(149h) Numerical Studies on Effects of Particle Rotation in Riser Flows

Particle-fluid drag correlation is the most essential part in the CFD modeling of Particle-laden flows. Researchers have invested enormous effort to obtain various drag relations. However, none of these drag relations have demonstrating their significant advantages over others in real applications, indicating that the interactions between the fluid phase and particles may be significantly affected by factors other than the drag force. Using an efficient immersed boundary-lattice Boltzmann method (IB-LBM), the Magnus lift force is computed in flows through random arrays of spheres. The results indicate that the lift force is insignificant at the rotational Reynolds number below 1. However, it can be larger than the drag force as the rotational Reynolds number increases up to O(100) especially at low solid volume fractions. The torque exerted on spheres by the fluid phase is also investigated since it is essential to account for addition energy dissipation of the two-phase system due to particle rotation. We then installed the proposed formulas for Magnus lift forces and torques in the open source software Multiphase Flow with Interphase eXchanges (MFiX). Computational fluid dynamics-discrete element model (CFD-DEM) simulations of a riser flow are performed to investigate the effects of particle rotation. Periodic boundary conditions are implemented in the vertical direction while non-slip conditions are used for lateral walls. It is found that the minimum riser width needed to reproduce the core-annular structure is around 100d, where d is the diameter of particles. The size of clusters is relatively smaller compared to results without considering particle rotation. This is believed to be caused by the Magnus lift force produced by fast rotating particles, which makes particles more dispersive in space and accelerates the breakup of clusters. The effects of particle rotation on the granular temperature, skewness and kurtosis of vertical velocity are also analyzed. CFD-DEM simulations of a bubbling fluidized bed are also performed in this study. The effects of particle rotation are found to be very marginal. This is due to that particles in bubbling fluidized bed are most rotating at low and moderating speed, making the Magnus lift force negligible compared to the drag force.