Although fire-powered organs may not be the next big thing, operating the cycle in reverse has a promising future. Thermoacoustic engineers have been keeping cool by designing TADOPTRs, or thermacoustically-driven orifice pulse tube refrigerators. These devices have many advantages over normal compressor fridges:

• High efficiency. Although TADOPTRs have yet to exceed conventional coolers in this aspect, efficiency is rising with newer models and can in theory more closely approach the ideal Carnot cycle than compressor refrigerators.
• No solid moving parts. A major cost in today's fridges is the compressor, and this is often the part that breaks first. By eliminating this component, thermoacoustic coolers boast exceptionally long life and superb reliability.
• No toxic chemicals. Compressor refrigerators rely on fluids such as CFCs and HFCs to move the heat from the refrigerated space. If leaked, these chemicals destroy the ozone layer and contribute to global warming. The working fluid in thermoacoustic refrigerators is often helium, which is inert.
• Low temperatures. Thermoacoustic coolers can lower temperatures enough to liquefy many gases. Los Alamos National Labs is conducting research in refrigerators for natural gas liquefaction that burn a portion of the gas for energy (right).

Penn State University is also doing research in thermoacoustic refrigeration, but they have something else in the freezer. Ben and Jerry's, concerned about the environmental impact of its ice cream freezers, is sponsoring research at Penn State to develop potentially "greener" coolers for temperatures appropriate for ice cream. Prototypes have already been demonstrated at Ben & Jerry's ice cream stores, although full working units are still something in the future.