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Research Papers: Multiphase Flows

Influence of Wall Inclination Angles on the Onset of Gas Entrainment During Single and Dual Discharges From a Reservoir

[+] Author and Article Information
M. Ahmed

Department of Mechanical Engineering, Assiut University, Assiut 71516, Egyptaminism@aun.edu.eg

J. Fluids Eng 130(2), 021305 (Feb 08, 2008) (16 pages) doi:10.1115/1.2813124 History: Received July 14, 2006; Revised July 16, 2007; Published February 08, 2008

A theoretical analysis was carried out to predict the influences of wall inclination angles of large reservoirs on the onset of gas entrainment during single and dual discharges from a stratified two-phase region. The findings reveal that when the wall inclination angle differs from zero, along with low values of Froude number, two distinct flow regimes occur: the gas-entrainment and no gas-entrainment regimes. A new criterion has been developed to predict the critical Froude number at the transition from the gas-entrainment to the no-gas-entrainment regime. The critical Froude number is defined as a function of the wall inclination angle for a single discharge. For dual discharge, the critical Froude number is found to be dependent on the wall inclination angle, the separating distance between the centerlines of the two branches, as well as the Froude number of the second branch. Furthermore, four different flow regions are mapped, representing the flow regime, as well as the two-phase flow for each branch. These maps serve to predict the flow regions, mass flow rates, and quality during single and dual two-phase discharges. For the gas-entrainment regime, the predicted values of the critical height at the onset of gas entrainment are compared with the experimental data reported in literatures. