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Solver for Diffusion of Species

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Old   January 16, 2018, 05:15
Default Solver for Diffusion of Species
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manu ebn
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Hi to everyone

Could you please give me an advice to choose the right solver?

Case:
I have a domain which is filled with oxygen (< 200ppm) and nitrogen (>99.9%). Furthermore there is an outlet and an inlet.
Through the inlet pure nitrogen flows into the domain, at the outlet nitrogen flows out of the domain (with Reynoldsnumber lower than 50). But, and here comes the tricky part, oxygen flows from the environment into the domain (probably by diffusion) - at the end i would like to have a steady state solution (laminar).

I could simulate this with a scalarTransportFoam, but there wouldn't be any interaction between the different species and in a steady-state solution everything would be just nitrogen.

So which solver would you advice?

Thanks for every single answer!
Triggin
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Old   January 19, 2018, 15:28
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manu ebn
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If someone could help me with this one, i would be very thankful.

Like i sad, scalarTransport could be an option, but i would like to know if it's possible to solve the interaction of a binary mixture? I think it could be tricky, because to simulate the interaction of particels in flow is already demanding.

This information would already be helpful.

Best wishes
Triggin
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Old   January 22, 2018, 04:42
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Sebastian
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Hi Triggin,

I am a little bit confused. You are writing that you want to use scalarTransportFoam, however, later you write that you have interaction of particles. Usually scalarTransportFoam works with the concentration of the quantity of interest and not with single particles. Sticking to concentration, you might have to look for a multiphase flow solver. I don't know if interFoam could be a suitable solver for your case.
Concerning the inflow oxygen: If you can not model it as a classical inflow, you might add a source term, possibly using fvOptions.

Regards

Sebastian
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Old   January 22, 2018, 08:58
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manu ebn
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Hi Sebastian

Thank you for your comments.

Quote:
You are writing that you want to use scalarTransportFoam, however, later you write that you have interaction of particles. Usually scalarTransportFoam works with the concentration of the quantity of interest and not with single particles.
You are completely right. I a modified scalarTransport solver does it.

I am not very familiar with multi-gas simulations (therefore i also thought about reactingFoam - without reactions). I thought the different gases (nitrogen and oxygen) might interact and turbulences even at low reynoldsnumbers can occur.

But assuming that i have only a very low oxygen concentration and the flow is mainly influenced by nitrogen, i can use a modified scalarTransportFoam for steady state cases.

Quote:
Concerning the inflow oxygen: If you can not model it as a classical inflow, you might add a source term, possibly using fvOptions.
I used the following conditions, U-file:
Code:
    outlet
    {
      type              pressureInletOutletVelocity;
      value             $internalField;
    }
C-file for concentrations:
Code:
    outlet
    {
        type            inletOutlet;
        inletValue      uniform 0.23;
        value           $internalField;
     }
Therefore: If flow goes out of the domain, i will have zeroGradient, if air enters the domain it will enter with a concentration of 0.77 nitrogen (an consequently 0.23 oxygen).

Thank you for your comments!
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diffusion, laminar, nitrogen, solver, steady-state

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