Thermo-economic performance evaluation of emerging liquid-separated condensation method in single-pressure and dual-pressure evaporation organic Rankine cycle systems

Abstract Liquid-separated condensation is an emerging and effective heat transfer enhancement method to reduce the condenser cost, which can help with the widespread application of organic Rankine cycle (ORC) systems. However, few related studies have focused on the shell-and-tube condenser even if it is widely used in ORC systems. The thermo-economic performance superiorities and applicable working conditions of shell-and-tube liquid-separated condenser should be investigated, especially in novel ORCs. This study introduced the liquid-separated condensation method into single-pressure and dual-pressure evaporation ORC systems with shell-and-tube condenser. R245fa, R600a, and R1234ze(E) were used as working fluids. Optimal liquid-separated thermodynamic states and decrements in condenser heat transfer area of one to four stages liquid-separated condensations were provided. Decrements in specific investment cost (SIC) of ORC system by adopting the liquid-separated condensation method were evaluated. Results show that the liquid-separated condensation method is more suitable for low tube diameter, low inlet velocity in tubes, high inlet velocity outside tubes, and low cooling water temperature rise. Optimal liquid-separated thermodynamic states remain constant with increasing the tube diameter and inlet velocities. The SIC of ORC system can be reduced by 4.6% at most by adopting the liquid-separated condensation over the conventional condensation method. Increasing the mass flow rate of heat source fluid and pinch point temperature difference during heat absorption process is beneficial to increase the superiority of liquid-separated condensation method. Compared with dual-pressure evaporation ORC, the effects of liquid-separated condensation method on reducing the SIC are more remarkable in single-pressure evaporation ORC.