Review: Calibration of the discrete element method

The reach of tribology has expanded in diverse fields and tribology related research activities have seen immense growth during the last decade. This review takes stock of the recent advances in research pertaining to different aspects of tribology within the last 2 to 3 years. Different aspects of tribology that have been reviewed including lubrication, wear and surface engineering, biotribology, high temperature tribology, and computational tribology. This review attempts to highlight recent research and also presents future outlook pertaining to these aspects. It may however be noted that there are limitations of this review. One of the most important of these is that tribology being a highly multidisciplinary field, the research results are widely spread across various disciplines and there can be omissions because of this. Secondly, the topics dealt with in the field of tribology include only some of the salient topics (such as lubrication, wear, surface engineering, biotribology, high temperature tribology, and computational tribology) but there are many more aspects of tribology that have not been covered in this review. Despite these limitations it is hoped that such a review will bring the most recent salient research in focus and will be beneficial for the growing community of tribology researchers.

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A review of recent advances in tribology

As a consequence of increasing computer power and more readily useable commercial and open source codes, Discrete Element Method (DEM) is becoming widely used across a range of applications to simulate increasingly complex processes. This is exacerbating the challenge of setting up simulations for industrial applications. The literature on input parameter selection is divided. A number of papers report methods for their direct measurement. Others, by contrast, propose a “calibration” approach where the particle properties are derived as adjustable parameters by quantitative comparison of experimental and simulation results. This paper reports on the calibration and validation of the input parameters for the specific case of cylindrical tablets represented by conjoined spheres. The initial steps are to not only assign and optimise the DEM input parameters but also optimise the shape representation; what degree of linearity of the edges and angularity of the corners are required to accurately reflect the cylindrical shape. The model was used to simulate two configurations of a rotating drum: an “attrition tester” with a single longitudinal baffle and an un-baffled drum. The results were compared qualitatively and quantitatively with experimental data. While the qualitative comparison was good in most cases, detailed quantitative comparison fared less well, with some significant errors. This study highlights some of the key issues for a wider-spread of industrial applications for DEM.

https://www.jstage.jst.go.jp/article/kona/32/0/32_2015016/_pdf

Discrete Element Method (DEM) for Industrial Applications: Comments on Calibration and Validation for the Modelling of Cylindrical Pellets

CFD-DEM modelling and simulation of pneumatic conveying: A review

The influence of particle shape on flow modes in pneumatic conveying

Velocity and porosity relationships within dense phase pneumatic conveying as studied using coupled CFD-DEM

