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electroosmotic switching
Posted Sep 19, 2014, 2:34 p.m. EDT Low-Frequency Electromagnetics, Microfluidics Version 4.4 1 Reply
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I am a couple weeks new to COMSOL, so please do not take for granted that I know even the basics.
Now I am trying to model electroosmotic flow in a Y/T-channel. I have been able to model flow, but I have failed to produce a model for switching the flow back and forth from one side of the Y/T-channel to the other as a function of time. For this I need to alternate the potentials on the two inlets between some value, say 100V, and floating. I found a couple other posts (linked below) with this same question but no solution was found. Has anyone been able to find a solution?
www.comsol.com/community/forums/general/thread/39614/
www.comsol.com/community/forums/general/thread/623/
Now I am trying to model electroosmotic flow in a Y/T-channel. I have been able to model flow, but I have failed to produce a model for switching the flow back and forth from one side of the Y/T-channel to the other as a function of time. For this I need to alternate the potentials on the two inlets between some value, say 100V, and floating. I found a couple other posts (linked below) with this same question but no solution was found. Has anyone been able to find a solution?
www.comsol.com/community/forums/general/thread/39614/
www.comsol.com/community/forums/general/thread/623/
1 Reply Last Post Sep 24, 2014, 2:36 p.m. EDT
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Posted:
1 decade ago
I have spent a full day on this problem since my last post, but have failed to make any progress. I would like to restate the problem for clarity and then discuss a possible workaround.
Problem: I need to set a boundary condition such that for example at time (t) t = t0 the boundary has electrical potential value V1, at t = t1 the boundary has a value V2, and at t=t3 a value V3 and so on. Here V1, V2, V3, etc. can be some specified voltage, ground, or floating. The main issue is I can’t figure out how to transition the boundary between floating and not floating.
Possible workaround: I can solve a model that produces EO flow on one side of the Y/T-channel and use the calculated velocity in a separate model. In a second model (different .mph file) everything is the same except I do not have EO flow (no electric current physics). Instead the inlet has a velocity boundary condition (in the first model I use pressure, no viscous stress with 0 pressure), and I use a Heaviside function to switch the flow on and off at that inlet using something like (2e-5)*flsmhs(t-2000,0.1) in the velocity field. Other than not being a very good work around, I get “Nonlinear solver did not converge” error in segregated group 2 at time: 0. There are several post on problems with Heaviside functions in COMSOL, but I have not come across a solution that works for me yet.
I would love to hear any solution to transitioning a boundary between floating and not floating, a better work around than what I have proposed, or a possible reason why my workaround is failing to converge.
Problem: I need to set a boundary condition such that for example at time (t) t = t0 the boundary has electrical potential value V1, at t = t1 the boundary has a value V2, and at t=t3 a value V3 and so on. Here V1, V2, V3, etc. can be some specified voltage, ground, or floating. The main issue is I can’t figure out how to transition the boundary between floating and not floating.
Possible workaround: I can solve a model that produces EO flow on one side of the Y/T-channel and use the calculated velocity in a separate model. In a second model (different .mph file) everything is the same except I do not have EO flow (no electric current physics). Instead the inlet has a velocity boundary condition (in the first model I use pressure, no viscous stress with 0 pressure), and I use a Heaviside function to switch the flow on and off at that inlet using something like (2e-5)*flsmhs(t-2000,0.1) in the velocity field. Other than not being a very good work around, I get “Nonlinear solver did not converge” error in segregated group 2 at time: 0. There are several post on problems with Heaviside functions in COMSOL, but I have not come across a solution that works for me yet.
I would love to hear any solution to transitioning a boundary between floating and not floating, a better work around than what I have proposed, or a possible reason why my workaround is failing to converge.