There are many open reservoirs on Earth, from the surface of which water evaporates: oceans and the sea occupy about 80% of the ground surface. Therefore, there are always water vapor in the air.
It is easier air, because the molar weight of the water (18 * 10-3 kg mol-1) is less molar mass Nitrogen and oxygen, of which the air mainly consists. Therefore, water vapor rises up. At the same time, it expands, since in the upper layers of the atmosphere, the pressure is lower than that of the surface of the Earth. This process can be approximately an adiabatic, because during that time until it occurs, the heat exchange pair with the surrounding air does not have time to happen.
1. Explain why the pairs are cooled.
They do not fall because the ascending air flows are hijacked in the rising air flows, just like the deltaplans (Fig. 45.1). But when drops in the clouds are becoming too big, they begin to fall after all: it's raining (Fig. 45.2).
We feel comfortable when water vapor pressure room temperature (20 ºС) is about 1.2 kPa.
2. What part of (in percent) is the specified pressure from the saturated pair pressure at the same temperature?
Prompt. Use the table of saturated water vapor pressure values \u200b\u200bat different temperatures. It was given in the previous paragraph. We give a more detailed table here.
You have now found relative air humidity. We give her definition.
The relative humidity of the air Φ is called the ratio of the partial pressure P of water vapor to the pressure of the PN of a saturated pair at the same temperature:
φ \u003d (P / PN) * 100%. (one)
Comfortable conditions for humans correspond to relative humidity of 50-60%. If a relative humidity Essentially less, the air seems to us dry, and if more - wet. When relative humidity approaches 100%, the air is perceived as raw. The puddles do not dry out, because the processes of evaporation of water and condensation of the couple compensate each other.
So, about the relative humidity of the air judges how much water vapor in the air is close to saturation.
If the air with an in unsaturated water vapor is isotherly compressed in it, it will increase both air pressure and pressure of an unsaturated pair. But the pressure of the water vapor will increase only until it becomes saturated!
With a further decrease in the volume of air pressure will continue to increase, and the water vapor pressure will be constant - it will remain equal to the pressing of the saturated pair at a given temperature. Excess couple is condensed, that is, it will turn into water.
3. In the vessel under the piston is air, the relative humidity of which is 50%. The initial volume under the piston is 6 l, the air temperature is 20 ºС. Air starts isothermally compressed. Please accept the volume of water formed from steam can be neglected compared to air and steam.
a) What will the relative humidity of the air be equal when the volume under the piston becomes 4 l?
b) With what volume under the piston of pairs will be saturated?
c) What is the initial mass of steam?
d) How many times will the mass of the pair decrease when the volume under the piston becomes 1 l?
e) What kind of water is condensed?
2. How depends relative humidity from temperature?
Consider how the nipper and the denominator in the formula (1) decreases with the relative humidity of the air.
In the numerator there is a pressure of an unsaturated water vapor. It is directly proportional to the absolute temperature (we recall that water steam is well described by the equation of the state of the ideal gas).
4. How much percent increases the pressure of an unsaturated pair with increasing temperature from 0 ºС to 40 ºС?
And now let's see how the pressure of a saturated pair standing in the denominator changes.
5. How many times the saturated pair pressure increases with increasing temperature 0 ºС to 40 ºС?
The results of these tasks show that with an increase in temperature, the pressure of the saturated steam increases much faster than the pressure of an unsaturated steam, therefore, determined by the formula (1) the relative humidity of the air is rapidly decreasing with increasing temperature. Accordingly, when the temperature decreases, the relative humidity increases. Below we consider it more.
When performing the next task, the equation of the state of the ideal gas and the table above will help.
6. At 20 ºС, the relative humidity of the air was equal to 100%. The air temperature increased to 40 ºС, and the mass of the water vapor remained unchanged.
a) What was the initial pressure of the water vapor?
b) What was the final water vapor pressure?
c) What is the saturated pair pressure at 40 ºС?
D) What is the relative air humidity in the final state?
e) How will this air be perceived by a person: how dry or how is wet?
7. In the raw autumn day, the temperature on the street 0 ºС. In the room, the temperature is 20 ºС, the relative humidity is 50%.
a) where is the more partial pressure of water vapor: in the room or on the street?
b) Which way will the water vapor go, if you open the window, is to a room or from the room?
c) What would be the relative humidity in the room if the partial pressure of water vapor in the room became equal to partial pressure of water vapor outside?
8. Wet objects are usually heavier dry: so, the grinding dress is heavier dry, and raw firewood is heavier dry. It is explained by the fact that the weight of the moisture contained in it is added to its own body weight. And with the air it is the other way around: wet air is easier dry! How to explain it?
3. Dew point
With a decrease in temperature, the relative humidity of the air increases (although the mass of water vapor in the air does not change).
When the relative air humidity reaches 100%, water vapor becomes saturated. (With special conditions, it is possible to obtain oversathedral steam. It is used in the Wilson chambers to detect traces (tracks) of elementary particles on accelerators.) With a further decrease in the temperature, the water vapor condensation begins: dew drops. Therefore, the temperature at which this water vapor becomes saturated, called the dew point for this steam.
9. Explain why the dew (Fig. 45.3) is usually falling into the preliminary hours.
Consider an example of finding a point of dew to air of a certain temperature with a given humidity. For this we need the following table.
10. A man in glasses entered the street to the store and found that his glasses were fucked. We assume that the temperature of the glasses and the air layer adjacent to them is equal to the air temperature on the street. The air temperature in the store is 20 ºС, the relative humidity is 60%.
a) Is water vapor in a layer of air adjacent to glasses saturated?
b) What is equal to the partial pressure of water vapor in the store?
c) at what temperature is the water vapor pressure equal to the pressure of a saturated pair?
d) What could be the air temperature on the street?
11. In the transparent cylinder under the piston there is air with a relative humidity of 21%. The initial air temperature is 60 ºС.
a) to which temperature need to cool the air at a constant volume so that Rosa falls in the cylinder?
b) How many times do you need to reduce the amount of air at a constant temperature so that dew in the cylinder?
c) the air is first isothermally compressed, and then cooled at a constant volume. The dew loss began when the air temperature fell to 20 ºС. How many times did the air volume reduced compared to the initial?
