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Research Papers: Multiphase Flows

Numerical Simulations for Hydrodynamics of Air-Water External Loop Airlift Reactor Flows With Bubble Break-Up and Coalescence Effects

[+] Author and Article Information
Deify Law

Department of Mechanical Engineering,
Baylor University,
Waco, TX 76711
e-mail: deify.law@gmail.com

Francine Battaglia

Department of Mechanical Engineering,
Virginia Tech,
Blacksburg, VA 24061

1 Corresponding author.

Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received August 24, 2012; final manuscript received May 1, 2013; published online June 5, 2013. Assoc. Editor: Olivier Coutier-Delgosha.

J. Fluids Eng 135(8), 081302 (Jun 05, 2013) (9 pages) Paper No: FE-12-1406; doi: 10.1115/1.4024396 History: Received August 24, 2012; Revised May 01, 2013

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns interconnected with two horizontal tubes and is often preferred over traditional bubble column reactors because it can operate over a wider range of conditions. In the present work, the gas-liquid flow dynamics in an ELALR were simulated using an Eulerian–Eulerian ensemble-averaging method with bubble breakup and coalescence effects in a three-dimensional system. The population balance models (PBM) of Luo and Svendsen (1996, “Theoretical Model for Drop and Bubble Breakup in Turbulent Dispersions,” AIChE J., 42, pp. 1225–1233) and Prince and Blanch (1990, “Bubble Coalescence and Breakup in Air-Sparged Bubble Columns,” AIChE J., 36, pp. 1485–1499) were used to simulate the bubble breakup and coalescence effects, respectively. The bubble breakup and coalescence closure models were implemented into CFDLib, a multiphase flow source code developed by Los Alamos National Laboratory, and validated with experiments. The computational fluid dynamics (CFD) simulations were then compared to experimental measurements from a 10.2 cm diameter ELALR for superficial gas velocities ranging from 1 to 20 cm/s. From this work, the 3D PBM simulations of an external loop airlift reactor were generally comparable with the 3D single bubble size simulations. However, the 3D PBM simulations have closer agreement with experimental findings than the single bubble size simulations especially regarding the length of gas bubbles in the downcomer.

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Figures

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Fig. 2

Schematic of the 14 cm diameter bubble column reactor of Degaleesan et al. [10]

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Fig. 1

Geometrical model of air-water external loop airlift reactor [1]

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Fig. 3

Comparison of (a) 2D and (b) 3D average axial liquid velocity predictions over 20–110 cm heights of each bubble size group with experiments at 9.6 cm/s superficial gas velocity with 14 cm bubble column diameter

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Fig. 4

Comparison of (a) 2D and (b) 3D average gas holdup predictions over 20–110 cm heights of each bubble size group at 9.6 cm/s superficial gas velocity with 14 cm bubble column diameter

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Fig. 5

Comparison of 2D and 3D time-averaged bubble size fraction distributions predicted by each size group and Chen et al. [12] at 40 cm height of the bubble column

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Fig. 6

Gas holdup as a function of superficial gas velocity comparing monodispersed simulations with population balance simulations for the ELALR

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Fig. 7

Riser superficial liquid velocity as a function of superficial gas velocity comparing monodispersed and PBM simulations with experiments [38] for the ELALR

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Fig. 8

Comparison of 3D time-averaged bubble size distributions in the riser of the ELALR predicted for each inlet superficial gas velocity

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Fig. 9

Comparison of instantaneous gas holdup contours of the 3D monodispersed and PBM simulations at Ug = (a) 15 cm/s and (b) 20 cm/s

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Fig. 10

Comparison of 3D (a) mono and (b) PBM instantaneous gas holdup simulations with (c) experiment [38] at 20 cm/s superficial gas velocity near the upper connector, where the arrows indicate the approximate length of experimental bubble near the upper connector in the downcomer

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