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Steam

Steam

In physical chemistry and in engineering, steam refers to vaporized water. It is a pure, invisible gas (for mist see below), which at standard atmospheric pressure has a temperature of around 100 degrees Celsius, and occupies about 1,600 times the volume of liquid water (steam can of course be much hotter than the boiling point of water; such steam is usually called superheated steam). When liquid water comes in contact with a very hot liquid 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'. A steam engine uses the expansion of steam to drive a piston or turbine and so to perform mechanical work. In other industrial applications steam is used as a repository of energy, 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. Steam is used in saunas and steam showers to produce warmth and therapeutic effects in human beings. In the U.S., more than 90% of electric power is produced using steam as the working fluid, mainly 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 carefully controlled to avoid excessive blade erosion. 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. After gaseous steam has intermixed with air, it is no longer properly called steam and is instead referred to as water vapor. The [http://www.iapws.org/ International Association for the Properties of Water and Steam (IAPWS)], 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).

Physical chemistry

Physical Chemistry is the combined science of physics, chemistry, thermodynamics, and quantum mechanics which functions to provide molecular-level interpretations of observed macroscopic phenomena. Typically, changes in temperature, pressure, volume, heat, and work of systems in the solid, liquid, and or gas phase are correlated to microscopic atomic and molecular interactions. Most cite Willard Gibbs as the founder of physical chemistry as stemming from his 1876 paper: “On the Equilibrium of Heterogeneous Substances”, wherein such cornerstones as free energy, chemical potential, and phase rule were developed. Modern physical chemistry is firmly grounded upon physics. Important areas of study include chemical thermodynamics, chemical kinetics, quantum chemistry, statistical mechanics, electrochemistry, surface and solid state chemistry, and spectroscopy. Physical chemistry is also fundamental to modern materials science.

Important physical chemists

- Svante Arrhenius
- Richard Bernstein
- E.J. Bowen
- Peter Debye
- Manfred Eigen
- Richard R. Ernst
- William Giauque
- J.W. Gibbs
- Fritz Haber
- Dudley R. Herschbach
- Gerhard Herzberg
- Jaroslav Heyrovský
- Cyril Norman Hinshelwood
- J.H. van 't Hoff
- Roald Hoffmann
- Erich Hückel
- Friedrich Kohlrausch
- Irving Langmuir
- Yuan T. Lee
- Gilbert N. Lewis
- Frederick Lindemann
- Rudolph A. Marcus
- Robert S. Mulliken
- Walther Nernst
- Lars Onsager
- Wilhelm Ostwald
- Linus Pauling
- John Charles Polanyi
- Michael Polanyi
- Stuart A. Rice
- E. Bright Wilson
- Richard N. Zare
- Ahmed H. Zewail

Literature

- Physical Chemistry, P.W. Atkins, 1978, Oxford University Press ISBN 0-7167-3539-3
- Introduction to Modern Colloid Science, R.J. Hunter, 1993, Oxford University Press ISBN 0198553862
- Principles of Colloid and Surface Chemistry, P.C. Hiemenz, R. Rajagopalan, 1997, Marcel Dekker Inc., New York ISBN 0824793978
- Physical Chemistry, W.J. Moore, 1963 (4th Edition), Longmans, London/Prentice Hall, NJ, ISBN ???? Category:Applied and interdisciplinary physics ko:물리화학 ja:物理化学 th:เคมีฟิสิกส์

Vapor

Vapor (US English) or vapour (British English) is the gaseous state of matter. Although vapor and gas are frequently used interchangeably, vapor often carries the connotation of gaseous matter in a state of equilibrium with identical matter in a liquid or solid state below its boiling point. See the entry on vapor pressure for more information on this topic. The constituent atoms or molecules of a vapor possess vibrational, rotational, and translational motion. More information can be found under the entry of the Kinetic theory of gases. ------- Vapor is also the name of the Third-party Online Distribution Client written by "Valtrain" (SOE Lead Programmer) and other members of the Fired Okrea Team. More information on this subject can be found at [http://www.vapour-online.com/ Vapor Online]

Gaseous phase

:For other meanings see gas (disambiguation). ---- A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. Thus, as energy in the form of heat is added, a solid (e.g. ice) will first melt to become a liquid (e.g. water), which will then boil or evaporate to become a gas (e.g. water vapor). In some circumstances, a solid (e.g. "dry ice") can directly turn into a gas: this is called sublimation. If the gas is further heated, its atoms or molecules can become (wholly or partially) ionized, turning the gas into a plasma.

Properties of a gas

#All collisions are perfectly elastic #The gas fills the entire container #The molecules have negligible volume In the gas phase, the atoms or molecules constituting the matter basically move independently, with no forces keeping them together or pushing them apart. Their only interactions are rare and random collisions. The particles move in random directions, at high speeds, whose range is dependent on the temperature and defined by the Maxwell-Boltzmann distribution. Therefore, the gas phase is a completely disordered state. Following the second law of thermodynamics, gas particles will immediately diffuse to homogeneously fill any shape or volume of space that is made available to them. The thermodynamic state of a gas is characterized by its volume, its temperature, which is determined by the average velocity or kinetic energy of the molecules, and its pressure, which is determined by the average velocity and density or number of molecules. These variables are related by the fundamental gas laws, which state that the pressure in an ideal gas is proportional to its temperature and number of molecules, but inversely proportional to its volume. Like liquids and plasmas, gases are fluids: they have the ability to flow and do not tend to return to their former configuration after deformation, although they do have viscosity. Unlike liquids, however, unconstrained gases do not occupy a fixed volume, but expand to fill whatever space they occupy. The kinetic energy per molecule in a gas is the second greatest of the states of matter (after plasma). Because of this high kinetic energy, gas atoms and molecules tend to bounce off of any containing surface and off one another, the more powerfully as the kinetic energy is increased. A common misconception is that the collisions of the molecules with each other is essential to explain gas pressure, but in fact their random velocities are sufficient to define that quantity. Mutual collisions are important only for establishing the Maxwell-Boltzmann distribution. Gas particles are normally well separated, as opposed to liquid particles, which are in contact. A material particle (say a dust mote) in a gas moves in Brownian Motion. Since it is at the limit of (or beyond) current technology to observe individual gas particles (atoms or molecules), only theoretical calculations give suggestions as to how they move, but their motion is different from Brownian Motion. The reason is that Brownian Motion involves a smooth drag due to the frictional force of many gas molecules, punctuated by violent collisions of an individual (or several) gas molecule(s) with the particle. The particle (generally consisting of millions or billions of atoms) thus moves in a jagged course, yet not so jagged as we would expect to find if we could examine an individual gas molecule.

Etymology

The word "gas" was apparently coined in the early 17th century by the Belgian chemist Jan Baptist van Helmont, as a re-spelling of his pronunciation of the Greek word chaos.

Mist

:This article is about the weather phenomenon. For the computer game series see Myst. Mist is a phenomenon of a liquid in small droplets floating through air. It can occur naturally as part of natural weather or volcanic activity, and is common in cold air above hot water, in exhaled air in the cold, and in a steam room of a sauna. It can also be created artificially with aerosol canisters. Fog is closely related to mist. In many weather service purposes, the difference is decided to be that the visibility in fog is one kilometer or less, while in mist the visibility is between one and ten (or eight) kilometers. Seen from a distance, mist is blueish, while haze is more brownish. Strong superstitious and religious connotations are associated with mist in some cultures. Image:Misty hill02.jpg|Misty Hill Image:Heavy mist.jpg|Heavy Mist Image:Mist-panorama.jpg|Mist Panorama

