A vapour compression refrigerator with Refrigerant 134a as t

A vapour compression refrigerator, with Refrigerant 134a as the working fluid, has a
refrigerant mass flow rate of 0.04 kg/s and evaporator and condenser pressures of
120 kN/m2 (gauge) and 950 kN/m2 (gauge) respectively. The vapour leaves the evaporator with 10 K of superheat and the liquid leaves the condenser with 5 K of sub- cooling. Assume the compressor operates with an isentropic efficiency of 0.8 and the expansion process is isenthalpic.

a) Sketch the process on a property diagram [3] and determine :

b) The enthalpy of the working fluid at each of the major points in the cycle [7]

c) The dryness fraction of the refrigerant after the expansion process [2]

d) The coefficient of performance of the refrigerator [4]

e) The Carnot coefficient of performance of a reversible refrigerator operating

between the same evaporator and condenser saturation temperatures. [5]

Briefly comment on;
f) the effect of raising the condenser pressure to 1200 kN/m2 [4]

2. A vapour compression refrigerator, with Refrigerant 134a as the working fluid, has a refrigerant mass flow rate of 0.04 kg/s and evaporator and condenser pressures of 120 kN/m2 (gauge) and 950 kN/m2 (gauge) respectively. The vapour leaves the evaporator with 10 K of superheat and the liquid leaves the condenser with 5 K of sub- cooling. Assume the compressor operates with an isentropic efficiency of 0.8 and the expansion process is isenthalpic. a) Sketch the process on a property diagram [3] and determine b) The enthalpy of the working fluid at each of the major points in the cycle [7] c) The dryness fraction of the refrigerant after the expansion process [2] The coefficient of performance of the refrigerator [4] The Carnot coefficient of performance of a reversible refrigerator operating between the same evaporator and condenser saturation temperatures. [5] e) Briefly comment on; f) the effect of raising the condenser pressure to 1200 kN/m2 [4]

Solution

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