Performance study of asymmetric looped travelling-wave thermoacoustic engine driven by low-grade heat.

Thermoacoustic engine is a promising approach in recovering heat energy with the attracting characteristics of high reliability and environmental friendliness. However, a traditional thermoacoustic engine/refrigerator cannot utilize low-grade thermal energy. This work aims to initiate the thermoacoustic oscillation at very low hot end temperature and to realize the efficient thermoacoustic conversion when driven by low grade heat. Looped thermoacoustic engines with asymmetric configuration are proposed and constructed. The lowest onset temperature is only 29°C (with the temperature difference of 17°C). A thermoacoustic electricity generator is then developed. A thermal-to-electric efficiency of 5% and an output electric power of 87 W are achieved when the hot end temperature is about 180°C, with He-Ar mixture as the working fluid. The results indicate that the asymmetric looped thermoacoustic engine can be utilized as a novel technical method for the recovery of low-grade heat.