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TECHNICAL PAPERS

Hybrid Two-Fluid DEM Simulation of Gas-Solid Fluidized Beds

[+] Author and Article Information
Jin Sun1

Department of Mechanical Engineering, Iowa State University, Ames, IA 50011jinsun@iastate.edu

Francine Battaglia, Shankar Subramaniam

Department of Mechanical Engineering, Iowa State University, Ames, IA 50011

1

Corresponding author.

J. Fluids Eng 129(11), 1394-1403 (Jun 09, 2007) (10 pages) doi:10.1115/1.2786530 History: Received August 28, 2006; Revised June 09, 2007

Simulations of gas-solid fluidized beds have been performed using a hybrid simulation method, which couples the discrete element method (DEM) for particle dynamics with the averaged two-fluid (TF) continuum equations for the gas phase. The coupling between the two phases is modeled using an interphase momentum transfer term. The results of the hybrid TF-DEM simulations are compared to experimental data and TF model simulations. It is found that the TF-DEM simulation is capable of predicting general fluidized bed dynamics, i.e., pressure drop across the bed and bed expansion, which are in agreement with experimental measurements and TF model predictions. Multiparticle contacts and large contact forces distribute in the regions away from bubbles, as demonstrated from the TF-DEM simulation results. The TF-DEM model demonstrates the capability to capture more heterogeneous structural information of the fluidized beds than the TF model alone. The implications to the solid phase constitutive closures for TF models are discussed. However, the TF-DEM simulations depend on the form of the interphase momentum transfer model, which can be computed in terms of averaged or instantaneous particle quantities. Various forms of the interphase momentum transfer model are examined, and simulation results from these models are compared.

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Copyright © 2007 by American Society of Mechanical Engineers
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Figures

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Figure 2

Schematic showing computational domains for the experiments of (a) Tsuji (9) and (b) Goldschmidt (25)

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Figure 3

Pressure drop at 20cm above the inlet boundary fluctuates with time for the central-jet fluidized bed

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Figure 4

The averaged (5–10s) particle volume fractions for the central-jet fluidized bed for (a) the coarse grid with Δx=1cm and Δy=2cm and (b) the fine grid with Δx=1cm and Δy=1cm. The domain in the figure only shows 45cm above the inlet.

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Figure 11

The ratio of particles in multicontacts to the total number of particles in contact as a function of time

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Figure 12

Particle contact forces, drag forces, and their ratios for the uniform inflow fluidized bed for (a) the instantaneous distribution at 5s and (b) the time-averaged distribution at 5–10s. The left panels show contact forces, the middle panels show drag forces, and the right panels show the ratios of contact forces to drag forces. The left legends are the magnitudes of forces scaled by the gravitational force of a particle. The right legends are the ratios, where −1 indicates that the drag force is zero at that position.

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Figure 13

Time average in the range of 5–10s of the particle volume fractions for the uniform inflow fluidized bed predicted by the method using (a) averaged particle velocities and (b) instantaneous particle velocities

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Figure 5

The bulk coordination numbers as a function of time

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Figure 1

Schematic of two particles i and j in contact and position vectors ri and rj, respectively, with overlap δij

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Figure 6

Instantaneous particle positions and velocities for the central-jet fluidized bed, denoted by points and vectors. The contour levels show the magnitudes of Nc. The domain in the figure only shows 45cm above the inlet.

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Figure 7

Particle contact forces, drag forces, and their ratios for the central-jet fluidized bed for (a) the instantaneous distribution at 5s and (b) the time-averaged distribution at 5–10s. The left panels show contact forces, the middle panels show drag forces, and the right panels show the ratios of contact forces to drag forces. The left legends are the magnitudes of forces scaled by the gravitational force of a particle. The right legends are the ratios, where −1 indicates that the drag force is zero at that position. Note that the highest ratio of 100 is not shown in order to distinguish the majority of ratios below 20. The domain in the figure only shows 45cm above the inlet.

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Figure 8

Particle volume fractions for the central-jet fluidized bed for (a) the instantaneous distribution at 5s and (b) the time-averaged distribution at 5–10s. The left panel shows the TF-DEM simulation and the right panel shows the TFM simulation. The domain in the figure only shows 45cm above the inlet.

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Figure 9

The mean particle height as a function of time for the uniform inflow fluidized bed calculated from the TF-DEM model and TFM

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Figure 10

Instantaneous particle positions and velocities for the uniform inflow fluidized bed denoted by points and vectors. The contour level shows the magnitude of Nc.

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