Generation and validation of virtual nonwoven, foam and knitted filter (separator/coalescer) geometries for CFD simulations

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Abstract Pivotal to efficient optimization of filter media using highly resolved pore-scale computational fluid dynamics (CFD), is the ability to generate virtual filter geometries with controllable geometric properties including packing density, fibre (or element) diameters, morphology and pore sizes. Yet, current design frameworks rely heavily on scans of available filters for representation of the pore-scale geometry in CFD simulations. This study demonstrates novel methodologies for fully customizable generation of realistic virtual nonwoven, open-cell foam and knitted filter geometries, using open-source tools in Gmsh, Blender, Python, OpenFOAM libraries and Fortran scripts. Further, a methodology for the generation and validation of a computational mesh for pore-scale CFD simulations, using open-source tools within OpenFOAM is described. The structure of the virtual filter media generated using the present techniques are validated by comparison against electron-microscopy (SEM) scans and photographic images of real media, as well as comparison of the mathematical structure and pore-scale statistics against the literature. Subsequently, steady state CFD simulations using OpenFOAM are performed to compare the predicted pressure drops across the virtual filters against both, measurements carried out for this study with similar filters, as well as theoretical models in the literature. It is found that there is good and consistent qualitative and quantitative agreement between the structures of the virtual media and real media, as well as between predicted and measured or theoretical pressure drops. The agreement found from the rigorous validations carried out in this study establish the suitability of the proposed methodology for efficient and cost-effective development and optimization of filter media.