Natural Convection Flow Modelling
 

I am simulating a natural convection flow(density gradient driven) using Boussinesq model. water enters at pressure inlet boundary because i do not know flow and pass through annulus (over surface of a cylinder) to pressure outlet boundary. Even with very high heat flux of surface of cylinder, outlet temperature is not gonna change. Can anyone having experience of natural convection or buoyancy driven suggest me what i am missing.