Thermoacoustics studies coupling between thermal processes and acoustic motion. Oscillatory compression changes gas temperature; heat exchange at the right phase can amplify a sound wave or let sound transport heat.
In an engine, a maintained temperature difference can drive acoustic oscillations. In a refrigerator, externally supplied acoustic work can pump heat. The timing and location of heat exchange determine the energy transfer, so a temperature gradient alone does not guarantee self-sustained sound. Viscous and thermal boundary layers are important near the heat-exchanging structures.
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Thermoacoustics is a field of study that explores the interaction between thermal and acoustic (sound) phenomena. It typically involves the generation of sound waves through temperature gradients or thermal processes. The basic principle behind thermoacoustic processes is that when a temperature gradient exists in a medium (like a gas), the variation in thermal energy can lead to changes in pressure and density, which can generate sound waves.