# 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.
Bibliographical Information:

Advisor:

School:Ohio University

School Location:USA - Ohio

Source Type:Master's Thesis

Keywords:standing waves sound heat exchangers

ISBN:

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