1、原文Particle scale modelling of the multiphase ow in a dense medium cyclone:Effect of uctuation of solids owrateK.W. Chua, S.B. Kuanga, A.B. Yua, A. VincebaLaboratory for Simulation and Modelling of Particulate Systems, School of Materials Science and Engineering, The University of New South Wales, Sy
2、dney, NSW 2052, Australia.b Elsa Consulting Group Pty. Ltd., PO Box 8100, Mt. Pleasant, QLD 4740, Australiaa b s t r a c t: Dense medium cyclone (DMC) is widely used to upgrade run-of-mine coal in the coal industry. The ow dynamics/uctuation in a DMC is important but has not been studied previously.
3、 In this work, thedynamics is studied by numerically with special reference to the effect of the uctuation of solid mass owrate. 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 m
4、ineral particle phase is obtained by DEM which applies Newtons equations of motion to every individual particle and the ow of medium (mixture of water, air and ne magnetites) phase by the traditional CFD which solves the NavierStokes equations at a computational cell scale. The simulated results are
5、 analysed in terms of medium and coal ow patterns, and particleuid, particleparticle and particlewall interaction forces.It is shown that under high uctuation frequency and current conditions, the performance of DMC is not sensitive to both the uctuation amplitude and period of coal ow at the DMC in
6、let. However, under low uctuation frequency, as uctuation amplitude increases, the separation performance deteriorates slightly and the ow is obviously affected at the spigot. A notable nding is that the near-gravity particlesthat tend to reside at the spigot and/or have longer residence time in the
7、 DMC would be affected more than other particles. The work shows that this two-way coupled CFDDEM model could be a useful tool to study the dynamics of the ow in DMCs.Keywords: Dense medium cyclone Multiphase ow Computational uid dynamics Discrete element method Dynamics Fluctuation1. Introduction D
8、ense medium cyclone (DMC) is a high-tonnage device that hasbeen widely used to upgrade run-of-mine coal in the modern coal industry by separating gangue from product coal. It is also used in a variety of mineral plants treating iron ore, dolomite, diamonds,potash and leadzinc ores. In this work, DMC
9、 refers to that used in the coal industry. It involves multiple phases: air, water, coal and magnetic/nonmagnetic particles of different sizes, densities and other properties. Normally, the slurry including water, magne- tite, and nonmagnetic particles is named medium in practice. In the past, many
10、studies have been conducted to understand the ow and performance of DMCs. For convenience, the overall back- ground for the present research is discussed in connection with our previous studies (e.g., Chu et al., 2009a,b).The general working principle of DMC has been well docu-mented in literature (
11、King and Juckes, 1984; Svarovsky, 1984;Wills, 1992; Chu et al., 2009a). As schematically shown in Fig. 1a,the feed, which is a mixture of raw coal and magnetite particles carried by water, enters tangentially near the top of the cylindrical, section, thus forming a strong swirling ow. Centrifugal fo
12、rces cause the refuse or high ash particles to move towards the wall, where the axial velocity points predominantly downward, and to discharge through the spigot. The lighter clean coal particles, driven by pressure gradient force and radial uid drag force, move to-wards the longitudinal axis of the
13、 DMC, where there is usually an air core, and the predominant axial velocity points upward and thecoal exits through the vortex nder.Despite being widely used, problems are frequently encoun-tered inthe operation of DMCs. Typical problems are the so-called surging phenomenon which may occur frequent
14、ly and can lead to a large portion of coal product reporting to reject (Wood,1990), vortex nder overloading (Hu et al., 2001), severe wearing of DMC walls (Zughbi et al., 1991), difculties in scale-up and system instability.The experimental work on DMC has been notoriously cumbersome and expensive,
15、and seldom conducted. The majority of the previous studies were devoted to the quantication of key macroscopic parameters (e.g., pressure drop and overall separation efciency) under different conditions (Scott, 1990; Wood, 1990;Restarick and Krnic, 1991; He and Laskowski, 1994; Ferrara et al.,2000;
16、Hu et al., 2001; Sripriya et al., 2007; Magwai and Bosman,2008). On the other hand, the measurement at a microscopic scale has only been made to the medium ow (coal is not included) using X-ray and gamma ray tomography (Galvin and Smitham, 1994; Subramanian, 2002a). It is very difcult to measure the internal ow and force structures in DMCs. Without such microscopic information, DMC is largely operated
