What is the dew point? Calculation of dewpoint temperature

Those who have lived in villages for a long time know that even on a summer morning the grass is almost always wet with dew. But probably few people thought, why this happens. Where does this water come from, and what is the nature of this phenomenon in general?

What is the dew point?

In weather forecasts, we usually only talk about air temperature, precipitation, wind and atmospheric pressure. Meanwhile, there are still many important characteristics that give an idea of the environmental conditions. Among them is the dew point of the air. This term is familiar to many people, but far from everyone knows what it is and what this indicator affects. So what is the dew point?

By this phrase is meant such an indicator of air temperature at which the limit of its saturation with moisture is reached, as a result of which water starts to condense either in the form of water drops on the surface or in the form of fog. Sometimes this does not really matter, and in some places this information must be taken into account.

Water vapor is always contained in the air to some extent. And the dew point is a combination of certain factors under which there is a transition from the gaseous aggregate state to the liquid state. In this case, the condensate is formed on objects with the lowest temperature, as well as on the lid of a pot of boiling water. Sometimes it causes problems, for example, tenants of poorly insulated houses or owners of improperly installed insulating glass can face constant dampness and fogging of glasses.

The mechanism of education

So, what happens when the air temperature falls at night or in the early morning? That is, what is the dew point in the opinion of physics, and what processes occur when it is achieved? Extremely interesting.

Near the surface of the coldest objects a thin layer of gas of the same temperature is formed. Its thickness can be scanty, but it is in it that condensate forms on the surface of the object. On the street, it can primarily be stones, metal structures, grass. This is the case if the air temperature is above the dew point. In winter everything happens a little differently. This phenomenon can be observed when breathing in the frost, when steam escapes from the mouth. Instantly cooling, the water in the gaseous state turns into the smallest droplets. Something similar happens and is high in the atmosphere when clouds are formed.

Factors of influence

But why does this happen? First of all, the formation of condensate is affected by the ambient temperature and objects. In addition, the relative and absolute humidity of the air is important. The higher these figures, the higher the dew point temperature. With 100% humidity, this indicator will coincide with actual weather conditions.

Also the pressure has a value, especially if it is necessary to calculate the dew-point temperature under compressed air conditions. Physicists continue to conduct experiments in a variety of conditions. And in this case, distinguish between varieties of the atmospheric indicator and it under pressure. Other things being equal, the second indicator will be much lower.

Calculating the value

So, now it became clear what the dew point is, and what affects it. But how to calculate, at what value of temperature and humidity of air water vapor will condense? There are special tables and formulas with which you can calculate this figure with a small error. The calculation of the dew point temperature by these methods takes into account only the relative humidity of the air and its temperature, so that for gases under pressure, none of these methods will work.

Of course, there are also special instruments that allow this indicator to be recorded - psychrometers. Their main purpose - to determine the humidity, but to determine the dew point they are also great.

Importance in construction

First of all, determining the temperature of the dew point is important in the design of buildings. Water has a harmful effect on metals, because of it, corrosion begins, so that the formation of excess moisture can cause premature wear of the structure. If the temperature is high enough, the process will proceed at a high speed.

It is also important for people for whom the problems of warming the dwelling in winter are extremely urgent. In winter, the outside of the building is much colder than the inside. Thus, the temperature difference is inevitable. And here it is important that the dew point in the wall is as far as possible from the inner surface. Otherwise, residents are at risk of encountering eternal humidity, dampness, mold and other consequences. So when building residential, both multi-family and private houses, this factor must be taken into account. The dew point in the wall will be reached in any case with a drop in air temperature, but the task of the builders is to make it as close as possible to the outer layer.

And all metal structures must be covered with special anti-corrosive compounds, and also to organize effective removal of excess moisture from them. In the walls of the houses, not only hygroscopic materials are used for this, but also special waterproofing materials. In the complex, this allows residents not to suffer because of eternally wet and cold corners or window sills.

Significance in Aviation

Aircraft fly high in the air, where the temperature is lower than that of the ground. And the formation of condensation can affect the aerodynamics. This is especially important for takeoff and landing, therefore, among other environmental indicators, aeronautical meteorologists necessarily expect a dew point. This helps to take into account the possible formation of clouds and fog, if the actual temperature is close to it. In winter, this information is also important, since in cold weather it is necessary to think about the possible icing of the aircraft and prevent it with the help of special reagents that are applied to the body of the aircraft.

Value in other areas and countermeasures

In addition, this indicator is also taken into account by manufacturers of varnishes, paints, protective compounds. Naturally, manufacturers and users of high-precision optics should also remember this factor so as not to damage the technology, especially if it is necessary to bring devices into a warm room from the street.

In order to avoid condensation inside buildings, it is necessary to ensure good ventilation and proper drainage. For example, some people who want to save can face the problem of constant fogging or leaking windows. Poor-quality or improperly installed double-glazed windows can become a source of constant problems. So it's better to entrust such work to good professionals.

Microclimate and comfort

And what is the dew point for people? How do they feel when condensate is formed? The relative humidity is of primary importance here. At a sufficiently high temperature and an indicator of the saturation of air with water vapor, it seems to people that it is stuffy in the street or in the room. Especially well it is felt by the inhabitants of the temperate climatic belt, coming in the summer to the tropics or subtropics. With almost 100% humidity, the dew point practically coincides with the actual air temperature, and people literally have nothing to breathe, especially if it's very hot. In such conditions, some may experience problems with the cardiovascular system, and you can get a heat stroke, so with a sharp deterioration in the state of health, you need to contact the doctors.