Transient characteristics and stability analysis of standing wave thermoacoustic-piezoelectric harvesters Mostafa Nouh Mechanical Engineering Department, University of Maryland, College Park, Maryland 20742
Osama Aldraihema) Mechanical Engineering Department, King Saud University, Riyadh 11421, Saudi Arabia
Amr Bazb) Mechanical Engineering Department, University of Maryland, College Park, Maryland 20742
(Received 19 July 2013; revised 24 October 2013; accepted 3 December 2013) Standing wave thermoacoustic-piezoelectric (TAP) energy harvesters convert thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The input thermal energy generates a steep temperature gradient along a porous medium called “stack.” At a critical threshold of the temperature gradient, self-sustained acoustic waves are developed inside an acoustic resonator. The associated pressure fluctuations impinge on a piezoelectric diaphragm, placed at the end of the resonator, to generate electricity. The behavior of this multi-field system is modeled using the electrical analogy approach. The developed model combines the descriptions of the acoustic resonator and the stack with the characteristics of the piezoelectric diaphragm. The equivalent electric network is analyzed to determine the system’s stability and predict the temperature gradient necessary to developing self-sustained oscillations inside the harvester. The developed network is utilized also to investigate the transient performance of the harvester by employing the network theory and Simulation Program with Integrated Circuit Emphasis software package. The established stability boundaries are validated against the predictions of the root locus technique. Furthermore, the obtained results are compared with experimental results extracted from testing a prototype of the harvester. The developed approach presents an innovative tool for the design of TAP energy harvesters. C 2014 Acoustical Society of America. [http://dx.doi.org/10.1121/1.4861236] V PACS number(s): 43.38.Fx [MRB]
Pages: 669–678
I. INTRODUCTION
Special emphasis has been placed recently on the development of various configurations of thermoacoustic engines. Distinct among these efforts are the studies of Swift1,2 and Backhaus and Swift.3,4 Such efforts have been motivated by the fact that these engines are compact, environmentally friendly, and low cost devices. The development of the first concepts of such thermoacoustic engines can be credited to the Bell Telephone Laboratories (BTL) whereby heat energy was converted into acoustic pressure waves and then into electricity by using reversed acoustical speakers.5,6 Although the BTL concepts were attractive because of their simplicity and reliability, their conversion efficiency was relatively low (
Osama Aldraihema) Mechanical Engineering Department, King Saud University, Riyadh 11421, Saudi Arabia
Amr Bazb) Mechanical Engineering Department, University of Maryland, College Park, Maryland 20742
(Received 19 July 2013; revised 24 October 2013; accepted 3 December 2013) Standing wave thermoacoustic-piezoelectric (TAP) energy harvesters convert thermal energy, such as solar or waste heat energy, directly into electrical energy without the need for any moving components. The input thermal energy generates a steep temperature gradient along a porous medium called “stack.” At a critical threshold of the temperature gradient, self-sustained acoustic waves are developed inside an acoustic resonator. The associated pressure fluctuations impinge on a piezoelectric diaphragm, placed at the end of the resonator, to generate electricity. The behavior of this multi-field system is modeled using the electrical analogy approach. The developed model combines the descriptions of the acoustic resonator and the stack with the characteristics of the piezoelectric diaphragm. The equivalent electric network is analyzed to determine the system’s stability and predict the temperature gradient necessary to developing self-sustained oscillations inside the harvester. The developed network is utilized also to investigate the transient performance of the harvester by employing the network theory and Simulation Program with Integrated Circuit Emphasis software package. The established stability boundaries are validated against the predictions of the root locus technique. Furthermore, the obtained results are compared with experimental results extracted from testing a prototype of the harvester. The developed approach presents an innovative tool for the design of TAP energy harvesters. C 2014 Acoustical Society of America. [http://dx.doi.org/10.1121/1.4861236] V PACS number(s): 43.38.Fx [MRB]
Pages: 669–678
I. INTRODUCTION
Special emphasis has been placed recently on the development of various configurations of thermoacoustic engines. Distinct among these efforts are the studies of Swift1,2 and Backhaus and Swift.3,4 Such efforts have been motivated by the fact that these engines are compact, environmentally friendly, and low cost devices. The development of the first concepts of such thermoacoustic engines can be credited to the Bell Telephone Laboratories (BTL) whereby heat energy was converted into acoustic pressure waves and then into electricity by using reversed acoustical speakers.5,6 Although the BTL concepts were attractive because of their simplicity and reliability, their conversion efficiency was relatively low (
