Hi all, new to the forum so sorry if I'm asking a repeat question.
I have to simulate the transport of a dilute species in a small fluid flow device that houses electrodes.
I have to set it so that initial conditions concentration of solution is 0 and body is filled with water then have an inflow (set at 1mol/m^3) and see how the concentration changes across the face of the electrode over time (time period is set at 30sec). It's a laminar flow situation.
I started with a 2D axis-symmetric model without the electrodes to view the velocity behavior, time to flush system (starting at c =1 ending at c=0) and time taken to reach a overall steady state concentration with my given fluid velocity. I used a parameter sweep to make small changes to the geometry so that I could figure out which one would be an appropriate starting point for the 3D model.
Once this worked I created a 3D model that is 1/4 of the full model with 2 planes of symmetry. This also solved successfully though there are other minor problems to be addressed at the end of this thread.
For both of the above steps I used a physics defined mesh set at coarse just for a proof of concept.
Once I added one of the 3 electrodes I keep getting an error message from the mesh having inverted elements. I looked at a user controlled mesh but my skills in FEA is novice at best so I had no idea what to truly change. I think the problem is the electrode is quite big for the chamber and there is a very tight space between a few of the boundary layers.
My method of drawing the "electrode" was simply to draw it's geometry and subtract it from the fluid domain. My other alternative was actually drawing the electrode geometry and adding a solid material. Neither of the above methods worked so I'm not sure what's the correct way to go about it when I simply want to measure solution concentration on the face of the electrode.
For the 3D model without the electrode I have another problem I mentioned above. I used parameters in both 2D and 3D model to define geometric measurements and values such as velocity and diffusion coefficients. in the 2D model everything ran fine but with 3D when I use my defined parameter as velocity it keeps giving me an error of the solution not converging, when I enter a value for velocity it seems to work fine. I have tried to replicate the settings for fluid flow and transport of dilute species in the 3D model exactly as I had it in the 2D model but it does not work. I have to enter the actual velocity in the velocity box and cannot use my assigned v parameter.
My third problem is when I solve for just fluid flow I can go through the time steps and see the change in velocity of the fluid as time progresses. When I've solved for both fluid flow and transport of a dilute species I cannot do this for velocity and it only shows the plot of a steady state velocity. Plots for concentration works. If it helps I have it set up as one study but 2 steps, step 1 solves for velocity and step 2 solves for transport.
Sorry I know it's a lot but it's for my bachelor's thesis and I am really having a hard time teaching myself how to use COMSOL. I will attempt to attach files if that will help.
I have to simulate the transport of a dilute species in a small fluid flow device that houses electrodes.
I have to set it so that initial conditions concentration of solution is 0 and body is filled with water then have an inflow (set at 1mol/m^3) and see how the concentration changes across the face of the electrode over time (time period is set at 30sec). It's a laminar flow situation.
I started with a 2D axis-symmetric model without the electrodes to view the velocity behavior, time to flush system (starting at c =1 ending at c=0) and time taken to reach a overall steady state concentration with my given fluid velocity. I used a parameter sweep to make small changes to the geometry so that I could figure out which one would be an appropriate starting point for the 3D model.
Once this worked I created a 3D model that is 1/4 of the full model with 2 planes of symmetry. This also solved successfully though there are other minor problems to be addressed at the end of this thread.
For both of the above steps I used a physics defined mesh set at coarse just for a proof of concept.
Once I added one of the 3 electrodes I keep getting an error message from the mesh having inverted elements. I looked at a user controlled mesh but my skills in FEA is novice at best so I had no idea what to truly change. I think the problem is the electrode is quite big for the chamber and there is a very tight space between a few of the boundary layers.
My method of drawing the "electrode" was simply to draw it's geometry and subtract it from the fluid domain. My other alternative was actually drawing the electrode geometry and adding a solid material. Neither of the above methods worked so I'm not sure what's the correct way to go about it when I simply want to measure solution concentration on the face of the electrode.
For the 3D model without the electrode I have another problem I mentioned above. I used parameters in both 2D and 3D model to define geometric measurements and values such as velocity and diffusion coefficients. in the 2D model everything ran fine but with 3D when I use my defined parameter as velocity it keeps giving me an error of the solution not converging, when I enter a value for velocity it seems to work fine. I have tried to replicate the settings for fluid flow and transport of dilute species in the 3D model exactly as I had it in the 2D model but it does not work. I have to enter the actual velocity in the velocity box and cannot use my assigned v parameter.
My third problem is when I solve for just fluid flow I can go through the time steps and see the change in velocity of the fluid as time progresses. When I've solved for both fluid flow and transport of a dilute species I cannot do this for velocity and it only shows the plot of a steady state velocity. Plots for concentration works. If it helps I have it set up as one study but 2 steps, step 1 solves for velocity and step 2 solves for transport.
Sorry I know it's a lot but it's for my bachelor's thesis and I am really having a hard time teaching myself how to use COMSOL. I will attempt to attach files if that will help.