A two-stage cascade refrigeration system operates between the pressure limits of16 bar in the upper stage condenser and 2 bar in the lower stage evaporator. Each stage operates on an

R134a vapour compression cycle with 85% isentropic compression efficiency in each stage, 10°C of super heat at compressor inlet and saturated liquid at condenser outlet. Heat rejection from the lower cycle to the upper cycle takes place in a perfect adiabatic heat exchanger where both refrigerant streams are at 7 bar. The mass flow of the refrigerant through the upper cycle is 0.5 kg/s. Sketch the process on a P-h chart. the enthalpies of the major points around the system. the mass flow rate of refrigerant through the lower cycle. the cooling capacity of the refrigerator. the total power input to the compressors. COP of each cycle and the complete system. the COP of a Carnot refrigerator operating between the same condenser and evaporator saturation temperatures found in the two-stage system. If the same system is used as a heat pump, calculate: the Coefficient of Performance (COP) of the complete heat pump system. [2 marks] the COP of a Carnot heat pump operating between the same condenser and evaporator saturation temperatures found in the two-stage system.