Thermalacoustics

Thermalacoustics is the study of the interaction between thermal fields (temperature and heat transfer) and acoustic fields (pressure, density, and particle velocity) in gases, liquids, and, in some cases, solids. The field examines how temperature gradients and heat transfer influence sound propagation and, conversely, how acoustic oscillations transport and convert thermal energy.

In fluids, sound waves couple to temperature variations through thermoviscous effects and the energy equation, which includes conduction and viscous dissipation. Under certain conditions, a sustained temperature gradient can amplify or damp acoustic waves, enabling devices that convert heat into sound power or use sound to move heat. The governing relations typically involve the Navier–Stokes equations, the continuity equation, and the energy equation with heat transfer terms.

Applications of thermalacoustics include thermoacoustic engines, which convert heat to acoustic power in resonators and generally employ a regenerator or stack to enhance coupling, and thermoacoustic refrigerators, which use acoustic power to pump heat and achieve cooling without moving mechanical parts. These technologies promise high reliability and the potential to exploit waste heat or solar thermal energy.

Devices are commonly configured as standing-wave or traveling-wave systems, with a regenerating material that mediates thermoacoustic coupling. Research areas cover modeling and optimization of efficiency and power density, material selection for regenerators, and the management of dissipative and nonlinear effects. Experimental work ranges from fundamental demonstrations to scaled prototypes for heat-to-power and cooling applications.

The field began to mature in the mid-20th century and remains active, driven by interests in energy conversion, waste-heat recovery, and silent cooling solutions.