Tip 1: How to find the absolute humidity
Tip 1: How to find the absolute humidity
Absolute humidity is this mass of water vapor,which is in the unit volume of this gas, in simple terms, it is the density of water vapor. Depending on the temperature, this value may vary. It can be measured by obtaining a dew point or by calculating it in terms of relative humidity.
You will need
- - mercury thermometer;
- - Sealed vessel;
- - table of the dependence of saturated water vapor on temperature;
- psychrometer.
Instructions
1
For direct measurement of humidity, take a sample of air in a sealed vessel and begin to cool it. At a certain temperature, dew will appear on the walls of the vessel (the vapor condenses), record the temperature at which this will occur. On a special table, find the density of saturated vapor at the temperature that it condenses. This will be absolute humidity of air, the sample of which was selected.
2
Take a sensitive mercury thermometer,Wrap the vial with mercury cloth. Remove his readings after he comes to a temperature equilibrium with the surrounding air. From the table, determine the density of saturated steam at the temperature shown by the thermometer. This will be absolute humidity, but the value will not be very accurate.
3
Calculate the absolute humidity at a certain relative humidity. This value is measured in percentage and shows how many times the real density of water vapor in the air is less than saturated at a given temperature. To determine the absolute humidity, measure the temperature of air. Then, from the saturated vapor density table, find this value for the measured temperature. To find the absolute humidity, the relative humidity φ multiply by the density of saturated vapor at a given temperature ρn and divide by 100% (ρ = φ ∙ ρн / 100%).
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Example Relative humidity at a temperature of 20 ° C is 45%. To get the absolute humidity, find the density of saturated water vapor attemperature of 20 ºС, which air has. This value is 17.3 g / m³. After that, apply the formula for calculating absolute humidity ρ = 45 ∙ 17,3 / 100 = 7,785 g / m³. This will be absolute humidity of air.
Tip 2: How to measure moisture
Humidity measurements are necessary for both physicists andsynoptics. And we ourselves should also be interested in this issue, especially if we sit in the same room for a long time. After all, the humidity of the air affects the human body, that's why it has to be controlled. There are two main types of instruments that measure the humidity of the air. They differ in the device and principle of operation. These are hygrometers and psychrometers.
Instructions
1
The principle of the hygrometers consists in the analysisthe influence of moisture fluctuations on certain bodies and matter. For example, hair hygrometers are based on the ability of a fat-free human hair to change its length in response to changes in air humidity. These hygrometers measure the humidity of air in the range of 30-100%. In film hygrometers, the moisture sensitive element is an organic film.
2
Although both film and hair hygrometers are notare able to give such an accuracy of measurements, which gives a psychrometer. But in winter, the main means of measuring the relative humidity of air are hygrometers, which are also weight, electrolytic, condensation and ceramic. Each of these types of hygrometers has its own characteristics. But the base is one for all: the hygrometric method of measurement or the determination of the dew point.
3
Psychrometric method of measuring relativeair humidity is also very popular. At hygrometers, the error can reach 5%, but psychrometers are much more accurate. The standard simple psychrometer consists of two thermometers. One is dry and the other is wet. The second is wrapped in water-soaked cotton cloth. Evaporating water cools the thermometer, and at this time the second (dry) thermometer detects the temperature of the surrounding air. The readings are ultimately transmitted to a recording device that determines the relative humidity of the air in the room based on the temperature difference between the dry and wet thermometers.
4
If you do not have a psychrometer or a hygrometer,Humidity can be measured without them. Put a cold tap water in a pile and put it in the refrigerator for a couple of hours. Make sure that the water temperature does not drop below the mark at 5 ° C. Place the stack in the room so that it is away from the heaters. Now watch the pile for a few minutes.
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If the walls of the stack began to fog up and dry upin just five minutes, then the air humidity is very low, that is, the air is dry, About the average humidity you will "report" the walls of the stack, and the remaining misted. If on the surface of the glass for five minutes, small streams of water form, the room is high.
Tip 3: How to find the relative humidity of air
To determine the relative humidity of air find the real pressure or vapor density atTo this temperature, divide by the saturated vapor pressure at a given temperature, which can be found in the table and multiply by 100%. Also the relative humidity of air can be found depending on the difference in the readings of dry and wet thermometers or changes in hair length depending on humidity.
You will need
- two identical thermometers, a piece of gauze, a hairdresser's psychrometer, a psychrometric table, and a dew point chart.
Instructions
1
Determination of the relative humidity through the dew point Measure the temperature of air and use the table to determine the saturated vapor pressure at a given temperature. Then select the sample of air and cool it, constantly monitoringTemperature, until the water vapor in it begins to condense, forming dew. Measure the temperature at this point and use the table to determine the saturated vapor pressure. It will be equal to the actual vapor pressure at the initial temperature. After that, divide the saturated vapor pressure obtained by cooling into saturated vapor pressure at this temperature, and multiply the result by 100%. The result is a relative humidity in percentages.
2
Determination of the relative humidity of twothermometers Take two identical thermometers. Liquid mercury thermometers are best suited. On a bubble with a working liquid of one of them wind up a gauze, then abundantly moisten it with water. After waiting a while, read the thermometer readings in degrees Celsius. Then find the temperature difference on a wet and dry thermometer, the wet thermometer readings will be either the same or lower than the dry one. In the psychrometric table, find the column of the dry thermometer readings and find the closest to what the measurement showed. Then, on the line, find the value that corresponds to the calculated difference between the dry and wet thermometer readings, the cell will have a relative humidity of air in percentages.
3
Determination of the relative humidity of the hair hygrometer Since the horsehair changes its length depending on the humidity of air, pull it and attach it to a sensitive dynamometer. By the force of tension, one can determine the relative humidity of air. This measurement will be the least accurate.
Tip 4: How to find the relative humidity
Humidity indicates how much water vaporis contained in the air. Relative humidity is an important environmental indicator of the environment. If it takes too low or too high values, a person quickly becomes tired, his perception, memory and health worsen.
Instructions
1
Humidity can be absolute and relative. Absolute humidity f shows the actual amount of water vapor by mass, which is in one cubic meter of air. To find the absolute humidity of the air, divide the mass of steam to the total volume of moist air. Units of measurement - gram per cubic meter, g / m³.
2
There is the concept of the maximum absolutehumidity at a fixed temperature. The point is that the density of water vapor can not increase to infinity, at a certain point, thermodynamic equilibrium sets in. This is a state of the system in which macroscopic parameters, such as temperature, volume, pressure, entropy, are constant in time. These values fluctuate near their average values, if the system is maximally isolated from the effects of the external environment.
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So, when the thermodynamicthe balance between steam and air says that the air is saturated with steam. The humidity of the air saturated with steam is maximum. It is also called the saturation boundary. It is also measured in g / m³. We can denote it by F.
4
To determine the relative humidity of air,find the ratio of absolute humidity to maximum: φ = f / F. The same result will be obtained if we divide the vapor pressure into saturated vapor pressure. Relative humidity - a dimensionless value, can be recorded in percent.
5
The saturation of the air with steam depends on the temperature. The temperature at which this quantity of water vapor saturates the air is called the dew point. When this temperature is reached, condensation appears, or, in other words, dew drops out. In general, the higher the temperature, the more steam is needed to saturate the air.
Tip 5: What is absolute and relative humidity
Humidity is a characteristic thatexpresses the amount of water vapor in the air. This is one of the most significant indicators describing the weather and climate. In general, in the Earth's atmosphere, humidity varies widely, depending on the height and climatic zone.
