convection heat flux
 

Hello
I hope somebody can help me!

I'm doing the simulation of a small furnace. First I'm doing a simple model: -only walls with inlet and outlet (no combustion).

-I activated the energy equation (no radiation)

-air 500 K in the inlet, also similar temperature on wall 570 k, and the same inlet temperature at the outlet.

-k-epsilon.



The temperatura of walls is according to saturarion temperatura of the water in the wall.



Results:

The mass balances is not fantastic, but is ok. The rest of residuals are ok. The energy balance shows, more or less, the same energy at the outlet as in the inlet. The walls, without thickness, have a global flux =0.4% of the inlet energy.
What can i do for improve the heat flux of the walls? I don't think the thicknes should be so important...



Thanks
maria

One point about your model: unless you have backflow at the outlet, the specified temperature here is not needed. It is only need for the fluid that "returns" to the domain. Do you have any? If not, it is not critical (until you get to radiation).

So is your question how to you reduce the error by improving the model to reduce the heat flux of the walls? Do you have a good boundary layer mesh on the walls? Look at the turbulence model you are using and is it appropriate. Are you using the coupled solver? Sometimes that will help push the continuity residuals down.