David Pinson

Coordination number of binary mixtures of spheres

This paper presents an experimental study of the coordination number of binary packings by the use of the liquid bridge technique and provides detailed information about the distributed coordination numbers corresponding to different types of contacts between small and large components and their dependence on particle size distribution. The results indicate that increasing the volume fraction of small component increases the small-to-small and large-to-small contacts and decreases the small-to-large and large-to-large contacts; and this trend is more apparent for a packing with a large size difference. For the packings under gravity, the overall mean coordination number is essentially a constant and independent of particle size distribution.

A New Approach for Studying Softening and Melting Behavior of Particles in a Blast Furnace Cohesive Zone

The cohesive zone where ferrous burden materials soften and melt plays a critical role in determining the performance and stability of a blast furnace. The softening and melting behavior of ore particles significantly affects the layer permeability and structure, and subsequently changes the gas/liquid distribution and heat transfer in the cohesive zone. Wax balls are often used in physical experiments to study the ore softening and melting behavior because of their low melting temperature. In this work, a new approach on the basis of discrete element method is established. The relationship between Young’s modulus (E) and temperature (T) of wax balls is first proposed based on the experimental data, and then implemented into a DEM model. The particle deformation, temperature, coordination number, and gas pressure drop under conditions relevant to blast furnace operations are then examined. The results show that the proposed approach can capture the main features of softening and melting behavior of particles. On this basis, the effects of a few variables are investigated. The approach and results should be useful to the establishment of a comprehensive picture about softening and melting behavior, and its effect on blast furnace operations.

Gas-liquid-powder flow in moving particles : Operational and non-operational regimes

Abstract An experimental study has been carried out for gas–liquid–powder–solid four-fluid flow in a packed bed. This system simulates the complex flow conditions in an ironmaking blast furnace which involves the upward flow of gas and unburnt coal/char and the downward flow of coke and molten iron and slag. It is shown that depending on the flow conditions, both steady and unsteady state flows can be observed, giving the so-called operational and non-operational regimes. The effects of solid, liquid, powder and gas flow conditions on the two regimes have been quantified. The non-operational regime stems from the flooding caused by high superficial gas and liquid velocities, and powder mass flux and/or hanging caused by high powder mass flux and low gas velocity. The operational regime expands with an increase in solid velocity, and contracts with an increase in gas and liquid velocities and/or powder mass flux.

Impaction of particle streams on a granular bed

Impaction of particle streams on granular beds can be observed in various processes. One typical example is the burden distribution in an ironmaking blast furnace. The stream of heavy iron-bearing pellets impacts the pre-formed coke surface at the blast furnace throat region. The coke layer then can move and collapse. The formed burden profile is important in controlling the radial distribution of gas flow, and hence productivity and stability. In this paper, the impaction of pellets on the coke surface is investigated using discrete element method. A 90 degree sector is modelled with a pre-formed coke surface impacted by pellets flowing from a rotating chute. Microscopic analysis on the flow and force structures is carried out to examine the impaction with different chute angles and discharge rates.

Segregation of binary mixtures of spheres and ellipsoids

Segregation can occur under vibration for a mixture of particles with different shapes. In this work, binary mixtures of spheres and ellipsoids are used to investigate segregation under one-dimensional, vertical vibration. The experimental results show that the convection is very much related to the segregation observed. Along the wall, particles move downwards to the bottom and then return to the top in the center of the particle bed. Ellipsoids with small or large aspect ratios can easily travel to the voids near the wall, move downwards and to be trapped at the bottom of the bed. Segregation is confirmed by analyzing the distribution of different types of contacts.

Discrete modelling of the packing of ellipsoidal particles

Particle shape affects the packing characteristics significantly. Such a topic has been investigated extensively in the literature by physical experiments or mathematical modelling. In this paper, we give a summary of packing of ellipsoidal particles using discrete element method. As ellipsoidal particles can represent a large number of shapes, e.g. from platy to elongated, the relationships between packing properties (such as packing fraction, coordination number and radial distribution function) and aspect ratios are established. Flow and force structures are also presented to illustrate how the shape affects those microscopic properties for further fundamental understanding. The results demonstrate that discrete element method provides a useful method to investigate the packing dynamics of ellipsoidal particles.

Microscopic analysis of Hopper flow with ellipsoidal particles

Hoppers are widely used in process industries. With such widespread application, difficulties in achieving desired operational behaviors have led to extensive experimental and mathematical studies in the past decades. Particularly, the discrete element method has become one of the most important simulation tools for design and analysis. So far, most studies are on spherical particles for computational convenience. In this work, ellipsoidal particles are used as they can represent a large variation of particle shapes. Hopper flow with ellipsoidal particles is presented highlighting the effect of particle shape on the microscopic properties.