Three-phase numerical simulation of bubble-particle interaction regimes in viscous liquids using a VOF-IBM approach

This study investigates bubble-particle interactions in viscous liquids through three-phase numerical simulations, with the aim of understanding the hydrodynamic mechanisms governing their interaction regimes in real-scale slurry bubble column reactors. The simulation method combines a Volume of Fluid (VOF) approach for tracking the interface between the fluids, and an Immersed Boundary Method (IBM) for resolving the solid-fluid one. The numerical framework is first validated against the data from two existing experimental studies in the literature, showing correctness of implementation and accuracy in predicting relevant interfacial physics. Afterwards, it is used for the small-scale investigation of bubble-particle interactions in a background liquid of varying viscosity, unveiling different possible physical regimes: penetration, bouncing, and shuttling. An energy analysis is conducted on the system, with particular focus on the exchange between the particle kinetic energy and the bubble interfacial energy. The results prove how the energy interplay is a key factor for the transition from one regime to another. Two different simulation campaigns are carried out: one related to an in-line collision between a settling particle and a rising bubble, and one related to an off-center collision, where the particle and bubble center are misplaced with an initial offset. The two sets reveal fundamental differences that are closely investigated in this study. The main contribution of the findings lies in providing small-scale physical insights into the hydrodynamics of bubble-particle interactions, which are essential for future development of upscaling simulation methods for real-scale liquid-gas-solid systems.