Fig. 2.31, a gas typically has two inversion temperatures, one at high temperature and
the other at low.
The ‘Linde refrigerator’ makes use of Joule–Thompson expansion to liquefy gases
(Fig. 2.32). The gas at high pressure is allowed to expand through a throttle; it cools
and is circulated past the incoming gas. That gas is cooled, and its subsequent expansion
cools it still further. There comes a stage when the circulating gas becomes so cold
that it condenses to a liquid.
For a perfect gas, μ = 0; hence, the temperature of a perfect gas is unchanged by
Joule–Thomson expansion. (Simple adiabatic expansion does cool a perfect gas,
because the gas does work, Section 2.6.) This characteristic points clearly to the
involvement of intermolecular forces in determining the size of the effect. However,
the Joule–Thomson coefficient of a real gas does not necessarily approach zero as the
pressure is reduced even though the equation of state of the gas approaches that of
a perfect gas. The coefficient behaves like the properties discussed in Section 1.3b in
the sense that it depends on derivatives and not on p, V, and T themselves
Fig. 2.31, a gas typically has two inversion temperatures, one at high temperature andthe other at low.The ‘Linde refrigerator’ makes use of Joule–Thompson expansion to liquefy gases(Fig. 2.32). The gas at high pressure is allowed to expand through a throttle; it coolsand is circulated past the incoming gas. That gas is cooled, and its subsequent expansioncools it still further. There comes a stage when the circulating gas becomes so coldthat it condenses to a liquid.For a perfect gas, μ = 0; hence, the temperature of a perfect gas is unchanged byJoule–Thomson expansion. (Simple adiabatic expansion does cool a perfect gas,because the gas does work, Section 2.6.) This characteristic points clearly to theinvolvement of intermolecular forces in determining the size of the effect. However,the Joule–Thomson coefficient of a real gas does not necessarily approach zero as thepressure is reduced even though the equation of state of the gas approaches that ofa perfect gas. The coefficient behaves like the properties discussed in Section 1.3b inthe sense that it depends on derivatives and not on p, V, and T themselves
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