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Evaporation and condensation

In this article we will reveal the meaning of such concepts as "evaporation" and "condensation".

Steam formation is characterized by the transition of matter from liquid to gaseous state. This can be done in two ways: by boiling, or by evaporation.

Evaporation is the process of evaporation that occurs from the surface of a liquid substance. Next, let us explain in more detail how evaporation and condensation occurs, that is, the reverse process - the return of molecules to the liquid. The process of evaporation is carried out this way: in view of the fact that the molecules of any substance in the liquid state randomly move continuously, and at different rates. There is a mutual attraction between them, thanks to which they can not fly out, but if a molecule with a high kinetic energy index appears on the surface of the substance, it will overcome the forces of attraction between the molecules and fly out of the substance. The same process will be repeated with other molecules. Departing outward, the molecules form vapor above the liquid. This is evaporation.

In view of the fact that molecules that have the highest velocity emerge from the liquid during evaporation , the average kinetic energy index of the molecules that remain in the substance goes down. As a result, the temperature of the evaporating liquid is lowered and it cools. At the same time, it is known that water in the glass for a long time also evaporates, but it does not cool continuously until it freezes. Why? It's all about the heat exchange of water with the warm air that surrounds the glass.

The rate of evaporation depends on the type of liquid, its temperature, the surface area of the liquid substance, and the presence of wind over the surface of the liquid substance.

Cooling of the substance in the liquid state during evaporation is more important when the evaporation process is rapid. Substances that evaporate rapidly are used in engineering. Cooling of the liquid during evaporation is also used in devices that measure the humidity of the air.

With the help of simple experiments it can be determined that the rate of evaporation will grow together with the increase in the temperature of the liquid substance, and also in proportion to the increase in the area of the free surface.

Evaporation and condensation are opposite processes. Above we learned what evaporation is, and now consider how condensation takes place. The liquid evaporates faster in the presence of wind, but why? This is due to the fact that during the evaporation, the reverse process is also carried out, which is called "condensation". It arises because some of the molecules of the vapor, moving over the liquid substance, return to it back. And the wind takes the molecules out of the distance, not allowing them to return back.

Condensation of water vapor occurs when it does not come into contact with the liquid substance. The formation of clouds is a process of condensation, in which the molecules of vapor rising above the earth are grouped into small water drops in cold atmospheric layers. Rain and dew are also consequences of the condensation of water vapor in the natural environment.

The liquid, cooled during evaporation, becoming colder than the surrounding environment, begins to absorb its energy. The amount of energy absorbed is called the "latent heat of evaporation."

And with condensation, the opposite happens: energy is released into the environment, thereby increasing its temperature index. There are two types of condensation: film and droplet. Film forms on the wettable surface and is accompanied by the appearance of a film. On a surface that is not wetted, a droplet condensate forms.

Evaporation and condensation in practice are used during the operation of refrigeration equipment.

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