Fundamental measurements in standing-wave and traveling-wave thermoacoustics
Abstract (Summary)PETCULESCU, GABRIELA, Ph.D. June 2002. Physics Fundamental measurements in standing-wave and traveling-wave thermoacoustics (177 pp.) Director of Dissertation: Larry A. Wilen The periodic compressions and expansions of the gas in an acoustic wave, combined with heat exchange with external reservoirs, generate a rich variety of thermoacoustic processes. A new class of heat pumps and prime-movers make use of these e ects. In a traditional standing-wave thermoacoustic device, the energy conversion occurs in the stack, in uencing the device e ciency. A major part of the dissertation focuses on fundamental measurements of stack properties. Di erent geometries and nonlinear e ects are studied with a versatile volume-modulation technique yielding the complex compressibility, C(!) (equivalent to the cycle P-V diagram), for a variety of temperature gradients and frequencies. The thermoacoustic function FT, describing the uid oscillatory temperature eld in the stack, can be calculated from compressibility measurements with azerotemperature gradient. When a gradient is imposed on the stack, thermoacoustic gain can be empirically determined from the compressibility, forany stack geometry. The method was rst tested with a circular geometry for which theoretical calculations were possible. Good agreement was found between theory and experiment. The technique was further adapted to look at the e ect of high displacement amplitudes relative tothestack length, beyond the range of validity ofthelinear theory. The measurements were extended to look at pin-array stacks, which are particularly interesting because of their convex geometry, which enhances the ratio of useful power to viscous dissipation. Pins parallel and perpendicular to the acoustic axis were studied. The results of the zero temperature gradient experiment tested theoretical assumptions regarding thermal and viscous e ects. With a nonzero gradient, thermoacoustic gain was measured and found to be the same for both geometries. Traveling-wave thermoacoustics is discussed in the last chapter. Earlier work showed that ampli cation of pure traveling waves is surmounted by viscous losses, unless the acoustic impedance in the regenerator is increased. Traveling and standing waves were produced in a resonator in a controlled ratio, with the regenerator placed at the velocity node of the standing wave. Traveling-wave ampli cation across the regenerator was signi cantly improved by the addition of the standing wave component. An optimal standing-wave-ratio, speci c to a given regenerator/heat-exchanger geometry was observed.
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:standing waves sound heat exchangers
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