Performance of a looped thermoacoustic engine with multiple loads capable of utilizing heat source below 200 °C

Highlights: • A 3-stage looped thermoacoustic engine with multiple loads is built and tested. • The output power of the system was measured with multiple R-C loads. • A highest thermal efficiency 9.6% is achieved at the heating temperature of 195 °C. • A highest relative Carnot efficiency 26% is achieved at the heating temperature of 173 °C. -- Abstract: Thermoacoustic engine is a promising approach to low-grade heat recovery with the outstanding characteristics of high reliability and environmental friendliness. In this work, systematic experiments were conducted on a three-stage looped thermoacoustic engine to drive one to five loads, with the hot temperatures below 200 °C. The R-C load method was adopted to measure the output acoustic power. In the experiments, the highest thermal efficiency achieved is 9.6% at the hot temperature of 195 °C when five loads are installed, and the corresponding relative Carnot efficiency is 25.6%. The highest relative Carnot efficiency is 26.4%, achieved at the hot temperature of 173 °C in the case with four loads. The thermoacoustic engine was also modeled to discuss the mechanism for the efficiency gain by adding the quantity of loads. The results show that the increased quantity of loads can reduce the proportion of acoustic power loss and increase the proportion of output acoustic power. This work will be instructive for increasing the thermal efficiency of the low-grade heat driven thermoacoustic engine systems.