Apr. 22, 2004 Penn State acousticians put their new prototype for a compact chiller, based on "green" technology that substitutes sound waves for environment-damaging chemical refrigerants, on first public display in conjunction with Earth Day in New York City.
The roll-out took place at a Ben & Jerry's scoop shop in New York City where the chiller was hooked up to a standard ice cream sales freezer cabinet and successfully kept the creamy merchandise in delicious condition. Ben & Jerry's partnered with Penn State, with financial and scientific support from its parent company, Unilever, to develop a more environmentally friendly prototype freezer cabinet.
Dr. Steven Garrett, the United Technologies Corporation professor of acoustics at Penn State who leads the thermoacoustic chiller research team, says, "We expect this new compact approach to thermoacoustic chillers to be used first in applications that are difficult for chemical refrigeration, such as beverage vending machines, cooling microprocessor chips in computers and, of course, ice cream sales cabinets.
"If chemical refrigerants are banned due to global warming effects, then it will be more likely that thermoacoustic refrigeration will start appearing in kitchens and home air conditioners if cheap manufacturing methods for these products can be developed," he adds. The team that developed the new thermoacoustic chiller at Penn State's Applied Research Laboratory, included Garrett, Dr. Matthew Poese, who in his recent master's and doctoral degree work under Garrett's direction helped lead the way to the new chiller, and Robert W. Smith, ARL research engineer and co-inventor, who has worked with Garrett's group on thermoacoustic projects for the past eight years.
Garrett explains that conventional refrigeration uses chemicals, such as CFCs and HFCs that absorb heat when they turn from liquid to vapor. The chemicals that work best also damage the atmosphere. In 1995, the Montreal Protocols instituted a worldwide ban on CFC production because of damage to the ozone layer that protects Earth from harmful radiation that causes skin cancer and cataracts. HFCs were introduced to replace CFCs but they contribute to global warming.
The Penn State thermoacoustic chiller uses helium gas instead of chemical refrigerants. Helium, which is used to keep birthday party balloons aloft, doesn't burn, explode or combine with other chemicals. If released into the atmosphere, helium drifts harmlessly into outer space.
The Penn State chiller takes advantage of helium's inertness and high thermal conductivity as well as the fact that a sound wave is a rapid succession of compressions and expansions of the gas that carries it.
"When a gas is compressed, its heats up. When it expands, it cools down," Garrett explains. "In thermoacoustics, we arrange the compressions and expansions so that all of the heat of compression is deposited at one end of the system where it can be exhausted into the room. We arrange for all of the expansions to occur at a different location where the cooling due to expansion can be used to refrigerate ice cream, for example. Our compact unit also makes this happen with no mechanical valves or cams or linkages."
The thermoacoustic chiller is patented by Penn State and negotiations for a license are in progress with a start-up company formed to commercialize the technology.
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