Absolute and relative air humidity physics. Absolute and relative humidity. Dew point. Examples of problem solving

Signs of pregnancy after embryo implantation

For a quantitative assessment of air humidity, absolute and relative air humidity is used.

Absolute air humidity is measured by the density of water vapor in the air, or its pressure

A clearer idea of \u200b\u200bthe degree of air humidity is given by the relative humidity B. The relative humidity of the air is measured by a number showing how many percent is the absolute humidity of the density of water vapor required to saturate the air at its available temperature:

The relative humidity can also be determined by the vapor pressure, since practically the vapor pressure is proportional to its density .. Therefore, B can be determined as follows: the relative humidity is measured by a number showing how many percent the absolute humidity is from the pressure of water vapor saturating the air at its available temperature:

Thus, relative humidity is determined not only by absolute humidity, but also by air temperature. When calculating the relative humidity, the values \u200b\u200bor must be taken from the tables (see Table 9.1).

Let's find out how a change in air temperature can affect its humidity. Let the absolute humidity of the air be at. Since the density of saturating water vapor at 22 ° C is (Table 9.1), the relative humidity B is about 50%.

Let us now assume that the temperature of this air drops to 10 ° C, and the density remains the same. Then the relative humidity of the air will be 100%, i.e. the air will be saturated with water vapor. If the temperature drops to 6 ° C (for example, at night), then kg of water vapor will condense from each cubic meter of air (dew will fall).

Table 9.1. Pressure and density of saturating water vapor at different temperatures

The temperature at which the air becomes saturated with water vapor during its cooling is called the dew point. In the above example, the dew point is equal.Note that at a known dew point, the absolute humidity can be found from Table. 9.1, since it is equal to the density of the saturating vapor at the dew point.

The amount of moisture contained in one cubic meter of air. Due to its small value, it is usually measured in g / m³. But due to the fact that at a certain air temperature it can contain only a certain amount of moisture (with an increase in temperature this maximum possible amount of moisture increases, with a decrease in air temperature the maximum possible amount of moisture decreases), the concept of relative humidity was introduced.

Relative humidity

An equivalent definition is the ratio of the molar fraction of water vapor in air to the maximum possible at a given temperature. It is measured as a percentage and is determined by the formula:

where: - relative humidity of the considered mixture (air); - partial pressure of water vapor in the mixture; - equilibrium pressure of saturated steam.

The pressure of saturated water vapor increases strongly with increasing temperature. Therefore, with isobaric (that is, at constant pressure) cooling of air with a constant vapor concentration, a moment (dew point) occurs when the vapor is saturated. In this case, the "extra" steam condenses in the form of fog or ice crystals. The processes of saturation and condensation of water vapor play a huge role in the physics of the atmosphere: the processes of cloud formation and the formation of atmospheric fronts are largely determined by the processes of saturation and condensation, the heat released during the condensation of atmospheric water vapor provides the energy mechanism for the emergence and development of tropical cyclones (hurricanes).

Relative humidity assessment

The relative humidity of the water-air mixture can be estimated if its temperature is known ( T) and dew point temperature ( T d). When T and T d are expressed in degrees Celsius, then the expression is true:

where the partial pressure of water vapor in the mixture is estimated:

and the wet vapor pressure of water in the mixture at a temperature is estimated:

Supersaturated water vapor

In the absence of condensation centers, with a decrease in temperature, a supersaturated state may form, that is, the relative humidity becomes more than 100%. Ions or aerosol particles can act as condensation centers, it is on the condensation of a supersaturated vapor on ions formed during the passage of a charged particle in such a vapor that the principle of operation of the Wilson chamber and diffusion chambers is based: water droplets condensing on the formed ions form a visible trace (track) of charged particles.

Another example of condensation of supersaturated water vapor is the contrails of aircraft, which appear when the condensation of supersaturated water vapor on the soot particles of engine exhaust.

Means and methods of control

Devices called psychrometers and hygrometers are used to determine air humidity. The August psychrometer consists of two thermometers - dry and wet. A wet thermometer shows a temperature lower than a dry thermometer, since its reservoir is wrapped in a cloth soaked in water, which evaporates and cools it. Evaporation rate depends on the relative humidity of the air. According to the indications of dry and wet thermometers, the relative humidity of the air is found according to psychrometric tables. Recently, integral moisture sensors (usually with voltage output) have become widely used, based on the property of some polymers to change their electrical characteristics (such as the dielectric constant of the medium) under the action of water vapor in the air.

To increase the relative humidity in residential premises, use electric humidifiers, pallets filled with wet expanded clay and regular spraying.

Notes


Wikimedia Foundation. 2010.