12. Why is the strong heat are harder tolerated with high humidity?
4. Measuring moisture
Air humidity is measured often with a psycho metro (Fig. 45.4). (From the Greek "Psychos" - cold. This name is due to the fact that the testimony of a wet thermometer is lower than dry.) It consists of dry and wet thermometers.
The testimony of a wet thermometer is lower than dry, because when evaporated, the liquid is cooled. The smaller the relative humidity of the air, the more intense there is evaporation.
13. What thermometer in Figure 45.4 is it located left?
So, according to thermometers, you can determine the relative humidity of the air. To do this, use a psychrometric table, which is placed often on the psychrometer.
To determine the relative humidity of the air, it is necessary:
- Remove the thermometers (in this case 33 ºС and 23 ºС);
- find a string in the table corresponding to the testimony of a dry thermometer, and a column, the correspondences of the difference difference of thermometers (Fig. 45.5);
- At the intersection of the string and column, read the value of the relative humidity of the air.
14. Using a psychrometric table (Fig. 45.5), determine under what indications of thermometers relative air humidity is 50%.
Additional questions and tasks
15. In the greenhouse of 100 m3, it is necessary to maintain relative humidity of at least 60%. Early in the morning at a temperature of 15 ºС in the greenhouse dropped dew. Temperature in the daytime in the greenhouse rose to 30 ºС.
a) What is equal to the partial pressure of water vapor in the greenhouse at 15 ºС?
b) What is the mass of water vapor in the greenhouse at this temperature?
c) What is the minimum allowable partial pressure of water vapor in the greenhouse at 30 ºС?
d) What is the mass of water vapor in the greenhouse?
e) What kind of water is needed to evaporate in a greenhouse to support the necessary relative humidity in it?
16. On a psychrometer, both thermometers show the same temperature. What is the relative humidity of the air? Explain your answer.
Word moisture
The word moisture in the Dalian dictionary
g. Liquid in general: | wet, dampness; water. Volga, oil, oil, oil, oil. Without moisture and heat, no vegetation, there is no life.
What does the air humidity depend on?
In the air now foggy moisture. Wet, resulted in moisture, raw, wet, wet, wet. Wet summer. Wet meadows, fingers, air. Wet place. Humidity Dampness, wet, wet, wet state. Welcome to, moisten, make wet, water or drink water. Moistimer m.
hygrometer, gear showing air humidity.
The word moisture in the dictionary of Ozhegov
Moisture, - and g. Dampness, water contained in any. Air saturated air.
The word moisture in the Efremova dictionary
Accent: moisture
- Liquid, water or evaporation, contained in anything
Wagist's word in the FAS Max dictionary
moisture
borrow.
from the TsSlav., Wed. St.-Slav. moisture (sup.). See Volga.
Word moisture in the dictionary D.N. Ushakova
Moisture, moisture, mn. No, · wives (· Book.). Dampness, water, evaporation. Plants require a lot of moisture. Air is saturated with moisture.
The word moisture in the Synonyms Dictionary
alcohol, water, wet, humidity, liquid, dampness, raw materials
The word moisture in the dictionary Synonyms 4
water, wet, damp
Wague word in the dictionary Full accentuated paradigm by A. A. Zaliznya
moisture,
moisture
moisture
moisture
moisture
moisture
moisture
moisture
moisture
moisture
moisties,
moisture
moisture
The psychrometer of Augustus consists of two mercury thermometers, fortified at the tripod or located in the general case.
The ball of one thermometer wrapped with a thin batted tissue, lowered into a cup with distilled water.
When using a psychrometer of August, the calculation of absolute humidity is produced by the Rainier formula:
A \u003d f-a (T-T1) H,
where a is absolute humidity; F is the maximum voltage of water vapor at a humid thermometer temperature (see
table 2); a - psychrometric coefficient, T - the temperature of the dry thermometer; T1 - the temperature of the wet thermometer; H - barometric pressure at the time of definition.
If the air is completely immobile, then a \u003d 0.00128. With a weak air movement (0.4 m / s) A \u003d 0.00110. The maximum and relative humidity is calculated as indicated on page.
What is air humidity? What does it depend on?
| Air temperature (° C) | Air temperature (° C) | Voltage of water vapor (mm Hg. Art.) | Air temperature (° C) | Voltage of water vapor (mm Hg. Art.) | |
| -20 - 15 -10 -5 -3 -4 0 +1 +2,0 +4,0 +6,0 +8,0 +10,0 +11,0 +12,0 |
0,94 1.44 2.15 3.16 3,67 4,256 4,579 4,926 5,294 6,101 7,103 8.045 9,209 9,844 10,518 |
+13,0 +14,0 +15,0 +16,0 +17,0 +18,0 +19,0 +20,0 +21,0 +22,0 +24,0 +25,0 +27,0 +30,0 +32,0 |
11,231 11,987 12,788 13,634 14,530 15,477 16.477 17,735 18,650 19,827 22,377 23,756 26,739 31,842 35,663 |
+35,0 +37,0 +40,0 +45,0 +55,0 +70,0 +100,0 |
42,175 47,067 55,324 71,88 118,04 233,7 760,0 |
Table 3.
Determination of relative humidity according to indications
Aspiration psychrometer (in percent) 
Table 4. Determination of the relative humidity of air according to the testimony of dry and wet thermometers in the psychrometer of August under normal conditions of calm and uniform air movement in the room at a speed of 0.2 m / s 
To determine the relative humidity there are special tables (Tables 3, 4).
More accurate indications gives psychrometer Assman (Fig. 3). It consists of two thermometers enclosed in metal tubes through which the air is evenly sucked using a wreck fan located in the upper part of the instrument.
The mercury tank of one of the thermometers will be wrapped by a piece of batistist, which, before each definition, is wetted by distilled water with a special pipette. After the thermometer is worried, the fan is cut the key and hang the device to tripod.
After 4-5 minutes, the readings of dry and wet thermometers are recorded. Since from the surface of the mercury ball, moistened thermometer, there is evaporation of moisture and the absorption of heat, it will show a lower temperature. The calculation of absolute humidity is made according to the Sprung formula: 
where a is absolute humidity; F is the maximum voltage of water vapor at a humid thermometer; 0.5 is a constant psychrometric coefficient (correction for air traffic); t - the temperature of the dry thermometer; T1 - the temperature of the wet thermometer; N - barometric pressure; 755 - Average barometric pressure (defined in table 2).
