Bubble movement under a solid surface

在铝电解中，气泡是在阳极下产生的。这些气泡形成气泡层，它们的运动加强了传输过程，改善了温度和浓度场的均匀性。另一方面，气泡部分堵塞了电流通道的传导段，增加了电池的电阻和能量消耗，最终导致不稳定。此外，气泡的成核、运动和合并使电池电压波动。尽管近年来在单相流和多相流的数学建模方面取得了进展，但对固体表面下气泡行为的定量描述并不令人满意。研究的目的是描述气泡在固体表面下运动时的大小和形状的演化，确定气泡在不同演化阶段的阻力系数，并定量描述单个气泡通过时对液相内流场的扰动。固体和运动气泡之间液体分离层中的流体动力学或大气泡运动过程中形成“头部”等现象，对确定气泡的最终速度，最终在气液之间的动量传递中起着决定性的作用。这种方法包括实验和数学建模的结合。在透明的实验室模型中，将使用高速摄像和图像分析来研究气泡的形状演变和运动学。分析了不同的液体和固体对材料性能的影响。阻力系数将通过测量气泡的速度来提取。数学模型将被用来确定被测液体分离层中的流型和耗散率，以及大气泡周围的液泡相互作用。预期的结果将有助于改进铝电解槽的设计，使其更安全、更经济地运行。

In aluminium electrolysis, gas bubbles are generated under the anode. These bubbles form a bubble layer and their movement enhances the transport processes, improving the homogeneity of the temperature and concentration fields. On the other hand, the gas bubbles partially block the conducting section of the passage of electric current, increasing the electrical resistance and energy consumption of the cell, ultimately leading to instabilities. Furthermore, the nucleation, movement and coalescence of the bubbles make the cell voltage fluctuating. Despite of the recent developments in mathematical modeling of single and multiphase flows, the quantitative description of bubble behaviour under a solid surface is not satisfactory. The objective of the proposed research is to characterize the size and shape evolution of gas bubbles moving under a solid surface, to determine the drag coefficients of the bubbles at different stages of their evolution and to describe quantitatively the perturbation of the flow field in the liquid phase by the passage of the individual bubbles. Phenomena like the hydrodynamics in the liquid separation layer between the solid and the moving bubbles or the formation of a "head" during the movement of big bubbles play a decisive role in establishing the terminal velocity of bubbles and ultimately in the transfer of momentum between the liquid and gas. The methodology involves a combination of experiments and mathematical modeling. The shape evolution and kinematics of the bubbles will be studied in transparent laboratory models, using high-speed videography and image analysis. The influence of the material properties will be analyzed by using different liquids and solids. The drag coefficients will be extracted from the measurement of the velocity of the bubbles. Mathematical modeling will be used to determine the flow pattern and rate of dissipation in the measured liquid separation layer as well as to clarify the liquid-bubble interaction around the large bubbles. The expected results will help both the improvement of the design of the aluminium electrolysis cells and their safer and more economical operation.