Aerosol Capture in Granular Beds in the Sedimentation and Diffusion Dominated Regimes

Abstract

Single grain capture efficiencies η for low speed gas flow through clean granular beds are reported. The aerosol particles were liquid dioctyl phthalate droplets ranging in diameter D p from 0.15 to 4.7 μm. The grains were spheres of diameter D G equal to 2.13, 3.69, or 15.6 mm and crushed oil shale rock with volume equivalent spherical diameter of 2.2 or 17 mm. The superficial gas velocity was downward and varied from 2.5 to 80 mm/s. Sedimentation and Brownian diffusion are the dominant capture mechanisms for these conditions. Consequently, the Gravity number Grv = ρpD2 pCpg/18μU and the Peclet number Pe = DGU/ D p=3πμDpDGU/KTCp are important dimensionless groups for correlating data. An approximate solution to the convective diffusion equation for point particles shows that η/Grv is a function of the combination 21/3A1/3Pe−2/3Grv−1 only, when Grv « 1 and Pe » 1. A(αG, Re) is a known function of the fraction solids αG in the bed and the grain Reynolds number Re = ρDGU/μ. Our data are successfully correla...