External links

Category:Clouds Category:Meteorology Category:Psychrometrics Category:Weather

Boiling point

:Alternate use: Boiling Point, a film by Takeshi Kitano; Boiling Points, a television series The boiling point of a substance is the temperature at which it can change its state from a liquid to a gas throughout the bulk of the liquid. A liquid may change to a gas at temperatures below the boiling point through the process of evaporation. Any change of state from a liquid to a gas at boiling point is considered vaporization. However, evaporation is a surface phenomenon, in which only molecules located near the gas/liquid surface could evaporate. Boiling on the other hand is a bulk process, so at the boiling point molecules anywhere in the liquid may be vaporized, resulting in the formation of vapor bubbles. A somewhat clearer definition of boiling point is that it is the temperature at which the vapor pressure of the liquid equals the pressure of the environment. Something that should be remembered is that boiling is evidenced by the appearance of bubbles containing vapor from the liquid. Production of this vapor requires energy and thus does not occur without some source of energy. This source can be a hot surface or even the liquid itself. Hot liquid will boil as it rises through the bulk liquid when the pressure of the environment drops to the vapor pressure of the liquid at its temperature. This production of vapor will quickly stop because the temperature of the liquid will be reduced by the vaporization thus reducing the vapor pressure. The element with the lowest boiling point is helium. Both the boiling points of rhenium and tungsten exceed 5000 K at standard pressure. Due to the experimental difficulty of precisely measuring extreme temperatures without bias, there is some discrepancy in the literature as to whether tungsten or rhenium has the higher boiling point. The boiling point corresponds to the temperature at which the vapor pressure of the substance equals the ambient pressure. Thus the boiling point is dependent on the pressure. Usually, boiling points are published with respect to standard pressure (101.325 kilopascals or 1 atm). At higher elevations, where the atmospheric pressure is much lower, the boiling point is also lower. The boiling point increases with increased ambient pressure up to the critical point, where the gas and liquid properties become identical. The boiling point cannot be increased beyond the critical point. Likewise, the boiling point decreases with decreasing ambient pressure until the triple point is reached. The boiling point cannot be reduced below the triple point. The process of changing from a liquid to a gas requires an amount of heat called the latent heat of vaporization. As heat is added to a liquid at its boiling point, all of this heat goes toward the phase change from liquid to gas, thus the temperature of the substance remains constant even though heat has been added. The word latent, which comes from Latin and means hidden, is used to describe this "disappearing" heat that is added, but doesn't result in an increase in temperature. Since heat is added with no corresponding change in temperature, the heat capacity of the liquid is essentially infinite at the boiling point.
Intermolecular interactions
In terms of intermolecular interactions, the boiling point represents the point at which the liquid molecules possess enough heat energy to overcome the various intermolecular attractions binding the molecules into the liquid (eg. dipole-dipole attraction, instantaneous-dipole induced-dipole attractions, and hydrogen bonds). Therefore the boiling point is also an indicator of the strength of these attractive forces. The boiling point of water is 100 °C (212 °F) at standard pressure. On top of Mount Everest the pressure is about 260 mbar (26 kPa) so the boiling point of water is 69 °C. For purists with a knowledge of thermodynamics, the normal boiling point of water is 99.97 degrees Celsius (at a pressure of 1 atm, i.e. 101.325 kPa). Until 1982 this was also the standard boiling point of water, but the IUPAC now recommends a standard pressure of 1 bar (100 kPa). At this slightly reduced pressure, the standard boiling point of water is 99.61 degrees Celsius. (Cf. DeVoe, Howard, Thermodynamics and Chemistry. Prentice-Hall, 2001)
See also

- Leidenfrost effect
- flash point
- boiling delay
- critical temperature
- triple point
- boiling-point elevation Category:Chemical properties Category:Thermodynamics Category:Fluid dynamics ko:끓는점 ja:沸点 th:จุดเดือด

Steam explosion

A steam explosion (also called a littoral explosion, or fuel-coolant interaction, fci) is a violent boiling or flashing of water into steam, occurring when water is either superheated, or rapidly heated by fine hot debris produced within it. Pressure vessels that operate at above atmospheric pressure can also provide the proper conditions for a steam explosion. The water changes from a liquid to a gas with extreme speed, increasing dramatically in volume. A steam explosion sprays steam and boiling-hot water and the hot medium that heated it in all directions (if not otherwise confined, e.g. by the walls of a container), creating a danger of scalding and burning. Steam explosions are not normally chemical explosions, although a number of substances will react chemically with steam (for example, zirconium reacts with steam to give off hydrogen, which burns violently in air) so that chemical explosions and fires often follow. Some steam explosions appear to be special kinds of Boiling Liquid Expanding Vapor Explosion, and rely on release of stored superheat. But many large-scale events (eg 'Foundry Accidents') show evidence of an energy-release front propagating through the material (see description of fci below), where the forces created fragment and mix the hot phase into the cold volatile one; the rapid heat transfer at the front sustains the propagation. Steam explosions are often encountered where hot lava meets sea water. A dangerous steam explosion can be created when liquid water encounters hot, molten metal. As the water explodes into steam, it splashes the burning hot liquid metal along with it, causing an extreme risk of severe burns to anyone located nearby and creating a fire hazard. Events of this general type are also possible if, under extreme circumstances, the fuel of a liquid-cooled nuclear reactor becomes molten. Such explosions are known as fuel-coolant interactions or FCI. In these events the passage of the pressure wave through the predispersed material creates flow forces which further fragment the melt, resulting in rapid heat transfer, and thus sustaining the wave. Much of the destruction in the Chernobyl accident is thought to have been due to such a steam explosion. In a full-fledged nuclear meltdown, the most severe outcomes would be those leading to early containment failure. Two possibilities are the ejection at high pressure of molten fuel into the containment,causing rapid heating; or an in-vessel steam explosion causing ejection of a missile (eg the upper head) into, and through, the containment. Less onerous but still significant would be that the molten mass of fuel and reactor core melts through the floor of the reactor building and reaches ground water; a steam explosion might occur, but the debris would probably be contained, and would in fact, being dispersed, probably be more easily coolable. See WASH-1400 for details.

Other rapid boiling phenomena

High steam generation rates are possible under other circumstances, such as boiler-drum failure, or at a quench front (for example when water re-enters a hot dry boiler!). Though potentially damaging, they are usually less energetic than events in which the hot ('fuel') phase is molten and so can be finely fragmented within the volatile ('coolant') phase. Some examples follow:- When a pressurized container such as the waterside of a steam boiler ruptures it is always followed by some degree of steam explosion. A common operating temperature and pressure for a marine boiler is around 950 P.S.I. and 850 degrees F at the outlet of the superheater. A steam boiler has an interface of steam and water in the steam drum which is where the water is finally evaporating due to the heat input, usually oil fired burners. When a water tube fails due to any variety of reasons it will cause the water in the boiler to expand out of the opening into the furnace area that is only a few P.S.I. above atmospheric pressure. This will likely extinguish all fires and expands the large surface area on the sides of the boiler. To decrease the likelihood of a devastating explosion, boilers have gone from the “firetube” designs where the heat was added by burning inside of the tubes as the pressure vessel of water surrounded the tubes, to “watertube” boilers that have the water inside of the tubes and the furnace area is around the tubes. Old “firetube” boilers were known to blow up inside of the “firetubes” which was enough to damage the pressure vessel of water surrounding it which lead to a steam explosion that was at the very minimum the end of the ship’s propulsion plant and normally the end of the ship. See also:
- BLEVE Category:Explosives Category:Nuclear accidents Category:Water in gas

Steam engine

A steam engine is a heat engine that makes use of the thermal energy that exists in steam, converting it to mechanical work. Steam engines were used in pumps, locomotives, steam ships and steam tractors, and were essential to the Industrial Revolution. They are still used for electrical power generation using steam turbines. A steam engine needs a boiler to boil water to produce steam under pressure. Any heat source can be used, but the most common is a fire fueled by wood, coal, or oil. (However, anything that can be burned can be used as fuel for the fire: paper, trash, used crankcase oil, ground-up corncobs, manure, natural gas, gasoline, high proof alcohol, dry grass, hay, dry weeds, etc). The steam expands and pushes against a piston or turbine, whose motion does the work of turning wheels or driving other machinery. In British English, the term steam engine my also refer to an entire steam locomotive.

