Abstract
•Turbulent Natural convection heat transfer between two concentric cylinders with open ended was studied experimentally and numerically.•The angle of orientation for outer cylinder, ϕ, was varied from 0° to 90° with 15° increment.•The axis ratio of the outer cylinder was changed from 1.0 to 2.0.•Axial velocity and turbulent intensity were showed at different parameters.•The numerical results are in a good agreement with experimental results.•Maximum enhancement reaches 25% at axis ratio 2.0 and vertical position to the outer cylinder comparing to circular outer cylinder.
Turbulent natural convection between two horizontal concentric cylinders with different orientation and axis ratios for the outer cylinder with both open-ended has been investigated experimentally and numerically. A Constant heat flux was imposed at the outer cylinder at five different heat fluxes 503, 751, 1002, 1251 and 1508 W/m2, while the inner cylinder was insulated. The hydraulic diameter was kept constant at 60 mm.
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.