JouleThomsonKühlung

Joule-Thomson cooling, also known as the Joule-Thomson effect or Kelvin-Joule effect, describes the temperature change of a real gas or liquid when it is subjected to a throttling process, meaning it expands freely through a valve or porous plug while its enthalpy remains constant. This phenomenon is distinct from adiabatic expansion, where the gas does no external work and its internal energy changes.

The Joule-Thomson effect depends on the initial temperature and pressure of the gas and its specific properties. For most gases at room temperature and atmospheric pressure, this effect results in cooling when they expand. However, there are inversion temperatures above which the gas will heat up upon throttling. For example, hydrogen and helium must be pre-cooled below their inversion temperatures before they can be liquefied using the Joule-Thomson effect.

This principle is fundamental to many refrigeration and liquefaction processes. It is employed in industrial applications such as the liquefaction of gases like nitrogen and oxygen, and in cryogenic systems. Understanding the Joule-Thomson effect allows for the design of efficient cooling cycles by selecting appropriate gases and operating conditions. The magnitude of the temperature change is quantified by the Joule-Thomson coefficient, which relates the change in temperature to the change in pressure at constant enthalpy.