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Time Varying Heat Flux for Internal Energy Boundary Condition

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Old   October 5, 2017, 08:34
Default Time Varying Heat Flux for Internal Energy Boundary Condition
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fouad abi
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Dear All,

I am working on a solver that computes the energy dissipation, from an external heat source, in a confined Liquid Helium channel, and the energy equations are solved with Specific Internal Energy as the "main variable". The temperature field and the thermodynamic properties are computed using thermodynamic libraries at every time step, and a custom PISO loop was developed for this purpose.

The geometry of the problem at hand is quite simple, with a narrow channel (in middle) connecting two baffles (right and left), the whole region being filled with Liquid Helium. A certain (time depending) heat flux is generated through both the upper and lower boundaries of the channel, and this energy is dissipated in the L. Helium towards the end baffles.

I managed to build a solver that runs simple cases where the heat flux is constant using the default BC:
Code:
hell_channel_to_solid2
    {
        type                     externalWallHeatFluxTemperature;
        kappa                    lookup;
        q                        uniform 1e7;  //Boundaries S=1e-3 [m2]; Q=1e-4 [W.m-2]
        //Ta                     uniform 20.0;
        //h                      uniform 10.0;
        thicknessLayers          (1.5e-3);
        kappaLayers              (8.5634e-1);
        value                    uniform 15.0;
        kappaName                kEff;
        Qr                       none;
        relaxation               no;
    }
But I can't find a way to make this "q" time varying. If anyone has a suggestion and/or can guide me through the process that would be highly appreciated.

I have a question also, I'm not sure what is the "value uniform 15.0" supposed to be, I re-used it from an existing case, does anyone have an answer to that?


Thanks a lot !
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Old   March 21, 2019, 13:49
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Chenguang Li
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Hi I have same problem. Is there any solution for this? Thank you!
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Old   April 15, 2019, 05:42
Post KappaLayers definition
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vamshi
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If I want to define one layer of material with thermal conductivity in externalWallHeatFluxTemperature Boundary condition, The following error appears in paraview

ERROR: In C:\bbd\7cc78367\build\superbuild\paraview\src\VTK\ IO\Geometry\vtkOpenFOAMReader.cxx, line 7486
vtkOpenFOAMReaderPrivate (000001E93C169D60): Error reading line 13270 of D:\latest\baffledtower\newPit8\20/T: Unmatched )

In the source code the syntax is given as

Description
This boundary condition applies a heat flux condition to temperature
on an external wall in one of three modes:

- fixed power: supply Q
- fixed heat flux: supply q
- fixed heat transfer coefficient: supply h and Ta

where:
\vartable
Q | Power [W]
q | Heat flux [W/m^2]
h | Heat transfer coefficient [W/m^2/K]
Ta | Ambient temperature [K]
\endvartable

For heat transfer coefficient mode optional thin thermal layer resistances
can be specified through thicknessLayers and kappaLayers entries.

The thermal conductivity \c kappa can either be retrieved from various
possible sources, as detailed in the class temperatureCoupledBase.

The ambient temperature Ta is specified as a Foam::Function1 of time but
uniform is space.

Usage
\table
Property | Description | Required | Default value
mode | 'power', 'flux' or 'coefficient' | yes |
Q | Power [W] | for mode 'power' |
q | Heat flux [W/m^2] | for mode 'flux' |
h | Heat transfer coefficient [W/m^2/K] | for mode 'coefficent' |
Ta | Ambient temperature [K] | for mode 'coefficient' |
thicknessLayers | Layer thicknesses [m] | no |
kappaLayers | Layer thermal conductivities [W/m/K] | no |
relaxation | Relaxation for the wall temperature | no | 1
emissivity | Surface emissivity for radiative flux to ambient | no | 0
qr | Name of the radiative field | no | none
qrRelaxation | Relaxation factor for radiative field | no | 1
kappaMethod | Inherited from temperatureCoupledBase | inherited |
kappa | Inherited from temperatureCoupledBase | inherited |
\endtable

Example of the boundary condition specification:
\verbatim
<patchName>
{
type externalWallHeatFluxTemperature;

mode coefficient;

Ta constant 300.0;
h uniform 10.0;
thicknessLayers (0.1 0.2 0.3 0.4);
kappaLayers (1 2 3 4);

kappaMethod fluidThermo;

value $internalField;
}

What if my geometry has only one thickness material??
How to define thicknessLayers and kappaLayers .

I defined it as

shellw
{
type externalWallHeatFluxTemperature;
mode coefficient;
Ta constant 320;
h uniform 13;
thicknessLayers ( 0.005 );
kappaLayers ( 45 );
kappa none;
kappaMethod fluidThermo;
value uniform 318;
}

This one gives above stated error.. Please respond..
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Old   April 18, 2019, 10:47
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hi all


i have a problem with heat flux varying coductivty ... and finally i used the groovy bc for this purpose ..my bc is :

heater

{

type groovyBC;

valueExpression "325.15";

gradientExpression "q/(K1*alpha1+K2*(1.0-alpha1))";

fractionExpression "0";

variables "q=14000;K1=0.06;K2=0.01;";

timelines ();

value uniform 327.15;

}
perhaps this bouandry condition can help you

best
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Old   March 12, 2020, 13:57
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Raj Niraj Patil
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Hi regard,

Thank you for the answer but I have some doubts.



1]When we set it as groovyBC, are we making it partial derivative there or we need to specify fractionExpression to be 0 for that.


2]For your case you have used fractionExpression to be 0, so it is using only gradientExpression. So, what is your left hand side of the gradient equation? Is it the normal derivative of the temperature?


It will be kind of you if you explain the actual physics represented by these all terms in this BC.


thank you in advance.


regards,
Raj

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Old   July 24, 2021, 08:50
Default Varying Heat Flux
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Shailesh
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Dear Fellow,
How to give varying heat flux with respect to temperature in CFD?
Kindly, provide solution?
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Old   July 24, 2021, 08:53
Default Varying Heat Flux problems
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Shailesh
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Dear Fellow,
How to give varying heat flux with respect to temperature and time in CFD?
Kindly, provide solution?
Udf code for unit step or (Heaviside function) function in variable heat flux (Y-axis, Temperature Vs X-axis, Time)
please provide with udf code
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Last edited by Yadav067; August 10, 2021 at 02:50.
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Old   March 7, 2022, 12:29
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Gerhard Holzinger
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Quote:
Originally Posted by vamshinallan View Post
If I want to define one layer of material with thermal conductivity in externalWallHeatFluxTemperature Boundary condition, The following error appears in paraview

...

I managed to receive a similar error message by ParaView with a CHT case in which I used the externalWallHeatFluxTemperature BC.

However, using a newer version of ParaView solved the issue.

Using ParaView-5.10.0, which I installed along OpenFOAM-2112, showed no error.
Using ParaView-5.6.3, which I installed along OpenFOAM-9, did show the error.

This issue, i.e., the error regarding the unmatched ), has also been discussed in this issue at the GitLab issue board of KitWare
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