THE EFFECT OF GRAVITY ON THE DEPOSITION OF MICRON-SIZED PARTICLES ON SMOOTH SURFACES

Particle deposition on smooth surfaces from liquid suspensions involve s transport and attachment steps. Transport is considered to be influe nced by particle Brownian diffusivity and inertia, while attachment is the outcome of competition of hydrodynamic and physicochemical forces . In the literature, micron-size particle transport is usually modeled as a mass transfer process determined by the magnitude of Brownian di ffusivity. However, even in this (colloidal particle) size range, grav ity or a constant body force towards the deposition surface may signif icantly affect the deposition process. Image processing techniques hav e been used to obtain measurements of the deposition rate of micron-si zed glass particles, in a horizontal narrow channel, under laminar how conditions. Over a fairly wide range of flow rates, deposition fluxes are nearly constant. This trend, supported by a theoretical analysis, suggests that tin that range) gravity controls the particle transfer boundary layer thickness and the deposition rate. However, above a cer tain threshold flow rate, a rather sharp reduction of the deposition r ate is observed indicating that the attachment process becomes importa nt. The implications are discussed of the above experimental and theor etical results on modeling particulate deposition for various problems of practical interest; e.g. fouling of heat exchange surfaces or filt ration membranes. (C) 1998 Elsevier Science Ltd. All rights reserved.