Particle agglomeration and capture as a result of synergism between inertial impaction and eddy diffusion

Abstract

AbstractParticle capture experiments conducted in turbulent cross flow with various aerosols involving liquid and/or solid particulates have resulted in collection efficiencies which are in excess of the values predicted by the various known models of particle capture, i.e., inertial impaction, interception and Brownian diffusion.In one type of experiment the turbulent air stream, carrying submicron dust particles, is flowing past a cylindrical collector (such as a piece of wire) with its axis orientated perpendicular to the direction of flow. Collecting efficiencies ranging up to about 20% have been found under conditions where the conventional models of particle capture predict practically zero collection efficiencies.In another type of experiment involving injecting a fog (2–80 μm diameter water droplets) into the dusty gas stream carrying submicron size dust particles which subsequently enters a slow turning fan. While passing through the fan, the fog agglomerates into raindrops while scavenging most of the dust particles. For example, a 0.8 μm median particle size aluminum silicate pigment was collected with 97–99.5% efficiency, the exact value depending on the operating conditions.Theoretical analysis of these phenomena may be based on the idea of synergism involving inertial impaction and eddy diffusion: the smaller dust particles/drops are captured by the larger drops in the fan and the dust particles are captured by the wires because (a) there is a significant relative velocity between them and (b) because the particles undergo eddy diffusion.