In a system sealed by dry gas

the Joule-Thomson (JT) effect occurs when the gas flows through the components of filters

valves

orifices and end faces

which may cause the temperature drop of sealing gas

even the appearance of liquid condensation. Generally

the Joule-Thomson effect is represented by Joule-Thomson coefficient. As to the hydrogen

nitrogen

air and carbon dioxide

which are often encountered for the cases of sealing by dry gas

the corresponding Joule-Thomson (JT) coefficients were calculated by four classical equations of state (EOS) of VDW

RK

SRK and PR. Subsequently

those calculated coefficients are compared with the experimental data in the literatures. The JT coefficient curves and Joule-Thomson inversion curves (JTIC) were plotted using the optimal equation of state. As to air and nitrogen through the end faces of dry sealing gas

the gas temperature drops caused by JT effect were calculated by applying the computer program. It shows that the Joule-Thomson effect of real gas

which have important influence on the throttle of dry sealing gas. At room temperature

hydrogen showed exothermic effect

while nitrogen

air and carbon dioxide endothermic (cooling) effect. The corresponding Joule-Thomson (JT) coefficients were calculated by the four classical EOS

the average relative error and maximum relative error of RK equation were the minimum

less than 4% and 10%

respectively. The JT effect of real gas causes large temperature difference in the dry sealing gas

of which the gas pressure more influences on the temperature drop than the gas temperature does. When the pressure is small

the temperature drop by the JT effect can be negligible.