Analytical modelling of the permeability of filter media exhibiting a bimodal fibre diameter distribution—Beyond empirical models

Abstract The prediction of the permeability of bimodal fibrous media dedicated to air filtration, that is, highly porous media, is addressed. Two types of models, using similar input parameters (mean porosity and mean fibre diameter), are compared: several analytical models and the empirical models still commonly used by the air filtration community. It is demonstrated than even if every model under‐predicts the media permeability, the isotropic versions of the analytical representative unit cell (RUC) model and Tomadakis and Robertson model yield significantly better predictions than the empirical models. The additional improvement in the analytical model predictions, by including the bimodal fibre diameter distribution as a unimodal equivalent diameter, is furthermore outlined. This model comparison is made possible due to new accurate experimental data, obtained from the characterization of the structural properties of a commercial bimodal fibrous medium. The fibre diameter distribution and mean medium porosity are determined from SEM analyses and mercury porosimetry, respectively. The anisotropic/isotropic and homogeneous/heterogeneous nature of the medium is evaluated based on X‐ray micro‐tomography data. Finally, to go further than the prediction of one permeability value based on mean media properties, permeability mappings are generated based on the porosity mappings and the adapted RUC permeability model.