Particle size segregation of bulk material in dustiness testers via DEM simulation

Dustiness testers are used to quantify the level of dust within a bulk material. The generation of dust can occur as a result of many bulk material handling activities, including filling or discharge from storage bins, during free-fall, material impact on conveyor transfers, or impact with other materials. Dust generation can have a serious impact to the environment as well as workers and nearby communities. This paper presents the findings of a discrete element modeling (DEM) study of the flow behavior of a range of binary granular mixes tested in the European Standard and the Australian Standard dustiness testers. Due to current computing limitations, a nondusty material has been chosen for these simulations to determine the underlying characteristics of particle migration within the rotating drums. A range of simulations have been performed using different starting positions of the simulated test product within the rotating drums to determine if this has any overall effect on the particle interactions. Additionally, simulated binary mixtures containing varied size ratios of the same product have been used in an attempt to uncover possible trends, especially in terms of axial and radial segregation.     

Predicting dust emissions – Experimental study compared to coupled DEM/CFD simulations using a reference test bulk material

The awareness of dust emissions is crucial regarding safe industrial processes, environmental protection and health care. For this purpose, closely linked experimental and numerical investigations are performed. This work presents the results of an experimental study which is used for the calibration of a modelling framework based on the Discrete Element Method (DEM) coupled with Computational Fluid Dynamics (CFD) and applied for the calculation of dust emissions for predictive purposes. The key objective of the approach is to come up with a dust source term which enables to describe and to quantify the release of particle emissions. For the presented experimental study, a wind tunnel and a rotating drum setup, which cover various handling types of bulk materials, are used in order to gain data about parameters having an impact on the dust release. The special feature of the investigations is the use of a reference test bulk material which represents a bulk material in its generally main fractions, the fine and the coarse material, keeping the discrepancy between experiments and simulations low. With the help of the experimental results the calibration of the simulation model was carried out and followed by a comparison.     

Technologies for laboratory generation of dust from geological materials

Dusts generated in the laboratory from soils and sediments are used to evaluate the emission intensities, composition, and environmental and health impacts of mineral aerosols. Laboratory dust generation is also utilized in other disciplines including process control and occupational hygiene in manufacturing, inhalation toxicology, environmental health and epidemiology, and pharmaceutics. Many widely available and/or easily obtainable laboratory or commercial appliances can be used to generate mineral aerosols, and several distinct classes of dust generators (fluidization devices, dustfall chambers, rotating drums/tubes) are used for geological particulate studies. Dozens of different devices designed to create dust from soils and sediments under controlled laboratory conditions are documented and described in this paper. When choosing a specific instrument, investigators must consider some important caveats: different classes of dust generators characterize different properties (complete collection of a small puff of aerosol versus sampling of a representative portion of a large aerosol cloud) and physical processes (resuspension of deposited dust versus in situ production of dust). The quantity "dustiness" has been used in industrial and environmental health research; though it has been quantified in different ways by different investigators, it should also be applicable to studies of geological aerosol production. Using standardized dust-production devices and definitions of dustiness will improve comparisons between laboratories and instruments: lessons learned from other disciplines can be used to improve laboratory research on the generation of atmospheric dusts from geological sources.     

VALIDATING A MODEL FOR THE PREDICTION OF DUST GENERATION

Modifications were made to a bench-top dustiness tester to allow for the simultaneous collection of dust generation and separation force data. Tests were performed on limestone, glass beads, titanium dioxide, and lactose, and their results compared to data from a previous study for a large-scale tester. The results of tests on these and four additional materials (instant tea mix, copier toner, baby powder, fly ash) were then compared to a model by Plinke et al. (1995) for predicting the amount and size distribution of dust generation. All of the test materials except glass beads followed the trends in dust generation of the previous study. The results of these tests were then compared to the proposed model. Titanium dioxide and limestone both followed the model very well with 91% and 86% of the data within one standard error of the model respectively. Glass beads and lactose did not perform as well as the other materials each having 45% of their data within one standard error. Overall, 67% of the tests fell within one standard error. Of the four additional materials used to verify the model, only data for the instant tea mix was not within one standard error of the model. These results provide independent confirmation for the ability of the model by Plinke et al. (1995) to predict the amount and size distribution of dust produced by material handling operations.     

