Abstract
Ocean thermal energy conversion (OTEC) systems using an ammonia/water mixture (AWM) can achieve better thermodynamic performance than comparable single fluid cycles. However, the effects of the working fluid flow rate on the operating pressures, heat exchanger performance, and net power output have not been fully clarified. This study experimentally investigates the effects of the working fluid flow rate (5–12 t/h) and heat source flow rates (400–500 m3/h) using a 30 kW class OTEC facility equipped with low-pressure drop embossed plate heat exchangers. Increasing the working fluid flow rate enhanced the overall heat transfer coefficients of the evaporator and condenser, but also increased parasitic pumping power and changed the vapor quality at the gas–liquid separator outlet. These competing effects produced a distinct maximum in net power output. Among the tested conditions, the maximum net power output of 15.6 kW was obtained at warm and cold water flow rates of 400 m3/h and a working fluid flow rate of 6 t/h. These findings demonstrate that the working fluid flow rate must be selected by considering heat transfer enhancement, vapor separation, pressure loss, and auxiliary pumping power simultaneously.