Reply To: How to enforce zero-gradient condition on a boundary for your UDS in FLUENT?

[Surya Deb]

Hello,
It is not very clear about the type of boundary condition here.
If you are modeling a wall, then not only the species but the flow itself stops there considering the wall to be impenetrable.
So you cannot expect a convective flux of the species across the wall in that scenario What you are referring to might be a permeable membrane kind of situation where the flow along with the species crosses it.
So yes, the type of boundary condition will make a difference here as far as I understand.
Regards SD