See what "Relative humidity" is in other dictionaries:

    The ratio of the molar fraction of moisture in a gas to the molar fraction of saturated water vapor over water [ice] in this gas at the same pressure and temperature. Unit of measurement% [RMG 75 2004] Subjects for measuring the moisture content of substances General terms quantities ... ... Technical translator's guide

    relative humidity - The percentage of the elasticity of water vapor contained in a unit volume of air to the elasticity of saturating vapor at the same temperature ... Geography Dictionary

    Relative humidity - 16. Relative humidity D. Relative Feuchtigkeit E. Relative humidity F. Humidite relative The ratio of the partial pressure of water vapor to the pressure of saturated vapor at the same pressure and temperature Source ... Dictionary-reference book of terms of normative and technical documentation

    The ratio of the elasticity of water vapor contained in air to that of saturated vapor at the same temperature; expressed as a percentage. * * * RELATIVE HUMIDITY RELATIVE HUMIDITY, ratio of water vapor pressure (see ELASTICITY ... ... encyclopedic Dictionary

    relative humidity - drėgnis statusas T sritis Standartizacija ir metrologija apibrėžtis Drėgmės ir ją sugėrusios medžiagos masių arba tūrių 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

One of the most important characteristics of compressed air used in industry, food processing, medicine and other industries is humidity. This article gives a definition of the concept of "air humidity", provides tables for determining the dew point depending on temperature and relative humidity, values \u200b\u200bof saturated vapor pressure over the surface of water and ice, values \u200b\u200bof absolute humidity. And also, a table of correction factors for converting the relative humidity of air saturated with respect to water into the relative humidity of air saturated with respect to ice.

The most general definition is: humidity is a measure that characterizes the content of water vapor in air (or other gas). This definition, of course, does not pretend to be "science intensive", but it gives the physical concept of moisture.

To quantify the "moisture" of gases, the following characteristics are most often used:

  • partial pressure of water vapor (p) - the pressure that water vapor would have in the composition of atmospheric or compressed air if it alone occupied a volume equal to the volume of air at the same temperature. The total pressure of the gas mixture is equal to the sum of the partial pressures of the individual components of this mixture .
  • relative humidity - is defined as the ratio of the actual humidity of the air to its maximum possible humidity, i.e., the relative humidity shows how much moisture is still lacking for condensation to begin under given environmental conditions. More "scientific" is the following formulation: relative humidity is a value defined as the ratio of the partial pressure of water vapor (p) to the pressure of saturated vapor at a given temperature, expressed as a percentage.
  • dew point temperature (frost) is defined as the temperature at which the partial pressure of vapor saturated with respect to water (ice) is equal to the partial pressure of water vapor in the gas being characterized. That is, it is the temperature at which the moisture condensation process begins. The practical meaning of the dew point is that it shows what the maximum amount of moisture can be contained in the air at a specified temperature. Indeed, the actual amount of water that can be held in a constant volume of air depends only on temperature. Dew point is the most convenient technical parameter. Knowing the value of the dew point, we can safely say that the amount of moisture in a given volume of air will not exceed a certain value.
  • absolute humidity, defined as the mass content of water per unit volume of gas. This is a value that shows how much water vapor is contained in a given volume of air, this is the most general concept, it is expressed in g / m3. At very low gas humidity, a parameter such as moisture content, the unit of which is ppm (parts per million). It is an absolute value that characterizes the number of water molecules per million molecules of the entire mixture. It does not depend on temperature or pressure. This is understandable, the number of water molecules cannot increase or decrease with changes in pressure and temperature.

The temperature dependences of saturated vapor pressure over a flat surface of water and ice, obtained theoretically on the basis of the Clausius - Clapeyron equation and verified with experimental data of many researchers, are recommended for meteorological practice by the World Meteorological Organization (WMO):

ln p sw \u003d -6094.4692T -1 + 21.1249952-0.027245552 T + 0.000016853396T 2 +2.4575506 lnT
ln p si \u003d -5504.4088T -1 - 3.5704628-0.017337458T + 0.0000065204209T 2 + 6.1295027 lnT,

where p sw is the saturated vapor pressure above the flat surface of water (Pa);
p si — saturated vapor pressure over the flat ice surface (Pa);
T - temperature (K).

The formulas given are valid for temperatures from 0 to 100ºC (for p sw) and from -0 to -100ºC (for p si). At the same time, WMO recommends the first formula for negative temperatures for supercooled water (down to -50ºC).

Obviously, these formulas are quite cumbersome and inconvenient for practical work, therefore, in calculations it is much more convenient to use ready-made data summarized in special tables. Some of these tables are shown below.

