Abstract
The deposition of small particles, charged or polarized, on a fiber embedded in a coupled field of electrostatics and viscous flow, has received renewed attention due to the technological needs of PM2.5 capture as well as the challenges of unresolved fundamental physics. In this paper, we introduce a general computational method for this complex particle-electric-flow interactions, in which a boundary-element method (BEM) for the electrostatic field induced by the macroscopic fiber, an optimized multiple expansion method for the long-range electrostatic field induced by the particles, and a Discrete Element Method (DEM) that accounts for electrostatic, fluid and adhesive contact forces on particles are combined for the 3D simulation. The deposition mechanisms of charged and polarized particles on the fiber are investigated using the combined approach. First, it is found that the pre-polarization of fine particles dramatically enhances the deposition rate even by nearly an order of magnitude. Second, the effect of particle charge on the deposition is two-fold. The attractive particle-fiber interaction increases the initial deposition rate, and affects the further filtration process because of particle loading effect in this initial stage. The particle-particle repulsion always inhibits the deposition. Third, the charged particles tend to form new small dendrites rather than deposit on existing dendrites, causing the dendrite number larger than that in the cases of polarized or neutral particles.
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