氧化铝颗粒的溶解控制机制及其临界特征

Control mechanisms and critical characteristics in dissolution of alumina particles

在铝电解工艺中,氧化铝在电解质中的溶解同时受传热与传质的控制。通过建立氧化铝颗粒溶解的传热控制模型、传质控制模型以及收缩核模型,基于Open FOAM开源软件平台,采用自编程的方法开发氧化铝溶解求解模块,对氧化铝颗粒在两种控制机制下的溶解进行数值模拟。结果表明:在传质机制控制下,其颗粒的质量溶解速率及其速率的变化梯度均随粒径的减小而降低;在传热机制控制下,其颗粒质量溶解速率也随颗粒粒径的减小而减小,但速率梯度变化不大。为了区分氧化铝溶解过程中传热与传质两种控制机制中哪种机制占主导作用,提出临界直径的定义及其判定。研究得出氧化铝颗粒临界直径为560μm,小于560μm的氧化铝颗粒溶解受传质机制的控制,大于560μm的氧化铝颗粒溶解受传热机制的控制。

In the aluminum electrolytic process, alumina was dissolved in the electrolyte under the control of both heat and mass transfer mechanism. Heat transfer control model, mass transfer control model and the shrinking core model of alumina dissolution were established, Based on the OpenFOAM open source software platform, alumina dissolution solution module was set up by the custom code. Numerical simulations of the dissolution of alumina particles under the two mechanisms were conducted. The results show that under the control of mass transfer mechanism, the mass dissolution rate and the varying gradient of the mass dissolution rate of alumina particles reduce with decreasing the particle size. Under the control of heat transfer mechanism, the mass dissolution rate decreases with decreasing the particle size, while the varying gradient of the mass dissolution rate shows little change. In order to distinguish the dominance of the heat transfer or mass transfer control mechanism, the definition and judgement of the critical diameter were put forward. Considering the dissolution process of alumina particle is governed by mass transfer as well as heat transfer mechanism together, the critical diameter is 560 μm. The dissolution of alumina particles with the size of less than 560μm is governed by mass transfer mechanism, while the dissolution of alumina particles with the size of more than 560μm is under the control of the heat transfer mechanism.