[Uday512]

I have 2 electrodes (solid anode electrode and solid cathode electrode) separated by electrolyte in between them. I have enabled UDS and specified conductivity for anode, cathode and electrolyte and outer surface of anode has potential BC (V = 10V) and outer surface of cathode has potential BC (V = 0v). I have got the potential distribution from anode to cathode through the electrolyte. Now, I have calculated current based on the potential drop. Now, I can calculate the velocity of chlorine gas produced on the surface of electrode( iM/nF.row) based on current obtained using UDF. I want to give the chlorine gas velocity BC at the interface of solid anode and fluid electrolyte and also at interface of solid cathode and fluid electrolyte (the arrow lines are interfaces as shown in image 1). How to give this velocity UDF at the interface wall? As you can see in the images, there is no UDS option visible at chlorine gas phase. Even the momentum tab is no slip as it is a wall. But I want chlorine gas bubble produced at the interface of anode and electrolyte based on the current at that interface. How to handle this?

pontetial drop in anode,electrolyte,cathode.png

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[Thore850]

I am not completely sure i completely understood your question, but the reason there is no UDS option is most probably because you defined your UDS equation in the mixture domain and not in the sub-domain of the chlorine gas mixture. (In Eulerian you always have a mixture (Top) domain and the sub-domains of the phases you defined, which in your case are chlorine gas and electrolyte)

If you want the UDS option in the chlorine gas you will have to change the phase in the UDS tab (see picture).

Regarding the question of the BC for the velocity, the only thing i can think of ist that you could calculate the mass source of chlorine gas using your current density (in kg m^-3 s^-1) and apply this source in the cell right next to the boundary wall. This will lead to a velocity field.

I hope this helps, good luck!

Best Regard

Thore

[Uday512]

Thank you for the reply. It helped me. If I define 4 UDS, one UDS for solid anode, one UDS electrolyte, one UDS for chlorine gas (which has zero electrical conductivity) and one UDS for solid cathode. The left end of anode has 10V and right end of cathode has 0V. So, will all the 4 UDS be coupled? like after solving UDS-0 in anode, the UDS-1 of electrolyte starts from the potential value obtained at the anode?

Also, If I have one UDS-0 solved for the mixture phase in all zones (solids and fluids) and if I give a UDF at the interface surface to the mixture phase itself (the UDF can be like taking potential values at the interface and calculate some drop in potential at the interface), does the UDS-0 defined for all zones, calculates taking potential after the UDF drop potential? or will it solve directly before hooking UDF potential value in electrolyte?

Regarding the vel BC, so I need to give mass source in the cell zone conditions tab for the cl2 gas which will add to the continuity equation and not to the UDS-scalar in source terms. Right?

Thank you!

[Thore850]

Hello,

regarding your first question:

No, the UDS will not be automatically coupled. If you want to solve it that way you will need to provide fittig boundary conditions for each UDS. I wouldnt recommend this approach, as it would be to complicated.

Regarding the second question:

I think what you are asking is the sequence in which fluent handles the calculations? This will depend on the Macros you are using, but if you utilize a DEFINE_ADJUST to calculate your potential drop and the provide the new potential value with a DEFINE_PROFILE on the boundary in your UDF you should be fine.

To your last question:

Yes you must provide this mass source to the chlorine gas phase not to the UDS.

[Uday512]

Thanks for the helpful suggestions! I will try the approach you suggested for the second question and keep you posted if I run into any issues.