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Radiation boundary conditions

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Old   January 14, 2014, 05:01
Default Radiation boundary conditions
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Masoud Ami
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Dear All!
Hello. Hope you are fine and happy.

I am working on a case which is a vertical parallel plates channel. Walls are kept at different constant temperatures. I want to model turbulent radiation heat transfer in this geometery.

I wanted to know which boundary conditions i must use. I have to model the medium as participating and I want to change wall emissivities, optical thickness and scattering albedo in order to get results.

I wanted to know what the difference between Marshak radiation b.c. and greydiffusive radiation b.c. is. I should assume that walls are gray and diffusive (and also the medium) but I am somehow confused about these b.cs in openFOAM.

I would be really grateful if you please help me with this.

Thank you very much.
Mas
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Old   February 5, 2015, 09:41
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Pedro
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Hi,

Could you find a detailed explanation for this?
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Old   February 5, 2015, 21:50
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Alex
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Hi all!

·MarshakRadiation (Do not click here if you do not want to learn where to find info on your own!)
Code:
Group
    grpThermoBoundaryConditions
Description
    A 'mixed' boundary condition that implements a Marshak condition for the
    incident radiation field (usually written as G)
    The radiation temperature is retrieved from the mesh database, using a
    user specified temperature field name.
    \heading Patch usage
    \table
        Property     | Description             | Required    | Default value
        T            | temperature field name  | no          | T
    \endtable
    Example of the boundary condition specification:
    \verbatim
    myPatch
    {
        type            MarshakRadiation;
        T               T;
        value           uniform 0;
    }
    \endverbatim
·GreyDiffusive (Never click here! You could even find useful info...)
Code:
Description
    This boundary condition provides a grey-diffuse condition for radiation
    intensity, \c I, for use with the finite-volume discrete-ordinates model
    (fvDOM), in which the radiation temperature is retrieved from the
    temperature field boundary condition.
    \heading Patch usage
    \table
        Property     | Description             | Required    | Default value
        T            | temperature field name  | no          | T
        emissivityMode | emissivity mode: solidThermo or lookup | yes |
    \endtable
    Example of the boundary condition specification:
    \verbatim
    myPatch
    {
        type            greyDiffusiveRadiation;
        T               T;
        emissivityMode  solidThermo;
        value           uniform 0;
    }
    \endverbatim
·GreyDiffusiveViewFactor (You shall not clik! Gandalf dixit)
Code:
Description
    This boundary condition provides a grey-diffuse condition for radiative
    heat flux, \c Qr, for use with the view factor model
    \heading Patch usage
    \table
        Property     | Description             | Required    | Default value
        Qro          | external radiative heat flux | yes    |
        emissivityMode | emissivity mode: solidThermo or lookup | yes |
    \endtable
    Example of the boundary condition specification:
    \verbatim
    myPatch
    {
        type            greyDiffusiveRadiationViewFactor;
        Qro             uniform 0;
        emissivityMode  solidThermo;
        value           uniform 0;
    }
    \endverbatim
You could even find it inside your own computer!

Code:
find $FOAM_SRC -name Marshak*
Code:
find $FOAM_SRC -name greyDiffusive*
Enjoy it!

Regards,

Alex
__________________
Web site where I present my Master's Thesis: foamingtime.wordpress.com

The case I talk about in this site was solved with chtMultiRegionSimpleFoam solver and involves radiation. Some basic tutorials are also resolved step by step in the web. If you are interested in these matters, you are invited to come in!
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