JOULE-THOMSON PROCESS

JOULE-THOMSON EFFECT

The Joule–Thomson effect (also known as the Joule–Kelvin effect or Kelvin–Joule effect) describes the temperature change of a real gas or liquid (as differentiated from an ideal gas) when it is forced through a valve or porous plug while keeping it insulated so that no heat is exchanged with the environment.

When a fluid flows through a restriction, such as an orifice, a partly closed valve, or a porous plug, without any appreciable change in lunatic or potential energy, the primary result of the process is a pressure drop in the fluid. Such a throttling process produces no shaft work and in the absence of heat transfer. The process, therefore, occurs at constant enthalpy. Since the enthalpy of an ideal gas depends on temperature only, a throttling process does not change the temperature of an ideal gas. For most real gases at moderate conditions of temperature and pressure, a reduction in pressure at constant enthalpy generally results in a decrease in temperature.

In order to determine whether the temperature is going to increase or decrease, the inversion temperature of the real gas should be considered. The inversion temperature in thermodynamics is the critical temperature below which a non-ideal gas (all gases in reality) that is expanding at constant enthalpy will experience a temperature decrease and above which will experience a temperature increase. This temperature change is known as the Joule-Thomson effect and is exploited in the liquefaction of gases.

DAILY LIFE EXAMPLE:

• Natural gas pressure reduction

NATURAL GAS PRESSURE REDUCTION

Natural gas is transferred through high-pressure pipelines. But, the pressure is needed to be reduced to supply local chain lines. For pressure reduction, restriction valves are used. While natural gas passes through the restriction valve, pipelines are covered with a thin layer of ice due to the cooling effect of pressure reduction.