Soot filtration simulation - generation of porous media on the micro scale from soot deposition on the nano scale

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 nanometer scale, at 10 nanometer resolution, a three-dimensional computer model of 43 microns of the filter media 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 keeping 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 nanometer 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 nanometer 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.