Abstract
An experimental study is made of natural convection in gallium melts enclosed by vertical circular cylinders with localized heating from the circumference. The heating is done at the mid-height, and the both ends of the cylinder are cooled. The cylinder aspect (Ar = height/diameter) ratio ranges from 2 to 10, and the Rayleigh number (Ra) ranges from 9.0 × 104 to 3.0 × 107. The Prandtl number is 0.021. Temperature measurements are made at six levels along the circumference of the cylinder to study the thermal convection in the melt. Numerical analysis is also conducted to supplement the experimental information. When Ra is small, the melt is in steady toroidal motion. Above a certain Ra the flow becomes non-axisymmetric as a result of a thermal instability in the case of Ar larger than 3. With increasing Ra the motion becomes oscillatory mainly in the upper-half. When Ar is smaller than 3, the toroidal flow becomes non-axisymmetric and oscillatory at the same time beyond a certain Ra. The conditions for the appearance of oscillations and the oscillation frequencies are investigated in detail.
