铝电解槽熔体内阳极气泡分布特性的数值模拟

Numerical simulation of anodic bubble distribution in aluminum reduction cells

采用欧拉双流体模型与群体平衡模型耦合的方法,考虑阳极气泡影响的修正k-ε湍流模型,对铝电解槽熔体内阳极气泡-电解质气液两相流进行数值模拟,研究不同电流密度下电解质流场、气泡体积分数和气泡尺寸分布等流体力学信息。研究结果表明:极间区域的电解质流动呈局部循环运动形式;电流密度相同时,距阳极底掌面越远,气泡体积分数越低、气泡平均Sauter直径越小;在同一水平高度下,气泡体积分数随着电流密度的提高而增大,气泡平均Sauter直径随电流密度的提高而减小;极间气泡层呈方形分布,中心区域气泡体积分数较高,边缘部分体积分数较低;极间气泡主要以小尺寸气泡为主,而中等尺寸和大尺寸的气泡数量比较少,气泡数量和气泡尺寸之间的关系可以近似看作双曲线分布;气泡体积分率表示的气泡尺寸分布呈3个单峰分布。本文计算得到的气泡分布特性与一系列文献试验结论一致。

The complex anodic bubble/electrolyte two-phase flow in the melts of aluminum reduction cells were investigated by using an Euler-Euler two-fluid model coupled with the population balance model （PBM）. A modified k-ε turbulence model was used to describe liquid phase turbulence in the simulation, by assuming the pseudo turbulence resulted from anodic bubbles. The effects of current density on the electrolyte fluid field, bubble volume fraction and bubble size distribution were investigated. The results show that the fluid field adopts a local loop flow pattern. The bubble volume fraction and bubble mean Sauter diameter both decrease with the increase of distance from the anode bottom at the same current density. At the same level, the bubble volume fraction increases and the bubble mean Sauter diameter decreases with the increase of the current density. The bubble layer has a thin square shape, with higher bubble volume fraction in central area, but lower in boundary area. It seems to be evident that a big number of small bubbles coexist with a few numbers of medium and big bubbles. The correlation between the number of bubbles and bubble diameter has nearly a hyperbolic shape, but the volume fraction distribution of bubble classes show a shape of three unimodal distributions. The simulation results are in accordance with a series of literature experimental results.