What is this article

Definition

In addition to relative humidity, there is also such a magnitude as absolute humidity. Number of water vapor in unit of air volume absolute humidity air. Since the mass is taken as a unit of measurement, and its values \u200b\u200bfor steam in cubic meter The air is small, it was customary to measure absolute humidity in g / m³. These indicators vary from units of measurement to more than 30 g / m³, depending on the time of year and geographic location The surface above which humidity is measured.

Absolute humidity is the main indicator characterizing the condition of the air and great importance To determine its properties has a comparison of humidity with ambient temperatureSince these parameters are interconnected. For example, water vapor, with a decrease in temperature, reaches the saturation state, after which the condensation process begins. The temperature at which it occurs is called a dew point.

Devices for determining absolute humidity

The determination of the absolute humidity value is based on its calculations according to the thermometers. In particular, according to the testimony of the psychrometer of August, consisting of two mercury thermometers - One of which is dry, and the other is wet (in the figure image a). The evaporation of water from the surface that is indirectly in contact with the tip of the thermometer leads to a decrease in its testimony. The difference between the testimony of both thermometers and underlies the formula of August, which determines the absolute humidity. The error of such measurements may have air flow and thermal radiation.

More accurate aspiration psychrometer proposed by Assman (in the figure image b). Its design provides a protective tube that limits the effect of thermal radiation, and an aspiration fan that creates a stable air flow. Absolute humidity is determined by the formula that displays its dependence on thermometer testimony and barometric pressure during this period of time.

The value of absolute humidity measurements

Control of absolute humidity values \u200b\u200bare needed in meteorology, as these readings play a large role in predicting possible precipitation. Also, psychrometers also enjoy in mining mining mines. The need for constant control of absolute humidity in many automation systems is a prerequisite for creating more modern meters. These are electronic sensors that produce the necessary measurements, analyze the readings and display already you numerical value absolute humidity.

For quantitative assessment Air humidity use absolute and relative air humidity.

Absolute air humidity measure the density of the water vapor in the air, or its pressure

A clearer view of the degree of humidity of air gives relative humidity. The relative humidity of the air is measured by the number showing how many percent is absolute moisture from the density of the water vapor necessary to saturate air when the temperature is available:

Relative humidity can be determined by vapor pressure, since practically the vapor pressure is in proportion to its density. Therefore, in can be determined so: the relative humidity is measured by the number indicating how many percent is the absolute humidity of the water vapor pressure of the air of the air when the temperature exists:

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

We find out how the change in air temperature can be reflected on its humidity. Let the absolute humidity of the air be equal to as the density of the saturable water vapor at 22 ° C is equal to (Table 9.1), then the relative humidity of at about 50%.

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

Table 9.1. Pressure and density of saturated water vapor when various temperatures

The temperature in which the air in the process of its cooling becomes saturated with water vapor, is called a dew point. In the example above, the dew point is equal to note that at a well-known dew point, the absolute air humidity can be found along table. 9.1, since it is equal to the density of the saturated pair at the dew point.

Water vapor in the atmosphere. Water steam in the air, despite the huge surfaces of the oceans, seas, lakes and rivers, is not always saturated. Move air mass leads to the fact that in the places of our planet in this moment The evaporation of water prevails over condensation, and in others, on the contrary, condensation prevails. But in the air almost always there is some amount of water vapor.
The content of water vapor in the air, i.e. its humidity, can be characterized by several values.
Water vapor density in the air is called absolute humidity. Absolute humidity is measured, therefore, in kilograms per meter cubic (kg / m 3).
Partial pressure of water vapor. Atmospheric air It is a mixture of various gases and water vapor. Each of the gases contributes to the total pressure produced by air into the body in it. Pressure that would produce water vapor if all other gases were absent, called partial pressure of water vapor. The partial pressure of the water vapor is taken for one of the indicators of air humidity. It is expressed in units of pressure - Pascals or millimeters mercury pillar.
Atmosphere pressure Determined by the amount of partial pressures component of dry air (oxygen, nitrogen, etc.) and water vapor.
Relative humidity. According to partial pressure of water vapor and absolute humidity, it is also impossible to judge how much water vapor in these conditions is close to saturation. Namely, the intensity of the evaporation of water and the loss of moisture by living organisms depends. That is why the magnitude showing how much water vapor is close to saturation at this temperature - relative humidity.
Relative humidity Call attitude partial pressure r water vapor contained in air at a given temperature, pressure r N.P. Saturated pair at the same temperature, expressed as a percentage:

