What is relative humidity. Absolute and relative humidity. Dew point. The word Moisture in the dictionary Complete accentuated paradigm according to A. A. Zaliznya
Absolute humidity
Absolute humidity is the amount of moisture (in grams) contained in one cubic meter of air. Due to the 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 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
An equivalent definition is the ratio of the mass 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 vapor .
The saturation vapor pressure of water increases strongly with increasing temperature (see graph). Therefore, with isobaric (that is, at constant pressure) cooling of air with a constant vapor concentration, there comes a moment (dew point) when the vapor is saturated. In this case, the "extra" vapor condenses in the form of fog or ice crystals. The processes of saturation and condensation of water vapor play a huge role in atmospheric physics: 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 an energy mechanism for the emergence and development of tropical cyclones (hurricanes).
Relative Humidity Estimation
The relative humidity of a water-air mixture can be estimated if its temperature is known ( T) and dew point temperature ( T d). When T and T d 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 water in the mixture at temperature is estimated e s :
Supersaturated water vapor
In the absence of condensation centers, when the temperature decreases, 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 supersaturated vapor on ions formed during the passage of a charged particle in such a pair that the principle of operation of a cloud chamber and diffusion chambers is based: water droplets condensing on the formed ions form a visible trace (track) of a charged particles.
Another example of the condensation of supersaturated water vapor is the contrails of aircraft that occur when supersaturated water vapor condenses on soot particles in engine exhaust.
Means and methods of control
To determine the humidity of the air, devices called psychrometers and hygrometers are used. August's psychrometer consists of two thermometers - dry and wet. A wet bulb indicates a lower temperature than a dry bulb because its tank is wrapped in a cloth soaked in water, which, evaporating, cools it. The rate of evaporation depends on the relative humidity of the air. According to the testimony of dry and wet thermometers, the relative humidity of the air is found according to psychrometric tables. Recently, integral humidity 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 influence of water vapor contained in the air. To calibrate instruments for measuring humidity, special installations are used - hygrostats.
The amount of moisture contained in one cubic meter of air. Due to the 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 as much as possible (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 vapor .
The saturation vapor pressure of water rises strongly with increasing temperature. Therefore, with isobaric (that is, at constant pressure) cooling of air with a constant vapor concentration, there comes a moment (dew point) when the vapor is saturated. In this case, the "extra" vapor condenses in the form of fog or ice crystals. The processes of saturation and condensation of water vapor play a huge role in atmospheric physics: 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 an energy mechanism for the emergence and development of tropical cyclones (hurricanes).
Relative Humidity Estimation
The relative humidity of a water-air mixture can be estimated if its temperature is known ( T) and dew point temperature ( T d). When T and T d 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 temperature is estimated to be:
Supersaturated water vapor
In the absence of condensation centers, when the temperature decreases, the formation of a supersaturated state is possible, that is, the relative humidity becomes more than 100%. Ions or aerosol particles can act as condensation centers, it is on the condensation of supersaturated vapor on ions formed during the passage of a charged particle in such a pair that the principle of operation of a cloud chamber and diffusion chambers is based: water droplets condensing on the formed ions form a visible trace (track) of a charged particles.
Another example of the condensation of supersaturated water vapor is the contrails of aircraft that occur when supersaturated water vapor condenses on soot particles in engine exhaust.
Means and methods of control
To determine the humidity of the air, devices are used that are called psychrometers and hygrometers. August's psychrometer consists of two thermometers - dry and wet. A wet bulb temperature is lower than a dry bulb because its tank is wrapped in a cloth soaked in water, which cools it down as it evaporates. The rate of evaporation depends on the relative humidity of the air. According to the testimony of dry and wet thermometers, the relative humidity of the air is found according to psychrometric tables. Recently, integral humidity 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 influence of water vapor contained in the air.
To increase the relative humidity in residential areas, use electric humidifiers, pallets filled with wet claydite and regular spraying.
