Water vapor: refers to the existence form of water in a specific space is gas-liquid two-phase, in which the liquid phase can exist in the form of "fog" dispersion (water vapor is the gaseous form of water), or in the form of a large number of liquid droplets, which must also meet certain physical conditions and other environmental conditions.In practical applications, most of the contact refers to "water vapor".There is a difference between gas and steam.Steam (such as water, mercury, ether, ammonia, gasoline, etc.) is such a gas. It is generated from liquid, exists with liquid at ordinary atmospheric pressure, and can easily become liquid.Gases (such as hydrogen, oxygen, nitrogen, etc.) are relatively stable, and can only be turned into liquid at very low temperature and high pressure.[1]
steam: 1. Gases formed by heating liquids or some solids, such as water vapor formed by water;2. Water vapor:Steam turbine、steamer。
gas: 1. Gas.2. Air in particular.4. Cold, hot, cloudy, sunny and other phenomena in natureAmong them, 1 and 4 are also《Dictionary of Common Words in Ancient Chinese》Explanations on.Liezi Tianrui:RainbowAlso, clouds and fog, wind and rain, four seasons, this accumulation of gas into the sky.
Saturation state
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When water is placed in a sealed container that exhausts air, molecules will escape from the water surface and return to the water from the vapor space.At the same time, if the number of molecules escaping from the water is the same as that of the returned water, and the dynamic balance is reached, the water and water vapor will be in a saturated state, which are called saturated water and saturated water vapor respectively, and the corresponding pressure and temperature are called saturated pressure andSaturation temperature。The higher the saturation temperature, the higher the saturation pressure.
Related charts
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Water and steam chart: water steam cannot be usedIdeal gas equation of stateDescription.For the convenience of calculation, its thermodynamic properties are often made into graphs and tables.It is specified in the figure and tableThree phase pointThe internal energy and entropy of saturated water are zero,enthalpy It is also close to zero.Water and steam diagrams include: pressure temperature diagram, pressure volume diagramTemperature entropy diagramandEnthalpy entropy diagram。There are two kinds of water and steam meters: saturated water steam meter, unsaturated water meter andsuperheated steamTable.
Pressure temperature diagram
Figure 1 Steam
It is used to indicate the relationship between the three phases of water.In Figure 1, the evaporation line represents the set of equilibrium saturation states of water vapor coexistence, and the melting line and sublimation line represent the set of equilibrium saturation states of ice water and ice vapor respectively.ThreeSaturation curveThe existing form of water is divided into three regions: ice, water and steam.The vertex C of the evaporation line is calledcritical point。exceedcritical pressureThe mutual transformation process of liquid phase and gas phase is continuous, and there is no coexistence of two phases.The critical pressure of water p0=22.1287 MPa, and the critical temperature T0=647.3K.stayThree phase pointT, ice, water and steam are in dynamic balance.Three phase point of waterPressure pT=610.76 Pa, temperature TT=273.16K.
Pressure volume diagram
The state of water vapor and its change process can be represented by water pressure volume diagram.A0a ′ a ″ a line indicates the formation process line of water vapor at a certain pressure, AT is the saturated water line coexisting with ice and water, and the left side of AT is the ice area of solid phase;TC issteamCoexisting saturated water lines, and the water area between AT and TC lines is liquid phase;CV is drySaturated steamThe area between TC and CV lines is the wet steam area where water and steam coexist, and the dryness x represents the dry saturated steam content per kilogram of wet steam;The right side of the CV line representssuperheated steamZone.
Temperature entropy diagram
The temperature entropy diagram is often used to analyze the thermal process or thermal cycle of water steam.TC is saturated waterline, CV is drySaturated steamLine, according to the definition of specific entropy, the area below the constant pressure process line a0a ′ a ″ a represents the heat absorption per kilogram of water in the reversible constant pressure process.Wherein, the area under a0a 'line represents the heat required to heat unsaturated water to saturated water under this pressure, qL, and the area under a' a 'line representsvaporizationHeat absorption of the process, i.eLatent heat of vaporizationγ. A ″ a indicates the transformation from saturated steam tosuperheated steamHeating capacity qS.
Enthalpy entropy diagram
It is more convenient to use the enthalpy entropy diagram in the calculation of steam power engineering.CV is the saturation curve, C is the critical point, the lower side of the saturation curve is the wet steam area, and the upper side issuperheated steamZone.The constant dryness line and constant pressure line (at this time, the constant temperature line) are drawn in the wet steam area, and the constant pressure line and constant temperature line are respectively drawn in the superheated steam area.
