The solid-liquid two-phase flow with a large particle is a basic research object in the two-phase transportation field, such as the deep-sea mineral transportation. This paper presents a coupled Resolved CFD-DEM approach to simulate settling and floating movements of a sphere particle with different diameter flowing in a vertical pipe, and numerical results are compared with experimental studies. The numerical simulation results are in good agreement with the experimental results. The paper also performs a numerical study on hydraulically collecting a sphere particle to analyze the flow field and particle movements. The method used in this study is suitable for studies of large particle solid-liquid two-phase flow.
The deep-sea mining system is to pick up the solid particles or solids in alluvial form, including heavy mineral particles from the deep-ocean floor, convey the solid particles to the mining ship on the sea. The basic research object is the solid-liquid two-phase flow, specifically, the particle-water two-phase flow. The mineral particles are mostly spherical or ellipsoidal, with their long-axis length varying from 2 cm to 10 cm, and the hydraulic lifting process is the large particle solid-liquid two-phase flow. The movement mechanism of the particle-water mixture is the key to the hydraulic lifting technology. However, the solid-liquid two-phase flow is difficult to solve directly through theoretical research due to the complexity, and the actual engineering solution is dependent on experience and experimental research (Chen et al., 2010; Wang et al. 2014). In recent years, with the fast development of computer technology, numerical method is to get the large scale, and avoid to solve directly the theoretical equation and its cost is much lower than the experimental research. Currently in the numerical study of the solid-liquid two-phase flow, the fluid phase is generally consider as the continuous phase. For the processing of solid particles, there are two kind ways: the solid particles are considered as a continuum, and the representative method is Euler-Euler method (Jackson, 1965); the other way is to treat solid particles as Discrete Particle phase, and the representative method is Discrete Particle Method (DPM) (Ottjes, 1978). Euler-Euler method is to treat fluid and solid particles as the continuum, but is not appropriate for the large particle solid-liquid two-phase flow. Otherwise, a large error between the numerical models with the actual solution occurs. DPM is to treat the liquid phase as continuous phase and solid particles as the discrete phase, but the interaction between particles is not considered. DPM is only suitable for small particles (particle size is smaller than CFD grid) at low concentrations. Furthermore, DEM is a method that calculates the interaction between particles. Tsuji et al combines the Computational Fluid Dynamics (CFD) and DEM to predict successfully the gas-solid two-phase flow in fluidized bed, and the method is called coupled CFD-DEM approach. Now, CFD-DEM approach is an important method in the research field of solid-gas two-phase fluidization technology (Zhang et al., 2007; Du et al., 2014) and the solid-liquid two-phase flow (Huang et al., 2014; Su et al., 2016).
