Optimized Mass Velocity for Evaporator of Organic Rankine Cycle Using R1234ze(E) for 373.15-423.15 K Geothermal Water

Organic Rankine cycle (ORC) is a promising technology for medium and low temperature geothermal water power generation due to its simple structure, good applicability, and user-friendliness. The evaporator absorbs heat from heat source and facilitates the evaporation of working fluid, the performance of it has an important influence on ORC system. The working fluid mass velocity is the important parameter for evaporator, the increment of mass velocity can enhance heat transfer coefficient and decrease heat transfer temperature, but it also increases pressure drop and heat transfer area, the selection of working fluid mass velocity is important for ORC system. There has been few studies on the working fluid mass velocity for ORC evaporator. The thermodynamic and economic performance of geothermal water ORC system using R1234ze(E) are analyzed, the working fluid mass velocity influences of evaporator on geothermal water outlet temperature, net power output, thermal efficiency, exergy efficiency and electricity generation cost (EGC) are studied, the optimal mass velocities for maximizing net power output and minimizing EGC are obtained for 373.15-423.15 K geothermal water respectively. The results show increasing mass velocity can increase net power output and exergy efficiency, EGC initially decreases and then increases with increasing mass velocity; optimal mass velocities increase with increasing geothermal water inlet temperature; when geothermal water inlet temperature is 418.15K, the EGC of case 2 can decreases by 22.73% compared with case 1.