Heat flux within solid material
 

Hi Everyone,

I am doing simulation about heatsink cooling a heat source under airflow. The structure is simplified as below:

Heatsink Fin
--------
Heatsink Base
--------
Source


Both fin and base are made of aluminium. Fins on the heatsink are separated into three regions due to its design. The result shows normal on conduction within heatsink and convection on heatsink surface.
Then, I want to know the amount of heat flux passed from base to each fin region. I chose the interface between fin and base as I calculate in Fluent (Report definition -> Flux report -> Total heat transfer rate). The heat flux value is zero for all three regions. However, the heat flux at contact surface between base and heatsink source is normal, there's a value after calculation.
I can't figure out why.

Does anyone face the same problem?
Thanks in advance.