Wouldn't it be cool if the music of the Grateful Dead could keep Cherry Garcia ice cream cold? Ben & Jerry's recently announced the development of a working thermoacoustic refrigeration prototype -- an environmentally friendly, alternative refrigeration technology that chills out to sound waves.
Conventional refrigeration relies on vapor compression technology, a resource-intensive process involving complex mechanical equipment and gases such as hydrochlorofluorocarbons (HCFC's) and hydrofluorocarbons (HFC's), which are key contributors to ozone depletion and global warming. Thermoacoustic refrigeration uses sound waves at 173 decibels -- many times louder than an average rock concert -- instead of chemicals like HCFCs and HFCs to generate cooling.
The prototype, that uses a 'Bellows Bounce' resonator, was developed by acousticians at The Pennsylvania State University, led by former drummer Dr. Steven Garrett, Professor of Acoustics and Senior Scientist. Ben & Jerry's partnered with Penn State, with financial and scientific support from parent company Unilever, to develop a more environmentally friendly, prototype freezer cabinet.
"The thermoacoustic refrigeration process has many benefits," said Dr. Garrett. "We can eliminate a lot of the mechanical equipment in a refrigerator, allowing for less maintenance and better temperature control, as well as a potentially more efficient and compact refrigerator. But the real benefit is the use of naturally occurring inert gases which is the key to long-term positive environmental changes."
Dr. Garrett and his two colleagues Robert Smith and Matt Poese have successfully used the refrigerator to cool to a temperature of twenty-four degrees below zero Celsius (-11° F) -- well below the freezing point of water, and plenty cold enough to store ice cream.
Thermoacoustics? Sounds Cool!
The thermoacoustic chilling unit works much like a traditional refrigerator, except that it uses sound waves instead of a compressor to create cooling. In basic terms, the thermoacoustic chiller is a closed-pressure vessel that contains a stack of fine-mesh window screens called a 'regenerator,' along with two heat exchangers, and a source of acoustic energy. The source, in this case, is a souped-up loudspeaker that generates high-amplitude sound energy in an environmentally safe inert gas (helium), which is converted into cooling power.
By "high amplitude" sound, we mean mega-high -- cranked up way beyond what you'd encounter, say, if you hung out near the loudspeakers at a rock concert, or if you stood a few dozen feet away from a jet's engines. No need for ear plugs, though -- sound levels that high can only be reached in contained, pressurized gas, so there's no need to fear getting an earful. To a nearby observer, the sound is barely audible (<60 dB).
Ben & Jerry's Search for a Better Way to Chill Out
Three years ago, Ben & Jerry's began a company-wide audit of its refrigeration use and the adverse impact on the environment. The conclusion wasn't promising -- from an environmental and safety perspective, today's refrigerants are not the answer for refrigeration systems in the U.S. Additional research led the company to Dr. Steven Garrett, a leader in the field for more than 20 years, and his colleagues Bob Smith and Matt Poese who have been working with him for the past decade.
The Penn State research team first developed a "pre-prototype" thermoacoustic chiller in 2002; further development and testing in 2003 resulted in a final prototype that met targets for cooling power, size, and performance. The finished prototype chilling unit is now ready to be introduced to the public. Its final stop will be Ben & Jerry's Waterbury, Vermont factory where it will be showcased for Factory Tour visitors.
"When Dr. Garrett told us the prototype was finished, it was music to our ears," said Pete Gosselin, Ben & Jerry's Director of Engineering, or as he's known at Ben & Jerry's -- Gearhead. "The research has shown that a strong potential exists to engineer a cooling system that utilizes inert gas and operate it with no performance trade-off against standard vapor-compression technology. We're very excited about the promise of this novel prototype, which could someday lead to a whole new generation of refrigerators and freezers that would be efficient, cost-competitive, and environmentally sustainable."
There are hundreds of millions of commercial and residential cooling appliances in the United States that currently rely on vapor compression technology. With the advent of a working thermoacoustic refrigerator, the possibilities for greener refrigerators, air conditioners and freezers in the future sound better than ever.
For an animated, interactive tutorial on thermoacoustics, visit www.benjerry.com.