The maximum humidity (f) is determined using Table 2 for the temperature of the dry thermometer.
Relative humidity (R) are calculated by the formula:
where R is relative humidity; A - absolute humidity; F is the maximum humidity at a dry thermometer temperature.
To determine the oscillations of relative humidity in time, use the instrument of a hygrograph.
The device is arranged similarly to the thermographer, but perceiving part of the hygrograph is a fatged hair beam.
Fig. 3. Aspiration psychrometer Assman:
1 - metal tubes;
2 - mercury thermometers;
3 - holes for the release of amusement air;
4 - clamp for hanging a psychrometer;
5 - Pipette for wetting a wet thermometer.
The weather forecast for tomorrow
Compared with yesterday's day in Moscow, it's a bit cold, the ambient temperature dropped from 17 ° C yesterday to 16 ° C today.
Weather forecast for tomorrow does not promise significant changes in temperature, it will remain at the same level from 11 to 22 degrees of heat.
The relative humidity of the air increased to 75 percent and continues to rise. Atmosphere pressure Over the past day, it has not significantly decreased by 2 mm mercury post, and it became even lower.
Actual weather today
According to N. 2018-07-04 15:00 In Moscow, shower blowing a weak wind
Weather norms and conditions in Moscow
Weather features in Moscow are determined primarily by the location of the city.
The capital is located on the Eastern European Plain, and warm and cold air masses are freely moving above the metropolis. Atlantic and Mediterranean cyclones are influenced by the weather in Moscow, which is why the precipitation level is higher here, and in winter warmer than in cities that are on this latitude.
Weather in Moscow reflect all the phenomena characteristic of a moderately continental climate. The relative instability of weather is expressed, for example, in cold Winter, with sudden thaws, sharp cooling in the summer, losing a large amount of precipitation. These and other weather phenomena are not uncommon. In the summer and autumn in Moscow, fogs are often noted, the cause of which lies in part and in human activity; Thunderstorms, which happened even in winter.
In June 1998, a strong flurry was lost to eight people, 157 people were injured. In December 2010 strong ice rain, due to the temperature difference at height and on Earth, turned the streets to the rink, and the giant icicles and the trees fell under the weight of ice fell on people, buildings and cars.
The temperature minimum in Moscow was recorded in 1940, it was -42.2 ° C, the maximum - + 38.2 ° C was noted in 2010.
The average temperature of July in 2010 - 26.1 ° - close to normal Arab Emirates And Cairo. And in general, 2010 became a record holder in the number of temperature maxima: during the summer 22 daily records were installed.
Weather in the center of Moscow and the outskirts of Nodinakov.
What does the relative humidity of the air depend on?
Temperature B. central regions Above, in winter, the difference can be up to 5-10 degrees. Interestingly, official weather data in Moscow is provided with weather station at the All-East of the city, and this is a few degrees below the temperature setting of the meteorological station on the ballot in the center of the metropolis.
Weather in other cities in Moscow Region\u003e
Dry substances and humidity
Water is one of the most common substances on the ground, it is prerequisite life and is part of all food products and materials.
Water, without actually nutrient, is vital as a body temperature stabilizer, carrier of nutrients (nutrients) and digestive waste, reagent and reaction medium in a number of chemical transformations, a stabilizer of the conformation of biopolymers and, finally, as a substance that facilitates the dynamic behavior of macromolecules, including The manifestation of catalytic (enzymatic) properties.
Water is the most important component of food.
It is present in a variety of plant and animal products as a cellular and extracellular component, as a dispersing medium and a solvent, conditioning consistency and structure. Water influences on appearanceThe taste and stability of the product during storage. Thanks to physical interaction with proteins, polysaccharides, lipids and salts, water makes a significant contribution to the structure of food.
The total humidity of the product indicates the amount of moisture in it, but does not characterize its involvement in chemical and biological changes in the product.
In ensuring its stability during storage important role Plays the ratio of free and bound moisture.
Related moisture - These are associated water, firmly associated with various components - proteins, lipids and carbohydrates due to chemical and physical connections.
Free moisture - This is a moisture not bound by a polymer and affordable for the flow of biochemical, chemical and microbiological reactions.
Direct methods from the product are extracting moisture and set its number; indirect (drying, refractometry, in density and electrical conductivity of the solution) - determine the content of dry substances (dry residue). Independent also includes a method based on the interaction of water with certain reagents.
Definition of moisture content drying to constant mass (arbitration method) Based on the separation of hygroscopic moisture from the object under study at a certain temperature.
Drying is carried out to a constant mass or accelerated methods at elevated temperatures for the specified one.
Drying sintering in dense mass is produced with crystal sand, the mass of which should be 2-4 times the mass of the sample.
The sand gives a porosity on the sample, increases the surface of the evaporation, prevents the formation of a crust on the surface that impede moisture removal. Drying is made in porcelain cups, aluminum or glass fuques for 30 minutes, at a certain temperature depending on the type of product.
The mass fraction of dry substances (x,%) is calculated by the formula
where m is the mass of fuces with a glass stick and sand, r;
m1 - Mass of fuces with glass stick, sand and
jerk to drying, r;
m2 - Mass of fuces with glass wand, sand and hitch
after drying, G.
Drying in the RF apparatus is made due to infrared radiation in the apparatus, consisting of two interconnected massive circles round or rectangular shape (Figure 3.1).
Figure 3.1 - WPC device for determining humidity
1 - handle; 2 - upper stove; 3 - control unit; 4 - bottom stove; 5 - electrocontact thermometer
In working condition between the plates, the clearance is set 2-3 mm.
The temperature of the heating surface is controlled by two mercury thermometers. To maintain a constant temperature, the device is equipped with a contact thermometer enabled in series with a relay. A set temperature is set on the contact thermometer. The device includes a network for 20 ... 25 minutes before the start of drying to heat up to a predetermined temperature.
The product is dried in a rotary paper package with a size of 20x14 cm for 3 minutes at a certain temperature, cooled in the desiccator 2-3 minutes and quickly weighed up to 0.01.
