REFRIGERATION CYCLES 777
dharm
\M-therm\Th14-4.pm5
Take : Specific enthalpy of fusion of ice = 336 kJ/kg
Specific heat of water = 4.187 kJ/kg. [Ans. 4.97, 10.9°C, 91.3 kg]- A vapour compression refrigerator circulates 4.5 kg of NH 3 per hour. Condensation take place at 30°C and
evaporation at – 15°C. There is no under-cooling of the refrigerant. The temperature after isentropic
compression is 75°C and specific heat of superheated vapour is 2.82 kJ/kg K. Determine :
(i) Co-efficient of performance.
(ii) Ice produced in kg per hour in the evaporator from water at 20°C and ice at 0°C. Take : Enthalpy of
fusion of ice = 336 kJ/kg, specific heat of water = 4.187 kJ/kg.
(iii) The effective swept volume of the compressor in m^3 /min.
Properties of ammonia :
Sat. temp. Enthalpy (kJ/kg) Entropy (kJ/kg K) Volume (m^3 /kg)
(K)
hf hg sf sg vf vg
303 323.1 1469 1.204 4.984 0.00168 0.111
258 112.3 1426 0.457 5.549 0.00152 0.509
[Ans. 4.95, 682 kg/h, 2.2 m^3 /min]