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Research Papers: Multiphase Flows

Characterizing Jetting in an Acoustic Fluidized Bed Using X-Ray Computed Tomography

[+] Author and Article Information
David R. Escudero

Colegio Politécnico,
Departamento de Ingeniería Mecánica,
Universidad San Francisco de Quito,
Quito 170901, Ecuador
e-mail: descudero@usfq.edu.ec

Theodore J. Heindel

Department of Mechanical Engineering,
Iowa State University,
Ames, IA 50011
e-mail: theindel@iastate.edu

1Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received November 17, 2014; final manuscript received August 17, 2015; published online December 8, 2015. Assoc. Editor: E. E. Michaelides.

J. Fluids Eng 138(4), 041309 (Dec 08, 2015) (9 pages) Paper No: FE-14-1668; doi: 10.1115/1.4031681 History: Received November 17, 2014; Revised August 17, 2015

Understanding the jetting phenomena near the gas distributor plate in a fluidized bed is important to gas–solid mixing, heat and mass transfer, and erosion to any bed internals, which can all affect the performance of the bed. Moreover, acoustic vibration in a fluidized bed can be used to enhance the fluidization quality of the particulate matter and influence the jetting behavior. Characterizing the jetting structure using X-ray computed tomography (CT) in a three-dimensional (3D) fluidized bed, with and without acoustic intervention, is the focus of this study. A 10.2 cm ID fluidized bed filled with glass beads and ground walnut shell, with material densities of 2500 kg/m3 and 1440 kg/m3, respectively, and particle sizes ranging between 212 and 600 μm, is used in these experiments. X-ray CT imaging is used to determine local time-average gas holdup. From this information, qualitative and quantitative characteristics of the hydrodynamic structure of the multiphase flow system are determined. Local time-average gas holdup images of the fluidized bed under acoustic intervention at a high superficial gas velocity show that jets produced near the aeration plate merge with other jets at a higher axial position of the bed compared to the no acoustic condition. Acoustic fluidized beds also have a fewer number of active jets than the no acoustic fluidized bed, which allowed for a more homogeneous gas holdup region deep in the bed. Hence, the acoustic presence has a significant effect on the jetting phenomena near the aeration plate in a fluidized bed.

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Figures

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Fig. 1

Actual aeration plate used in this study

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Fig. 6

Single slice images of jetting for 500–600 μm ground walnut shell with and without acoustic intervention for Ug = 1.5Umf and Ug = 3Umf

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Fig. 7

Single slice images of jetting at Ug = 3Umf for glass beads with different particle size ranges

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Fig. 5

Single slice images of jetting for 500–600 μm glass beads with and without acoustic intervention for Ug = 1.5Umf and Ug = 3Umf

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Fig. 4

Geometrical parameters of the jets

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Fig. 3

Different threshold percentages for glass beads and ground walnut shell

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Fig. 2

X-ray CT horizontal slice at 4 mm from the aeration plate, showing jet locations and various local average gas holdup regions. The lighter regions indicate a higher gas holdup, indicating a jet location.

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Fig. 8

Three-dimensional image of the jets for a fluidized bed of glass beads (425–500 μm, 500–600 μm) and ground walnut shell (500–600 μm) with and without acoustic intervention. (a) and (b) 425–500 μm glass beads, Ug = 3Umf; (c) and (d) 500–600 μm glass beads, Ug = 3Umf; and (e) and (f) 500–600 μm ground walnut shell, Ug = 3Umf.

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Fig. 9

Average jet length as a function of jet velocity for a fluidized bed of 500–600 μm glass beads with and without acoustic intervention

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Fig. 10

Average jet length as a function of jet velocity for a fluidized bed of 500–600 μm ground walnut shell with and without acoustic intervention

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Fig. 11

Average jet length as a function of Ug/Umf for glass beads with different particle sizes with and without acoustic intervention

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Fig. 12

Average jet length as a function of Ug/Umf for ground walnut shell with different particle sizes with and without acoustic intervention

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Fig. 13

Average expansion angle as a function of jet velocity for a fluidized bed of 500–600 μm glass beads with and without acoustic intervention

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Fig. 14

Average expansion angle as a function of Ug/Umf for glass beads with different particle sizes with and without acoustic intervention

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