NATURAL-CONVECTION OF A LIQUID-METAL IN VERTICAL CIRCULAR-CYLINDERS HEATED LOCALLY FROM THE SIDE

An experimental study is made of natural convection in gallium melts e nclosed by vertical circular cylinders with localized circumferential heating. Heating is done in an axial band at the mid-height, and both ends of the cylinder are cooled. In the present study, the cylinder as pect (Ar = height/diameter) ratio ranges from 2 to IO, and the Rayleig h number (Ra) ranges from 9.0 x 10(4) to 3.0 x 10(7). The Prandtl numb er is 0.021. Temperature measurements are made at six axial levels aro und the circumference of the cylinder to study thermal convection in t he melt A numerical analysis is also conducted to supplement the exper imental information. When Ra is small, the melt is in steady toroidal motion. Above a certain Ra, the flow becomes nonaxisymmetric as a resu lt of a thermal instability, in the case of Ar larger than 3. With inc reasing Ra, the motion becomes oscillatory mainly in the upper half: W hen Ar is smaller than 3, the toroidal flow becomes nonaxisymmetric an d oscillatory at the same time beyond a certain Ra. The conditions for the appearance of oscillations and the oscillation frequencies are in vestigated in detail.