Refrigerant-134a at 1 mpa and 90°c is to be cooled to 1 mpa and 30°c in a condenser by air. the air enters at 100 kpa and 27°c with a volume flow rate of 640 m3/min and leaves at 95 kpa and 60°c. determine the mass flow rate of the refrigerant. the gas constant of air is 0.287 kpa·m3/kg·k. the constant pressure specific heat of air is cp = 1.005 kj/kg·°c. the enthalpies of the r-134a at the inlet and the exit states are 324.66 kj/kg and 93.58 kj/kg.