Experimental and numerical investigation of turbulent natural convection between two horizontal concentric cylinders at different axis ratios and orientation angles

The Rayleigh number Ra was varied from 1.017 × 107 to 3.25 × 107. The outer cylinder orientation angle, ϕ was varied from 0° to 90° with 15° increment. The influence of the axis ratio (major to minor axis) for the outer cylinder was studied at range from 1.0 to 2.0. A finite difference method for the governing equations related with the standard k-ε model has been utilized. The surface temperature distribution at outer cylinder, the axial velocity and average Nusselt number were estimated at different orientation angles and axis ratios of the outer cylinder. Turbulent intensity and axial velocity distribution were estimated numerically. Both experimental and numerical results for the average Nusselt number show good agreement. The results show that the heat transfer enhancement starts as the outer cylinder orientation angle increase more than the critical angle. The maximum increase in the average Nusselt number reaches 25% at vertical position and axis ratio at 2 for the outer cylinder.