The dependence of filter properties such as pressure drop, filter efficiency, and filter life-time on the geometric structure of fibrous filter media is of great practical importance. In particular electrostatic forces are highly dependent on this structure. Many textiles have an irregular structure, which cannot be represented by functions of, say, porosity. Thus, it is necessary to model the three-dimensional structure of the textiles and electrostatic charges on their surfaces. To study the filtration properties, we use a Lagrangian formulation of particle transport in the calculated complex flow field and solve a Poisson equation with jumps in the electric conductivity and singular source terms on the fibre surfaces. The electric field is obtained as the negative gradient of the potential. Depending on the size of particles, the microsturtcture of the filter, the electric field and the shape of the fibers, we simulate pressure drops, filter efficiencies and filter lifetimes. Since controlled variations of structural parameters like fibre orientation, fiber shape, spatially varying pore size distribution or gradients in the fibre density and the distribution of electrostatic charges on the fibre surfaces are easily achieved within the simulation, our results constitute a systematic and quantitative approach for the simulation of air filtration in fibrous filter media.
Computer simulation of air filtration including electric surface charges in three-dimensional fibrous microstructures
