Scaling and Fouling
also known as heat exchanger fouling · crusting
Scaling is the crystallization or precipitation of sparingly soluble salts such as calcium sulfate or magnesium hydroxide directly on heat transfer surfaces; fouling is the broader term for any deposit, including suspended solids and organic films. Either adds a thermal resistance in series with the metal wall and reduces the achievable heat flux.
Why it matters in practice
Scaling is the most common reason an evaporator loses capacity over a campaign, and the lost capacity is often misread as a feed chemistry change. Because the deposit also reduces flow area, cleaning intervals — not design heat flux — frequently set the practical availability of the unit.
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Reference entry GL-SCALING-FOULING. Definitions on this page describe engineering practice in hydrometallurgical process design; they are not a substitute for test work on your own material.