Types of steam engine

Steam engines can be classified in two main ways:
- By the technology used. Most steam engines use either piston engines or turbines.
- By the application. Steam engines are used as:
- Stationary engines. Stationary steam engines again divide into two main classes:
- Winding engines, rolling mill engines, and similar applications which need to frequently stop and reverse.
- Engines providing power, which stop rarely and do not need to reverse. These include nearly all thermal power stations, and were also used in mills, factories and to power cable railways and cable tramways before the widespread use of electric power.
- Vehicle engines:
- Steamboats and steamships.
- Land vehicles:
- Steam locomotives.
- Steam cars.
- Steam rollers.
- Steam shovels.
- Traction engines.

Invention

Traction engine Traction engine.]] The first steam device, the aeolipile, was invented by Heron of Alexandria, a Greek, in the 1st century AD, but used only as a toy. Incidently 700 years earlier in Corinth, Greece, rail tracks were invented; however the Greeks never thought of putting the two together. In 1665 Edward Somerset, Marquis of Worcester, installed a steam-powered engine for pumping water in Raglan Castle. Denis Papin, a French physicist, built a working model of a steam engine in about 1687, and he is credited with a number of significant gadgets such as the safety valve. Sir Samuel Morland also developed ideas for a steam engine during the same period, he built a number of steam-engine pumps for Louis XIV in the 1680s. Early industrial steam engines were designed by Thomas Savery (The "fire-engine", 1698) and Thomas Newcomen (1712), and in 1769 James Watt patented what is essentially the modern steam engine - all later developments are refinements of Watt's principle changes rather than new features. Humphrey Gainsborough produced a model condensing steam engine in the 1760s. In 1802 William Symington built the "first practical steamboat", and in 1807 Robert Fulton used the Watt steam engine to power the first commercially successful steamboat. Early engines worked by the vacuum of condensing steam, whereas later types (such as steam locomotives) used the power of expanding steam.

Use and development

steam locomotive The first industrial applications of the vacuum engines were in the pumping of water from deep mineshafts. The Newcomen engine operated by admitting steam to the operating chamber, closing the valve, and then admitting a spray of cold water. The water vapor condenses to a much smaller volume of water, creating a vacuum in the chamber. Atmospheric pressure, operating on the opposite side of a piston, pushes the piston to the bottom of the chamber. In mineshaft pumps, the piston was connected to an operating rod that descended the shaft to a pump chamber. The oscillations of the operating rod are transferred to a pump piston that moves the water, through check valves, to the top of the shaft. The first significant improvement, 60 years later, was creation of a separate condensing chamber with a valve between the operating chamber and the condensing chamber. This improvement was invented on Glasgow Green, Scotland by James Watt and subsequently developed by him in Birmingham, England, to produce the Watt steam engine with greatly increased efficiency. The next improvement was the replacement of manually operated valves with valves operated by the engine itself. Such early vacuum, or condensing, engines are severely limited in their efficiency but are relatively safe since the steam is at very low pressure and structural failure of the engine will be by inward collapse rather than an outward explosion. Their power is limited by the ambient air pressure, the displacement of the working chamber, the combustion and evaporation rates, and the condenser capacity. The maximum theoretical efficiency is limited by the relatively low boiling point of water at near atmospheric pressure (100 °C, 212 °F). The next big improvement in efficiency came with Richard Trevithick's use of pressurized steam, which used a far greater pressure, but more importantly (from a thermodynamic standpoint) operates at a higher temperature differential. But with this added pressure came much danger and many disasters due to exploding boilers and machinery. The most important refinement at this point was the safety valve, which releases excess pressure. Reliable and safe operation came only with a great deal of experience and codification of construction, operating, and maintenance procedures.

Boilers

safety valve Supplement, Vol. XIX, No. 470, Jan. 3, 1885. Now on display in the National Museum of Science and Industry (The Science Museum), London.]] Boilers are of two main types:
- Fire tube construction is typical of early maritime installations for boats and ships and the boilers of steam locomotives. In a fire tube boiler, the hot gases from the firebox (a combustion chamber) are passed through tubes connecting perforated end plates. The gases then enter a smokebox or smoke chest and pass on to a smokestack. The boiler may be vertical or horizontal. For an example of a vertical boiler of this type observe the boiler in the small riverboat used in the movie The African Queen. This type is also used in some boilers that provide steam for steam heating of a building and was also used in the steam shovel. Locomotives and early ships used a horizontal orientation and early ships would usually require a tall smokestack to provide draft, not having a fan to provide a forced draft. In a steam locomotive the draft is generally augmented at startup by directing the steam exhaust through the smokestack, which provides a partial vacuum.
- In a water tube boiler the water is heated in multiple tubes exposed to the hot gases. The tubes are joined to a steam collector chamber at the top. A significant advantage of this type is that there is less chance of catastrophic failure, as there is not a great amount of water in the boiler, nor are there large mechanical elements subject to failure. There may be additional tubes above the collector in the upper portion of the hot gas exhaust - this device, called a superheater, provides additional temperature (the pressure being unchanged) and increases the thermal efficiency of the entire mechanism. Superheaters were also used in some of the later versions of the steam locomotive. There are also rarer variants, for example the drum boiler used in some steam cars. There is also another division between boilers: natural aspiration, which is nearly all of them, and forced-draft, or "pressure-fired" boilers. This technology, equivalent to supercharging for an internal combustion engine, was developed by the Germans and acquired by the US Navy to be used in some frigates built after the Second World War. In it, a fan is used to increase the rate of burning; the boiler must be constructed to get that extra heat to the water. An engine using this kind of boiler has the greatest acceleration from a standing start of any marine powerplant.

Engines

High pressure steam engines are of various types but most are either reciprocating piston or turbine devices.

Reciprocating

Double-acting

After the development of pressurized steam technology, the next major advance was the use of double-acting pistons, with pressurized steam admitted alternately to each side while the other side is exhausted to the atmosphere or to a condenser. Most reciprocating engines now use this technology. Power is removed by a sliding rod, sealed against the escape of steam. This rod in turn drives (via a sliding crosshead bearing) a connecting rod connected to a crank to convert the reciprocating motion to rotary motion. An additional crank or eccentric is used to drive the valve gear, usually through a reversing mechanism to allow reversal of the rotary motion. When a pair of double acting pistons is used, their crank phasing is offset by 90 degrees of angle; this is called quartering. This ensures that the engine will always operate, no matter what position the crank is in. Some ferryboats have used only a single double-acting piston, driving paddlewheels on each side by connection to an overhead rocker arm. When shutting down such an engine it was important that the piston be away from either extreme range of its travel so that it could be readily restarted.

Multiple expansion

eccentric Another type uses multiple (typically three) single-acting cylinders of progressively increasing diameter and stroke (and hence volume). High pressure steam from the boiler is used to drive the first and smallest diameter piston downward. On the upward stroke the partially expanded steam is driven into a second cylinder that is beginning its downward stroke. This accomplishes further expansion of the relatively high pressure exhaust from the first chamber. Similarly, the intermediate chamber exhausts to the final chamber, which in turn exhausts to a condenser. The image at the right shows a model of such an engine. The steam travels through the engine from left to right. The valve chest for each of the first two cylinders is to the left of the corresponding cylinder while that of the third is to the right. One modification of the triple-expansion engine is to use two smaller pistons that sum to the area of the third piston to replace it. This results in the more balanced unit of a total of four pistons arranged in a vee-configuration. The development of this type of engine was important for its use in steamships, for the condenser would, by taking back a little of the power, turn the steam back to water for its reuse in the boiler. Land-based steam engines could exhaust much of their steam and be refilled from a fresh water tower, but at sea this was not possible. This sort of engine dominated merchant marine applications prior to and during World War II. It even was used in warships before the HMS Dreadnought of 1905. Multiple expansion can also result in greater efficiency, as the steam expends more of its energy driving pistons before leaving the engine. Some steam locomotives used double expansion. The most common arrangement was two sets of driving wheels. A set of high pressure cylinders drove one set and the low pressure cylinders drove the other set. A rarer arrangement was called the tandem compound, in which the high and low pressure cylinders were coaxial and had a common piston rod. Other steam locomotives were simple, or single, expansion only. Most compound steam locomotives had a "simpling valve" which fed high pressure steam to all cylinders to help start a train.

