Possibility of optimal efficiency prediction of an organic Rankine cycle based on molecular property method for high-temperature exhaust gases

Abstract

Working fluid selection is critical for the system design of an organic Rankine cycle (ORC). Computer-aided molecular design (CAMD) provides a new approach to search novel working fluids. In this study, the possibility of using molecular properties to predict the optimal system performance of an ORC is investigated. First, for a heat source of high-temperature exhaust gases, the influences of the molecular properties including the critical temperature and the specific heat capacity on the exergy efficiency of an ORC using 10 alkanes as working fluid are estimated. Then, the possibility of using the parameters of PC-SAFT to assess the optimal efficiency of the ORC is explored. The relation of the optimal temperature difference between the heat source and the molecular properties is determined. The prediction precision of PC-SAFT method is compared with the other four different molecular property methods. The results indicate that the parameters of PC-SAFT can be used to predict the optimal exergy efficiency of ORC system and the corresponding optimal heat source temperature. The average deviations of the exergy efficiency predicted is only 1.44% for the PC-SAFT method. The search range of the optimal working fluid can be decreased and the computation load is reduced significantly.