An example of a particle simulation with GeoDict is the experimental and numerical examination of the transport of particles in a fractured rock (Glatt et al., 2011). Here, three figures from the simulation are shown:

1. The 3D fracture geometry,

2. The water velocity computed in the fracture,

3. And a visualization of the particles from the transport simulation.

Modeling exhaust treatment bears many challenges at different scales. To predict the behavior of a catalytic converter, the following effects have to be taken into account:

• Flow through the support structure channels.
• Flow and diffusion through the support structure walls (ceramic).
• Diffusion movement inside the wash coat layer.
• Inner-grain (Knudsen-)diffusion to the catalytic reaction sites.

GeoDict provides the possibility to simulate on all these scales and to determine the relevant parameters for the upscaling.

In AddiDict, the features aiming especially on the simulation of catalytic processes and exhaust treatment are:

• Providing residence times in all pore and porous materials.
• Computing first order reactions.
• Simulate slip flow with improved molecule tracking near surfaces.
• Model reflection probability for porous media.
• Simulate effective molecule diffusivity.
• Simulate the influence of short-time adsorption on surfaces.
• Provide the possibility of choosing a maximal displacement as particle end position.

To simplify modeling and simulation of catalytic converters:

Simulate the effective diffusivity of a porous microstructure. Use the result to simplify the structure by replacing the microstructure with porous voxels and reduce the runtime significantly. See the effective diffusivity for details. This allows to simulate the behavior on a larger scale but with the correct diffusivity of the microstructure.

Model the wash coat layer of a channel as porous material. A reflection probability for this material that defines the probability that molecules enter the wash coat layer can be defined.

AddiDict tracks the molecules on their way through the channel. Evaluate the residence time of the molecule trajectories in each material, to investigate how long the molecules stay in the reaction zone (the wash coat layer). In the example shown here, the following behavior of the molecules can be observed from the residence times:

1. All molecules spent between 0.02 s and 0.04 s in air in the channel.
2. The time spent in the wash coat layer is very different for individual molecules.
3. Some molecules have not spent any time in the wash coat at all.

Finally, the residence times can be used to compute chemical reactions of first order in the AddiDict post-processing, by defining reaction rate constants. In the example here, the following behavior can be observed:

1. On average, more than 80% of the molecules did not react at all but left the catalytic converter at the end of the channel.
2. The best reaction was down to only 60% of the initial species amount.
3. There is much room for improvement in the example here.

These results can be used to increase the reaction rate, by varying the channel geometry, the temperature (to change the diffusivity) or the reaction rate of the wash coat layer.

Simulate the particle motion in a long, but thin, channel by simulation of a shorter channel with periodic boundary conditions and a maximum displacement as particle end position.