An ammonia refrigerator operates on the simple vapor compression cycle. The pressure of liquid ammonia before throttling is 12.3 kgf/cm2 and its temperature is 27.2°C. The evaporator pressure is 2.53 kgf/cm2. Ammonia gas leaves the evaporator at -9.5°C. The power input to the compressor is 2.12 kW and the mass flow rate of ammonia is 27 kg/h. Determine the dryness fraction of the gas after throttling, the heat absorbed per hour in the evaporator and the coefficient of performance of the refrigerator. Sketch the cycle on the T-s and the p-h diagrams.
Properties of ammonia are given below:
|
Temperature (0C)
|
Pressure (kgf/cm2)
|
hf
(kcal/kg)
|
hg
(kcal/kg)
|
|
-13.8
|
2.53
|
27.5
|
341
|
|
31.1
|
12.30
|
77.5
|
351
|
Specific heat of liquid at 12.3 kgf/cm2 may be taken to be 1.14 kcal/kg°C and the specific heat of superheated vapor at 2.53 kgf/cm2 may be taken to 0.6 kcal/kg°C.