# Heat source using fvOptions in laplacianFoam

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July 17, 2014, 08:09
Heat source using fvOptions in laplacianFoam
#1
New Member

Kalli
Join Date: Jul 2014
Posts: 9
Rep Power: 9
Hello Foamers,

I am working on a solid conduction problem using laplacianFoam where I wish to add a heat generation term Q [W/m^3] on selected cells (using topoSet) in the mesh. I have modified the laplacianFoam in following way:

Quote:
 fvm::ddt(T) - fvm::laplacian(DT, T) - fvOptions(T)
But I need to apply the heat generation term which I intend to keep constant. I am not sure how I achieve that with the above formulation.

After reading on fvOptions, I realized that I could use scalarExplicitSetValue to define a scalar explicit source. But this method will only fix temperature in the selected cellZone whereas I intend to fix the heat generation rate.

I do not intend to define the heat generation region in geometry this is why fvOption is more suitable for my problem. I am looking forward to your insights.

Thank you.

July 17, 2014, 10:32
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#2
New Member

Kalli
Join Date: Jul 2014
Posts: 9
Rep Power: 9
As I was digging further I glanced upon semiImplicitSource and tried to use it. I am not sure if my formulation is right as my results are highly non-physical.

Here is what I tried. The heat generation rate Q [W/m^3] can be written as

Quote:
 Q=rho*Cp*(T-T_old)
which implies

Quote:
 T = T_old + Q/(rho*Cp)
So, I define injectionRateSuSp as

Quote:
 T (Q/(rho*Cp) 1<---[for T_old] )
Do you think the above method make sense?

Though, I am not sure as the temperature field gives out unreal numbers. The absolute temperature goes down to 0.

Any insight will be much appreciated.

Thank you.

 March 21, 2017, 11:32 #3 New Member   Edoardo Cascioli Join Date: Mar 2017 Posts: 3 Rep Power: 6 Have you found another solution? I used scalarExplicitSetValue for the same purpose, but I have also achieved constant temperature field with no iterations for the temperature equation during the simulation. I was intended to set a average temperature field for the energy balance for my cyclic pipe flow case with incompressible fluid.

 March 22, 2017, 09:05 #4 Senior Member   Agustín Villa Join Date: Apr 2013 Location: Fuenlabrada Posts: 282 Rep Power: 12 Hello I am using semiImplicitSource and I have no problem. If you pay atention Code: ```Description Semi-implicit source, described using an input dictionary. The injection rate coefficients are specified as pairs of Su-Sp coefficients, i.e. \f[ S(x) = S_u + S_p x \f] where \vartable S(x) | net source for field 'x' S_u | explicit source contribution S_p | linearised implicit contribution \endvartable Example of the source specification: \verbatim SemiImplicitSourceCoeffs { volumeMode absolute; // specific injectionRateSuSp { k (30.7 0); epsilon (1.5 0); } } \endverbatim Valid options for the \c volumeMode entry include: - absolute: values are given as \ - specific: values are given as \/m3``` Once you know your heat source, you should divide by rho and Cp so you get the units of your equation. Take a look in the units of your heat source, if it is absolute (W) or specific (W/m3). Haveing a fixed heat source, just do as above, set T (Q/(rho*Cp) 0); PS:hello again Edoardo

October 27, 2020, 05:28
#5
New Member

UOCFD
Join Date: Oct 2020
Posts: 27
Rep Power: 3
Quote:
 Originally Posted by agustinvo Hello I am using semiImplicitSource and I have no problem. If you pay atention Code: ```Description Semi-implicit source, described using an input dictionary. The injection rate coefficients are specified as pairs of Su-Sp coefficients, i.e. \f[ S(x) = S_u + S_p x \f] where \vartable S(x) | net source for field 'x' S_u | explicit source contribution S_p | linearised implicit contribution \endvartable Example of the source specification: \verbatim SemiImplicitSourceCoeffs { volumeMode absolute; // specific injectionRateSuSp { k (30.7 0); epsilon (1.5 0); } } \endverbatim Valid options for the \c volumeMode entry include: - absolute: values are given as \ - specific: values are given as \/m3``` Once you know your heat source, you should divide by rho and Cp so you get the units of your equation. Take a look in the units of your heat source, if it is absolute (W) or specific (W/m3). Haveing a fixed heat source, just do as above, set T (Q/(rho*Cp) 0); PS:hello again Edoardo

I have to use a source, the only data is that it is a ignitor of 10kJ.

I am doing it now as:
Code:
```type            semiImplicitSource;

timeStart       0;
duration        1;
selectionMode   cellSet;
cellSet         ignitionCells;

volumeMode      absolute;

sources
{
h
{
explicit 1e4;
implicit 0;
}
}```

I'm obtaining so high temperatures, is it being set properly? how can I estimate the duration of the source??

 Tags conduction, fvoptions, heat generation rate, laplacianfoam