The Experts below are selected from a list of 3405 Experts worldwide ranked by ideXlab platform
Wei Chen - One of the best experts on this subject based on the ideXlab platform.
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modelling mineral slurries using coupled discrete element method and smoothed particle hydrodynamics
Powder Technology, 2020Co-Authors: Wei Chen, Damian Glowinski, Craig WheelerAbstract:Abstract Slurry in wet Grinding Mills is critical for transporting fine progenies out of the system to downstream floatation process. It is commonly modelled as Newtonian fluids when simulating Grinding Mills with numerical tools. However, rheology of the slurry exhibits shear thinning non-Newtonian behaviours. This study aims to investigate the non-Newtonian characteristics of mineral slurries both experimentally and numerically. Non-Newtonian smoothed particle hydrodynamics (SPH) and its coupling to discrete element modelling (DEM) framework was initially described. Non-Newtonian rheology of a copper slurry with various solids concentrations was determined experimentally by a rotary viscometer. SPH-DEM modelling of the viscometry test was conducted with both Newtonian and Power-law non-Newtonian settings in fluid phase, and comparisons were performed. Results suggested that the non-Newtonian SPH based method better reflects actual rheological behaviours of the slurry. In addition, DEM parameters exhibited limited impacts on rheology of the solids-liquid mixture, particularly at low solids concertation and high shear rate states. The findings suggested that the non-Newtonian based SPH-DEM method should be used to more accurately model the slurry flows within Grinding Mills.
M H Moys - One of the best experts on this subject based on the ideXlab platform.
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exploring ball size distribution in coal Grinding Mills
Powder Technology, 2014Co-Authors: Murray M Bwalya, M H Moys, G J Finnie, Francois K MulengaAbstract:Abstract Tube Mills use steel balls as Grinding media. Due to wear in the abrasive environment it is necessary to charge new balls periodically to maintain a steady balanced ball charge in the mill. The amount and ball size distribution in this charge, as well as the frequency with which new balls are added to the mill, have significant effects on the mill capacity and the milling efficiency. Small balls are effective in Grinding fine particles in the load, whereas large balls are required to deal with large particles of coal or stone contaminant. The steady state ball size distribution in the mill depends on the top-up policy. The effect of the ball size distribution on the milling rate of coal has been measured as a function of ball size distribution. The change in ball size distribution as affected by wear and ball top-up policy has been modelled. From this a best ball top-up policy can be recommended that will ensure a close approximation to the desired steady-state ball size distribution that gives the required PF size distribution for the selected mill demand.
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a new approach to optimising the life and performance of worn liners in ball Mills experimental study and dem simulation
International Journal of Mineral Processing, 2007Co-Authors: Augustine B Makokha, M H Moys, Murray M Bwalya, Kiangi KimeraAbstract:Abstract The need to improve and sustain the capacities of Grinding Mills over a longer time while mitigating the operating costs, is of prime concern in the milling industry today. This has emerged in the wake of escalating costs of liner material and increased mill down times alongside power expenditures. One possible way of addressing this issue is through proper design and selection of liners/lifters. The practice in the industry has hitherto been to rely on experience for liner selection, which limits the possibility of applying novel techniques that may enhance mill performance. Our recent experience suggests that there is an opportunity to improve the liner performance and life using retrofits. However, the challenge lies in selecting an efficient profile and configuration for the retrofits. The Discrete Element Method is emerging as a tool that holds possibilities for exploration of various profiles by simulation. This paper presents an experimental investigation and the corresponding numerical simulation of a new approach of optimising the performance of liners over an extended life period. An integrated aim is to assess the ability of 3D DEM simulator to model the effect of lifter profile on mill load behaviour and hence its potential as a tool for design optimisation of mill liners. Two liner profiles, bevel and bevel retrofitted with detachable cone-shaped lifters are utilised in the investigation. A comparison of the measured to the simulated results shows a fairly good match in terms of load position and power draw at sub-critical speeds. In both cases there is a discernible improvement in mill load behaviour and power draw with the optimised liner which clearly indicates the benefit of liner retrofits.
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further validation of dem modeling of milling effects of liner profile and mill speed
Minerals Engineering, 2003Co-Authors: O Hlungwani, J Rikhotso, H Dong, M H MoysAbstract:Grinding Mills are usually lined with lifters to improve their efficiency. During the course of operation, the lifters are worn away. This will affect the energy efficiency and capacity of Mills and the behavior of the load in the mill and finally leads to a relining to replace the worn lifters. However, the effects of the profiles of lifters are not taken into account in all the previous power models for rotary Mills. Discrete element method (DEM) is capable of demonstrating the effects of lifter profiles on mill power and load behavior. In this paper, two types of lifter profiles, square and trapezoidal, are investigated in terms of mill power and load behavior with a 2D mill and a DEM simulator, Millsoft, over a wide range of rotational speed. DEM satisfactorily predicted the load behavior and power draw for different lifter profiles at sub-critical speeds comparing with the experimental results. It is found that the trapezoidal lifters draw more power than the square lifters. An attempt has been made to explain the difference between measured and simulated power using photographs of experimental load behavior.
