A two-stage cascade refrigeration system is shown below. The refrigerant is R134a. It consists of two ideal vapor-compression cycles with heat exchange between the condenser of the lowertemperature cycle and the evaporator of the higher-temperature cycle. The hotter cycle operates between 0.7 MPa and 0.35 MPa, while the cooler cycle operates between 0.35 MPa and 0.12 MPa. If the fl ow rate in the hotter cycle is 0.5 mol/s, determine the following:

(a) What is the fl ow rate in the cooler cycle?
(b) What is the rate of heat removal from the refrigerated unit?
(c) What is the power input needed to the compressors?
(d) What is the COP?
(e) Compare the performance with the cycle in Problem 3.62.

Problem 3.62

Consider a refrigeration system based on an ideal vapor-compression cycle using R-134a as the refrigerant. It operates between 0.7 MPa and 0.12 MPa with a fl ow rate of 0.5 mol/s. 

Transcribed Image Text:

Refrigeration unit at low T 5 6 P= 0.12 MPa Evaporator Valve W Condenser 7 8- Compressor 2 P = 0.35 MPa Valve Evaporator 2 W Compressor 1 P= 0.7 MPa |QH High T reservoir Condenser