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other usesstack| Steam is the technical term for water vapor , the gaseous phase of water , which is formed when water boiling|boils . In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air . At lower pressures, such as in the upper atmosphere or at the top of high mountains water boils at a lower temperature than the nominal convert|100|°C|°F at standard temperature and pressure . If heated further it becomes superheated steam .
The enthalpy of vaporization is the energy required to turn water into the gaseous form when it increases in volume by 1,600 times at standard temperature and pressure; this change in volume can be converted into Work (physics)|mechanical work by steam engine s and steam turbine s. Steam engines played a central role to the Industrial Revolution and modern steam turbines are used to generate electricity . If liquid water comes in contact with a very hot substance (such as lava , or molten metal) it can create a steam explosion . Steam explosions have been responsible for many foundry accidents and may also have been responsible for much of the damage to the plant in the Chernobyl accident .
Types of steam and conversion
Water vapor that includes water droplets is described as wet steam . As wet steam is heated further, the droplets evaporate, and at a high enough temperature (which depends on the pressure) all of the water evaporates and the system is in vapor-liquid equilibrium .cite book|author=Singh, R Paul|year=2001|title=Introduction to Food Engineering|publisher=Academic Press|isbn=ISBN 978-0-12-646384-2
Superheated steam is steam at a temperature higher than its boiling point for the pressure which only occurs where all the water has evaporated or has been removed from the system.cite web|url= http://www.spiraxsarco.com/resources/steam-engineering-tutorials/steam-engineering-principles-and-heat-transfer/superheated-steam.asp|title=Superheated Steam : International site for Spirax Sarco
Steam table s contain thermodynamic data for water/steam and are often used by engineers and scientists in design and operation of equipment where thermodynamic cycles involving steam are used. Additionally, thermodynamic phase diagram s for water/steam, such as a temperature-entropy diagram or a Mollier diagram shown in this article, may be useful. Steam charts are also used for analysing thermodynamic cycles.
enthalpy-entropy (h-s) diagram for steam
Uses
Agricultural
In agriculture , steam is used for soil steam sterilization|soil sterilization to avoid the use of harmful chemical agents and increase soil health.
Domestic
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.
Electricity generation (and cogeneration)
About 90% of all electricity is Electricity generation|generated using steam as the working fluid , nearly all by steam turbine s.cite book |title=Energy resources: occurrence, production, conversion, use|last= Wiser |first= Wendell H. |authorlink= Wendell H. Wiser |year= 2000 |publisher= Birkhäuser |isbn= 978-0-387-98744-6 |page= 190 |url= http://books.google.com/books? id=UmMx9ixu90kC& pg=PA190& dq=electrical+power+generators+steam+percent& hl=en& ei=JppoTpVexNmBB4C72MkM& sa=X& oi=book_result& ct=result& resnum=2& ved=0CDgQ6AEwATgK#v=onepage& q=steam& f=false
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 through a district heating system to provide heat energy after its use in the electric generation cycle. The world's biggest steam generation system is the New York City steam system which pumps steam into 100,000 buildings in Manhattan from seven cogeneration plants.Carl Bevelhymer, http://www.gothamgazette.com/article/issueoftheweek/20031110/200/674 "Steam", Gotham Gazette , November 10, 2003
Energy storage
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 thermal energy because of water's high heat of vaporization .
Fireless locomotive#Steam|Fireless steam locomotive s were steam locomotive s that operated from a supply of steam stored on-board in a large tank resembling a conventional locomotive's boiler. This tank was filled by process steam , as is available in many sorts of large factory, such as paper mill s. The locomotive's propulsion used pistons and connecting rods, as for a typical steam locomotive. These locomotives were mostly used in places where there was a risk of fire from a boiler's firebox, but were also used in factories that simply had a plentiful supply of steam to spare.
Lifting gas
Owing to its low molecular mass, steam is an effective lifting gas , providing approximately 60% as much lift as helium and twice as much as hot air. It is not flammable, unlike hydrogen, and is cheap and abundant, unlike helium. The required heat, however, leads to condensation problems and requires an insulated envelope. These factors have limited its use thus far to mostly demonstration projects. http://www.flyingkettle.com/jbfa.htm Steam Balloon JBFA Article
Mechanical effort
A steam engine and steam turbines use the expansion of steam to drive a piston or turbine to perform mechanical work . The ability to return condensed steam as water-liquid to the boiler at high pressure with relatively little expenditure of pumping power is important. Condensation of steam to water often occurs at the low-pressure end of a steam turbine, since this maximizes the Energy conversion efficiency|energy efficiency , but such wet-steam conditions have to be limited to avoid excessive turbine blade erosion. Engineers use an idealised thermodynamic cycle , the Rankine cycle , to model the behavior of steam engines. Steam turbines are often used in the production of electricity.
Sterilization
An autoclave , which uses steam under pressure, is used in microbiology laboratories and similar environments for Sterilization (microbiology)|sterilization .
Steam in piping
Steam is used in piping for utility lines. It is also used in jacketing and tracing of piping to maintain the uniform temperature in pipelines and vessels.
Wood treatment
Steam is used in the process of wood bending, killing insects and increasing plasticity.
Concrete treatment
Steam is used to accentuate drying especially in prefabricates.
Cleaning
Used in cleaning of fibers, sometimes prior to painting.
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
Oxyhydrogen
Psychrometrics — moist air/vapor 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.steamtablesonline.com Free Steam Tables Online calculator based on IAPWS-IF97 (MegaWatSoft)
http://www.dofmaster.com/steam.html Online Steam Tables Calculator based on IFC-67
http://freesteam.sourceforge.net freesteam a free software|free ( GPL ) Library_(computer_science)|library for calculation of steam properties using the IAPWS-IF97 standard.
http://www.i2c2.aut.ac.nz/Resources/Software/JSteamDLL.html JSteam A Windows library and free calculator for the calculation of steam properties using the IAPWS-IF97-07 standards.
http://www.i2c2.aut.ac.nz/Resources/Software/JSteamExcel.html JSteam Excel Add In An Excel add in for modelling and solving steam utility systems using the JSteam library.
Category:Forms of water Category:Water in gas Category:Steam power|
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