A vapour compression refrigeration system using refrigerant 12 is employed to produce 8640 kg of ice per day. The condensing and evaporating temperatures of the refrigerant are 48°C and –200C, respectively. Saturated liquid leaves the condenser and saturated vapour leaves the evaporator. Compression is isentropic. Water at 35°C is used to form ice. The temperature of ice should be -8°C. Heat flows into the brine tank from the surroundings may be taken to be 10 percent of the total heat removed from water to form ice at the specified temperature. Determine the power required to drive the compressor, in kW. Take specific heat of ice = 2.26kJ/kg.K, latent heat of ice = 334.72 kJ/kg and specific heat of water = 4.187 kJ/kgK. The following data for refrigerant 12 may be used:
|
Temperature
0C
|
Pressure
bar
|
hf (kJ /kg )
|
hg(kJ / kg)
|
sf
(kJ/kg.K)
|
sg (kJ / kg.K)
|
|
48
|
11.64
|
82.83
|
205.83
|
0.2973
|
0.6802
|
|
–20
|
1.51
|
17.82
|
178.74
|
0.0731
|
0.7087
|
Specific heat of vapour = 0.82 kJ/kg. K