Uniflow

Another type of reciprocating steam engine is the "uniflow' type. In this, valves (which act similarly to those used in internal combustion engines) are operated by cams. The inlet valves open to admit steam when minimum expansion volume has been reached at the top of the stroke. For a period of the crank cycle steam is admitted and the poppet inlet are then closed, allowing continued expansion of the steam during the downstroke. Near the bottom of the stroke the piston will expose exhaust ports in the side of the cylindrical chamber. These ports are connected by a manifold and piping to the condenser, lowering the pressure in the chamber to below that of the atmosphere. Continued rotation of the crank moves the piston upward. Engines of this type always have multiple cylinders in an inline arrangement and may be single or double acting. A particular advantage of this type is that the valves may be operated by the effect of multiple camshafts, and by changing the relative phase of these camshafts, the amount of steam admitted may be increased for high torque at low speed and may be decreased at cruising speed for economy of operation, and by changing the absolute phase the engine's direction of rotation may be changed. The uniflow design also maintains a constant temperature gradient through the cylinder, avoiding passing hot and cold steam through the same end of the cylinder. (The uniflow concept is also employed in two stroke supercharged diesel engines used for marine, locomotive, and stationary applications. Such diesels do not need the economizer feature and use a simpler sliding camshaft for reversing.)
Turbine type
Steam turbines for high power applications use a number of rotating disks containing propeller-like blades at their outer edge. These moving "rotor" disks alternate with stationary "stator" blade rings affixed to the turbine case that serve to redirect the steam flow for the next stage. Owing to the high speed of operation such turbines are usually connected to a reduction gear to drive another mechanism such as a ship's propeller. Steam turbines are more durable, and require less maintenance than reciprocating engines. They also produce smoother rotational forces on their output shaft, which contributes to their lower maintenance requirements and lower wear on the machinery they power. The main use for steam turbines is in electricity generation stations where their high speed of operation is an advantage and their relative bulk is not a disadvantage. They are also used in marine applications, powering large ships and submarines. Virtually all nuclear power plants generate electricity by heating water and powering steam turbines. A limited number of steam locomotives were manufactured that used turbine technology. While they met with some success for long haul freight operations in Sweden and elsewhere, steam turbine technology did not last long in the railway world and was rapidly replaced by diesel locomotives.
Rotary type
In theory, it might be possible to use a mechanism based on a pistonless rotary engine such as the Wankel engine in place of the cylinders and valve gear of a conventional reciprocating steam engine. Lack of control of the cutoff is a major problem with such designs, and none has been demonstrated in practice.
Steam powered vehicles
cutoff Nicolas-Joseph Cugnot demonstrated the first functional self-propelled steam vehicle, his "fardier" (steam wagon), in 1769. Arguably, this was the first automobile. While not generally successful as a transportation device, the self-propelled steam tractor proved very useful as a self mobile power source to drive other farm machinery such as grain threshers or hay balers. Steam engine powered automobiles continued to compete with other motive systems into the early decades of the 20th century. However steam engines are less favored for automobiles, which are generally powered by internal combustion engines, because steam requires at least thirty seconds (in a flash boiler) or so to develop pressure. On February 21, 1804 at the Pen-y-Darren ironworks in Wales, the first self-propelled railway steam engine or steam locomotive built by Richard Trevithick was demonstrated.
Advantages
The strength of the steam engine for modern purposes is in its ability to convert heat from almost any source into mechanical work. Unlike the internal combustion engine, the steam engine is not particular about the source of heat. Most notably, without the use of a steam engine nuclear energy could not be harnessed for useful work, as a nuclear reactor does not directly generate either mechanical work or electrical energy - the reactor itself simply heats water. It is the steam engine which converts the heat energy into useful work. Steam may also be produced without combustion of fuel, through solar concentrators. A demonstration power plant has been built using a central heat collecting tower and a large number of solar tracking mirrors, (called heliostats). Similar advantages are found in a different type of external combustion engine, the Stirling engine, which offers efficient power in a compact engine, but which is difficult to operate over a wide range of operating conditions, difficulties which are readily addressed by the modern hybrid vehicle. Steam locomotives are especially advantageous at high elevations as they are not especially adversely affected by the lower atmospheric pressure. This was inadvertently discovered when steam engines operated at high altitudes in the mountains of South America were replaced by diesel-electric engines of equivalent sea level power. They were quickly replaced by much more powerful locomotives capable of producing sufficient power at high altitude. In Switzerland (Brienz Rothhorn) and Austria (Schafberg Bahn) new rack steam locomotives have proved very successful. They were designed based on a 1930s design of Swiss Locomotive and Machine Works (SLM) but with all of today's possible improvements like roller bearings, heat insulation, light-oil firing, improved inner streamlining, one-man-driving and so on. These resulted in 60 percent lower fuel consumption per passenger and massively reduced costs for maintenance and handling. Economics now are similar or better than with most advanced diesel or electric systems. Also a steam train with similar speed and capacity is 50 percent lighter than an electric or diesel train, thus, especially on rack railways, significantly reducing wear and tear on the track. Also, a new steam engine for a paddle steam ship on Lake Geneva, the "Montreux" was designed and built, being the world's first ship steam engine with an electronic remote control. The steam group of SLM in 2000 created a wholly-owned company called DLM to design modern steam engines and steam locomotives.
Efficiency
To get the efficiency of an engine, divide the number of joules of mechanical work that the engine produces by the number of joules of energy input to the engine by the burning fuel. In general, the rest of the energy is dumped into the environment as heat. No pure heat engine can be more efficient than the Carnot cycle, in which heat is moved from a high temperature reservoir to one at a low temperature, and the efficiency depends on the temperature difference. Hence, steam engines should ideally be operated at the highest steam temperature possible, and release the waste heat at the lowest temperature possible. In practice, a steam engine exhausting the steam to atmosphere will have an efficiency (including the boiler) of 5%, but with the addition of a condenser the efficiency is greatly improved to 25% or better. A power station with exhaust reheat, etc. will achieve 30% efficiency. Combined cycle in which the burning material is first used to drive a gas turbine can produce 60% efficiency. It is also possible to capture the waste heat using cogeneration in which the residual steam is used for heating. It is therefore possible to use about 90% of the energy produced by burning fuel - only 10% of the energy produced by the combustion of the fuel goes wasted into the atmosphere. One source of inefficiency is that the condenser causes losses by being somewhat hotter than the outside world, although this can be mitigated by condensing the steam in a heat exchanger and using the recovered heat, for example to pre-heat the air being used in the burner of an external combustion engine. The operation of the engine portion alone is not dependent upon steam; any pressurised gas may be used. Compressed air is sometimes used to test or demonstrate small model "steam" engines.
Festivals and museums

- [http://www.dartmouth.org.uk/newcomen.htm The Newcomen Engine House, Dartmouth, Devon, England, UK]
- Steam Era in Milton, Ontario
- Ontario Agricultural Museum in Milton, Ontario
- Missouri River Valley Steam Engine Association [http://www.mrvsea.com/fall_show.htm Back to the Farm Reunion] in central Missouri, USA. This is not a steam-only festival, but it has always had a good showing of running steam engines.
- [http://collections.ic.gc.ca/hamilton/pump.htm Hamilton Museum of Steam and Technology] in Hamilton, Ontario. An old municipal pumphouse dating to 1860 with it's original two Woolf Compound Rotative Beam Engines, one of which still operates.
See also

- Timeline of steam power
- Newcomen steam engine
- Watt steam engine
- Steam power during the Industrial Revolution
- Stationary steam engine
- Steam donkey
- Steam locomotive for details of steam powered railway 'engines'
- Crosshead bearing
- steam car
- Stanley Steamer
- Live steam
- Beam engine
External links

- [http://www.avero.de/?links/dampfmaschine Interactive Steam Engine] See how it works and manipulate the speed
- [http://www.keveney.com/Engines.html Animated engines - Illustrates a variety of steam engines]
- [http://www.fantasyarts.net/nanotechnology-gallery.htm The World's Smallest Steam Engine]
- [http://www.history.rochester.edu/steam/thurston/1878/Chapter5.html A history of the growth of the steam-engine]
- [http://www.dself.dsl.pipex.com/MUSEUM/POWER/uniflow/uniflow.htm Uniflow locomotives]
- [http://www.dself.dsl.pipex.com/MUSEUM/TRANSPORT/mower/mower.htm Steam powered lawn mower]
- [http://www.saunalahti.fi/animato/steam Building Model Steam trains]
- [http://www.cincinnati.com/travel/stories/053099_steamer.html Steamboat revival on Lake Geneva] Category:Energy conversion Category:Engines Category:Piston engines ja:蒸気機関

Turbine

:For the developers of Massively Multiplayer Online Role Playing Games, see Turbine Inc.. Turbine Inc. Turbine Inc. A turbine is a rotary engine that extracts energy from a fluid flow. Claude Burdin coined the term from the Latin turbinis, or vortex, during an 1828 engineering competition. The simplest turbines have one moving part, a rotor-blade assembly. Moving fluid acts on the blades to spin them and impart energy to the rotor. Some modern turbines are among the most powerful machines ever made. Early turbine examples are windmills and water wheels. A turbine operating in reverse is called a compressor or Turbopump. Gas, steam, and water turbines usually have a casing around the blades that focuses and controls the fluid. The casing and blades may have variable geometry that allow efficient operation for a range of fluid flow conditions.

