Learning Forum

[user deleted]

I am modeling 11-species air mixture. And I have to define binary diffusion coefficients for full multicomponent diffusion. The only instrument that is given by fluent is polynomial approximation of temperature dependence. But for ionic species binary coefficients depends also from electrons gas pressure. Can I somehow take this dependence into account through UDF, or any other way? Why isn't it possible to set binary coefficients as udfs like species viscosity and thermal conductivity? DEFINE_DIFFUSIVITY works as I understand only for Fickian diffusion model because it depends only from one species index.

[Surya Deb]

Hello,
If I understand correctly, the electron gas pressure will be a function of temperature as well . You might also want to check the Kinetic Theory approach for the diffusivity.
Check literature to see if you find such polynomial correlations with temperature.
Regards SD

[user deleted]

Actually, this is partial pressure of all electrons which depends of pressure of gas in some point and chemical conditions in it. So it's more complicated parameter for diffusifivity. I think I've found the answer myself. If one enables full multicomponent diffusivity in the species meny DEFINE_DIFFUSIVITY works different way.