A revised methodology for the determination of bulk material cohesion and adhesion

The determination of the wall liner properties and more importantly the flow properties of a bulk material is critical for the design of any bulk materials handling system. The design of such materials handling systems will be most effective when handling bulk materials at the physical properties they were designed to handle. Due to the fast-paced nature of expansion in the mining industry and demand of mineral resources, it is quite common for materials handling systems to handle bulk materials that were not intended for the system. Wet and Sticky Materials (WSM) within the materials handling stream can cause significant downtime, due to events such as blockages of bins, hoppers and transfer chutes, remains left in train wagons and dump trucks as well as conveyor belt carry back (Roberts, 2005; Connelly, 2011 [2]).WSM are problematic within the materials handling stream due to the inter-particle and boundary cohesion and adhesion forces. The current measurement techniques for WSM have limitations and new methods must be considered. The development of new testers that can measure the wall adhesion and inter-particle adhesion of a bulk material can give a quantitative value for the adhesion present in a bulk material sample. The following paper will present a revised methodology for the estimation of the adhesion of bulk materials determined from the extrapolation of the Instantaneous Yield Locus (IYL). The predicted adhesion values from this methodology will be compared to experimental measurements using an inter-particle adhesion tester.     

Numerical modelling of rough particle contacts subject to normal and tangential loading

Granular Matter - While there are plenty of experimental studies pertaining to the dust generation from and dustiness of powders, few of them aim at reaching a theoretical understanding of the...     

The effect of silica nanoparticles on the dustiness of industrial powders

Industrial powders are prompt to be airborne during processing. High dustiness levels may cause process complications like cross-contamination, product loss and filter clogging while increasing the risk of inhalation, dust explosion and fire. Thus, dustiness is often associated with occupational exposure. Despite this, powder products are usually composed of multiple ingredients with silica nanoparticles (S-NP) systematically added to ease their handling. Surprisingly, the relationship between dustiness and product formulation has not been commonly studied. This work investigates the influence of S-NP, SIPERNAT D10 (SD10), on the dustiness of four industrial powders–Avicel PH102, wheat flour, joint filler, and glass beads–using two standard methods: the rotating drum (EN 15051–2) and the vortex shaker (EN 17199–5). Our results show that the dustiness of mixtures powder + SD10 are statistically higher than those of the powder alone and can reach the levels of SD10. TEM micrographs from airborne particles collected in the vortex shaker showed that SD10 detached from the surface of the powder during aerosolisation, emitting nanometric dust; adding SD10 increases the potential for inhalation exposure during industrial processing and handling. Surface energy analysis by inverse gas chromatography (IGC) leads us to conclude that stronger powder-to-SD10 interactions result in less dust emission.     

Evaluation of a small-scale cushion tester

A small-scale cushion tester using small-area test pieces was constructed primarily to evaluate the shock absorbing properties of corrugated fibreboard. Experiments were set up to compare results between the small-area tester and a commercially available model, using samples of cross-linked polyethylene foam from 2 to 4.2cm thick, and thus validate the results obtained with the former. A regression equation was developed to correlate the two testers. The findings indicate that there is a strong correlation between the results obtained by the two testers and that the small-scale tester may be used when experimental design requires that the samples be exposed to extreme conditions of humidity and temperature and when there is a large number of samples of thin cushioning materials to evaluate. This paper does not suggest a replacement to commercially available testers but offers an option for handling experiments involving samples of thin cushioning materials that will be exposed to extreme environmental conditions.     

散状物料转载系统设计DEM仿真方法的研究

颗粒仿真技术可以对散状物料的运动进行观察、机理分析、受力分析、磨损(寿命)估计和系统优化.比较了散状物料转载计算方法,给出了采用DEM方法的建模与模型检验的基本步骤.针对DEM计算方法存在所需计算时间过长的问题,实验比较了降低剪切模量和增大颗粒粒度等方法对DEM计算时间和实验结果的影响,结果表明,在不影响计算结果的前提下可通过降低剪切模量和增大颗粒粒度来缩短DEM仿真计算时间.利用EDEM软件实现了散料转载过程的可视化,比较分析了直线型溜槽、折线型溜槽和曲线型溜槽中物料转载效果.仿真表明：采用变曲率半径效果更好;U型溜槽截面能够减少物料不对中情况的发生.     

