Cleaning of simple cohesive soil layers in a radial flow cell

Abstract

A radial flow cell (RFC, inlet tube radius 0.95 mm and gaps of 1–4.2 mm) was used to investigate the removal of two thin (80–230 µm thick) model soil layers from glass and 304 stainless steel substrates by the flow of water at 20 °C. Under the flow conditions employed (Reynolds numbers 200–1400), inertial effects give rise to recirculation zones and regions of high shear stress on the bottom, soiled plate. The soils were dried layers of (i) instant coffee and (ii) a domestic abrasive cleaning suspension comprising fine particulates in a soluble matrix. Cleaning data exhibited a constant local erosion rate which varied strongly with radial position. For both soils, cleaning involved the growth of a circular cleaned region and redeposition of particulate matter in a ring at locations close to the foot of the secondary recirculation zone predicted by 2D axisymmetric CFD simulations. Removal beyond this location was observed with the coffee layers, indicating that cleaning for this soil was controlled primarily by simple diffusion mechanisms. The effect of channel aspect ratio and flow rate on the location of recirculation zones and shear stress distributions was investigated. The local cleaning rate in these steady flows was not linked simply to local wall shear stress.