Chilling With Sound

Have a hankering to chill your Cherry Garcia™ and to listen to Jerry Garcia using the same system? The concept may not be too far off. The Office of Naval Research has long funded researchers at Penn State who now have proved they can build a compact freezer case substituting sound waves for chemical refrigerants.

"The Navy has been looking for years for alternatives to freon-based cooling systems aboard Navy ships to save energy as well as the environment," says ONR's Steve McElvany, science manager for Navy's TRITON (for 3-ton chillers) program. "The Navy would like to find an ecologically friendly way for distributed cooling aboard our carriers. The early research we funded in this area has led to Garrett's freezer concept."

Although freon-based refrigerants were banned in 1996 over concerns about the hole in the ozone layer, the use of other chemicals still add to greenhouse gasses. The thermo-acoustic freezer case envisioned by Dr. Steven Garrett and Matt Poese at Penn State — partially funded by Ben & Jerry's as well as the Office of Naval Research — would use high amplitude sound energy to cool itself.

In tests, Garrett's team used a "souped-up" loudspeaker to generate high-amplitude sound energy in inert pressurized gasses. While you might not be able to safely listen to Jerry Garcia at decibels higher than 120 (about the loudest racket one could tolerate at a rock concert), Garrett's team reached sound levels hundreds of thousands of times higher (173dB), and reached a temperature differential of -8 degrees below zero — cool enough for that tub of ice cream. And quite enough, too, to take care of distributed cooling systems in the U.S. Navy fleet.

* Ben & Jerry's Homemade, Inc., the Vermont-based manufacturer of ice cream, professes a philosophy that "business can be a powerful, positive force for social change." Over the past two years, Ben & Jerry's—with the financial and scientific support of parent company, Unilever—has been working with Dr. Garrett and Penn State to develop a prototype for a Ben &Jerry's ice cream display cabinet that could prove thermoacoustics as the environmentally-friendly solution to chemical refrigerants.