Simulation of bubbling fluidized beds with cohesive particles by incorporating a novel structure-Based drag model into the two-fluid model

AbstractLattice-Boltzmann simulations of fluid flow through sheared assemblies of monodisperse spherical particles have been performed. The friction coefficient tensor extracted from these simulations is found to become progressively more anisotropic with increasing Péclet number, $Pe= \dot {\gamma } {d}^{2} / D$, where $\dot {\gamma } $ is the shear rate, $d$ is the particle diameter, and $D$ is the particle self-diffusivity. A model is presented for the anisotropic friction coefficient, and the model constants are related to changes in the particle microstructure. Linear stability analysis of the two-fluid model equations including the anisotropic drag force model developed in the present study reveals that the uniformly fluidized state of low Reynolds number suspensions is most unstable to mixed mode disturbances that take the form of vertically travelling waves having both vertical and transverse structures. As the Stokes number increases, the transverse-to-vertical wavenumber ratio decreases towards zero; i.e. the transverse structure becomes progressively less prominent. Fully nonlinear two-fluid model simulations of moderate to high Stokes number suspensions reveal that the anisotropic drag model leads to coarser gas–particle flow structures than the isotropic drag model.

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Numerical Simulation of Effect of Internals on Slugging Fluidization and Analysis of Nonuniformity Index

International Journal of Chemical Reactor Engineering ◽

10.1515/1542-6580.3079 ◽

2012 ◽

Vol 10 (1) ◽

Author(s):

Xiaoling Wang ◽

Liang Yu ◽

Jun Wang

Keyword(s):

Experimental Data ◽

Granular Flow ◽

Fluidized Beds ◽

Fluid Model ◽

Two Fluid Model ◽

Reasonable Prediction ◽

Two Fluid ◽

Radial Nonuniformity ◽

Flow Nonuniformity

Abstract The Two-Fluid Model (TFM) using the Kinetic Theory of Granular Flow (KTGF) was applied to simulate 3-D dense fluidized beds with different complex internals. The slugging fluidization was found in the simulated results. When the internals were placed into the reactors, the simulated results showed that the slugs were broken up and bubbling fluidization was formed instead of slugging fluidization. The formation, growth, size, and shape of bubbles were validated to ensure a reasonable prediction. Furthermore, the simulated pressure drop was compared with the corresponding experimental data from the dense fluidized beds with different complex internals, and good agreements were observed. Finally, the flow nonuniformity in the dense fluidized beds was evaluated by a developed method. This method extended Radial Nonuniformity Index (RNI) to Face Nonuniformity Index (FNI) and Volume Nonuniformity Index (VNI). From the calculated FNI and VNI, the fluidization quality of the fluidized beds was quantitatively judged as follows: No.3 > No.1> No.2 > No.4 > Without Internal.

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A Coarse-Grained Two-Fluid Model for Gas-Solid Fluidized Beds

The Journal of Computational Multiphase Flows ◽

10.1260/1757-482x.6.1.29 ◽

2014 ◽

Vol 6 (1) ◽

pp. 29-47 ◽

Cited By ~ 15

Author(s):

S. Schneiderbauer ◽

S. Pirker

Keyword(s):

Fluidized Beds ◽

Fluid Model ◽

Coarse Grained ◽

Two Fluid Model ◽

Two Fluid

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

Fluids Engineering ◽

10.1115/imece2006-14831 ◽

2006 ◽

Author(s):

Jin Sun ◽

Francine Battaglia ◽

S. Subramaniam

Keyword(s):

Momentum Transfer ◽

Fluidized Beds ◽

Structural Information ◽

Fluid Model ◽

Fluid Phase ◽

Transfer Model ◽

Dem Simulation ◽

Dem Simulations ◽

Two Fluid Model ◽

Two Fluid

Simulations of gas-solid fluidized beds have been carried out using a hybrid simulation method, which couples the discrete element method (DEM) for particle dynamics with the ensemble-averaged two-fluid (TF) equations for the fluid 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 two-fluid 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 two-fluid model predictions. In addition, the TF-DEM model demonstrates the capability to capture more heterogeneous structural information of the fluidized beds than the two-fluid model alone. The microstructures in fluidized beds are analyzed and the implications to kinetic theory for granular flows 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 their suitability to the hybrid TF-DEM simulation approach is evaluated.

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