Thermoacoustic - Piezoelectric Systems with Dynamic Magnifiers

Title of Document: THERMOACOUSTIC-PIEZOELECTRIC SYSTEMS WITH DYNAMIC MAGNIFIERS Mostafa Nouh, Doctor of Philosophy, 2013 Directed By: Professor Amr Baz Department of Mechanical Engineering Thermoacoustic energy conversion is an emergent technology with considerable potential for research, development, and innovation. In thermoacoustic resonators, self-excited acoustic oscillations are induced in a working gas by means of a temperature gradient across a porous body and vice versa with no need of moving parts. In the first part of this dissertation, thermoacoustic resonators are integrated with piezoelectric membranes to create a new class of energy harvesters. The incident acoustic waves impinge on a piezo-diaphragm located at one end of the thermoacoustic-piezoelectric (TAP) resonator to generate an electrical power output. The TAP design is enhanced by appending the resonator with an elastic structure aimed at enhancing the strain experienced by the piezo-element to magnify the electric energy produced for the same input acoustic power. An analytical approach to model the thermal, acoustical, mechanical and electrical domains of the developed harvester is introduced and optimized. The performance of the harvesters is compared with experimental data obtained from an in-house built prototype with similar dimensions. In an attempt to further understand the dynamics and transient behavior of the excited waves in the presence of piezoelectric coupling, a novel approach to compute and accurately predict critical temperature gradients that onset the acoustic waves is discussed. The developed model encompasses tools from electric circuit analogy of the lumped acoustical and mechanical components to unify the modeling domain. In the second part of the dissertation, piezo-driven thermoacoustic refrigerators (PDTARs) are presented. The PDTARs rely on the inverse thermoacoustic effect for their operation. A high amplitude pressure wave in a working medium is used to create a temperature gradient across the ends of a porous body located in an acoustic resonator. Finally, PDTARs with dynamic magnifiers are introduced. The developed design is shown, theoretically and experimentally, as capable of potentially enhancing the cooling effect of PDTARs by increasing the temperature gradient created across the porous body. THERMOACOUSTIC-PIEZOELECTRIC SYSTEMS WITH DYNAMIC MAGNIFIERS