The Joule-Thomson effect describes the temperature change of a real gas during isenthalpic expansion – that is, when the gas expands through a valve, nozzle, or porous medium without any exchange of heat with its surroundings. Whether the gas cools down or heats up during this process depends on its inversion temperature: below this temperature, the gas cools upon expansion; above it, the gas warms up.

Application in refrigeration and heat pump systems

The effect is intentionally used in refrigeration and heat pump cycles, particularly during the expansion of the refrigerant  after condensation. The cooling generated during this process allows for efficient heat absorption in the evaporator. In high-temperature heat pumps, the suitability of the refrigerant and its inversion temperature must be carefully considered to ensure effective cooling during expansion.