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Q2 As schematically shown in Figure Q2, a vapour compression cycle refrigeration system uses R134a as refrigerant and the condensing temperature is 35 C. It has two evaporators for different cooling loads. The intermediate-temperature evaporator provides cooling at 0 C, and its cooling capacity is 400 kW. The low-temperature evaporator provides cooling at -20 C, and its cooling capacity is 500 kW. Assume the states of refrigerant at the exit of the evaporator, the condenser and the flash tank are saturated, and the compression processes are isentropic. The enthalpies of some states are shown as Table Q2. Table Q2 Enthalpy of several state points. State 1 2 3 4 5 7 h (kJ/kg) 386.4 402.46 398.52 421.57 248.79 227.26 i. Sketch a Pressure-Enthalpy diagram for the system as shown in Figure Q2 and indicate the state points 1-8 on the Pressure-Enthalpy diagram. ii. Describe the function of the flash tank in this system and explain its benefits. iii. Determine the mass flow rates of refrigerant passing through the two compressors. [kg/s] iv. Determine the COP of this refrigeration system. V. Determine the heat rejection by refrigerant within the condenser. 5 5 4 Condenser Compressor 11 Expansion valve III m3 Evaporator 11 6 3 Expansion valve 11 2 m2 6 O Flash tank III 0467041 Compressor mi 7 Evaporator 8 1 Expansion valve Figure Q2