Table 1. Definitions of dew point depending on temperature and relative humidity

Air temperature Relative humidity
30% 35% 40% 45% 50% 55% 60%& 65% 70% 75% 80% 85% 90% 95%
-10 ° C ;-23,2 -21,8 -20,4 -19,0 -17,8 -16,7 -15,8 -14,9 -14,1 -13,3 -12,6 -11,9 -10,6 -10,0
-5 ° C -18,9 -17,2 -15,8 -14,5 -13,3 -11,9 -10,9 -10,2 -9,3 -8,8 -8,1 -7,7 -6,5 -5,8
0 ° C -14,5 -12,8 -11,3 -9,9 -8,7 -7,5 -6,2 -5,3 -4,4 -3,5 -2,8 -2 -1,3 -0,7
+ 2 ° C -12,8 -11,0 -9,5 -8,1 -6,8 -5,8 -4,7 -3,6 -2,6 -1,7 -1 -0,2 -0,6 +1,3
+ 4 ° C -11,3 -9,5 -7,9 -6,5 -4,9 -4,0 -3,0 -1,9 -1,0 +0,0 +0,8 +1,6 +2,4 +3,2
+ 5 ° C -10,5 -8,7 -7,3 -5,7 -4,3 -3,3 -2,2 -1,1 -0,1 +0,7 +1,6 +2,5 +3,3 +4,1
+ 6 ° C -9,5 -7,7 -6,0 -4,5 -3,3 -2,3 -1,1 -0,1 +0,8 +1,8 +2,7 +3,6 +4,5 +5,3
+ 7 ° C -9,0 -7,2 -5,5 -4,0 -2,8 -1,5 -0,5 +0,7 +1,6 +2,5 +3,4 +4,3 +5,2 +6,1
+ 8 ° C -8,2 -6,3 -4,7 -3,3 -2,1 -0,9 +0,3 +1,3 +2,3 +3,4 +4,5 +5,4 +6,2 +7,1
+ 9 ° C -7,5 -5,5 -3,9 -2,5 -1,2 +0,0 +1,2 +2,4 +3,4 +4,5 +5,5 +6,4 +7,3 +8,2
+ 10 ° C -6,7 -5,2 -3,2 -1,7 -0,3 +0,8 +2,2 +3,2 +4,4 +5,5 +6,4 +7,3 +8,2 +9,1
+ 11 ° C -6,0 -4,0 -2,4 -0,9 +0,5 +1,8 +3,0 +4,2 +5,3 +6,3 +7,4 +8,3 +9,2 +10,1
+ 12 ° C -4,9 -3,3 -1,6 -0,1 +1,6 +2,8 +4,1 +5,2 +6,3 +7,5 +8,6 +9,5 +10,4 +11,7
+ 13 ° C -4,3 -2,5 -0,7 +0,7 +2,2 +3,6 +5,2 +6,4 +7,5 +8,4 +9,5 +10,5 +11,5 +12,3
+ 14 ° C -3,7 -1,7 -0,0 +1,5 +3,0 +4,5 +5,8 +7,0 +8,2 +9,3 +10,3 +11,2 +12,1 +13,1
+ 15 ° C -2,9 -1,0 +0,8 +2,4 +4,0 +5,5 +6,7 +8,0 +9,2 +10,2 +11,2 +12,2 +13,1 +14,1
+ 16 ° C -2,1 -0,1 +1,5 +3,2 +5,0 +6,3 +7,6 +9,0 +10,2 +11,3 +12,2 +13,2 +14,2 +15,1
+ 17 ° C -1,3 +0,6 +2,5 +4,3 +5,9 +7,2 +8,8 +10,0 +11,2 +12,2 +13,5 +14,3 +15,2 +16,6
+ 18 ° C -0,5 +1,5 +3,2 +5,3 +6,8 +8,2 +9,6 +11,0 +12,2 +13,2 +14,2 +15,3 +16,2 +17,1
+ 19 ° C +0,3 +2,2 +4,2 +6,0 +7,7 +9,2 +10,5 +11,7 +13,0 +14,2 +15,2 +16,3 +17,2 +18,1
+ 20 ° C +1,0 +3,1 +5,2 +7,0 +8,7 +10,2 +11,5 +12,8 +14,0 +15,2 +16,2 +17,2 +18,1 +19,1
+ 21 ° C +1,8 +4,0 +6,0 +7,9 +9,5 +11,1 +12,4 +13,5 +15,0 +16,2 +17,2 +18,1 +19,1 +20,0
+ 22 ° C +2,5 +5,0 +6,9 +8,8 +10,5 +11,9 +13,5 +14,8 +16,0 +17,0 +18,0 +19,0 +20,0 +21,0
+ 23 ° C +3,5 +5,7 +7,8 +9,8 +11,5 +12,9 +14,3 +15,7 +16,9 +18,1 +19,1 +20,0 +21,0 +22,0
+ 24 ° C +4,3 +6,7 +8,8 +10,8 +12,3 +13,8 +15,3 +16,5 +17,8 +19,0 +20,1 +21,1 +22,0 +23,0
+ 25 ° C +5,2 +7,5 +9,7 +11,5 +13,1 +14,7 +16,2 +17,5 +18,8 +20,0 +21,1 +22,1 +23,0 +24,0
+ 26 ° C +6,0 +8,5 +10,6 +12,4 +14,2 +15,8 +17,2 +18,5 +19,8 +21,0 +22,2 +23,1 +24,1 +25,1
+ 27 ° C +6,9 +9,5 +11,4 +13,3 +15,2 +16,5 +18,1 +19,5 +20,7 +21,9 +23,1 +24,1 +25,0 +26,1
+ 28 ° C +7,7 +10,2 +12,2 +14,2 +16,0 +17,5 +19,0 +20,5 +21,7 +22,8 +24,0 +25,1 +26,1 +27,0
+ 29 ° C +8,7 +11,1 +13,1 +15,1 +16,8 +18,5 +19,9 +21,3 +22,5 +24,1 +25,0 +26,0 +27,0 +28,0
+ 30 ° C +9,5 +11,8 +13,9 +16,0 +17,7 +19,7 +21,3 +22,5 +23,8 +25,0 +26,1 +27,1 +28,1 +29,0
+ 32 ° C +11,2 +13,8 +16,0 +17,9 +19,7 +21,4 +22,8 +24,3 +25,6 +26,7 +28,0 +29,2 +30,2 +31,1
+ 34 ° C +12,5 +15,2 +17,2 +19,2 +21,4 +22,8 +24,2 +25,7 +27,0 +28,3 +29,4 +31,1 +31,9 +33,0
+ 36 ° C +14,6 +17,1 +19,4 +21,5 +23,2 +25,0 +26,3 +28,0 +29,3 +30,7 +31,8 +32,8 +34,0 +35,1
+ 38 ° C +16,3 +18,8 +21,3 +23,4 +25,1 +26,7 +28,3 +29,9 +31,2 +32,3 +33,5 +34,6 +35,7 +36,9
+ 40 ° C +17,9 +20,6 + 22,6 +25,0 +26,9 +28,7 +30,3 +31,7 +33,0 +34,3 +35,6 +36,8 +38,0 +39,0

