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Cooling With Sound
| Article
# : |
20712 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
9 / 1992 |
2,757 Words |
| Author
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Mike Holcomb
Mike Holcomb is pursuing a doctorate in physics at the
University of Colorado at Boulder. |
A hundred thousand times louder than a front-row seat at a Rolling Stones concert! That is the deafening volume at which the working element deep inside the refrigerators and air conditioners of the next century will operate. Called thermoacoustic refrigeration, this nascent technology uses high-amplitude sound waves and inert gases in place of the mechanical compressors and chlorofluorocarbons (CFCs) found in today's cooling systems.
Due to increasing global concern over the adverse effects of CFCs on the stratospheric ozone layer, the United States and other industrialized nations have committed to a 50 percent reduction in CFC manufacture by 1995 and complete elimination by the end of the decade. The difficult task of finding a replacement technology belongs to industry. Designers, for the past 50 years, have been consistently improving the efficiencies of compressor refrigerators. Any new products using alternative technologies will have to meet the efficiency standards of existing systems, and do so in a relatively short time. Since cooling systems consume about one-fifth of the electricity produced in the United States, a slight difference in efficiency could mean saving--or squandering--billions of dollars per year. Greater efficiency also means cleaner air, since most of this electricity is produced by burning fossil fuels. The new generation of heat pumps being developed shows promise of being more efficient and will not require CFCs or other environmentally hazardous chemicals.
The Last Icebox
Prior to World War II, most families kept food cold in an icebox--a simple though labor-intensive device. We know that heat flows from a hot to a cold object if the two are in thermal contact. In the icebox, heat flows form the food and air to the block of ice. This heat transfer has two effects: since heat flows from the food, it cools down, and since heat flows to the ice, it melts.
The days of the iceman are long past. By the late 1940s, most households had electric refrigerators and, a little later, air conditioners. These devices use a more complicated process, called the Rankine cycle, to pump heat. The Rankine cycle is best described in terms of how it is applied in a window air conditioner.
An air conditioner cools a room by drawing in the room's warm air, cooling it, and blowing it back into the room; the extracted heat is exhausted to the outside. The Rankine cycle accomplished this in a five-step process
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