I am new to Fluent and so may be asking obvious questions. I'm trying to model a sphere ("blob") of liquid contaminant immersed in a large volume of water. We want to begin with zero water velocity, and model simple steady state diffusion. I want the species to diffuse *out* of the surrounding "control volume" of water. I do not want the diffusing species to "fill up" that volume as if it had impermeable walls.

My problem is that the solution converges immediately - without iteration. Why is this?

Setup: Fluent 6.2.16 2DDP, axisymmetric, cutting through the blob. (picture a setting sun, half cut off by the bottom of your monitor!) Solver: Multiphase diffusion B/C: all boundaries pressure outlet

At first we tried this with three sides of the "control volume" box assigned as velocity inlets (zero velocity), with the fourth side a pressure outlet. But that kept diffusing species from leaving the control volume on 3 sides...

Thank you for your patience and advice.

Perhaps my level of understanding is too low to make use of this forum. Can anyone direct me to another source of information to help learn about Fluent and its diffusion capabilities?

i don't have multiphase simulation experience so can not comment on that part,

only part where you say it converges immidiately without iteration, this means one of the two things, either all the quantities are zero adn solver comes to zero residuals for all the quantities and tell you it si converged,

second , it might happen that in residual monitor you have n't lowered the residual restrictions,