Page 45 - Handbook of Natural Gas Transmission and Processing Principles and Practices

For ideal gases:

(1.31)
where R is the universal gas constant.

1.6.2.2. Joule–Thomson Coefficient
When a nonideal gas suddenly expands from a high pressure to a low pressure there is often a
temperature change. Note that this is far from a reversible effect. It is however an adiabatic effect
due to the fact that the pressure change occurs too quickly for a significant heat transfer to occur.
Thermodynamically, the Joule–Thomson coefficient is defined as:

(1.32)

Using thermodynamic relationships, alternative expressions can be written. For example, using
the cycling rule we may write:

(1.33)

An interesting observation from the previously mentioned expressions for the Joule–Thomson
coefficient is that the Joule–Thomson coefficient of an ideal gas is identically equal to zero.
However, real fluids take positive or negative Joule–Thomson values.

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