CAJ | 학술논문

A comparison on subcritical and transcritical organic Rankine cycle (ORC) system with a heat source of 110 °C geothermal water was presented. The net power output, thermal and exergy efficiencies and the products of the heat transfer coefficient (U) and the total heat exchange area (A) (UA values) were calculated for parametric optimization. Nine candidate working fluids were investigated and compared. Under the given conditions, transcritical systems have higher net power outputs than subcritical ones. The highest net power output of transcritical systems is 18.63 kW obtained by R218, and that of subcritical systems is 13.57 kW obtained by R600a. Moreover, with the increase of evaporating pressure, the thermal and exergy efficiencies of transcritical systems increase at first and then decrease, but the efficiencies of subcritical ones increase. As a result, the efficiencies of transcritical systems cannot always outperform those of the subcritical ones. However, the subcritical systems have lower minimum UA values and lower expansion ratios than the transcritical ones at the maximum net power output. In addition, the transcritical cycles have higher expansion ratios than the subcritical ones at their maximum net power output.