Question 15 - A Two-Stage Cascade Refrigeration Cycle
17
MEE 4042 Refrigeration Machines
2022-2023, Spring
Consider a two-stage cascade refrigeration system operating
between the pressure limits of 0.8 and 0.14 MPa. Each stage
operates on an ideal vapor-compression refrigeration cycle with
refrigerant-134aas the working fluid. Heat rejection from the
lower cycle to the upper cycle takes place in an adiabatic
counterflow heat exchanger where both streams enter at about
0.32 MPa. (In practice, the working fluid of the lower cycle is at a
higher pressure and temperature in the heat exchanger for
effective heat transfer.) If the mass flow rate of the refrigerant
through the upper cycle is 0.05 kg/s, determine
(a) the mass flow rate of the refrigerant through the lower cycle,
(b) the rate of heat removal from the refrigerated space and the
power input to the compressor, and
(c) the coefficient of performance of this cascade refrigerator.