Theory of operation

A working fluid contains potential energy (pressure head) and kinetic energy (velocity head). The fluid may be compressible or non-compressible. Several physical principles are employed by turbines to collect this energy; kinetic energy Impulse turbines change the direction of flow of a high velocity fluid jet. The resulting impulse spins the turbine and leaves the fluid flow with diminished kinetic energy. There is no pressure change of the fluid in the turbine rotor blades. Pressure head is changed to velocity head by accelerating the fluid with a nozzle, prior to hitting the turbine blades. Pelton wheels and de Laval turbines use this concept. Impulse turbines do not require a pressure casement around the runner, since the fluid jet is prepared by a nozzle prior to hitting the turbine. Newton's second law describes the transfer of energy for impulse turbines. Reaction turbines develop torque by reacting to the fluid's pressure or weight. The pressure of the fluid changes as it passes through the turbine rotor blades. A pressure casement is needed to contain the working fluid as it acts on the turbine runner, or the turbine must be fully immersed in the fluid flow (wind turbines). The casing contains and directs the working fluid, and for water turbines, maintains suction imparted by the draft tube. Francis turbines and most steam turbines use this concept. For compressible working fluids, multiple turbine stages may by used to efficiently harness the expanding gas. Newton's third law describes the transfer of energy for reaction turbines. Velocity triangles are used to calculate the basic performance of a turbine stage. Gas exits the turbine nozzle guide vanes at absolute velocity Va1. The rotor rotates at velocity U. Relative to the rotor, the velocity of the gas as it impinges on the rotor entrance is Vr1. The gas is turned by the rotor and exits, relative to the rotor, at velocity Vr2. However, in absolute terms the rotor exit velocity is Va2. The velocity triangles are constructed using these various velocity vectors. Velocity triangles can be constucted at any section through the blading (e.g. hub , tip, etc), but are usually shown at the mean radius. Mean performance for the stage can be calculated from the velocity triangles at this radius as follows:

\delta\,H = U\cdot \delta\,Vw/g

where:

g =

acceleration of gravity

\delta\,H =

enthalpy drop across stage

\delta\,Vw =

delta whirl velocity Turbine designs will use both these concepts to varying degrees whenever possible. Wind turbines use a foil to generate lift from the moving fluid and impart it to the rotor (this is a form of reaction), they also gain some energy from the impulse of the wind, by deflecting it at an angle. Crossflow turbines are designed as an impulse machine, with a nozzle, but in low head applications maintain some efficiency through reaction, like a traditional water wheel. Classical turbine design methods were developed in the mid 19th century. Vector analysis related the fluid flow with turbine shape and rotation. Graphical calculation methods were used at first. Formulas for the basic dimensions of turbine parts are well documented, and a highly efficient machine can be reliably designed for any fluid flow condition. Some of the calculations are empirical 'rule of thumb' formulae, and others are based on classical mechanics. As with most engineering calculations, simplifying assumptions were made. Modern turbine design carries the calculations further. Computational fluid dynamics dispenses with many of the simplifying assumptions used to derive classical formulas, and computer software facilitates optimization. These tools have led to steady improvements in turbine design over the last forty years. The primary numerical classification of a turbine is its specific speed. This number describes the speed of the turbine at its maximum efficiency with respect to the power and flow rate. The specific speed is derived to be independent of turbine size. Given the fluid flow conditions and the desired shaft output speed, the specific speed can be calculated and an appropriate turbine design selected. The specific speed, along with some fundamental formulas can be used to reliably scale an existing design of known performance to a new size with corresponding performance. Off-design performance is normally displayed as a turbine map or characteristic.

Types of turbines

- Steam turbine
- Gas turbine engines are sometimes referred to as turbine engines. Such engines usually feature a compressor, combustor, nozzle, etc, in addition to one or more turbines.
- transonic turbine The gasflow in most turbines employed in gas turbine engines remains subsonic throughout the expansion process. In a so-called transonic turbine, the gasflow becomes supersonic as it exits the nozzle guide vanes, although the downstream velocities normally become subsonic. Transonic turbines operate at a higher pressure ratio than normal, but are usually less efficient.
- contra-rotating turbines Some efficiency advantage can usually be obtained if a downstream turbine rotates in the opposite direction to an upstream unit.
- statorless turbine Most turbines have a set of static (i.e. stationary) inlet guide vanes that direct the gasflow onto the rotating rotor blades. In a statorless turbine, the gasflow exiting an upstream rotor impinges onto a downstream rotor, without an intermediate set of nozzle guide vanes being encountered.
- Water turbine
- Wind turbine :Water and Wind turbines have a thermodynamic cycle that is part of weather.

Uses of turbines

Almost all electrical power on Earth is produced with a turbine of some type, the exceptions being solar panels and fuel cells. All jet engines rely on turbines to supply mechanical work from their fuel, as do all nuclear warships and power plants. Turbines are often part of a larger machine. A Gas turbine, for example, may refer to an internal combustion machine that contains a turbine, compressor, combustor, and alternator. Piston engines, especially for aircraft, can use a turbine powered by their exhaust to drive an intake compressor, a configuration known as a turbocharger (turbine supercharger) or colloquially as a "turbo". Turbines can have incredible power density (with respect to volume and weight). This is because of their ability to operate at very high speeds. The Space Shuttle fuel pump turbine, for example, is slightly larger than an automobile engine and produces 25,000 hp (19 MW).

External links

- [http://www.du.edu/~jcalvert/tech/fluids/turbine.htm Turbine introductory math]
- [http://www.power.alstom.com/home/equipment___systems/turbines/7385.EN.php?languageId=EN&dir=/home/equipment___systems/turbines/ ALSTOM Power]
- [http://www.siemenswestinghouse.com/en/gasturbinesitem/index.cfm Siemens Westinghouse] Category:Mechanical engineering Category:Turbines Category:Jet engines ja:タービン

Heat of vaporization

The standard enthalpy change of vaporization is a physical property of substances. It is defined as the amount of heat (or energy) required per unit mass of a substance to completely vaporize the substance at its boiling point. The heat of vaporization is expressed in kJ/mol, or calories/gram. The use of kJ/kg is also possible, but less customary. Other units still in use in certain places include Btu/lb. Because vaporization is the opposite process of condensation, the term heat of condensation is also used. The latter is defined as the heat released when a unit mass of a substance is completely condensed at its boiling point. The standard enthalpy change of vaporization of water is about 2260 kJ/kg which is equal to 40.8 kJ/mol. This is quite a lot: it is five times the energy needed for heating the water from 0 °C to 100 °C.

