[osha]

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:

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.

[osha]

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

Q=rho*Cp*(T-T_old)

which implies

T = T_old + Q/(rho*Cp)

So, I define injectionRateSuSp as

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.

[CI8]

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.

[agustinvo]

Hello

I am using semiImplicitSource and I have no problem. If you pay atention

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
     <Type>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 \<quantity\>
     - specific: values are given as \<quantity\>/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

[uosilos]

Originally Posted by agustinvo

Hello

I am using semiImplicitSource and I have no problem. If you pay atention

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
     <Type>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 \<quantity\>
     - specific: values are given as \<quantity\>/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:

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??