The gas bubble laden layer under the anode plays an important role in the operation of the aluminium electrolysis cell. It influences the cell's electric resistance, it participates in the formation of the so-called bubble-driven flow. It is in this layer that the drastic changes in the morphology of the three phases (liquid bath, solid anode and the gas) lead to the anode effect. The noise spectrum of the cell's voltage is directly linked to the events in the bubble layer. After analysing the dynamics of growth of individual bubbles, in the present study the emphasis was put on the study of the collective behaviour of the bubbles. After their detachment from the nucleation site, the bubbles start their voyage toward the edge of the anode. During that travel they collide and coalesce as well as interact with other bubbles still in the growing phase, before detachment. Big flat gas pockets are formed incorporating dozens of separated bubbles. The fluctuations in the bubble layer reflect both the effect of the individual bubbles' dynamics and the formation of such gas pockets. A mathematical simulation tool was developed that takes into account the most important interactions between the bubbles and follows their movement and their growth. The velocity of the bubble layer is calculated by using a simplified momentum balance equation. The fraction of the anode covered by the gas is calculated in function of the movement and growth of the individual bubbles and shows a character very similar to the measured voltage fluctuations.
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