A. Methods of classifying types of fouling

There is more than one way to classify the types of fouling which occur on heat transfer surfaces. One can classify, according to the type of heat transfer service, which is being provided, (e.g. change-of-phase (boiling, condensation) vs. sensible (heating, cooling) vs. chemical reaction (endothermic, exothermic) heat transfer); according to the type of fluid, which is causing the fouling, e.g. aqueous solutions, petroleum fractions, flue gases, etc.; according to the type of equipment undergoing fouling, e.g. plain vs. extended vs. enhanced heat transfer surfaces, tubular vs. plate vs. spiral heat exchangers, etc.; according to the type of phase interface involved, e.g. liquid-solid, gas-solid, gas-liquid-solid; according to the type of industry in which the fouling occurs; and according to the key chemical/physical mechanism giving rise to the fouling. Here the focus is primarily on the last mentioned method of classification, on the grounds that a mechanistic approach gives rise to greater insight and generalization. Differences involved with different phase interfaces and with different industry groups will also be briefly discussed.

B. Types of fouling according to key mechanism

(a) Crystallization fouling

This broad category, which connotes nucleation and crystal growth on the heat transfer surface, is conveniently subdivided into precipitation fouling and solidification fouling: