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-   -   How can I get mole fraction on boundary condition instead of mass fraction? (https://www.cfd-online.com/Forums/openfoam-pre-processing/243746-how-can-i-get-mole-fraction-boundary-condition-instead-mass-fraction.html)

alpercftc July 4, 2022 08:18
How can I get mole fraction on boundary condition instead of mass fraction?
 
This is my N2 initial conditions. But it's mass fraction. How can I get mole fraction on boundary condition instead of mass fraction?

Code:
/*--------------------------------*- C++ -*----------------------------------*\
  =========                |
  \\      /  F ield        | OpenFOAM: The Open Source CFD Toolbox
  \\    /  O peration    | Website:  https://openfoam.org
    \\  /    A nd          | Version:  9
    \\/    M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    format      ascii;
    class      volScalarField;
    location    "0";
    object      N2;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [0 0 0 0 0 0 0];

internalField  uniform 0.76162;

boundaryField
{
    inletfuel
    {
        type            fixedValue;
        value          uniform 0.74819;
    }
    inletair
    {
        type            fixedValue;
        value          uniform 0.76162;
    }
    outlet
    {
        type            inletOutlet;
        inletValue      uniform 0.76162;
        value          uniform 0.76162;
    }
    axis
    {
        type            empty;
    }
    leftside
    {
        type            zeroGradient;
    }
    burnerwall
    {
        type            zeroGradient;
    }
    burnertip
    {
        type            zeroGradient;
    }
    front
    {
        type            wedge;
    }
    back
    {
        type            wedge;
    }
}


// ************************************************************************* //

Tobermory July 6, 2022 12:04
When you say "how can I get" what do you mean? Do you want to:
- set the value on the fixedValue boundary as a mole fraction, rather than a mass fraction;
- or do you want to plot the value on another type of boundary, say an outlet, as a mole fraction?

If it's the first, then the short answer is that you cannot. You must supply the boundary conditions for the variables that the solver uses, and the solvers all work with mass fractions. Actually, if you were really set on using mole fraction, you COULD do it, but you'd have to write your own version of the solver, and add coding to do the input/output of the scalar fields as mole fraction, with the calculation still being done on a mass fraction basis. Doable, but messy.

If it's the latter, then that's just post-processing (ie converting mass to mole fractions).

alpercftc July 7, 2022 13:36
Quote:
If it's the first, then the short answer is that you cannot. You must supply the boundary conditions for the variables that the solver uses, and the solvers all work with mass fractions.
Dear Tobermory,
Thank your reply sir. I meant the first situation that setting the value on the fixedValue boundary as a mole fraction and got my answer.
Good day sir.


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