Effects of Slotted and Inclined Anodes on Gas Removal and Bubble Dynamics in an Air–Water Model of the Hall–Héroult Cell

The effects of slotted and inclined anodes on multibubble dynamics were investigated using a low-temperature air-water model with four scaled carbon anodes: traditional (nonslotted, noninclined), semislotted, fully slotted, and a nonslotted anode inclined at 1°. Beyond geometric effects, the study captures multiple factors governing the flow field, including bubble-induced momentum transfer, transient acceleration events, gas removal phenomenon, and local turbulence induced by bubble transient motion. Gas removal, resistance-based efficiency, bubbly layer resistance, bubble kinematics, and bubble-induced liquid flow over the anode-to-cathode distance (ACD) were quantified. Relative to the traditional anode, resistance-based efficiency increased by 58.5% (inclined), 56.8% (fully slotted), and 39.7% (semislotted), while gas removal ratios through slot valleys reached 3.8% (fully slotted) and 3.2% (semislotted). Despite shorter slots, the semislotted anode more effectively accelerated bubble escape and reduced residence time, likely due to stronger capillary forces, yielding higher slot effectiveness (17.2%) than the fully slotted design (11.7%). Time-averaged bubble acceleration from generation to release was highest for the inclined anode, followed by the traditional, semislotted, and fully slotted cases; however, transient slot-induced accelerations exceeded time-averaged values for all configurations, including the inclined case, due to sudden velocity increases within slot valleys. Slotted and inclined anodes significantly reduced bubble size, residence time, coverage ratio, and bubbly layer resistance relative to the traditional configuration. Laser-based visualization showed that multibubble motion induces vortical and turbulent flow in the ACD for all cases, with stronger vortex activity for the traditional anode, suggesting implications for alumina transport.