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

今天的生产技术消耗的电能大约是理论上将氧化铝还原成金属铝所需电能的两倍。在电流通过期间，过剩能量的重要部分在熔融电解质中耗散。在氧化铝的电化学还原过程中产生的气泡占据了水平电极间空间的一部分，并增加了电阻，引起寄生热的产生。 减少这种过度加热的一种方法是通过减少电极间空间，即所谓的阳极-阴极距离ACD。然而，阳极下的气泡层的厚度对ACD的减少设定了限制，因为气泡可以扰动电解质-金属界面，导致电解池的电流效率降低。 早期的研究表明，阳极下气泡的大小在很宽的范围内变化，从几微米到几十厘米。还研究了非常大的气泡的产生和行为，并且确定它们对电解质的运动和由气泡引起的过电压具有非常强的影响。 减少阳极-阴极距离的努力的效率基本上取决于对气泡层的更好理解和控制。 该研究项目的目的是扩大知识的形态和气液流动的动态行为时，阳极-阴极距离减少和接近的气泡层的厚度。实验和数学建模的方法将被用来发现和描述气泡的形态和运动。 预期的结果将直接有助于提高现有工厂的能源效率，以及开发创新的新还原技术，这对保持加拿大在铝生产方面的领导地位至关重要。所提出的研究的基本方面可以代表对其他电解方法如氟和氢生产的改进的贡献。

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.