Table 2. Values \u200b\u200bof saturated vapor pressure over a flat surface of water (p sw) and ice (p si).

Т, ° C p sw, Pa p si, Pa Т, ° C p sw, Pa p si, Pa Т, ° C p sw, Pa p si, Pa
-50 6,453 3,924 -33 38,38 27,65 -16 176,37 150,58
-49 7,225 4,438 -32 42,26 30,76 -15 191,59 165,22
-48 8,082 5,013 -31 46,50 34,18 -14 207,98 181,14
-47 9,030 5,657 -30 51,11 37,94 -13 225,61 198,45
-46 10,08 6,38 -29 56,13 42,09 -12 244,56 217,27
-45 11,24 7,18 -28 61,59 46,65 -11 264,93 237,71
-44 12,52 8,08 -27 67,53 51,66 -10 286,79 259,89
-43 13,93 9,08 -26 73,97 57,16 -9 310,25 283,94
-42 15,48 10,19 -25 80,97 63,20 -8 335,41 310,02
-41 17,19 11,43 -24 88,56 69,81 -7 362,37 338,26
-40 19,07 12,81 -23 96,78 77,06 -6 391,25 368,84
-39 21,13 14,34 -22 105,69 85,00 -5 422,15 401,92
-38 23,40 16,03 -21 115,32 93,67 -4 455,21 437,68
-37 25,88 17,91 -20 125,74 103,16 -3 490,55 476,32
-36 28,60 19,99 -19 136,99 113,52 -2 528,31 518,05
-35 31,57 22,30 -18 149,14 124,82 -1 568,62 563,09
-34 34,83 24,84 -17 162,24 137,15 0 611,65 611,66

Table 3. Values \u200b\u200bof saturated vapor pressure over a flat surface of water (p sw).

Т, ° C p sw, Pa Т, ° C p sw, Pa Т, ° C p sw, Pa Т, ° C p sw, Pa
0 611,65 26 3364,5 52 13629,5 78 43684,4
1 657,5 27 3568,7 53 14310,3 79 45507,1
2 706,4 28 3783,7 54 15020,0 80 47393,4
3 758,5 29 4009,8 55 15759,6 81 49344,8
4 814,0 30 4247,6 56 16530,0 82 51363,3
5 873,1 31 4497,5 57 17332,4 83 53450,5
6 935,9 32 4760,1 58 18167,8 84 55608,3
7 1002,6 33 5036,0 59 19037,3 85 57838,6
8 1073,5 34 5325,6 60 19942,0 86 60143,3
9 1148,8 35 5629,5 61 20883,1 87 62524,2
10 1228,7 36 5948,3 62 21861,6 88 64983,4
11 1313,5 37 6282,6 63 22878,9 89 67522,9
12 1403,4 38 6633,1 64 23936,1 90 70144,7
13 1498,7 39 7000,4 65 25034,6 91 72850,8
14 1599,6 40 7385,1 66 26175,4 92 75643,4
15 1706,4 41 7787,9 67 27360,1 93 78524,6
16 1819,4 42 8209,5 68 28589,9 94 81496,5
17 1939,0 43 8650,7 69 29866,2 95 84561,4
18 2065,4 44 9112,1 70 31190,3 96 87721,5
19 2198,9 45 9594,6 71 32563,8 97 90979,0
20 2340,0 46 10098,9 72 33988,0 98 94336,4
21 2488,9 47 10625,8 73 35464,5 99 97795,8
22 2646,0 48 11176,2 74 36994,7 100 101359,8
23 2811,7 49 11750,9 75 38580,2
24 2986,4 50 12350,7 76 40222,5
25 3170,6 51 12976,6 77 41923,4

Table 4. Values \u200b\u200bof the absolute humidity of a gas with a relative humidity of 100% for water at various temperatures.

