Modern Engineering Thermodynamics

3.9 Thermodynamic Equations of State 81
Table 3.7 Properties of Various Gases at Low Pressure (also see Table C.13)
R c p c v
Substance M Btu/lbm · R kJ/kg · K Btu/lbm · R kJ/kg · K Btu/lbm · R kJ/kg · K k = c p /c v
Air 28.97 0.0685 0.286 0.240 1.004 0.172 0.718 1.40
Argon (Ar) 39.94 0.0497 0.208 0.125 0.523 0.075 0.315 1.67
Carbon dioxide (CO 2 ) 44.01 0.0451 0.189 0.202 0.845 0.157 0.656 1.29
Carbon monoxide (CO) 28.01 0.0709 0.297 0.249 1.042 0.178 0.745 1.40
Helium (He) 4.003 0.4961 2.077 1.24 5.200 0.744 3.123 1.67
Hydrogen (H 2 ) 2.016 0.9850 4.124 3.42 14.32 2.435 10.19 1.40
Methane (CH 4 ) 16.04 0.1238 0.518 0.532 2.227 0.408 1.709 1.30
Nitrogen (N 2 ) 28.02 0.0709 0.296 0.248 1.038 0.177 0.742 1.40
Oxygen (O 2 ) 32.00 0.0621 0.260 0.219 0.917 0.157 0.657 1.39
Source: Reprinted by permission of the publisher from Reynolds, W. C., Perkins, H. C., 1977. Engineering Thermodynamics, second ed. McGraw-Hill, New York.
4.5
4.0
3.5
3.0
H 2
10,000 psia
1000 psia
0 psia
c p
c v , 0 psia
H 2
2.5
2.0
0.4
Air, 0 psia
Air, 1000 psia
Air, 5000 psia
c p
CO 2 , 10,000 psia
CO 2 , 5000 psia c p
CO 2 , 0 psia
O 2 , 0 psia
0.3
0.2
1.5
CO 2
CO 2
k = c p /c v
Specific heats, c p , c v , Btu/(lbm . R)
0.1
Air
c p , 0 psia
1.4
1.2
0
Air O 2
O 2
H 2
k, 0 psia
1.3
and
1.1
0 1000 2000 3000 4000 5000
Temperature, T, °F
FIGURE 3.21
Specific heats of selected gases (data from the National Bureau of Standards). (Source: Reprinted by permission of the publisher from
Reynolds, W. C., Perkins, H. C., 1977. Engineering Dynamics. McGraw-Hill, New York.)
h 2 − h 1 =
Table C.16 in Thermodynamic Tables to accompany Modern Engineering Thermodynamics contains values for these
integrals for air. (Note: The p r and v r columns are used for entropy values introduced later in this textbook).
Z T2
T 1
c p dT