= Liquefaction of gases
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= Liquefaction
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Liquefaction converts a <gas> into a <liquid>. For a pure substance below its <liquid-gas critical point>, compression can cross the liquid–vapor coexistence boundary; cooling can also bring a vapor to its saturation condition. Above the critical <temperature>, pressure alone does not produce a distinct liquid–vapor transition.
A practical cycle removes compression heat and cools the gas before collecting the liquid. The <Joule-Thomson effect> can provide cooling during expansion in the appropriate regime, but its sign depends on the gas and operating conditions. The collected liquid releases <latent heat> as it forms, so sustained production requires continued heat removal. These requirements explain why a high-pressure vessel alone is not a general liquefier.
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