The tabulation provides typical fouling factors as fouling resistances. Fouling is also frequently specified as a fouling coefficient, which is the reciprocal value ( 1/x). Fouling factors are widely used to cater for the additional resistance that deposits which accumulate on the heat transfer surface cause. Most deposits have a thermal conductivity that is much lower than the tube wall and this will significantly reduce the total coefficient. To be able to meet the required duty at the end of the lifetime or between two maintenance / cleaning periods the surface needs to be oversized at the start.

Fouling can be caused by several mechanisms:

• Crystallization (Mg- and Ca- bicarbonates)
• Decomposition of organic products resulting in tar or cokes
• Polymerization and or oxidation
• settlement of sludge, rust or dust particles
• Biological deposits
• Corrosion layer

Some tips to prevent or slow down fouling:
It is advisable to certify during design that the fluid velocities are not too low. For cooling water below 0.8 m/s, preferably between 1.8 and 2 m/s. The effluent temperature of cooling water should not be higher than 40 ° C. The scaling that starts at 45 ° C has been well documented. Limiting the heat flux (W/m²) can also reduce the fouling tendecy.

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