Implementing Electrostatic Boundary Condition on Substrate

Alexander Castaneda Worcester Polytechnic Institute, Multi-Scale Heat Transfer Laboratory

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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.

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Alexander Castaneda


1 Reply Last Post Aug 30, 2024, 2:13 p.m. EDT
Robert Koslover Certified Consultant

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Posted: 2 months ago Aug 30, 2024, 2:13 p.m. EDT

Perhaps I am misunderstanding something in your problem description, but it seems to me that any good electrical conductor boundary will exhibit that boundary condition. So... just set/define it as a conductor. For example, a ground, a fixed electric potential, or a floating potential, whichever is more appropriate for your particular problem.

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Scientific Applications & Research Associates (SARA) Inc.
www.comsol.com/partners-consultants/certified-consultants/sara
Perhaps I am misunderstanding something in your problem description, but it seems to me that any good electrical conductor boundary will exhibit that boundary condition. So... just set/define it as a conductor. For example, a ground, a fixed electric potential, or a floating potential, whichever is more appropriate for your particular problem.

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