The capture of aerosol particles by surfaces

Abstract

Abstract Although small particles are known to attach strongly to surfaces through the action of intermolecular attractive forces, they are not always captured upon striking a surface. The mechanics of a solid particle and solid surface collision are described and an expression relating reflected and incident velocity is derived. The expression contains two parameters: the coefficient of restitution e and the particle-surface interaction energy E . An expression for the “particle capture limit,” i.e., the range of system properties such as particle size, velocity, and interaction energy within which particle capture will occur, is derived. The coefficient of restitution is estimated and used with an estimate of E in example calculations of the particle capture limits for silica and polystyrene particles. Also of practical interest is the capture of particles on thin plates and cylinders, the latter representing fiber filter elements. For these thin bodies, an additional mechanism of energy dissipation is described. The theory of Zener for the e of thin plates is reviewed and extended to cylinders. Examples are calculated for these bodies. Design characteristics of a filter element are discussed with respect to capture efficiency. The theory suggests a unique technique for measuring particle-surface interaction energies.