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third-type temperature BC - outside convection boundary condition with interTempFoam

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Old   September 26, 2016, 11:53
Default third-type temperature BC - outside convection boundary condition with interTempFoam
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Perry Uhlig
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Hello Foamers,

who knows a good way to apply the temperature-BC for (natural) convection at the outside of a boundary?
It is known that for first-type (dirichlet) and second-type (neumann) BC there are fixedValue and fixedGradient BC in vanilla openFOAM. However there is no third-type BC available to my knowledge, which I want to apply using the outside temperature (e.g. "T_sur") and a heat transfer coefficient (e.g. "h_sur").
What makes it difficult is, that I am investigating a non-isothermal two phase flow. For that I use the self-compiled solver interTempFoam (its "making off" has been covered in my other thread).
Also the BC is required to take into account that the fluid properties at the boundary are not constant due to the presence of two different phases (air or water).

First I was thinking about the BC "externalWallHeatFluxTemperature". Though I got to the conclusion that this BC is specifically applicable with the solvers chtMultiRegionFoam and chtMultiRegionSimpleFoam.
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Old   September 26, 2016, 14:39
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You already found the best boundary condition to use. I am not sure if you need to modify it to use with your solver, but from my point of view that can be easily achieved. You could of course program your own boundary condition from scratch with ease. Simply use a fixedValue boundary condition. And use deltaCoeffs to add the gradient part by approximating it with the value of the next cell. This is in fact how all robin type boundaries within openfoam work.
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Old   September 27, 2016, 03:07
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thanks for your quick reply

I already tried to apply "externalWallHeatFluxTemperature". It was not working because I wasn't able to supply the value of kappa properly, which I tried in several ways. My guess was that the BC looks up kappa in a way that is only compatible with the folder structure of a multiRegion case (see tutorial multiRegionHeater in OF 2.3), which I can't imitate due to my case being an interFoam case.

I wanted to evade programming a BC because I have never done it and timewise I am strongly limited, so that I won't be able to work into that.
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Old   September 27, 2016, 03:55
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Try kappa lookup and kappaName = whatever interFoam uses. Probably something like the alphaEff field.
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Old   September 27, 2016, 05:17
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I tried everyone of the 4 possible keywords in conjunction with supplying kappa as an additional entry in transportProperties as well as an added thermophysicalProperties file taken from a working multiRegionFoam case. Also supplying the files thermophysicalProperties.air and thermophysicalProperties.water didn't lead to the solver finding kappa in any event.
That's why I think, that the "externalWallHeatFluxTemperature" BC only works with the multiRegionFoam solver group.
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