Notes
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See what "Relative Humidity" is in other dictionaries:
The ratio of the mole fraction of moisture in a gas to the mole fraction of saturated water vapor over water [ice] in that gas at the same pressure and temperature. Unit of measurement % [RMG 75 2004] Topics for measuring the moisture content of substances Generalizing the terms of the quantity ... ... Technical Translator's Handbook
relative humidity- The percentage ratio of the elasticity of water vapor contained in a unit volume of air to the elasticity of saturating steam 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 the elasticity of saturated vapor at the same temperature; expressed as a percentage. * * * RELATIVE HUMIDITY RELATIVE HUMIDITY, water vapor pressure ratio (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: engl. relative humidity vok. relative Feuchte, f; relative… … Penkiakalbis aiskinamasis metrologijos terminų žodynas
relative humidity- santykinis drėgnis statusas T sritis chemija apibrėžtis Drėgmės ir drėgnos medžiagos, kurioje ji yra, masių arba tūrių santykis (%). atitikmenys: engl. relative humidity. relative humidity ... Chemijos terminų aiskinamasis 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
Air humidity- the content in the air, characterized by a number of values. The water evaporated from the surface when they are heated enters and concentrates in the lower layers of the troposphere. The temperature at which the air reaches saturation with moisture for a given water vapor content and unchanged is called the dew point.
Humidity is characterized by the following indicators:
Absolute humidity(lat. absolutus - complete). It is expressed as the mass of water vapor in 1 m of air. It is calculated in grams of water vapor per 1 m3 of air. The higher , the greater the absolute humidity, since more water changes from liquid to vapor when heated. During the day, the absolute humidity is higher than at night. The indicator of absolute humidity depends on: in polar latitudes, for example, it is up to 1 g per 1 m2 of water vapor, at the equator up to 30 grams per 1 m2 in Batumi (, coast) the absolute humidity is 6 g per 1 m, and in Verkhoyansk ( , ) - 0.1 grams per 1 m The vegetation cover of the area largely depends on the absolute humidity of the air;
Relative Humidity. This is the ratio of the amount of moisture in the air to the amount that it can hold at the same temperature. Relative humidity is calculated as a percentage. For example, the relative humidity is 70%. This means that air contains 70% of the amount of vapor that it can hold at a given temperature. If the daily course of absolute humidity is directly proportional to the course of temperatures, then relative humidity is inversely proportional to this course. A person feels good when equal to 40-75%. Deviation from the norm causes a painful state of the body.
The air in nature is rarely saturated with water vapor, but always contains some amount of it. Nowhere on earth has a relative humidity of 0% been recorded. At meteorological stations, humidity is measured using a hygrometer device, in addition, recorders are used - hygrographs;
The air is saturated and unsaturated. When water evaporates from the surface of the ocean or land, the air cannot hold water vapor indefinitely. This limit depends on . Air that can no longer hold moisture is called saturated. From this air, at the slightest cooling, water droplets in the form of dew begin to stand out. This is because water, when cooled, changes from a state (vapor) to a liquid. Air above a dry and warm surface usually contains less water vapor than it could at a given temperature. Such air is called unsaturated. When it is cooled, water is not always released. The warmer the air, the greater its ability to absorb moisture. For example, at a temperature of -20°C, the air contains no more than 1 g/m of water; at a temperature of + 10°C - about 9 g/m3, and at +20°C - about 17 g/m
DEFINITION
Absolute air humidity is the amount of water vapor per unit volume of air:
In the SI system, the unit of measure for absolute humidity
Humidity is a very important environmental parameter. It is known that most of the Earth's surface is occupied by water (the World Ocean), from the surface of which evaporation continuously occurs. In different climatic zones, the intensity of this process is different. It depends on the average daily temperature, the presence of winds and other factors. Thus, in certain places the process of water vaporization is more intense than its condensation, and in some places it is vice versa.
The human body actively reacts to changes in air humidity. For example, the process of sweating is closely related to the temperature and humidity of the environment. At high humidity, the processes of evaporation of moisture from the surface of the skin are practically compensated by the processes of its condensation, and the removal of heat from the body is disturbed, which leads to violations of thermoregulation; at low humidity, the processes of evaporation of moisture prevail over the processes of condensation and the body loses too much fluid, which can lead to dehydration.
