A two-scale approach for the computation of flow through pleated filters based on real image data
Pleated filters have been the subject of a lot of research and development activities for decades. In order to optimize pleated panels and cartridges in terms of pressure loss,efficiency and dust holding capacity, it turned out that in many cases, the geometrical design of the pleated filter can be compared in significance to the selected filtering media. Consequently, numerous experimental studies were (and still are) devoted to the modeling of the influence of pleat length, pleat distance, cartridge height etc. on initial pressure drop and efficiency and their evolution during loading. Thanks to more powerful computer hardware and significant advances in the development of numerical methods, Computational Fluid Dynamics (CFD) is well-established in this field of research, too. The majority of models and simulation studies simplifies and idealizes the filter pleats in terms of both shape and material distribution. Properties such as solid volume fraction and permeability distribution are frequently assumed to be uniform for the entire pleat, or, in the case of heterogeneous media, for each filter material or layer, respectively. There are relatively few works on flow simulation for pleated filters addressing the impact of variations of shape and/or material distribution caused by the manufacturing of the pleats, e.g. local material deformation due to embossing and the pleating process itself. In cases in which these phenomena cannot be neglected, it would certainly be helpful to enhance the CFD using data from real filter pleats. To this end, we propose a simulation approach based on computer tomography (CT) data of real-world pleated filters: A set of CT images is generated from samples taken from different regions of the pleat, providing information on the material volume fraction in the corresponding zones. By performing structural mechanics simulations and flow computations, the material distribution can be translated into a permeability distribution. This information is then used for more realistic flow and filtration simulations on the scale of the entire filter pleat. It is seen that this approach is able to reproduce the shorter lifetime of filter pleats compared to the lifetime of homogeneous filter pleats of the same shape.