Humidity (x,%) are calculated by the formula
where m is the mass of the package, r;
m1 - a mass of a package with a hitch to drying, r;
m2 - Mass of a package with a dried jacket,
Refractometric method Apply for production control in determining the content of dry substances in objects of sucrose rich: sweet dishes, drinks, juices, syrup.
The method is based on the relationship between the refractive index of the object under study or an aqueous exhaust from it and the concentration of sucrose.
Air humidity
The refractive index depends on the temperature, so the measurement is carried out after thermostatting the prisms and the underlying solution.
Mass of dry substances (x, d) for drinks with sugar are calculated by the formula
where a is massive for dry substances defined
refractometric method,%;
P is the volume of the drink, cm3.
for syrups, fruit and berry and dairy kissels, etc.
according to the formula
where a is the mass fraction of dry substances in solution,%;
m1 - mass of dissolved hitch, g;
m - weight of the mood,
In addition to these common methods for determining dry substances, another number of methods are applied to determine the content of both free and related moisture
Differential scanning colorimetry.
If the specifies to the temperature is less than 0 ° C, then the free moisture will freeze the associated - no. When the frozen sample is heated, heat consumed when melting ice can be measured in colorimeter.
Unimagressive water is defined as the difference between the common and freezing water.
Dielectric measurements. The method is based on the fact that at 0 ° C value of the dielectric permeability of water and ice is approximately equal. But if part of the moisture is connected, its dielectric properties should differ much from the dielectric properties of volumetric water and ice.
Measuring heat capacity.
Water heat capacity is greater than ice heat capacity, because With an increase in temperature in the water, hydrogen bonds take place. This property is used to study the mobility of water molecules.
The value of heat capacity, depending on its content in the polymers, provides information on the number of bound water. If at low concentrations the water is specifically connected, then its contribution to the heat capacity is small. In the area of \u200b\u200bhigh humidity values, it basically determines the free moisture, the contribution of which to the heat capacity is about 2 times more than ice.
Nuclear magnetic resonance (NMR). The method is to study water mobility in a fixed matrix.
In the presence of free and associated moisture, two lines are obtained in the NMR spectrum instead of one for volumetric water.
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Air humidity. Units. Impact on the work of aviation.
Water is a substance that can simultaneously be in various aggregate states at the same time: gaseous (water vapor), liquid (water), solid (ice). These states and call sometimes phase state of water.
Under certain conditions, water from one (phase) state can go to another. So water vapor can go into a liquid state (condensation process), or by bypassing the liquid phase, go to solid state - ice (sublimation process).
In turn, water and ice can go into the gaseous condition - water vapor (evaporation process).
Under moisture is understood as one of the phase states - a water vapor contained in the air.
It enters the atmosphere by evaporation from water surfaces, soil, snow, vegetation cover.
As a result of evaporation, part of the water goes into a gaseous state, forming a steam layer over the evaporating surface.
Relative humidity
This pair of air flow is transferred in vertical and horizontal directions.
The evaporation process continues until over the evaporating surface, the amount of water vapor does not reach full saturation, that is, the maximum amount of possible in this volume with constant pressure and air temperature.
The amount of water vapor in the air characterizes the following units:
Elasticity of water vapor.
Like any other gas, water vapor has its own elasticity and puts pressure that is measured in MM.RT.st or GPa. The amount of water vapor in these units is indicated: actual - e.saturated - E. On weather stages by measuring elasticity in the GPA, observations of water vapor humidity are observed.
Absolute humidity. It is the amount of water vapor in grams contained in one cubic meter of air (g /).
Letter but - denotes the actual number, letter BUT - Satisfying space. Absolute moisture is close to the elasticity of water vapor expressed in MM RT Art, but not in the GPA, at a temperature of 16.5 s. e. and but equal to each other.
Specific humidity It is the amount of water vapor in grams contained in one kilogram of air (g / kg).
Letter q -denotes the actual number, letter Q -satisfy space. The specific moisture content is a convenient value for theoretical calculations, as it does not change when heating, cooling, compressing and expanding air (if only air condensation does not occur). The value of the specific humidity is used for all sorts of calculations.
Relative humidityit represents the percentage of the amount of water vapor contained in the air, to the amount that this space would be saturated at the same temperature.
Relative humidity is indicated by the letter r..
According to the definition
r \u003d E / E * 100%
The amount of water vapor saturation can be different, and depends on how many pair molecules can fly out of the evaporating surface.
Air saturation with water vapor depends on air temperature, the higher the temperature, the greater the amount of water vapor, and the lower the temperature, the more.
Dew point - This is the temperature to which air should be cooled so that the water steam contained in it has reached full saturation (at r \u003d 100%).
The difference between air temperature and dew point temperature (TDD) is called deficiency point of dew.
It shows how much it is necessary to cool the air so that the water vapor contained in it reached the saturation state.
With a small deficiency, air saturation occurs significantly faster than with a large saturation shortage.
The amount of water vapor depends on the aggregate state of the evaporating surface, from its curvature.
Under the same temperature, the amount of saturated pair is greater above the same ice (ice has durable molecules).
At the same temperature, the amount of steam will be large above the convex surface (the surface of the droplets) than above the smooth evaporating surface.
All these factors play a major role in the formation of fogs, clouds and precipitation.
The decrease in temperature leads to saturation of the water vapor existing in the air, and then to the condensation of this pair.
Air humidity has a significant impact on the nature of the weather by determining the conditions of flight. The presence of water vapor leads to the formation of fog, hasshes, clouds, complicating the flight of thunderstorms, ice rain.
The amount of moisture contained in one cubic air meter. Because of the low size is usually measured in g / m³. But due to the fact that at a certain temperature of the air, it can maximally contain only a certain amount of moisture (with increasing temperature, this maximum possible amount of moisture increases, with a decrease in air temperature, the maximum possible amount of moisture decreases), introduced the concept of relative humidity.
Relative humidity
Equivalent definition is the ratio of the molar fraction of water vapor in the air to the maximum possible at a given temperature. It is measured as a percentage and is determined by the formula:
where: - the relative humidity of the mixture under consideration (air); - partial pressure of water vapor in the mixture; - equilibrium pressure of saturated steam.
