Problem in temperature distribution in Ansys Fluent
 

Hi everyone;
I am using ANSYS 16.0 FLUENT module to study natural convection phenomena inside the casing. But there is a problem in temperature distribution while examining results i.e. temperature close to heater is low and away from heater is high.

I have few questions beside this problem please adress them;
1.How to apply boussinesq approximation in fluent
2.How to draw nusselt number along the wall

This is the modeling in ansys;
Point close to heater (cube) has low temperature while point away from heater has high temperature,,

Attachment 45712

Suggestions are warmly welcomed;
Please share the link of any guide or tutorial related to natural convection study in ansys fluent 16.0