Experimental assessment of an Organic Rankine Cycle with a partially evaporated working fluid

The Organic Rankine Cycle (ORC) has the potential to play a vital role in the mitigation of climate change by enabling low-temperature heat sources for power generation. This paper describes an experimental investigation of a variant of the ORC, known as the partially evaporated ORC (PEORC), and compares its power generating performance for a variety of heat source conditions to that of a conventional ORC. In contrast to the latter, the working fluid is only partially evaporated in the PEORC, which allows better matching of the temperature profiles of the heat source and working fluid during heat transfer. In the power cycle, the low GWP refrigerant R1233zdE was employed as working fluid. The mass flow and temperature of the heat source were varied from 0.25 to 0.35 kg/s and 110 to 140 °C, respectively. For each combination of heat source mass flow and temperature, the optimum operating point was identified by experiment in terms of exergy efficiency. Therefore, the evaporation pressure was varied in case of the ORC. In case of the PEORC, evaporation pressure and vapor quality at the evaporator outlet were varied. The results show that the PEORC outperforms the ORC in terms of exergy efficiency by up to 80 % for all investigated heat source conditions due to the much higher heat source utilization of the PEORC. The net thermal efficiency however is higher with the ORC due to the higher exergy level of the working fluid at the evaporator outlet.