Spacial Variable

Hi everyone,

I want to model ICEO, which involves electric field and electroosmosis flow. Firstly, I can get zeta potential by simply take the difference between double layer, this potential drop is a spacial variable on surface. For flow calculation, I want to use that variable and also electric field on the boundary.

So first question: how to define spacial variable on the surface?
the second question: how to get access to that variable from electric modeling to flow modeling?

Thanks a lot.

Ming