Exploring electroacoustic conversion in a standing-wave thermo-acoustic generator: An experimental study

Abstract

Thermoacoustic generators (TAGs) present an attractive solution for converting low-grade thermal energy into useable electrical power. Despite their relatively modest fabrication, TAGs face significant efficiency challenges that impede their broader adoption. Current research efforts in thermoacoustics are primarily focused on overcoming these limitations. A critical factor influencing TAG efficiency is the design of the acoustic-to-electric (ATE) device. This component plays a vital role in converting the acoustic energy generated within the thermoacoustic engine (TAE) into electricity. Despite its importance, the impact of ATE design on overall TAG performance has often been overlooked in previous studies. This research aims to address this gap by investigating how different ATE configurations influence the efficiency of power conversion within thermoacoustic systems. Specifically, this study delves into the potential of electromagnetic devices: linear alternators and loudspeakers, as ATE converters in a Standing Wave Thermoacoustic Generator (SWTAG) framework using air at atmospheric conditions. Firstly, a comparative analysis was conducted between two types of linear alternators—moving magnet and moving coil and tested with different magnet types (rare earth and ferrie anisotropic) to evaluate their impact on voltage generation. Secondly, the influence of various factors on energy conversion using loudspeakers was investigated, including loudspeaker type (paper cone vs. polypropylene cone), housing geometry (diameter and length), housing material (galvanized steel vs. PVC), open versus closed ATE housing design and utilizing dual loudspeakers. The generated electricity was utilized to power a light bulb. Linear alternators resultsMoving coil configuration outperformed the moving magnet design due to its lighter weight. Rare earth disc magnets generated higher voltage outputs compared to ferrie anisotropic magnets. The moving coil configuration achieved a maximum voltage output of 454 mV, while the moving magnet design reached a maximum of 312 mV. Both linear alternator configurations displayed low overall efficiencies. This is likely due to a mismatch between the magnet and coil diameters, leading to inefficiencies in capturing the generated magnetic field. Loudspeakers resultsPaper cone loudspeakers demonstrated superior performance due to their greater displacement capability. The Saknyo-Paper cone loudspeaker configuration achieved a voltage output of 4.11 V. Optimal voltage generation was achieved when the loudspeaker diameter matched the ATE device housing diameter. Galvanized steel housing offered better performance than PVC housing due to reduced vibration losses. The voltage outputs for the galvanized steel and PVC configurations were 4.11 V and 2.21 V, respectively. Closing the loudspeaker housing resulted in decreased voltage output due to wave interference. The voltage outputs for the galvanized steel and PVC configurations were 3.33 V and 1.62 V, respectively. Dual loudspeakers significantly enhanced voltage generation compared to a single loudspeaker. The maximum voltage recorded for the dual loudspeaker configuration was 6.5 V.The developed thermoacoustic generator achieved an output voltage exceeding the target of 6 V and thermal-to-electric efficiency of 3.42 % with an output electric power of 10.56 W, surpassing previous air-powered TAGs operating at atmospheric conditions. The generator successfully illuminated a light bulb, demonstrating its ability to generate useable electricity. This study provides valuable insights into optimizing the design of acoustic-to-electric conversion devices in TAGs. The findings highlight the importance of factors such as material selection, housing geometry, and magnet type for maximizing energy conversion efficiency.