Iso-permeable nonwoven media: how structural parameters impact the filtration efficiency

: Fibrous media are widely used for air filtration and purification. Designing an "ideal" fibrous structure for a given application requires balancing low pressure drop and high filtration efficiency, both of which are influenced by structural characteristics such as the packing density, the thickness, and the fiber size distribution. This paper presents a joint analysis of these performance parameters, investigating the impact of iso-permeable fibrous structures composed of micron-sized fibers on their filtration efficiency. Using a permeability model developed and validated in a previous study, iso-permeable structures were identified and numerically generated using the CFD software GeoDict (Math2Market GmbH). Structures with an identical packing density and an equivalent diameter, and a fine-to-coarse fiber diameter ratio below 4, exhibited very similar fractional efficiencies, regardless of their fiber diameter distribution. Conversely, iso-permeable structures with varying packing densities and equivalent diameters led to significant differences in collection efficiency. The determination of the figure of merit parameter for different structures revealed that the most optimized fiber entanglement for a given application strongly depends on the targeted particle size. Identifying the optimal configuration thus requires precise knowledge of the aerosol characteristics to adjust the media’s structural parameters accordingly. This work provides an initial framework for evaluating the performance of iso-permeable media, aiming to determine the characteristics of the most "ideal" fibrous structure for specific applications.