The pressure of saturated vapor water is growing greatly with increasing temperature. Therefore, with an isobaric (i.e., at constant pressure), the cooling of the air with a constant concentration of steam occurs the moment (dew point) when the pair is saturated. At the same time, the "extra" steam condenses in the form of fog or ice crystals. The processes of saturation and condensation of the water vapor play a huge role in the atmosphere physics: the processes of formation of clouds and the formation of atmospheric fronts in a large part is determined by the processes of saturation and condensation, the heat released during the condensation of the atmospheric water vapor provides energy mechanism The emergence and development of tropical cyclones (hurricanes).
Evaluation of relative humidity
The relative humidity of the water mixture can be estimated if its temperature is known ( T.) and dew point temperature ( T D.). When T. and T D. Celsius is expressed in degrees, then true expression:
where the partial pressure of the aqueous pair in the mixture is estimated:
and wet pressure steam water in the mixture at a temperature is estimated:
Limited water par
In the absence of condensation centers, with a decrease in temperature, the formation of an impregnated state is possible, that is, relative humidity becomes more than 100%. The condensation centers may be ions or particles of aerosols, it is on the condensation of a delayed steam on the ions formed during the passage of the charged particle in such a pair, the principle of operation of the Wilson chamber and diffusion cameras are based: water droplets condensing on the formed ions form a visible trail (track) charged Particles.
Another example of condensation of the oversaturated water vapor is the inversion traces of aircraft arising from condensation of a surprised water vapor on particles of engine exhaust pipes.
Means and methods of control
To determine air humidity, devices are used, which are called psychrometers and hygrometers. The psychrometer of August consists of two thermometers - dry and wet. A wet thermometer shows the temperature below than dry, since its tank is wrapped with a cloth moistened in water, which evaporated, cools it. The intensity of evaporation depends on the relative humidity. According to the testimony of dry and wet thermometers, relative humidity of air in psychrometric tables are found. Recently, integral humidity sensors have been widely used (as a rule, with voltage output), based on the property of some polymers change its electrical characteristics (such as dielectric permeability of the medium) under the action of water vapor contained in the air.
To increase relative humidity in residential premises, electric humidifiers filled with wet clamsite pallets and regular spraying are used.
Notes
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Watch what is "relative humidity" in other dictionaries:
The ratio of the molar fraction of moisture in the gas to the molar fraction of a saturated water vapor over water [ice] in this gas with the same pressure and temperature. Unit of measurement% [RMG 75 2004] Themes of measuring moisture of substances generalizing terms of magnitude ... ... Technical translator directory
relative humidity - the percentage of the elasticity of the water vapor contained in a unit of air volume, to the elasticity of the saturated pair at the same temperature ... Dictionary on geography
Relative humidity - 16. Relative humidity D. Relative Feuchtigkeit E. Relative Humidity F. Humidite Relative The ratio of partial pressure of water vapor to the pressure of saturated steam with the same pressure I am a temperature source ... Dictionary directory terms of regulatory and technical documentation
The ratio of the elasticity of the water vapor contained in the air to the elasticity of a saturated pair at the same temperature; It is expressed as a percentage. * * * Relative humidity relative humidity, the ratio of elasticity of water vapor (see elasticity ... ... encyclopedic Dictionary
relative humidity - Drėgnis Statusas T Sritis Standartizacija Ir Metrologija apibrėžtis drėgmės Ir Ją Sugėrusios Medžiagos Masių Arba Tūriń Dalmuo, Dažniausiai Išreikštas Procentais. Atitikmenys: Angl. Relative Humidity Vok. relative feuchte, f; Relative ... ... Penkiakalbis AiškinaMasis Metrologijos Terminų žodynas
relative humidity - SantyKinis Drėgnis Statusas T Sritis Chemija apibrėžtis drėgmės Ir Drėgnos Medžiagos, Kurioje Ji Yra, Masių Arba Tūrių Santykis (%). Atitikmenys: Angl. RELATIVE HUMIDITY RUS. Relative humidity ... Chemijos Terminų aiškinamasis žodynas
relative humidity - Drėgnis Statusas T Sritis Fizika Atitikmenys: Angl. Relative Humidity Vok. relative feuchte, f; Relative Feuchtigkeit, F Rus. Relative humidity, F PRANC. Humidité Relative, F ... Fizikos Terminų žodynas
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- provide assimilationconcepts humidity ;
- develop Independence of students; thinking; ability to draw conclusions; development of practical skills when working with physical equipment;
- showthe practical application and importance of this physical quantity.
Type of lesson: Lesson studying new material .
Equipment:
- for front work: a glass with water, a thermometer, a piece of gauze; Threads, psychrometric table.
- for demonstrations: Psychrometer, hair and condensation hygrometers, pear, alcohol.
During the classes
I. Repetition and checking homework
1. Word the definition of vaporization and condensation processes.
2. What types of vaporization do you know? What do they differ from each other?
3. What should the fluid evaporate occur?
4. Speed \u200b\u200bevaporation depends on any focus?
5. What is the dedication of vaporization?
6. What is the resulting amount of heat during vaporization?
7. Why is Hisrezhar postponed easier?
8. Is the internal energy of 1 kg of water and steam at a temperature of 100 ° C
9. Why water in a bottle, tightly closed plug, does not evaporate?
II. Studying new material
Water steam in the air, despite the huge surfaces of rivers, lakes, the ocean is saturated, the atmosphere is an open vessel. The movement of the air masses leads to the fact that in some places in this moment Water evaporation prevails over condensation, and in others, on the contrary.
The atmospheric air is a mixture of various gases and water vapor.
Pressure that would produce water vapor if all the others are gasesotsed, called partial pressure (or elasticity) water vapor.
The water vapor density contained in the air can be taken for air humidity. This magnitude is called absolute humidity [g / m 3].
Knowledge of partial pressure of water vapor or absolute humidity say nothing to the water vapor is far from saturation.
To do this, enter the magnitude showing how much water steam at this temperature is close to saturation - relative humidity.
Relative humidity call the ratio of absolute humidity to the density of 0 saturated water vapor at the same temperature expressed as a percentage.
P - partial pressure at a given temperature;
P 0 - the pressure of saturated steam at the same temperature;
Absolute humidity;
0 is the density of saturated water vapor at a given temperature.
The pressure and density of the saturated pair at different temperatures can be found using special tables.
