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Old   November 9, 2012, 22:41
Default Surface reactions
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Aashish Priye
Join Date: Sep 2010
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Hello everyone.
I have been trying to model surface reactions for while now and thought I could seek some guidance from the experts. I appreciate you taking the time to help me out with this. My problem is the following:

The problem:
My geometry is a cylindrical pore of a given height and diameter (dimensions are in the order of mm). The cylinder is filled with water and some other species. The bottom of the cylinder is maintained at a higher temperature (say 95 C) than the top (say 55 C). Due to buoyancy, the aqueous solution circulates within the cylinder (just like the flow in lava lamps). Lets say the solution contains species "A" with a specified initial concentration [A]o. Now I want the species A in the aqueous solution to bind/adsorb on the curved side walls of the cylinder as the fluid circulates within the entire volume of the cylinder. If there the fluid were static i.e. no circulation, the species A will be transported to the side walls purely by diffusion (I specify the diffusion coefficient). However, the fluid circulation due to buoyancy would enhance the transport of the species to the side walls. This a transient problem, so I hope to obtain the concentration of the adsorbed species as function of time. I am also interested to determine the locations on the sidewalls where adsorption is more/less as time evolves.

The modeling approach:
3 dimensional
Implicit unsteady
Multi-component liquid
Coupled flow
Coupled energy
Coupled species
Partially premixed combustion
Eddy break-up
Constant density

I was able to model the convective circulatory flow aspect of problem successfully (added a momentum source term for buoyancy forces). To model the reactions, I used "kinetics only" and defined a reaction in which A-->B. The rate constant was specified as a field function which localized the reactions within a very thin boundary layer (150 microns) near the surface so that the reaction only occurs near the surface (ideally at the surface). I could now monitor the decrease in concentration of species A in the domain. But as you can see, I cannot obtain the location where A is adsorbed at the surface with this approach.
A surface reaction model would be able to capture this best. I would have to apply a heterogeneous reaction model which would enable the species A to react/bind/adsorb only at the surface. I went through the STARCCM+ manual for surface chemistry model and found it required input from Dars-CFD library. I could not find any information on how to implement this (no tutorials/additional info provided).

First of all I wanted to know what all modeling options I have to model such surface reactions. Secondly, If Dars-CFD is the only way, how do I create the FORTRAN files with the reaction definitions (STARCCM+ is on our departmental cluster).

Let me know If I missed any information or if other clarification is required regarding my problem. I have been trying to resolve this for a while now and any help from your side would be highly appreciated. I thank you in advance for you time.

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