Mt Pleasant, Australia
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Dong K.J.,University of New South Wales | Kuang S.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd. | Hughes T.,Gekko Systems | Yu A.B.,University of New South Wales
Minerals Engineering | Year: 2010

This paper presents a numerical study of the multiphase flow in an in-line pressure jig (IPJ), which is a high yield and high recovery gravity separation device widely used in ore processing but may have potential in coal preparation. The mathematical model is developed by use of the combined approach of computational fluid dynamics (CFD) for liquid flow and discrete element method (DEM) for particle flow. It is qualitatively verified by comparing the calculated and measured results under similar conditions. The effects of a few key variables, such as vibration frequency and amplitude, and the size and density of ragging particles, on the flow and separation performance of the IPJ are studied by conducting a series of simulations. The results are analyzed in terms of velocity field, porosity distribution and forces on particles. The findings would be helpful in the design, control and optimisation of an IPJ unit. © 2009 Elsevier Ltd. All rights reserved.


Wang B.,Lanzhou University | Wang B.,University of New South Wales | Chu K.W.,University of New South Wales | Yu A.B.,University of New South Wales | And 3 more authors.
Minerals Engineering | Year: 2011

This paper presents a numerical study of the gas-liquid-solid flow in 1000 mm dense medium cyclones (DMCs) with different body dimensions, which includes the spigot diameter, cylinder length, cone length and inlet size by means of a computer model which we recently proposed. In this model, mixture multiphase model is used to describe the flow of the dense medium (comprising finely ground magnetite contaminated with non-magnetic material in water) and the air core, where the turbulence is described by the well-established Reynolds Stress Model. The stochastic Lagrangian Particle Tracking method is used to simulate the flow of coal particles. It is found that the spigot size is very sensitive to the performance. The operational head and medium split reporting to overflow, decrease dramatically as the spigot diameter increases. The density differential decreases rapidly, and then passes through a minimum and increases slowly. The long body including cylinder and cone is helpful to particle separation, particularly for fine and heavy particles. The inlet size plays a remarkable role on the performance on DMCs. The operational head, the density differential and the medium split increase dramatically as the inlet size decreases. Both the upward flow and the downward flow become very strong in the DMC with a small inlet when medium feed rate is constant, which results in a very low Ep. © 2010 Elsevier Ltd. All rights reserved.


Ghodrat M.,University of New South Wales | Kuang S.B.,University of New South Wales | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd. | And 2 more authors.
Minerals Engineering | Year: 2014

Hydrocyclones generally follow a conventional design and may have some limitations on separation performance. This paper presents a numerical study of hydrocyclones with different conical configurations by a recently developed computational fluid dynamics method. The feed solids concentration considered is up to 30% (by volume), which is well beyond the range reported before. The numerical results show that the cyclone performance is sensitive to both the length and shape of the conical section, as well as the feed solids concentration. A longer conical section length leads to decreased inlet pressure drop, cut size d50, and Ecart probable Ep, and at the same time, an increased water split (thus larger by-pass effect). When conical shape varies from the concave to convex styles gradually, a compromised optimum performance is observed for the cyclone with a convex cone, resulting in a minimum Ep and relatively small inlet pressure drop and water split. Almost all these effects are pronounced with increasing feed solids concentration. Based on the numerical experiments, a new hydrocyclone featured with a long convex cone is proposed. It can improve the performance of the conventional cyclone at all the feed solids concentrations considered. © 2013 Elsevier Ltd. All rights reserved.


Kuang S.,University of New South Wales | Qi Z.,University of New South Wales | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd. | And 2 more authors.
Minerals Engineering | Year: 2014

A computational fluid dynamics (CFD) model is proposed to describe the multiphase flow in a dense-medium cyclone (DMC). In this model, the volume of fluid (VOF) multiphase model is first used to determine the initial shape and position of the air core, and then the so called mixture model is employed to describe the flows of the medium, coal particles and air, where the turbulence is described by the Reynolds stress model. The validity of the proposed approach is verified by the reasonably good agreement between the measured and calculated results in terms of separation efficiency. On this base, this model is used to quantify the effects of the ratios of spigot to vortex finder diameters (U:O) and medium to coal (M:C) on performance. The results are shown to be generally comparable to those reported in the literature. It reveals that when vortex finder or spigot diameter is varied at the same U:O ratio, the offset and medium split nearly remain the same, however, the coal feed rate and Ep are different under the conditions considered. It is also shown that the fish-hook phenomenon is observed when spigot diameter is equal to or slightly larger than vortex finder diameter, and a normal operation becomes less stable with decreasing U:O ratio. The key phenomena predicted are explained by the calculated inner flows. © 2013 Elsevier Ltd. All rights reserved.


