Relative humidity of the air in the vessel. Humidity

IN this lesson The concept of absolute and relative air humidity will be introduced, terms and quantities associated with these concepts will be discussed: saturated steam, dew point, instruments for measuring humidity. During the lesson we will get acquainted with tables of density and saturated vapor pressure and a psychrometric table.

For humans, humidity is a very important parameter. environment, because our body reacts very actively to its changes. For example, a mechanism for regulating the functioning of the body, such as sweating, is directly 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 disrupted, which leads to disturbances in thermoregulation. At low humidity, moisture evaporation processes prevail over condensation processes and the body loses too much fluid, which can lead to dehydration.

The amount of humidity is important not only for humans and other living organisms, but also for the flow of technological processes. For example, due to known property conduct water electric current its content in the air can seriously affect the correct operation of most electrical appliances.

In addition, the concept of humidity is the most important evaluation criterion weather conditions, which everyone knows from weather forecasts. It is worth noting that if we compare the humidity in different times years in our usual climatic conditions, then it is higher in summer and lower in winter, which is associated, in particular, with the intensity of evaporation processes at different temperatures.

Main characteristics humid air are:

density of water vapor in the air;
relative air humidity.

Air is a composite gas and contains many different gases, including water vapor. To estimate its amount in the air, it is necessary to determine what mass water vapor has in a certain allocated volume - this value is characterized by density. The density of water vapor in the air is called absolute humidity.

Definition.Absolute air humidity- the amount of moisture contained in one cubic meter of air.

Designationabsolute humidity: (as is the usual designation for density).

Units of measurementabsolute humidity: (in SI) or (for the convenience of measuring small amounts of water vapor in the air).

Formula calculations absolute humidity:

Designations:

Mass of steam (water) in air, kg (in SI) or g;

The volume of air containing the indicated mass of steam is .

On the one hand, absolute air humidity is an understandable and convenient value, since it gives an idea of the specific water content in the air by mass; on the other hand, this value is inconvenient from the point of view of the susceptibility of humidity by living organisms. It turns out that, for example, a person does not feel the mass content of water in the air, but rather its content relative to the maximum possible value.

To describe such perception, the following quantity was introduced: relative humidity.

Definition.Relative humidity air– a value indicating how far the steam is from saturation.

That is, the value of relative humidity, in simple words, shows the following: if the steam is far from saturation, then the humidity is low, if it is close, it is high.

Designationrelative humidity: .

Units of measurementrelative humidity: %.

Formula calculations relative humidity:

Designations:

Water vapor density (absolute humidity), (in SI) or ;

Density of saturated water vapor at a given temperature, (in SI) or .

As can be seen from the formula, it includes absolute humidity, with which we are already familiar, and saturated vapor density at the same temperature. The question arises: how to determine the latter value? There are special devices for this. We will consider condensinghygrometer(Fig. 4) - a device that is used to determine the dew point.

Definition.Dew point- the temperature at which steam becomes saturated.

Rice. 4. Condensation hygrometer ()

An easily evaporating liquid, for example, ether, is poured into the container of the device, a thermometer (6) is inserted, and air is pumped through the container using a bulb (5). As a result of increased air circulation, intense evaporation of ether begins, the temperature of the container decreases because of this and dew (droplets of condensed steam) appears on the mirror (4). At the moment dew appears on the mirror, the temperature is measured using a thermometer; this temperature is the dew point.

What to do with the obtained temperature value (dew point)? There is a special table in which data is entered - what density of saturated water vapor corresponds to each specific dew point. It should be noted useful fact, that as the dew point increases, the value of the corresponding saturated vapor density also increases. In other words, the warmer the air, the more it can contain moisture, and vice versa, the colder the air, the lower the maximum vapor content in it.

Let us now consider the principle of operation of other types of hygrometers, instruments for measuring humidity characteristics (from the Greek hygros - “wet” and metreo - “I measure”).

Hair hygrometer(Fig. 5) - a device for measuring relative humidity, in which hair, for example human hair, acts as an active element.

The action of a hair hygrometer is based on the property of defatted hair to change its length when air humidity changes (with increasing humidity, the length of the hair increases, with decreasing it decreases), which makes it possible to measure relative humidity. The hair is stretched over a metal frame. The change in hair length is transmitted to the arrow moving along the scale. It should be remembered that a hair hygrometer does not give exact values relative humidity, and is used primarily for domestic purposes.

