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What is Thermoacoustic Refrigeration?

Cassie L. Damewood
Cassie L. Damewood

Thermoacoustic refrigeration, like conventional refrigeration, uses a closed-pressure unit. Beyond that commonality, the two refrigeration methods are vastly different. Instead of chilling through vapor compression involving intricate mechanical components and ozone depleting gases, thermoacoustic refrigeration uses sound waves in place of a compressor to create cooling power.

A thermoacoustic unit is comprised of a regenerator, consisting of a stack of fine-mesh window screening material, much like a sieve; two heat exchangers; and a loudspeaker to supply acoustic energy. The loudspeaker is modified to generate extremely highly amplified sound in a contained environment of helium, an environmentally sound inert gas that is converted into cooling energy. The sound wave levels are so high, around 170 decibels, they can barely be heard by humans; this level is many times louder than an average rock concert. These sound levels can only be attained in an atmosphere of contained, pressurized gas.

Man with a drill
Man with a drill

Thermoacoustic refrigeration was developed at Penn State University by acousticians led by former drummer, Dr. Steven Garrett, Professor of Acoustics and Senior Scientist. US ice cream moguls Ben Cohen and Jerry Greenfield had been researching alternative refrigeration methods that were environmentally friendly. They got financial help from their parent company, Unilever, and joined as partners on the Penn State project.

Thermoacoustic refrigeration is promoted as being better than traditional refrigeration on many levels. It not only eliminates the need for much of the mechanical components of conventional refrigeration units, it also requires less maintenance and is more environmentally friendly since it uses natural inert gases. The temperature is more easily controlled, which boosts the potential for increased efficiency and lower operating costs.

The method was successfully used in the prototype to cool a unit to -11° F (-24° C). This is very much below the freezing point of water, and more than adequate to successfully store ice cream. Since the Penn State research that began in 2002, many thermoacoustic refrigeration units were extensively developed and tested. The final working prototype was unveiled at Ben & Jerry's Waterbury, Vermont, facility on Earth Day in 2004.

Throughout the United States and the world, there are hundreds of millions of residential, industrial, and commercial refrigeration, freezer, and air conditioning units that use traditional cooling mechanisms and chemicals. Many traditional refrigerant gases, such as hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), are believed to have an impact on global warming if disposed of improperly. If the thermoacoustic refrigeration method proves to be a viable and affordable alternative, the negative environmental impact of older refrigeration techniques could be minimized and eventually eliminated.

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