CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   Multicomponent diffusion modeling (http://www.cfd-online.com/Forums/cfx/76919-multicomponent-diffusion-modeling.html)

 gsbhatia89 June 8, 2010 11:05

Multicomponent diffusion modeling

Hello everybody,

I would like to ask for help regarding a problem I m trying to solve on CFX 12.1. It is related to multicomponent diffusion (air and syngas(Co/h2) ) in a specific fuel injection geometry at high reynolds number (highly turbulent).

I would like to specify air and syngas at different temperatures and analyse their fractions after mixing. The air has to be a temperature approx 800K and syngas is at 300K. The syngas is injected through 5 orifices in two tubes intersecting inside a main tube through which air is passed.

I am facing a problem that after a certain distance from mixing...they start to "demix" and isosurfaces turn from a conical structure into a thin sheet at the outlet which is physically wrong.
However, when I tried to check with say Air and Ch4, the thin sheet is never formed and something physically possible is simulated. Therefore, I concluded that mesh is not the issue.

However, I am still not sure about several things:
A. I am not sure about how diffusion is modeled in CFX.
B. In post cfx I cannot see any temperature field. The temperate for all the components everywhere is 298K even though I changed it in materials tab.
C. How does it define inter-component diffusivity constants at non default temperatures?

Regards,
Gagan

 gsbhatia89 June 8, 2010 16:50

bump!

Well I was able to generate the temperature field.

However, I really wished to know how well the CFX code is when it comes to modeling multicomponent diffusion. All I get is conical isosufaces of all the components after mixing.

One thing I ve found out is how CFX only consider Ficks Law of Diffusion and does not simulate Stefan Maxwell Equations.

Does anybody know how I could simulate for that? Chemkin or something else?

 ghorrocks June 8, 2010 18:31

Quote:
 A. I am not sure about how diffusion is modeled in CFX.
This is described in the documentation.

Quote:
 B. In post cfx I cannot see any temperature field. The temperate for all the components everywhere is 298K even though I changed it in materials tab.
Sounds like a setup error, but looks like you have fixed that now.

Quote:
 does not simulate Stefan Maxwell Equations.
After a quick search I have not been able to understand what the additional physics the Stefan Maxwell Equations add. Can you explain what the SM Equations are about?

 All times are GMT -4. The time now is 14:42.