Heat Transfer in Cooling Tower

Two kind of heat transfer occur within the tower between warm water and air.

Latent heat of vaporization: Some of the liquid changes to vapor with the absorption of heat. This energy, called the latent heat of vaporization, is that necessary to overcome the attractive forces between molecules in the liquid state. Absorption of latent heat accounts for 75-80 percent of the heat transferred in cooling towers.

As long as the wet-bulb temperature, which is a measure of the heat content of the atmospheric air, is lower than the water temperature heat is transferred from the water to the air, raising its temperature and lowering that of the water. This is called sensible heat; it accounts for the remaining 20-25 percent of heat transferred.