The make-up water source is used to replenish water lost to evaporation. Hot water from heat exchangers is sent to the cooling tower. The water exits the cooling tower and is sent back to the exchangers or to other units for further cooling. Natural draft designs use very large concrete chimneys to introduce air through the media. Usually these types of towers are only used by utility power stations in the United States.
Mechanical draft cooling towers are much more widely used.
These towers utilize large fans to force air through circulated water. The water falls downward over fill surfaces which help increase the contact time between the water and the air. This helps maximize heat transfer between the two. Mechanical Draft Crossflow Tower Mechanical draft towers offer control of cooling rates in their fan diameter and speed of operation. Cooling Tower Theory Heat is transferred from water drops to the surrounding air by the transfer of sensible and latent heat.