T, ° C A, g / m 3 T, ° C A, g / m 3 T, ° C A, g / m 3 T, ° C A, g / m 3
-50 0,063 -10 2,361 30 30,36 70 196,94
-49 0,070 -9 2,545 31 32,04 71 205,02
-48 0,078 -8 2,741 32 33,80 72 213,37
-47 0,087 -7 2,950 33 35,64 73 221,99
-46 0,096 -6 3,173 34 37,57 74 230,90
-45 0,107 -5 3,411 35 39,58 75 240,11
-44 0,118 -4 3,665 36 41,69 76 249,61
-43 0,131 -3 3,934 37 43,89 77 259,42
-42 0,145 -2 4,222 38 46,19 78 269,55
-41 0,160 -1 4,527 39 48,59 79 280,00
-40 0,177 0 4,852 40 51,10 80 290,78
-39 0,196 1 5,197 41 53,71 81 301,90
-38 0,216 2 5,563 42 56,44 82 313,36
-37 0,237 3 5,952 43 59,29 83 325,18
-36 0,261 4 6,364 44 62,25 84 337,36
-35 0,287 5 6,801 45 65,34 85 349,91
-34 0,316 6 7,264 46 68,56 86 362,84
-33 0,346 7 7,754 47 71,91 87 376,16
-32 0,380 8 8,273 48 75,40 88 389,87
-31 0,416 9 8,822 49 79,03 89 403,99
-30 0,455 10 9,403 50 82,81 90 418,52
-29 0,498 11 10,02 51 86,74 91 433,47
-28 0,544 12 10,66 52 90,82 92 448,86
-27 0,594 13 11,35 53 95,07 93 464,68
-26 0,649 14 12,07 54 99,48 94 480,95
-25 0,707 15 12,83 55 104,06 95 497,68
-24 0,770 16 13,63 56 108,81 96 514,88
-23 0,838 17 14,48 57 113,75 97 532,56
-22 0,912 18 15,37 58 118,87 98 550,73
-21 0,991 19 16,31 59 124,19 99 569,39
-20 1,076 20 17,30 60 129,70 100 588,56
-19 1,168 21 18,33 61 135,41
-18 1,266 22 19,42 62 141,33
-17 1,372 23 20,57 63 147,47
-16 1,486 24 21,78 64 153,83
-15 1,608 25 23,04 65 160,41
-14 1,739 26 24,37 66 167,23
-13 1,879 27 25,76 67 174,28
-12 2,029 28 27,22 68 181,58
-11 2,190 29 28,75 69 189,13

Let's give an example of using the above tables in practice: with a capacity of 10 m 3 / min, it "sucks" 10 cubic meters per minute atmospheric air.

Let's find the amount of water contained in 10 cubic meters of atmospheric air with the parameters temperature +25 ° С, relative humidity 85%. According to table 4, air with a temperature of +25 ° C and 100% humidity contains 23.04 g / m 3 of water. This means that at 85% humidity, one cubic meter of air will contain 0.85 * 23.04 \u003d 19.584 g of water, and ten - 195.84 g.

In the process of compressing the air, the volume occupied by it will decrease. The reduced compressed air volume at 6 bar can be calculated using the Boyle-Mariotte law (the air temperature does not change significantly):

P1 x V1 \u003d P2 x V2

V2 \u003d (P1 x V1) / P2

where Р1 - atmospheric pressure equal to 1.013 bar;
V2 \u003d (1.013 bar x 10 m 3) / (6 + 1.013) bar \u003d 1.44 m 3.

That is, 10 cubic meters of atmospheric air, during the compression process, "turned" into 1.44 m 3 of compressed air, with an overpressure of 6 bar, at the outlet of the compressor.

Absolute humidity

Absolute humidity is the amount of moisture (in grams) contained in one cubic meter of air. Due to its small value, it is usually measured in g / m3. But due to the fact that at a certain air temperature, only a certain amount of moisture can be maximally contained in the air (with an increase in temperature, this maximum possible amount of moisture increases, with a decrease in air temperature, the maximum possible amount of moisture decreases), the concept of Relative Humidity was introduced.

Relative humidity

Equivalent definition - the ratio of the mass 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: - relative humidity of the considered mixture (air); - partial pressure of water vapor in the mixture; - equilibrium pressure of saturated steam.

