Thermodynamic analysis of double flash organic flash cycle using R600a/R601a mixtures

Double flash organic flash cycle (OFC) exhibits perfect temperature matching during heat absorption and low throttling loss. Zeotropic mixtures could decrease the irreversible loss during the phase change process due to their non-isothermal characteristic. This study combines double flash OFC with R600a/R601a mixtures to efficiently utilize low-grade thermal energy. The high- and low-stage flash pressures are optimized for maximal net power output. The influences of the R600a mole fraction and the heat source temperature on net power output, exergy efficiency, and cycle parameters are analyzed. Optimal mixture compositions and flash pressures are obtained, and the exergy loss distribution is investigated. The proposed system is compared with the basic single flash OFC using R600a/R601a mixtures. Research shows that the optimized flash pressures have upper limits as heat source temperature increases. The net power output decreases with increasing R600a mole fraction when the heat source temperature is high. The proposed system has more net power output than that using pure working fluid for the 100 °C–180 °C heat source, and the relative net power output growth rates are 3.22%–5.24%. Moreover, the net power outputs of double flash OFC are 15.13%–55.70% higher than basic single flash OFC.