Development of a three-stage looped thermoacoustic electric generator capable of utilizing heat source below 120 °C

Thermoacoustic engine, with the outstanding characteristics of high reliability and environmental benignity, is one of the most attractive and promising energy conversions to recover low-grade thermal energy. In this paper, a three-stage looped thermoacoustic electric generator, consisting of a three-stage looped thermoacoustic engine and a linear alternator, was proposed and built. To obtain a better coupling between the thermoacoustic engine and the linear alternator, the acoustic impedance of the linear alternator has been adjusted by modulating the external electric resistance/compliance and the frequency. The frequency was adjusted by adopting the He-Ar mixture. Additionally, the location and the length of compliance tube have been optimized to improve the acoustic field in the system. Upon optimization, a maximal thermal-to-electric efficiency of 1.51% can be achieved at the hot temperature of 120 °C with He-Ar mixture as the working fluid, in which the mole fraction of helium was 0.63. Furthermore, the system has also been tested in the hot temperature range of 90 °C-200 °C. Results show that the thermal-to-electric efficiency stabilizes at around 1.5% when hot temperature is in the range of 120 °C-170 °C.