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Liquefaction of gases

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Title: Liquefaction of gases  
Author: World Heritage Encyclopedia
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Subject: Liquefaction, Noble gas, Liquefied gas, Inversion temperature, List of industrial processes
Collection: Gas Technologies, Industrial Gases, Industrial Processes, Phases of Matter
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Liquefaction of gases

Liquid nitrogen

Liquefaction of gases is physical conversion of a gas into a liquid state (condensation).


  • Details 1
  • History 2
  • Liquid air 3
    • Linde's Process 3.1
    • Claude's Process 3.2
  • See also 4
  • External links 5


The processes are used for scientific, industrial and commercial purposes. Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as carbon dioxide, require pressurization as well. Liquefaction is used for analyzing the fundamental properties of gas molecules (intermolecular forces), for storage of gases, for example: LPG, and in refrigeration and air conditioning. There the gas is liquefied in the condenser, where the heat of vaporization is released, and evaporated in the evaporator, where the heat of vaporization is absorbed. Ammonia was the first such refrigerant, and is still in widespread use in industrial refrigeration, but it has largely been replaced by compounds derived from petroleum and halogens in residential and commercial applications.

phosgene gas.

Liquefaction of helium (4He) with the precooled Hampson-Linde cycle led to a Nobel Prize for Heike Kamerlingh Onnes in 1913. At ambient pressure the boiling point of liquefied helium is 4.22 K (-268.93°C). Below 2.17 K liquid 4He becomes a superfluid (Nobel Prize 1978, Pyotr Kapitsa) and shows characteristic properties such as heat conduction through second sound, zero viscosity and the fountain effect among others.

The liquefaction of gases is a complicated process that uses various compressions and expansions to achieve high pressures and very low temperatures, using, for example, turboexpanders.

The liquefaction of air is used to obtain nitrogen, oxygen, and argon and other atmospheric noble gases by separating the air components by fractional distillation in a cryogenic air separation unit.


Liquid air

Linde's Process

Air is liquefied by the Linde process, in which air is alternately compressed, cooled, and expanded, each expansion results in a considerable reduction in temperature. With the lower temperature the molecules move more slowly and occupy less space, so the air changes phase to become liquid.

Claude's Process

Air can also be liquefied by Claude's process in which the gas is allowed to expand isentropically twice in two chambers. While expanding, the gas has to do work as it is led through an expansion turbine. The gas is not yet liquid, since it would destroy the turbine. Final liquefaction takes place by isenthalpic expansion in a Joule-Thomson-Valve.

See also

External links

  • Liquefaction of Gases
  • History of Liquefying Hydrogen - NASA

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