Power and efficiency optimizations of a simple irreversible supercritical organic Rankine cycle

Abstract

Based on finite time thermodynamics, a simple irreversible supercritical organic Rankine cycle (SORC) model is set up. Subjected to the total heat conductance constraint of heat exchangers, the power output (PO) and thermal efficiency (TE) of the SORC are maximized firstly by varying the heat conductance distributions of heat exchangers and mass flow rate of organic working fluid. The results reveal that in the discussed variation ranges of the optimization variables, the PO and TE of the SORC after triple optimizations are augmented by 39.45% and 7.13%, respectively, and the optimization effects of the triple optimizations are remarkable. Moreover, the optimization results gained by the triple maximizations of the PO and TE, respectively, are evidently different. In the discussed working fluids, the order of the triple maximum POs of the SORCs is R143a > R218 > R125 > R41 > R245fa, thus the recommended working fluid corresponding to the largest PO is R143a. The multi-optimization of the PO and TE are secondly performed by using NSGA-II, the optimal parameters of the SORCs with R125 and R143a acquired by TOPSIS and Shannon Entropy decision-making methods are taken for the optimal design schemes, respectively. The gained results in this paper offer useful design guidelines for the practical SORCs.