Intrinsic-group-contribution PC-SAFT and its application in performance analysis of high-temperature organic Rankine cycle with siloxanes and alkanes

Abstract

Thermodynamic property prediction of working fluids is of great importance on the performance analysis of high-temperature organic Rankine cycles (ORCs) for utilizing low-grade heat sources. In this study, an intrinsic-group-contribution perturbed-chain statistical associating fluid theory (iGC-PC-SAFT) is proposed for the high-temperature ORC performance analysis with 8 siloxanes and 10 alkanes. By adjusting the initial values and corresponding value ranges of PC-SAFT parameters repeatedly according to the changes in molecular structures, the PC-SAFT parameters were fitted to determine the initial iGC-PC-SAFT parameters. Afterwards, the final iGC-PC-SAFT parameters for each working fluid were obtained based on a global optimization algorithm. Furthermore, the iGC-PC-SAFT equation of state (EoS) was used to calculate the thermodynamic properties of working fluids. Compared with the results from Coolprop database, maximum relative deviations for the saturated liquid density and the compressibility factor in the superheated region are 0.95% for MM, and 0.84% for MD2M, respectively. Besides, the average absolute relative deviations of ORC performance parameters calculated by the iGC-PC-SAFT EoS at different input pressures of turbine, including the thermal efficiency, turbine power output, pump power consumption, heat rejection, mass flow, and exergy efficiency are less than 2.04% for siloxanes (except for MM) and 6.09% for alkanes, respectively.