Heats of vaporization of the elements

Element	Heat of vaporization (kJ/mol)
Actinium	n/a
Aluminium	293.4
Antimony	77.14
Argon	6.447
Arsenic	34.76
Astatine	114
Barium	142
Beryllium	292.40
Bismuth	104.8
Boron	489.7
Bromine	15.438
Cadmium	100
Caesium	67.74
Calcium	153.6
Carbon	355.8
Cerium	414
Chlorine	10.2
Chromium	344.3
Cobalt	376.5
Copper	300.3
Fluorine	3.2698
Gallium	258.7
Germanium	330.9
Gold	334.4
Hafnium	575
Helium	0.0845

Element	Heat of vaporization (kJ/mol)
Hydrogen	0.44936
Indium	231.5
Iodine	20.752
Iridium	604
Iron	349.6
Krypton	9.029
Lanthanum	414
Lead	177.7
Lithium	145.92
Magnesium	127.4
Manganese	226
Mercury	59.229
Molybdenum	598
Neon	1.7326
Neptunium	n/a
Nickel	370.4
Niobium	696.6
Nitrogen	2.7928
Osmium	627.6
Oxygen	3.4099
Palladium	357
Phosphorus	12.129
Platinum	510
Polonium	60.1
Potassium	79.87
Radium	37

Element	Heat of vaporization (kJ/mol)
Radon	16.4
Rhenium	715
Rhodium	493
Rubidium	72.216
Ruthenium	595
Scandium	314.2
Selenium	26.3
Silicon	384.22
Silver	250.58
Sodium	96.96
Strontium	144
Sulfur	1.7175
Tantalum	743
Technetium	660
Tellurium	52.55
Thallium	164.1
Thorium	514.4
Tin	295.8
Titanium	421
Tungsten	824
Vanadium	452
Xenon	12.636
Yttrium	363
Zinc	115.3
Zirconium	58.2
Methanol	37.4

Reference

Sears, Zemansky et. al., University Physics, Addison-Wessley Publishing Company, Sixth ed., 1982, ISBN: 0-201-07199-1 Category:Chemical properties Category:Thermodynamics Category:Heat ko:기화열 ja:気化熱

Rankine cycle

diagram of a Rankine cycle, showing both ideal and non-ideal processes.]] The Rankine cycle is a thermodynamic cycle. Like other thermodynamic cycles, the maximum efficiency of the Rankine cycle is given by calculating the maximum efficiency of the Carnot cycle. This article will deal with the Rankine cycle from an engineering point of view.

Processes of the Rankine cycle

There are four processes in the Rankine cycle, each changing the state of the working fluid. These states are identified by number in the diagram above.
- Process 4-1: First, the working fluid is pumped (ideally adiabatically and isentropically) from low to high pressure by a pump. Pumping requires a power input (for example mechanical or electrical).
- Process 1-2: The high pressure liquid enters a boiler where it is heated at constant pressure by an external heat source to become a superheated vapor. Common heat sources for power plant systems are coal, natural gas, or nuclear power.
- Process 2-3: The superheated vapor expands through a turbine to generate power output. Ideally, this expansion is adiabatic and isentropic. This decreases the temperature and pressure of the vapor.
- Process 3-4: The vapor then enters a condenser where it is cooled to become a saturated liquid. This liquid then re-enters the pump and the cycle repeats.

Description

Rankine cycles describe the operation of steam heat engines commonly found in power generation plants. In such vapor power plants, power is generated by alternately vaporizing and condensing a working fluid (in many cases water, although refrigerants such as ammonia may also be used). The working fluid in a Rankine cycle follows a closed loop and is re-used constantly. Steam seen billowing from power plants is evaporating cooling water, not working fluid.

Variables

$\dot_$	heat input rate (energy per unit time)
$\dot$	mass flow rate (mass per unit time)
$\dot$	mechanical power used by or provided to the system (energy per unit time)
$\eta$	thermodynamic efficiency of the process (power used for turbine per heat input, unitless)
$h_1, h_2, h_3, h_4$	these are the "specific enthalpies" at indicated points on the T-S diagram

Equations

Each of the first four equations are easily derived from the energy and mass balance for a control volume. The fifth equation defines the thermodynamic efficiency of the cycle as the ratio of net power output to heat input.

Real Rankine cycle (non-ideal)

In a real Rankine cycle, the compression by the pump and the expansion in the turbine are not isentropic. In other words, these processes are non-reversible and entropy is increased during the two processes (indicated in the figure as ΔS). This somewhat increases the power required by the pump and decreases the power generated by the turbine. It also makes calculations more involved and difficult.

Variations of the basic Rankine cycle

Two main variations of the basic Rankine cycle are used in modern practice.

Rankine cycle with reheat

In this variation, two turbines work in series. The first accepts vapor from the boiler at high pressure. After the vapor has passed through the first turbine, it re-enters the boiler and is reheated before passing through a second, lower pressure turbine. Among other advantages, this prevents the vapor from condensing during its expansion which can seriously damage the turbine blades.

Regenerative Rankine cycle

The regenerative Rankine cycle is so named because after emerging from the condenser (possibly as a subcooled liquid) the working fluid is heated by steam tapped from the hot portion of the cycle. This increases the of heat addition which in turn increases the thermodynamic efficiency of the cycle.

References

- Moran & Shapiro 'Fundamentals of Engineering Thermodynamics' (ISBN 0471274712)
- [http://wikibooks.org/wiki/Applications_(Engineering_Thermodynamics)#Rankine_Cycle Wikibooks Engineering Thermodynamics] Category:Thermodynamics Category:Mechanical engineering Category:Thermodynamic cycles

Steam shower

In addition to acting as a normal shower, a steam shower produces water vapor using a humidifying steam generator. These types of showers provide a pleasant bathing experience that is becoming more and more popular around the United States and abroad. Steam showers are generally found in self-contained enclosures that don't allow the water vapor into the main part of the bathroom, thus avoiding damage to drywall, paint, or wallpaper. Most steam shower rooms are sold as stand alone shower units with between 12 and 30 jets, while many have additional features such as foot massagers, ceiling rain showers, radios, telephones, and CD players. Steam showers have become a more common bathroom fixture in recent years, primarily due to technical innovations resulting in lower costs, along with an overall increase in the appearance of luxury spa products in the bathrooms of middle and high income families. The water vapor produced by these shower units is often referred to as "steam," but this is a misnomer. Actual steam, or super-heated water, is invisible and would result in intense burns if applied in the shower.

Links

- [http://www.russiansauna.com/jetted_steam_showers.asp Jetted and Steam Showers]
- [http://www.wasauna.com/steam_shower_rooms.htm Steam Shower Pictures] Category:Water in gas

Working fluid

: working mass

Water vapor

Water vapor or water vapour, also aqueous vapour, is the gas phase of water. On the Earth, water vapor is one state of the water cycle within the hydrosphere. Water vapor can be produced from the evaporation of liquid water or from the sublimation of ice. Under normal atmospheric conditions, water vapor is continuously evaporating and condensing. Normally, water vapor is invisible to the naked eye.

General properties of water vapor

Evaporation/sublimation

condensing Whenever a water molecule leaves a surface, it is said to have evaporated. Each water molecule that becomes water vapor takes a parcel of heat with it. This process is called evaporative cooling. The amount of water vapor in the air will determine how fast each molecule will return back to the surface or not. So, when a net evaporation occurs, that body of water will undergo a net cooling directly related to the loss of water. Evaporative cooling is restricted by atmospheric conditions. The amount of water vapor in the air is referred to as humidity. Measurement of the vapor content of air is accomplished with devices known as hygrometers. The measurements are expressed as specific humidity or percent relative humidity. The temperature of the atmosphere and the water surface determines the equilibrium vapor pressure, 100% relative humidity occurs when the partial pressure of water vapor is equal to the equilibrium vapor pressure. This is often referred to as complete saturation. Another form of evaporation is sublimation, in which water molecules become gaseous from ice instead of liquid water. Under the same principle, when ice has a higher temperature than the surrounding atmosphere, sublimation occurs. It is sublimation that accounts for the slow, mid-winter disappearance of ice and snow at temperatures too low to cause melting.