Relative air humidity is usually less than 100%.
Psychrometer. Air humidity is measured using special devices. We will tell about one of them - psychrometer.
The psychrometer consists of two thermometers ( fig. 11.4.). The reservoir of one of them remains dry, and it shows the air temperature. The reservoir of another is surrounded by a strip of fabric, the end of which is omitted into the water. Water evaporates, and thanks to this, the thermometer is cooled. The more relative humidity, the less intensively there is evaporation and the temperature shown by the thermometer surrounded by a damp cloth, closer to the temperature of the dry thermometer.

With a relative humidity equal to 100%, water will not evaporate and the readings of both thermometers will be the same. By the difference in the temperatures of these thermometers using special tables, air humidity can be determined.
The value of humidity. The intensity of the evaporation of moisture from the surface of the skin of man depends on the humidity. And the evaporation of moisture is of great importance for maintaining the body temperature constant. IN spacecraft The most favorable relative air humidity (40-60%) is supported.
It is very important to know moisture in meteorology - due to weather prediction. Although the relative amount of water vapor in the atmosphere is relatively small (about 1%), the role of it in atmospheric phenomena significant. The condensation of the water vapor leads to the formation of clouds and the subsequent fallout of precipitation. At the same time stands out a large number of Warm. Conversely, the evaporation of water is accompanied by the absorption of heat.
In weaving, confectionery and other industries, a certain humidity requires a certain humidity.
Storage of works of art and books requires maintenance of air humidity at the required level. Therefore, in museums on the walls you can see psychrometers.
It is important to know ne. absolute number water vapor in the atmosphere, and relative. Relative humidity is measured by a psychrometer.
Dew point
The point of dew with this pressure is called the temperature to which the air should cool, so that the water vapor contained in it reached the saturation state and began to condense into the dew.
The dew point is determined by the relative humidity of the air. The higher the relative humidity, the point of the dew above and closer to the actual air temperature. The lower the relative humidity, the point of the dew below the actual temperature. If the relative humidity is 100%, then the dew point coincides with the actual temperature.
The dew point can not be adjusted. It is not on the windows or in double-glazed windows. It can only be seen on the charts where the fat black line, the defects spent between the temperature axes and humidity, separates two zones: the dry zone and the zone in which condensate is begins.
With a point of dew, however, we are faced daily. We raise the glass cover from a frying pan on which we cook, water flows from the lid abundantly. In the bathroom after the adoption of the hot soul, we discover that the mirror is filled. We enter in winter from the street in a warm shop - glasses instantly fog. It's all - jokes of the dew point.
The main thing, about what should be remembered that it is necessary to understand what is necessary - that both factors are influenced by condensing: temperature and humidity. If a cold item is brought into the room - its temperature and humidity of the room can contribute to the formation of condensate. If simply, with constant humidity, lower the temperature is the same story, condensation will start directly in the air, so formed by all drivers fog on the tracks - in low-spirits and in the areas of reservoirs.

G. Y. Mikishev, B.B. Bukhovtsev, N.N.Sotsky, physics Grade 10, http://ru.wikipedia.org/wiki/Tocho_

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Absolute and relative humidity

IN previous section We used a number of physical terms. Because of their great importance remember school Course Physics and explain what is the humidity of the air, the dew point and how to measure them.