Erfahrungen mit mobilen Härteprüfgeräten

Experiences with mobile hardness testers During recent years the use of mobile electronically operating hardness testers has become more and more significant for in-process inspections and shop and site inspections. The field and limits of application for this equipment are determined chiefly by the material to be tested, the geometry of the component as well as the information required of the test. The purpose of our work was to establish, with the help of two mobile hardness testers involving the dynamic and static testing procedure on more than 50 metallic materials, the way in which an alteration to various test parameters (surface condition of the components, tester calibration) would affect the hardness values indicated. Furthermore the scatter of readings for the mobile hardness tester was examined.     

Tribological investigations of high‐performance coatings for internal combustion engines used in motor vehicles

The goal of this study is to investigate the tribological properties of a high‐performance coating, intended to be used for internal combustion engine components, in comparison to conventional materials. By applying the performance material, the manufacturer's objective is to extend the lifetime of the specific component of the engine. In order to highlight the benefits of using performance coatings, a direct comparison between the conventional material used in the engine (named reference material) and the performance material, was necessary. The manufacturer provided four different types of performance material, and the reference material. The study was structured in several investigation phases. First, all investigated materials underwent an optical investigation of the surface, by using a scanning electron‐microscope (SEM). In the second phase, the mechanical properties were determined, by using a roughness‐meter and hardness tester. In the third phase, the friction properties of the materials were studied on a rotating tribometer, using two lubrication types. In the last phase, by replacing the rotating tribometer with an oscillating tribometer, the friction properties of the materials, in the case of boundary lubrication, were investigated. The final objective of this study was to determine the best performance material, among the four provided by the manufacturer and to quantify the benefits of using advanced materials in comparison to classic, conventional materials.     

Experiments and simulations of direct shear tests: porosity, contact friction and bulk friction

The direct shear testers, in particular the Jenike cell, are widely used to measure the bulk material properties for the design of bulk handling equipment. This paper describes a study of the Jenike shear tester using both experiments and discrete element simulations. A total of 90 tests on spherical glass beads and paired glass beads were performed to study the influence of the particle shape, stress level and packing density on the bulk friction at limiting shear. The data are thus useful for validating particle scale simulations of densely packed granular systems. In an attempt to verify the predictive capability of discrete element method, closely matching 3-dimensional discrete element simulations of the shear tests were performed and compared with the experimental observations. The comparison for single spheres shows good quantitative agreement for the limiting bulk friction when there is a good match in the sample porosity. Further research is needed to produce a comprehensive validation of the discrete element method. Several salient observations from this study provide further insight into the roles of particle shape and contact friction on the resulting packing porosity and bulk friction.     

Coupling of FEM and DEM simulations to consider dynamic deformations under particle load

Coupled FEM–DEM simulations enable the direct analysis of the load, the deformation and the stresses inside machine parts which interact with bulk materials. The analysis of large deformations of elastic parts is interesting as the deformation will significantly influence the bulk material behaviour. In this paper a bidirectional coupling method for the FEM software \(\hbox {ANSYS}^\circledR \) Classic and the DEM software \(\hbox {LIGGGHTS}^\circledR \) is presented. The coupling algorithm was verified and validated using a modified draw down test rig. The results from the experimental investigations and the FEM–DEM simulations are compared. A very good correlation between experiments and simulations could be found.     

Transverse bulk solid behaviour during discharge from troughed belt conveyors

Guidelines for the calculation of bulk solid material cross sectional dimensions and the influence of the belt conveyor transition length on the inclination of the trajectory at discharge are well established. However, not a great deal of research has been conducted on the influence of bulk solid material properties and conveyor belt transition geometry on the bulk solid material cross section at discharge. As such, assessment of cross section break-up associated with cohesive materials and transverse spreading of free flowing materials is missing. Conversely, the majority of discharge trajectory analysis techniques focus on analysis in a single vertical plane along the length of the belt.This paper presents an analysis of high speed conveyor discharge trajectories in three dimensions, taking into account transverse spreading of free flowing materials and shearing, or cross section discontinuity, exhibited by cohesive materials. Transverse bulk solid material behaviour and trajectory discharge is evaluated using a combination of experimental laboratory tests, a continuum mechanics approach incorporating CAD and Discrete Element Modelling (DEM). The work presented shows that bulk solid material behaviour at discharge is directly influenced by material characteristics and interactions resulting from the geometry of the belt conveyor transition zone.     

