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Joule-Thomson effect
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Joule-Thomson effect

physics
Also known as: Joule-Kelvin effect
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Last Updated: • Article History
Also called:
Joule-Kelvin effect
Key People:
James Prescott Joule
Related Topics:
gas
helium
heliumThe many uses for helium, but are we running out of it?
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Joule-Thomson effect, the change in temperature that accompanies expansion of a gas without production of work or transfer of heat. At ordinary temperatures and pressures, all real gases except hydrogen and helium cool upon such expansion; this phenomenon often is used in liquefying gases. The phenomenon was investigated in 1852 by the British physicists James Prescott Joule and William Thomson (Lord Kelvin). The cooling occurs because work must be done to overcome the long-range attraction between the gas molecules as they move farther apart. Hydrogen and helium will cool upon expansion only if their initial temperatures are very low because the long-range forces in these gases are unusually weak.

The Editors of Encyclopaedia BritannicaThis article was most recently revised and updated by Erik Gregersen.
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