When cooling wet air With constant pressure, its relative humidity increases, the lower the temperature, the closer the partial pressure of steam in the air to the pressure of the saturated steam.
Temperature t, to which the air should cool so that the steam in it reached the saturation state (with this humidity, air and constant pressure), is called dew point.
Pressure of saturated water vapor at an air temperature dew point There is a partial pressure of the water vapor contained in the atmosphere. When cooling the air to the dew point begins the condensation of vapors : fog appears, falls out dew.The dew point also characterizes the humidity.
Air humidity can be determined by special devices.
1. Condensation hygrometer
With it, they determine the dew point. This is the most accurate way to change relative humidity.
2. Hair hygrometer
Its effect on the properties of the human will fromand lengthened with increasing relative humidity.
Applied in cases where the collaboration of air humidity is not required of great accuracy.
3. Psychrometer
Usually enjoy in cases where a fairly accurate and rapid determination of air humidity is required.
Air humidity value for living organisms
At a temperature of 20-25 ° with the most favorable person, air with a relative humidity from 40% to 60% is considered to be air. When the environment has a temperature higher than the body temperature of a person, then a strengthened sweating occurs. Abundant selection of sweat leads to the cooling of the body. However, such a sweating is a significant burden for a person.
The relative humidity is below 40% at normal air temperature is also harmful, as it leads to enhanced loss of moisture of organisms, which leads to its dehydration. Especially low humidity indoor air in winter; It is 10-20%. With low air humidity occurs fast evaporation Moisture from the surface and drying of the mucous membrane of the nose, larynx, lungs, which can lead to deterioration of well-being. Also at low air humidity in external environment Pathogenic microorganisms remain longer, and more static charge accumulates on the surface of the items. Therefore, in the winter time, moisturizing with porous humidifiers produce in residential premises. Good humidifiers are plants.
If the relative humidity is high, then we say that the air wet and suffocating. High humidity is in oppressing, since evaporation occurs very slowly. The concentration of water vapors in the air in this case is high, as a result of which the air molecules return to the liquid almost as quickly as evaporated. If the sweat from the body evaporates slowly, then the body is cooled very weak, and we feel not entirely comfortable. With a relative humidity of 100%, the evaporation cannot occur at all - under such conditions, wet clothing or wet skin will never be dried.
From the course of biology, you know about the various fixtures of plants in arid areas. But plants are adapted to high humidity. So, Motherland Monster - wet equatorial forest Monster with relative humidity close to 100%, "crying", it removes excess moisture through the holes in the leaves - the guides. In modern buildings, air conditioning is available and maintaining air conditioning in closed rooms, the most profitable to the well-being of people. This automatically regulates temperature, humidity, air composition.
Exceptional importance for the formation of frost has air humidity. If the humidity is large and the air is close to the saturation of pairs, then when the temperature decreases, the air may become rich and starts to fall out. But when the water vapor is condensation, the energy (the specific heat of the vaporization at a temperature close to 0 ° C is 2490 kJ / kg), Therefore, the air at the surface of the soil during the formation of the dew will not be cooled below the dew point and the probability of frost occurs will decrease. The probability of freezing depends on the first, from the speed of lowering the temperature and,
Secondly, from air humidity. It is enough to know one of these data to more or less accurately predict the likelihood of freezing.
Questions for repetition:
- What is understood under the humidity of the air?
- What is called absolute humidity? What formula expresses the meaning of this concept? In which units of it express?
- What is the elasticity of water vapor?
- What is called relative humidity? What formulas express the meaning of this concept in physics and meteorology? In which units of it express?
- Relative air humidity 70%, what does this mean?
- What do they call the dew point?
With which devices are the air humidity determine? What are the subjective sensations of air humidity by man? Having drawn drawing, explain the device and the principle of operation of the hair and condensation hygrometer and psychrometer.
Laboratory work №4 "Measurement of relative humidity"
Purpose: learn how to determine the relative humidity of the air, develop practical skills when working with physical equipment.
Equipment: Thermometer, Gauze Bandage, Water, Psychometric Table
During the classes
Before performing the work, it is necessary to draw the attention of students not only to the content and course of work, but also on the rules for circulation of thermometers and glass vessels. It is necessary to remind you that all the time, while the thermometer is not used for measurements, it must be in the case. When measuring the temperature, the thermometer should be kept behind the top edge. This will determine the temperature with the greatest accuracy.
The first temperature measurements should be carried out with a dry thermometer. This temperature in the audience will not change during operation.
To measure the temperature, a wet thermometer is better to take a piece of gauze as a tissue. Marley absorbs very well and moves water from the wet edge to dry.
Using a psychrometric table, it is easy to determine the value of relative humidity.
Let be t C \u003d H\u003d 22 ° С, t M \u003d T 2\u003d 19 ° С. Then t \u003d t c- 1 w \u003d3 ° C.
On the table we find relative humidity. In this case, it is 76%.
For comparison, you can measure the relative humidity of the air outside. For this, a group of two or three students who successfully coped with the main part of the work can be asked to carry out similar dimensions on the street. This should take no more than 5 minutes. The resulting value of humidity can be compared with the humidity in the class.
The results of the work are summarized in conclusions. They should noted not only the formal values \u200b\u200bof the final results, but also indicate the reasons that lead to the errors.
III. Solving tasks
Since this laboratory work Such a simple content and is small in volume, the remaining part of the lesson can be devoted to solving the tasks on the topic under study. To solve problems, it is not necessary for all students to solve them at the same time. As the work performed, they can receive tasks individually.
You can offer the following simple tasks:
On the street there is a cold autumn rain. In which case, the lingerie will dry faster, awesome in the kitchen: when is the fortune point open, or when is closed? Why?
Air humidity is 78%, and the reading of the dry thermometer is 12 ° C. What temperature shows a wet thermometer? (Answer:10 ° C.)
The difference in the readings of dry and wet thermometers is equal to 4 ° C. Relative air humidity 60%. What are the testimony of a dry and wet thermometer? (Answer: T C -L9° С t M.\u003d 10 ° C.)
Homework
- Repeat paragraph 17 textbook.
- Task number 3. p. 43.
Messages of students on the role of evaporation in the life of plants and animals.
