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-   -   Convective boundary condition (http://www.cfd-online.com/Forums/openfoam-solving/58527-convective-boundary-condition.html)

andrea_barbera September 22, 2008 09:34

Dear OF community, I'm tryi
 
Dear OF community,

I'm trying to implement a convective boundary condition in OF. Essentially this condition should be applied in a solid domain and should guarantee the coherence of thermal fluxes at the interface between the solid and a hypotetic fluid. This condition should respect the known equation:

-k*dT/dn = HTC*(T-T_fluid)

Where k, HTC and T_fluid are parameters of the boundary condition (I think to have succesfully loaded them in my BC), and T and dT/dn are respectively the gradient and the value that I must impose.

From which BC should I start to obtain my BC? I tried to start from BC derived from fixedValue, fixedGradient and mixed, but I do not know how to impose a linear combination of two fields like T and dT/dn and where impose it.

I have tried some tricks:

---- Starting from fixedValue-derived BCs I try to discretize the gradient as

(T_to_set - this->patchInternalField())
*this->patch().deltaCoeffs())

getting an equation in "T_to_set", the value that I try to set as BC.


---- Starting from fixedGradient-based BCs I try to discretize T as

(gradient_to_set + *this->patch().deltaCoeffs()) + this->patchInternalField()

getting an equation in "gradient_to_set", the value that I try to set as BC.

Unfortunaley these triks had no results and I get no result, also for some problem related to type mismatch during compiling. I do not know how to start implement this BC starting from mixed-BC or if the trikc that I have followed are reasonable http://www.cfd-online.com/OpenFOAM_D...lipart/sad.gif

Can you help me?

Best regards

Andrea

7islands September 22, 2008 10:40

Hi Andrea, I think you can
 
Hi Andrea,

I think you can have a look at either
1. the mixed-derived advective b.c. in OF 1.5 or
2. [Advertisement] the fixedGradient-derived convectiveOutlet b.c. I posted here on Sep. 05, 2007.

1. is much more sophiscated but may require a bit of patience to read.

Takuya

andrea_barbera September 23, 2008 03:16

Hi Takuya, Thanks for your
 
Hi Takuya,

Thanks for your advise. I will check these boundary conditions and start from them!

Andrea

awacs September 24, 2009 06:45

Hi Andrea,

I am interested in this convective boundary condition too. Have you finished it?

I am study the heating process of a solid, which has several heating channels for hot gas or hot oil flowing through. So the boundary condition at the channel wall shuold belongs to the third-class, just as you described above:
-k*dT/dn = HTC*(T-T_fluid)

Please give me some suggestions. Thanks in advance.

Regards,
Jitao

bhh March 4, 2010 05:36

Hi Andrea,

I am also interested in implementing the mixed heat transfer BC. Did you manage to make it?

rgds
Bjorn


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