Efficient cascade waste heat utilization using thermoacoustic engine with variable temperature heat sources

Waste heat recovery is vital for greenhouse gas emissions reduction and meeting increasing power demands. Thermoacoustic engines present a promising solution. However, existing research predominantly focuses on single heating temperatures, which restricts their efficiency in harnessing heat sources with variable temperatures. To overcome this limitation, this work proposed a novel concept of thermoacoustic engine containing multistage heat exchangers capable of cascade waste heat recovery by incorporating bypass orifices to address this issue. By organizing decreasing temperatures of heat source across heat exchangers with decreasingly lower temperatures, multiple heat-to-power energy conversions can be achieved. Theoretical analyses demonstrate that the total exergy utilization efficiency of single-stage (37.7 %), two-stage (47.6 %), and three-stage systems (51.2 %) significantly increases when increasing the stage number up to three. Further increasing the stage number results in less efficiency improvement (only a 1.3 % increase in a four-stage system). Simulation results show that the three-stage thermoacoustic engine can achieve an acoustic power of 2.7 kW and a total exergy utilization efficiency of 51.2 % for recovering 12 kW variable-temperature heat sources. Coupling the engine with a linear alternator increases electricity production by 12 % with higher waste heat utilization rate compared to traditional single-stage thermoacoustic generators. The experimental results further underscore the capability of the proposed thermoacoustic generator to effectively utilize heat sources with variable temperatures.