Open Boundary Condition in Transport of Dilute Species

Hi all,

I have a question about the open boundary in Transport of Dilute Species physics.

I have a microchannel model with fluid flow going from A to B while the solute going from B to A due to electric field. Looking at the equations in open boundary condition, it would seems the condition is only based on vector "u".

Question: Is the vector "u" resultant of both fluid flow (convection) and electrophoretic motion? or is it only the fluid flow (convection)? in other words, can the "open boundary" has inflow condition even though the fluid flow (convection) is flowing outward?

Thanks.