...............................................................................................................1 CHAPTER 1: INTRODUCTION................................................................................2 1.1 Modes of Flow .........................................................................................................3 1.1.1 Plug flow.........................................................................................................4 1.1.2 Fluidised dense phase flow .............................................................................6 1.2 Thesis Overview ......................................................................................................8 1.2.1 Mode of flow...................................................................................................8 1.2.2 Solids friction..................................................................................................9 1.2.3 Solids velocity...............................................................................................11 CHAPTER 2: PREDICTING CONVEYING MODES OF FLOW.......................13 2.1 Bulk Material Parameters.......................................................................................14 2.1.1 Basic parameters ...........................................................................................14 2.1.1.1 particle size distribution.......................................................................14 2.1.1.2 particle density .....................................................................................14 2.1.1.3 bulk density..........................................................................................15 2.1.2 Air-particle parameters .................................................................................15 2.1.2.1 permeability .........................................................................................16 2.1.2.2 steady state fluidisation pressure .........................................................16 2.1.2.3 de-aeration............................................................................................16 2.2 Mode of Flow Data ................................................................................................17 2.3 Predictive Diagrams...............................................................................................21 2.3.1 Basic bulk material diagrams........................................................................21 2.3.1.1 Geldart’s fluidisation diagram .............................................................23 Dense Phase Pneumatic Conveying of Powders: Design Aspects and Phenomena v 2.3.1.2 Molerus’s fluidisation diagram ............................................................27 2.3.1.3 Dixon’s slugging diagram....................................................................31 2.3.1.4 Pan’s pneumatic conveying predictive diagram ..................................34 2.3.2 Air-particle bulk material diagrams ..............................................................35 2.3.2.1 Mainwaring and Reed diagram............................................................36 2.3.2.2 Jones diagram.......................................................................................39 2.3.2.3 Chambers et al parameter.....................................................................40 2.3.2.4 Fargette et al parameter........................................................................42 2.3.2.5 Sanchez et al diagram ..........................................................................44 2.4 Proposed Mode of Flow Diagram..........................................................................46 2.5 Summary ................................................................................................................47 CHAPTER 3: EXPERIMENTAL PROGRAM AND DATA.................................49 3.1 Bulk Material Testing Methods .............................................................................49 3.1.1 Basic parameter test methods........................................................................49 3.1.2 Air-particle parameter test methods..............................................................51 3.1.3 Flow property tests........................................................................................53 3.2 Bulk Material Data.................................................................................................54 3.2.1 Cement Meal .................................................................................................55 3.2.2 Flyash............................................................................................................57 3.2.3 Alumina.........................................................................................................59 3.3 Conveying Tests.....................................................................................................61 3.3.1 Feeding and receiving systems .....................................................................61 3.3.2 Calibration of instruments.............................................................................63 3.3.3 Air mass flow rate calibration.......................................................................65 Dense Phase Pneumatic Conveying of Powders: Design Aspects and Phenomena vi 3.3.4 Conveying pipeline configurations ...............................................................67 3.3.5 test procedure and analysis ...........................................................................71 3.3.5.1 test procedure .......................................................................................71 3.3.5.2 test analysis ..........................................................................................71 3.4 Jones Pneumatic Conveying Test Data [18] ..........................................................76 3.4.1 Pulverised Fuel Ash data sheet .....................................................................77 3.4.2 Democrat Flour .............................................................................................78 3.4.3 Iron Powder data sheet..................................................................................79 CHAPTER 4: SOLIDS FRICTION CORRELATIONS – REVIEW AND ANALYSIS .........................................................................................80 4.1 Current Pressure Models ........................................................................................81 4.1.1 Scale-up methods ..........................................................................................81 4.1.2 Empirical methods ........................................................................................82 4.2 Solids Friction and Two Phase Fluid Pressure Model ...........................................83 4.2.1 Air friction factors.........................................................................................83 4.2.2 Solids friction factors ....................................................................................84 4.2.3 Effect on pressure drop .................................................................................87 4.2.3.1 diameter scale-up analysis ...................................................................89 4.2.3.2 length scale-up analysis .......................................................................92 4.3 Comparison of Pressure Analysis with Experimental Tests ..................................95 CHAPTER 5: SOLIDS FRICTION – POWER LAW ..........................................100 5.1 Back Calculation of the Power Law ....................................................................100 5.1.1 Co-efficient and exponent behaviour..........................................................101 5.1.2 Scale-up behaviour......................................................................................107 5.1.2.1 pipeline length variations ...................................................................108 Dense Phase Pneumatic Conveying of Powders: Design Aspects and Phenomena vii 5.1.2.2 pipeline diameter variations ...............................................................113 5.1.3 Summary of power law back calculation....................................................118 5.2 Optimal Power Law Determination .....................................................................119 5.2.1 Empirical optimisation methods .................................................................119 Comparison of the optimal power law methods ...................................................124 5.2.2 Pressure drop prediction and bench scale based parameters.......................125 CHAPTER 6: NUMERICAL MODEL FOR SOLIDS VELOCITY...................130 6.1 Current modelling ................................................................................................131 6.2 The Initial Continuum Model Approach..............................................................131 6.2.1 Force equilibrium and conservation of mass ..............................................132 6.2.2 Force equilibrium equations........................................................................133 6.2.3 Conservation of mass ..................................................................................134 6.3 Pressure Drop.......................................................................................................134 6.4 Differential Equations ..........................................................................................134 6.5 Initial Conditions..................................................................................................135 6.6 Behaviour of the Non-Linear Differential Equations ..........................................136 6.7 Comparison of Continuum Model to Conveying Tests .......................................138 6.7.1 Constant solids friction along pipeline..........................................

Dense Phase Pneumatic Conveying of Powders: Design Aspects and Phenomena

The value and variation in bulk density is highly influential in the economics associated with biomass valorisation. Due to its importance, increased feedstock demand is directly related to understanding the characteristics affecting bulk density and the design of biomass processing and handling systems, along the renewable resource supply chains. This paper presents assessment of the elastic response of sugarcane bagasse, wheat straw and wattle, sourced from a second generation lignocellulosic ethanol plant. The study includes testing bulk solids “springiness” and the strain response to stress. While the results of this paper are a preliminary study, the ultimate aim of this work is to establish a relationship between compaction, dilation rates and magnitude with variations in the stress applied. Benchmark tests to characterise the elastic response were performed in a small cell compressibility tester. Testing was also undertaken in a larger cylinder and included preliminary evaluation using a uniaxial test apparatus. Furthermore, preliminary assessment of the stress/stain behaviour during compaction and dilation using Discrete Element Modelling (DEM) was undertaken and a comparison to experimental results is provided. Limitations of the available testing method prevented testing at higher consolidation loads and as such this work will be used to further develop the methodology and design of a new apparatus.

Assessment of biomass bulk elastic response to consolidation

Inertial measurement unit as a tool within dense phase pneumatic conveying. Investigation into velocity measurement accuracy, pressure and velocity relationships in slug flow

Kenneth Williams

Papers

Velocity and porosity relationships within dense phase pneumatic conveying as studied using coupled CFD-DEM

Dense Phase Pneumatic Conveying of Powders: Design Aspects and Phenomena

Assessment of biomass bulk elastic response to consolidation

Inertial measurement unit as a tool within dense phase pneumatic conveying. Investigation into velocity measurement accuracy, pressure and velocity relationships in slug flow

A phenomenological model for the pressure drop applicable across both dilute and dense phase pneumatic conveying