Page 119 - Mechanical Engineers' Handbook (Volume 4)

108 Thermodynamics Fundamentals

Table 1 Values of Ideal-Gas Constant and Specific Heat at
Constant Volume for Gases Encountered in Mechanical
Engineering 1

R
c P
J
J
Ideal Gas kg K kg K
Air 286.8 715.9
Argon, Ar 208.1 316.5
143.2 1595.2
Butane,C 4 H 10
188.8 661.5
Carbon dioxide, CO 2
Carbon monoxide, CO 296.8 745.3
276.3 1511.4
Ethane, C 2 H 6
296.4 1423.5
Ethylene, C 2 H 4
2076.7 3152.7
Helium, He 2
Hydrogen, H 4123.6 10216.0
518.3 1687.3
Methane, CH 4
Neon, Ne 412.0 618.4
296.8 741.1
Nitrogen, N 2
72.85 1641.2
Octane, C 8 H 18
259.6 657.3
Oxygen, O 2
188.4 1515.6
Propane, C 3 H 8
Steam, H 2 O 461.4 1402.6
P v
s s c ln c ln
0
v
p
P 0 v 0
The ideal-gas model rests on two empirical constants, c and c ,or c and R,or c and R.
P
v
P
v
The ideal-gas limit is also characterized by
1 1

0 K c 0
T
P P
The extent to which a thermodynamic system destroys available work is intimately tied
to the system’s entropy generation, that is, to the system’s departure from the theoretical
limit of reversible operation. Idealized processes that can be modeled as reversible occupy
a central role in engineering thermodynamics, because they can serve as standard in assessing
the goodness of real processes. Two benchmark reversible processes executed by closed
ideal-gas systems are particularly simple and useful. A quasistatic adiabatic process 1 → 2
executed by a closed ideal-gas system has the following characteristics:
2
Q 0
1
2 PV 1 1
V
W 22 2
1 1 V
1
where c /c v
P
• Path

PV PV PV 2 (constant)
1
2
1