Which concept refers to the change in sign of the Joule-Thomson coefficient?

The Joule-Thomson coefficient is a measure of how a gas's temperature changes when it expands at constant enthalpy. The sign of this coefficient indicates whether the gas cools or heats upon expansion. At temperatures below the inversion temperature, most gases cool upon expansion, while above this temperature, they heat. Therefore, the inversion temperature is the point where the Joule-Thomson coefficient changes sign.

This concept is significant in thermodynamics and understanding gas behavior during processes such as throttling, where a gas expands through a valve or porous plug under adiabatic conditions. Recognizing the inversion temperature helps in selecting applications for gas liquefaction, cooling systems, and understanding thermodynamic cycles.

Phase transitions refer to changes between states of matter, while adiabatic and isothermal processes describe specific conditions of temperature and heat exchange, but do not specifically address the conditions under which the Joule-Thomson coefficient changes sign.