[NBad]

Hi everyone!

I'm in desperate need of help!

I set up a case in which a cylindrical heating element 2 cm in diameter and 4 cm long is heated with a power of 404 W and irradiates the surroundings.

The heater is surrounded by vacuum (modeled as air with very low kappa and cp, frozen flow), and everything is enclosed in a reradiating furnace wall, except that two stripes of this wall are actually held at 600K and so absorb all the exceding heat.

I used fvDOM as radiation model.

The analytical calculation shows that the heater, which is made of silicon carbide, should heat up at a rate of 52 K/s, while calculation with cht shows a heating of only 8K/s, which is much lower.

The setup can be seen in the image I attached (PS there is a mesh in between the heater and the external wall)

I'll post here the configuration files related to the heating element:

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant/heater";
    object      fvOptions;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //
heatSource 
{ 
    type            scalarSemiImplicitSource; 
    active          true;  
    scalarSemiImplicitSourceCoeffs 
    { 
		selectionMode       all;
        volumeMode      	absolute; //specific;//absolute; 
        injectionRateSuSp 
        { 
			rho (3200 0); //TODO: is this required?
            h (404 0); //TODO: 404 W is this the right unit?
		}
	}
}
//************************************************************************* //

Here I set up a heat source for the heating element

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       dictionary;
    location    "constant/solid";
    object      thermophysicalProperties;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

thermoType
{
    type            heSolidThermo;
    mixture         pureMixture;
    transport       constIso;
    thermo          hConst;
    equationOfState rhoConst;
    specie          specie;
    energy          sensibleEnthalpy; //sensibleEnthalpy;
}

mixture
{
    // Silicon carbide

    specie
    {
        molWeight       1000;		
    }
    equationOfState
    {
        rho             3200;//3200; //g/cm2		
    }
    transport
    {
        kappa           120;//120; //W/cm*K	
    }
    thermodynamics
    {
        Hf              0;
        Cp              190;	//J/(g*K)	
    }
}

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

And here are the thermophysical properties of the heating element.

/*--------------------------------*- C++ -*----------------------------------*\
  =========                 |
  \\      /  F ield         | OpenFOAM: The Open Source CFD Toolbox
   \\    /   O peration     | Website:  https://openfoam.org
    \\  /    A nd           | Version:  7
     \\/     M anipulation  |
\*---------------------------------------------------------------------------*/
FoamFile
{
    version     2.0;
    format      ascii;
    class       volScalarField;
    location    "0/solid";
    object      T;
}
// * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * //

dimensions      [ 0 0 0 1 0 0 0 ];

internalField   uniform 300;

boundaryField
{
    #includeEtc "caseDicts/setConstraintTypes"

    front_cyc
    {
        type            cyclic;
    }

    back_cyc
    {
        type            cyclic;
    }

    heater_to_air
    {
        type            compressible::turbulentTemperatureRadCoupledMixed;
        value           uniform 300;
        Tnbr            T;
		T				T;
        kappaMethod     solidThermo;
        qrNbr           qr;
        qr              none;
/*		type			zeroGradient;*/
    }
}


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

Last but not least the boundary condition file that couples temperature in this solid to radiation in the neighbour solid.

the whole case can be found here:
https://drive.google.com/open?id=1xi...5dn-LkhGKw7QKl

Any idea of what could be causing this issue? Wrong unit in the thermophysical properties? Wrong injection of heat?

Please help!

[crubio.abujas]

Hi Nicoló,

I think the heatSource may have different units. The field h is defined inside the source code as solidThermo::he, which have units of [J/kg]. So the rate of change may be [W/kg] if the volumeMode is absolute, as it seems your case. If that is correct and you want the cylinder to provide 404W, you need to set the scalarSemiImplicitSource to be around 5050 W/kg (according to some rough calculations).

That is in the order of the error you mentioned, so may be reasonable to try.
Hopes it helps!

[NBad]

Hi Crubio!

Turns out that the units were right, but there was an error in the fvSolution file, that was making my solver use the PGC algorithm for the solution of the enthalpy equation instead of GAMG.

All solved now!