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Time Varying Heat Flux for Internal Energy Boundary Condition 

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October 5, 2017, 08:34 
Time Varying Heat Flux for Internal Energy Boundary Condition

#1 
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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=1e3 [m2]; Q=1e4 [W.m2] //Ta uniform 20.0; //h uniform 10.0; thicknessLayers (1.5e3); kappaLayers (8.5634e1); value uniform 15.0; kappaName kEff; Qr none; relaxation no; } I have a question also, I'm not sure what is the "value uniform 15.0" supposed to be, I reused it from an existing case, does anyone have an answer to that? Thanks a lot ! 

March 21, 2019, 13:49 

#2 
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Chenguang Li
Join Date: Sep 2011
Posts: 15
Rep Power: 13 
Hi I have same problem. Is there any solution for this? Thank you!


April 15, 2019, 05:42 
KappaLayers definition

#3 
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vamshi
Join Date: Nov 2018
Posts: 3
Rep Power: 6 
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.. 

April 18, 2019, 10:47 

#4 
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...
Join Date: May 2018
Posts: 37
Rep Power: 6 
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*(1.0alpha1))"; fractionExpression "0"; variables "q=14000;K1=0.06;K2=0.01;"; timelines (); value uniform 327.15; } perhaps this bouandry condition can help you best 

March 12, 2020, 13:57 

#5 
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Raj Niraj Patil
Join Date: Mar 2019
Location: Nashik, India
Posts: 2
Rep Power: 0 
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 

July 24, 2021, 08:50 
Varying Heat Flux

#6 
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Shailesh
Join Date: Jul 2021
Posts: 2
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Dear Fellow,
How to give varying heat flux with respect to temperature in CFD? Kindly, provide solution? 

July 24, 2021, 08:53 
Varying Heat Flux problems

#7 
New Member
Shailesh
Join Date: Jul 2021
Posts: 2
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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 (Yaxis, Temperature Vs Xaxis, Time) please provide with udf code Last edited by Yadav067; August 10, 2021 at 02:50. 

March 7, 2022, 12:29 

#8  
Senior Member
Gerhard Holzinger
Join Date: Feb 2012
Location: Austria
Posts: 317
Rep Power: 26 
Quote:
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 ParaView5.10.0, which I installed along OpenFOAM2112, showed no error. Using ParaView5.6.3, which I installed along OpenFOAM9, 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 

Tags 
heat transfer boundary, heat transfer modelling, time vayring bc 
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