Temperature BC - Constant heat flux
 

Hi all,

I have some problems deciding which boundary condition to use to assign a constant heat flux to a wall in my specific problem.
My geometry is a backward facing step (simulating generic ideal fluid flowing inside, incompressible, steady state), after the step I want to assign the given heat flux to the wall.
I use turbulence modelling. Solver: buoyantBoussinesqSimpleFoam
I can't use a fixedGradient-BC since the thermal conductivity of the wall is unknown and more important I need to calculate the gradient in the fluid not in the wall, right?

So I found three avaiable options for doing this:
1) turbluentHeatFluxTemperature
https://github.com/OpenFOAM/OpenFOAM...luxTemperature
But it asks for alphaeff, and I am not sure what this parameter means?
If alhaeff is a thermal diffusivity, as stated at some point, the dimension [kg/m/s] does not match.
In the .C code I found :
gradient() = q_/(Cp0*alphaEffp);
Does that mean
temperature gradient= sp heat flux/(thermal capacity*effective thermal diff coeff)
?


2) externalWallHeatFluxTemperature
https://github.com/OpenFOAM/OpenFOAM...luxTemperature

From the code I guess it use the conductivity to calculate the T-gradient which is not suitable for this case:
this->refGrad()[i] = q[i]/KWall[i]

3) Using groovyBC
http://www.cfd-online.com/Forums/ope...acianfoam.html
Using
type groovyBC;
variables "htot=100.0;Tinf=298.15;rho=2700.0;cp=900.0;k=DT*r ho*cp;";
valueExpression "Tinf";
fractionExpression "1.0/(1.0 + k/(mag(delta())*htot))";

Which I do not really understand at all.

Every help or advise is appreciated!
If you need further information to give a good answer, do not hesitate to ask!

Best

More questions :D
 

Is it also possible to sample the calculated heat transfer coefficient h?
I want to calculate the Stanton number using h.
St(x) = h(x) / (uref*rhoinf*cpinf)

I am also intereted in these BCs, Have you found some ideas? Which one is more suitable? Thank you.