In this article, we will reveal the meaning of such concepts as “evaporation” and “condensation”.
Vaporization is characterized by the transition of a substance from a liquid to a gaseous state. This can be done in two ways: by boiling, or by evaporation.
Evaporation refers to the process of vaporization that occurs from the surface of a liquid substance. Next, we describe in more detail how evaporation and condensation occur, that is, the reverse process is the return of molecules to a liquid. The evaporation process is carried out as follows: due to the fact that the molecules of any substance in a liquid state randomly continuously move, and at different speeds. There is a mutual attraction between them, due to which they cannot fly out, but if a molecule with a high kinetic energy index appears on the surface of the substance, it will overcome the attractive forces between the molecules and fly out of the substance. The same process will be repeated with other molecules. Having flown out, the molecules form a vapor above the liquid. This is evaporation.
Due to the fact that the molecules with the highest speed fly out of the liquid during evaporation , the average kinetic energy of the molecules that remain in the substance decreases. As a result, the temperature of the evaporating liquid decreases and it cools. At the same time, it is known that water in a 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 warm air that surrounds the glass.
The evaporation rate depends on the type of liquid, its temperature, the surface area of the liquid substance, and the presence of wind above the surface of the liquid substance.
The cooling of a substance in a liquid state during evaporation is more significant with a rapid evaporation process. Substances that evaporate quickly are used in technology. Liquid cooling during evaporation is also used in apparatuses that measure air humidity.
With the help of simple experiments, it can be determined that the evaporation rate will increase along with an increase in the temperature of the liquid substance, as well as in proportion to an increase in the free surface area.
Evaporation and condensation are opposite processes. We learned above what evaporation is, and now we will consider how condensation occurs. Liquid evaporates faster when there is wind, but why? This is due to the fact that during the evaporation the reverse process, called “condensation”, is also carried out. It arises due to the fact that some molecules of the vapor, moving above the liquid substance, return to it back. And the wind carries the released molecules to a large distance, preventing them from returning back.
Water vapor condensation occurs when it does not come into contact with a liquid substance. Cloud formation is a condensation process in which vapor molecules rising above the earth are grouped into small water droplets in cold atmospheric layers. Rain and dew are also a consequence of condensation of water vapor in the natural environment.
The liquid cooled during evaporation, becoming colder than the environment, begins to absorb its energy. The amount of energy absorbed is called the "latent heat of evaporation."
But the opposite happens during condensation: energy is released into the environment, thereby increasing its temperature index. There are two types of condensation: film and drip. Film is formed on a wettable surface and is accompanied by the appearance of a film. On the surface, which is not wetted, droplet condensation forms.
Evaporation and condensation are used in practice during the operation of refrigeration equipment.