[SZymon]

Hello!

I'm working on a steam reformer microreactor. I used the grimech 3.0 with Pt chemkin mechanism. Fluid simulation looks the same without the introduction of platinum channels as with. I don't know what to do to make the reaction take into account the catalyst.

Appreciate any help!

[vinerm]

Do you have a surface defined as site surface for reactions? The mechanism only brings in reaction kinetics and material database, however, user has to include the reactions and apply those to walls. If that is not done, reactions won't take place.

[SZymon]

Thank you for your quick reply Vinerm.

Unfortunately I did not define the reaction surface. How can I do it? Can I do it directly in the program or using udf?

Regards,
Szymon

[vinerm]

Reactions at the walls need a few things; site surface species, site surface reaction mechanisms, and selection of the mechanism at the wall boundary. You need to go to wall under Boundary Conditions and then choose mechanism under Reactions tab.

[SZymon]

Thank You very much for your help Vinerm.

Regards,
Szymon

[SZymon]

Hello again

For simple geometry everything works well but in case of under example, something is wrong. I did the model as in the picture and simple mesh. In fluent I set:
models: energy on, viscous- k-epsilon, species transport

In species transport: I imported chemkin mechanizm Grimech 3.0 Pt and surface mechanizm Pt, the rest of the settings as in the picture.

In material- I created new material platinum
In boundary condition-

I set inlet - velosity 0.1m/s ; intensity and hydraulic diameter (turbulence 10%, diameter 0.01; thermal 1172 degres, species- mole fraction 0.5 h20 and 0.5 ch4

outlet- presure outlet -intensity and hydraulic diameter( turbulency 5%, and diameter 0.01)


In the wall between the fluid and the platinum channels, I picked reactions in species another wall without changes.

methods- coupled and pseudo transient.

In results most of the hydrogen is in front of the platinum channels and it is in them that the reaction will take place.

Thank You for help.

Regards,
Szymon
[ATTACH]results.png[/ATTACH]

[vinerm]

Sorry, I could not understand what issue are you facing. Is it the species mass fraction that is not what you expected it to be?

[SZymon]

Thank you for your answer.

In geometry only the channels are made of platinum as in the picture. model.png
I understand that the reaction should start there.

The problem is that the most hydrogen is formed before the platinum tubes. I wonder why this is happening and where I made a mistake.

Regards,
Szymon

[vinerm]

Do you have separate boundaries defined for the channels and for the walls upstream and downstream of channels? If not, then whole boundary will act as reacting wall. If the boundaries are separate then check under Boundary Conditions if reactions are active on those walls as well.

[SZymon]

Yes, the boundares were separated. In the model there are 3 contacts regions and only for platinum channels I made reactions. contact region.jpg.

In boundary condition when I picked reactions, I can choose mechanism1(I think this is from chemkin-grimech3.0) and catalyst(propably from surface chemkin file). reactions.jpg. In contact region between fluid and pt channels, I picked mechanism1 and in shadow wall (Pt) i choosed catalyst.


I'm not sure about the settings in species model and methods.
Could You see if they are well positioned scalenie.jpg hh.png, ff.jpg


Thank you very much for help

Best regards
Szymon

[vinerm]

You should not use any contact regions in CFD until and unless you have a moving mesh. Go back to Mesh, delete Contacts under Connections and ensure that you have single part but multiple bodies under Geometry branch of Tree within Meshing. Reactions Mechanisms and Reactions are all defined under Materials. Choose mixture or whatever name you are using for the mixture that imported and then click on Edit on the right of Mechanisms to see the defined Mechanisms. Same for reactions.

[SZymon]

Thank you very much for your help and time Vinerm. Now everything looks good.

[SZymon]

Sorry for bothering you again Vinerm.
Could you explain to me again how to set up the model so that the reaction was only from the catalyst wall?
In geometry I have fluid, pt tubes and casing. In boundary condition- wall-casing, wall-fluid, and wall-pt tubes. Offcourse I can pick reactions only in wall-fluid and this wall is between fluid and all geometry. I have no idea how to separate this fluid.

Regards,
Szymon

[vinerm]

If you have enabled reaction only on wall-pt, then reactions can occur only on wall-pt. Do you have any volumetric reactions as well? Since those can take place everywhere.

[SZymon]

Thank You for Your answear.
Volumetric reaction is disabled. I have only catalyst reaction but not in wall-pt but in wall-fluid. In wall-pt I cant set reactions.
wall fluid.jpg wall pt.jpg

[vinerm]

You should enable reaction only on the wall you want it to? If you want it on wall-fluid, then let it be on wall-fluid. If you want it on wall-pt, then enable it on wall-pt and disable on wall-fluid. If you want reactions on both but different, then define two different mechanisms. Apply one on wall-fluid and the other on wall-pt.

[SZymon]

Thank You for Your answear.

Ok I undarstand but the problem is that in pt-wall I can't pick reaction because it is solid. Reaction is available only when I change pt-tube in zone conditions on fluid. Do I have to do this?

Regards
Szymon

[vinerm]

There are cells zone and there are boundary zones. Cell zones can be solid or fluid. However, boundary zones are boundaries. Reactions can only be applied on the fluid side of the boundary, i.e., the boundary should belong to fluid. You don't really require a solid zone for solid species. Only fluid zones are required. So, whichever boundary of the fluid touches the platinum solid, solid may or may not be there, that boundary should have reaction enabled.

[SZymon]

Thank You very much Vinerm. Now it makes sense.

Best Regards,
Szymon