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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.
For real gasses, the molecules do interact via attraction or repulsion depending on temperature and pressure, and heating or cooling does occur. This is known as the Joule–Thomson effect. For reference, the Joule–Thomson coefficient μ JT for air at room temperature and sea level is 0.22 °C/bar. [7]
Whereas the Siemens cycle has the gas do external work to reduce its temperature, the Hampson–Linde cycle relies solely on the Joule–Thomson effect; this has the advantage that the cold side of the cooling apparatus needs no moving parts. [1]
On the other hand, real-gas models have to be used near the condensation point of gases, near critical points, at very high pressures, to explain the Joule–Thomson effect, and in other less usual cases. The deviation from ideality can be described by the compressibility factor Z.
Joule's apparatus for measuring the mechanical equivalent of heat. Most established scientists, such as William Henry, [13] as well as Thomas Thomson, believed that there was enough uncertainty in the caloric theory to allow its adaptation to account for the new results. It had certainly proved robust and adaptable up to that time.
If a steady-state, steady-flow process is analysed using a control volume, everything outside the control volume is considered to be the surroundings. [2]Such a process will be isenthalpic if there is no transfer of heat to or from the surroundings, no work done on or by the surroundings, and no change in the kinetic energy of the fluid. [3]
In 2023, the U.S. imported $4.6 billion worth of tequila and $108 million worth of mezcal from Mexico, according to the Distilled Spirits Council of the United States, a trade group.
This temperature change is known as the Joule–Thomson effect, and is exploited in the liquefaction of gases. Inversion temperature depends on the nature of the gas. For a van der Waals gas we can calculate the enthalpy using statistical mechanics as