Steam utilization
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The heat energy of water vapor can be transformed into mechanical energy, heating and evaporating liquid, etc.The first attempt to use water vapor to do work (to lift water high) began in the 17th century.[1]
In 2002, Oshima Keren used the steam treatment unit to conductCryptomeria fortuneiStudy on the mechanical properties of specimens.
In April 1998,AnshanJiangxi Coking Refractory Design and Research InstituteJingdezhenThe industrial gas production device designed by Coking Gas General Plant has selected this technology toYimaLong flame coalAs the raw material, air steam is used as the gasifying agent to produce industrial gas. The gas production capacity of a single furnace is lxl lined/h, which has been put into use in February 2001.
In 1997, the working group proposed a formula for calculating the thermodynamic properties of industrial water and steam.
Wang LiangenEqual to that of Fuzhou Plastic Rubber Factory and Fujian Sanfeng Shoes Co., LtdTriphenylWaste gas is treated byactivated carbon adsorption - Combined technology of steam desorption and industrial water condensation.
In January 1997, a set of gravity devices was installed in the gap between the shutdown of the sintering plantspray The dust remover uses the density difference between the moisture vapor flue gas and the atmosphere, does not need any external power, and works by natural ventilation.
After being sealed with glass glue along the water lap joint of the aluminum plate, the aluminum plate not only plays a protective role, but also acts as a damp proof layer. However, due to the large number of lap joints in the actual construction, most of the work of gluing and sealing is neglected, and the water vapor in the outside air is easy to penetrate into the polyurethane pores, causing damage due to thermal expansion and cold contraction,Therefore, we paid special attention to this work in the thermal insulation of the continuation project of the new 12 large tanks in 1995.
In 1990, the International Society for Water and Steam Properties IAPWS established a working group composed of scientists from many countries to study new calculation formulas.
The "atmospheric thermal deaeration method without water steam" invented by Jinling Petrochemical Company Refinery was introduced on March 12, 1986Patent Office of the People's Republic of ChinaHe applied for a patent for invention. After nearly five years of examination, the China Patent Office granted the patent on December 12, 1990Invention patent。
Of the 18 major hidden dangers identified in the safety month of 1984, 10 have been rectified,XiangshanThe original design lifting load of the foundry workshop building of the metallurgical machinery factory was 8 tons, but it was oftenOverloadOperation, causing many cracks on the roof;The steel roof truss of the water explosion room was corroded by steam and gas, and the weld seam was severely corroded, and the cement hanging strip had peeled off outside.
In the middle of November 1982, the high temperature of 37 ℃ appeared again in the upper corner of the working face, accompanied by water vapor and "sweat" phenomenon,Spontaneous combustion of coalThe symptoms are quite obvious.
This means that no waterproof coating is needed to block the wind and rain drops, but for the water vapor emitted by the human body, it is enough to escape, that is, it can "breathe" moisture permeability and weather resistance, such as SavinaDP ultra dense waterproof fabric developed by Zhongfang Company in 1981.
Later, in 1975 and 1977, the International Association for the Properties of Water Vapor (IAPS) successively released the latest test data sheets of viscosity and thermal conductivity that had been identified.
During the pre test of the electrolytic cell in February 1972, under the attack of 90 ℃ wet chlorine and salt water vapor, the cell cover blistered and fell off within a few hours of use. The bottom of the cell had many cracks due to poor quality of cement curing, salt water penetrated, and salt water leaked from the anode head joints and around the bottom edge. At the same time, the asphalt was softened and leaked out of the bottom surface of the cell in the form of bacteria.
In 1972, the corrosion resistance test of various covers of the sulfide ore thickener was conducted in the medium containing hydrogen sulfide and water vapor at 80 ℃.
APV andToriAfter the first production type vacuum steam defrosting device jointly developed by (Torrey) Research Institute came out, this defrosting method entered a practical stage and played an important role in the defrosting process of frozen products.
In 1971, in a plan to reduce the escape of effective gas, fly ash and water vapor from the odor thickener in two stages, one of the first plants to use PFR thickener at 470 tons/day was to set up a daily recovery furnace system and replace it with a PFR thickener directly in the United StatesMontanaThe contact evaporator of Hoerner Waldorf Co., Ltd., and an economizer and a static plant are installed at the same time.
