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Problem about water spliting chemical reaction !!

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Old   May 31, 2006, 15:53
Default Problem about water spliting chemical reaction !!
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Luke
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Hellow~ I try to do the water spliting with two electrodes. The considering equations are below: anode: H2O --> 1/2 O2 + 2 H+ cathode: 2H+ --> H2

Does anybody ever do this problem? Can you get me some suggestion and discussion for this problem?

Thank you ~
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Old   June 4, 2006, 03:18
Default Re: Problem about water spliting chemical reaction
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Swarup
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Is it purely mass transfer problem without any convective flows?
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Old   June 4, 2006, 23:41
Default Re: Problem about water spliting chemical reaction
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Luke
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It contains the heat and mass transfer, include convective flows.
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Old   June 6, 2006, 07:54
Default Re: Problem about water spliting chemical reaction
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Swarup
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Reactions appear to be localized to two zones. Diffusivity specification appears critical and you have to use Nernst equation for diffusivity calculation. I am not sure what kind of convective flow you have but are you also interested in knowing what happens around solid electrodes? That will be an added complication. If you are also considering whether water level falls down then you need to look at interface and this is additional detail.

Swarup.
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Old   June 6, 2006, 14:39
Default Re: Problem about water spliting chemical reaction
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Luke
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Thank you for your reply. I can do the reaction with two electrodes and H2 + O2 can be produced. But I want to see the water temperature convected by the outside air. So I set the water face to the "WALL" and select the "CONVECTION" to the WALL boundary. It can show the convection at the wall boundary, but the H2 and O2 can not release at the wall. Do you have any approach to set the boundary of the water face?

THX.
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Old   June 12, 2006, 23:26
Default Re: Problem about water spliting chemical reaction
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Swarup
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Hi,

I regret late reply.

You are talking about "interphase/interface mass transfer" and hence you need to take care of mass balance. Is there any boundary condition which will allow you to specify outgoing mass flux using a formula very similar to Fourier's law? This is a lumped model of the form mass_flux=k*(Cin-Cout). You should consult a mass transfer related book (Bird-Stewart-Lightfoot will do) for more details. k is called mass transfer coefficient. Any such boundary will also allow to specify heat loss I guess in the form of a "SINK" or through temperature.

Another approach may be to look for a multiphase model. I will try this first as it is fundamentally more appealing and also may be easy to do. V6.2 allows reaction in virtually all models now. Choose a suitable one based on Model Compatibility in Manual.

Note that you can model your reactions in terms of source terms also distributed locally. This is the classic segregation of terms in transport equations.

Regards. Swarup.

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