Steam
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224364358
2008-07-08T15:05:03Z
EdJogg
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Reverted edits by [[Special:Contributions/70.240.197.127|70.240.197.127]] ([[User talk:70.240.197.127|talk]]) to last version by HenkvD
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{| align="right"
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|[[Image:Yellowstone Steam.jpg|thumb|300px|Mist rises from a [[hot spring]] in [[Yellowstone Park]]]]
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|[[Image:TS-Wasserdampf engl.png|thumb|300px|A temperature-versus-entropy diagram for steam]]
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|[[Image:HS-Wasserdampf engl.png|thumb|300px|A [[Richard Mollier|Mollier]] enthalpy-versus-entropy [[Mollier diagram|diagram]] for steam]]
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In [[physical chemistry]], and in [[engineering]], '''steam''' refers to vaporized water. It is a pure, completely invisible [[gaseous phase|gas]] (for [[mist]] see below). At [[standard temperature and pressure]], pure steam (unmixed with air, but in equilibrium with liquid water) occupies about 1,600 times the volume of liquid water. In the atmosphere, the [[partial pressure]] of water is much lower than 1 atm, therefore gaseous water can exist at temperatures much lower than 100 C (see [[water vapor]] and [[humidity]]).
''In common speech,'' '''steam''' most often refers to the white [[mist]] that condenses above boiling water as the hot vapor ("steam" in the first sense) mixes with the cooler air. This mist is made of tiny droplets of liquid water, not gaseous water, so it is no longer technically steam. In the spout of a steaming kettle, the spot where there is no condensed water vapor, where there appears to be nothing there, is steam.
==Uses==
A [[steam engine]] uses the expansion of steam in order to drive a [[piston]] or [[turbine]] to perform [[mechanical work]]. In other industrial applications steam is used for [[energy storage]], which is introduced and extracted by heat transfer, usually through pipes. Steam is a capacious reservoir for energy because of water's high [[heat of vaporization]]. The ability to return condensed steam as water-liquid to the boiler at high pressure with relatively little expenditure of pumping power is also important. Engineers use an idealised thermodynamic cycle, the [[Rankine cycle]], to model the behaviour of steam engines.
In the U.S., more than 86% of electric power is produced using steam as the [[working fluid]], nearly all by steam turbines. Condensation of steam to water often occurs at the low-pressure end of a steam turbine, since this maximises the energy efficiency, but such wet-steam conditions have to be limited to avoid excessive turbine blade erosion.
When liquid water comes in contact with a very hot substance (such as [[lava]], or molten metal) it can flash into steam very quickly; this is called a '''[[steam explosion]]'''. Such an explosion was probably responsible for much of the damage in the [[Chernobyl accident]] and for many so-called 'foundry accidents'.
Steam's capacity to transfer heat is also used in the home: for cooking vegetables, steam cleaning of fabric and carpets, and heating buildings. In each case, water is heated in a boiler, and the steam carries the energy to a target object. "[[Steam shower]]s" are actually low-temperature mist-generators, and do not actually use steam.
In electric generation, steam is typically condensed at the end of its expansion cycle, and returned to the boiler for re-use. However in [[cogeneration]], steam is piped into buildings to provide heat energy after its use in the electric generation cycle. The world's biggest steam generation system is [[Con Edison]] in [[New York City]] which pumps steam into 100,000 buildings in [[Manhattan]] from seven cogeneration plants.<ref>Carl Bevelhymer, [http://www.gothamgazette.com/article/issueoftheweek/20031110/200/674 "Steam"], ''[[Gotham Gazette]]'', [[November 10]], [[2003]]</ref>
{{clear}}
==See also==
{{wiktionary}}
{{commonscat|Water vapor}}
*[[Electrification]]
*[[Food steamer]] or steam cooker
*[[Geyser]]—''geothermally-generated steam''
*[[IAPWS]]—''an association that maintains international-standard correlations for the [[thermodynamic]] properties of steam, including IAPWS-IF97 (for use in industrial simulation and modelling) and IAPWS-95 (a general purpose and scientific correlation).''
*[[Industrial Revolution]]
*[[Live steam]]
*[[Mass production]]
*[[Nuclear power]]—and [[power plant]]s ''use steam to generate electricity''
*[[Psychrometrics]]—''moist air/vapour mixtures, humidity and air conditioning''
*[[Steam locomotive]]
==References==
{{reflist}}
==External links==
*[http://webbook.nist.gov/chemistry/fluid/ Steam Tables & Charts by National Institute of Standards and Technology, NIST]
* [http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-engineering-principles-and-heat-transfer/what-is-steam.asp What Is Steam?] ''(general article about the properties of water/steam)''
* [http://www.cheresources.com/steam_tracing.shtml Steam Tracing]
* [http://www.spiraxsarco.com/resources/steam-tables.asp Online steam properties] calculator (Spirax Sarco)
* [http://twt.mpei.ac.ru/ochkov/WSPHB/Engindex.html] Steam Tables & Charts with Mathcad Calculation server
[[Category:Forms of water]]
[[Category:Water in gas]]
[[Category:Steam power| ]]
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