Acoustic approach to thermal management

Miniature thermoacoustic engines can be used quite effectively for thermal management of certain systems. Heat applied to a stack of high surface area material inside an acoustic resonator generates sound when the temperature gradient along the stack exceeds a critical value. Here heat is injected to a hot heat exchanger in thermal contact to one end of the stack. A cold heat exchanger in contact with the other end of the stack is anchored to ambient temperature by means of cooling fins. When heat is coupled to a ¼ wave resonator, 4.3 cm long, an intense sound is generated at ~2.0 kHz. An acoustic cavity is attached to the open end of the resonator to provide extra positive feedback for oscillation. This self sustained oscillator starts at a temperature difference along the stack of ΔT ≈ 100°C, about 15 seconds from the time heat is applied to the hot heat exchanger. The generated sound is converted to electricity using a 3 cm diameter piezoelectric material, PZT, in the unimorph configuration. Thus the device provides thermal management for the source of heat by converting heat to sound at an efficiency, which is a substantial fraction of the Carnot efficiency and directly converting the sound to electricity.