Energy conversion using thermoacoustic devices

Thermoacoustic engines offer the possibility for simple and efficient energy conversion devices. They can be prime movers where heat produces sound or heat pumps and refrigerators where sound pumps heat. An important element in such engines is the secondary thermodynamic medium, the stack which provide the phasing between heat transfer and pressure changes at acoustical frequencies. Other elements are a resonator, working fluid (usually a gas), heat exchangers and a driver or source of heat. Similar to thermoelectric devices, the engines require a temperature difference for their operation and when run in a conjugate mode they produce a temperature difference. They are interesting because they are simple and they have essentially no moving parts.