CFD Online Discussion Forums - Temperature-dependent emissivity for DOM boundary condition

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Temperature-dependent emissivity for DOM boundary condition

Hi, I am learning how to use buoyantSimpleRadiationFoam and looking at the tutorial
tutorials/heatTransfer/buoyantSimpleRadiationFoam/hotRadiationRoomFvDOM. In this tutorial a constant emissivity is used for DOM:

Code:

dimensions      [1 0 -3 0 0 0 0];



internalField   uniform 0;



boundaryField

{

    ".*"

    {

        type            greyDiffusiveRadiation;

        T               T;

        emissivity      0.5;

        value           uniform 0;

    }

}

I wonder how to modify it for temperature-dependent emissivity (i.e., polynomial functions of temperature). Thanks in advance!

Hi,

1) a quick and 'not recommended' option would to modify the boundary condition and recompile it

in the following file

src/thermophysicalModels/radiation/lnInclude/greyDiffusiveRadiationMixedFvPatchScalarField.C

you will find

refValue() =
emissivity_*4.0*radiation::sigmaSB.value()*pow4(Tp )
/Foam::mathematicalConstant::pi;

you can replace it by (e.g.)

emissivity_*(Tp/1000)*4.0*radiation::sigmaSB.value()*pow4(Tp)
/Foam::mathematicalConstant::pi;

where Tp is the wall temperature and 1000 a linear factor

you will need to recompile the boundary condition by executing "wmake libso" in the directory 'src/thermophysicalModels/radiation'

2) recommended method: read "Implement boundary condition" at http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2007/
It is explained how to copy the boundary condition (including .H file) in your own 'run' directory, modify it and recompile it.

I hope this helps...

Jean

Thanks for your help, Jean. I will follow your second suggestion.

Now I have another question about how to use temperature-dependent absorption coefficient. I am studying the case tutorials/heatTransfer/buoyantSimpleRadiationFoam/hotRadiationRoom. To use greyMeanAbsorptionEmision model, the radiationProperties dictionary was modified as

Code:

radiation       on;



radiationModel  P1;



noRadiation

{

}



P1Coeffs

{

}



// Number of flow iterations per radiation iteration

solverFreq 1;



absorptionEmissionModel greyMeanAbsorptionEmission;



greyMeanAbsorptionEmissionCoeffs

{

    lookUpTableFileName "speciesTable";

    EhrrCoeff           0.0;

}



scatterModel    constantScatter;



constantScatterCoeffs

{

    sigma           sigma [ 0 -1 0 0 0 0 0 ] 0;

    C               C [ 0 0 0 0 0 0 0 ] 0;

}

The speciesTable dictionary was created as well:

Code:

air

{

  Tcommon    300.;

  invTemp    true;

  Tlow        300.;

  Thigh        2500.;



  loTcoeffs

  (

    0

    0

    0

    0

    0

    0

  );

  hiTcoeffs

  (

    18.741

    -121.31e3

    273.5e6

    -194.05e9

    56.31e12

    -5.8169e15

  );



}

When I tried to run it, I got the following message:

Code:

keyword fields is undefined in dictionary "/home/navier/foam/buoyantSimpleRadiationFoam/hotRadiationRoom/constant/speciesTable"



file: /home/navier/foam/buoyantSimpleRadiationFoam/hotRadiationRoom/constant/speciesTable from line 20 to line 42.



    From function dictionary::lookupEntry(const word&, bool, bool) const

    in file db/dictionary/dictionary.C at line 388.



FOAM exiting

What's wrong/missing in my dictionaries? I know probably it's a simple problem but I am new in OF.