Morphological parameters investigation of deposits formed on pleated filters using DLA

Abstract

Pleated filters are widely used as they offer a greater filtration area leading to lower pressure losses. However, their geometry impacts the air flow fields inside their pleats, which can evolve as more aerosol matter accumulates. This leads to different behavior between flat and pleated filters with respect to pressure loss evolution with both filtration velocity and deposited mass. To study the effect of streamlines inclination on deposit morphology the possibility of producing numerical deposits is here investigated. A custom DLA (Diffusion Limited Aggregation) code is used which can handle both poly-dispersed particles population and streamline tilt for spherical particles. The morphological parameters here considered are the porosity, the contact angle distribution and the coordination number distribution. The DLA approach, by accounting for stochastic and deterministic forces, is well-suited for simulating nanoparticle behavior where Brownian motion is significant. It provides detailed insights into deposit microstructures and the influence of pleat geometry and flow incidence angles, offering a powerful tool for advancing both theoretical models and practical applications in aerosol filtration systems. Computations were carried to reproduce experimental results on porosity obtained with mono-dispersed PSL (Polystyrene Latex) and poly-dispersed CsCl particles. Comparison show good agreement between the experimental porosities and the ones computed using the custom DLA code. Contact angles and coordination number distributions give physically coherent results. Theoretical probability density functions for the contact angle distributions in both the diffusion and ballistic regimes were obtained and shown to agree with the distributions numerically obtained. Based on the adequacy between simulation results and experimental data, the effect of streamlines tilt on deposit porosity was investigated. In the simulations carried out, inclination of gas flow direction increases the limiting porosity in the ballistic regime when the tilt is higher than $45{}^o$ with respect to capture plane normal vector.