An R – 12 vapour compression plant producing 10 tones of refrigeration operates with condensing and evaporating temperatures of 350 C and – 100 C respectively. A suction line heat exchanger is used to subcool the saturated liquid leaving the condenser. Saturated vapour leaving the evaporator is superheated in the suction line heat exchanger to the extent that a discharge temperature of 600 C is obtained after isentropic compression. Calculate
(i) The subcooling achieved in the heat exchanger,
(ii) The refrigerant flow rate in kg/s,
(iii) The cylinder dimensions of the two cylinder compressor, if the speed is 900 rpm, stroke – to bore ratio is 1 : 1 and the volumetric efficiency is 80%,
(iv) The COP of the plant and
(v) The power required to drive the compressor in kW.
Draw the cycles on P – h and T – s diagrams.
Average specific heat of desuperheating vapour at condenser = 0.796 kJ/kg – K.
Average specific heat of vapour between evaporator outlet and compression suction = 0.658 KJ/kg – K.
You may use the following table :
|
Temperature (0C)
|
Specific Volume (m3/kg) Vapour (vg)
|
Specific Enthalpy, kJ/kg
|
Specific Entropy,
kJ/kg – K
|
|
Liquid (hf)
|
Vapour (hg)
|
Liquid (sf)
|
Vapour
(sg)
|
|
-10
|
0.0766
|
190.88
|
347.13
|
0.9660
|
1.5600
|
|
+35
|
0.0206
|
233.50
|
365.92
|
1.1139
|
1.5419
|