The effect of gravity on the deposition of micron-sized particles on smooth surfaces

Abstract

Particle deposition on smooth surfaces from liquid suspensions involves transport and attachment steps. Transport is considered to be influenced 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 diffusivity. However, even in this (colloidal particle) size range, gravity or a constant body force towards the deposition surface may significantly affect the deposition process. Image processing techniques have been used to obtain measurements of the deposition rate of micron-sized glass particles, in a horizontal narrow channel, under laminar flow conditions. Over a fairly wide range of flow rates, deposition fluxes are nearly constant. This trend, supported by a theoretical analysis, suggests that (in that range) gravity controls the particle transfer boundary layer thickness and the deposition rate. However, above a certain threshold flow rate, a rather sharp reduction of the deposition rate is observed indicating that the attachment process becomes important. The implications are discussed of the above experimental and theoretical results on modeling particulate deposition for various problems of practical interest; e.g. fouling of heat exchange surfaces or filtration membranes.