Scale Control in Cooling Water Systems
By William F. Harfst
Scale deposition is a fundamental problem in cooling water systems. Scale interferes with heat transfer by forming an insulating barrier on heat transfer surfaces. Scale also promotes corrosion, restricts water flow, and provides a habitat for microbiological growths. Scale deposits form when the solubility of dissolved minerals in the cooling water is exceeded. Cooling towers function by evaporating a percentage of the recirculating water into the atmosphere. This water is ﾓpureﾔ in that it does not contain any of the dissolved minerals found in the makeup water. As the evaporation process continues, the scale-forming minerals concentrate in the recirculated cooling water. If left unchecked, this process continues until the solubility of the dissolved minerals is exceeded. At this point, precipitation of the mineral salt occurs, resulting in the formation of an adherent scale deposit. Alternatively, mineral impurities may produce a loose, fouling sludge in the tower fill, basin or distribution piping.
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