Purdue's Miniature Refrigeration System (Credit: Purdue University)

The concept of refrigeration-based cooling systems has been pursued before. The Purdue research team is focusing on the design of miniature components called compressors and evaporators, which are critical for these systems. The researchers developed an analytical model for designing tiny compressors that pump refrigerants using penny-sized diaphragms. This model has been validated with experimental data. The elastic membranes are made of ultra-thin sheets of a plastic called polyimide and 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, or "electrostatic diaphragm compression." 

The lead researcher, Suresh Garimella, Professor of Mechanical Engineering in Purdue University, said: "We feel we have a very good handle on this technology now, but there are still difficulties in the implementation in practical applications; one challenge is that it's difficult to make a compressor really small that runs efficiently and reliably." She elaborated and explained that new types of cooling systems will be needed for future computer chips that are expected to generate 10 times more heat than today's microprocessors, especially in small "hot spots." Eckhard Groll, the research's second lead scientist, described the benefits of the new cooling system: "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." Besides the obvious result of smaller, more powerful computers, this improved cooling ability may improve the computer systems' reliability by reducing heat-induced long-term damage to chips. 

Although the new technology seems promising, there are still several challenges. One complication is that many diaphragms must operate in parallel in order to pump a large enough volume of refrigerant for the cooling system; "So you have an array of 50 or 100 tiny diaphragm compressors, and you can stack them," Professor Groll said. According to Groll, the findings show that by stacking the diaphragms it is possible to design a prototype system small enough to fit inside a laptop. The design is optimized using a model, which enables the computer engineers to determine how many diaphragms to use and how to stack them, either in parallel to each other or in series. According to Groll, stacking in one direction might increase the pressure, while stacking in the other direction allows the necessary volume to be pumped. Another major challenge is learning how to manufacture the devices at a low cost. The industry currently requires a cost of about $30 each, but the researchers say it is not yet possible to meet these demands. 

"This overall project represents the first comprehensive research to carefully obtain data showing what happens to heat transfer in arrays of micro channels 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." 

TFOT has covered Clemson University's recent research of the computer chip’s cooling process. We have also reported on the development of Ionic Wind, a new type of ultra-thin, silent cooling technology for processors, by Kronos Advanced Technologies. 

For more information on the new miniature refrigerating units see Purdue University's website.