Inertial impaction-dominated fibrous filtration with rectangular or cylindrical fibers

Fibrous filter, being simple in structure and low cost in material, is wide ly used in fine particulate removal. The collection efficiency of a fibrous filter is heavily dependent on the collection efficiency of a single fiber . Despite the availability of a reasonable formulation for single fiber col lection by diffusion, most expressions of collection efficiencies by interc eption and impaction are empirically based and few simple analytical formul ations are available, especially for impaction-dominated collection. In thi s paper, impaction-dominated fibrous filtration with rectangular fibers for particulate size much smaller than that of the collecting fibers are both numerically and analytically investigated. The effects of fiber aspect rati o, filter packing density, particulate size and Stokes number on the collec tion efficiency of a rectangular fiber in the impaction-dominated filtratio n are numerically determined. In addition, simple analytical expressions of single fiber collection efficiencies due to interception and inertial impa ction of fine powders are derived based on Kuwabara flow analysis around a cylinder. Hence, using the equivalent hydraulic diameter concept for rectan gular fibers with moderate fiber aspect ratios, the effect of particulate p olydispersion on the filter collection efficiency is investigated based on presumed mass-based Gaussian size distribution and log-normal size distribu tion, respectively. Differences between overall size-averaged collection ef ficiency and mean size collection efficiency can, thus, be estimated. (C) 2 000 Elsevier Science S.A. All rights reserved.