Axial segregation in bubbling gas-fluidized beds with Gaussian and lognormal distributions of Geldart Group B particles

A commercially available Computational Fluid-Dynamics code, CFX-4, has been chosen to carry out computer simulations of gas fluidized beds. In this study, the Eulerian-Eulerian granular kinetic model, which is a standard option of the code, has been used. Fluid-bed simulations of Geldart Group B materials have been performed using the granular kinetic model, spanning three hydrodynamic regimes: bubbling, slugging and turbulent fluidization. Furthermore, an alternative Eulerian-Eulerian model, the so-called "particle-bed model", has been implemented for the first time within a commercial code, and results are presented from simulations of the bubbling and slugging fluidization of a Geldart Group B material, and for the homogeneous fluidization of a Group A material. A numerical procedure has been developed to allow for a tight control of the fluid-bed voidage at maximum packing during the simulations with the particle-bed model. Results show that both the granular kinetic model approach and the particle-bed model are able to describe significant aspects of the investigated fluidization regimes.

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2D and 3D CFD Simulations of Bubbling Fluidized Beds Using Eulerian-Eulerian Models

International Journal of Chemical Reactor Engineering ◽

10.2202/1542-6580.1083 ◽

2003 ◽

Vol 1 (1) ◽

Cited By ~ 32

Author(s):

Luca Cammarata ◽

Paola Lettieri ◽

Giorgio D. M. Micale ◽

Derek Colman

Keyword(s):

Kinetic Model ◽

Bubble Size ◽

Fluidized Beds ◽

Numerical Procedure ◽

Cfd Simulations ◽

3D Simulations ◽

Gas Fluidized Beds ◽

Group B ◽

Particle Bed ◽

2D And 3D

This paper reports on CFD simulations of freely bubbling gas fluidized beds using CFX-4, a commercial code developed by CFX Ltd. (formerly AEA Technology). Two Eulerian-Eulerian modelling approaches, the granular kinetic model and the particle-bed model (Gibilaro, 2001), have been investigated. The particle bed model has been recently implemented in CFX-4 for 2D simulations and a numerical procedure was developed to allow for a tight control of the fluid-bed voidage at maximum packing during the simulations, see Lettieri et al. (2003). The work has now been extended to 3D simulations and qualitative and quantitative results are presented in this paper for both the 2D and 3D simulations of the bubbling fluidization of a Geldart Group B material. Results on bed expansion, bubble size and bubble hold-up are reported. In particular, simulated bubble size is compared with predictions given by the Darton et al. (1977) equation at different bed heights. The paper shows that the bubble size predicted by both the granular kinetic model and the particle-bed model is in good agreement with the Darton's equation.

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Heat transfer coefficients between gas fluidized beds and immersed spheres: dependence on the sphere size

International Journal of Multiphase Flow ◽

10.1016/s0301-9322(97)88530-8 ◽

1996 ◽

Vol 22 ◽

pp. 142

Author(s):

G Donsi

Keyword(s):

Heat Transfer ◽

Fluidized Beds ◽

Transfer Coefficients ◽

Heat Transfer Coefficients ◽

Sphere Size ◽

Gas Fluidized Beds

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Gas‐Fluidized Beds

Two‐Phase Heat Transfer ◽

10.1002/9781119618652.ch9 ◽

2021 ◽

pp. 311-345

Keyword(s):

Fluidized Beds ◽

Gas Fluidized Beds

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Expulsion of particles from a buoyant blob in a fluidized bed

Journal of Fluid Mechanics ◽

10.1017/s0022112094003617 ◽

1994 ◽

Vol 278 ◽

pp. 63-81 ◽

Cited By ~ 15

Author(s):

G. K. Batchelor ◽

J. M. Nitsche

Keyword(s):

Fluidized Bed ◽

Fluidized Beds ◽

Particle Concentration ◽

Small Concentration ◽

Numerical Calculations ◽

Significant Feature ◽

Average Particle ◽

Remarkable Property ◽

Gas Fluidized Beds ◽

Secondary Instabilities

It is a significant feature of most gas-fluidized beds that they contain rising ‘bubbles’ of almost clear gas. The purpose of this paper is to account plausibly for this remarkable property first by supposing that primary and secondary instabilities of the fluidized bed generate compact regions of above-average or below-average particle concentration, and second by invoking a mechanism for the expulsion of particles from a buoyant compact blob of smaller particle concentration. We postulate that the rising of such an incipient bubble generates a toroidal circulation of the gas in the bubble, roughly like that in a drop of liquid rising through a second liquid of larger density, and that particles in the blob carried round by the fluid move on trajectories which ultimately cross the bubble boundary. Numerical calculations of particle trajectories for practical values of the relevant parameters show that a large percentage of particles, of such small concentration that they move independently, are expelled from a bubble in the time taken by it to rise through a distance of several bubble diameters.Similar calculations for a liquid-fluidized bed show that the expulsion mechanism is much weaker, as a consequence of the larger density and viscosity of a liquid, which is consistent with the absence of observations of relatively empty bubbles in liquid-fluidized beds.It is found to be possible, with the help of the Richardson-Zaki correlation, to adjust the results of these calculations so as to allow approximately for the effect of interaction of particles in a bubble in either a gas- or a liquid-fluidized bed. The interaction of particles at volume fractions of 20 or 30 % lengthens the expulsion times, although without changing the qualitative conclusions.

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