A cycle research methodology for thermo-chemical engines: From ideal cycle to case study

Highlights: • Electrochemical systems for heat harvesting are positioned as thermo-chemical engines. • A cycle research methodology for thermo-chemical engines is proposed. • The ideal cycle of thermo-chemical engines is presented and analyzed. • Configuration and irreversibility analyses are applied to thermo-chemical engines. The current researches on thermo-chemical engines that convert heat into chemical work lack a systematic thermodynamic research methodology, which hinders the deepening and generalization of the study on thermo-chemical engines. In this study, a cycle research methodology for thermo-chemical engines is proposed with respect to the basic concepts, physical picture, ideal cycle and degradation analysis. Firstly, the ideal cycle of thermo-chemical engines is presented and analyzed in detail based on the concept of chemical work and the physical picture. Then, a comparison between the presented ideal cycle and the Carnot cycle is performed, which indicates significant differences between the two except for the temperature-entropy diagram. In addition, with reference to conventional heat engines, the degradation from the ideal cycle to actual cycles is extended to analyses for configuration degradation and irreversibility of thermo-chemical engines. Finally, a case study for the thermally regenerative electrochemical cycle is performed to support the applicability of the cycle research methodology for thermo-chemical engines. The proposed cycle research methodology fills the theoretical gap in the conversion of heat to chemical work, and is expected to guide the improvement and innovation of actual thermo-chemical engines.