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Research Papers: Flows in Complex Systems

Mixing Flow Characteristics in a Vessel Agitated by the Screw Impeller With a Draught Tube

[+] Author and Article Information
Yeng-Yung Tsui1

Department of Mechanical Engineering, National Chiao Tung University, Hsinchu 300, Taiwanyytsui@mail.nctu.edu.tw

Yu-Chang Hu

Department of Mechanical Engineering, National Chiao Tung University, Hsinchu 300, Taiwan

1

Corresponding author.

J. Fluids Eng 130(4), 041103 (Apr 03, 2008) (10 pages) doi:10.1115/1.2903815 History: Received January 31, 2007; Revised October 18, 2007; Published April 03, 2008

The circulating flow in a vessel induced by rotating impellers has drawn a lot of interests in industries for mixing different fluids. It used to rely on experiments to correlate the performance with system parameters because of the theoretical difficulty to analyze such a complex flow. The recent development of computational methods makes it possible to obtain the entire flow field via solving the Navier–Stokes equations. In this study, a computational procedure, based on multiple frames of reference and unstructured grid methodology, was used to investigate the flow in a vessel stirred by a screw impeller rotating in a draught tube. The performance of the mixer was characterized by circulation number, power number, and nondimensionalized mixing energy. The effects on these dimensionless parameters were examined by varying the settings of tank diameter, shaft diameter, screw pitch, and the clearance between the impeller and the draught tube. Also investigated was the flow system without the draught tube. The flow mechanisms to cause these effects were delineated in detail.

Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

A sketch of the mixing system

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Figure 2

Illustration of a principal node and a neighboring node with a common face

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Figure 3

A computational mesh

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Figure 4

Typical flow field

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Figure 5

Comparison of predicted and measured axial velocities in the annular region outside the tube

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Figure 6

Variation of (a) circulation number, (b) power number, and (c) mixing energy against tank diameter D

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Figure 7

Variation of (a) circulation number, (b) power number, and (c) mixing energy against shaft diameter ds

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Figure 8

Distribution of circumferential velocity along the radial direction in the draught tube for different shaft diameters

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Figure 9

A schematic drawing of the flow channel inside the draught tube

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Figure 10

Pressure distribution on the impeller shaft from two different view angles

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Figure 11

Variation of (a) circulation number, (b) power number, and (c) mixing energy against screw impeller pitch S

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Figure 12

Variation of (a) circulation number, (b) power number, and (c) mixing energy against clearance C

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Figure 13

Variation of (a) circulation number, (b) power number, and (c) mixing energy against tank diameter D for the screw impellers with and without a draught tube

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Figure 14

Distribution of axial velocity along the radial direction for the screw impellers with and without a draught tube

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Figure 15

Variation of circulation center with tank diameter for the case without a draught tube

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Figure 16

Flow streamlines on a vertical plane for the screw mixer (a) with a draught tube and (b) without a draught tube

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