Solution Found!
Estimate the constant specific heats for R-134a from Table
Chapter 3, Problem 129HP(choose chapter or problem)
Estimate the constant specific heats for R-134a 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.
Questions & Answers
QUESTION:
Estimate the constant specific heats for R-134a 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.
ANSWER:
Solution 129HP
Step 1 of 3:
We are going to compare the constant specific heats for R-134a 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/kg-K) |
(kJ/kg-K) |
(m3/kg) |
(kJ/kg) |
(kJ/kg) |
(kJ/kg-K) |
|
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