Design and construction of a two-phase fluid piston engine based on the structure of fluidyne

Engines that extract energy from low-grade heat sources, e.g., from other processes, have received considerable attention recently. The use of Fluidyne, which is a liquid piston Stirling engine, is quite popular. Herein, we explore the use of liquid-to-vapor phase change in a Fluidyne. This provides two considerable differentiators; (1) exploitation of very low temperature difference ΔT≈30 K, and (2) relatively low temperature ΔT≈330 K heat sources, for producing mechanical work, and thus electrical energy. The influence of three operating parameters, i.e., input heat flux, working fluid, and filling ratio, on the performance of the engine was characterized. Their optimum values, which yield the best efficiency of the engine, were determined. Increasing the input heat flux led to enhanced energy production. The highest performance was achieved when Acetone was used as the working fluid, attributed to Acetone's lower evaporation temperature, viscosity, and enthalpy of evaporation. A filling ratio of 18% resulted in the highest performance. The efficiency of the engine was compared to Carnot efficiency.