The primary objective physical parameter is the absolute (actual) air humidity - mass concentration (content) gaseous water (evaporated water, water vapor) in the air, for example, the number of water kilograms, steamed in one cubic meter of air (more precisely, in one cubic meter of space). If there is little water vapor in the air, then the air is dry, if much is wet. But what does a lot mean? For example, 0.1 kg of water vapor in one cubic meter of air - is it a lot? And not much, and not enough, just just so much and nothing more. But if you ask, a lot of whether 0.1 kg of water vapor in one cubic meter of air at 40 ° C, then you can definitely say that there is a lot, so much that never happens.

The fact is that how many water evaporates a lot of water, because under normal bath conditions, water is still liquid, and only a very small part of its molecules flies out of the liquid phase through the surface of the section in the gas phase. Let us explain this on the example of the same conditional layout of the Turkish bath - a model vessel ("Pans"), bottom (floor), walls and cover (ceiling) of which have the same temperature. In the technique, such an isothermal vessel is called a thermostat (oven).

At the bottom of the model vessel (on the floor of the bath) water and, changing the temperature, measure the absolute humidity of the air at different temperatures. It turns out that when the temperature is lifting the temperature, the absolute air humidity rapidly increases, and with a decrease in temperature, it is quickly reduced (Fig. 23). This is the result of the fact that with increasing temperature rapidly (exponentially), the number of water molecules with energy sufficient to overcome the energy barrier is growing phase transition. The increase in the number of gasifying ("evaporated") molecules leads to an increase in the amount (accumulation) of water molecules in the air (to an increase in the amount of water vapor), which leads to an increase in the number of water molecules, again "flying" into water (liquefied). When the speed of water gasification is compared with the veligation rate of water vapors, an equilibrium occurs, which is described by the curve in Fig. 23. It is important to keep in mind that in a state of equilibrium when it seems that nothing happens in the bath, nothing evaporates and nothing is condensed, in fact, it is in reality gasiforn (and immediately liquefied) tons of water (and water vapor respectively). However, in the future we will be considered evaporation precisely the resulting effect - exceeding the rate of gasification over the velocity rate, when the amount of water is really reduced, and the number of water vapors is actually increasing. If the vein rate exceeds the speed of gasification, then such a process will be called condensation.

The values \u200b\u200bof the equilibrium absolute humidity of air are called the density of a saturated steam of water and are the maximum possible absolute air humidity at a given temperature. With increasing temperature, water begins to evaporate (turn into gas), striving for an increased value of a saturated pair density. When the temperature is reduced, the water vapor condensation occurs either on the cooling walls in the form of small drops of dew (then merging into large drops and flowing in the form of crops), or in the volume of coolant air in the form of small droplets of a fog of less than 1 microme (including in the form "Couples").

Fig. 23. Absolute humidity of air DO over water in equilibrium conditions (saturated pair density) and the corresponding pressure of a saturated pair of RO at different temperatures. Dotted arrows - Determination of the dew point TR for an arbitrary value of absolute humidity d.

So, at a temperature of 40 ° C, the equilibrium absolute humidity of air over water in isothermal conditions (the density of the saturated steam) is 0.05 kg / m 3. Conversely, for an absolute humidity of 0.05 kg / m 3, the temperature of 40 ° C is called a dew point, since with this absolute humidity and at this temperature begins to appear to appear (with a decrease in temperature). With dew, everyone is familiar with the swollen stalks and mirrors in the bathrooms. The absolute humidity of the air definitely determines (according to the graph in Fig. 23) the point of air dew and vice versa. Note that the dew point is 37 ° C, equal normal temperature Human bodies correspond to the absolute humidity of air 0.04 kg / m 3.

Now consider the case when the condition of thermodynamic equilibrium is violated. For example, at the beginning, the model vessel, together with the water being in it and air, was heated to 40 ° C, and then suppose purely hypothetically, that the temperature of the walls, water and air suddenly rose sharply to 70 ° C. Initially, we have absolute air humidity of 0.05 kg / m 3, corresponding to the density of saturated steam at 40 ° C. After the air temperature rise to 70 ° C, the absolute air humidity should gradually rise to a new value of the density of the saturated pair of 0.20 kg / m 3 due to the evaporation of the added amount of water. And on all over the evaporation, the absolute air humidity will be below 0.20 kg / m 3, but will increase and strive to the value of 0.20 kg / m 3, which sooner or later is set at 70 ° C.

