Numerical Modeling of Wet Milling Process by an Improved CFD-DEM-VOF Model

Wet ball mill that has been extensively used to comminute the raw materials in various industries possesses the advantages of large production capacity, high grinding efficiency, low investment and so on. Wet mill is a typical gas-liquid-solid three-phase system, and the interaction between these three phases is quite complex, resulting in the difficulty to simulate the wet milling process. As a consequence, a numerical model by coupling computational fluid dynamics (CFD), discrete element method (DEM) and volume of fluid (VOF) is developed to accurately simulate the wet milling process. A novel scheme is also devised and incorporated into CFD-DEM-VOF model to treat the interphase coupling when the particles and CFD cells have the comparable size that will be encountered in simulating the wet milling process. The accuracy of the established CFD-DEM-VOF coupling model is then validated by several test cases, including the single particle sedimentation in air-liquid domain, water entry of particle assembly and three-phase flows in a lab-scale wet mill and an industrial-scale wet mill. Furthermore, the effects of CFD cell size (2.5, 5 and 10 mm) and mill rotation speed (10, 30 and 50 r/min) on the prediction accuracy are also explored by the test case of lab-scale mill. The results indicate that using the quite coarse CFD cells can deteriorate the simulation accuracy, and increasing the mill rotation speed will enhance this influence. Nevertheless, adopting the very fine CFD cells (e.g., 2.5 mm in this work) in our model is not necessary in terms of the accuracy in simulating the particle behaviors, and the reliable prediction of particle behaviors can still be obtained while using the relatively large CFD cells (e.g., 5 mm in this paper).