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To: maceng2 who wrote (150)	12/4/2002 2:22:42 PM
From: maceng2	of 603

Novel fridge cools with sound news.bbc.co.uk Some of the coolest sounds in the world are coming out of a laboratory in Pennsylvania. At the lab, two US researchers are working on ways to use sound to chill food. They have produced a sonic fridge that converts very loud sounds to directly cool a fridge containing ice cream. The researchers hope that their work will end reliance on gases that can contribute to global warming. Louder than rock The researchers have exploited the fact that sound waves travel by compressing and expanding the gas that they are generated in. In the 1980s, Scott Backhaus and Greg Swift at the Los Alamos National Laboratory realised that this compression/expansion action could be used to cool and heat metal plates placed in the path of the sound wave. A temperature gradient can be generated by putting a stack of plates in the right place in a tube in which the sound wave is bouncing around. Some plates in the stack will get hotter and others colder. The novel fridge will be used to cool ice cream All it takes to make a refrigerator out of this system is to attach heat exchangers to the ends of the stack. Now, Matt Poese and Steve Garratt of the Applied Research Laboratory at Penn State University are doing work on a small chiller cabinet that will be used to keep ice cream cool. The research is being sponsored by ice cream makers Ben & Jerry's and Unilever. The pair are using enormously loud sounds to keep their chiller cabinet cool. Humans feel pain when they hear sounds of 120 decibels, a level typically reached next to the speakers at a rock concert. The sounds pumped through the Penn State fridge reach 173 dB, tens of thousands of times more intense than any rock concert. Sounds of 165 dB would cause a person's hair to catch fire from the frictional heating caused by air undergoing such intense compression and expansion. Thankfully, even if the fridge cracks open the vast sounds generated within will not escape because the intense noise can only be generated in the pressurised gas locked inside the cooling system. Prototypes of fully functioning acoustic fridges have already been built and one has even flown on the space shuttle. The pair are hoping that their work will end reliance on the gases currently used in fridges that can contribute to global warming. The research could also make refrigerators more reliable because a thermoacoustic fridge has fewer moving parts.

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