Research Note: Computer simulation of air filtration including electric surface charge in 3-dimensional fibrous microstructures

Dr. S. Rief, Priv.-Doz. Dr. A. Latz* and Dr. A. Wiegmann

Fraunhofer Institute for Industrial Mathematics (ITWM)
Kaiserslautern, Germany

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.

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