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Hot concept, cool freezer

For centuries, glassblowers have heard their creations “sing” when heat is discharged as acoustic energy. Thermoacoustic refrigeration (TAR) takes advantage of the opposite phenomenon, using high-decibel sound waves to produce pressure oscillations in a closed chamber full of an inert gas. As the gas molecules are compressed and then allowed to expand, they are forced back and forth through the channels of a metal-mesh stack, releasing heat at one end and absorbing it at the other.

In search of alternatives to the environmental impact of conventional vapor-compression refrigeration, Ben & Jerry’s teamed up with Penn State University researchers Steven Garrett, Matt Poese, and Robert Smith to produce the world’s first thermo-acoustic ice cream chiller. With $600,000 in funding from the ice cream maker, researchers created a working prototype—a standard ice cream display case, hooked up to a knee-high metal cylinder filled with helium. The power comes from a souped-up audio speaker that emits a single note at 190 decibels, 100 times per second, with a “bellows bounce” resonator set to regulate acousto-mechanical frequency.

The public introduction of the thermoacoustic chiller at a Ben & Jerry’s scoop shop in Manhattan on Earth Day 2004 garnered terrific media attention. “We’re going to end the cycle of chemical dependency for the refrigeration industry,” Gosselin told the Wall Street Journal, making the point that TAR relies on environmentally benign noble gases rather than hydrochlorofluorocarbons (HCFCs) and hydrofluoro-carbons (HFCs), which are key contributors to ozone depletion and global warming. The exposure helped the TAR group secure venture capital funding for another three years of research toward commercial applications, which ultimately could include home heating and air-conditioning, as well as power generation. Ben & Jerry’s continues to work with the newly formed Thermoacoustic Corporation to explore the economic feasibility of building more cabinets for beta testing in scoop shops next year. “TAR is clearly ‘out of the lab,’ and we hope to be part of the next wave of commercial development,” says Gosselin.

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Last modified: Aug 25, 2005, 13:41 EDT
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