Rijke tube
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The Rijke tube is a cylindrical tube with both ends open, inside of which a heat source is placed that turns heat into sound, by creating a self-amplifying standing wave. It is an entertaining phenomenon in acoustics and is an excellent example of resonance.
Interior of a Rijke tube being heated by a gas torch
Thermoacoustics
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Thermoacoustics is the interaction between temperature, density and pressure variations of acoustic waves. Thermoacoustic heat engines can readily be driven using solar energy or waste heat and they can be controlled using proportional control. They can use heat available at low temperatures which makes it ideal for heat recovery and low power applications. The components included in thermoacoustic engines are usually very simple compared to conventional engines. The device can easily be controlled and maintained.
Fig. 1. a: Plot of the amplitudes of the velocity and displacements, and the pressure and temperature variations in a half-wavelength tube of a pure standing wave. b: corresponding δT – δx plots of a standing wave. c: δT – δx plots of a pure traveling wave.
Fig. 2. a: schematic diagram of a thermoacoustic prime mover; b: schematic diagram of a thermoacoustic refrigerator.
Fig. 3. Schematic drawing of a travelling-wave thermoacoustic engine