In
thermodynamics, the
Joule–Thomson effect (also known as the
Joule–Kelvin effect,
Kelvin–Joule effect, or
Joule–Thomson expansion) describes the temperature change of a
real gas or liquid (as differentiated from an
ideal gas) when it is forced through a
valve or porous plug while kept insulated so that no heat is exchanged with the environment. This procedure is called a
throttling process or
Joule–Thomson process. At room temperature, all gases except
hydrogen,
helium and
neon cool upon expansion by the Joule–Thomson process; these three gases experience the same effect but only at lower temperatures.