In this study, the thermal performance of an internal heat exchanger-organic flash cycle system driven by geothermal water was investigated.R600a/R601a mixtures were selected as the working fluid. The effects of the mole fraction of mixtures on the heat absorption capacity of the heater, the temperature rise of cold working fluid in the internal heat exchanger, net power output, thermal efficiency, and electricity generation costs were analyzed. The net power outputs, electricity generation costs, and thermal efficiency of the internal heat exchanger-organic flash cycle and simple organic flash cycle systems were compared. Results showed that the system using theR600a/R601a mixtures (0.7/0.3mole fraction) has the largest net power output, which increased the net power output by 3.68% and 42.23% over the R601a and R600a systems, respectively. WhentheR600a mole fraction was 0.4, the electricity generation costs reduction of the internal heat exchanger-organic flash cycle system was the largest (1.77% compared with the simple organic flash cycle system).The internal heat exchanger can increase the thermal efficiency of organic flash cycle, but the net power output does not necessarily increase.

Keeping output stable is necessary for solar organic rankine cycle (SORC) considering variable solar irradiation conditions. In this study, zeotropic mixtures are introduced into SORC with stable output. Evaporation pressure and turbine inlet temperature are optimized with the overall system efficiency as optimization objective. Comparisons are drawn between the basic SORC and regenerative SORC. The influences of zeotropic mixture composition on the overall system efficiency, ORC efficiency, heat source outlet temperature, mass flow rate of heat source and working fluids and temperature rise of internal heat exchanger (IHE) are analyzed. The results show that zeotropic mixtures can slightly increase the overall system efficiency of the basic SORC system compared with the optimal pure working fluid system, but for the regenerative SORC system, the optimal overall system efficiency is higher when pure cyclohexane is used. When cyclopentane mole fraction is 0.4, the overall system efficiency of the basic SORC system reaches maximal value of 16.08%, which is 0.12% higher than for the optimal pure working fluids system, relatively. Under the optimum conditions, the optimal overall system efficiency of the regenerative SORC system is 52.11% higher than that of the basic SORC system.

Organic flash cycle (OFC) can effectively use low‐ and medium‐temperature heat sources. The non‐isothermal phase change characteristic of R600a/R601a mixtures can improve the thermal match between the cycle and heat sink. In this study, a thermodynamic model of the OFC system was proposed. The OFC system was driven by heat source temperatures of 100–200 °C. R600a/R601a mixtures were selected as the working fluids. The effects of the mole fraction of the mixtures and the heat source temperature on the net power output, cycle efficiency, and second‐law efficiency were investigated. The exergy destruction in the component was also discussed. Results showed that when the heat source temperature was 100–180 °C, the relative increments in the net power outputs of the mixture systems were 0.62–5% compared with that of the R601a system. At 190–200 °C, the R601a system demonstrated the largest net power output. A characteristic temperature (Tct) was also observed. When THS,in ≤ Tct, the net power output was mainly affected by the thermal match between the cycle and the heat sink, flashing process destruction, and low‐pressure throttle valve destruction. When THS,in > Tct, the net power output was mainly affected by the thermal match between the cycle and the heat sources.