Chu K.W.,University of New South Wales | Kuang S.B.,University of New South Wales | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd. | And 2 more authors.
Minerals Engineering | Year: 2014

Dense medium cyclone (DMC) is a high-tonnage device that is widely used to upgrade run-of-mine coal in modern coal preparation plants. It is known that wear is one of the problems in the operation of DMCs, but it is not well understood. In this work, the wear rate of DMC walls due to the impact of coal particles is predicted by a combined computational fluid dynamics and discrete element method (CFD-DEM) approach, using the Finnie wear model from the literature. In the CFD-DEM model, DEM is used to model the motion of discrete coal particles by applying Newton's laws of motion and CFD is used to model the motion of the slurry medium by numerically solving the local-averaged Navier-Stokes equations together with the volume of fluid (VOF) and mixture multiphase flow models. According to the Finnie wear model, the wear rate is calculated according to the impact angle of particles on the wall, particle velocity during an impact and the yield stress of wall material; the relevant particle-scale information can be readily obtained from the CFD-DEM simulation. The numerical results show that the severe wear locations are generally the inside wall of the spigot and the outside wall of the vortex finder. The wear rate depends on both the operational conditions and solids properties. It increases generally with the decrease of medium-to-coal (M:C) ratio. For a given constant M:C ratio, the wear rate for thermal coal is higher than that for coking coal, especially at the spigot. Large particles may cause a non-symmetric wear rate due to the gravity effect. The effect of a worn spigot wall on the multiphase flow and separation performance is also studied. This work suggests that the proposed approach could be a useful tool to study the effect of wear in DMCs under different conditions. © 2013 Elsevier Ltd. All rights reserved.


Chen J.,University of New South Wales | Chu K.W.,University of New South Wales | Zou R.P.,University of New South Wales | Yu A.B.,University of New South Wales | And 3 more authors.
Minerals Engineering | Year: 2014

The dense medium cyclone (DMC) is a high-tonnage device widely used to upgrade run-of-mine coal in the modern coal industry. It is known that a small improvement on the performance of DMC may greatly enhance industrial profitability. Therefore, it is very useful to develop an effective method to help optimize the design and operation of DMCs. Recently, based on the numerical experiments performed by Computational Fluid Dynamics and its combination with Discrete Element Method; the authors have established a PC-based mathematical model that looks promising to achieve this design and operational goal. In this paper, the authors will first discuss how to use this model to design high capacity or high efficiency DMCs for coal preparation through representative examples, in comparison with several typical designs in the industry. Some rules for DMC scale-up are then proposed for general application. The results further demonstrate that this DMC model can indeed offer a convenient way for optimum design and/or operation of DMCs under different conditions. © 2013 Elsevier Ltd. All rights reserved.


Ghodrat M.,University of New South Wales | Kuang S.B.,University of New South Wales | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd. | And 2 more authors.
Industrial and Engineering Chemistry Research | Year: 2013

This paper presents a numerical study of multiphase flow in hydrocyclones with different configurations of cyclone size and spigot diameter. This is done by a recently developed mixture multiphase flow model. In the model, the strong swirling flow of the cyclone is modeled using the Reynolds stress model. The interface between liquid and air core and the particle flow are both modeled using the so-called mixture model. The solid properties are described by the kinetic theory. The applicability of the proposed model has been verified by the good agreement between the measured and predicted results in a previous study. It is here used to study the effects of cyclone size and spigot diameter when feed solids concentration is up to 30% (by volume), which is well beyond the range reported before. The flow features predicted are examined in terms of the flow field, pressure drop, and amount of water split to underflow, separation efficiency and underflow discharge type. The simulation results show that the multiphase flow in a hydrocyclone varies with cyclone size or spigot diameter, leading to a different performance. A smaller cyclone results in an increased cut size, a decreased pressure drop and a sharper separation, and, at the same time, an increased water split (thus worse bypass effect) and a more possibly unstable operation associated with rope discharge, particularly at relatively high feed solids concentrations. Both large and small spigot diameters may lead to poor separation performance. Accordingly, an optimum spigot diameter can be identified depending on feed solids concentration. It is also shown that for all the considered hydrocyclones, a better separation performance and a smoother running state can be achieved by the operation at a lower feed solid concentration. © 2013 American Chemical Society.


