Large Gas Bubbles under the Anodes of Aluminum Electrolysis Cells

The gas bubble laden layer under the anodes during the electrolysis of alumina plays an important role in the hydrodynamics and the voltage balance of the reduction cells. Under certain geometrical and operational conditions, very large gas pockets, in the order of hundred cubic centimeters can be formed. The particular shape of these large gas bubbles was first described by Fortin et al in 1984 [1]. In the present paper the results of a combined experimental and numerical approach are described. In the experiments, the shape and the kinematics of the Fortin bubbles were analyzed by videography and Particle Image Velocimetry (PIV). A finite element method (FEM) combined with a Volume of Fluid (VOF) method was used to reproduce the experimentally observed phenomena, with particular attention to the reduction of the numerical diffusion of the liquid-gas interfaces. The morphology of the large bubbles and their movement including the velocity field around them are described.