Experimental and numerical investigation of two‐phase flow patterns in magnesium electrolysis cell with non‐uniform current density distribution

Abstract

In a magnesium electrolysis cell, the electrolyte flow pattern can be affected by the chlorine gas bubbles release from the anodes. A 2D gas‐liquid mathematical model was developed to simulate the liquid velocity and gas volume fraction. A Particle Image Velocimetry (PIV) experimental set‐up was employed to determine the characteristics of velocity field in a cold model and to validate the mathematical model. The numerical results show good agreement with the experimental data. The local production rate of gas evolution is related to the anode current density according to Faraday's law. To make the bubble generation close to the reality, the non‐uniform current density distribution over the anode surfaces, derived from the thermoelectric model, has been added to the gas‐liquid model as initial boundary conditions. According to the analysis, the use of non‐uniform conditions is necessary. The flow patterns in the side channels are found to be quite different from that in the middle channels, where the velocity is much lower. It is noted that both current intensity and bubble size can significantly affect the velocity field and gas volume fraction distributions. The velocity can be increased with higher current intensities and larger bubble size, and the gas volume fraction can be enhanced with higher current intensities and lower bubble diameters. Additionally, the liquid velocity will decrease sharply when the bubble diameter smaller than the critical value (0.9 mm). It is better to keep the bubble diameter larger than the critical size for the electrolyte circulation.

Computational fluid dynamics simulation as a tool for optimizing the hydrodynamic performance of membrane bioreactors

“…Two different approaches have been developed to simulate multiphase ow, based on Lagrangian or Eulerian models. 31 The former method employs liquid as the continuous phase and bubbles considered as the discrete phase, which enables motion trajectories to be tracked in each discrete phase. The latter method considers the two phases to be a continuous phase that coexist at the same spatial point, thus enabling processes to be modelled using their respective momentum, mass, and energy transfer equations.…”

Mass Transfer Study inside a Li Production Electrolysis Cell Based on a Rigorous CFD Analysis

“…The cell dynamics obtained in a simulation without modeling the Cl2,gas upward motion would be completely different, close to a common batch reactor. Therefore, a two phase Euler-Euler model is employed assuming that: only the drag force is relevant when compared to other interfacial forces [8]; bubbles are introduced with a constant size and spherical shape identified by the graphical scheme regime for bubbles and drops [9]; and the Schmidt number is fixed to 1.…”

“…(3) (4) (5) where the subscript i identifies the ith phase, U the velocity, R the turbulent Reynolds stresses, and M the interfacial momentum transfer term considering the resistance force felt by each gas-bubble (Eq. 6) (6) dgas is the fixed bubble's diameter, here set to 1.5 mm according to a similar experimental study [8], and CD is the drag coefficient modeled as in Eq. 7 [12]: (7) νliq is the liquid kinematic viscosity.…”

“…Since the authors are not aware of available experimental measurements published on this type of cell configuration for lithium production, a magnesium cell with a similar behavior is used for the validation of the model. This cell has a slightly different configuration with two vertical parallel anodes, a cathode placed in between and an electrolytic solution with a fixed flow rate injected from the bottom [8]. After matching the initial conditions of the experimental data [8], the calculated gas distribution is plotted on top of the PIV data image in Figure 5 with the permission of the Canadian Journal of Chemical Engineering.…”

“…This cell has a slightly different configuration with two vertical parallel anodes, a cathode placed in between and an electrolytic solution with a fixed flow rate injected from the bottom [8]. After matching the initial conditions of the experimental data [8], the calculated gas distribution is plotted on top of the PIV data image in Figure 5 with the permission of the Canadian Journal of Chemical Engineering. The image shows in grey that the presence of bubbles is mostly concentrated close to the anodes and to the free surface.…”