Water steam researched and developed by ChinaDesorptionfixed bedMolecular sieve dewaxingTechnology, which has a history of more than 20 years, has been in Nanjing, YanhuaDaqingRefinery, Jingmen Refinery and Linyuan Refinery have built five sets to produce light liquid wax orHeavy liquidWax production equipment.
Most of the boiler thermal calculation schemes refer to the Japanese white paper, the steam turbine is subject to the simplified thermal test (specifications of the Ministry of Water and Electricity), and the formula refers to the Japanese white paper, water and steamstate equation Use the 1968 IFC formula.
The equipment was put into production in 1967, and the operating medium is cokeresidual oil, oil, gas and water vapor, etc.
In order to adapt to the above changes, based on the "1967 IFC formula for industry" proposed by the International Formulation Committee, we developed a general software for calculating the thermodynamic properties of water and steam, and realized the general computer solution of the thermodynamic properties of water and steam.
When preparing the general program for calculating the thermodynamic properties of water and steam, the formula fitted by the Soviet Institute of Thermal Engineering was used for some inaccurate areas, and the individual coefficients in the formula were slightly modified, mainly in accordance with the 1967 IFC formula for industry.
The IFC formula was proposed by the International Formulation Committee (IFC) in 1967, and the chart and table of water and steam properties adopted until 2013 were based on the IFC formula.
The 1967 IWi formula is used for the property table of water and steam.
The calculation scope covers the whole region specified in the "1967 IFC Formula for Industry" formulated by the International Formulation Committee (IFC) of the Sixth International Conference on the Nature of Water and Steam.
The calculation procedure of water and steam table adopts the currently internationally recognized "IFC Formula 1967 for Industry" as the calculation basis, which can calculate theSaturation temperature, saturation pressure, enthalpy h, entropy sSpecific volumev、Exergy e.
Based on Baker's flow diagram, in 1961, Goldman [obtained the flow diagram of adiabatic steam water two-phase flow, making the research of two-phase flow enter the stage of steam liquid two-phase flow.
In 1960, Mr. Zhou Chang and Mr. Yang Hongshi of Wuhan University used warm steam stored in ordinary thermos bottles to treat Ji Sui, so as to hasten the flowering of Yi Xiong.
In 1959, I finally engaged in the production of pine needle oil. The crushed needles were distilled with steam, and the distillate was separated from oil and water to collect pine needle oil.
In 1956, a new tail gas absorption tower was built in a factory. After it was put into operation, a stream of self smoke emitted from the tail gas chimney. At that time, we didn't know enough about it. Which is the tail gas absorption tower that uses ammonia water to recycle and absorb? There must be water vapor generated. Self smoke is water vapor, which is inevitable.
In just a few years from 1954 to 2013, Yingtan held the sex play of water and steam at the Yuhui International Conference.
From 1954 to 2013, two international conferences were held consecutively to discuss the nature of water and steam.
Since 1954, the nitrogen concentration in atmospheric water vapor and rainwater has gradually increased due to the nuclear test in the atmosphere.
In 1941, Harteck of Germany and urey of the United States put forward the idea of water steam and hydrogen exchange productionheavy water, shortly afterNorwayBuild the world's first hydrogen waterIsotope exchange methodHeavy Water Production Factory Association, L.
In 1929, Miyada and others in Japan inventedAluminum anodizingMembrane steam sealing method, boiling water andpotassium dichromateThe solution sealing method has thus laid a practical technical foundation for the industrialization of aluminum anodization.
16. Moliere, a German, proposed the enthalpy entropy diagram of water vapor in 1904.
In early 1895,WilsonThe method created by J. Aitken: Aitken discovered as early as 1880 that the gas rising from the flame can cause the deposition of water vapor in the saturated gas. Aitken called the device that can allow water vapor to self condense "dust meter"
In 1705, British blacksmith Newcomen made the first mine steam pump.
Steam distillation
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principle
The operation of steam distillation is to introduce water vapor into the organic matter that is insoluble or insoluble in water but has certain volatility (the vapor pressure is at least 1333.9Pa at nearly 100 ℃), so that the organic matter can be distilled out together with water vapor at a temperature below 100 ℃.
Of two immiscible liquid mixturesVapor pressure, equal to the sum of vapor pressure of two liquids when they exist alone.When the sum of the vapor pressures of the two liquids that make up the mixture is equal to the atmospheric pressure, the mixture begins to boil.The boiling point of immiscible liquefied mixture is lower than that of each substance alone.Therefore, in the organic matter insoluble in watersteamDuring steam distillation, the material can be distilled out at a temperature much lower than the boiling point of the material, and even lower than 100 ℃.