Condensation

Water vapor will only condense onto another surface when that surface is cooler than the temperature of the water vapor, or when the water vapor equilibrium in air has been exceeded. When water vapor condenses onto a surface, a net warming occurs on that surface. The water molecule brings a parcel of heat with it. In turn, the temperature of the atmosphere drops slightly. In the atmosphere, condensation produces clouds, fog and precipitation--usually only when facilitated by cloud condensation nuclei. The dew point of an air parcel is the temperature to which it must cool before condensation in the air begins to form. Also, a net condensation of water vapor occurs on surfaces when the temperature of the surface is at or below the dew point temperature of the atmosphere. Deposition is a type of condensation. Frost and snow are examples of deposition (or sublimation). Deposition is the direct formation of ice from water vapor.

General Discussion

The amount of water vapor in an atmosphere exists due to the restrictions of partial pressures and temperature. Dew point temperature and relative humidity act as guidelines for the process of water vapor in the water cycle. Energy input, such as sunlight, can trigger more evaporation on an ocean surface or more sublimation on a chunk of ice on top of a mountain. The balance between condensation and evaporation gives the quantity called vapor partial pressure (abbreviated to Vapor pressure). The maximum partial pressure (saturation pressure) of water vapor in air varies with temperature of the air and water vapor mixture. A variety of empirical formulae exist for this quantity; the most used reference formula is the Goff-Gratch equation for the SVP over liquid water: :

\log_ p =  -7.90298 (373.16/T-1) + 5.02808 \log_(373.16/T) - 1.3816 . 10^ (10^ -1) + 8.1328 . 10^ (10^ -1) + \log_(1013.246)

Where T, temperature of the moist air, is given in units of kelvins, and p is given in units of millibars (hectopascals). The formula is valid from about −50 to 102 °C; however there are a very limited number of measurements of the vapor pressure of water over supercooled liquid water. A number of other formulae are listed and compared at [http://cires.colorado.edu/~voemel/vp.html]. Under adverse conditions, such as when the boiling temperature of water is reached, a net evaporation will always occur during standard atmospheric conditions regardless of the percent of relative humidity. This immediate process will dispel massive amounts of water vapor into a cooler atmosphere. Exhaled air is almost fully at equilibrium with water vapor at the body temperature. In the cold air the exhaled vapor quickly condenses, thus showing up as a fog or mist of water droplets and as condensation or frost on surfaces. Supermarket buildings that utilise open chiller cabinets are able to significantly lower vapor pressure (lowering humidity). This practice delivers several benefits and other problems.

Water vapor in Earth's atmosphere

Gaseous water represents a small but environmentally significant constituent of the atmosphere. Most of it is contained in the troposphere. Besides accounting for most of Earth's natural greenhouse effect, which warms the planet, gaseous water also condenses to form clouds, which may act to warm or cool, depending on the circumstances. In general terms, atmospheric water strongly influences, and is strongly influenced by weather, and weather is modified by climate. Fog and clouds form through condensation around cloud condensation nuclei. In the absence of nuclei, condensation will only occur at much lower temperatures. Under persistent condensation or deposition, cloud droplets or snowflakes form, which precipitate when they reach a critical mass. precipitate The average residence time of water molecules in the troposphere is about 1 week. Water depleted by precipitation is replenished by evaporation from the seas, lakes, rivers and the transpiration of plants, and other biological and geological processes. Measurements of vapor concentration are expressed as specific humidity or percent relative humidity. The annual mean global concentration of water vapor would yield about 25 mm of liquid water over the entire surface of the Earth if it were to instantly condense. However, the mean annual precipitation for the planet is about 1 meter, which indicates a rapid turnover of water in the air.

Radar and satellite imaging

relative humidity global mean atmospheric water vapor ]] Because water molecules absorb microwaves and other radio wave frequencies, water in the atmosphere attenuates radar signals. In addition, atmospheric water will reflect and refract signals to an extent that depends on whether it is vapor, liquid or solid. Generally, radar signals lose strength progressively the farther they travel through the troposphere. Different frequencies attenuate at different rates, such that some components of air are opaque to some frequencies and transparent to others. Radio waves used for broadcasting and other communication tend to suffer the same effect. Water vapor reflects radar to a less extent than do water's other two phases. In the form of drops and ice crystals, water acts as a prism, which it does not do as a gas. A comparison of GOES-12 satellite images shows the distribution of atmospheric water vapor relative to the oceans, clouds and continents of the Earth. Vapor surrounds the planet but is unevenly distributed.

Lightning generation

Water vapor plays a key role in lightning production in the atmosphere. From cloud physics, usually, clouds are the real generators of static charge as found in Earth's atmosphere. But the ability, or capacity, of clouds to hold massive amounts of electrical energy is directly related to the amount of water vapor present in the local system. The amount of water vapor directly controls the permittivity of the air. During times of low humidity, static discharge is quick and easy. During times of higher humidity, fewer static discharges occur. However, permittivity and capacitance work hand in hand to produce the megawatt outputs of lightning. After a cloud, for instance has started its way to becoming a lightning generator, atmospheric water vapor acts as a substance (or insulator) that decreases the ability of the cloud to discharge its electrical energy. Over a certain amount of time, if the cloud continues to generate more static electricity, the barrier that was created by the atmospheric water vapor will ultimately break down. This energy will be released to a locally, opposite charged region in the form of lightning. The strength of each discharge is directly related to the atmospheric permittivity, capacitance, and the source's charge generating ability. See also, Van de Graaff generator.

Extraterrestrial water vapor

The brilliance of comet tails comes largely from water vapor. On approach to the sun, the ice many comets carry sublimates to vapor, which reflects light from the sun. Knowing a comet's distance from the sun, astronomers may deduce a comet's water content from its brilliance. Bright tails in cold and distant comets suggests carbon monoxide sublimation. Scientists studying Mars hypothesize that if water moves about the planet, it does so as vapor. Most of the water on Mars appears to exist as ice at the northern pole. During Mars' summer, this ice sublimates, perhaps enabling massive seasonal storms to convey significant amounts of water toward the equator.

External links

- [http://www.nsdl.arm.gov/Library/glossary.shtml#water_vapor National Science Digital Library - Water Vapor]
- [http://avc.comm.nsdlib.org/cgi-bin/wiki_grade_interface.pl?Measuring_Water_Vapor Measuring Water Vapor] : A lesson plan from the National Science Digital Library.
- [http://www.ems.psu.edu/~fraser/Bad/BadClouds.html psu.edu science misconceptions - Bad Clouds]
- [http://fermi.jhuapl.edu/people/babin/vapor/index.html Water Vapor Myths: A Brief Tutorial]
- [http://www.agu.org/sci_soc/mockler.html AGU Water Vapor in the Climate System - 1995] Category:Climatology Category:Meteorology Category:greenhouse gases Category:Psychrometrics Category:Forms of water Category:Water in gas ja:水蒸気 simple:Water vapor

Thermodynamic

Thermodynamics (from the Greek thermos meaning heat and dynamis meaning power) is a branch of physics that studies the effects of temperature, pressure, and volume changes on physical systems at the macroscopic scale. In simpler terms, heat means ‘energy in transit’ and dynamics relates to ‘movement’. Thus, in essence thermodynamics studies how energy instills movement. The starting point for most thermodynamic considerations are the laws of thermodynamics. These laws postulate that energy can be exchanged between physical systems in the form of heat and work, as well as the existence of a quantity named entropy, which can be associated with every system. From its inception, thermodynamics developed out of the need to increase the efficiency of early steam engines. The first engine constructed was the 1698 Savery engine as shown below: steam engines]

Overview

Thermodynamics in most regards is held to be a difficult subject. In chemical engineering for example, which teaches one of the more rigorous variations of such, thermodynamics is considered a weeder course. One of the better ways to learn thermodynamics is to follow a ground up development of its concepts and principles, beginning with units as SI and English, parameters as pressure, temperature, and volume, etc., properties of substances as gas, vapor, liquid, and solid, etc., phase diagrams, the laws of thermodynamics, equations of state, continuing onward through such advanced subjects as multi-phase reaction thermodynamics, high-speed gas flow thermodynamics, or molecular thermodynamics, etc. A difficult concept in thermodynamics is that of "entropy". In particular, the entropy of a system exchanging no heat with the outside can never decrease with time. As such, entropy allows predictions on the transformations and energy exchanges that are accessible to a given system. Related to entropy, Statistical mechanics or statistical thermodynamics is one of the underlying theories that sustain thermodynamics; it provides a way to predict the entropy of a thermodynamic system, based on the statistical analysis of the fluctuations the system experiences over a set of microstates