The pressure of saturated water vapor increases strongly with increasing temperature (see graph). Therefore, with isobaric (that is, at constant pressure) cooling of air with a constant vapor concentration, a moment (dew point) occurs when the vapor is saturated. In this case, the "extra" steam condenses in the form of fog or ice crystals. The processes of saturation and condensation of water vapor play a huge role in the physics of the atmosphere: the processes of cloud formation and the formation of atmospheric fronts are largely determined by the processes of saturation and condensation, the heat released during condensation of atmospheric water vapor provides the energy mechanism for the emergence and development of tropical cyclones (hurricanes).

Relative humidity assessment

The relative humidity of the water-air mixture can be estimated if its temperature is known ( T) and dew point temperature ( T d). When T and T d are expressed in degrees Celsius, then the expression is true:

Where the partial pressure of water vapor in the mixture is estimated e p :

And the wet vapor pressure of the water in the mixture at the temperature is estimated e s :

Oversaturated steam

In the absence of condensation centers, with a decrease in temperature, the formation of a supersaturated state is possible, i.e., the relative humidity becomes more than 100%. Ions or aerosol particles can act as condensation centers, it is on the condensation of a supersaturated vapor on ions formed during the passage of a charged particle in such a vapor that the principle of operation of the Wilson chamber and diffusion chambers is based: water droplets condensing on the formed ions form a visible trace (track) of charged particles.

Another example of condensation of supersaturated water vapor is the contrails of aircraft, which appear when the condensation of supersaturated water vapor on the soot particles of engine exhaust.

Means and methods of control

Devices called psychrometers and hygrometers are used to determine air humidity. The August psychrometer consists of two thermometers - dry and wet. A wet thermometer shows a temperature lower than a dry thermometer, because its reservoir is wrapped in a cloth dipped in water, which evaporates and cools it. Evaporation rate depends on the relative humidity of the air. According to the indications of dry and wet thermometers, the relative humidity of the air is found according to psychrometric tables. Recently, integral moisture sensors (usually with voltage output) have become widely used, based on the property of some polymers to change their electrical characteristics (such as the dielectric constant of the medium) under the action of water vapor in the air. To verify instruments for measuring humidity, special installations are used - hygrostats.

DESIGN OF WATER SUPPLY AND SEWERAGE

Write: [email protected]

Working hours: Mon-Fri from 9-00 to 18-00 (without lunch)

Air humidity table

Below is a table of absolute and relative air humidity.

Relative humidity 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Air temperature, C Absolute humidity, g / m3
Dew point, C
50 8,3 16,6 24,9 33,2 41,5 49,8 58,1 66,4 74,7 83
8 19 26 32 36 40 43 45 48 50
45 6,5 13,1 19,6 26,2 32,7 39,3 45,8 52,4 58,9 65,4
4 15 22 27 32 36 38 41 43 45
40 5,1 10,2 15,3 20,5 25,6 30,7 35,8 40,9 46 51,1
1 11 18 23 27 30 33 36 38 40
35 4 7,9 11,9 15,8 19,8 23,8 27,7 31,7 35,6 39,6
-2 8 14 18 21 25 28 31 33 35
30 3 6,1 9,1 12,1 15,2 18,2 21,3 24,3 27,3 30,4
-6 3 10 14 18 21 24 26 28 30
25 2,3 4,6 6,9 9,2 11,5 13,8 16,1 18,4 20,7 23
-8 0 5 10 13 16 19 21 23 25
20 1,7 3,5 5,2 6,9 8,7 10,4 12,1 13,8 15,6 17,3
-12 -4 1 5 9 12 14 16 18 20
15 1,3 2,6 3,9 5,1 6,4 7,7 9 10,3 11,5 12,8
-16 -7 -3 1 4 7 9 11 13 15
10 0,9 1,9 2,8 3,8 4,7 5,6 6,6 7,5 8,5 9,4
-19 -11 -7 -3 0 1 4 6 8 10
5 0,7 1,4 2 2,7 3,4 4,1 4,8 5,4 6,1 6,8
-23 -15 -11 -7 -5 -2 0 2 3 5
0 0,5 1 1,5 1,9 2,4 2,9 3,4 3,9 4,4 4,8
-26 -19 -14 -11 -8 -6 -4 -3 -2 0
-5 0,3 0,7 1 1,4 1,7 2,1 2,4 2,7 3,1 3,4
-29 -22 -18 -15 -13 -11 -8 -7 -6 -5
-10 0,2 0,5 0,7 0,9 1,2 1,4 1,6 1,9 2,1 2,3
-34 -26 -22 -19 -17 -15 -13 -11 -11 -10
-15 0,2 0,3 0,5 0,6 0,8 1 1,1 1,3 1,5 1,6
-37 -30 -26 -23 -21 -19 -17 -16 -15 -15
-20 0,1 0,2 0,3 0,4 0,4 0,5 0,6 0,7 0,8 0,9
-42 -35 -32 -29 -27 -25 -24 -22 -21 -20
-25 0,1 0,1 0,2 0,2 0,3 0,3 0,4 0,4 0,5 0,6
-45 -40 -36 -34 -32 -30 -29 -27 -26 -25

This page provides tabular information on the absolute and relative air humidity.

