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-   -   diffusion in general (http://www.cfd-online.com/Forums/fluent/124949-diffusion-general.html)

Lilly October 16, 2013 04:26

diffusion in general
 
Dear all,

I have got a general question about diffusion of a species of small mass fraction inside a "carrier" fluid of high concentration which I am simulating with Fluent.
Is it enough in this case to define the diffusion coefficient of the dilute species inside the carrier fluid or do I have to define a diffusion coefficient for the carrier fluid as well? It's probably a stupid question, but I was just thinking about that the diffusion of the carrier fluid (inside the dilute fluid) would also influence the diffusion of the dilute species at which I am interested.
Does anybody have an idea about this?

Thank you in advance!
Lilly

Lilly November 5, 2013 06:08

mass diffusivity at fluent
 
Dear all,

I am still thinking about the same problem: I have a small amount of species in a large amount of carrier fluid.
When I use the "constant-dilute" method at Fluent, Fluent uses the same diffusion coefficient for both species. Do I have to use the "dilute-approx." method and set the diffusion coefficient of the carrier fluid to zero? On the other hand, the diffusion coefficient of the carrier fluid should not be included at the mass transport equation for my species anyway, so does it matter?
I also found this citation at the fluent user guide: "Coefficient:
sets the diffusion coefficient for Species Di in Species Dj (which is equivalent to the diffusion coefficient for Species Dj in Species Di)." Does this means everything is fine, when I am using the "constant-dilute" method and have the same diffusion coefficient for both species?
It would be really nice, if somebody could help me!
Lilly


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