11-19
11-26 A vapor-compression refrigeration cycle with refrigerant-134a as the working fluid is considered. The rate of
cooling, the power input, and the COP are to be determined. Also, the same parameters are to be determined if the cycle
operated on the ideal vapor-compression refrigeration cycle between the same pressure limits.
Assumptions 1 Steady operating conditions exist. 2 Kinetic and potential energy changes are negligible.
Analysis (a) From the refrigerant-134a tables (Tables A-11 through A-13)
Tsat@200 kPa  10.1C
P1  200 kPa
h1  253.05 kJ/kg

T1  10.1  10.1  0C s1  0.9698 kJ/kg  K
T
2
·
QH
P2  1400 kPa 
 h2 s  295.90 kJ/kg
s1  s1

Tsat@1400 kPa  52.4C
3
200 kPa

h3  h f@48C  120.39 kJ/kg
T3  52.4  4.4  48C
h4  h3  120.39 kJ/kg
0.88 
·
Win
1.4 MPa
P3  1400 kPa
C 
2s
1
·
QL
4
s
h2 s  h1
h2  h1
295.90  253.05

 h2  301.74 kJ/kg
h2  253.05
Q L  m (h1  h4 )  (0.025 kg/s)( 253.05  120.39)  3.317 kW
Q H  m (h2  h3 )  (0.025 kg/s)(301.74  120.39)  4.534 kW
W in  m (h2  h1 )  (0.025 kg/s)(301.74  253.05)  1.217 kW
COP 
Q L 3.317 kW

 2.725
W in 1.217 kW
(b) Ideal vapor-compression refrigeration cycle solution
From the refrigerant-134a tables (Tables A-11 through A-13)
P1  200 kPa h1  244.46 kJ/kg

x1  1
 s1  0.9377 kJ/kg  K
P2  1400 kPa 
 h2  285.08 kJ/kg
s1  s1

P3  1400 kPa 
h3  127.22 kJ/kg
x3  0

h4  h3  127.22 kJ/kg
T
·
QH
2
3 1.4 MPa
·
Win
200 kPa
4s
4
·
QL
1
s
Q L  m (h1  h4 )  (0.025 kg/s)(244.46  127.22)  3.931 kW
Q H  m (h2  h3 )  (0.025 kg/s)(285.08  127.22)  3.947 kW
W in  m (h2  h1 )  (0.025 kg/s)(285.08  244.46)  1.016 kW
COP 
Q L 3.931 kW

 2.886
W in 1.016 kW
Discussion The cooling load increases by 18.5% while the COP increases by 5.9% when the cycle operates on the ideal
vapor-compression cycle.
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