how to define natural convection
 

Hello

How should i define the natural convection boundary condition on the outer side of wall. Flow is taking place in the pipe, axis-symmetric case is taken. When I define this boundary condition by selecting the convective boudary condition. Results of fluent say that both on inner and outer side of wall the film coefficient is same(5w/sq-m k).

What i am doing wrong.

thanx in advance.

Ejaz Ahmed