GB2360578A

GB2360578A - Cooling electric circuits

Info

Publication number: GB2360578A
Application number: GB0007004A
Authority: GB
Inventors: Nick Walker; James Farrer
Original assignee: Continental Microwave Ltd
Current assignee: Continental Microwave Ltd
Priority date: 2000-03-22
Filing date: 2000-03-22
Publication date: 2001-09-26
Also published as: GB0007004D0

Abstract

A method of transferring heat between an electrical circuit element 4 and a fluid medium comprises constraining a flowing fluid medium in a vessel 1, one wall 1a of which is of an efficient heat transfer material, placing the vessel 1 in juxtaposition to the circuit element 4, enclosing the fluid medium to increase the pressure in the vessel 1 whereby to expand the vessel 1 to bring said one wall 1a of the vessel 1 into intimate, heat transferring abutment with the circuit element 4. The circuit element 4 may be provided with a heat spreading element 6 of larger area than the circuit element 4. There is also disclosed a device for enabling heat transfer between an electric circuit element 4 and a fluid medium which comprises a vessel 1 having a main portion provided with an inlet 2 and an outlet 3 for a heat transfer medium and at least one wall 1a formed from a heat conducting material and connected to the main portion. The vessel 1 is adapted to deform upon increase in static pressure within the vessel 1 whereby, in use, to cause the said one wall 1a to be in heat conductive relationship with the electrical circuit element 4.

Description

2360578 The present invention relates to a method and apparatus for

transferring heat between electrical circuits and a third medium. More particularly the invention relates to the cooling of electrical circuits.

The cooling of electrical circuits is a well-known problem which has been dealt with to a greater or lesser extent in a number of different ways.

Initially, finned heat sinks were attached to heat generating components in order to increase the surface area available for cooling purposes. If this was not sufficient, then it was traditional to blow air over the heat generating elements and/or the finned heat sinks and for most uses such procedures have been satisfactory.

However, there exist a number of circuits which produce more heat than can conveniently be handled by these simple cooling systems and it has previously been proposed to deal with the cooling of these circuits by using a liquid cooling scheme. One such scheme is disclosed in Japanese publication No P-A-57015450 where water is supplied to a finned heat sink attached to a heat generating circuit element. While such an arrangement provides good cooling of the element, if the heat generating circuit element needs to be replaced as would be the case if it were part of a modular circuit, there is a need for disconnection and reconnection of the liquid parts which have traditionally meant that isolating valves and/or self-sealing couplings have been required. The difficulty with this is that there is a high probability of fluid loss due to leaking valves or imperfect sealing at the points of isolation. Additionally, there is concern about corrosion, contamination and hazard caused by the coolant loss.

An alternative approach when using a cooling liquid is to arrange the cooling system such that it is not removed when the heat generating circuit element needs to be replaced. The difficulty with this proposal is that it is difficult to achieve a good thermal junction which must be obtained and maintained on refitting of the assembly since it is difficult to guarantee flatnesses and surface 2 finishes. One approach to overcoming certain of these difficulties would be to use a thermally conductive compound such as silicon grease but in this case contamination from dust and other particles would occur at the boundaries of contact and when the module is removed. Another approach would be to use a dry gap filler instead of the silicon grease to form a thermally conductive pad but in this case high clamping forces are required which can cause difficulties.

The present invention provides an arrangement for heat transfer from/to an electrical circuit element using a flowing fluid cooling medium which is constrained in a vessel that achieves and maintains thermal conduction with the circuit element by self-deformation of the vessel produced by an internal pressure.

In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawing which shows a diagrammatic side view of a heat transfer system according to the present invention.

The present invention relates to a heat transfer system for use with electrical circuit elements where the heat transfer is achieved by means of a fluid in a system which is not removed when there is a need to replace the electrical circuit element. Since the need to replace electrical circuit elements is most common in relation to modular equipment, the present invention will be described in relation to this application but it will be appreciated that the invention is of wider use.

