Effect of flow losses in heat exchangers on the performance of organic Rankine cycle

Abstract No pressure loss or constant pressure loss were usually used in theoretical study of organic Rankine cycle (ORC). However, in a practical cycle, pressure losses will occur in heat exchangers and pipes. The pressure losses can influence the evaporating and condensing process and further influence the overall performance of ORC. In this study, the flow loss coefficients of evaporator and condenser are defined and the differences of performance between practical cycle and ideal cycle are compared. The process of practical cycle is established based on a series of experiments. Three pumps are used respectively with a scroll expander and two plate heat exchangers as evaporator and condenser. R245fa is used as working fluid. The results show that the irreversibility in evaporator and condenser increases by 14.4% and 37.0%, respectively. The flow losses result in performance reduction. The maximum relative increase of total irreversibility is 9.7%, while the maximum decrease of net work output, thermal efficiency and exergy efficiency are 16.1%, 17.0% and 16.9%, respectively. The relationships of total irreversibility, net work output, thermal efficiency and exergy efficiency between the practical cycle and ideal cycle are almost linear. In addition, the maximum expander isentropic efficiency reaches 95.4% when using centrifugal pump.