Fouling and biological growth

The situation is often compounded by interaction among the three. They have a direct impact on heat exchange efficiency, on the operation of the apparatus requiring cooling and on the lifetime of die system. 

What is involved here are compounds that may readily form deposits in cooling systems, excluding scale as such, and corrosion products. The following can be mentioned  

can form deposits in zones where the flow slows down or where the cross-sectional area is small. 

Colloids coagulate as the temperature rises. As a result, they tend to form a layer on heat exchanger surfaces and hinder proper heat transfer. 

They are often the main cause of system fouling, whether they come from the make up water or from the air in the cooling tower. 

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Airside fouling is negligible when compared to the water-cooling problems of scale, corrosion and biological growths. 

Fig. 23. Visualization of membrane fouling by scanning electron microscopy (A) inorganic fouling dne to calcinm carbonate, calcium sulfate, silica, iron, barium and strontium sulfate (35,000x) (B) organic fonling dne to humic acid (35,000x) (C) flow channels in membrane fouled with biological growth.

Chemicals are added to the circulation system to prevent fouling. Dispersants are added to prevent deposit of solids, corrosion inhibitors to prevent corrosion and biocides to inhibit biological growth. 

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