On the Thermodynamic Cycle of a MEMS-Based External Combustion Resonant Engine

In this work we investigate the thermodynamic cycle of a resonant, MEMS-based, micro heat engine. The micro heat engine is made of a cavity encapsulated between two membranes. The cavity is filled with saturated liquid-vapor mixture working fluid. Heat is added/rejected from the engine at a frequency equal to its resonant frequency. Both pressure-volume and temperature-entropy diagrams of the resonant engine are used to investigate the thermodynamic cycle of the resonant micro heat engine. The results show that the thermodynamic cycle of the engine consists of four major processes: heat addition, expansion, heat rejection, and compression. pressure-volume and temperature-entropy diagrams are bounded by two constant temperature processes and two constant volume processes. The temperature-entropy and pressure-volume diagrams show deviations from this ideal description and are rounded due to the presence of irreversible effects. Major sources of irreversibility in the engine are heat transfer over finite temperature differences during heat addition and rejection, heat transfer into and out of engine thermal mass and viscous losses due to liquid working fluid motion. The measured second law efficiency of the micro heat engine is about 16%.