DEM calibration of cohesive material in the ring shear test by applying a genetic algorithm framework

This research demonstrates capturing different stress states and history dependency in a cohesive bulk material by DEM simulations. An automated calibration procedure, based on the Non-dominated Sorting Genetic Algorithm, is applied. It searches for the appropriate simulation parameters of an Elasto-Plastic Adhesive contact model such that its response is best fitted to the shear stress measured in experiments. Using this calibration procedure, the optimal set of DEM input parameters are successfully found to reproduce the measured shear stresses of the cohesive coal sample in two different pre-consolidation levels. The calibrated simulation resembles the stress history dependent values of shear stress, bulk density and wall friction. Through the case study of the ring shear tester, this research demonstrates the robustness and accuracy of the calibration framework using multi-objective optimization on multi-variable calibration problems irrespective of the chosen contact model.     

Development and validation of calibration methods for discrete element modelling

Discrete element method (DEM) is proving to be a reliable and increasingly used tool to study and predict the behaviour of granular materials. Numerous particle-scale mechanisms influence the bulk behaviour and flow of bulk materials. It is important that the relevant measurable input parameters for discrete element models be measured by laboratory equipment or determined by physical calibration experiments for rational results. This paper describes some of the bench-scale experiments that have been developed to calibrate the DEM simulations to reflect actual dynamic behaviour. Relevant parameters such as static and rolling coefficients of friction, coefficient of restitution and inter-particle cohesion forces from the presence of liquid bridges have been investigated to model the bulk behaviour of dry and moist granular materials. To validate the DEM models, the results have been checked against experimental slump tests and hopper discharge experiments to quantitatively compare the poured and drained angles of repose and solids mass flow rate. The calibration techniques presented have the capability to be scaled to model and fine tune DEM parameters of granular materials of varying length scales to obtain equivalent static and dynamic behaviour.     

GZ-10型高精度数字式表面电阻测试仪的研制

静电火花是煤矿、加气站等有危险气体场所发生爆炸的主要点火源之一。为防止静电火花产生,关键是设备和材料必须具有抗静电性能,而评价聚合物制品抗静电性能的主要方法是用表面电阻测试仪测量其表面电阻。本文介绍了研制的新型GZ-10型高精度数字式表面电阻测试仪的系统组成及硬件设计。该表面电阻测试仪采用低阻档和高阻档两组测试电路,高阻档测试电路测量双取样电阻的电压,低阻档电路采用比例法,克服了普通表面电阻测试仪因被测电压或电流的变化而变化的缺点,保证了测量的准确性。     

DEM modelling for flow of cohesive lignocellulosic biomass powders: Model calibration using bulk tests

Biomass feeding problems greatly hinder the industrialization of entrained-flow gasification systems for production of 2nd generation biofuels. Appropriate DEM modelling could allow engineers to design solutions that overcome these flow problems. This work shows the application of a DEM calibration framework to produce a realistic, calibrated and efficient material model for lignocellulosic biomass. A coarse (500–710?µm) and a fine (200–315?µm) sieving cut of milled poplar were used in this study. The elongated shape and the cohesive behavior were respectively simulated using a coarse-grained multisphere approach and a cohesive SJKR contact model. Measurements of three physical responses (angle-of-repose, bulk density, a retainment ratio) allowed calibration of the sliding (µ_s) and rolling friction (µ_r) coefficients and the cohesion energy density (CED). Using a statistical analysis, the most influential calibration parameters for each bulk response were identified. A Non-Dominated Sorting Genetic Algorithm was used to solve the calibration multi-objective optimization problem. Several sets of optimal solutions reproduced accurately the three physical responses and the experimental shear responses were closely reproduced by simulations for the population of coarse particles. The DEM calibration framework studied here aims to produce material models useful for assessing flow behavior and equipment interaction for biomass particles.