Effect of Coke Properties on the Bubble Formation at the Anodes During Aluminium Electrolysis in Laboratory Scale

The anodic reaction of aluminium electrolysis cells leads to the formation of CO2 bubbles, which partly screen the anode surface and leads to an increase in the cell voltage. An advantage of these bubbles is that the formation and release contribute to the stirring of the electrolyte, however, the screening of the surface increases the irreversible energy losses. The voltage and current oscillation due to the bubble evolution during electrolysis for different anode materials have been determined in a laboratory cell. The effect of coke sulphur content and grain sizes were investigated. Anodes with finer coke fraction showed lower oscillations than coarser fraction equivalents. Additionally, the influence of current density on the amplitude of the anode potentials was measured. A 64% increase of current density caused an increase of anode potential oscillations from 79 to 170%

A heat and mass transfer problem for the dissolution of an alumina particle in a cryolite bath

We investigate the spherically symmetric dissolution of an initially cold alumina particle in a bath of molten cryolite. The cryolite initially freezes on the particle, forming a shell that must melt before the particle can dissolve. We derive asymptotic solutions valid in the limits of small-superheat and of small Stefan number. In the small-superheat limit, the evolution of the boundary exhibits a two-scale behaviour. In the small Stefan number limit, we find that the behaviour of a particle could be limited by either the dissolution (in the case where the temperature differences are small) or by heat transfer (when the latent heat is large and the temperature gradients are large). Our asymptotic predictions are validated by a front fixing numerical scheme that we initiate using the early-time asymptotics