Anodic bubble behaviour in hall-héroult cells

Abstract

A phenomenological model for the creation and transport of anodic gas bubbles in Hall-Héroult cells is presented. Due to the large variation in length scales and bubble topology, a multiscale approach is introduced in which molecular gas is assumed to be formed as supersaturated CO2 in the electrolyte. This paper describes models and constitutive relations that are intended for the simulation of anodic bubbles, ranging from the generation of molecular gas species through Faraday’s law and subsequent bubble nucleation, to the evolution of macroscopic bubbles by means of a Volume of Fluid (VOF) model. The coupling between macro- and micro scales is performed by means of a population balance. The complete model is implemented in ANSYS FLUENT. The model is applied to a 2D-cross section of a lab scale electrolysis cell, showing that essential properties are well represented by the proposed approach. Finally, the influence of Lorentz forces on the global bubble behaviour is investigated.