Theoretical performance characteristics of a travelling-wave phase-change thermoacoustic engine for low-grade heat recovery

There is a critical need for environmentally benign, cost-effective technologies to utilize the vast amount of untapped low-grade heat sources. In this work, we report a novel travelling-wave thermoacoustic engine, which incorporates phase change of a condensable component into the classical thermoacoustic conversion, and thus can work efficiently at a low-temperature difference (<50 K). A numerical model was experimentally validated, based on which a thorough analysis of the engine's onset and steady state under different working conditions was performed. It was found that the presence of phase change can significantly enhance thermoacoustic conversion, leading to increased efficiency and energy density. The presented engine exhibits a thermal-to-acoustic efficiency >40% of the Carnot efficiency when working at a temperature difference <50 K. Moreover, the addition of phase change reduces the required mean pressure in the thermoacoustic engine by at least one order of magnitude, which is significant in terms of increasing safety and reducing cost of practical devices.