[sieginc.]

I want to be able to compare the effect of forced vs. natural convection on a heat generating element. Right now I am not sure how to model a natural convection simulation. I have a cube with a constant heat flux on each side sitting in a big room. The top of the room is a pressure outlet with all sides being walls. The initial condition of the room is 25 C.

I have selected:

-Boussine model
-Constant density
-Gas
-Gravity
-Implicit unsteady
-Segregated flow
-Segregated fluid temperature
-Laminar
-3D

The problem is when I run it the residuals do not converge and I keep getting reversed flow on all the faces which does not go away. Can someone give me some tips on this? Thanks.