Heat Capacity Ratio

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Heat Capacity Ratio

\gamma = rac{C_P}{C_V}

It should be noted that chemical engineers and many others commonly refer to the heat capacity ratio as

\kappa

rather than

\gamma

.

For a monoatomic Ideal Gas ,

\gamma = rac{5}{3}

, while a diatomic Ideal Gas has

\gamma = rac{7}{5}

.

For a first approximation assuming Ideal Gas and

C_P

,

C_V

, and

\gamma

are constants, it can be written:

C_P = rac{\gamma R}{\gamma - 1}

C_V = rac{R}{\gamma - 1}

The value of

\gamma

for various gases @ 1 atm, 20°C is as follow:

Gas	$\gamma$
H2	1.41
He	1.66
H2O	1.33
Ar	1.67
Dry Air	1.40
CO2	1.30
CO	1.40
O2	1.40
NO	1.40
N2O	1.31
Cl2	1.34
CH4	1.32

Source: Fluid Mechanics 4th edition McGraw Hill, Frank M. White

C_P

and

C_V

increase with increasing temperature and

\gamma

decreases. Some correlations exist to provide values of

\gamma

as a function of the temperature.

SEE ALSO

Thermodynamics

Thermodynamics Equations

Heat Capacity

Specific Heat Capacity

Volumetric Heat Capacity