In addition, the concept of humidity is the most important criterion for evaluating weather conditions, which is known to all from weather forecasts.
The absolute humidity of the air gives an idea of the specific water content in the air by mass, but this value is inconvenient from the point of view of the susceptibility of humidity by living organisms. A person feels not the mass amount of water in the air, but its content relative to the maximum possible value. To describe the reaction of living organisms to changes in the water vapor content in the air, the concept of relative humidity is introduced.
Relative humidity
DEFINITION
Relative humidity- this is a physical quantity showing how far the water vapor in the air is far from saturation:
where is the density of water vapor in the air (absolute humidity); density of saturated water vapor at a given temperature.
Dew point
DEFINITION
Dew point is the temperature at which water vapor becomes saturated.
Knowing the dew point temperature, you can get an idea of the relative humidity of the air. If the dew point temperature is close to the ambient temperature, then the humidity is high ( when the temperatures match, fog is formed). Conversely, if the values of the dew point and air temperature at the time of measurement differ greatly, then we can talk about a low content of water vapor in the atmosphere.
When something is brought into a warm room from frost, the air above it cools, becomes saturated with water vapor, and water droplets condense on things. In the future, the thing warms up to room temperature, and all the condensate evaporates.
Another, no less well-known example is the fogging of windows in a house. Many people have condensation on their windows in the winter. This phenomenon is influenced by two factors - humidity and temperature. If a normal double-glazed window is installed and the insulation is correctly carried out, and there is condensate, it means that the room has high humidity; Possibly poor ventilation or ventilation.
Examples of problem solving
EXAMPLE 1
| Exercise | The photo shows two thermometers used to determine the relative humidity of the air using a psychrometric table. What will a wet bulb thermometer show if relative humidity increases by 7% at a constant air temperature? |
| Decision | Let's write down the readings of the dry and wet thermometers shown in the photo: Let's determine the difference in thermometer readings: According to the psychrometric table, we determine the relative humidity of the air: If the air humidity increases by 7%, it will become 55%. According to the psychrometric table, we determine the readings of a dry thermometer and the difference between the readings of dry and wet thermometers: So the wet bulb will show: |
| Answer | Wet bulb readings. |
EXAMPLE 2
| Exercise | Relative humidity in the evening at a temperature of 50%. Will dew fall if the temperature drops to ? at night? |
| Decision | Relative Humidity:
|
The weight, or more precisely the mass, of water vapor contained in 1 m3 of air is called absolute humidity. In other words, this water vapor density in the air. At the same temperature, the air can absorb quite a certain amount of water vapor and reach a state of complete saturation. in the state of its saturation is called moisture capacity.
The moisture content of air increases sharply with increasing temperature. magnitude ratio absolute air humidity at a given temperature to the value of its moisture capacity at the same temperature is called relative humidity.
To determine the temperature and relative humidity use a special device - a psychrometer. The psychrometer consists of two thermometers. The ball of one of them is moistened with a gauze cover, the end of which is lowered into a vessel with water. The other thermometer stays dry and shows the ambient temperature. A wet-bulb thermometer shows a lower temperature than a dry-bulb thermometer, because the moisture from the gauze requires a certain amount of heat. The wet bulb temperature is called cooling limit. The difference between dry and wet bulb readings is called psychrometric difference.
Between the value of the psychrometric difference and the relative there is a certain relationship. The greater the psychrometric difference at a given air temperature, the lower the relative humidity of the air and the more moisture the air can absorb. When the difference is zero, the air is saturated and further evaporation of moisture in such air not happening.
Absolute humidity
(f)- this is the amount of water vapor actually contained in 1m 3 of air:f\u003d m (mass of water vapor contained in the air) / V (volume)
A commonly used unit of absolute humidity is: (f)\u003d g / m 3
Relative Humidity
Relative humidity: φ = (absolute humidity)/(maximum humidity)Relative humidity is usually expressed as a percentage. These quantities are related to each other by the following relationship:
φ = (f×100)/fmax
What is dew point