Turbulent convective heat transfer in a closed cylinder with aspect ratio L = 5D (D is the diameter and L is the cylinder length) filled with liquid sodium, heated at one end face and cooled at the other, is studied experimentally for three different positions: vertical, inclined at 45 degrees to the vertical and horizontal. The Rayleigh number, which is determined by the superimposed temperature difference and the cylinder diameter, varies within the range . It is shown that the convective heat transfer along the cylinder is most effective in the inclined cylinder, where an intense large-scale circulation exists on a background of developed small-scale turbulence. In the horizontal cylinder, the turbulence is weak, but the large-scale circulation provides moderate heat transfer. In the vertical cylinder, the large-scale circulation is absent, the turbulent fluctuations are most active, but the heat transfer is the weakest. The dependence of the Nusselt number on the Rayleigh and the Prandtl numbers, and the dependence of the Reynolds number on the Grashof number are shown and discussed.

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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 exper imentally. The experiments are performed for a fixed Rayleigh number Ra = 2.4 × 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° 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 incli nation (α = 20°-30°) and reduce the heat flux along the channel, although in the limit of small angles (ver tical 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.

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