August's psychrometer consists of two mercury thermometers mounted on a tripod or located in a common case. The ball of one thermometer is wrapped in a thin cambric cloth dipped in a glass of distilled water.

When using the August psychrometer, the calculation of absolute humidity is carried out according to the Rainier formula:
A \u003d f-a (t-t1) H,
where A is the absolute humidity; f is the maximum voltage of water vapor at wet bulb temperature (see.

table 2); a - psychrometric coefficient, t - dry bulb temperature; t1 - wet bulb temperature; H - barometric pressure at the time of determination.

If the air is completely motionless, then a \u003d 0.00128.

In the presence of weak air movement (0.4 m / s) a \u003d 0.00110. The maximum and relative humidity is calculated as indicated on page

Air temperature (° С) Air temperature (° С) Water vapor tension (mmHg) Air temperature (° С) Water vapor tension (mmHg)

Air humidity
-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 (percentage)

Table 4.

Determination of the relative air humidity according to the readings of dry and wet thermometers in the August psychrometer under normal conditions of calm and uniform air movement in the room at a speed of 0.2 m / s

There are special tables for determining the relative humidity (tables 3, 4).

More accurate readings are given by Assman's psychrometer (Fig. 3). It consists of two thermometers enclosed in metal tubes, through which air is evenly sucked in by means of a winding fan located at the top of the device.

The mercury reservoir of one of the thermometers is wrapped in a piece of cambric, which is moistened with distilled water using a special pipette before each determination. After wetting the thermometer, turn on the fan with a key and hang the device on a tripod. After 4-5 minutes readings of dry and wet thermometers are recorded. Since moisture evaporates and heat is absorbed from the surface of a mercury ball moistened with a thermometer, it will show a lower temperature.

The calculation of the absolute humidity is made according to the Sprung formula:

where A is the absolute humidity; f is the maximum voltage of water vapor at a wet bulb temperature; 0.5 - constant psychrometric coefficient (correction for air velocity); t is the dry bulb temperature; t1 - wet bulb temperature; H is barometric pressure; 755 - average barometric pressure (determined according to table 2).

The maximum humidity (F) is determined using Table 2 by dry bulb temperature.

Relative humidity (R) is calculated using the formula:

where R is relative humidity; A - absolute humidity; F is the maximum humidity at dry bulb temperature.

To determine fluctuations in relative humidity over time, a hygrograph device is used.

The device is designed similarly to a thermograph, but the sensing part of the hygrograph is a defatted bunch of hair.


Figure: 3. Assman's aspiration psychrometer:

1 - metal tubes;
2 - mercury thermometers;
3 - holes for suctioned air outlet;
4 - clamp for hanging the psychrometer;
5 - pipette for wetting a wet thermometer.

1. Readings of a dry thermometer of an aspiration psychrometer 20 ° С, humid 10 ° С. Find the relative humidity in the living area. Give her a hygienic grade.

2. Readings of the dry thermometer of the aspiration psychrometer in the living room 22 ° C, humid 14.5 ° C. Assess the temperature and humidity conditions in the room.

In the blacksmith shop, the temperature of the dry thermometer of the aspiration psychrometer is 23 ° C, the wet one is 13.5 C. Assess the temperature and humidity conditions in the shop.

4. In what ways will a person lose heat if the temperature of the air and walls in the room is 37 ° C, humidity is 45%, air velocity is 0.4 m / s?

Relative air humidity at temperature determination with a psychrometer (Table)

Determine in what conditions a person's thermal well-being will be better:

a) at an air temperature of 30 ° C, humidity 40%, movement speed
air 0.8 m / sec.

b) at an air temperature of 28 ° C, humidity 85%, movement speed
air 0.2 m / sec.

6. In what conditions will a person be colder:

a) at an air temperature of 14 ° C, humidity 40%

b) at an air temperature of 14 ° C, humidity 80%

In what conditions will a person overheat:

a) at an air temperature of 40 ° C, humidity 40%

b) at an air temperature of 40 ° C, humidity 90%

8. In which workshop the microclimate is preferable;

a) in workshop 1, the air and wall temperature is 38 ° C, the air humidity is 70%,
air speed 0.3 m / sec.

b) in the 2nd workshop, the air and wall temperature is 39 C, the air humidity is 35%,
air speed 0.8 m / sec.

In the operating room, the air temperature is 22 C, the humidity is 43%, the air velocity is 0.3 m / sec. Give a hygienic assessment of the operating room microclimate.

10. In the chambers of the burn center, the air temperature is 25 ° C, the relative humidity is 52%, the air velocity is 0.15 m / sec.

