What is Evaporation?
There are some very active molecules in liquids flying out of the liquid surface and becomes vapor molecules when the air is unsaturated, this is evaporation.
The molecules must have heat taken while flying out of the liquid into vapor. This heat is taken from the water that remains in the liquid state when evaporation occurs. It results in cooler liquid water. Evaporative cooling is a universal natural phenomenon. For example, in summer, we would feel cool when the wet arm exposes to the air. It is because of the evaporation of water, which absorbs heat to cool our body, but not temperature shift. We feel cool if we sweat or sponge the body with alcohol. It is also because of evaporative cooling. In fact, evaporative cooling is a powerful and economical cooling technology.
There are four main factors affecting evaporation:
- Firstly, the relative humidity. There are always some molecules that fly out of the water into vapor molecules as long as the relative humidity of air is lower than 100% saturation. The lower the relative humidity, the faster the evaporation.
- Secondly, the temperature of the water, The higher the temperature of the water, the faster the water will be, the more easily it will be evaporated into the air.
- Thirdly, the air velocity. The vapor molecules may return liquid water because of the collision with other vapor molecules. If the air flows fast, the vapor molecules have less chance to return, resulting in more evaporation
- Fourthly, the surface area. The molecular number near to air increases when the liquid surface area enlarges, more molecules may fly out of the liquid. Consequently, liquid surface area increases, evaporating faster.