Thermodynamics Mech3001 - Week 11 - Problem 4 (11.56)

11.56 Consider a two stage cascade refrigeration system operating between the pressure limits of 1.4 MPa and 160 kPa with refrigerant – 134a as the working fluid. Heat rejection from the lower cycle to the upper takes place in an adiabatic counter flow heat exchanger where the pressure in the upper and the lower cycles are 0.4 and 0.5 MPa, respectively. In both cycles, the refrigerant is a saturated liquid at the condenser exit and a saturated vapour at the compressor inlet, and the isentropic efficiency of the compressor is 80 percent. If the mass flow rate of the refrigerant through the lower cycle is 0.11 kg/s, determine a) mass flow rate of the refrigerant through the upper cycle (Answer: 0.1689 kg/s) b) The rate of heat removal from the refrigerated space (Answer: 18.46 kW) c) the COP of the refrigerator (Answer: 2.12)