I created a mixture material out of two fluid species: carbon and liquid iron. Carbon is the dilute and liquid iron is the solvent. In the materials panel, I got confused with the mass coefficient of species. I guess in my case only fickian diffusion exists since the carbon mass fraction is around 0.4%. But should I choose the dilute approximation or constant dilute approximation?

I prefer the dilute approximation but how can I specify the bulk species(liquid iron) in the mixture? I wonder if someone can give me a helping hand? Thanx!

nobody knows it?