We numerically study and then experimentally validate the flow resistivity of commercial nonwoven fabric filters used for a bag filter system. To represent a realistic flow field inside the filters during simulation, a numerical method that coordinates the filter structure obtained by X-ray computed tomography imaging with computational fluid dynamics using the immersed boundary method is developed. The effects of superficial velocity, porosity of the filter domain, and type of filter on pressure drop are investigated and analyzed based on Darcy's law. The predictions from our numerical method are quantitatively in good agreement with the experimental measurements. We demonstrate that the Kozeny constants of the filters can be estimated by utilizing the solid volume fraction. These results demonstrate that our simulation method can be used to clarify the effects of porosity, fiber arrangement, and fiber shape on the pressure drop. Finally, its application to water droplet permeation is demonstrated.

We numerically study the droplet coalescence of an oilin-water (O/W) emulsion permeating through a fibrous filter. Our numerical simulation method is based on the phase-field model for capturing a free interface, the immersed boundary method used to calculate fluid−solid interactions, and the wetting model that assigns an order parameter to the solid surface according to the wettability. To represent realistic flow inside the filter during simulation, the voxel data obtained from X-ray computed tomography (CT) images of the filter microstructure are used in the simulation. The effects of the filter microstructure, such as fiber arrangement and orientation of the droplet coalescence, are investigated by using several filter domains. Our simulations demonstrate that the arrangement of closely attached fibers placed at the permeate-side surface enhances droplet coalescence. In addition, the parallel orientation of the fiber to the main flow direction suppresses droplet enlargement due to the coalescence but reduces the number of droplet passages without coalescence in the filter.

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