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Research Papers: Multiphase Flows

Transition of Bubbly Flow in Vertical Tubes: Effect of Bubble Size and Tube Diameter

[+] Author and Article Information
A. K. Das

Department of Mechanical Engineering, IIT Kharagpur, 721302, Indiaarup@mech.iitkgp.ernet.in

P. K. Das1

Department of Mechanical Engineering, IIT Kharagpur, 721302, Indiapkd@mech.iitkgp.ernet.in

J. R. Thome

LCTM, EPFL, Lausanne CH-1015, Switzerlandjohn.thome@epfl.ch

1

Corresponding author.

J. Fluids Eng 131(9), 091304 (Aug 18, 2009) (6 pages) doi:10.1115/1.3203206 History: Received January 13, 2009; Revised June 23, 2009; Published August 18, 2009

In a companion paper (“Modelling Bubbly Flow by Population Balance Technique Part I: Axial Flow Development and Its Transitions,” ASME J. Fluids Eng), a two fluid model along with a multiclass population balance technique has been used to find out comprehensive criteria for the transition from bubbly to slug flow, primarily through a study of axial flow development. Using the same basic model the transition mechanism has been investigated in the present paper covering a wide range of process parameters. Though the dominating rate of bubble coalescence during the axial development of the flow acts as the main cause for the transition to slug flow, the simultaneous transformation of the radial voidage pattern cannot be overlooked. Appearance of core, intermediate, wall, and two peaks are observed in the radial voidage distribution depending on the phase superficial velocities. A map has been developed indicating the boundaries of the above subregimes. It has been observed that not only the size of the bubbles entering the inlet plane but also the size distribution (monodispersion or bidispersion) changes the voidage peak and shifts the transition boundary. It is interesting to note that the bubbly flow only with a core peak void distribution transforms into slug flow with a change in the operating parameters. Transition boundary is also observed to shift with a change in the tube diameter. The simulation results have been compared with experimental data taken from different sources and very good agreements have been noted.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Comparison of the void distribution of the present model and the experimental observations of Lucas (20) at low phase flow rates

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Figure 2

Comparison of the void distribution of the present model and the experimental observations of Prasser (21) at high phase flow rates

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Figure 3

Comparison of the two peak void distributions; present model versus experimental observations of Zun (3)

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Figure 4

Comparison of the two peak void distributions; present model versus experimental observations of Song (4)

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Figure 5

Comparison of the existing flow pattern maps with the present prediction

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Figure 6

Effect of bubble size (homogeneous distribution) at the inlet on the flow pattern map

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Figure 7

Effect of bubble size (nonhomogeneous distribution) at the inlet on the flow pattern map

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Figure 8

Ranges of wall and core peakings

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Figure 9

Subregimes in the bubbly flow based on the voidage profile

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Figure 10

Effect of tube diameter on the void fraction profile at low phase velocities

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Figure 11

Effect of tube diameter on the void fraction profile at high phase velocities

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Figure 12

Bubbly to slug transition boundary for different tube diameters

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