Similar non-equilibrium air transition modes from one state to another are described using the concept of relative humidity, the value of which is calculated and equal to the ratio of the current absolute moisture to the saturated pair density at the current air temperature. Thus, at first we have a relative humidity of 100% at 40 ° C. Then, with a sharp rise in air temperature up to 70 ° C, the relative humidity of the air dropped dramatically to 25%, after which, due to evaporation, it began to rise to 100%. Since the concept of a saturated pair density is meaningless without specifying the temperature, the concept of relative humidity is also meaningless without specifying the temperature. Thus, the absolute air humidity of 0.05 kg / m 3 corresponds to the relative humidity of 100% at an air temperature of 40 ° C and 25% at an air temperature of 70 ° C. The absolute humidity of the air is purely massive and does not require binding to any temperature.

If the relative humidity of the air is zero, then there is no water vapor in the air (absolutely dry air). If the relative humidity of the air is 100%, then the air is maximally wet, the absolute humidity of the air is equal to the density of the saturated steam. If the relative air humidity is equal to, for example, 30%, then it means that only 30% of the amount of water is evaporated in the air, which, in principle, you can evaporate in the air at this temperature, but not yet evaporated (or can not be evaporated due to Absence liquid water). In other words, the numerical meaning of relative humidity indicates whether water can still evaporate and how much it can evaporate, that is, the relative humidity of the air actually characterizes the potential air moisture. We emphasize that the term "relative" correlates the mass of water in the air not to the mass of air, but to the maximum possible mass content of water vapor in the air.

But what will happen if there is no single temperature in the vessel? For example, the bottom (floor) will have a temperature of 70 ° C, and the lid (ceiling) is only 40 ° C. Then the unified concept of a density of saturated steam and relative humidity cannot be introduced. At the bottom of the vessel, the absolute humidity of the air tends to rise to 0.20 kg / m 3, and at the ceiling to decrease to 0.05 kg / m 3. At the same time, water on the day will evaporate, and water vapors will be condensed on the ceiling and then flush in the form of condensate down, in particular, at the bottom of the vessel. Such a non-equilibrium process (but maybe quite stable in time, that is, stationary) is called distillation in industry. This process is characteristic of real Turkish baths, in which the dew on the cold ceiling is constantly condensed. Therefore, in Turkish baths, there are compulsory ceilings with gutters (grooves) for the flow of condensate.

Nonequilibrium may occur in many other (and in almost all real) cases, in particular, with the equality of all temperatures, but with a lack of water. So, if in the process of evaporation water at the bottom of the vessel disappears (evaporated), then it will be evaporated to evaporate, and the absolute humidity will be fixed at one level. It is clear that reaching the relative humidity of air 100% in this case elevated temperatures It is not possible that it is a useful factor, in particular, to obtain a dry sauna or a lung couple in the Russian bath. But if we begin to reduce the temperature, then with a certain reduced temperature, called dew point, water in the form of condensate will again appear on the walls of the vessel. At the dew point, the relative humidity of the air is always equal to 100% (by the very determination of the dew point).

On the basis of the appearance of condensate, with a decrease in air temperature, the device is created widely known in the industry to determine the dew point in gases. In a glass chamber, through which the gas studied is passed through a low rate, a polished metal surface is mounted, which is slowly cooled (Fig. 24). At the time of the appearance of dew (fogging), the surface temperature is measured. This temperature is accepted for dew point. The exact definition of the moment of the appearance of the dew is possible only with the help of a microscope, since dew drops at the primary moment are very small. Cooling surfaces produce heat selection with liquid coolant or any other way. The surface temperature on which the dew drops is measured by any thermometer, preferably thermocouple. The principle of action of the device becomes clear if you "breathe" on a cold mirror, especially brought from cold to a warm room - as the mirror heated, the fogging is steadily reduced, and then stops at all.

