Flash evaporation strategy of organic Rankine cycle for geothermal power performance enhancement: A case study

The performance of organic Rankine cycle (ORC) is poor due to the high irreversible losses in evaporator. To improve system performance, organic Rankine single flash cycle (ORSFC) and organic Rankine double flash cycle (ORDFC) are proposed, in which the traditional evaporation process is split into incomplete evaporation and flash evaporation. Thermal and exergetic efficiencies are taken as the objective functions, and the effects of the related operating parameters and the number of the flash stage on the thermodynamic performance of the system is conducted. The results show that for the ORSFC and ORDFC, in the direction of the rise of the heat source temperature, the net power output increases, the optimal evaporation temperature and flash temperature corresponding to different performance criteria also gradually increase. Besides, the dryness of the evaporator outlet is inversely proportional to the net power output, while it is directly proportional to the system efficiencies. When the dryness increases by 0.1, the net power output of the ORSFC and ORDFC decreases by an average of 148.5 kW, the thermal efficiency and exergetic efficiency of the ORSFC and ORDFC increase by an average of 0.56% and 1.37%, respectively. Moreover, with the flash stages increase, the performance criteria are improved at different magnitude. When a specific thermodynamic parameter is optimized, the ORDFC always obtains the best value for this parameter.