Assessment of pinch point characteristics in heat exchangers and condensers of ammonia-water based power cycles

In heat exchanging devices of ammonia-water based power generation cycles for the recovery of waste heat in the form of sensible energy, assessment of pinch point (PP) is far more complicated compared to the case of working fluid of pure substance. In this study, efficient and novel method is suggested for PP assessments in source heat exchanger and condenser in ammonia-water based power generation cycles. The concept of imaginary source and coolant outlet temperatures is proposed in the present method and PP characteristics can be efficiently evaluated by using the proposed approach. The present method is especially useful when PP occurs in the middle between bubble and dew points during variable temperature phase transition due to the nature of binary mixture. The effects of system parameters are investigated on the PP characteristics including PP location and the corresponding mass flow ratios of working fluid to source and coolant fluids. The analysis shows that the PP characteristics are affected quite complicatedly and sensitively with changing ammonia concentration or working fluid pressure. Depending on the working conditions, the PP location within heat exchanging devices exhibit abrupt changes between a middle point between bubble and dew points and usual PP locations such as device inlet/exit or bubble point of working fluid.