Liquid air: Difference between revisions
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== Application == |
== Application == |
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In manufacturing processes the liquid air product is fractionated into its constituent gases in liquid or gaseous form, as the oxygen is especially useful for use in [[Oxy-fuel welding and cutting|fuel gas welding and cutting]], and the argon is useful as an oxygen-excluding [[shielding gas]] in |
In manufacturing processes the liquid air product is fractionated into its constituent gases in liquid or gaseous form, as the oxygen is especially useful for use in [[Oxy-fuel welding and cutting|fuel gas welding and cutting]], and the argon is useful as an oxygen-excluding [[shielding gas]] in [[gas tungsten arc welding]], while [[Liquid nitrogen]] is useful in various low-temperature applications, being nonreactive at normal temperatures (unlike the oxygen) and boiling at {{convert|77|K|0}}. During World War Two, Nazi Germany reportedly experimented with a bomb made from liquid air and coal dust. <ref>Stevens, Henry, ''Hitler's Supressed and Still-Secret Weapons, Science and Technology.'' Adventures Unlimited Press: Kempton, Illinois. 2007, pp. 30-36, 91-102.</ref> |
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== See also == |
== See also == |
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Revision as of 04:20, 10 September 2011
- For the automobile, see Liquid Air.
- For the Air Liquide album, see Liquid Air (EP).
 | This article needs attention from an expert in Chemistry. Please add a reason or a talk parameter to this template to explain the issue with the article. (August 2008) |
Liquid air is air that has been cooled to very low temperatures (cryogenic temperatures) so that it has condensed to a pale blue mobile liquid. To protect it from room temperature, it must be kept in a vacuum flask. Liquid air can absorb heat rapidly and revert to its gaseous state. It is often used for condensing other substances into liquid and/or solidifying them, and as an industrial source of nitrogen, oxygen, argon, and other inert gases through a process called air separation. Liquid air is also replacing liquid nitrogen for theatrical smoke and fog effects.
Properties
Liquid air has a density of approximately 870 kg/m3 (0.87 g/cm3), though the density may vary depending on the elemental composition of the air. Since gaseous air has 78% nitrogen and 21% oxygen, the density of liquid air at standard composition is calculated by the percentage of the components and their respective liquid densities, see liquid nitrogen and liquid oxygen. The boiling point of liquid air is approximately 78 K (-195 °C)(-319 F), and it freezes at approximately 58 K (-215 °C)(-355 F). Liquid air is hard to keep at a stable composition, since the nitrogen will boil preferentially to the oxygen, and it can easily become oxygen rich air.
Preparation
Principle of production
The constituents of air were once known as "permanent gases" as they could not be liquified solely by compression at room temperature. A compression process will raise the temperature of the gas. This heat is removed by cooling to the ambient temperature in a heat exchanger and then the gas is expanded by venting into a chamber. This expansion causes a lowering of the temperature and by counter-flow heat exchange of the expanded air the pressurized air entering the expander is further cooled. With sufficient compression, flow, and heat removal eventually droplets of liquid air will form which may then be employed directly for low temperature demonstrations. (A device for such production is simple enough to be fabricated by the experimenter using commonly available materials.)
Process of manufacture
The most common process for the preparation of liquid air is the two-column Hampson-Linde cycle using the Joule-Thomson effect. Air is fed at high pressure >60 psig (520 kPa) into the lower column, in which it is separated into pure nitrogen and oxygen-rich liquid. The rich liquid and some of the nitrogen are fed as reflux into the upper column, which operates at low pressure <10 psig (170 kPa), where the final separation into pure nitrogen and oxygen occurs. A raw argon product can be removed from the middle of the upper column for further purification.[1]
Application
In manufacturing processes the liquid air product is fractionated into its constituent gases in liquid or gaseous form, as the oxygen is especially useful for use in fuel gas welding and cutting, and the argon is useful as an oxygen-excluding shielding gas in gas tungsten arc welding, while Liquid nitrogen is useful in various low-temperature applications, being nonreactive at normal temperatures (unlike the oxygen) and boiling at 77 K (−196 °C; −321 °F). During World War Two, Nazi Germany reportedly experimented with a bomb made from liquid air and coal dust. [2]
See also
References
- ^ "Air liquefaction, "Linde Air", rectification: into new markets with new research findings". The Linde Group. Retrieved 2007-08-09.
- ^ Stevens, Henry, Hitler's Supressed and Still-Secret Weapons, Science and Technology. Adventures Unlimited Press: Kempton, Illinois. 2007, pp. 30-36, 91-102.