All this means that at temperatures above the dew point, the surface is always dry, and if the water is still specifically pouring, it will certainly evaporate, the surface will dry. And at a temperature below the dew point, the surface is always wet, and if the surface is still artificially dry (wiper), then the water will immediately appear "herself" in the sense that it falls out of the air in the form of dew (condensate).

Fig. 24. The principle of the device device to accurately determine the dew point in the gas. 1 - polished metal surface for observing the fact of the appearance of dew drops, 2 - metal case, 3 - glass, 4 - input and output of the gas flow, 5 - microscope, 6 - illumination lamp, 7 - thermocouple thermometer with sweep thermocouples installed in close proximity To the polished surface, 8 is a glass with a cooled liquid (for example, a waterparty gauge with solid carbon dioxide - dry ice), 9 is a glass lift.

A completely different situation occurs if the surface is porous (wooden, ceramic, cement-sand, fibrous, etc.). Porous materials are characteristic of what they have voids, and emptiness have the type of channels with a small transverse size (diameter) up to 1 μm and even less. The liquid in such channels (capillaries, pores) behaves differently than on a non-porous surface or in channels with a large transverse size. In the event that the surface of the channels is wetted with water, the water from the surface absorbs deep into the material and evaporate it later, as everyone knows, it will be difficult. And if the surface of the channels is not wetting the water, then the water is deeply absorbed, and if it is even specially "injected" deep into the material (for example, a syringe), then it will all equalize (evaporated) outward. This is because a concave meniscus surface of the fluid surface is formed in wetting capillaries, and the forces of the surface tension are drawn into a capillary (Fig. 25). The thinner of the capillaries, the stronger the fluid absorbs, and the height of the lifting of the fluid column in the capillary due to the forces of the surface tension can be tens of meters. Therefore, the absorbent fluid is gradually distributed throughout the volume of porous material, which is used by trees to deliver feed solutions from the roots in the crown leaves.

Fig. 25. Illustration of the properties of the porous material presented in the form of a set of channels (capillaries, pores) of different transverse size D (diameter). 1 - Non-porous substrate, 2 - water spilled on the substrate, 3 - capillaries of porous material, sucking due to surface tension F water from the substrate at the greater height than thinner capillary (conditional transverse size of the "channel" d0 for water out of the capillary is equal to infinity ). The thinner of the capillary, the smaller the equilibrium value of the water vapor pressure (the equilibrium absolute air humidity, the density of the saturated pair), as a result of which the water pairs formed at the surface of the water on the substrate are condensed on the surface of the water in the capillary (vapor movement is shown by the bar-dotted arrow 4 is the phenomenon of moisturizing a porous material with water with water from the air is called hygroscopicity.

Porous materials have another one an important featuredue to the fact that the density of saturated steam above the concave surface of the water is less than above a flat flat surface of water, that is less valuesspecified in Fig. 23. This is due to the fact that water molecules from the steam phase are more often flying into compact (liquid) water with a concave meniscus (since the compact water is largely "surrounded"), and the air is depleted with water vapor. All this leads to the fact that the water with a flat surface evaporates and condenses inside a porous material in capillaries with wetting walls. This property of porous material is moisturized due to wet air is called hygroscopicity. It is clear that sooner or later all the water from non-porous surfaces will "translate" in the capillaries of porous material. This means that if the non-porous materials are dry, it does not mean at all that the porous materials under these conditions are also dry.

Thus, even at low humidity (for example, with relative humidity, 20%), porous materials can be moistened (even at a temperature of 100 ° C). So, wood is porous, so when stored in the warehouse can not be absolutely dry, no matter how long it was dried, and maybe only "air-dry". To obtain absolutely dry wood, it must be heated to as high temperatures as possible (120-150 ° C and above) with relative humidity of air as low as possible (0.1% and lower).

