Effect of Anode Geometry on Bubble-Driven Transport, Recirculation, and Mixing in Aluminum Electrolysis

Abstract

Gas-evolving electrodes generate buoyancy-driven flows that control gas removal, liquid-phase transport, and mixing in many electrochemical and metallurgical reactors. In Hall–Héroult aluminum electrolysis cells, these processes occur beneath carbon anodes, where bubble accumulation, detachment, and transport influence bath circulation and operational stability. Here, a one-fifth-scale air–water model of the Hall–Héroult electrolytic cell is used to quantify how anode geometry modifies gas–liquid transport beneath three industrially relevant prebaked anode configurations: flat, inclined, and grooved. High-speed imaging and particle image velocimetry are combined to measure bubble size, gas coverage, bubble residence time, mean and fluctuating velocity fields, vorticity, vortex occurrence, Reynolds stresses, strain rate, enstrophy, turbulent kinetic energy, and fluctuation spectra in the anode-to-cathode gap and side-channel regions. The results show that anode geometry controls the transition between accumulation-dominated transport, directional gas evacuation, and recirculation-enhanced mixing. The inclined anode reduces gas coverage and bubble residence time by promoting continuous bubble sliding toward the side channel, producing organized transport with weaker recirculation in the ACG and suppressed shear-driven instabilities. In contrast, the grooved anode increases bubble–geometry interactions and bubble residence time relative to the inclined case, generating localized shear, vortex formation, multiscale fluctuations, and stronger recirculation-driven mixing; in the anode-to-cathode gap, vortex activity and strain rate increase by up to approximately 30 and 57%, respectively. Engineering metrics based on gas coverage, residence time, flow directionality, and recirculation are used to construct regime maps linking bubble transport to liquid-flow organization.