Although we are not able to distinguish it with the naked eye, the evaporation of water plays a very important role, both in the ecosystems in which we live and in the industrial environment or even in our own homes.
Keep reading Green Ecologist to know what is water evaporation and some examples, as well as its difference with the boiling of water and the condensation of water.
What is water evaporation
The evaporation of water is a physical process by which the water passes from being in liquid state to be in gaseous state. For this, it must have accumulated enough energy in the form of heat to overcome its surface tension. It is not necessary that the entire body of water has passed the boiling point (read on to understand the latter concept). Different factors influence this process:
- Steam saturation: the difference in vapor pressure between liquid water and the environment contributes to the evaporation of the water. Basically, the water tends to be distributed evenly, moving from where there is greater saturation to where there is less saturation. As a simple rule of thumb, the drier the environment (or in other words, the lower the vapor saturation), the more evaporation will occur.
- Atmospheric pressure: the lower the atmospheric pressure, the easier evaporation will take place. In nature we do not care so much, since in the mountains, where the pressure drops, the temperature also drops, so it does not become a significant phenomenon.
- Temperature: molecules need to have a kinetic energy such that it is capable of breaking the surface tension barrier. The higher the temperature, the greater the evaporation.
Examples of evaporation
Some of the most important examples of water evaporation are as follows:
Surface water evaporation
The evaporation of the water that passes by the terrestrial surface is one of the sources of water to the atmosphere. It occurs especially in hot and dry environments and in large areas of water, such as lakes or reservoirs. It can also occur in different soil horizons, being much more prominent in the surface ones. In this case, the surface tension of the water is not exceeded, but the adhesion of the water molecules to the soil.
Plant transpiration
Plants need to open small pores called stomata, which are usually located on the underside of the leaf, and which allow them to carry out gas exchange. This exchange includes the release of water and its release into the atmosphere. For the plant, this process is essential: it is the one that contributes most to the plant being able to continue taking water from the soil. As for the environment, plants have a direct action in the water cycle; its action can be summarized in taking water from the ground to release it into the atmosphere in the form of vapor.
Evapotranspiration
This concept includes both the evaporation of surface waters and the transpiration of plants, giving rise to the formation of clouds and contributing to the water saturation of each ecosystem. This combination of phenomena makes the so-called "water cycle" possible.
Learn more about What is the water cycle with this other Green Ecologist article.
Refrigeration in animals
Many animals, especially mammals, use the evaporation of water as a means of cooling. For example, humans sweat, which allows the heat that is in our skin to "store" in the water molecules of our sweat, which disappears with evaporation. Other animals (a very close example are dogs), open their mouths when they breathe, allowing a higher rate of evaporation of the water.
Evaporation in industrial processes
Some industrial processes also release a considerable amount of water into the atmosphere. For example, nuclear power plants and thermal power plants have cooling circuits based on the "storage" of excess heat in the form of water vapor, which is subsequently released. On the other hand, these plants also use water vapor (in a closed circuit) to move the turbines that will eventually generate electrical energy.
Difference between evaporation and boiling
The evaporation of water can occur from 32ºC. However, for it to boil it needs to reach 100ºC, at which point the pressure of the water and that of the air equalize.
What is boiling water
Boiling is a phenomenon in which water evaporates, which occurs when its boiling point is reached, that is, when the pressures of the water and the atmosphere equalize. Normally, it is given to 100ºC, under conditions of a pressure atmosphere.
However, when the pressure drops, the boiling point also drops. For example, the boiling point can occur below 100ºC in the mountains, as the atmospheric pressure drops. Once the boiling point is reached, the temperature remains constant until the process ends.
Difference between evaporation and condensation
Evaporation and condensation are basically opposite processes. While evaporation consists of the transformation of water in a liquid state to water in a gaseous state, in the condensation in water it goes from a gas state to a liquid state.
What is condensation
In order to change from a gaseous state to a liquid state, water molecules must lose kinetic energy, usually in the form of heat. This energy is lost, the molecules adopt less mobility and end up joining each other.
Learn more about What is water condensation and examples with this other post from Green Ecologist.
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