Turbulent convective heat transfer in an inclined tube filled with sodium

Turbulent free convection of liquid sodium in a straight thermally insulated tube with a length equal to 20 diameters and with end heat exchangers ensuring a fixed temperature drop is investigated experimentally. The experiments are performed for a fixed Rayleigh number Ra = 2.4 $\times$ 10$^6$ and various angles of inclination of the tube relative to the vertical. A strong dependence of the power transferred along the tube on the angle of inclination is revealed: the Nusselt number in the angular range under investigation changes by an order of magnitude with a maximum at the angle of 65$^\circ$ with the vertical. The characteristics of large-scale circulation and turbulent temperature pulsations show that convective heat transfer is mainly determined by the velocity of large-scale circulation of sodium. Turbulent pulsations are maximal for small angles of inclination ($\alpha$ = 20$^\circ$–30$^\circ$) and reduce the heat flux along the channel, although in the limit of small angles (vertical tube), there is no large-scale circulation, and the convective heat flux, which is an order of magnitude larger than the molecular heat flux, is ensured only by small scale (turbulent) flow.