CFD Online Discussion Forums - Calculating and Export Volume Fraction out of Mass Fraction

Hi,

I am quite new to multi phase / multi species problems and I am new to fluent as well (great combination :(). English isn't my first language, but I hope it will be okay.

The simulation I try to make:
I try to simulate a large air volume with a slow velocity inlet of a second gas (miscible, very similar to air, just slightly higher density). I tried VOF and Mixture multi phase model and I got the Volume Fraction as export (which is what I need).

I realized that through the slow velocity inlet, the diffusion part will be dominant and that is not covered by the multi phase models. Therefore, I want to use the multi species model "species transport".

These models are returning the mass fraction though and that is were I am stuck.

The problem:
My simulation returns mass fractions but I need volume fractions. I know from the math point of view how to calculate it, but I don't know how to tell fluent to do it for me. Like I want for every cell the volume fraction.

I want either calculate the volume fraction during the simulation (I would prefer that) or find a way to calculate that in the post processing (in ansys).

Maybe someone has some best practice experience for this kind of situation too? I would be very thankful for any advice.

Kind Regards

Kosch

PS: I searched the forum, but I do not even know which keywords I should search for my kind of problem. Sorry if I asked a very common question again.