Harvesting low-grade heat by coupling regenerative shape-memory actuator and piezoelectric generator

Abstract

Low-grade thermal energy is ubiquitous in nature with different scales. Being concise in nature, solid-state energy conversion technologies based on ferroic materials experienced fast development over the years, yet their efficiencies are still not as competitive as the conventional Rankine cycle. To improve the efficiency of solid-state generators, this study proposed a novel composite device leveraging the strain coupling between the regenerative shape-memory actuator and the piezoelectric generator. Taking the realistic losses into account, our experimentally validated numerical model indicated that the new concept has 14.4% efficiency, equivalent to 57% second-law efficiency, when the length and cross-sectional area of the shape-memory actuator and the piezoelectric generator is properly matched. It was also found that relaxor ferroelectric materials are more efficient than the baseline PZT ceramics. The impact and design guideline of other parameters were also investigated, including the utilization factor, transmission factor, and transition temperature. The proposed concept provides a new path for harvesting the low-grade thermal energy, and could potentially be integrated with caloric cooling counterparts to provide power and refrigeration simultaneously as a next-generation co-generation and tri-generation technology.