[AlessandroChiodi]

Hi everyone!
It's the first time for me using Ansys Fluent for simulations, so maybe my problem can appear trivial for lots of you. Basically I'm going to simulate the diffusion of drug molecules through a liquid-water domain: geometry is quite simple, we just have two concentrical spheres, the internal sphere represents the polymeric carrier charged with the drug, and the external sphere is the liquid water (external surface can be modeled as a perfect sink, with homogeneous Dirichlet BC). Well, I have some troubles:
1- I'm proceding with Species Transport model, am I right? There's something better?
2- In the definition of boundary conditions, it is possible to set null Neumann BC in the center of the whole system? Thus simulating the fact that, being a spherical symmetry, drug diffuses in the same way in all directions.
3- How can I do to specify that, at time t=0, all the drug concentration is located within the polymeric carrier (so, within the internal sphere)?