A 20 ton vapour compression refrigeration system using Freon 12 operates between evaporator pressure of 1 .004 bar and condenser pressure of 13.663 bar. The system uses a sub-cooling superheating heat exchanger with 10° of superheat added. Determine (i) the mass flow rate, (ii) the COP, (iii) the degree of sub-cooling and (iv) the power required. The refrigerant leaving the condenser is dry saturated liquid and leaving the evaporator is dry saturated vapour. The compression in compressor is isentropic.
Properties for for R -12
|
Pressure
bar
|
Temperature
oC
|
Enthalpy ( kJ/kg)
|
Entropy (kJ/kg)
|
Specific heat,
kJ/kg K
|
|
|
|
liquid
|
Vapour
|
liquid
|
Vapour
|
liquid
|
Vapour
|
|
1.004
|
–30
|
8.854
|
174.076
|
0.0371
|
0.7165
|
|
0.579
|
|
13.663
|
55
|
90.201
|
207.766
|
0.3194
|
0.6777
|
1.074
|
|