Natural convection heat transfer in horizontal concentric annulus between outer cylinder and inner flat tube using nanofluid

Natural convection heat transfer in two-dimensional region formed by constant heat flux horizontal flat tube concentrically located in cooled horizontal cylinder was studied numerically by using nanofluid. The model solved using the FLUENT CFD package. The numerical simulations covered a range of hydraulic radius ratio (5, 7.5, and 10) at orientation angles from 0° up to 90°.The results showed that the average Nusselt number increases with hydraulic radius ratio, orientation angles and Rayleigh number, as well as enhancement ratio for Nusselt number at orientation angle 90° and hydraulic radius ratio 7.5 is equal to 24.87%. Both the nanofluid flow and heat transfer characteristics for different cases are illustrated that obtained from the CFD code. The results for the average Nusselt numbers are compared with previous works and show good agreement.