[FlyingCat]

Hello,

I would like to impose a basic boundary condition for temperature at a realistic wall:

h * (T_w - T_g) + K/d * (T_w - T_x) = Qr

with h the convection heat transfer coefficient, T_w the wall temperature, T_g the gas temperature (within the walls), T_x the temperature in the wall at a distance d, Qr the total radiation.

Is there a boundary condition in OpenFOAM to do that ? It is with a turbulent flow.

Perhaps, OpenFOAM make it alone like FDS ?

Thank you.

[Jack80]

I have no idea what you are asking for.

If you are looking for a boundary condition where you can set a convection coefficient and a temperature (such as convection to environment), then you can do this by using "externalWallHeatFluxTemperature"

[FlyingCat]

Yes but it is external. I want it inside the walls with variable temperature and variable h.

[laurentD]

What do you want to fix exactly ?
The value of Qr with h and T which are variable depending of space? of time ?
Am i on the good way ?

[FlyingCat]

Actually, I want to calculate T_w by solving this equation. Qr and Tg are calculated inside the walls. And h is also calculated by an empirical Nusselt number.

[laurentD]

Okay.
Steady-state ? Transient ?
I mean : are the values of the variables function of time ?
And what do you call (K/d) ?
Many questions, i know...
But it is to understand perfectly what you are looking for.

[FlyingCat]

Actually, I am using firefoam to run a calculation with a fire within walls. It is a LES calculation and it is unsteady.

So all the parameters are function of time but it is firefoam that gives the values.

K is the conductivity of the wall and "d" would be the width of the wall knowing that it is an ambient temperature outside of this wall.
For example, FDS (fire dynamic simulator) create a virtual mesh in the wall to solve in 1D the heat equation and make this balance at the boundary between each heat transfer: convection, conduction, radiation.

No problem, you can ask, I do not know if I am clear.

[Jack80]

If I understand you correctly, you just want to know how to solve the thermal interaction between a fluid (the gas inside your walls) and the wall, am I right?

Have you meshed your walls? If so, the BC you are looking for is compressible::turbulentTemperatureCoupledBaffleMix ed. This is the boundary you use for thermal coupling a solid and a fluid. It automatically calculates h, Tw and everything related to the heat exchange

[FlyingCat]

Yes, that is what I would like. Thank you for your reply. And if I have not meshed the walls ? I have already a big case and using a multiregion just to solve the heat transfer at the boundary seems to be excessive. Some other softwares do a virtual mesh for example to solve it. It solves a 1D heat equation.

It is a common boundary condition I think and I have not seen any calculation with the walls meshed in fire publications (perhaps it exists, I have not seen all publications).


Again thank you for your response, you have understood what I would like.