The cooling systems use the air to reduce the cooling water temperature. The air against the water flow "steals" the heat and gets rid of the solid particles, oily residues and bacteria. The particles retained by the droplets add to the contaminating elements in water, and the more serious are due to: deposits, scale and corrosion.

DEPOSITS:
Originated from the suspension solids, from the system corrosion products, or a result of live organism metabolism. Many times, the corrosion products are joined to particles originated in the air to form bulky deposits which reduce the water flow. The deposits of microbial origin grows quickly, distinguished by bulky volumes and low density. Those are very dangerous as being "habitat" to bacteria colonies development. After a certain thickness, and depending on the "Dead Zones" of the tower, they become inaccessible to the biocides, arising conditions to create resistance in the new bacteria generations.

SCALE:
Originated within the deposits that lose water of hydration. The most common are of calcium carbonate and emerge mixed to the products of corrosion, particularly with iron oxide. When the scale shelter microbiological colonies, they present typical formations known as tubercles or alveolus. Under these develops corrosion due to acids of the bacterial metabolism. Scaling not only reduces heat transfer as well as is responsible for generalized corrosion or for "pitting".

CORROSION:
In synthesis, corresponds to the passage of iron to the stage of superior oxidation and, therefore, its withdrawal from the carbon-alloy. This process not only reduces the line thickness as well as the wall resistance. The destruction of the line is spontaneously processed within the alkaline and neutral media forming ferrous hydroxide, ferric hydroxide and magnetite. The ferrous hydroxide, Fe (OH)₂, is greenish-black and occurs within alkaline media and aired waters. The ferric hydroxide, Fe (OH)₃, is reddish-orange and is formed in neutral media. The Magnetite, Fe₃ O₄, is a black and magnetic compound, formed in the absence of air. The ferrous hydroxide and the ferric hydroxide are bulky and mixed to residues of biological metabolism and solid particles which agglutinate forming adherent mud. Therefore the water and contaminants should be strictly controlled in order to prevent the systems destruction.

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