without departing from the scope thereof. Accordingly, the invention should not be considered to be limited to the described embodiments, but defined only by the following claims, which are intended to embrace all equivalents thereof.

Claims

WE CLAIM:

1. An apparatus for transporting away heat from heated elements, comprising a block (9; 18; 27) of a material having good thermal conductivity on to which the elements are provided in thermal contact, and channels (7, 8; 17; 5) in the block, through each of which a liquid flows, characterized by the following combination: path means (10, 11; 15, 16; 28, 29; 43) in the channels providing a spiral path for the liquid; and whirl means (7, 8; 17; 25; 44) in the liquid path providing both an extended outer surface of the channel and turbulence to the streaming water.

2. An apparatus according to claim 1, characterized in that the path means comprise core bar means (10; 16; 28; 41) in the centre of the chan- nels and means (11; 15; 29; 43) for conveying the liquid in spiral around the core bar means.

3 An apparatus according to claim 2, characterized in that the means (11; 15) for conveying the liquid is cord means (11; 15) wound in spiral around the core bar means.

4. An apparatus according to claim 2, characterized in that the means (11; 15) for conveying the liquid is threads on the core bar means.

5. An apparatus according to claim 2, characterized in that the means (11; 15) for conveying the liquid is provided by providing the core bar with a polygonal section an turned in spiral around its axis.

6. An apparatus according to anyone of the preceding claims, characterized in that the extended surface of the channels are corrugated to provide the whirl means (7, 8; 17; 25; 44) for the liquid flowing along the channel.

7. An apparatus according to any of the preceding claims, characterized in that the rising gradient of the means (15) for conveying the liquid in spiral around the core bar means is varying in relation to the heat to be transported from components to be cooled.

8. An apparatus according to any of the preceding claims, characterized in that the rising gradient of the channel walls (25) is varying in relation to the heat to be transported from components to be cooled.

9. An apparatus according to anyone of the preceding claims, characterized in that each channel is a tube having thin walls, which is fastened in the block.

10. An apparatus according to claim 9, characterized in that the channel or chan- nels are cast or sintered or compacted by powder in the block.

11. An apparatus according to claim 9 or 10, characterized in that the tube is made by a non-corrosive material against the liquid.

12. An apparatus according to claim 11, characterized in that the material is steel, preferably acid proof stainless steel.

13. An apparatus according to anyone of the preceding claims, characterized in that the material of the block is a good thermally conducting material

14. An apparatus according to anyone of the preceding claims, characterized in that the thermally conducting material is aluminium.

15. An apparatus according to anyone of the preceding claims, characterized in that the path means (10, 11; 15, 16; 28, 29) in the channels is made by a non-corrosive material against the liquid, and the material is preferably steel, preferably acid proof stainless steel.

16. An apparatus according to any of the preceding claims, characterized in that the channels are provided by forming a half channel (32, 33) in each of two aluminium blocks (30, 31), providing an overlay (34, 35) in each half channel, and then firmly join the blocks having the half channels turned towards each other.

17. An apparatus according to claim 16, characterized in that the overlay is made by an inert material, such as gold or silver.

18. Method of manufacturing an apparatus for transporting away heat from heated elements, comprising a block (9; 18; 27) of a material having good thermal conductivity on to which the elements are provided in thermal contact, and channels (7, 8; 17; 5) in the block through which a liquid flows, characterized by a) providing a corrugated tube of a non-corrosive material against the liquid and having thin walls; b) placing a core bar means (10; 16; 28) having means (11; 15; 29) for conveying the liquid in spiral around the core bar means in the centre of the tube; c) providing the tubes in the block in close contact with the material having good thermal conductivity.

19. Method according to claim 18, characterized by casting or sintering or compacting by powder the tubes (8; 17; 25) of non-corrosive material in the material having good thermal conductivity to bring them in close contact with it.

20. Method according to claim 18, characterized in that the steps a) and c) are provided by forming a half channel (32, 33) in a surface of each of two aluminium blocks (30, 31) and providing an overlay (34, 35) in each half channel, thereafter placing the core bar means in one of the half channels; and then firmly joining the blocks having the half channels turned towards each other.

21. An apparatus according to claim 20, characterized by electrochemically providing the overlay by an inert material, such as gold or silver.