Multiscale Simulation of Bubble Behavior in Aluminum Reduction Cell Using a Combined Discrete-Bubble-Model–Volume-of-Fluid–Magnetohydrodynamical Method

Abstract

The physics of aluminum electrolysis process involves many spatial scales, generating a wide variety of bubbles of different sizes in the magnetohydrodynamical (MHD) flow. To capture the dynamics of bubble nucleation, growth, coalescence and the interactions among bubble–bath–metal, each scale needs to be resolved with the appropriate method. The present study proposes a three-dimensional (3D) multiscale multiphase flow model for bubble behaviors and bath–metal MHD flow, where the large-scale interfaces of bubble–bath and bath–metal are resolved by the volume of fluid (VOF) approach and the dispersed microbubbles are resolved by Lagrangian discrete bubble model (DBM). A discrete-continuum transition model is proposed to bridge different scales and handle the multiscale bubbles coexisting at the anode bottom. The predicted gas coverage and bubble thickness are validated by the experimental data in the literature. The numerical results indicate that bath–metal MHD flow accelerates the bubble motion and decreases gas coverage.

Single and Multiscale Bubble Motions Beneath an Inclined Downward-Facing Surface in the Aluminum Reduction Cell

“…To overcome the limitation of the large bubble deformation in the DPM model, the discrete-continuum transition (DCT) model is used to convert the dispersed microbubbles to macrolarge ones. ,, Two criteria should be satisfied for the DCT model. The first criterion is to compare the bubble and cell volumes.…”

“…The second criterion is applied based on the relative position between the small dispersed bubbles and the continuum bubble surface. When the dispersed bubble moves near to the continuum bubble surface and they are in the same cell and the volume fraction of the continuum bubble surface is larger than 0.5, the dispersed bubble is absorbed by the continuum large bubble. ,, Once the DCT occurs, the transitioned bubble can be solved by the VOF method to trace the evolution of the bubble surface, considering the surface tension force in the Eulerian framework. , The mass of the transitioned bubble should be implemented into the mass conservation equation as a source term, which is achieved by the UDF, as seen in eqs – in Table . The interaction between the discrete and continuum phases is calculated with the momentum exchange term F ⃗ me using the two-way coupling method. , The related equations for the microbubble motion, the discrete-continuum transition, and the macrobubble motion are given in Table .…”

“…The present study is the expansion of our previous research works, ,, where we have studied single and multiscale bubble motions under a horizontal anode surface in the aluminum reduction cell. The bubbles beneath a horizontal anode surface do not move in a specific direction, and they are distributed randomly, while beneath an inclined anode surface the bubble flow dynamics are expectedly different in terms of the discrete-continuum transition (DCT) development, bubble motion direction, and bubble detachment direction.…”

“…Many studies have been carried out to study the bubble motion under horizontal surfaces, mainly using experimental approaches based on air-water models, − as well as low-temperature reaction models, high-temperature transparent models, − and numerical simulation methods. ,,− …”

Effects of the Application of a Perforated Anode in an Aluminum Electrolysis Cell on the Gas–Liquid Two-Phase Flow and Bubble Distribution Characteristics

“…For this bubble layer problem, some researchers have focused on the formation and motion of the bubbles. Sun et al , proposed a multiscale multiphase flow model to simulate the bubble behaviors and bath-metal MHD flow in the aluminum reduction cell. The transition of bubbles from the micro- to macrolevel was studied.…”