抄録
This paper refers to the working fluids selection for Rankine cycle engine driven by the heat source with a small temperature difference. The temperature range of the heat reservoir is from 80oC to 300oC. The heat sink temperature is set at 40oC. Non-fluorocarbon refrigerants are chosen as working fluids. According to the characteristics of the saturated vapor line on T-s diagram, the working fluids are sorted into three groups. Comparing the condensation pressure to the atmospheric pressure, the working fluids are classified into two types. Under some constraints for the reasonable formation of Rankine cycle such as avoiding the condensation in the expansion process, the thermal efficiency and net specific work are calculated by using the database of thermodynamic properties. It is found that the thermal efficiencies are distributed in the range from 10% to 25%, depending on the heat source temperature. The working fluids selection is strongly affected by the heat source temperature, the latent heat around the condensation temperature and the pressure difference between the evaporator and condenser. In addition, the performance evaluation method, based on the irreversible loss in Rankine cycle, is proposed. It is confirmed that the smaller irreversibility brings the higher thermal efficiency.
