Most cooling towers and evaporative condensers normally evaporate 1.8 gallons of water per hour per ton of capacity. This evaporation gets rid of the heat from the system. But only pure water evaporates, the minerals are left behind. Fresh water replaces the evaporated water, bringing in more minerals. This adds more solids to the same volume of water, which will only hold a certain amount of minerals in solution. When this limit is exceeded, the solids come out of solution and deposit, as scale, on the equipment, usually in the condenser first.
A water bleed or blowdown will limit the concentration of minerals in the system’s water. Every gallon of water bled from the system removes a greater amount of minerals than is brought in by a gallon of makeup water.
Nature of Scale
Scale is primarily made up of salts, more specifically of the carbonates of calcium and magnesium. Usually salts in water are expressed as grain of hardness or TDS (Total Dissolved Solids) of calcium carbonate. The normal factor for converting grains of hardness to TDS is 14. Water with 10 grains of hardness will be about 140 ppm (parts per million) TDS.
Formation of Scale
Calcium carbonate (CaCO3) is a positive ion having a dendritic or tree like structure. Heat exchangers, boilers, pipes and other water side surfaces are grounded and have a negative charge. Thus there is a natural affinity for the salt ions to attach themselves to these negative surfaces. Over time, the scale formed by this phenomena grows in thickness and hardness, becoming very difficult and costly to remove by either physical or chemical means. The inside diameters of pipes can be reduced from two inches to 1/4: or less due to scale formation. Energy costs rise and systems efficiency suffers due to restricted flows and the insulating effect of scale which reduces heat transfer capabilities.
Altering the Nature of Salts
It has long been known that a magnetic field will change the nature of salt molecules. Electron microscopes allow scientists to observe this molecular change. Water flowing through specially designed magnetic molecules changing them from positive ions to bipolar crystalline structures having North and South poles. This causes the molecules to be attracted to each other rather than to the water side surfaces. The bipolar particles grow in size as more and more molecules are attracted or agglomerated. The larger particles become of sufficient size to be caught in filter media and removed by back washing.
Scale Removal
The change in molecular structure allows some electrons to be released from original molecules. These “free electrons” carry a negative charge and are attracted to the positive molecular scale formations clinging to waterside surfaces. The salt molecules are thereby converted into bipolar particles that release from the scale surface. It has been observed that descaling often takes place in layers or strata with periods of reduced or minimal activity interspersed with period of rapid scale removal as various strata levels are converted.
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