Abstract
The Uehara cycle for OTEC uses ammonia/water as the working fluid. The mass fraction of the ammonia/water mixture affects the cycle thermal efficiency. In this paper, we analyzed the influence of various parameters using two regenerator models for heat transfer performance in order to bring out the optimum mass fraction that provides the maximum cycle thermal efficiency. In addition, we study how the heat transfer performance of the regenerator affects the cycle thermal efficiency. The given parameters were the evaporator outlet pressure, the evaporator outlet temperature, the condenser outlet temperature, the ratio of extraction flow rate, the extraction pressure and the evaporator outlet mass fraction. As a result, an optimum mass fraction was found to exist because changing the mass fraction alters factors that influence cycle thermal efficiency, such as the ratio of vapor separation at the separator, the condensate pressure and the heat transfer rate of the evaporator. Because a high optimum mass fraction causes an increased ratio of vapor separation at the separator, the influence of the regenerator on cycle thermal efficiency is reduced. The optimum mass fraction is affected more by the evaporator outlet temperature of the working fluid than the condenser outlet temperature of the working fluid. The condenser outlet temperature affects the optimum mass fraction significantly if the heat transfer performance of the regenerator is lower.
