Examination of the expander leaving loss in variable organic Rankine cycle operation

The organic Rankine cycle (ORC) favorably operates at low temperature. It differs significantly from the steam Rankine cycle in fluid enthalpy drop during expansion and reaction to change in condensation temperature. In current method for ORC-based energy conversion the expander leaving loss is generally neglected. Shortcomings of this method are outlined in this paper. Theoretical analysis of the expander leaving loss varying with the condensation temperature, evaporation temperature, and inlet pressure is first performed. Experimental test is subsequently carried out. The results indicate that unlike in the steam Rankine cycle, the leaving loss in the ORC on using R123 or R245fa increases by about 10 times as the condensation temperature changes from 30 to 0 °C, and is comparable with the enthalpy drop. With an inlet temperature of about 97 °C and a deviation of about 20 °C from the design condensation temperature, the ratio of the leaving loss to the enthalpy drop is about 10.4%. Besides, variation in the leaving loss may lead to expansion wave or shock wave inside the expander. The leaving loss becomes an important factor and should be included to determine the ORC year-round performance.