Evaporation in the life of plants
For the normal existence of the plant cell requires its saturation with water. For algae, it is a natural consequence of the conditions of their existence, sushi plants are achieved as a result of two opposite processes: water absorption roots and evaporation. For successful photosynthesis of chlo-! Rophillonal cells of land plants must maintain the closest contact with the surrounding atmosphere, which supplies them necessary for them with carbon dioxide gas; However, this close contact inevitably leads to the fact that the saturating cells water continuously evaporates into the surrounding space, and the same solar energy that delivers the plant necessary for photosynthesis, absorbing chlorophyll, contributes to the heating of the sheet, and thus enhance the evaporation process.
Very few, and moreover, low-organized, plants, nimeximer MAs and lichens, can withstand long interruptions in water supply and transfer this time in a state of complete yyankiy. From higher plants, only some representatives of the rock and desert flora are capable of this, such as the Oskow, common in the sands of the doodles. For the enormous majority of W. King Plants, such a drying would be mortally, and therefore, they are approximately equal to its coming.
To imagine the scale of water evaporation by plants, we give such an example: in one growing season, one blooming of sunflower or corn evaporates to 200 kg and more water, i.e. solid sizes barrel! With this energetic flow, no less energetic production is required. To do this (the root system is hurt, the size of the roots of the roots and root hairs for winter rye gave the following amazing numbers: the roots were almost four minutes to minutes of millions, the total length of all the roots of 600 km, and their total top is about 225 m 2. On these The roots were about 15 billion root hairs with a total area of \u200b\u200b400 m 2.
The amount of water consumed by the plant during its lives is largely depends on the climate. In the hot dry climate, the plants consume no less, and sometimes even more in dy, than in the climate more wet, these plants are more developed root system and less development has a sheet surface. The flooding plants of raw, shady tropic forests, shores of reservoirs are consumed the least: they have thin wide leaves, weak root and conductive systems. In the plants of dry locally, where water in the soil is very small, and the air is hot and dry, a variety of techniques are observed to these harsh conditions. Interesting plants desert. This, for example, cacti plants with thick fleshy trunks, the leaves of which turned into spines. They have a minor surface with a large volume, thick covers, few permeable for water and water vapor, with a few, almost always closed astians. Therefore, even in a strong heat, cacti evaporates little water.
Other plants are desert zones (camel spines, steppe alfalfa, wormwoods) Thin leaves with wide open dusts, which are vigorously assimilated and evaporate, due to which the temperature of the leaves is significantly reduced. Often, the leaves are covered with a thick layer of gray or white hairs, representing a translucent screen that protects plants from overheating and reduces the intensity of evaporation.
Many desert plants (nick, rolling-field, heather) have hard, leathery leaves. Such plants are capable of transfering a long building. At this time, their leaves are twisted into the tube, and the stomaps are inside it.
The evaporation conditions in the winter change dramatically. From the frozen soil roots can not suck water. Therefore, due to the leaf fall, the evaporation of moisture is reduced by the plant. In addition, in the absence of leaves, less snow is delayed on the crown, which protects plants from mechanical damage.
The role of evaporation processes for animal organisms
Evaporation is the most easily adjustable method of smallerizing internal energy. All conditions implanting complaints are disturbed by the regulation of the organism heat transfer. So, the elaper, rubber, adhesive, synthetic clothing makes it difficult to cheer the body temperature.
For the thermoregulation of the body, the Poto-Eagle plays an important role, it ensures the constancy of the body temperature of whether the animal. Due to the evaporation of the sweat, internal irregular decreases, due to this the body is cooled.
Normal person is considered air with a relative humidity of 40 to 60%. When the environment has a temperature higher than a person's body, then it is reinforced. Abundant selection of sweat leads to the cooling of the body, helps to work in conditions high temperatures. However, such an active sweating is a significant load for a person! If yet the absolute moisture is high, it is still harder to live and work (wet tropics, some shops, such as dyeing).
The relative humidity is below 40% at normal air temperature is also harmful, as it leads to enhanced loss of moisture by the body, which leads to its dehydration.
Very interesting from the point of view of thermoregulation and the role of evaporation processes, some living beings. It is known, for example, that a camel can not drink two weeks. This is explained by the fact that it is very economically spending water. The camel almost does not sweat even to the forty-portus heat. His body is covered with thick and dense wool - wool saves from overheating (on the back of a camel in a sultry noon she is heated to eighty degrees, and the skin under it is to forty!). Wool prevents both the evaporation of moisture from the body (at a cut-off camel, the sweating increases by 50%). Camel Never, even the strongest heat, does not reveal the mouth: because with the mucous membrane of the oral cavity, if you open the widespread mouth, evaporate a lot of water! Camel breathing frequency is very low -8 times a minute. Due to this, the less water leaves the body with air. In the heat, however, the frequency of breathing increases to 16 times per minute. (Compare: Byk under the same conditions breathe 250, and the dog is 300-400 times per minute.) In addition, the body temperature of the camel drops at night to 34 °, and in the afternoon, in the heat, rises to 40-41 °. It is very important for water saving. The camel has a very curious device for conserving the water of the future it is known that out of fat, when he "burns" in the body, it turns out a lot of water - 107 g out of 100 g of fat. Thus, from their hubbles, a camel can, if necessary, can be removed to half antenna.
From the point of view of savings in water spending even more amazing American carcass jumpers (kangaroic rats). They never drink. Kangaroic rats live and the desert of Arizona and nibble seeds and dry herbs. Almost all the water, which is available in their body, endogenous, i.e. It turns out in cells when digesting food. Experiments have shown that from 100 g of pearl crook, which was fed by Kangarochi rats, they received, digest and oxidized it, 54 g of water!
In the thermal regulation of birds, air bags play a major role. In the hot time from the inner surface of the air mesh, moisture evaporates, which contributes to the cooling of the body. II links with this bird in hot weather opens the beak. (Katz //./\u003e Biophysics in physics lessons. - M.: Enlightenment, 1974).
n. independent work
What the amount of heat is highlighted by Mreyfull combustion of 20 kg of stone coal? (Answer:418 MJ)
What amount of heat is highlighted with complete combustion of 50 liters of methane? Methane density Please note 0.7 kg / m 3. (Answer: -1.7MJ)
On a cup with yogurt, it is written: the energy value of 72 kcal. Express the energy value of the product in J.
