In 1987 an international group of scientists and Government Officials established the Montreal protocol, an agreement to control the use and release of CFC and to schedule a time frame for eliminating their production. This agreement is a historic step in the on going process of building consensus regarding environmental impact of CFC. Both the Montreal protocol and provisions for 1990 clean Air Act specify schedules for phasing out CFC production by year 2000.
This forced a new wave of research and development in refrigeration technologies. Existing technologies are being adapted to new chemicals, processes are being refined to become more energy efficient, and innovative approaches to refrigeration are being tested.
A new technology under development is cooling by sound or Thermoacoustic refrigeration. We ordinarily think of a sound wave in a gas as consisting of coupled pressure and displacement oscillations. However temperature oscillations always accompany the pressure changes. The combination of all these oscillations, and their interaction with solid boundaries produces a rich variety of Thermoacoustic effects. Although these effects as they occur in everyday life are too small to be noticed, one can harness extremely loud sound waves in acoustically sealed chambers to produce powerful heat engines, heat pumps and refrigerators. Whereas typical engines and refrigerators have different moving parts Thermoacoustic engines and refrigerators have almost a single flexing moving part (loud speaker) with no sliding seals.
In thermoacoustic primemovers heat flow from a high temperature source to a low temperature sink generates acoustic power (Which may be converted into electric power using a transducer). In thermoacoustic heat pumps and refrigerators acoustic power is used to pump heat from a low temperature source to high temperature sink.
Thermoacoustic devices may be of practical use where simplicity, reliability or low cost is more important than the highest efficiency.