Estimate the constant specific heats for R134a from Table B.5.2 at 100 kPa and 125°C. Compare this to the specific heats in Table A.5 and explain the difference.
TABLE B.5.2 Superheated R134a
Temp. 
v 
u 
h 
s 
v 
u 
h 
s 
(°C) 
(m3/kg) 
(kJ/kg) 
(kJ/kgK) 
(kJ/kgK) 
(m3/kg) 
(kJ/kg) 
(kJ/kg) 
(kJ/kgK) 

50 kPa (−40.67°C) 

100 kPa (−26.54°C) 


Sat. 
0.36889 
354.61 
373.06 
1.7629 
0.19257 
362.73 
381.98 
1.7456 
20 
0.40507 
368.57 
388.82 
1.8279 
0.19860 
367.36 
387.22 
1.7665 
10 
0.42222 
375.53 
396.64 
1.8582 
0.20765 
374.51 
395.27 
1.7978 
0 
0.43921 
382.63 
404.59 
1.8878 
0.21652 
381.76 
403.41 
1.8281 
10 
0.45608 
389.90 
412.70 
1.9170 
0.22527 
389.14 
411.67 
1.8578 
20 
0.47287 
397.32 
420.96 
1.9456 
0.23392 
396.66 
420.05 
1.8869 
30 
0.48958 
404.90 
429.38 
1.9739 
0.24250 
404.31 
428.56 
1.9155 
40 
0.50623 
412.64 
Solution 129HP
Step 1 of 3:
We are going to compare the constant specific heats for R134a from the tables B.5.2 and A.5 for the given temperature and pressure values.
The given pressure P = 100 kPa
The given temperature T = 125°C
The table B.5.2 for the corresponding temperatures is listed below.
Temp. 
v 
u 
h 
s 
v 
u 
h 
s 
(°C) 
(m3/kg) 
(kJ/kg) 
(kJ/kgK) 
(kJ/kgK) 
(m3/kg) 
(kJ/kg) 
(kJ/kg) 
(kJ/kgK) 

50 kPa (−40.67°C) 

100 kPa (−26.54°C) 


120 
0.63835 
480.44 
512.36 
2.2128 
0.31797 
480.16 
511.95 
2.1555 
130 
0.65479 
489.63 
522.37 
2.2379 
0.32626 
489.36 
521.98 
2.1807 
The specific enthalpy at T120 (h1) = 511.95 kJ/kg
The specific enthalpy at T130 (h2) = 521.98 kJ/kg
The specific internal energy at T120 (u1) = 480.16 kJ/kg
The specific internal energy at T130 (u2) = 489.36 kJ/kg
The approximate specific heats at the temperature T are given by
The specific heat at constant pressure is expressed as
Putting the values
The specific heat at constant volume is expressed as
Putting the values