In this work, permeability of bimodal filter media is computed by solving the Stokes equations in the 3-D void space between the fibers. Our simulation results are utilized to establish a unimodal equivalent diameter for the bimodal media thereby taking advantage of the existing expressions of unimodal filters for capture efficiency prediction. Our results indicate that the cube root relation of Tafreshi et al. (2009) offer the best predictions for the most practical range of coarse fiber number fractions, 0 ≤ n_c ≤ 0.2, with fiber diameter ratios , 1 ≤ R_(cf) ≤ 5 , and solidities of 5 to 15 percent.
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