Ammonia enters a counterflow heat exchanger at -20°C, with a quality of 35%, and leaves as saturated vapor at -20°C. Air at 300 K, 1 atm enters the heat exchanger in a separate stream with a flow rate of 4 kg/s and exits at 285 K, 0.98 atm. The heat exchanger is at steady state, and there is no appreciable heat transfer from its outer surface. Neglecting kinetic and potential nergy effects, determine the mass flow rate of the ammonia, in kg/s, and the rate of entropy production within the heat exchanger, in kW/K.