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The most efficient thermoacoustic devices have an efficiency approaching 40% of the Carnot limit, or about 20% to 30% overall (depending on the heat engine temperatures). [ 11 ] Higher hot-end temperatures may be possible with thermoacoustic devices because they have no moving parts , thus allowing the Carnot efficiency to be higher.
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.
A very simple mechanism of acoustic amplification was first identified by Lord Rayleigh in 1878. [4] [5] In simple terms, Rayleigh criterion states that amplification results if, on the average, heat addition occurs in phase with the pressure increases during the oscillation. [1].
Thermoacoustic combustion instabilities can be explained by distinguishing the following physical processes: the feedback between heat-release fluctuations (or flame fluctuations) with the combustor or combustion chamber acoustics; the coupling of these two processes in space-time; the strength of this coupling in comparison with acoustic losses
Fig. 4: Generic thermoacoustic imaging instrumentation. Any thermoacoustic imaging device requires a source of electromagnetic radiation, be it a laser or a microwave antenna, to deliver energy to the anatomy being studied, and one or more acoustic detectors coupled acoustically to the outside surface of the anatomy, as is illustrated in Fig. 4.
A thermoacoustic heat pump operates as a thermoacoustic heat engine without refrigerant but instead uses a standing wave in a sealed chamber driven by a loudspeaker to achieve a temperature difference across the chamber. [33] Electrocaloric heat pumps are solid state. [34]
Another group of noncombustive engines includes thermoacoustic heat engines (sometimes called "TA engines") which are thermoacoustic devices that use high-amplitude sound waves to pump heat from one place to another, or conversely use a heat difference to induce high-amplitude sound waves. In general, thermoacoustic engines can be divided into ...
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