Heat combustion daily diet Nutrition for schoolchildren of your age is about 1.2 MJ.
1) whether consumption is enough for you for 100 g of fat curd, 50 g of wheat bread, 50 g of beef and 200 g potatoes. Required additional data:
- cottage cheese 9755;
- wheat bread 9261;
- beef 7524;
- potatoes 3776.
2) Do you have enough consumption during the day 100 g of perch, 50 g of fresh cucumbers, 200 g grapes, 100 g of rye bread, 20 g sunflower oil and 150 g of cream ice cream.
Specific heat combustion Q x 10 3, J / kg:
- perch 3520;
- fresh cucumbers 572;
- grapes 2400;
- rye bread 8884;
- sunflower oil 38900;
- ice cream cream 7498.,
(Answer: 1) consumed about 2.2 MJ - enough; 2) Consued to3.7 MJ - enough.)
When preparing for lessons within two hours you spend about 800 kJ of energy. Do you restore the stock of energy if you drink 200 ml of skimmed milk and eat 50 g of wheat bread? The density of low fat milk is equal to 1036 kg / m 3. (Answer:Consucted about 1 MJ - enough.)
Water from the menzurka was overflowed into the vessel heated by the flame of the alcohol, and evaporated. Calculate the mass of burnt alcohol. Heating the vessel and losses for air heating can be neglected. (Answer:1.26)
- What amount of heat is highlighted with complete combustion of 1 tons of anthracite? (Answer:26.8. 109 J.)
- What kind of biogas weight should be burned to be distinguished 50 MJ heat? (Answer: 2.kg.)
- What amount of heat is highlighted during the combustion of 5 liters of fuel oil. Raft nostamazuta Take 890 kg / m 3. (Answer:about 173 MJ.)
On a candy box, it is written: caloric content of 100 g 580 kcal. Express the nicerity of the product in J.
Examine labels of different food products. Write down the energy I, S.kuyu value (caloric content) of products, expressing it in Joules or Ka-Yurii (kilocalories).
When riding a bike in 1 hour you spend about 2,260,000 J. Schchergia. Do you restore the reserve of energy if you eat 200 g cherries?
When it comes to our health, the knowledge of the relative humidity of the air and the formula of its definition becomes first. However, it is not necessary to know the exact formula, but it's not bad at least in general, to imagine what it is, why measure moisture in the house, and in which methods it can be done.
What should be the optimal humidity
Humidity indoors where a person works, conducts leisure or sleeps, is of particular importance. Our respiratory organs are designed in such a way that the air is too dry or saturated with water vapors for them is destroyed. Therefore, there are state standards that regulate what air humidity in the room should be.
Zone of optimal humidity
In general, there is a dozen ways to control the humidity of the air and bring it back. This will create the most favorable conditions for study, sleep, sports, will increase efficiency and improve well-being.
... How does the relative humidity of the air affect the parameters of drying the water paints?
The relative humidity of the air - has a significant effect on speed, and on the completeness of the drying of the water and varnish coating.
Relative humidity is a parameter that determines how much water air is ready to take a pair.
Relative humidity
Relative air humidity is the ratio of the amount of water vapor in the air to the maximum possible amount of steam at a given temperature.
From the definition, at least it becomes clear that the air may contain only a limited amount of water and this quantity depends on the temperature.
When air humidity is 100% - this means that in the air there is a maximum possible amount of water vapor and can not receive more air. In other words, evaporation of water in these conditions is impossible.
The lower the relative humidity of the air, the more water can go to steam and the higher the evaporation rate. But this process is not infinite, - if evaporation occurs in a closed space (for example, there is no exhaust in dry), then at some point the evaporation stops.
Absolute humidity
The table shows the values \u200b\u200bof absolute air humidity with the relative humidity of 100% in the temperature range of interest to us and the behavior of the relative humidity of air with an increase in temperature.
| Temperature, ° C | Absolute Humidity, g / m³ | Relative Humidity,% 5 ° C | Relative Humidity,% 15 ° C |
| - 20 | 1,08 | - | - |
| - 15 | 1,61 | - | - |
| - 10 | 2,36 | - | - |
| - 5 | 3,41 | - | - |
| 0 | 4,85 | - | - |
| 5 | 6,80 | 100 | - |
| 10 | 9,40 | 72,35 | - |
| 15 | 12,83 | 53,01 | 100 |
| 20 | 17,30 | 39,31 | 74,17 |
| 25 | 23,04 | 29,52 | 55,69 |
| 30 | 30,36 | 22,40 | 42,26 |
| 35 | 39,58 | 17,19 | 32,42 |
From the given data it can be seen that while maintaining the value of absolute humidity, with increasing temperature, the value of relative humidity decreases.
The value of the maximum absolute humidity at a certain temperature makes it possible to calculate the effectiveness of the dryer, or to be more accurate, the inefficiency of the dryer without supply ventilation.
Suppose our dryer - room 7 on 4 and 3 meters high, which is 84 cubic meters. And suppose that we want to dry 100 PVC profiles for windows or 160 facade plates from glass or fibro-cement plates with a size of 600 per 600 mm; What is about 60 sq.m. Surfaces.
For coloring of such a surface, 6 liters of paint will be spent; For complete drying, the paint should evaporate about 2 liters of water. At the same time, according to the table, at a temperature of 20 ° C 84 cubic meters. Air may contain a maximum of 1.5 liters of water.
That is, if even air initially had zero absolute humidity, water paint in this room does not dry without supply ventilation.
Reducing relative humidity
Since for the polymerization of a paint coating on a water basis, a necessary condition is the complete evaporation of water, the value of the relative humidity of the air has a significant effect on the drying speed and even on the operational qualities of the polymer coating.
But everything is not so scary as it may seem. For example, if you download air outside, which has 100% relative humidity and a temperature of 5 ° C, and warm it up to 15 ° C, the air will have only 53% relative humidity.
The moisture from the air did not disappear anywhere, that is, the absolute humidity has not changed, but the air is ready to take two times more water than at low temperatures.
That is, there is no need for the acceptable parameters of the drying of the paint coating, use dryers or capacitors - it suffices to raise the temperature above ambient temperature.
The greater the temperature difference between air outside and air that is supplied to the dryer, the smaller the relative humidity of the latter.