Sound waves may offer green alternative to cool buildings

Building mechanical engineers and acoustic engineers may end up having a lot more in common than we think. Researchers at Penn State University’s Applied Science laboratory have achieved proof of concept for a green technology that substitutes sound waves for chemical refrigerants. The traditional coolant in building cooling systems, CFCs, destroy the ozone layer in the atmosphere and are largely phased out. The HCFCs that have replaced CFCs don’t destroy the ozone layer, but they too are seen as environmentally harmful because they are potent greenhouse gases.
Steven Garrett, a professor and Matthew Poese, doctoral candidate in acoustics at Penn State University, developed a possible alternative to HCFCs using thermoacoustic technologies. They presented a paper on the subject on December 4 at the First Pan-American/Iberian Acoustics Meeting in Cancun, Mexico.
The Penn acoustics team have developed a test compact thermoacoustic chiller that achieved eight degrees below zero. The system uses a souped-up loudspeaker to generate high amplitude sound energy in an environmentally safe gascurrently the air we breathethat is converted directly into useful cooling. The high amplitude sound levels are hundreds of thousands of times beyond rock concert levels. However, there is a difference. The loudspeakers used in thermoacoustics do not need to produce a range of tones like in a radio, but rather are operated at resonance, or at the tones they produce by the natural free oscillation of the system. Instead of loudspeaker cones, there are metal bellows to compress the gas.
"We have been operating loudspeakers at resonance and using bellows in thermoacoustic devices for 20 years," Garrett adds. "Now, by putting the entire refrigeration core inside the bellows, we’ve substantially reduced the size."
Garrett notes, "What began as basic research on the fundamental connections between sound waves and heat transport, funded by the Office of Naval Research, is getting closer to providing an environmentally benign substitute for traditional engine and refrigeration technology."
The project was funded by Ben & Jerry’s Ice cream. Robert Smith, the third member of the Penn State Applied Research Laboratory team working on the project, made important contributions in his master’s thesis.
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