The preferred embodiment uses a vessel for containing a heat transfer fluid in the vicinity of an electrical circuit element. The vessel is shaped such that as fluid flows through it, an internal pressure is created in the vessel which is provided with a surface abutting the circuit element so as to conform to the contours of the surface of the circuit element whereby to ensure efficient heat transfer between the fluid medium and the circuit element.

Turning now to the drawing, there is shown a vessel 1 having an inlet 2 and an outlet 3 for a heat transfer medium. An electrical circuit element 4 3 is shown and in this case it is assumed that it is wished to cool the circuit element.

Consequently, the heat transfer fluid is chosen to be a suitable coolant, eg water and the shape of the vessel and the flow rate of the water are chosen so as to create a positive pressure within the vessel 1. The construction and material of the vessel is such that under a suitable positive pressure, the wall 1 a of the vessel adjacent the circuit element 4 is thin and is arranged to deform and is provided or formed by a suitable heat transfer material so that the heat transfer material can conform to the surface formation or contours of the circuit element 4 to ensure efficient heat transfer.

In the present example shown in the drawing, it is assumed that the circuit element 4 is provided with a heat spreader element 6 of larger area than the circuit element 4. Additionally, it is more convenient to design the heat transfer system for use with two electrical circuit elements, one on either side of the vessel as is shown in the drawings. This is not essential as the additional heat spreader element 6a can be replaced by a simple substrate. It is assumed that the electrical circuit element 4 will be constrained in some fashion eg by being on a circuit board received in a rack, and consequently the force generated by the internal pressure in the vessel 1 and acting between the heat spreader 6 and the additional heat spreader 6a or substrate will be sufficient to retain the vessel in position.

The area of the contact surface between the vessel and the heat spreader, the heat transfer medium and the heat spreader thickness can all be optimised to suit the characteristics of the system.

While the construction of the vessel 1 is also capable of being modified, it is preferred to form the vessel by means of a central core section 10 which is joined to the heat transfer wall l a via a deformable section 12. Currently, the vessel is made of copper with the deformable section 12 being an expandable copper structure. It will be appreciated that any thermally conductive. non corrosive substance may be used or indeed a composite vessel may be formed with different parts of the vessel being constructed from different materials.

4 While the principal use of the apparatus described above will be for cooling heat generating electrical circuit elements, it is equally possible to provide heating to electrical circuit elements utilising the same equipment and simply replacing the coolant with a suitable heating fluid which again may be water but this time at a higher temperature.

Claims

Claims:

1. A method of transferring heat between an electrical circuit element and a fluid medium, comprising constraining a flowing fluid medium in a vessel, one wall of which is of an efficient heat transfer material, placing the vessel in juxtaposition to the circuit element, enclosing the fluid medium to increase the pressure in the vessel whereby to expand the vessel to bring said one wall of the vessel into intimate,, heat transfering abuttment with the circuit element.

2. A method according to claim 1, wherein the circuit element is provided with a heat spreading element of larger area than the circuit element, the said one wall of the vessel being in intimate heat transferring abuttment with the heat spreading element.

3. A method of transfering heat between an electrical circuit element and a fluid medium substantially as hereinbefore described with reference to the accompanying drawing.

4. A device for enabling heat transfer between an electrical circuit element and a fluid medium, comprising a vessel having a main portion provided with an inlet and an outlet and at least one wall formed from a heat conducting material and connected to the main portion, the vessel being adapted to deform upon increase in static pressure within the vessel whereby, in use, to cause the said one wall to be in a heat conductive relationship with the electrical circuit element.

5. A device according to claim 3 wherein a heat spreader member is disposed between the said one wall of the vessel and the electrical circuit element and the said one wall of the vessel is arranged to conform to the surface of the heat spreader member.

6

6. A device for enabling heat transfer between an electrical circuit element and a fluid medium substantially as hereinbefore described with reference to the accompanying drawings.