Liquid air


 * For the automobile, see Liquid Air

Liquid air is air that has been liquified by compression and cooled to very low temperatures. It must be kept in a Dewar flask at room temperature. Liquid air can absorb heat rapidly and revert to its gaseous state. It is often used for freezing other substances, and as a source of nitrogen, oxygen, argon, and other inert gases.

Properties
Liquified air has a density of approximately 870 kg/m3, 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 decimal percentage of the components by their respective liquid densities. See liquid nitrogen and liquid oxygen. Freezing Point: -216.7°C the Boiling Point is: -194.35°C

Manufacture of liquid air
The most common process for the preparation of liquid air is Carl von Linde's two-column 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.