Natural convection
 

Hi everybody
My CFX problem is:
water flow inside the pipe, conduction heat transfer in the pipe and Natural convection outside the pipe with ambient(stationary air). I want to estimate heat transfer coefficient outside the pipe.
1.when i active buoyancy at air domain, this option is selected automatically for other domains(water).
2.how can i use different turbulence models for different domains?
3.what are the boundary conditions for air domain?
thanks.