Joule-Thomson effect

Joule-Thomson effect
/joohl"tom"seuhn, jowl"-/, Thermodynam.
the change of temperature that a gas exhibits during a throttling process, shown by passing the gas through a small aperture or porous plug into a region of low pressure. Cf. free expansion.
[1895-1900; named after J. P. JOULE and Sir W. THOMSON]

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      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 utilized in liquefying gases. The phenomenon was investigated in 1852 by the British physicists James Prescott Joule (Joule, James Prescott) and William Thomson (Lord Kelvin (Kelvin, William Thomson, Baron)). 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.

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  • Joule-Thomson effect — /dʒul ˈtɒmsən əfɛkt/ (say joohl tomsuhn uhfekt) noun the change of temperature exhibited by a gas when it is expanded through a small hole or a porous plug. Also, Joule Kelvin effect. {from JP Joule and Sir William Thomson (see Lord Kelvin) …  

  • joule-thomson effect — ˈ ̷ ̷ˈtäm(p)sən noun Usage: usually capitalized J&T Etymology: after J. P. Joule and Sir William Thomson (Lord Kelvin) died 1907 British physicist : the change in temperature of a gas on expansion through a porous plug from a high pressure to a… …   Useful english dictionary

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