In thermodynamics, the Joule–Thomson effect or Joule–Kelvin effect or Kelvin–Joule effect or Joule–Thomson expansion describes the temperature change of a gas or liquid 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.
The effect is named for James Prescott Joule and William Thomson, 1st Baron Kelvin who discovered it in 1852 following earlier work by Joule on Joule expansion, in which a gas undergoes free expansion in a vacuum.
In the Joule experiment, the gas expands in a vacuum and the temperature drop of the system is zero, if the gas were ideal.
The throttling process is of the highest technical importance. It is at the heart of thermal machines such as refrigerators, air conditioners, heat pumps, and liquefiers. Furthermore, throttling is a fundamentally irreversible process. The throttling due to the flow resistance in supply lines, heat exchangers, regenerators, and other components of (thermal) machines is a source of losses that limits the performance.
Read more about Joule–Thomson Effect: Description, Physical Mechanism, The Joule–Thomson (Kelvin) Coefficient, Applications, Proof That The Specific Enthalpy Remains Constant, Throttling in The Ts Diagram, Derivation of The Joule–Thomson (Kelvin) Coefficient
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... Section a derivation of the formula for the Joule–Thomson (Kelvin) coefficient is given ... ideal gas αT = 1, so the temperature change of an ideal gas at a Joule–Thomson expansion is zero ...
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