Bubble driven flow in narrow channels between the electrodes of an aluminium electrolysis cell

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Today's production technologies consume about twice of the electrical energy needed theoretically to reduce alumina into metallic aluminum. An important part of the excess energy is dissipated in the molten electrolyte during the passage of the electrical current. The gas bubbles that are generated during the electrochemical reduction of alumina occupy a part of the horizontal interelectrode space and increase the electrical resistance provoking a parasite heat generation. One method of reducing that excess heating is by reducing the interelectrode space, the so-called anode-cathode distance, ACD. However, the thickness of the bubble layer under the anode sets a limit to the reduction of the ACD as the bubbles can perturb the electrolyte-metal interface, causing a reduction in the current efficiency of the electrolysis cell. Earlier research has shown that the size of the bubbles under the anode varies over a very wide range from few micrometers up to tens of centimeters. The generation and behavior of the very large bubbles were also studied and it was determined that they have a very strong influence on the movement of the electrolyte and on the overvoltage caused by the bubbles. The efficiency of the efforts of reducing the anode-cathode distance depends essentially on the better understanding and control of the bubble layer. The proposed research project aims at the extension of knowledge about the morphology and dynamic behavior of the gas-liquid flow when the anode-cathode distance is reduced and approaches of the thickness of the bubble laden layer. Both experiments and mathematical modeling methods will be used to discover and describe the morphology and movement of bubbles. The expected results will aid directly the improvement of the energy efficiency of the existing plants as well as the development of innovative, new reduction technologies, which is important to maintain Canada's leadership in aluminum production. The fundamental aspects of the proposed research can represent a contribution to the improvement of other electrolysis methods like fluorine and hydrogen production.