Effect of the Bubble Growth Mechanism on the Spectrum of Voltage Fluctuations in the Reduction Cell

Abstract

The spectrum of the voltage oscillations in the aluminum reduction cell depends on the size of the anode. Small laboratory cells and industrial size cells exhibit different fluctuation patterns. The growth of bubbles can be divided into two periods controlled by different physical mechanisms. The detachment frequency of the bubbles from the nucleation sites depends on the current density and detachment size, the latter being influenced by the material, microstructure and shape of the anode bottom. After detachment the main factor causing growth of the traveling bubbles is coalescence. A mathematical model that keeps track of each and every individual gas bubbles generated under the anode was developed and used to analyze the character of the fluctuations of the cell voltage. It is shown that in the case of industrial size anodes the voltage oscillations are dominated by the dynamics of the bubble interactions (coalescence) in the two-phase layer, while in small size laboratory systems the frequency of nucleation of the individual bubbles can be observed.