On boundary conditions in liquid sodium convective experiments

Turbulent convection of liquid sodium in a cylindrical cell, heated at one end face and cooled at the other, inclined to the vertical at angle 0 and π/4 is studied experimentally and numerically by solving the Oberbeck-Boussinesq equations with the LES (Large Eddy Simulation) approach for small-scale turbulence. The aspect ratio is one, i.e. cylinder length is equal to diameter L = D = 200 mm. The simulations were done using fixed heat flux thermal boundary conditions for the cylinder faces. To resolve the general problem of boundary condition in convective experiment with low Prandtl number liquids, a special kind of heat exchanger were designed for the experimental setup. Each heat exchanger is a temperature-controlled MHD (magnetohydrodynamic) stirrer, filled with sodium and separated from the convective cell by a thin copper plate. We demonstrate the efficiency of MHD stirring for the temperature control. In convective experiments the Rayleigh number, determined by the cylinder diameter, was in the range from 4.7 · 106 to 1.7 · 107. We show that the structure of the flow and the efficient heat transfer strongly depend on the inclination angle.