A two-stage cascade refrigeration system is to provide cooling at -40ºC while operating with the high-temperature condenser at 1.6 MPa. Each stage operates on the ideal vapor-compression refrigeration cycle. The upper vapor compression refrigeration system uses water as its working fluid and operates its evaporator at 5ºC. The lower cycle uses refrigerant-134a as its working fluid and operates its condenser at 400 kPa. This system produces a cooling effect at 20 kJ/s. Determine (a) The heat transfer rate within the heat exchanger connecting the two refrigeration systems. (b) The mass flow rate of R-134a and water in their respective cycles, and (c) The required heat transfer area A inside the heat exchanger if the overall heat transfer coefficient U is 25 W/m2K . (25 pt.)