Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.2 MPa and 200 kPa with refrigerant-134a as the working fluid. Heat rejection from the lower to the upper cycle takes place in a countercurrent adiabatic heat exchanger where the pressures in the upper and lower cycles are 0.4 and 0.5 MPa, respectively. In both cycles the refrigerant is a saturated liquid at the condenser outlet and a saturated vapor at the compressor inlet, and the isentropic efficiency of the compressor is 80 percent. The mass flow rate of the refrigerant in the lower cycle is 0.15 kg/s. Determine the following: a) the mass flow of the refrigerant through the upper cycle, b) the rate of removal from the refrigerated space and c) the COP of this refrigerator. d) Draw the T-s graph of the complete system and the diagram with all the components and processes of both cycles, indicate all the states in both cases (1, 2, 3….)
1. Consider a two-stage cascade refrigeration system operating between the pressure limits of 1.2 MPa and 200 kPa with refrigerant-134a as the working fluid.
Heat rejection from the lower to the upper cycle takes place in a countercurrent adiabatic heat exchanger where the pressures in the upper and lower cycles are 0.4 and 0.5 MPa, respectively. In both cycles the refrigerant is a saturated liquid at the condenser outlet and a saturated vapor at the compressor inlet, and the isentropic efficiency of the compressor is 80 percent.
The mass flow rate of the refrigerant in the lower cycle is 0.15 kg/s.
Determine the following:
a) the mass flow of the refrigerant through the upper cycle,
b) the rate of removal from the refrigerated space and
c) the COP of this refrigerator.
d) Draw the T-s graph of the complete system and the diagram with all the components and processes of both cycles, indicate all the states in both cases (1, 2, 3….)
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