A standing-wave, phase-change thermoacoustic engine: Experiments and model projections

Phase-change (‘wet’) thermoacoustic engines offer significant potential for efficient and clean conversion of low-grade heat. Previous work has demonstrated the effectiveness of phase-change in enhancing thermoacoustic conversion. However, this has thus far been limited to low mean pressure and low amplitude oscillations. In this work, we present a phase-change thermoacoustic engine able to work with high mean pressure and large amplitudes. In particular, we overcome issues related to liquid replenishment within the stack by using cellulose paper strips. The capillary action of the strips provides the means for rapid liquid absorption and circulation. Experimental results show that the temperature difference required to drive the engine is significantly decreased, to less than 90 °C, by phase change, while maintaining a pressure amplitude as high as 40 kPa under steady state. These results indicate that the offered design provides a promising pathway for advancing practical phase-change thermoacoustic devices. Furthermore, a theoretical investigation demonstrates the potential to reach a high efficiency (>40% of Carnot limit) when driven by low-grade heat sources at temperatures as low as 50 °C, provided that the heat transfer between the solid wall of heat exchangers and the fluid can be significantly improved, and the mass can be efficiently transported.