Adhesion and Removal of Particles II

Abstract

Cleaning fouled surfaces is mostly a process whereby ‘particulate material’ is removed from a solid surface, predominantly by liquid flow. Cleaning problems may arise if the flow of the liquid cannot reach the fouled surface, e.g. when particles are trapped in crevices, or when adhesion forces between the contaminating material and the support are very strong. In the latter case, acids and/or alkalis are mostly used in combination with a detergent to ‘detach’ the deposit. In some specific cases, also enzymes are used to break down or digest the material deposited, in particular proteinaceous components. In most cases, the mechanism of removal can be described in terms of colloid chemistry and fluid dynamics because in fouled systems, predominantly submicron or colloidal particles are involved as shown in part I and because the cleaning operations are mainly based on the flow of liquid solutions along the fouled surface. In this review, both aspects are described in detail, including the van der Waals forces of attraction and the electrostatic double-layer forces of repulsion as well as the flow of a fluid in a laminar boundary layer. The equations given in part I are used to describe the colloid chemistry aspects. On the basis of the results obtained from model experiments, conditions will be given to optimise the removal of ‘particulate’ dirt.