• Energy Research

The flow of particles in a horizontal rotating drum is studied based on the results generated by Distinct Element Method (DEM). The simulation conditions are comparable to those measured by means of Positron Emission Particle Tracking (PEPT), with a drum being 100 mm in diameter, 35% filled by spheres of 3 mm diameter, and rotating at a speed from 10 to 65 rpm. The simulation method is validated from its good agreement with the PEPT measurement in terms of the dynamic angle of repose and spatial velocity fields. The dependence of flow behaviour on rotation speed is then analysed based on the DEM results, aiming to establish the spatial and statistical distributions of microdynamic variables related to flow structure such as porosity and coordination number, and force structure such as particle interaction forces, relative collision velocity and collision frequency. An attempt has also been made to explain the effect of rotation speed on agglomeration based on the present findings.

This paper presents a numerical study of multiphase flow in hydrocyclones with different configurations of cyclone size and spigot diameter. This is done by a recently developed mixture multiphase flow model. In the model, the strong swirling flow of the cyclone is modeled using the Reynolds stress model. The interface between liquid and air core and the particle flow are both modeled using the so-called mixture model. The solid properties are described by the kinetic theory. The applicability of the proposed model has been verified by the good agreement between the measured and predicted results in a previous study. It is here used to study the effects of cyclone size and spigot diameter when feed solids concentration is up to 30% (by volume), which is well beyond the range reported before. The flow features predicted are examined in terms of the flow field, pressure drop, and amount of water split to underflow, separation efficiency and underflow discharge type. The simulation results show that the mult...

Abstract The Computational Fluid Dynamics-Discrete Element method (CFD-DEM) approach for cylindroid particles was developed to study the effects of particle shape on spouting behaviors in a flat-bottomed spouted bed. The gas motion was modelled with k-e turbulent model, and the particles was represented with the realistic cylindroid shapes. The various particle contact scenarios and contact forces between cylinders, as well as the drag force model for non-spherical particles were comprehensively involved to describe the particle motions more accurately. With the aspect ratio of particle varying from L/d = 0.25 to 3.0, spouting behaviors including flow pattern, particle velocity, orientation and contact details were studied. Results found that cylindroid particles show the clear different orientations in the three regions of spouted bed. In spout, cylindroid particles tend to put their longer dimension parallel to the (vertical) flow direction, while in annulus the orientation tendency is contrary and particles tend to put their larger dimension perpendicular to their falling direction. The particle with L/d = 1.0 obtains the maximum projected area in spout and thus the largest drag force and the highest particle velocities. When L/d deviates from 1.0, with particle shape becoming flatter or longer, the particle projected area in spout accordingly decreases, resulting in the decreasing particle velocity and particle circulation rate. On the other hand, when aspect ratio deviates from 1.0, the obviously increasing particle contact number in annulus reflects their increasing interlocking effects and worse flowability.

Abstract Ribbon mixers are widely used in practice because they are capable of providing high speed convective mixing. Here, the discrete element method (DEM) is used to investigate the effects of impeller speed and fill level on the mixing behaviors of mixtures of particles with different cohesion in two-bladed and four-bladed ribbon mixers, each having a horizontal cylindrical vessel. The mixing behaviors are characterized by a particle-scale mixing index. Simulations show that the mixing rate increases with the impeller speed for both the cohesive and non-cohesive particle mixtures up to a certain speed, beyond which it shows a reduction. The mixing rate becomes poorer at higher impeller speeds for mixing of cohesive particles in the 2-bladed mixer. Inspection of velocity fields shows that many localized recirculation flows exist when the mixing non-cohesive particles, preventing the overall mixing. By contrast, when mixing cohesive particles, there exist circumferential flow about the shaft axis and convective flow in the horizontal axial direction, improving the particle mixing. The mixing rate deteriorated with an increase of the fill level in both the two-bladed and four-bladed mixers. The mixing rate of the particles is higher in the four-bladed mixer compared to the two-bladed mixer. With the increase of fill level, the particle flow changes successively from the sliding type of flow to recirculation flow and then to cascading flow for non-cohesive particles. The four-bladed mixer performs better for mixing at high fill levels and stronger cohesion, consolidating its advantage for mixing cohesive particles.

AbstractThe pneumatic transport of granular material is a common operation frequently employed to transport solid particles from one location to another. It is well established in the literature that different flow regimes can arise in such transportation processes depending on the system geometry and operating conditions used. In this study, the pneumatic transports of solid particles in both vertical and horizontal conveying lines were studied numerically using the discrete element method coupled with computational fluid dynamics. The simulation outputs corresponded well with reported experimental observations in terms of the different flow regimes obtained at different operating conditions. In the vertical pneumatic conveying simulations, two different flow patterns corresponding to the experimentally observed dispersed flow and plug flow regimes were obtained at different gas velocities and solid concentrations. Similarly, the homogeneous flow, stratified flow, moving dunes, and slug flow regimes previously reported to occur in horizontal pneumatic conveying were also reproduced computationally in this study. Solid concentration profiles obtained by spatial averaging along the length of the pipe showed a symmetrical but non‐uniform distribution for dispersed flow and an almost flat distribution for plug flow in vertical pneumatic conveying. The profile for stratified flow in horizontal pneumatic conveying showed higher solid concentration near the bottom wall due to the effects of gravitational settling, while that for slug flow was flat. Hysteresis in solid flow rates was observed in vertical pneumatic conveying near the point where transition between the dispersed and plug flow regimes was expected to occur. Solid flow rates were also found to be more sensitive towards the coefficient of friction than the coefficient of restitution of particles and the pipe walls in a sensitivity analysis study of these parameters. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Pneumatic conveying is an important technology in industries to transport bulk materials from one location to another. Different flow regimes have been observed in such a transportation process dep...

Abstract Particle mixtures with a wide range of sizes, shapes, and densities may experience significant segregation. In the hopper discharging process, segregation predominantly happens on the free surface of mixtures with size ratio