In 2002, ice-cream manufacturer Ben & Jerry’s funded research at Penn State University to develop an environmentally friendly in-store ice-cream-storage cabinet using thermoacoustics. Because they used conventional vapor-expansion/compression (RVEC) technology, most existing freezers generally were not energy-efficient and used the same potentially environmentally damaging refrigerants as direct-expansion air conditioning. The Penn State solution, using sound waves to cool, became a working prototype in less than two years. The technology depends on the same gas-law (PV = nRT) relationship as does RVEC equipment, but uses inert gases (e.g., helium) in place of refrigerant as the working fluid and employs sonic energy to do the work of the compressor. In much the same way the speakers in a stereo system convert electric signals to audible sounds by moving air inside a resonator (sound waves merely are oscillations in pressure, temperature, and displacement), the thermoacoustic system compresses gas on one side and expands it on the other, absorbing heat during the compression cycle and releasing heat when the gas expands.
The concept of thermoacoustics is not new. It is believed European glass blowers in the 19th century observed the phenomenon of a cold glass placed in close proximity to a hot stem producing sound. The theory of thermoacoustics refrigeration was formally recognized in 1975, and in 1985, the principle was used to produce a cryocooler. However, it was not until 1992, when the Space Thermoacoustic Refrigerator (STAR) was launched aboard Space Shuttle Discovery, that the practical applications were fully realized.
Although not yet commercially available, thermoacoustic air conditioning offers the promise of several advantages over RVEC processes, including no ozone-depleting potential or greenhouse effects, high energy efficiency with the ability to use solar photovoltaics for all of its energy, relatively low first cost, and a long operating life with little required maintenance.
We need to keep this one on our radar; it could be a game changer!