A more convenient and accurate device for measuring relative humidity is a psychrometer (from the ancient Greek ψυχρός - “cold”) (Fig. 6).

A psychrometer consists of two thermometers, which are fixed on a common scale. One of the thermometers is called a wet thermometer because it is wrapped in cambric fabric, which is immersed in a reservoir of water located on the back of the device. Water evaporates from the wet fabric, which leads to cooling of the thermometer, the process of reducing its temperature continues until the stage is reached until the steam near the wet fabric reaches saturation and the thermometer begins to show the dew point temperature. Thus, the wet bulb thermometer shows a temperature less than or equal to the actual ambient temperature. The second thermometer is called a dry thermometer and shows the real temperature.

On the body of the device, as a rule, there is also a so-called psychrometric table (Table 2). Using this table, you can determine the relative humidity of the surrounding air from the temperature value shown by the dry bulb thermometer and from the temperature difference between the dry and wet bulb bulbs.

However, even without such a table at hand, you can approximately determine the amount of humidity using the following principle. If the readings of both thermometers are close to each other, then the evaporation of water from the humid one is almost completely compensated by condensation, i.e., the air humidity is high. If, on the contrary, the difference in thermometer readings is large, then evaporation from the wet fabric prevails over condensation and the air is dry and humidity is low.

Let us turn to the tables that allow us to determine the characteristics of air humidity.

Temperature,	Pressure, mm. rt. Art.	Vapor density

Table 1. Density and pressure of saturated water vapor

Let us note once again that, as stated earlier, the value of the density of saturated steam increases with its temperature, the same applies to the pressure of saturated steam.

Table 2. Psychometric table

Let us recall that relative humidity is determined by the value of the dry bulb readings (first column) and the difference between the dry and wet readings (first row).

In today's lesson we learned about an important characteristic of air - its humidity. As we have already said, humidity decreases in the cold season (winter) and increases in the warm season (summer). It is important to be able to regulate these phenomena, for example, if it is necessary to increase humidity, place the room in winter time several reservoirs of water to enhance evaporation processes, however, this method will only be effective at the appropriate temperature, which is higher than outside.

In the next lesson we will look at what gas work is and the principle of operation of an internal combustion engine.

References

Gendenshtein L.E., Kaidalov A.B., Kozhevnikov V.B. / Ed. Orlova V.A., Roizena I.I. Physics 8. - M.: Mnemosyne.
Peryshkin A.V. Physics 8. - M.: Bustard, 2010.
Fadeeva A.A., Zasov A.V., Kiselev D.F. Physics 8. - M.: Enlightenment.

Internet portal “dic.academic.ru” ()
Internet portal “baroma.ru” ()
Internet portal “femto.com.ua” ()
Internet portal “youtube.com” ()

Homework

A little water was poured into a glass flask and closed with a stopper. The water gradually evaporated. At the end of the process, only a few drops of water remained on the walls of the flask. The figure shows a graph of concentration versus time n molecules of water vapor inside the flask. Which statement can be considered correct?

o 1) in section 1 the steam is saturated, and in section 2 it is unsaturated

o 2) in section 1 the steam is unsaturated, and in section 2 it is saturated

o 3) in both areas the steam is saturated

2. Task No. D3360E

Relative humidity in a closed vessel is 60%. What will the relative humidity be if the volume of the vessel at a constant temperature is reduced by 1.5 times?

5. Task No. 4aa3e9

Relative humidity in the room at a temperature of 20 ° C
equal to 70%. Using the pressure table saturated vapors water, determine the water vapor pressure in the room.

o 1)21.1 mm Hg. Art.

o 2)25 mm Hg. Art.

o 3)17.5 mmHg. Art.

o 4)12.25 mm Hg. Art.

32. Task No. e430b9

The relative humidity in the room at a temperature of 20°C is 70%. Using the table of density of saturated water vapor, determine the mass of water in a cubic meter of room.

o 3)1.73⋅10 -2 kg

o 4)1.21⋅10 -2 kg

33. Task No. DFF058

In the figure there are pictures: dotted line - graph of saturated vapor pressure water from the temperature, and a continuous line - process 1-2 due to the change in steam pressure water.

As the water vapor pressure changes, the absolute humidity of the air

1) increase

2) decreases

3) not from me

4) can either increase or decrease

34. Task No. e430b9

To determine the humidity of the air, they use the difference between the dryness and moist thermometer (see ri-su-nok). Using the given ri-sun-ka and the psi-chro-met-ri-che-table, determine what temperature ( in cities Celsius) is called a dry thermometer if the relative humidity of the air in the room -NII 60%.

