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Multiphase Flows

Comparisons of Annular Hydrodynamic Structures in 3D Fluidized Beds Using X-Ray Computed Tomography Imaging

[+] Author and Article Information
Joshua B. Drake1

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

Theodore J. Heindel

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

1

Corresponding author.

J. Fluids Eng 134(8), 081305 (Aug 09, 2012) (8 pages) doi:10.1115/1.4007119 History: Received October 14, 2011; Revised June 11, 2012; Published August 09, 2012; Online August 09, 2012

Fluidized beds are common equipment in many process industries. Knowledge of the hydrodynamics within a fluidized bed on the local scale is important for the improvement of scale-up and process efficiencies. This knowledge is lacking due to limited observational technologies at the local scale. This paper uses X-ray computed tomography (CT) imaging to describe the local time-average gas holdup differences of annular hydrodynamic structures that arise through axisymmetric annular flow in a 10.2 cm and 15.2 cm diameter cold flow fluidized bed. The aeration scheme used is similar to that provided by a porous plate and hydrodynamic results can be directly compared. Geldart type B glass bead, ground walnut shell, and crushed corncob particles were studied at various superficial gas velocities. Assuming axisymmetry, the local 3D time-average gas holdup data acquired through X-ray CT imaging was averaged over concentric annuli, resulting in a 2D annular and time-average gas holdup map. These gas holdup maps show that four different types of annular hydrodynamic structures occur in the fluidized beds of this study: zones of (1) aeration jetting, (2) bubble coalescence, (3) bubble rise, and (4) particle shear. Changes in the superficial gas velocities, bed diameters, and bed material densities display changes in these zones. The 2D gas holdup maps provide a benchmark that can be used by computational fluid dynamic (CFD) users for the direct comparisons of 2D models, assuming axisymmetric annular flow.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 11

Radial εg,r for a fluidized bed of glass beads, ground walnut shell, and crushed corncob in the 10.2 cm and 15.2 cm diameter reactor with Ug  = 2Umf at h = 0.75D

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Figure 1

Schematic of annuli inscribed inside of the 15.2 cm reactor (not to scale)

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Figure 2

Comparison of smoothed and unsmoothed gas holdup data in the bed center and near the bed wall of a fluidized glass bead bed in the 15.2 cm diameter reactor with Ug  = 2Umf

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Figure 3

Local time-average annular gas holdup surface maps for a fluidized glass bead bed in the (left) 10.2 cm diameter reactor, and (right) 15.2 cm reactor at Ug  = 1.5Umf

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Figure 4

Radial εg,r for a fluidized glass bead bed in the 10.2 cm and 15.2 cm diameter reactors with Ug  = 1.5Umf at h = 0.75D

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Figure 5

Local time-average annular gas holdup surface maps for fluidized glass bead beds in the 10.2 cm diameter reactor at (upper left) Ug  = 1.25Umf , (upper right) Ug  = 1.5Umf , (lower left) Ug  = 1.75Umf , and (lower right) Ug  = 2Umf

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Figure 6

Local time-average annular gas holdup surface maps for fluidized glass bead beds in the 15.2 cm diameter reactor at (upper left) Ug  = 1.25Umf , (upper right) Ug  = 1.5Umf , (lower left) Ug  = 1.75Umf , and (lower right) Ug  = 2Umf

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Figure 7

Radial εg,r for a fluidized glass bead bed in the 10.2 cm and 15.2 cm diameter reactor with Ug  = 1.25Umf , 1.5Umf , 1.75Umf , and 2Umf at h = 0.75D

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Figure 8

Radial εg,r for a fluidized glass bead bed in the 10.2 cm and 15.2 cm diameter reactor with Ug  = 2Umf at h = 0.25D, 0.5D, 0.75D, and 2D

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Figure 9

Local time-average annular gas holdup surface maps for fluidized beds of decreasing density (left to right) in the 10.2 cm reactor at Ug  = 1.5Umf

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Figure 10

Local time-average annular gas holdup surface maps for fluidized beds of increasing density in the 10.2 cm reactor at Ug  = 2Umf

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