Modelling the Dynamics of Granular Particle Interactions in a Vortex Reactor using a Coupled DPM-KTGF Model

Journal article, 2020

In this work, a shear-driven two-phase particulate flow of monodispersed and polydispersed granular materials has been studied experimentally and numerically as a function of solids concentration and restitution coefficients for different operating speeds N (70 -130 rpm) in a lab-scale rotor-stator agglomeration reactor. A coupled computational fluid-particle dynamics (CFPD) model was developed consisting of a steady-state flow field of the continuous phase coupled to a transient particle tracking of the discrete phase. This was achieved via a one-way coupling between the continuous and the discrete phase by including the effect of drag, lift, pressure gradient, virtual mass forces, as well as granular collisional forces in describing the particle-particle, particle-wall and the fluid-particle interactions. The spatiotemporal evolution of the flow pattern, discrete phase properties, and influence of the operating conditions on the granular properties were characterized. The validation of the numerical model developed in this study was carried out based on the theoretical analysis of the rotor-stator flow and the PIV flow measurements. The results showed that the particle sizes were uniformly distributed within the reactor after steady-state conditions, while a small region of high particle concentration was observed near the rotor due to low vorticity and turbulent intensity around the region. In terms of the operating conditions, the restitution coefficients and the operating speeds do not have a significant influence on the granular properties apart from the small region around the shaft where there is a correlation between these parameters. The particle sizes, however, show a positive correlation with the granular properties. Also, a wider particle size distribution was observed axially towards the stator, which might be attributed to the pumping effect of the Batchelor flow in this direction. It was also concluded that the discrete phase velocity does not seem to vary significantly with the restitution coefficients. Furthermore, the vertical velocity and vorticity profiles give a reasonably good agreement between the CFPD model predictions and PIV measurements. The minor observed deviations were mainly due to some of the experimental limitations rather than the robustness of the CFPD model or the numerical code.