Acoustic approach to thermal management: miniature thermoacoustic engines

An acoustic approach to thermal management in electronics can be efficient and it can be directly interfaced with electronic devices. It is based on two types of thermoacoustic heat engines, which are being developed for microcircuit applications. One type of device, the prime mover, converts heat to sound; energy is radiated away acoustically. This is achieved with essentially no moving parts. The other type of device, a heat pump or refrigerator, moves heat from one reservoir to another reservoir using sound waves. Both devices are resonant and hence their size scales inversely with operating frequencies. Devices presented here operate in the frequency range of 4 kHz to 21 kHz, depending on their size. The components are simple and they can be fabricated using microcircuit techniques. They consist of an acoustic resonator, heat exchangers, a stack of high surface area material for heat storage, and a working gas such as air or helium or gas mixture (He - Ar). The cooler has a loudspeaker to generate the sound for pumping heat, while the prime mover has a coupler to the source of heat. Working devices range in size from 2 cm to a few millimeters. Their efficiency, which depends on geometrical actors, is an appreciable fraction of Carnot. An important feature is a high power density. Working models and modeling show that power densities of several watts per cubic centimeter can be achieved by optimizing the parameters and working conditions. Performance characteristics of miniature prime movers and refrigerators will be presented.