Validation of a Discrete Element Method (DEM) Model of the Grinding Media Dynamics within an Attritor Mill Using Positron Emission Particle Tracking (PEPT) Measurements

Abstract

Positron emission particle tracking (PEPT) was used to investigate the grinding media dynamics in a laboratory-scale attritor mill in the absence of powder. The grinding media motion was analysed as a function of the equipment’s typical operating parameters: impeller speed, impeller clearance and bead fill level. It was observed that the impeller speed had the strongest influence on the media motion. An increase of the impeller speed from 300 rpm to 600 rpm led to a change in the bead recirculation patterns with the increasing formation of well segregated upper and lower recirculation loops that fully developed at the maximum speed of 600 rpm. For a constant impeller speed, an increase of the bead loading did not majorly affect the bead velocity as remarked by minor changes on the flow field. For all the impeller clearance values, the occupancy plots revealed an inefficient dead region at the bottom of the attritor where the beads were moving at very low velocity. In this region the beads were tightly packed under their own weight and, furthermore, there was an absence of direct contact with the impeller arms. The depth of this region increased proportionally to the distance between the bottom of the impeller and the vessel base indicating that a minimum value of clearance should be set to optimise the lower recirculation pattern. For two experimental conditions, the data generated by PEPT measurements were utilised to set-up a friction-adjusted discrete element method (DEM) model. Here, the simulation results were qualitatively and quantitatively compared against the PEPT data by assessing the averaged velocity flow fields and the average velocity profiles at different radial locations inside the vessel. Given the intrinsic uncertainty of the PEPT measurements, the DEM model results were in considerably good agreement with the experimental results. The major discrepancy was observed close to the vessel wall where the simulations overpredicted the velocity by about 10%.

Forces and flow induced by a moving intruder in a granular packing: coarse-graining and DEM simulations versus experiments

“…Mixing powders using intruders, such as blades, paddles, agitators… is widely used in chemical engineering [1,2], civil engineering [3], pharmaceutical [4,5], food science [6,7] or agronomy [8,9]. Common concerns regarding interactions between an intruder and a granular bed are shared by many unit operations like blending, kneading [10], wet agglomeration [11,12] or milling [13,14].…”

A Dynamic Coarse Grain Discrete Element Method for Gas-Solid Fluidized Beds by Considering Particle-Group Crushing and Polymerization

“…Here E p and σ p are respectively the elasticity modulus and the Poisson ratio of the collisions between particles, and σ w and E w are those of the collisions between particles and solid walls. The equivalent shear modulus of the colliding bodies G p in Equations (10) and (11) is given by:…”

“…The discrete element method (DEM) which was first described by Cundall and Strack [8] is one of the most used simulation tools for dense granular flows [9,10]. In the DEM, each particle is tracked individually based on Newton's second law of motion.…”

A Novel Particle-Based Approach for Modeling a Wet Vertical Stirred Media Mill

“…Positron emission particle tracking (PEPT) is a technique that has been used with some success to experimentally study the dynamics of grinding media as an attempt to quantify the grinding performance [20,21]. In [22], a combination of PEPT and DEM was used to study the grinding media dynamics in a vertical attritor mill. Particle breakage in a ball mill is modeled using DEM and a bonded-cell method in [23].…”