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Research Papers

Onset of Self-Excited Oscillations of Traveling Wave Thermo-Acoustic-Piezoelectric Energy Harvester Using Root-Locus Analysis

[+] Author and Article Information
O. Aldraihem

 Mechanical Engineering Department, King Saud University, Riyadh, Saudi Arabia, 11421; Full-Time Consultant at National Center for Nano Technology Research, King Abdulaziz City for Science and Technology, Riyadh, Saudi Arabia,

A. Baz

 Mechanical Engineering Department, University of Maryland, College Park, MD 20742; Mechanical Engineering Department, King Saud University, Riyadh, Saudi Arabiabaz@umd.edu

J. Vib. Acoust 134(1), 011003 (Dec 22, 2011) (8 pages) doi:10.1115/1.4004679 History: Received July 08, 2010; Revised February 18, 2011; Published December 22, 2011; Online December 22, 2011

The onset of self-excited oscillations is developed theoretically for a traveling wave thermo-acoustic-piezoelectric (TAP) energy harvester. The harvester is intended for converting thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The thermal energy is utilized to generate a steep temperature gradient along a porous regenerator. At a specific threshold of the temperature gradient, self-sustained acoustic waves are generated inside an acoustic resonator. The resulting pressure fluctuations excite a piezoelectric diaphragm, placed at the end of the resonator, which converts the acoustic energy directly into electrical energy. The pressure pulsations are amplified by using an acoustic feedback loop which introduces appropriate phasing that make the pulsations take the form of traveling waves. Such traveling waves render the engine to be inherently reversible and thus highly efficient. The behavior of this class of harvesters is modeled using the lumped-parameter approach. The developed model is a multifield model which combines the descriptions of the acoustic resonator, feedback loop, and the regenerator with the characteristics of the piezoelectric diaphragm. A new method is proposed here to analyze the onset of self-sustained oscillations of the traveling wave engine using the classical control theory. The predictions of the developed models are validated against published results. Such models present invaluable tools for the design of efficient TAP energy harvesters and engines.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Traveling wave thermo-acoustic piezoelectric energy harvester

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Figure 2

Root locus plot of a conventional open-ended thermo-acoustic engines with resonator length L = 2 m. (a) overall view and (b) close-up view.

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Figure 3

Effect of resonator length on root locus plot and onset parameters (τ and ω) of a conventional open-ended thermo-acoustic engines [(a) –L = 1 m, (b) –L = 2 m, (c) –L = 3 m]

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Figure 4

Effect of resonator length on the temperature ratio τ, frequency ω, and dimensionless frequency on onset oscillations for a conventional open-ended thermo-acoustic engines. [(a) temperature ratio τ, (b) frequency ω , (c) dimensionless frequency].

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Figure 5

Root locus plot of a closed-ended thermo-acoustic-piezoelectric energy harvester with resonator length L = 2m [(a) overall view, (b) close-up view]

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Figure 6

Effect of resonator length on root locus plot and onset parameters (τ and ω) of a closed-ended thermo-acoustic-piezoelectric energy harvester [(a) –L = 1 m, (b) –L = 2 m, (c) –L = 3 m]

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Figure 7

Root locus plot and onset parameters (τ and ω) of a closed-ended thermo-acoustic-piezoelectric energy harvester with resonator length L = 0.5 m

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Figure 8

Effect of resonator length on the temperature ratio τ frequency and dimensionless frequency of onset of oscillations for a closed-ended thermo-acoustic-piezoelectric energy harvester [(a) temperature ratio, (b) frequency, (c) dimensionless frequency]

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Figure 9

Electrical analog of the piezoelectric diaphragm

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Figure 10

Simplified electrical analog of the piezoelectric diaphragm

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