It followed upon earlier work by joule on joule expansion, in which a gas undergoes free expansion in a vacuum and the temperature is unchanged, if the gas is ideal. In 1852, working with william thomson (who would later become lord kelvin), joule conducted an experiment in which they pumped gas at a steady rate through a lead pipe that was cinched to create a construction. At ordinary temperatures and pressures, all real gases except hydrogen and helium cool upon such expansion This phenomenon often is used in liquefying gases. This process, known as a throttling or isenthalpic expansion, occurs when a gas is forced through a porous plug or valve from a region of high pressure to low pressure. Its role in gas dynamics, cooling, and pressure changes, and applications in refrigeration and engineering.
There is no heat exchange between the gas and the pipe. This process is done under adiabatic and constant enthalpy conditions.
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