History

microstate A short history of thermodynamics begins with the British physicist and chemist Robert Boyle who in 1656, in coordination with English scientist Robert Hooke, invented the air pump. Using this pump, Boyle and Hooke noticed the pressure-temperature-volume correlation. In time, the ideal gas law was formulated. Soon thereafter, in 1679, based on these concepts, an associate of Boyle's named Denis Papin built a bone digester, which is a closed vessel with a tightly fitting lid that confines steam until a high pressure is generated. Later designs implemented a steam release valve to keep the machine from exploding. By watching the valve rhythmically move up and down, Papin conceived of the idea of a piston and cylinder engine. He did not however follow through with his design. Nevertheless, in 1698, based on Papin’s designs, engineer Thomas Savery built the first engine. These early engines being crude and inefficient attracted the attention of the leading scientists of the time. One such scientist was Sadi Carnot, the “father of thermodynamics”, who in 1824 published “Reflections on the Motive Power of Fire”, a discourse on heat, power, and engine efficiency. This marks the start of thermodynamics as a modern science.

Thermodynamic systems

Of most importance in thermodynamics is the concept of the “system”. A system is the region of the universe under study. A system is separated from the remainder of the universe by a boundary which may be imaginary or not, but which, by convention delimits a finite volume. The possible exchanges of work, heat, or matter between the system and the surroundings take place across this boundary. There are four dominate classes of systems: matter #Isolated Systems – matter and energy may not cross the boundary. #Adiabatic Systems – heat and matter may not cross the boundary. #Closed Systems – matter may not cross the boundary. #Open Systems – heat, work, and matter may cross the boundary. For closed systems, as time goes by, internal differences in the system tend to even out; pressures and temperatures tend to equalize, as do density differences. A system in which all equalizing processes have gone practically to completion, is considered to be in a state of thermodynamic equilibrium. In thermodynamic equilibrium, a system's properties are, by definition, unchanging in time. Systems in equilibrium are much simpler and easier to understand than systems which are not in equilibrium. Often, when analyzing a thermodynamic process, it can be assumed that each intermediate state in the process is at equilibrium. This will also considerably simplify the situation. Thermodynamic processes which develop so slowly as to allow each intermediate step to be an equilibrium state are said to be reversible processes.

Thermodynamic parameters

The central concept of thermodynamics is that of energy, the ability to do work. As stipulated by the first law, the total energy of the system and its surroundings is conserved. It may be transferred into a body by heating, compression, or addition of matter, and extracted from a body either by expansion, cooling, or extraction of matter. Just as in mechanics, energy transfer is effected by a force causing a displacement, with the product of the two being the amount of energy transferred. In a similar way, thermodynamic systems can be thought of as transferring energy as the result of a generalized force causing a generalized displacement, with the product of the two being the amount of energy transferred. These thermodynamic force-displacement pairs are known as conjugate variables. The most common conjugate thermodynamic variables are pressure-volume (mechanical parameters), temperature-entropy (thermal parameters), and chemical potential-particle number (material parameters).

Thermodynamic instruments

There are two types of thermodynamic instruments, the meter and the reservoir. A thermodynamic meter is any device which measures any parameter of a thermodynamic systems. In some cases, the thermodynamic parameter is actually defined in terms of an idealized measuring instrument. For example, the zeroth law states that if two bodies are in thermal equilibrium with a third body, they are also in thermal equilibrium with each other. This principle, as noted by James Maxwell in 1872, asserts that it is possible to measure temperature. An idealized thermometer is a sample of an ideal gas at constant pressure. From the ideal gas law PV=NRT, the volume of such a sample can be used as an indicator of temperature; in this manner it defines temperature. Although pressure is defined mechanically, a pressure-measuring device, called a barometer may also be constructed from a sample of an ideal gas held at a constant temperature. A calorimeter is a device which is used to measure and define the internal energy of a system. A thermodynamic reservoir is a system which is so large that it does not appreciably alter its state parameters when brought into contact with the test system. It is used to impose a particular value of a state parameter upon the system. For example, a pressure reservoir is a system at a particular pressure, which imposes that pressure upon any test system that it is mechanically connected to. The earths atmosphere is often used as a pressure reservoir.

Thermodynamic states

When a system is at equilibrium under a given set of conditions, it is said to be in a definite state. The state of the system can be described by a number of intensive variables and extensive variables. The properties of the system can be described by an equation of state which specifies the relationship between these variables. State may be thought of as the instantaneous quantitative description of a system with a set number of variables held constant.

Thermodynamic processes

A thermodynamic process may be defined as the energetic evolution of a thermodynamic system proceeding from an initial state to a final state. Typically, each thermodynamic process is distinguished from other processes, in energetic character, according to what parameters, as temperature, pressure, or volume, etc., are held fixed. Furthermore, it is useful to group these processes into pairs, in which each variable held constant is one member of a conjugate pair. The five most common thermodynamic processes are shown below: #An isobaric process occurs at constant pressure. #An isochoric process occurs at constant volume. #An isothermal process occurs at a constant temperature. #An isentropic process occurs at a constant entropy. #An adiabatic process occurs without loss or gain of heat.

The laws of thermodynamics

In thermodynamics, there are four laws of very general validity, and as such they do not depend on the details of the interactions or the systems being studied. Hence, they can be applied to systems about which one knows nothing other than the balance of energy and matter transfer. Examples of this include Einstein's prediction of spontaneous emission around the turn of the 20th century and current research into the thermodynamics of black holes. The four laws are:
- Zeroth law of thermodynamics, about the transitivity of thermodynamic equilibrium
- If systems A and B are in thermal equilibrium, and systems B and C are in thermal equilibrium, then A and C are also in thermal equilibrium.
- Two systems in thermal equilibrium with a third system, all must be in equilibrium with each other.
- First law of thermodynamics, or a statement about the conservation of energy
- The work exchanged in an adiabatic process depends only on the initial and the final state and not on the details of the process.
- The heat energy flowing into a system is equal to the sum of the increase in the internal energy of the system and the work done by the system.
- The change in internal energy of a system is

\Delta

U = q + w, where q is heat flow and w is work.
- Second law of thermodynamics, about entropy
- The entropy of an isolated system never decreases (see Maxwell's demon)
- A system operating in contact with a thermal reservoir cannot produce positive work in its surroundings (Kelvin)
- A system operating in a cycle cannot produce a positive heat flow from a colder body to a hotter body (Clausius)
- Third law of thermodynamics, about absolute zero temperature
- All processes cease as temperature approaches zero.
- As temperature goes to 0, the entropy of a system approaches a constant

Thermodynamic potentials

As derived from the energy balance equation on a thermodynamic system there exist energetic quantities called thermodynamic potentials, being the quantitative measure of the stored energy in the system. The four most well known potentials are: Potentials are used to measure energy changes in systems as they evolve from an initial state to a final state. The potential used depends on the constraints of the system, such as constant temperature or pressure. Internal energy is the internal energy of the system, enthalpy is the internal energy of the system plus the energy related to pressure-volume work, and Helmholtz and Gibbs free energy are the energies available in a system to do useful work when the temperature and volume or the pressure and temperature are fixed, respectively.

Thermodynamic evolution

In 1875 Austrian physicist Ludwig Boltzmann declared: "the general struggle for existence of animate beings is a struggle for entropy". Ever since, there has been a continuous search to elucidate the thermodynamic mechanism behind evolution. As it is generally agreed that life evolved from non-life, a process called abiogenesis, by some form of chemical evolution, and as it is understood that both life and non-life abide by the laws of thermodynamics, then, in theory, it is reasoned that there should exist a functionable model of thermodynamic evolution. This line of research defines the field of thermodynamic evolution.

Quotes & humor

- A common scientific joke expresses the three laws simply and surprisingly accurately as: : Zeroth: "You must play the game." : First: "You can't win." : Second: "You can't break even." : Third: "You can't quit the game."