Three-dimensional simulation of gas-solid-liquid flows using the DEM-VOF method

Gas-solid-liquid flows are widely found in chemical engineering, e.g. the processes of mixing, wet ball milling, and screw kneading, for which the numerical modeling is now a pressing research topic to help improve the design and investigate operational conditions. On the other hand, computational challenges are posed for existing methods in modeling the interphase interactions and complex boundaries within such three-phase systems. In this paper, an Eulerian-Lagrangian numerical model, specifically the DEM-VOF method, is presented for three-dimensional simulations of gas-solid-liquid flows. The fluid motion is solved by using a computational fluid dynamics (CFD) based approach with gas-liquid interface capturing provided by the volume-of-fluid (VOF) method. The particle phase is tracked by the discrete element method (DEM) as discrete entities. The fluid-particle coupling is achieved by the volume-averaging technique wherein a well-established empirical closure is adopted for the description of hydrodynamic forces. Particularly, the modeling of arbitrary-shaped walls and moving boundaries is addressed via the introduction of signed distance function (SDF) representation and immersed boundary (IB) method, which was proved to be highly efficient for gas-solid-liquid systems interacting with complex geometries. Special attentions when computing fluid-particle interactions near those boundaries are raised and their treatments are also discussed. Various model verifications and validation tests are performed in this study to show the validity and capability of the DEM-VOF method. By comparing with analytical solutions and experimental data, we generally find good agreements from the simulation results, thereby highlighting its potential in accurately modeling complicated gas-solid-liquid flows. To the best of our knowledge, the proposed method is the first report that successfully couples the DEM to a VOF solver with non-trivial wall boundaries.