Discussion Forum

Hi

What kind of geometry do you wish? Electroanalysis module has cyclic voltammetry as a ready-made component.

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Lasse

Hi Lasse,
As I mentioned I want to model channel flow cell (30*4*1 mm) in which I am able to study cyclic voltamogram at different flow rates. I saw Electroanalysis module which has this capability however I need to couple it with another module in which cover hydrodynamic feature of this model. I don't know which module exactly I need to buy and work with.
Thanks for your help.

Add a laminar flow module. Solve the laminar flow at steady-state and then use that solution as the flow field in the diffusion module where you must activate the convection feature by checking the corresponding box. In the cyclic voltammetry (CV) solver settings there is a selection for variables not solved by the CV solver. Use there the steady-state solution.

I made quickly a model (attached) but I have not tested if it also works. Convective diffusion is known as a very difficult problem for numerical solutions, convergence can be quite slow. Please try the model and modify it according to your needs, I can try to help further if so wished.

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Lasse

Yes, it works, but the solution takes ca. 1 hour.

Hi
Thanks for your help.
I can run study 1 which is cyclic voltammogram. In both study I found that just cyclic option is selected. when I select cyclic voltamogram under laminar flow I am not able to get any result!
what is the problem?

The solution method is that you first solve the flow profile which is in steady-state, i.e. a steady-state solver is used. Then this flow profile is used as the convective term of the transport equations which is solved in transient (cyclic voltammetry) conditions. If you try to solve both the laminar flow and cyclic voltammetry with the time-dependent solver, then also the flow profile is calculated afresh, but the time-dependent Navier-Stokes equation is, first, very hard to converge and, second, against the physics of your problem, the solution flow is at steady-state.

best regards
Lasse

Hi,
I did it and it works for your design. But I changed base on my geometry in which electrode is located in the middle of channel.
But I run it and I haven't get any result!
In addition, is there any way to find how much simulation is done and how much is remaining? (Or time for computing)
Thanks
Fereshteh

Could you please export your geometry, or the entire model (minus the results data). Electrode in the centre of the channel may cause turbulence.

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Lasse

Hi
Attached is my design.

Hi

I got the solution, but it took almost 2.5 hours. I noticed a funny thing: progress percentage did not advance from 0%, which may have caused you to think that the calculation does not proceed at all. But the time is advancing from which you can see the progress. As I mentioned earlier, a convective diffusion equation is notoriously difficult to solve.

best wishes
Lasse

Thank you very much.
Although I run my simulation over night, I don't get any results yet. I think I have problem with my computer (Core i5- Ram:16GB). Is there any way to find remaining time for computing?

Thanks

I have only 8GB RAM! I have no idea how to estimate the remaining time, or why your calculation takes so long.

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Lasse

Hi Lassy,

I am working with trial version in which all modules are available. Now I want to buy the software. I found that in order to run simulation like this, I need different module. One is Electroanalysis and Laminar flow. So I don't know which module exactly I need to buy since packages are different in category. Would you please kindly advice me the right module for this simulation? In addition to that in future I need to run the same model at high temperature. If I want it, which extra module works in this situation?

Moreover, In this software I found that I can simulate this reaction with all of these condition, only if I introduce all parameters. One of the parameter which is needed for reaction on the electrode surface is “reaction rate”, which is needed to put a value in software. While this is what I am trying to find for different redox couples (or when reaction rate is unknown). The question is that how I can input experimental results and get reaction rate (for ex.).
In addition, Is there any way to optimist results? For instance, I am doing some experiment meanwhile I am doing simulation, so I want to compare this results. Thus I figure out that reaction rate or diffusion at that temperate needs to be verified. Indeed, I want to know how I can make a loop to optimize simulation parameter to get the same results as I get from experiment.

Thank you in advance
Fereshteh,

Look at www.comsol.com/products

You'll need CFD and Electrochemistry modules. Changing temperature does not require any extra module. I have never done optimization, hence I cannot say anything about that. For the determination of the rate constants I would not use a channel flow cell but an ordinary microelectrode with cyclic voltammetry or impedance spectroscopy. You should look at electrochemistry textbooks how rate constants are determined from these experiments.

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Lasse

Hi Lasse,
Regarding to our previous discussion about modules which I need for running hydrodynamic electrode simulation, you suggest CFD for fluid condition. I checked Electrochemistry module and it has a term "Flow in free and porous media". Can I use just one module (Electrochemistry) for my simulation, since I have problem with money and I want to reduce the number of module.

Hi

I do not know what that means because I haven't seen such functionality in the Electrochemistry Module. Yes, I saw the same text. You'd better ask your national dealer,

Lasse

Hi Lasse
I am wondering if you could please help me in meshing the geometry.
Would you please explain why you select this meshing for this simulation?
Moreover, I want to add a boundary condition (exactly before the electrode, and y between 0 and height of channel (h), concentration is C _bulk . I add an surface but I am not able to get result.
It would be highly appreciate if you could please take a look at my simulation.
Thanks for you time.
Fereshteh

Cannot open because I am using 5.0.

Lasse

I got some result but limiting current is not what I expect to get.
I choose automatic meshing here in this results.

Hi Lesse
I think I found it's problem. it is all about meshing. If I choose good meshing the answer will be close to what I am looking for. But I run to a problem. when I increase the flow rate to ml, there will be an error in simulation (laminar).
"Failed to find a solution.
Maximum number of Newton iterations reached.
There was an error message from the linear solver.
Very ill-conditioned preconditioner.
The relative residual is more than 1000 times larger than the relative tolerance.
Returned solution is not converged"

Would be please advise me in this case?
Thank you very much.
Fereshteh

Which one was unsuccesful, laminar flow or cyclic voltammetry? At which flow rate?

Laminar Flow.
actually I run 4 and 6 ml/min (v_in=V/0.04) and I got a good results. however I increased the flow rate to 8 ml/min and this error comes up.
Thanks alot

Try this (attached). I updated to version 5.1.

The idea of meshing is that close to the electrode very dense mesh is needed to reach better accuracy in current calculation. Swept mesh with distribution highlights the fact that the flow profile is parabolic and close to the boundaries changes are the largest. In y direction the mesh does not need to be very dense, except close to the electrode.

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Lasse