Discussion Forum

Hello,

I am trying to accurtely model electrohydrodynamic conduction pumping in 2D in COMSOL. I have had good success with modeling this when I assume the surface charge density on the substrate layer is set to zero. The substrate layer is the non-conducting material between adjacent conducting electrodes, and is typically electrically insulative. Please note that all other aspects of the model are working correctly (laminar flow, ionic species transport, phase-field, etc.).

In literature, a more accurate electrostatic boundary condition is as follows:

n・∇ɸ = ?_s /?

where ɸ is the potential, ?_s is the surface charge, and ? is the absolute permittivity of the working fluid. This essentially says that the normal dotted with the gradient of potential, is equal to the surface charge over the permittivity. I can solve for values for surface charge and I know the permittivity and applied voltage.

My issue arises in implementing this boundary condition on the substrate in COMSOL under the electrostatics module. I cannot find any built in boundary condition that would accomplish this, nor do I know how to implement this onto the substrate as a custom boundary condition. I tried to write it as an analytical function in the definitions tab at the start of the model, but I am struggling to correctly do this as well.

Any guidance on this would be extremely helpful! Thank you! A screenshot of my electrostatics section of my model is attached.