Adhesion of particles in fibrous air filters
A fundamental examination of particle impact has been carried out to determine the adhesion characteristics of particles in fibrous filters over a range of impact parameters. High speed films were taken of the impact of monosized glass particles onto the edge of a slowly rotating wheel. The subsequent adhesion probability was calculated from the films using a frame by frame digital analyser and a digital computer. The adhesion probability and the coefficient of restitution for particles of 4.7 μm, 8.6 μm and 11 μm diameter were determined for two angles of impact, over a range of impact velocities. The magnitude of the adhesion probability and the coefficient of restitution as a function of particle diameter and impact velocity is shown to be in agreement with theoretical reasoning. The effect of the surface properties on the adhesion probability were investigated by studying the impact of particles on wheels machined from differing materials. The adhesion characteristics were incorporated into a theoretical model to predict the single fibre efficiency of a fibrous filter over a range of operating conditions. The Kuwabara flow field was used in the model to describe the gas flow through the filter. The grade efficiency of a knitted stainless steel model filter operating in the high inertia regime was determined for feldspar particles of diameter between 2 μm and 22 μm. The effect of the operation conditions on the single fibre efficiency were shown to be in accordance with the effect predicted from theory. The influence of dust loading, test dust size distribution and filter depth on the single fibre efficiency was studied. The effect of these parameters is described mechanistically.