Sound Waves May
Replace Refrigerants
By Katrina Woznicki
UPI Science News

CANCUN, Mexico (UPI) -- Scientists said Wednesday they have developed technology that converts sound waves into refrigeration, which could lead to more environmentally efficient household and industrial products.
The research team, led by Steven Garrett, professor of acoustics at Pennsylvania State University in College Park, said the thermoacoustics process could be a viable alternative to chemical refrigerants.
Thermoacoustics can work both ways, by removing heat or adding heat. Scientists used tweaked loudspeakers to create high amplitude sound waves in the air.
The amplitude levels were far higher than those at rock concerts, where the decibel level is around 120. At 165 decibels, the sound level is so intense the friction could set fire to hair as gas undergoes such huge acoustic undulations.
In the thermoacoustics chilling system, Garrett's team used 173 decibels but those waves never escaped the system. Researchers said even if their resonator broke down, the sound could not reach human ears because levels that high can only be generated by conditions maintained by pressurized gas.
The loudspeakers did not produce sounds so they did not need to produce frequencies or tones and therefore were more efficient. Garrett and his team made the loudspeakers operate at their natural resonance frequencies then used metal bellows to replace the loudspeaker cones to pump compressed gas.
The thermoacoustic system demonstrated 5 kilowatts of power, the equivalent of nearly 7 horsepower, and managed to bring cooling temperatures down to 8 degrees below zero, well below the freezing point.
"Eventually, we may see thermoacoustic chillers in home refrigerators," Garrett told United Press International. "That day would come sooner if the hydrofluorocarbon refrigeration gases now in use for that application are also banned in the future because the hydrofluorocarbons are powerful global warming gases -- they are 3,000 times more potent than carbon dioxide."
There still are many hurdles to overcome before consumers see thermoacoustics used in household products.
"The thermoacoustic refrigeration machine we are developing for Ben & Jerry's (ice cream) would be just about what you would want for use in a home food refrigerator/freezer," Garrett said. "Some day, it may be used in that application, but the home refrigerator is a very difficult market to penetrate for a new technology."
He added, "That is one of the reasons we are first focusing on ice cream sales cabinets as our first entry into a commercial application. I suspect we might also try direct cooling of electronics and computer chips."
The study was funded by ice cream maker Ben & Jerry's and Unilever, its parent company, and presented Wednesday at the First Pan-American/Iberian Meeting on Acoustics in Cancun.
The U.S. Department of Energy and the Navy have tested the potential of thermoacoustics.
Ganesh Raman, an associate professor in the mechanical, materials and aerospace engineering department at Illinois Institute of Technology in Chicago, and editor of the International Journal of Aeroacoustics, called the research "revolutionary."
"The possibilities, I think, will go well beyond refrigeration," Raman told UPI. "This is an exciting development that only comes once in a while. And unlike other developments, this isn't an incremental step. This is a major leap."
This new step in sound wave technology is equivalent to the strides made in harnessing light waves into laser technology, he explained.
Sound wave refrigeration is more environmentally friendly but it might not be as efficient, which could make such technology more expensive, Raman said, and added it will be many years before sound wave refrigeration could possibly become the norm since all technologies in their infancy tend to be extremely expensive.
"It's going to take time to break into the existing market," Raman said. "(However) there are a host of applications. People are pretty tight-lipped (about those applications) because there are numerous patent possibilities."
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