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Minature fridge to cool computers

RESEARCHERS at Purdue University are developing a miniature refrigeration system small enough to fit inside laptops and personal computers.
Minature fridge to cool computers
The cooling research focuses on learning how to design miniature refrigeration components to boost performance and shrink the size of future computers.

'Unlike conventional cooling systems, which use a fan to circulate air through finned devices called heat sinks attached to computer chips, miniature refrigeration would dramatically increase how much heat could be removed', said Suresh Garimella, leading the research with Eckhard Groll, both professors of mechanical engineering.

The researchers have developed an analytical model for designing tiny compressors that pump refrigerants using diaphragms. Elastic membranes, made of ultra-thin sheets of a plastic called polyimide are coated with an electrically conducting metallic layer. The metal layer allows the diaphragm to be moved back and forth to produce a pumping action using electrical charges.

The technology would require many tiny diaphragms (50-100) operating in parallel to pump a large enough volume of refrigerant for the cooling system.

'We feel we have a very good handle on this technology now, but there still are difficulties in implementing it in practical applications,' said Garimella, director of the Cooling Technologies Research Center based at Purdue. 'One challenge is that it's difficult to make a compressor really small that runs efficiently and reliably.'

New types of cooling systems will be needed for future computer chips that will likely generate 10 times more heat than today's microprocessors, especially in small 'hot spots,' Garimella said.

'Miniature refrigeration has a key advantage over other cooling technologies', Groll said.

'The best that all other cooling methods can achieve is to cool the chip down to ambient temperature, whereas refrigeration allows you to cool below surrounding temperatures,' he added.

The technology's ability to cool below ambient temperature could result in smaller, more powerful computers and could improve reliability by reducing damage to chips caused by heating.

The researchers conducted experiments with the diaphragms and developed a analytic model for designing the compressor and validated the model with data from the lab. Findings showed that it is feasible to design a prototype system small enough to fit in a laptop, Garimella said.

The model enables the engineers to optimize the design, determining how many diaphragms to use and how to stack them, either parallel to each other or in series.

Research findings will be detailed in two papers being presented during the 12th International Refrigeration and Air Conditioning Conference and the 19th International Compressor Engineering Conference on July 14-17 at Purdue. The papers were written by doctoral students Stefan S. Bertsch and Abhijit A. Sathe, Groll and Garimella.

Researchers say industry is keen to manufacture the product at a cost of $30 each.

'We can't currently produce them at this price, but maybe in the future,' Groll said.

Another portion of the research focuses on learning how a refrigerant boils and vaporizes as it flows along tiny microchannels (thinner than a human hair) in an evaporator to vary this boiling rate for maximum chip cooling. Such evaporators would be placed on top of computer chips.

Bertsch, the doctoral student who led work to set up experiments at the university observed how refrigerant boils inside the channels and measured how much heat is transferred by this boiling refrigerant. He also created the mathematical equations needed to design the miniature evaporators.

'This overall project represents the first comprehensive research to carefully obtain data showing what happens to heat transfer in arrays of microchannels for miniature refrigeration systems and how to design miniature compressors,' Garimella said. 'Eventually, we will be able to design both the miniature compressors and evaporators.'

The research is funded by the National Science Foundation Cooling Technologies Research Center, a consortium of corporations, university and government laboratories working to overcome heat-transfer obstacles to develop new, compact cooling technologies.

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