Diffusion Deposition on Model Fibrous Filters with Intermediate Porosity

Abstract

Theoretical and experimental studies of the diffusional deposition of aerosols on model niters of intermediate packing density are reported. At low Reynolds number (Re« 1) and intermediate porosity (0.01 < α < 0.4), the Kuwabara flow field is applicable for parallel staggered model filters, and the diffusional deposition efficiency can be expressed as A = 2.92 n [(l-a)/k]^1/3 Pe ^−2/3. By applying a correction factor based on the ratio of pressure drops to this equation, the deposition efficiency for a fan model filter is n = A Pe ^−2/3, where A has a value of 2.4–2.6 for α = 0.05–0.4. The efficiency increases with the fiber solidity, α for the parallel staggered filter, but is essentially independent of a for the fan model filter. Experimental results of diffusional deposition of ultrafine aerosols on wire screens which is used as a fan model filter has been performed. Summary data on screens and the fan model filter reported in the literature show that the single fiber efficiency is independent of the solid volume fraction and can be expressed as n = 2.7 Pe ^−2/3 where Pe is the Peclet number (over the range of 0.02 < a < 0.35). The small difference between the experimental data and theory can be explained by the approximate nature of the flow field used in the theory.