Greener Freezers For Ben & Jerry's

By Roland Piquepaille

In order to boost its environmental image, Ben & Jerry's teamed with Penn State University to build 'green'-technology freezers which will replace existing ones inside its stores. These new greener chillers use sound waves for cooling instead of environment-damaging chemical refrigerants linked to global warming. In this article, the Wall Street Journal (sorry, paid subscribers only) reports that Ben & Jerry's invested $600,000 in the project and that the first acoustic chiller will be installed in New York next week. And these sound waves will really 'scream for ice cream': they will be attached to amplifiers generating 183 decibels, a sound level thousands of times beyond rock concert levels.

Here are some excerpts of the article.

Called a thermo-acoustic chiller, the freezer is set to make its debut in a New York scoop shop next Tuesday, and Ben & Jerry's hopes to have hundreds in place several years from now. "We're going to end the cycle of chemical dependency for the refrigeration industry," says Pete Gosselin, the ice-cream maker's director of engineering.

The freezer, which looks like a regular ice-cream freezer with a big metal cylinder sitting next to it, is the work of Penn State professor Steven Garrett, who holds the nation's only endowed chair in acoustics, and two other researchers, whose idea is to use high-powered sound waves and helium gas to keep the ice cream hard. The same technology could potentially be used to heat and cool homes, though commercial use is still five to 10 years off.

How does this work?

The freezer is based on a scientific concept that goes back 200 years -- that sound waves can change temperature of whatever they travel through. All air conditioners and refrigerators are based on the fact that an increase in pressure raises temperatures, while a decrease in pressure cools things off.

The freezer created by Mr. Garrett, who is 55 years old, working with researchers Matt Poese, 32, and Bob Smith, 38, uses a stack of small metal screens that can absorb and release more heat than air, and about 15 cents of helium. The sound waves compress and expand the gas while pushing it back and forth through the screens 100 times a second. Here, the freezer relies on another bit of physics -- that heat tends to move from a hot region to a cold one.

As its pressure falls, the gas gets colder than the freezer, sucking warmth away from the ice cream. As the gas moves in the other direction, its pressure increases and it gets hotter than the air outside, so the heat becomes the freezer's exhaust and is blown outside.

Will you be able to buy such a freezer? Probably not. Standard freezers are pretty cheap these days. But who knows? Maybe this technology will be licensed to a large appliance maker.

For more information about the technology, you can look at the U.S. Patent No. 5,953,921 filed by Steven Garrett under the name "Torsionally resonant toroidal thermoacoustic refrigerator". Just enter the patent number on this page.

Sources: Ken Brown, The Wall Street Journal, April 15, 2004; and various websites