In distillate, the mass ratio of organic matter distilled with water vapor to water is equal to the partial pressure (PA and PH2O) of both andrelative molecular mass(MA and 18), so the mass ratio of organic matter to water in distillate can be calculated as follows:
For example, when the mixture of aniline and water is distilled with water vapor, the boiling point of aniline is 184.4 ℃, and the mixture of aniline and water boils at 98.4 ℃.At this temperature, theVapor pressureIt is 5599.5Pa, the vapor pressure of water is 95725.5Pa, and the sum of the two is 101325Pa.The relative molecular weight of aniline is 93, so the mass ratio of aniline to water in distillate is equal to:
Since aniline is slightly soluble in water, this calculation is only approximate.
steamDistillation is one of the important methods used to separate and purify organic compounds. It is commonly used in the following situations: high boiling organic compounds that can be separated by distillation;The mixture contains a large amount of resin like or tar like and nonvolatile impurities, which are difficult to be separated by distillation, extraction and other methods;Separating the adsorbed liquid from the reaction mixture with more solids;Remove volatile organic matter from the reaction mixture.[1]
Steam distillation unit and operation
Steam distillation unit, mainly composed of steam generator A, three ports or two portsRound bottom flaskD and long straight water-cooled condenser pipe F.If the reaction is carried out in a round bottom flask, a distillation head (or a Kirschner distillation head) can be fitted on the round bottom flask insteadThree necked flask。The iron generator A can usually be replaced by a two or three mouth flask.The water contained in the device accounts for about 1/2 of its capacity, and the horizontal plane in the device can be viewed from the glass water level tube on its side.Long glass tube B is a safety tube.The lower end of the tube is close to the bottom of the device, and the water vapor pressure can be estimated according to the height of the water column in the tube.Round bottom flask D should be clamped with iron clamp, and its middle mouth should pass through the screw mouthConnector insertionThe side opening of the steam pipe C is inserted into the distillate pipe E.The outer diameter of conduit C is generally not less than 7mm to ensure
Steam distillation unit
A - Steam generator B - Safety pipe C - Steam pipe D - Three mouth round bottom flask
E - distillate pipe F - condenser pipe
steamIt shall be smooth, and its end shall be close to the bottom of the flask, so that water vapor and distilled substances can fully contact and stir.Conduit E should be slightly thicker, with an outer diameter of about 10mm, so that steam can enter the condenser tube smoothly.If the diameter of tube E is too small, the export of vapor will be hindered to some extent, which will increase the pressure in flask D.The section of conduit E before the bend shall be as short as possible;The later section at the bend is allowed to be slightly longer, because it can lift part ofcondensationeffect.The distillate can be fully cooled by using a long straight water-cooled condenser tube F.Since the evaporation latent heat of water is large, the flow rate of cooling water should also be slightly larger.One is used between the branch pipe of generator A and the steam pipe CT-tubeconnect.A short rubber pipe is sleeved on the branch pipe of the T-shaped pipe and screwed tightly with a screw clamp, which can be used to remove the condensed water from the steam.In case of abnormal phenomenon during operation, the clamp shall be opened immediately to connect with the atmosphere.
Pour the substance to be distilled into flask D, the amount of which is about 1/3 of the flask capacity.Before operation, the steam distillation unit shall be inspected and must be tight without air leakage.To start the distillation, first open the clamp on the T-tube and heat the water in the generator to boiling with a direct flame.When there is water vapor fromT-tubeWhen the branch pipe of is flushed out, tighten the clamp again to let the water vapor flow into the flask. At this time, the mixture in the flask can be seen tossing, and soon appears in the condenser pipeOrganic matterAnd water.Adjust the flame so that the mixture in the bottle will not splash too much, and control the speed of distillate to about 2-3 drops per second.In order to avoid excessive condensation of water vapor in the flask, the flask can usually be heated with low fire during distillation.During operation, pay attention to whether the water column in the safety pipe rises abnormally at any time, open the clamp immediately, remove the flame, and find out the cause of the fault;The distillation can be continued only after troubleshooting.
The distillation can be stopped when the distillate is clear and transparent and no longer contains oil drops of organic substances.At this time, first open the clamp, and then remove the flame[2]。
