Classical filtration models consider filter media as homogeneous and use an arbitrary inhomogeneity factor to account for the dif- ferences 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 effi- ciency 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 scan- ner are described in detail. The variations in local efficiencies are seen to have a Gaussian distribution, and the operating conditions and media behavior inOuence 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.
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