thermoacoustic

Thermoacoustic refers to the interaction between heat transfer and acoustic waves in gases or fluids that enables conversion between thermal energy and acoustic power. Thermoacoustic devices include engines that convert heat into sound and refrigerators or heat pumps that use sound to move heat.

The underlying principle relies on the Rayleigh criterion: if heat transfer occurs in phase with an acoustic pressure or velocity field in a resonator, energy is added to the wave, potentially creating self-sustained oscillations. A regenerator or stack made of porous material is placed in the acoustic field and maintained with a temperature gradient along its length by hot and cold heat exchangers. During a cycle, portions of the gas alternately absorb and release heat as they are compressed and expanded, amplifying or attenuating the acoustic wave depending on the phase relationship and losses. In standing-wave configurations, the energy transfer and resulting work come from the heat source, whereas traveling-wave configurations often use a driven acoustic source to produce cooling or pumping action.

Devices typically comprise a resonator tube, a regenerator or stack, heat exchangers at the ends, and sometimes an acoustic driver. Thermoacoustic engines generate usable work from a heat source without moving parts in the regenerator, while thermoacoustic refrigerators extract heat from a cold region and move it toward a hot region using acoustic power.

Applications include waste-heat recovery, compact cryogenic cooling, and alternative cooling technologies. The field continues to explore materials, geometries, and operating conditions to improve efficiency and scalability.