**4.2.1 Fouling mechanism**

Heat exchanger fouling is a dynamic process. The phenomenon continues to evolve, generally until equilibrium is reached or cleaning is required. The period of fouling can vary from a few hours to several months.

Müller (Müller-Steinhagen & Middis, 1989) looked at five stages in the process of the appearance and development of particulate fouling:


Generally, the initiation phase is rarely taken into account in particulate fouling models. The mechanisms that govern the deposit of particles are generally presented as being the transport of the particles to the surface, then the "adhesion" to the wall and finally the possible dislodging of the particles.
