Liquid air
Encyclopedia
- For the Air Liquide album, see Liquid Air (EP)Liquid Air (EP)Liquid Air EP is the second EP by German electronic band Air Liquide, which was released in 1992.-Side B:# "Liquid Men With Liquid Hearts"# "Psy 9"# "Liquid Air "...
.
Liquid air is air that has been cooled to very low temperatures (cryogenic temperatures
Cryogenics
In physics, cryogenics is the study of the production of very low temperature and the behavior of materials at those temperatures. A person who studies elements under extremely cold temperature is called a cryogenicist. Rather than the relative temperature scales of Celsius and Fahrenheit,...
) so that it has condensed to a pale blue mobile liquid. To protect it from room temperature
Room temperature
-Comfort levels:The American Society of Heating, Refrigerating and Air-Conditioning Engineers has listings for suggested temperatures and air flow rates in different types of buildings and different environmental circumstances. For example, a single office in a building has an occupancy ratio per...
, it must be kept in a vacuum flask
Vacuum flask
A vacuum flask is an insulating storage vessel which keeps its contents hotter or cooler than its surroundings. Invented by Sir James Dewar in 1892, the vacuum flask consists of two flasks, placed one within the other and joined at the neck...
. 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
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
, oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, argon
Argon
Argon is a chemical element represented by the symbol Ar. Argon has atomic number 18 and is the third element in group 18 of the periodic table . Argon is the third most common gas in the Earth's atmosphere, at 0.93%, making it more common than carbon dioxide...
, and other inert gas
Inert gas
An inert gas is a non-reactive gas used during chemical synthesis, chemical analysis, or preservation of reactive materials. Inert gases are selected for specific settings for which they are functionally inert since the cost of the gas and the cost of purifying the gas are usually a consideration...
es through a process called air separation
Air separation
An air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen sometimes also argon and rarely other inert gases. There are various technologies that are used for the separation process, the most common is via cryogenic distillation. This process was...
. Liquid air is also replacing liquid nitrogen for theatrical smoke and fog
Theatrical smoke and fog
Theatrical smoke and fog, also known as special effect smoke, fog or haze, is a category of atmospheric effects used in the entertainment industry. The use of fog can be found throughout motion picture and television productions, live theatre, concerts, at nightclubs and raves, amusement and theme...
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 nitrogenLiquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
and liquid oxygen
Liquid oxygen
Liquid oxygen — abbreviated LOx, LOX or Lox in the aerospace, submarine and gas industries — is one of the physical forms of elemental oxygen.-Physical properties:...
. 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.
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 cycleHampson-Linde cycle
The Hampson–Linde cycle is based on the Joule-Thomson effectand is used in the liquefaction of gases. W. Hampson and Carl von Linde independently filed for patent of the cycle in 1895.-External links:*...
using the Joule-Thomson effect
Joule-Thomson effect
In thermodynamics, the Joule–Thomson effect or Joule–Kelvin effect or Kelvin–Joule effect describes the temperature change of a gas or liquid when it is forced through a valve or porous plug while kept insulated so that no heat is exchanged with the environment. This procedure is called a...
. 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
Liquid
Liquid is one of the three classical states of matter . Like a gas, a liquid is able to flow and take the shape of a container. Some liquids resist compression, while others can be compressed. Unlike a gas, a liquid does not disperse to fill every space of a container, and maintains a fairly...
. 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.
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 cuttingOxy-fuel welding and cutting
Oxy-fuel welding and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop oxygen-acetylene welding in 1903...
, and the argon is useful as an oxygen-excluding shielding gas
Shielding gas
Shielding gases are inert or semi-inert gases that are commonly used in several welding processes, most notably gas metal arc welding and gas tungsten arc welding . Their purpose is to protect the weld area from atmospheric gases, such as oxygen, nitrogen, carbon dioxide, and water vapour...
in gas tungsten arc welding
Gas tungsten arc welding
Gas tungsten arc welding , also known as tungsten inert gas welding, is an arc welding process that uses a nonconsumable tungsten electrode to produce the weld...
, while Liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
is useful in various low-temperature applications, being nonreactive at normal temperatures (unlike the oxygen) and boiling at 77 K. During World War Two, Nazi Germany reportedly experimented with a bomb made from liquid air and coal dust.
See also
- Liquefaction of gasesLiquefaction of gasesLiquefaction of gases includes a number of phases used to convert a gas into a liquid state. 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...
- Air SeparationAir separationAn air separation plant separates atmospheric air into its primary components, typically nitrogen and oxygen sometimes also argon and rarely other inert gases. There are various technologies that are used for the separation process, the most common is via cryogenic distillation. This process was...
- Industrial gases