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Old   August 22, 2014, 03:33
Default externalWallHeatFluxTemperature
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Hello everybody,
I am doing a simple model with the boundary externalWallHeatFluxTemperature to understand how it is working. I am using it as in the example from openFOAM tutorials:
myPatch { type externalWallHeatFluxTemperature; kappa fluidThermo; Ta uniform 300.0; h uniform 10.0; thicknessLayers (0.1 0.2 0.3 0.4); kappaLayers (1 2 3 4) value uniform 300.0; kappaName none; }

My model is just a plate connected to the ambient through the externalWallHeatFluxTemperature boundary and a heat source.
I tried two cases:
ˇ In case 1: Initial temperature is 105ēC and the ambient temperature is 105. Heat source 25W. However, it seems that the temperature in the cold plate does not increase.
ˇ In case 2: Initial temperature is 105ēC and the ambient temperature is 0ĒC. Heat source 25W. However, the temperature does not decrease.
It looks to me that the ambient temperature is not working. Can somebody help me to understand how this boundary works?
Thanks in advance,
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File Type: jpg case1.jpg (57.8 KB, 41 views)
File Type: jpg case2.jpg (69.4 KB, 35 views)
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Old   August 25, 2014, 01:14
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Hi unbps. I use externalWallHeatFluxTemperature with the solver fireFoam and OF2.2 and it works OK. I use this BC for modelling heat flux from the internal gaseous environment of the fire compartment to the ambient environment. There are some moments here. thicknessLayers is a inverse value, i.e. if thicknessLayers is 0.1 m one must write 10. And one more. AlphaSgs or Alphat at the surface must have sufficient value to provide heat flux that you desire. You can set high value for h (heat transfer coef.) but the gaseous environment near the wall is not able to conduct such flux. Try high value for AlphaSgs or Alphat, eg. as fixedValue.
Best regards
Roman1
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Old   August 28, 2014, 08:10
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Hi Roman1,
Thanks for your response.
In my model I am using chtMultiRegionFoam.I tried with the inverse of the thickness layer but the result is still the same, there is not a big influence in my model. I think that, in my case, Alphat does not apply as the medium is solid, am I right?
Which are the units of the heat transfer coefficient (h)? Are they [W/m.K]?
If I want in my model free convection (5 W/m.K), should I write in my boundary:
h uniform 5.0;

Thanks in advanced,
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Old   August 29, 2014, 06:01
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Hi unbps. Sorry, I am not familiar with chtMultiRegionFoam. AlphaT (alpha turbulent) applies to the gaseous phases. The units of the heat transfer coefficient is W/m2/K. Try kappaLayers as a inverse value too.
Wish you good luck
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Old   November 4, 2014, 05:58
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Quote:
Originally Posted by Roman1 View Post
.... thicknessLayers is a inverse value, i.e. if thicknessLayers is 0.1 m one must write 10......
I am bit confused with this. In the example given in the header file it suggests that
Code:
thicknessLayers | list of thicknesses per layer [m].
This is from openFoam 2.3.0.

Is externalWallHeatFluxTemperature in openFoam 2.2.0 different than in 2.3.0??
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Old   November 7, 2014, 15:51
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Code may be different from version to version. I tried both direct and inverse values and inverse worked OK. It make sense to look at the source code.The bug is in OF2.3: http://www.openfoam.org/mantisbt/view.php?id=1258
Thanks to all
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