Answer to Question #110697 in Thermal Power Engineering for Mohd Amir Hussain

Question

restaurant food storage air conditioning working on air refrigeration cycle of 10
tonnes capacity works between 4 bar and 16 bar. The air leaves the cold chamber at
0
oC and discharges air at 25oC to the expansion cylinder after air cooler. The
expansion and compression cylinders are double acting. The mechanical efficiency of
compressor and expander are 85% and 80% respectively. The compressor speed is
250 r.p.m and has a stroke of 250mm Determine:
1. C.O.P
2. Power required
3. Bore of compression and expansion cylinder
(Assume isentropic compression and expansion as polytropic with n = 1.25)

Answer 1

Solution.

T₁= 273K;

T₃ = 298K;

p₂ = 4 bar;

p₁ = 16 bar;

n = 1.25;

l = 250mm;

1 tonne of refrigeration (TR) = (336 ×1000)/ 24 = 14000 kJ/h;

10 tonnes of refrigeration (TR) = 14000 kJ/h ×10 = 140000 kJ/h;

T₁/T₂ = (p₁/p₂)^(n-1)/n;

T₁/T₂ = (16/4)^0.2 = 4^0.2 = 1.32;

T₂ = T₁/1.32 = 207K;

C.O.P = T₂/(T₁ - T₂);

C.O.P = 207/(273-207) = 6.08;

C.O.P = R/W;

W = R/(C.O.P);

W = (140000 kJ/h)/6.08 = 23026kJ/h = 6.39kW;

Answer: C.O.P = 6.08;

W =6.39kW.