What is UDS diffusivity of a self-defined material?
 

Since the properties of my contaminant material are not in the fluent database, I created it.

The properties I found from different online sources and literature are: molecular weight, isobaric specific heat Cp, viscosity, diffusivity and density.

When I tried to choose these five properties, for diffusivity, there are only two: diffusivity in solid or UDS diffusivity, I had no choice but to choose the latter, even though I don't know what it is. then I defined this material, add it to air (air is in the bottom of the mixture I defined, as it is the bulk fluid) and I defined this gaseous mixture. then I looked at the properties of this mixture, I found that somehow fluent set a thermal conductivity (0.045W/mK) for me and a diffusivity 2.088*10^(-5), while my real contaminant diffusivity in air is 5.52*10^(-6), which I already input as UDS diffusivity.

Anyway, I changed this mixture diffusivity back to 5.52*10^(-6) m^2/s and saved this material. Am I doing this right? or I have to define this UDS transport equation? I've no idea about it right now.

And the thermal conductivity, I didn't input it, it was "determined" by fluent somehow, do you know why?

Thanks!