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measurement of impact behaviour between balls and walls in Grinding Mills
Minerals Engineering, 2003Co-Authors: H Dong, M H MoysAbstract:Experimental results of impacts of balls on walls mimicking the collision events in Grinding Mills are reported. The materials for balls include steel, malachite, glass as well as a billiard ball and a cricket ball. The walls used for the impact target are steel liner, rubber liner, and slate plate. Through the measuring of translational and rotational velocities, we present the impact properties as coefficient of normal restitution, coefficient of tangential restitution and impulse ratio (or dynamic coefficient of friction). The results obtained can be used to determine explicitly the mode of behaviours (roll or slide) of the contact point during impact. They can also be used to determine parameters for discrete element method simulation.
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a discrete element method investigation of the charge motion and power draw of an experimental two dimensional mill
International Journal of Mineral Processing, 2001Co-Authors: M A Van Nierop, G Glover, A L Hinde, M H MoysAbstract:Abstract The Discrete Element Method (DEM) has the potential to be a powerful tool for the design and optimisation of Mills. However, for DEM to gain acceptance within the minerals processing industry, it is necessary to show that the results obtained from a DEM simulation are valid, and that this validity extends over a wide range of mill operating conditions. Real Grinding Mills are complex multi-phase devices with a range of particle dynamics and material processes that depend on the exact operating point of the mill. Mill conditions will generally vary statistically over time. It is therefore difficult in this type of environment to systematically verify DEM, where some degree of precision in the mill operation is required. With these considerations in mind a programme of both experimental and DEM simulation work was developed. A “two-dimensional” laboratory mill was built in such a way that precise power measurement and monitoring of charge motion was possible. DEM simulation runs were matched to the experimental conditions. In this account of the work, particular attention is given to the effect of mill speed on power and charge motion, and also of particle behaviour at mill speeds above the critical. DEM predicts the power draft and charge motion of the mill well at speeds below the critical speed. At super-critical speeds, the centrifuging of material in the load was predicted, but power predictions were not as accurate.
Craig Wheeler - One of the best experts on this subject based on the ideXlab platform.
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modelling mineral slurries using coupled discrete element method and smoothed particle hydrodynamics
Powder Technology, 2020Co-Authors: Wei Chen, Damian Glowinski, Craig WheelerAbstract:Abstract Slurry in wet Grinding Mills is critical for transporting fine progenies out of the system to downstream floatation process. It is commonly modelled as Newtonian fluids when simulating Grinding Mills with numerical tools. However, rheology of the slurry exhibits shear thinning non-Newtonian behaviours. This study aims to investigate the non-Newtonian characteristics of mineral slurries both experimentally and numerically. Non-Newtonian smoothed particle hydrodynamics (SPH) and its coupling to discrete element modelling (DEM) framework was initially described. Non-Newtonian rheology of a copper slurry with various solids concentrations was determined experimentally by a rotary viscometer. SPH-DEM modelling of the viscometry test was conducted with both Newtonian and Power-law non-Newtonian settings in fluid phase, and comparisons were performed. Results suggested that the non-Newtonian SPH based method better reflects actual rheological behaviours of the slurry. In addition, DEM parameters exhibited limited impacts on rheology of the solids-liquid mixture, particularly at low solids concertation and high shear rate states. The findings suggested that the non-Newtonian based SPH-DEM method should be used to more accurately model the slurry flows within Grinding Mills.
Paul W. Cleary - One of the best experts on this subject based on the ideXlab platform.
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effect of operating condition changes on the collisional environment in a sag mill
Minerals Engineering, 2019Co-Authors: Paul W. Cleary, Phil OwenAbstract:Abstract Discrete Element Method (DEM) modelling of the motion of balls and rocks in Grinding Mills allows the flow structure and material transport to be understood. It also provides information on the energy dissipated in every collision of resolved particles (which here are 25–200 mm). These energy dissipation events control the nature and intensity of the Grinding. This Grinding environment can be characterised by the collisional energy spectra. In this paper we explore the quantitative structural change in the collisional environment in SAG (Semi-Autogenous Grinding) mill as measured by the energy spectra predicted using DEM. The simulations show that increasing mill speed has little effect the collision energy distribution between the different types of collisions. Three other mill operating conditions (separately) all lead to decreases in impact breakage and increases in Grinding activity for decreasing lifter height, increasing charge fill level, and decreasing rock-to-ball ratio.
