A ultra-high-temperature free-piston thermoacoustic Stirling heat pump capable of achieving above 200 °C

This study proposes and develops a prototype of a double-acting free-piston thermoacoustic Stirling ultra-high-temperature heat pump with bidirectional power flow regulation. By adjusting the phase relationship between the pistons from leading to lagging, the prototype overcomes the limitation of compressor performance imposed by temperature, enabling a heating supply temperature exceeding 200 °C. Meanwhile, benefiting from the inherent configuration of the double-acting design, the four-cylinder arrangement further enhances the system's power density, thereby improving its suitability for industrial heating applications. Experimental results demonstrate that the system achieves a substantial temperature lift from 25 to 166 °C, and within a temperature difference of 74 °C (from 45 to 119 °C), it attains a maximum coefficient of performance (COP) of 1.68. When the ambient temperature rises to 67 °C, the system delivers a heating supply temperature of 214 °C, with the corresponding COP and relative Carnot efficiency reaching 1.5% and 45.2%, respectively. These findings verify the potential of this system for high-temperature heat pump applications and highlight its advantages under extreme operating conditions. This work thus provides a solution for industrial high-temperature heat pumps, offering unique benefits in achieving large temperature lifts and high-temperature heating.