The compressor of a refrigeration plant having stroke volume of 500 c.c. runs at 500 r.p.m and works with CO2 gas. The evaporator and condenser temperatures are -15°C and 25°C respectively. The liquid in the condenser (using another Fr- 12 refrigerating system) is undercooled to 15°C, before passing on to the expansion valve. Assume isentropic compression with an initial quality of CO2 as x = 1 and volumetric efficiency of the compressor as 0.85. Draw a T-s diagram and calculate the following with the help of the tabulated data for saturated CO2
(a) C.O.P
(b) Power required by compressor assuming motor efficiency to be 0.9
(c) Actual tonnage capacity of the compressor
|
t(oC)
|
p(bar)
|
h(kJ/kg)
|
v(m3/kg)
|
s(kJ/kg0C)
|
|
|
|
liq
|
vap
|
liq
|
vap
|
liq
|
vap
|
|
–15
|
22.88
|
49.62
|
322.86
|
0.0010
|
0.0166
|
0.1976
|
1.2567
|
|
15
|
50.92
|
127.75
|
308.08
|
0.0013
|
0.0063
|
0.4697
|
1.0959
|
|
25
|
64.32
|
164.17
|
283.63
|
0.0015
|
0.0042
|
0.5903
|
0.9912
|
(Specific heat of vapor CO2 = 2.4 kJ/kg0C)