The air-dry moisture content of wood is determined not by absolute humidity of air, but relative humidity at a given temperature. Similar dependence is characteristic not only for wood, but also for bricks, plasters, fibers (asbestos, wool, etc.). The ability of porous materials to absorb water from the air is called the ability to "breathe". The ability to "breathe" is equivalent to hygroscopicity. This phenomenon will be discussed in more detail in section 7.8.

Some organic porous materials (fibers) are able to lengthen depending on their own humidity. For example, you can hire on the usual woolen thread Georgian and, moisturizing thread, make sure that the thread lengthened, and then as drying will again be crushed. This makes it possible, measuring the length of the thread, determine the humidity of the thread. And since the humidity of the thread is determined by the relative humidity, then the length of the thread can also determine the relative humidity of the air (though, approximately, with some error increasing with the increase in air humidity). In this principle, household hygrometers are working (devices for determining relative humidity), including baths (Fig. 26).

Fig. 26. The principle of the hygrometer device. 1 - hygroscopic thread, stretching for moisturizing (from natural or artificial material), fixed from two ends on the body of the device, 2 - wire thrust adjustable length for calibration of the device, 3 - axis of rotation of the device showing the arrow of the device, 4 - arrow lever, 5 - Stretched spring, 6 - arrow, 7 - scale.

When drying, fibers of wood are shortened. This explains the effects of changes in the shape of the branches of plants and the blocking of sawn timber during drying. On the hygroscopicity of the wood, numerous designs of homemade village hygrometers are based (Fig. 27 and 28).

Thus, the concave surfaces of water in wetting capillaries determine specific properties Porous materials (in particular, hygroscopicity and change mechanical properties). The convex surfaces of the water are played at least (on low-loading flat surfaces of substrates and in unmatched capillaries), above which pressure saturated vapor Waters are more than above flat and concave water surfaces. This means that the unmatched materials are more "dry" than wetting: water evaporates with unmatched materials and then the formed pairs are condensed on wetting. This is based on the effect of water-repellent impregnations of wood, not allowing not only the penetration of liquid water in the pores, but also the condensation of water vapor inside the wood. The bulge of the water droplets in the air is explained by the light evaporation of the fog, as well as the difficulty (compared with the dew) of its formation in the supercooling of wet gases (in particular, in the baths, in the clouds, in the clouds, etc.).

Fig. 27. The simplest homemade hygrometer from the dried and the skyr's wooden branch. 1 - the main escape, cut from two sides and attached to the wall (located in the sheet plane), 2 - a secondary side partition of a thickness of 3-6 mm and a length of 40-60 cm, 3 - a scale applied on the wall and built on a graduated certified hygrometer (or on weather shops of this area). With low relative humidity, escape wood dries out, the longitudinal fiber 4 is shortened and pulls out the side escape from the main one.

Fig. 28. The simplest homemade hygrometer based on an increase in the mass of moisturizing wood at high relative humidity. 1 - rocker (scales), 2 - thread of the suspension, 3 - cargo from nonhygroscopic material (for example, metal), 4 - cargo from hygroscopic wood (thin rounding from the cross-cutting loose wood type of linden or mesh with sawdust and chips). With increasing relative humidity of the air, wood is moisturized and increases in weight, which leads to a slope of the rocker in the direction of the hygroscopic cargo.

In conclusion, we note the features of household concepts and professional termsrelated to wet gases. Very many lovers of baths are still confident that the Kamenka of the Russian baths "give out" with "explosive" sacrifice by no means there are no water pairs, but gas suits (dust) small particles Hot water, and the most microscopic particles of hot water and there is the same "light pairs". Therefore, supporters of this beautiful household theory have to painfully rushing between the explicit expediency of "Turkish" sacrifice to large, but moderately hot surfaces of the floor (giving along this theory, like the most "light" pairs) and the "utility" of the Russian sacrifice on the relatively small surfaces of the split stones . In accordance with this theory and white clubs, a pair of kettle are represented by the primary act of "evaporation" of water in the kettle. Then these large particles of the "white" pair are "evaporated" (allegedly dissociate) again already with the formation of microscopic water particles invisible. It is clear that all these considerations are a consequence of ignorance of molecular theory of substances, and from here and the inability to imagine condensed water in the form of a set of mutually reacting molecules, from which, overcoming the barrier can fly into the air separate most energetic water molecules (capable of breaking the "bonds" of mutual attraction ), just forming gas in the form of gas.

