Cold and calculated

According to Moore's Law, the performance of electronic chips will double every 18 months. If this prediction holds true, it is feared it will soon be impossible to cool these powerful devices effectively using conventional, passive cooling techniques.

To solve this problem, UK researchers hope to develop a miniature refrigerator to be installed inside personal computers to keep their chips cool.

Excess heat can have a detrimental effect on the performance and reliability of electronic chips, so the cooler they can be kept, the faster they operate. Some specialist computers are even kept at sub-zero temperatures to maximise their power.

Dr Brian Agnew from

school of mechanical and systems engineering is leading a three-year, government-funded project, which involves industrial partners. Working with colleagues from the universities of

and

, Agnew's team hopes to design a low-cost micro-refrigerator that will be small enough to sit on top of an electronic chip.

'We are looking to improve the heat-transfer mechanism. We will have to find a way to get rid of heat on something as small as a chip by an order of magnitude,' said Agnew.

The Oxford team plans to use its aerospace expertise in building cryogenic devices to cool instrumentation on board satellites. In the 1980s the university's cryogenics group pioneered the development of reliable coolers that can work for more than five years without needing to be serviced. It has licensed its technology to defence firm Northrop Grumman, among others.

'We want to take the compressor from them and then re-engineer it for the home computing market,' said Agnew. 'At the moment it costs around £10,000. Hopefully we can get it down so it costs no more than a few pence.'

London South Bank will tackle the problem of entropy within the system. One big challenge in miniaturising a cooling device is in the thermodynamics and the entropy generation within the system itself, as the temperature differences between the components gradually evens itself out.

Agnew had experience of this problem 30 years ago when he was working on an MoD project to develop liquid-cooled fighter pilot suits for the Israeli Air Force.

A shoebox-sized refrigerator was developed that pumped cool liquid around the suit to keep pilots comfortable in the desert. However, entropy quickly made the system unstable. The problem, according to Agnew, has not changed.

While the evaporator for the refrigerator will have to be small enough to fit on a chip, a miniature pump will also have to be installed that is practically silent and which does not cause any vibrations in the PC. 'It will all be extremely small, but we are not going down to nanotechnology as the thermodynamics change when you get down to nano-systems because the molecules behave differently,' said Agnew.

'When it is miniature you can use scaling factors as if you were designing larger units.'

The system's condenser could be larger and may be fitted on the back of the computer. Agnew said it may be necessary to use a 'double-effect' system, meaning that two refrigerators could be stacked on top of each other so the condenser from one system becomes the evaporator for the other. This would allow the refrigeration system to reach even lower temperatures, he said.

Cooling technology specialists Honeywell Hymatic and UK firm Thermacore are both providing technical resources for the project. Thermacore develops passive cooling technologies for engine management systems for BMW and Rolls-Royce and hopes to learn more about miniaturised heat transfer systems during the project. Panasonic is also a partner.

According to Agnew, any system that is developed cannot help but further complicate how personal computers are built and he is aware this is something PC manufacturers would rather not do. However, he believes the increase in performance will be worth it.

'Yes, it will add to the complexity of the computer but if you can get it to run more efficiently and much faster — up to 15-20 per cent improvement in clockspeed — I think it could be very important,' he said.

The first prototype of a miniature cooling system should be ready by the end of the project, he added.