35. Task No. DFF034

In the co-su-de, under the piston, there is unsaturated steam. It can be re-vested into a full-fledged one,

1) iso-bar-but-high-temp-pe-ra-tu-ru

2) adding another gas to the vessel

3) increase the volume of steam

4) reducing the volume of steam

36. Task No. 9C5165

The relative humidity in the room is 40%. How-to-work-out-of-concentration n mo-le-kul of water in the air of the room and the concentration of mo-le-kul of water in saturated water vapor at the same temperature per-ra-tu-re?

1) n is 2.5 times less

2) n is 2.5 times larger

3) n is 40% less

4) n 40% more

37. Task No. DFF058

The relative humidity of the air in the cylinder under the piston is 60%. The air iso-ter-mi-che-ski was compressed, reducing its volume by half. The high humidity of the air has become

38. Task No. 1BE1AA

In a closed qi-lin-dri-che-sky so-su-de, there is moist air at a temperature of 100 °C. In order for you to have dew on the walls of this co-su-da, the volume of co-su-da is 25 once. What is the approximation of the initial absolute humidity of the air in the co-su-de? The answer is given in g/m 3, rounded to whole numbers.

39. Task No. 0B1D50

In a cylindrical vessel under the piston long time there are water and its steam. The piston begins to move out of the vessel. At the same time, the temperature of water and steam remains unchanged. How will the mass of liquid in the vessel change? Explain your answer by indicating what physical laws you used to explain

40. Task No. C32A09

Water and its steam are kept in a cylindrical vessel under the piston for a long time. The piston begins to be pushed into the vessel. At the same time, the temperature of water and steam remains unchanged. How will the mass of liquid in the vessel change? Explain your answer by indicating what physical laws you used to explain.

41. Task No. AB4432

In an experiment illustrating the dependence of boiling point on air pressure (Fig. A ), boiling water under the bell air pump occurs already at room temperature, if the pressure is low enough.

Using a pressure plot saturated steam on temperature (Fig. b ), indicate what air pressure needs to be created under the pump bell so that water boils at 40 °C. Explain your answer by indicating what phenomena and patterns you used to explain.


(A)	(b)

42. Task No. E6295D

Relative air humidity at t= 36 o C is 80%. Saturated vapor pressure at this temperature p n = 5945 Pa. What mass of steam is contained in 1 m 3 of this air?

43. Task No. 9C5165

A man with glasses walked into a warm room from the street and discovered that his glasses had fogged up. What must be the outside temperature for this phenomenon to occur? The room temperature is 22°C and the relative humidity is 50%. Explain how you got the answer. (Refer to the table for the vapor pressure of water to answer this question.)

44. Task No. E6295D

In a closed room there is steam and a certain amount of water. How do the following three quantities change with an iso-thermal decrease in volume: giving -le-nie in co-su-de, mass of water, mass of steam? For each ve-li-chi-ny, the definition of the co-responsible character is determined:

1) will increase;

2) decrease;

3) not from me.

Write down the selected numbers for each physical size in the table. The numbers in the text may be repeated.

45. Task No. 8BE996

The absolute humidity of the air in the qi-lin-dri-che-su-de-su-de under the piston is equal to . The temperature of the gas in the co-su-de is 100 °C. How and how many times is the iso-ter-mi-che-ski required to change the volume of co-su-da in order for it to form on its walls Was there dew?

1) reduce the sewing by 2 times 2) increase the sewing by 20 times
3) reduce the sewing by 20 times 4) increase the sewing by 2 times

46. Task No. 8BE999

In the ex-pe-ri-men it is established that at the same time the air is in the room on the wall of the st-ka-na with With cold water there is a condensation of water vapor from the air, if you reduce the temperature to . Based on the results of these ex-peri-men, the air humidity is determined. To decide, use the table. Does the relative humidity change when the air temperature in the room increases, if the condensation of water vapor from the air will be at the same temperature? Pressure and density of saturated water steam at different temperatures in the table -face:



7,7	8,8	10,0	10,7	11,4	12,11	12,8	13,6	16,3	18,4	20,6	23,0	25,8	28,7	51,2	130,5

Humidity is a measure of the amount of water vapor in the air. Relative humidity is the amount of water contained in the air at a given temperature compared to maximum number water, which can be contained in the air at the same temperature in the form of steam.