In this book we are not able to discuss numerous domestic (often very cunning, but dense) ideas, so characteristic of baths. This book provides for acquaintance with physics at least at the level school program. We clearly distinguish compact, liquid water, poured into a vessel, from a dispersed (fragmented) liquid water in the form of large droplets and splashes and / or in the form of small droplets - aerosols (slowly descending in the air) and / or in the form of ultra-like droplets and fog and Cheeks (practically not descending in the air). Water pairs (water vapors) are not water and not liquid (even if it is finely fragmented), and gas, these are separate water molecules in space, and these water molecules are so far from each other, which is almost not attracted to each other (but sometimes We interact as a result of collisions and because of this are constantly combined - condensed at low rates of collisions of molecules). Water molecules (in the form of water vapor in the bath) are always in the medium of air molecules, forming a special gas - wet air, that is, a water vapor air mixture (a mixture of water molecules, nitrogen, oxygen, argon, and other components constituting air). And if this wet air is hot, it is called "ferry" in the baths. Dissociated with water vapor is called dissociated water molecules H 2 o –> ON + H, formed at temperatures above 2000 ° C. With even more high temperatures Over 5000 ° C are formed various ionized pairs of water H 2 O - + H 3 O + \u003d OH + H 3 O + \u003d OH + N + E. ionization can occur at low pairs of vapors, but with electronic or ion irradiations , for example, in smoldering or corona electric discharges in the air.

Water pairs, like any gas (or any pairs, for example, evaporating gasoline), invisible, and fog, being not gas, and small droplets of water, scatters light and see in the form of white smoke. Every day we can observe how from the kettle or from under the pot of the pan comes steam water cooling in the air. When leaving the kettle, he first invisible (in the form of gas), gradually cooled in the spout of the kettle, begins to condense and turn into a jet of the fog ("couple clubs"). Then the fog droplets are mixed with air and, if it is sufficient dry (that is, it is capable of accepting moisture), evaporate again and "disappear." In a bathhouse, the unquestible pairs of water in the air usually understand correctly understand the ferry, including the ferry of the hot humid air in the bath: "There is a hot couple in a bath" or "Cold Cap Ban". Fog in a bath in the form of "Couple clubs" is an undesirable phenomenon. The fog is formed with the volunteer penetration of cold air through the drop-down doors in a wet bath, as well as with dimensions of insufficiently heated stones at low air temperatures in the bath (just as the fog is formed when the pair from the kettle is released). In any case, the formation of fog can be prevented by increasing the temperature of steam, as well as in the increase in temperature and a decrease in air humidity in which steam is entered (see section 7.5). If a fog is visible in the bath, then they say that steam in the Ban "Raw" (see section 7.6). If, at the entrance to the bath, the face feels moisture (sweats) and the points are fisted, they say that steam is "wet", and if the face does not feel moisture - pairs "dry". Of course, water vapor itself (like gas) dry, raw or moist can not be correct, it would be better to say dry, raw or wet air. In professional jargon plumbing often use technical terms "Wet" or "wet" couples, when they want to clarify that in the main steam loss (for example, the passing pairs directly into the city bath parigue) there is condensed water (including in the form of fog). The terms "dry", "superheated" or "sharp" pairs are used when the pipe of the main steam pipeline inside is dry, and pair inside the pipe does not contain fog. Thus, terminology is completely different, so sometimes additional clarifications are required. Scientific, professional and household terminology, as a rule, do not coincide.

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-T 1) 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; T 1 - the temperature of the wet thermometer; N - 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 34.

Table 2. Elasticity of saturated water vapor (selectively)

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. Definition 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 conventional conditions 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 a mercury ball, moistened thermometer, there is evaporation of moisture and the absorption of heat, it will show more low 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; T 1 - 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.