Effects of wettability on bubble characteristics in air-water and molten-metal bubble columns using level-set volume-of-fluid computational fluid dynamics

Abstract

This study compares bubble characteristics in wetting air-water bubble columns (AWBCs) and non-wetting N₂-Sn molten metal bubble columns (MMBCs) across bubbling and transient flow regimes using two gas injector types, aiming to guide mmBC reactor design where experimental data are limited. A level-set volume-of-fluid (LS-VOF) computational fluid dynamics (CFD) model was used to sharply track the interface between the gas and liquid phases. A mesh independence test was performed to identify a reasonable mesh density. The LS-VOF model was then validated against experimental bubble size data for the air-water and Ar-Fe systems. The gas holdup (${\alpha }_G$), Sauter mean bubble diameter ($d_{32}$), and specific interfacial area ($a_s$) were compared in AWBCs andMMBCs, which were equipped with either a single-hole nozzle or plate, at superficial gas velocities (u_G) of 3.4 (bubbling regime) and 57.8 mm/s (transient regime). At u_G = 3.4 mm/s, unimodal bubble size distributions (BSDs) were observed for the AWBCs andMMBCs. Under the transient flow regime, the AWBCs andMMBCs exhibited bimodal BSDs with almost identical hydrodynamic parameters (${\alpha }_G$, d₃₂, and a_s), which was attributed to the similar ratio of liquid density (ρ_L) to surface tension (σ) in the systems. In the bubble-shape diagram plotted on the plane of the Eötvös and Reynolds numbers, the AWBCs andMMBCs exhibited ellipsoidal wobbling bubbles, with distinctions identified based on the Morton number. This study offers valuable insights into the similarities and differences between AWBCs andMMBCs under the bubbling and transient flow regimes.