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A multiscale method for including fine particle effects in DEM models of Grinding Mills
Minerals Engineering, 2015Co-Authors: Paul W. ClearyAbstract:A multiscale model for including interstitial powder or fine particles in DEM simulations of Grinding Mills is proposed. This consists of a traditional DEM model at the macroscale which includes only Grinding media and potential coarser fractions of feed and product. Microscale models are embedded within this macroscale model. These can be sufficiently small that the fine powder can be included in a computationally affordable manner. The direct inclusion of the fine particles in the model allows predictions to be made of the effect of the local Grinding environment on these fine particles. A shear cell is a good choice for the microscale model as it can well represent the local flow conditions at different points within the mill macroscale model. Averaging the macroscale flow allows the local collisional environments to be characterised and provides estimates of the shear rate and normal stress at each of the microscale locations which then controls the configuration of each microscale shear cell. A 1-way coupled implementation of this multiscale model is demonstrated for a simple cement ball mill. The relative importance of each region of the flow is determined with the toe region being the dominant contributor to the Grinding. The Grinding action produced by the shearing of thin layers of powder between adjacent layers of media flowing over each other is clearly demonstrated by the behaviour predicted in the microscale models. Methods for calculating power draw that include the effect of powder and for constructing collision energy spectra for the powder are described. Finally, the importance of the cushioning effect of high powder loads on the flow behaviour of the media is demonstrated.
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prediction of mill liner shape evolution and changing operational performance during the liner life cycle case study of a hicom mill
International Journal for Numerical Methods in Engineering, 2010Co-Authors: Paul W. Cleary, Phil Owen, David I Hoyer, Steve MarshallAbstract:The prediction of wear and performance change over the life cycle of the consumable liners used to protect Grinding Mills is an important element of their optimization. Poor wear behaviour can lead to higher replacement costs and production loss during liner replacement. Prediction of wear behaviour using discrete element method (DEM) can provide valuable information about the impact of the design on the life cycle of the liner. Here, the DEM method is extended to predict the evolution of the shape of the liner throughout the life cycle. Using a Hicom 110 nutating mill as a case study, we demonstrate a process for constructing a wear model that is shown to be able to quantitatively predict the spatially varying wear rates over the surface of the liner. The functional dependence of wear rate on micro-mechanical flow quantities is not currently understood; hence, two model variants for each of the normal impact damage and the shear abrasion damage are considered. This model is validated by comparison with the actual erosion depths of a real liner. It is then used in a multi-step DEM simulation to predict the liner evolution and the operational changes in the mill performance over the full life cycle of the liner. For the Hicom mill, it is demonstrated that the wear is entirely dominated by abrasion and that the best measure of this was the shear energy dissipation of wall contacts. It was also to identify that the floor of the mill was constructed of a more abrasion resistance material. The life cycle analysis showed a 20% decline in power draw as the increasing Grinding chamber volume and eroding lifters lead to less efficient operation of the mill.
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smooth particle hydrodynamics status and future potential
Progress in Computational Fluid Dynamics, 2007Co-Authors: Paul W. Cleary, Mahesh Prakash, Nick Stokes, Craig ScottAbstract:SPH is a powerful mesh free method that is now able to solve very complex multi-physics flow and deformation problems in a broad number of fields. This paper concentrates on the use of SPH to simulate a broad range of complex industrial fluid flow problems. These include free surface fluid flow for the generation of digital content, geophysical flows such as volcanic lava flows and tsunamis, several types of die casting (gravity, high pressure and ingot casting), resin transfer moulding and flow in porous media, mixing of particulates in liquid, pyrometallurgy and slurry flow in semi-autogenous Grinding Mills. The strengths and weaknesses of SPH will be explored and future opportunities for using the method to make major modelling advances are discussed.
Francois K Mulenga - One of the best experts on this subject based on the ideXlab platform.
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exploring ball size distribution in coal Grinding Mills
Powder Technology, 2014Co-Authors: Murray M Bwalya, M H Moys, G J Finnie, Francois K MulengaAbstract:Abstract Tube Mills use steel balls as Grinding media. Due to wear in the abrasive environment it is necessary to charge new balls periodically to maintain a steady balanced ball charge in the mill. The amount and ball size distribution in this charge, as well as the frequency with which new balls are added to the mill, have significant effects on the mill capacity and the milling efficiency. Small balls are effective in Grinding fine particles in the load, whereas large balls are required to deal with large particles of coal or stone contaminant. The steady state ball size distribution in the mill depends on the top-up policy. The effect of the ball size distribution on the milling rate of coal has been measured as a function of ball size distribution. The change in ball size distribution as affected by wear and ball top-up policy has been modelled. From this a best ball top-up policy can be recommended that will ensure a close approximation to the desired steady-state ball size distribution that gives the required PF size distribution for the selected mill demand.