Chu K.W.,University of New South Wales | Wang B.,University of New South Wales | Wang B.,Lanzhou University | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd.
Chemical Engineering Science | Year: 2012

Dense medium cyclone (DMC) is widely used to upgrade run-of-mine coal in the coal industry. The flow within it is very complicated, with four phases (water, air, fine magnetite and coal) involved. To date, the underlying fundamentals are not well understood. In this work, the effect of particle density on the flow in a DMC is numerically studied to understand why coal type matters in DMC operation. The model used is a combined approach of discrete element method (DEM) and computational fluid dynamics (CFD). In the model, the motion of discrete mineral particles is obtained by DEM and the flow of medium (mixture of water, air and fine magnetites) phase by the traditional CFD. The simulated results are analysed in terms of medium and coal flow patterns, and particle-fluid, particle-particle and particle-wall interaction forces. It is shown that particles of different densities have significantly different effects on the flow in a DMC. The operational pressure, medium split and differential all decrease with the increase of particle density. The underlying mechanism is that different trajectories of particles of different densities lead to different spatial distributions of particle-fluid interaction forces which in turn yield different effects on the flow. The findings are useful to better understanding, designing and operating this complicated multiphase flow system. © 2012 Elsevier Ltd.


Chu K.W.,University of New South Wales | Kuang S.B.,University of New South Wales | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty. Ltd.
Minerals Engineering | Year: 2012

Dense medium cyclone (DMC) is widely used to upgrade run-of-mine coal in the coal industry. The flow dynamics/fluctuation in a DMC is important but has not been studied previously. In this work, the dynamics is studied by numerically with special reference to the effect of the fluctuation of solid mass flowrate. The simulation is carried out by use of a combined approach of Computational Fluid Dynamics (CFD) and Discrete Element Method (DEM). In the model, the motion of discrete mineral particle phase is obtained by DEM which applies Newton's equations of motion to every individual particle and the flow of medium (mixture of water, air and fine magnetites) phase by the traditional CFD which solves the Navier-Stokes equations at a computational cell scale. The simulated results are analysed in terms of medium and coal flow patterns, and particle-fluid, particle-particle and particle-wall interaction forces. It is shown that under high fluctuation frequency and current conditions, the performance of DMC is not sensitive to both the fluctuation amplitude and period of coal flow at the DMC inlet. However, under low fluctuation frequency, as fluctuation amplitude increases, the separation performance deteriorates slightly and the flow is obviously affected at the spigot. A notable finding is that the near-gravity particles that tend to reside at the spigot and/or have longer residence time in the DMC would be affected more than other particles. The work shows that this two-way coupled CFD-DEM model could be a useful tool to study the dynamics of the flow in DMCs. © 2011 Elsevier Ltd. All rights reserved.


Chu K.W.,University of New South Wales | Wang B.,University of New South Wales | Wang B.,Lanzhou University | Yu A.B.,University of New South Wales | Vince A.,Elsa Consulting Group Pty Ltd.
Minerals Engineering | Year: 2012

Dense medium cyclone (DMC) is widely used to upgrade run-of-mine coal in the coal industry. In practice, different designs of the outlet geometry of the vortex finder are used to achieve different purposes. However, the underlying mechanisms are not well understood. In this work, this phenomenon is studied numerically with reference to the effect of the pressure at the vortex finder. The simulation is carried out by use of a combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) (CFD-DEM). In the model, DEM is used to describe the motion of discrete coal particles, and CFD to describe the motion of medium slurry which is a mixture of gas, water and fine magnetite particles. It is shown that a relatively small change of the vortex finder pressure can cause significant variations of both the medium-coal flow and DMC performance. An important finding is that the flow direction of the axial velocity of the air phase in the "air-core" could reverse (changing from upward to downward) as the vortex finder pressure increases, which results in the downward viscous drag force on coal particles and consequently causes some low density coal to be misplaced to the reject/underflow. This work suggests that the control of the pressure at the outlet of the vortex finder is important for DMC performance. © 2011 Elsevier Ltd. All rights reserved.

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