Aerosol Capture in Liquid-Laden Granular Beds in the Sedimentation and Diffusion Dominated Regimes

Abstract

Apparent single grain capture efficiencies for simulated liquid-laden granular beds are reported. These are determined from measured penetrations using the clean bed solids fraction α_G and grain diameter. The aerosol particles were liquid dioctyl phthalate droplets ranging in diameter from 0.15 to 4.7 μm. The superficial velocity was downward, and varied from 2.5 to 100 mm/s. The grains were spheres of diameter equal to 2.13 mm or crushed oil shale rock with volume-equivalent spherical diameter of 2.2 mm. Liquid was applied as molten wax and allowed to solidify in the beds. Wax holdup varied from 0 to 76%. Sedimentation and Brownian diffusion are the dominant capture mechanisms for these conditions, although impaction becomes important for the large particles in beds with large wax holdup. Increasing wax holdup decreases the apparent single grain capture efficiency in the sedimentation-dominated regime roughly be the factor 0.77 (1 − α_G − α_L )/(1 − α_G − 0.12), where α_L is the fraction of bed occupied by wax. Increasing wax holdup has a minor influence in the diffusion-dominated regime until the holdup exceeds 55%. The data are correlated by an extension of the formula developed by Mann and Goren for aerosol capture in clean granular beds.