The determination and matching analysis of pinch point temperature difference in evaporator and condenser of organic rankine cycle for mixed working fluid

Exergo-economic analysis of the pinch point temperature difference (PPTD) in both evaporator and condenser of sub-critical organic Rankine cycle system (ORCs) are performed based on the first and second laws of thermodynamics. Taking mixture R13I1/R601a as a working fluid and the annual total cost per net output power Z as exergo-economic performance evaluation criterion, the effects of PPTD in evaporator T-e, and the PPTD ratio of condenser to evaporator y, on the exergo-economic performance of ORCs are analyzed. Moreover, how some other parameters influence the optimal PPTD in evaporator T-e,T-opt and the optimal PPTD ratio of condenser to evaporator y(opt) are also discussed. It has been found that the exergo-economic performance of ORCs is remarkably influenced by T-e and y, and there exists T-e,T-opt and y(opt). In addition, T-e,T-opt and y(opt) are affected by heat transfer coefficient ratio of condenser to evaporator ss, the temperature of working fluid at dew point in condenser T-1a, and composition of R13I1/R601a: larger ss and T-1a lead to lower T-e,T-opt and y(opt); by contraries, larger mass fraction of R13I1 makes T-e,T-opt and y(opt) increase, and y(opt) increases linearly. The effects of the temperature of working fluid at bubble point in evaporator T-3a, mass flow rate of exhaust flue gas m(g), and inlet temperature of exhaust flue gas T-gi on T-e,T-opt and y(opt) are very slight. For comparison, three additional working fluids, namely R601a, R245fa, and 0.32R245fa/0.68R601a, are also taken into account.