A numerical assessment of bubble-induced electric resistance in aluminium electrolytic cells

This paper reports on an assessment of the bubble-induced electrical resistance in the Hall-H,roult process for primary aluminium production through a combined use of physical and numerical modelling. Using a physical air-water model, the transient bubble dynamics beneath the bottom surface of an anode was captured using a digital camera. Bubble morphology information obtained from the experiment was used to set up a numerical model. Computational fluid dynamics (CFD) modelling was applied to predict the current flow and the corresponding voltage drop across the electrolytic cell with and without the presence of bubbles. The predicted bubble-induced voltage drop for a current density of 0.7 A cm(-2) is about 0.11 V for a bubble coverage of 37 % and 0.29 V for a bubble coverage of 50 %. These values are within the range of experimental measurements reported for commercial cells. The predictions show that the presence of bubbles does not greatly affect global current distribution within the whole cell, but it does significantly affect the local current flow at the anode-bath interface. Locally high current flow occurs at the contact point of the anode bottom surface, bubble and liquid. In addition to the effect of bubble coverage, the bubble size and bubble thickness affect the voltage drop significantly.