Experimental investigation of local efficiency variation in fibrous filters

Classical filtration models consider filter media as homogeneous and use an arbitrary inhomogeneity factor to account for the differences between theory and experiments. The variations in media-packing density have been experimentally observed and seen to be significant. There is minimal experimental information on the effect of these variations on filter performance. In this paper, local efficiency variations in commercial fibrous filters have been obtained for varying operating conditions. A filter scanner was developed to measure local filter efficiencies, and the features of the scanner are described in detail. The variations in local efficiencies are seen to have a Gaussian distribution, and the operating conditions and media behavior influence the variability in the local efficiency data. Theoretical modeling can be used to obtain two-dimensional packing density distribution data from the local efficiency measurements.