Thermodynamic Investigation of an Irreversible Combined Stirling-Organic Rankine Cycle for Maximum Power Output Condition

A pragmatic approach is adopted to investigate irreversible thermodynamic combined cycle devices. The finite-time thermodynamic model of combined Stirling-organic Rankine cycle is formulated and evaluated for maximum output power and thermal efficiency. The influence of effectiveness of heat exchangers, heat capacitance of external fluids, and inlet temperatures of heat exchangers at heat source, heat recovery unit and heat sink on the performance of Stirling-organic Rankine cycle are investigated to get their corresponding optimum. The maximum allowable heat capacitance of external fluids of heat source and heat recovery units are about 1.1 kW/K and 1.4 kW/K, respectively, for the operating conditions considered in the present study. The maximum power output is achieved only when the effectiveness of heat exchangers is ideal. The overall performance of Stirling-organic Rankine cycle combination will be higher than either of the performances of individual cycles provided that the isothermal heat rejection from Stirling cycle takes place at temperature above 540 K. Further, a 0.2 increase in the internal irreversibility parameter from an ideal/reversible condition reduced the maximum output power and the corresponding thermal efficiency of Stirling-organic Rankine cycle by 16.1 kW and 24%, respectively.