Refrigerant-12 enters a counter flow heat exchanger at -15oC, with a quality of 45%, and leaves as saturated vapor at -15oC. Air at 100 kPa enters the heat exchanger in a separate stream with a flow rate of 5 kg/s and is cooled from 25oC to 10oC with no significant change in pressure. The heat exchanger is at steady state, and there is no appreciable heat transfer from its outer surface. Determine the entropy generation rate.