[ser]

I am trying to model the transport of three drug, in water (carrier fluid). Each drug have a different molecular weight and diffusivity, the Ansys guide suggest to use the constant-dilute-approx or the diluite-approx.
The problem is that in the fist case it set a constant diffusivity for all the mixture component, in the second case instead is necessary to set the diffusivity for each component even for the water(which is the carrier so it doesn't have a diffusivity). I read some posts and someone suggest to use the user-define-scalar but I did't understand hot to properly use it. If you have some suggestion or if you can explain how to set the mixture propriety I wold appreciate it. Thank you!