In other words, relative humidity shows how much moisture is still needed for condensation to occur under given environmental conditions. This value characterizes the degree of saturation of air with water vapor. When calculating the optimal air humidity in a room, we talk specifically about relative humidity.

For example, at a temperature of 21°C, one kilogram of dry air can contain up to 15.8 g of moisture. If 1 kg of dry air contains 15.8 g of water, then the relative humidity is said to be 100%. If the same amount of air contains 7.9 g of water at the same temperature, then, compared to the maximum possible amount of moisture, the ratio will be: 7.9/15.8 = 0.50 (50%). Therefore, the relative humidity of such air will be 50%.

What humidity is optimal?

The ideal humidity in a living space is 40-60%. IN summer months the air is sufficiently humidified (especially rainy weather relative humidity can reach 80-90%), so there is no need for additional ways hydration.

However, in winter, central heating systems and other heating devices lead to dry air. This is because intense heating increases the temperature but does not increase the amount of water vapor. This causes increased evaporation of moisture from everywhere: from your skin and from your body, indoor plants and even furniture. Relative humidity in apartments in winter is usually no more than 15%. This is even less than in the Sahara Desert! There the relative humidity is 25%.

Table optimal humidity demonstrates how insufficient the 15% level is:

Human 45-65%Computer equipment and household appliances 45-65%Furniture and musical instruments 40-60%Libraries, exhibits of art galleries and museums 40-60%

How to achieve optimal humidity?

The only advice is to humidify the room.

There are many “folk” methods of moisturizing. You can, for example, hang wet towels and rags in the room. Place a water tank on the heater. The evaporation of water will sooner or later lead to an increase in air humidity. To protect the piano from drying out, it was previously recommended to place a jar of water inside. An option for those who spare no expense is a decorative fountain in the room.

However, these methods are inconvenient and ineffective. It is not possible to significantly increase the air humidity in a room using a jar of water. In addition, a can on a radiator and towels on ropes do not look very aesthetically pleasing.

The most effective and practical way to increase indoor humidity is to install humidifier. This climate control device is capable of maintaining a precisely specified level of humidification; moreover, it is inexpensive and easy to use. And the new generation of humidifiers themselves control the optimal humidity.

The air is to some extent filled with water vapor. Its quantity is characterized by such an indicator as humidity. It can be absolute and relative. The first indicator indicates the volume of water contained in one cubic meter of air. The second term is used to determine the ratio between the maximum possible amount of steam to the actual amount. If indoor air humidity is determined, this is a relative indicator.

Why measure and control indoor humidity?

Humidity in the house directly affects the health and well-being of all its inhabitants. If the indicators do not correspond to the norm, not only people suffer, but also indoor plants, furniture and other things. The amount of water vapor in the environment is not stable and changes all the time depending on the time of year.

Why is dry air dangerous?

Low indoor humidity is very often observed during the heating season. This leads to the fact that a person quickly loses water through the skin and respiratory tract. As a result of such negative phenomena, the following effects are observed:

decreased elasticity and dryness skin, which is accompanied by the appearance of microcracks, leads to the development of dermatitis;
drying of the mucous membrane of the eyes leads to redness, burning, and watery eyes;
the blood loses part of its liquid component, which reduces the speed of its movement, creating additional stress on the heart;
the person suffers from headaches, feels tired and loses normal performance;
the viscosity of gastric juice increases, which impairs digestion;
drying out of the mucous membranes of the respiratory tract occurs, which weakens local immunity;
an increase in the concentration of pathogenic microorganisms in the air, which are usually neutralized by air droplets.

To measure the air in an apartment, it is enough to buy the simplest device, which is usually combined with a thermometer or a clock. It has a small error of 3-5%, which is not critical.

Using a glass of water

To determine air humidity, you need to fill a regular glass with water and place it in the refrigerator for 3 hours so that the liquid cools to 3-5°C. The vessel is removed and placed on the table away from heating devices. For several minutes, observe the walls of the glass, where they detect the appearance of condensation in the form of water droplets. The results of the experiment are expressed as follows:

the glass has dried quickly - the humidity is reduced;
the walls remained fogged - the humidity standards in the room were met;
Water began to flow down the glass - the humidity was increased.

Assmann table

The Assmann table is designed to determine humidity using a psychrometer. It consists of two thermometers - a regular one and one with a humidification function. The indicators measured by the second device will be slightly lower. Air humidity is determined using a special table using the obtained values.

Using a fir cone

Take an ordinary fir cone and place it away from heating appliances. In dry air, its scales will open, and in humid air, they will shrink tightly.

