Neumann condition

[Bourriche Lahoussaine]

Hello everybody; 
How i can implement Neumann boundary condition, who depends in the variable, 
for example 

for a variable T : 
k*n*nabla(T)=h(T-T_ext) 
and n the outward unit normal vector 

I want to apply this condition in the boundary of an object and not in the 
boundary of the whole geometrie 




BR 

Lahoussaine BOURRICHE