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-   -   Radiation boundary conditions (https://www.cfd-online.com/Forums/openfoam-pre-processing/128497-radiation-boundary-conditions.html)

MasAmi January 14, 2014 04:01
Radiation boundary conditions
 
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

pedrojrebelo February 5, 2015 08:41
Hi,

Could you find a detailed explanation for this?

zfaraday February 5, 2015 20:50
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


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