I have a 3d structure comprised of multiple layers. An inner-middle layer exerts a heat flux of 650 W/m^2.

The whole "box" is in an enclosure of air with an inlet velocity.

I want to see how the box is cooled.

My steps:

Geometry: Created a cavity in the enclosure exact to the dimensions of the "box".

Mesh: Inserted inflation layers to the cavity.

Fluent:

*Steady state

*Energy: On

*Model: SST

*Bodies been assigned to solid/fluid

*Created interfaces between geometries that are in touch.

*Insert 650 heat flux at the interface side of the middle layer.

*All other walls from interfaces are either COUPLED or have checked the "via system COUPLING" option.

*Applied Monitors: Facet Average of Static or Wall Temperatures.

My residuals are fine. However, the energy readings quickly skyrocket from e-15 to e+01 and then just fluctuate forever. At the same instant my temperatures skyrocket from 300K to 5000K !

What do I do ? Should I change HEAT FLUX -->HEAT GENERATION ?

For the interfaced walls, should I check "convention" instead of "via system coupling" ? Should I insert heat transfer coefficient ? How do you get that number ?