Does the

microclimate of medical premises hygienic standards

Appendix No. 5

Table No. 1 Determination of relative humidity according to the readings of an aspiration psychrometer,%

Indications Wet thermometer readings, ° С
dry bulb temperature ° С 10,0 10,5 11,0 11,5 12,0 12,5 13,0 13,5 14,0 14,5 15,0 15,5 16,0 16,5 17,0 17,5 18,0 18,5 19,0 19,5 20,0 20,5 21,0 21,5 22,0 22,5 23,0
17,5
18,0
18,5
19,0
19,5
20,0
20,5
21,0
21,5
22,0
22,5
23,0

Appendix No. 6

Table 2 Hygienic standards for microclimate parameters for different premises

⇐ Previous1234567

Date of publication: 2015-09-17; Read: 3046 | Page copyright infringement

studopedia.org - Studopedia.Org - 2014-2018. (0.001 s) ...

Calculation of the absolute humidity (moisture content) of air

The absolute humidity is calculated using the formula:

where f is the maximum air humidity (see.

tab. 2.2 by the temperature of the "wet" bulb), g / m3;

tc and tв - temperatures of "dry" and "wet" thermometers, ° С;

B - barometric pressure, mm Hg.

Ways to ensure the required parameters of the microclimate
industrial premises

Creation of optimal meteorological conditions in industrial premises is a difficult task, the solution of which goes in the following directions.

Rational space-planning and design solutions for industrial buildings . Hot workshops are placed, if possible, in one-storey one- and two-span buildings.

Courtyards are arranged so that they are well ventilated. It is not recommended to place extensions around the perimeter of the building that interfere with the flow of fresh air.

The building itself is positioned so that the longitudinal axis of the aeration lantern makes an angle of 90 ... 60 ° with the direction of the prevailing summer wind. To protect against cold air entering the production premises, entrances are equipped with sluices, doorways with air curtains.

They use double glazed windows, insulate fences, floors, etc.

Rational placement of equipment.It is advisable to locate the main sources of heat directly under the aeration lamp, at the outer walls of the building and in one row at such a distance from each other that the heat fluxes from them do not intersect at the workplace. Cooling materials must not be placed in the path of fresh air.

Separate rooms should be provided for cooling hot products. The best solution is to place the radiant equipment in isolated rooms or in open areas.

Mechanization and automation of production processes.Much is being done in this direction. Mechanical loading of furnaces in metallurgy, pipeline transport for liquid metal, continuous casting installations, etc. are being introduced.

Remote control and surveillanceallows in many cases to bring a person out of adverse conditions. An example is the remote control of hoisting cranes in hot shops.

Implementation of more rational technological processes and equipment.For example, replacing the hot method of metal processing with cold, flame heating - induction, ring furnaces in brick production - tunnel, etc.

as well as rational thermal insulation of equipment, protection of working with various types of screens, rational ventilation and heating, rationalization of work and rest regimes, use of personal protective equipment.

How to calculate the relative humidity

Methodology for determining the microclimate parameters for workers
places of production personnel

Microclimate parameters in laboratory work are determined as follows:

1. Take measurements of the air temperature in the room according to the "dry" and "wet" thermometers of the Assman psychrometer, tsfand tvfaccordingly, record the result in the column "actual values" of the protocol.

Determine the barometric pressure, B (mm Hg) by the barometer.

3. Determine the speed of air movement at the workplace Сф using a cup anemometer with a digital display.

Determine the period of the year, taking into account the average daily outside temperature (e if tnar> +10 С, then the period of the year warm, if a tnar< +10 С, то период года cold ).

Table 2.1

Determine the excess of apparent heat Qsur in the room using the formula:

where QIZB - excess of sensible heat, (kJ / h · m3);

QЯВН - obvious warmth in the shop, (kJ / h);

t ° C F or f t ° C F or f t ° C F or f 7 7,51 12,79 23 21,07 8 8,04 16 13,63 22,38 9 8,61 17 14,53 23,76 10 9,21 18 15,48 25,91 11 9,84 19 16,48 26,74 12 10,52 20 17,54 30,04 13 11,23 21 18,65 31,04 14 11,99 22 19,83 31,82

Determine according to ДСН 3.3.6.042-99 the required values \u200b\u200bof temperature tн, relative humidity jн, the speed of air movement at the workplace Cn (Appendix A.2). The standard values \u200b\u200bof the microclimate parameters are selected depending on the period of the year, the category of labor severity, as well as the category of the room for the thermal regime. So, if the room is "hot", then the values \u200b\u200bfrom the column "admissible" are taken, if the room is "cold", then the values \u200b\u200bfrom the column "optimal" are taken. Permanent jobs correspond to the light category of work ( 1a, 16), non-permanent jobs - medium and heavy work categories ( ІІа, ІІb, III).

Enter the obtained data into the protocol table in the column "standard value".

12. Compare regulatory data with actual data. Make a conclusion about the compliance of the industrial premises microclimate with the standard values \u200b\u200bin accordance with GOST 12.1.003-88 and DSN 3.3.6.042-99.

Related publications