Single-bubble rise in liquid metals: CFD modeling, validation, and correlation assessment

This work presents a detailed numerical analysis of the rising motion of single bubbles in stagnant liquid metals (LM) over bubble diameters [[EQUATION]]. Simulations were performed using the geometric Volume-of-Fluid (VOF) method implemented in the open-source computational fluid dynamics (CFD) code OpenFOAM. Four bubble–LM systems of nuclear relevance were considered: helium in lead–lithium eutectic (He/LLE), steam in lead–bismuth eutectic (Steam/LBE), nitrogen in LBE (N₂/LBE), and nitrogen in mercury (N₂/Hg). The CFD model was validated against benchmark experimental data for N₂/Hg, yielding a mean absolute relative deviation (MARD) of 4.0%.The simulations revealed distinct trajectory regimes: small bubbles followed oscillatory zigzag paths, whereas larger bubbles rose predominantly vertically. Terminal velocities followed the trend He/LLE (187–206 mm/s) > Steam/LBE (180–185 mm/s) > N₂/LBE (178 mm/s) > N₂/Hg (175–180 mm/s). Notably, velocities for steam bubbles in LBE were up to ~30% lower than reported values from similarity experiments in transparent liquids, suggesting more conservative design margins are required for lead-based reactors. Sixteen published correlations were assessed (terminal-velocity and drag-coefficient models). Most terminal-velocity correlations predicted within 10–20% deviation, with Maneri and Vassallo (2000) performing best (MARD = 8.9%). Drag-coefficient correlations were generally less accurate; Yan et al. (2018) provided the highest predictive capability (MARD = 2.9%). This study provides reference data and a tested methodology for single-bubble dynamics in liquid metals, informing correlation selection and safety analyses in advanced fission and fusion systems.