Soot Filtration Simulation - Generation of Porous Media on the Micro Scale from Soot Deposition on the Nano Scale

A. Wiegmann*, S.Rief and A. Latz
* Affiliation: Fraunhofer Institute Techno- und Wirtschaftsmathematik
In soot filtration simulation, there exists a discrepancy of scales.
The filter media can be represented with a resolution of a micron,
while the soot particles can be as small as 20 nanometers. A
representative portion of the media is needed, but also the correct
deposition behavior of the soot particles in order to achieve
realistic clogging behavior.

A hierarchy of simulations may help with this. On the nano scale, at
10 nanometer resolution, a three-dimensional computer model of 4^3
microns of the filtermedia geometry is built. With this resolution,
soot particles are well resolved, and collisions with walls and other
particles are explicitly those of solid bodies. When significant
amounts of particles have been deposited, a porous region has grown
near the solid parts of the model. The exact nature of this region
depends on the process parameters, and the method allows also to keep
track of the dynamics of this buildup of the porous media. After this
step, a second simulation is run on the micro scale. Now, as much as a
cubic millimeter of the filter media is represented in the computer,
with a resolution of about two microns. The porous structure from the
nano scale simulation now shows as cells that are neither empty nor
solid, but rather porous cells. Changes of porosity and permeability
on the micro scale are governed by the precise information from the
nano scale simulations, and are used on the micro scale to eventually
predict effects like filter efficiencies and filter life time, that
can be measured for the real filter media.

keywords: nano scale deposition simulation, filter efficiency simulation,
          filter lifetime simulation

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