(Solved): Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.4MPa a ...

Consider a two-stage cascade refrigeration system operating between the pressure limits of $1.4\mathrm{MPa}$ and $280\mathrm{kPa}$ using refrigerant-134a as the working fluid. The heat rejection from the lower cycle to the upper cycle occurs in an adiabatic counterflow heat exchanger where the pressures in the upper and lower cycles are $0.5\mathrm{MPa}$ and $600\mathrm{kPa}$, respectively. In both cycles, the refrigerant exits the condenser as a saturated liquid and enters the compressor as a saturated vapor. The isentropic efficiency of the compressors is 85 percent. Given the mass flow rate of the refrigerant through the lower cycle is $0.18\mathrm{kg}/\mathrm{s}$, calculate: (a) The mass flow rate of the refrigerant through the upper cycle. (b) The rate of heat extraction from the cooling area. (c) The Coefficient of Performance (COP) of this refrigeration system.