Generally accepted standards

Indoor humidity standards depend on its purpose and time of year. Compliance with the recommended parameters will ensure good health and will not negatively affect human immunity.

Standards for an apartment

For an apartment, all standards regarding climatic parameters are specified in GOST 30494-96. According to this document air humidity in the cold season should fluctuate between 30-45%, and in the warm season - 30-60%. Despite the indicated values, the 30% indicator may be poorly perceived by the human body. Therefore, doctors recommend maintaining parameters of 40-60%, which are considered optimal at any time of the year.

Standards for a children's room

The child's body is unable to function properly in low air humidity. This leads to rapid drying of the mucous membranes, which can lead to a decrease in local immunity.

Workplace

The level of humidity in the workplace depends on the specifics of work. For example, for office workers it is 40-60%.

How to normalize the indoor microclimate?

To make the indoor microclimate comfortable for living, you need to use the following tips:

use of air humidifiers. Indispensable during the heating season in any room;
regular ventilation;
increasing the number of indoor plants;
presence of exhaust ventilation. The supply hood will supply the room fresh air and normalizes the amount of water vapor;
in some cases it is recommended to use special dehumidifiers equipped with absorbent substances;
It is prohibited to dry laundry in residential premises, which negatively affects their microclimate.

Video: How to measure air humidity

Home
Air conditioners

This video tutorial is available by subscription

Already have a subscription? Login

I-17="">Saturated steam, air humidity

We will devote today's lesson to discussing the concept of air humidity and methods for measuring it. The main phenomenon affecting air humidity will be the process of water evaporation, which we already talked about earlier, and the most important concept that we will use will be saturated and unsaturated steam.

If we distinguish different states of steam, they will be determined by the interaction in which the steam is with its liquid. If we imagine that some liquid is in a closed vessel and the process of evaporation occurs, then sooner or later this process will come to a state where evaporation at equal intervals of time will be compensated by condensation and the so-called dynamic equilibrium of the liquid with its vapor will occur (Fig. 1) .

Rice. 1. Saturated steam

Definition.Saturated steam is steam that is in thermodynamic equilibrium with its liquid. If the steam is not saturated, then there is no such thermodynamic equilibrium (Fig. 2).

Rice. 2. Unsaturated steam

With the help of these two concepts we will describe such important characteristic air like humidity.

Definition.Humidity– a value indicating the content of water vapor in the air.

The question arises: why is the concept of humidity important to consider and how does water vapor get into the air? 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 (Fig. 3). Of course, in various climatic zones the intensity of this process varies, which depends on the average daily temperature, the presence of winds, etc. These factors determine the fact that in certain places the process of water vaporization is more intense than its condensation, and in some cases it is the other way around. On average, it can be argued that the vapor that forms in the air is not saturated, and its properties must be described.

Rice. 3. Evaporation of liquid (Source)

For humans, the humidity level is a very important environmental parameter, since our body reacts very actively to its changes. For example, a mechanism for regulating the functioning of the body, such as sweating, is directly 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 disrupted, which leads to disturbances in thermoregulation. At low humidity, moisture evaporation processes prevail over condensation processes and the body loses too much fluid, which can lead to dehydration.

The amount of humidity is important not only for humans and other living organisms, but also for the flow of technological processes. For example, due to the known property of water to conduct electric current, its content in the air can seriously affect the correct operation of most electrical appliances.

In addition, the concept of humidity is the most important criterion for assessing weather conditions, which everyone knows from weather forecasts. It is worth noting that if we compare humidity at different times of the year in our usual climatic conditions, it is higher in summer and lower in winter, which is associated, in particular, with the intensity of evaporation processes at different temperatures.

Absolute air humidity

The main characteristics of humid air are:

density of water vapor in the air;
relative air humidity.

Definition.Absolute air humidity- the amount of moisture contained in one cubic meter of air.

Designationabsolute humidity: (as is the usual designation for density).

Units of measurementabsolute humidity: img="">

mass of steam (water) in air, kg (in SI) or g;

I-19="">Relative humidity

To describe such perception, the following quantity was introduced: relative humidity.

Definition.Relative humidity– a value indicating how far the steam is from saturation.

That is, the value of relative humidity, in simple words, shows the following: if the steam is far from saturation, then the humidity is low, if it is close, it is high.

Designationrelative humidity: .

Units of measurementrelative humidity: %.

