The basics of the Joule-Thomson Effect

…a temperature change can occur in a gas as a result of a sudden pressure change over a valve.

Summary of the Joule-Thomson Effect and Recommendations

Most gases at normal temperatures are slightly cooled at throttling, with the exception of hydrogen, helium, and neon. The internal cooling happens because heat is converted to work that is exerted to overcome intermolecular forces. Ideal gas relations disregard any intermolecular forces and thus miss out on the Joule-Thomson effect. As such, relying only on ideal gas law assumptions when doing flow calculations with computational tools can be risky…

Well said! We have this remarkable effect to thank for most refrigeration processes, such as air conditioners and heat pumps, which keep us cool in the summers and warm in the winters. My Dad was an HVAC contractor, so I learned at an early age about the Joule-Thomson effect, by feeling the lines into and out of the expansion valve or capillary tube. HooRah, science in action!

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The Joule-Thompson effect is a very minor part of standard refrigeration cycles, which rely mainly on the latent heat of the phase change between liquid and vapor. With J-T expansion there is no phase change.


Yep, better said than me!