Joule–Thomson effect

In thermodynamics, the Joule–Thomson effect (also known as the Joule–Kelvin effect or Kelvin–Joule effect) describes the temperature change of a real gas or liquid (as differentiated from an ideal gas) when it is expanding, typically caused by the pressure loss from flow through a valve or porous plug while keeping it insulated so that no heat is exchanged with the environment. This procedure is called a throttling process or Joule–Thomson process. The effect is purely due to deviation from ideality, as any ideal gas has no JT effect. At room temperature, all gases except hydrogen, helium, and neon cool upon expansion by the Joule–Thomson process when being throttled through an orifice; the temperature of hydrogen, helium and neon rises when they are forced through a porous plug at room temperature, but lowers when they are already at lower temperatures. The temperature at which the JT effect switches algebraic sign is the inversion temperature. The gas-cooling throttling process is commonly exploited in refrigeration processes such as liquefiers in air separation industrial process. Most liquids such as hydraulic oils will be warmed by the Joule–Thomson throttling process. In hydraulics, the warming effect from Joule–Thomson throttling can be used to find internally leaking valves as these will produce heat which can be detected by thermocouple or thermal-imaging camera. 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 their performance. Since it is a constant-enthalpy process, it can be used to experimentally measure the lines of constant enthalpy (isenthalps) on the ( p , T ) {\displaystyle (p,T)} diagram of a gas. Combined with the specific heat capacity at constant pressure c P = ( ∂ h / ∂ T )...