Helping Electronics Keep Their Cool

New thermal-management technology doesn't need cooling fans, say Georgia Tech researchers.

Loudspeakers are the inspiration for a new solution to the cooling challenges that are heating up in the electronics industry. The problem: "New processors are consuming more power, circuit densities are getting higher, and there is pressure to reduce the size of devices," notes Raghav Mahalingam, a research engineer at Atlanta's Georgia Institute of Technology. Traditional cooling techniques use metallic heat sinks to conduct thermal energy away from the devices, then transfer it to air being circulated by fans. That approach won't be adequate for future generations of laptops, PDAs, mobile phones, telecom switches and high-powered military equipment, says Mahalingam. His solution of synthetic jet ejector arrays (SynJets), co-developed with professor Ari Glezer, demonstrates benefits in efficiency. He claims two to three times as much cooling with two-thirds less energy input. (To commercialize its potential, Georgia Tech has helped the researchers form Atlanta-based Innovative Fluidics.) Simply designed and with no friction-producing parts to wear out, a synthetic jet module in principle resembles a tiny stereo speaker in which a diaphragm is mounted within a cavity that has one or more orifices. Electromagnetic or piezoelectric drivers cause the diaphragm to vibrate 100 to 200 times per second, sucking surrounding air into the cavity and then expelling it. The rapid cycling of air into and out of the module creates pulsating jets that can be directed to the precise locations where cooling is needed. "You get a much higher heat transfer coefficient with synthetic jets, thus eliminating the major cooling bottleneck seen in conventional systems," Mahalingam adds. He says the jet-cooling module takes up less space in cramped equipment housings, and can be flexibly conformed to components that need cooling -- even mounted directly within the cooling fins of heat sinks. Mahalingam explains that arrays of jets would provide cooling matched to component needs and the devices could even be switched on and off to meet changing thermal demands. Though the jets move 70% less air than fans of comparable size, the air flow they produce contains tiny vortices that make the flow turbulent, encouraging efficient mixing with ambient air and breaking up thermal boundary layers. For higher heat problems, the researchers' start-up also will offer another Georgia Tech developed technology-vibration-induced droplet atomization. It uses piezoelectric induced vibration to create sprays of tiny cooling liquid droplets inside a closed cell attached to the electronic component being cooled. "We have so far been able to cool about 420 watts per square centimeter, and ultimately expect to increase that to 1,000 watts per square centimeter," says researcher Samuel Heffington.

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