Formula calculations relative humidity:

Img="" i-20="">Condensation hygrometer

As can be seen from the formula, it includes absolute humidity, with which we are already familiar, and saturated vapor density at the same temperature. The question arises: how to determine the latter value? There are special devices for this. We will consider condensinghygrometer(Fig. 4) is a device that is used to determine the dew point.

Definition.Dew point– the temperature at which steam becomes saturated.

Rice. 4. Condensation hygrometer (Source)

What to do with the obtained temperature value (dew point)? There is a special table in which data is entered - what density of saturated water vapor corresponds to each specific dew point. It is worth noting a useful fact that as the dew point increases, the value of the corresponding saturated vapor density also increases. In other words, the warmer the air, the greater the amount of moisture it can contain, and vice versa, the colder the air, the lower the maximum vapor content in it.

Hair hygrometer

Let us now consider the principle of operation of other types of hygrometers, devices for measuring humidity characteristics (from the Greek hygros - “wet” and metreo - “I measure”).

Hair hygrometer(Fig. 5) is a device for measuring relative humidity, in which hair, for example human hair, acts as an active element.

Rice. 5. Hair hygrometer (Source)

The action of a hair hygrometer is based on the property of defatted hair to change its length when air humidity changes (with increasing humidity, the length of the hair increases, with decreasing it decreases), which makes it possible to measure relative humidity. The hair is stretched over a metal frame. The change in hair length is transmitted to the arrow moving along the scale. It should be remembered that a hair hygrometer does not give accurate relative humidity values, and is used mainly for domestic purposes.

Psychrometer

A more convenient and accurate device for measuring relative humidity is a psychrometer (from the ancient Greek ψυχρός - “cold”) (Fig. 6).

Humidity Characteristics Tables

Let us turn to the tables that allow us to determine the characteristics of air humidity.

Temperature,

Pressure, mm. rt. Art.

Vapor density

« Physics - 10th grade"

When solving problems, one must keep in mind that the pressure and density of saturated steam do not depend on its volume, but depend only on temperature. Equation of state ideal gas approximately applicable to describe saturated steam. But when saturated steam is compressed or heated, its mass does not remain constant.

When solving some problems, you may need values of saturated vapor pressure at certain temperatures. This data must be taken from the table.

Task 1.

A closed vessel with a volume V 1 = 0.5 m 3 contains water with a mass m = 0.5 kg. The vessel was heated to a temperature of t = 147 °C. How much should the volume of the vessel be changed so that it contains only saturated steam? Saturated vapor pressure pH. n at temperature t = 147 °C is equal to 4.7 10 5 Pa.

Solution.

Saturated steam at pH pressure. n occupies a volume equal to where M = 0.018 kg/mol - molar mass water. The volume of the vessel is V 1 > V, which means that the steam is not saturated. In order for the steam to become saturated, the volume of the vessel should be reduced by

Task 2.

The relative humidity of the air in a closed vessel at a temperature t 1 = 5 °C is equal to φ 1 = 84%, and at a temperature t 2 = 22 °C it is equal to φ 2 = 30%. How many times is the saturated vapor pressure of water at temperature t 2 greater than at temperature t 1?

Solution.

The pressure of water vapor in the vessel at T 1 = 278 K is where p n. n1 - saturated vapor pressure at temperature T1. At temperature T 2 = 295 K pressure

Since the volume is constant, then according to Charles’s law

From here

Task 3.

In a room with a volume of 40 m 3 the air temperature is 20 ° C, its relative humidity φ 1 = 20%. How much water must be evaporated so that the relative humidity φ 2 reaches 50%? It is known that at 20 °C the saturation vapor pressure рнп = 2330 Pa.

Solution.

Relative humidity from here

Vapor pressure at relative humidity φ 1 and φ 2

Density is related to pressure by the equality ρ = Mp/RT, whence

Masses of water in a room at humidity φ 1 and φ 2

Mass of water to evaporate:

Task 4.

In a room with closed windows at a temperature of 15 °C, relative humidity φ = 10%. What will the relative humidity be if the temperature in the room increases by 10 °C? Saturated vapor pressure at 15 °C pH. p1 = 12.8 mm Hg. Art., and at 25 °C pH p2 = 23.8 mm Hg. Art.

Since the steam is unsaturated, the partial pressure of the steam changes according to Charles’s law p 1 /T 1 = p 2 /T 2. From this equation you can determine the pressure of unsaturated steam p 2 at T 2: p 2 = p 1 T 2 / T 1. Relative humidity at T 1 is equal.