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Research Papers: Multiphase Flows

A Combined Numerical and Experimental Study of Hydrodynamics for an Air-Water External Loop Airlift Reactor

[+] Author and Article Information
Deify Law

Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061

Samuel T. Jones, Theodore J. Heindel

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

Francine Battaglia1

Department of Mechanical Engineering, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061fbattaglia@vt.edu

1

Corresponding author.

J. Fluids Eng 133(2), 021301 (Feb 04, 2011) (8 pages) doi:10.1115/1.4003424 History: Received June 21, 2010; Revised January 09, 2011; Published February 04, 2011; Online February 04, 2011

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns that are interconnected with two horizontal tubes and is often preferred over traditional bubble column reactors because they can operate over a wider range of conditions. In the present work, the gas-liquid flow dynamics in an ELALR was simulated using an Eulerian–Eulerian ensemble-averaging method in two-dimensional (2D) and three-dimensional (3D) coordinate systems. The computational fluid dynamics (CFD) simulations were compared to experimental measurements from a 10.2 cm diameter ELALR for superficial gas velocities ranging from 1 cm/s to 20 cm/s. The effect of specifying a mean bubble diameter to represent the gas phase in the CFD modeling was investigated, and 2D and 3D simulations were found to be in good agreement with the experimental data. The ELALR flow regimes were compared for the reactor operating in bubble column, closed vent, and open vent modes, and the 2D simulations qualitatively predicted the behavior of bubble growth in the downcomer. However, it was found that 3D simulations were necessary to capture the physics of the ELALR for gas holdup, bulk density differences, and riser superficial liquid velocity.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the air-water external loop airlift reactor

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Figure 2

Gas holdup as a function of superficial gas velocity comparing simulations with experiments for the BC mode. Unless specified otherwise, the k-ε turbulence model is used.

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Figure 3

Gas holdup profiles for the BC mode at Ug=15 cm/s comparing 2D and 3D simulations at different heights above the aeration plate

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Figure 4

Instantaneous gas holdup contours at Ug=10 cm/s comparing 2D simulations for (a) BC, (b) CV, and (c) OV modes of operation

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Figure 5

Instantaneous gas holdup for the CV mode at Ug=10 cm/s comparing the gas-rich regimes in the downcomer for the (a) experiment, (b) schematic, and (c) 2D simulation

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Figure 6

Instantaneous gas holdup for the OV mode at Ug=10 cm/s comparing the gas-rich regimes in the downcomer for the (a) experiment, (b) schematic, and (c) 2D simulation

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Figure 7

Gas holdup as a function of superficial gas velocity comparing simulations with experiments for the ELALR in OV mode. Unless specified otherwise, the k-ε turbulence model is used.

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Figure 8

Riser superficial liquid velocity as a function of superficial gas velocity comparing simulations with experiments for the ELALR in OV mode

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Figure 9

Relationship between driving force (αgr−αgd) and riser superficial liquid velocity comparing 3D simulations and experiments for the ELALR in OV mode

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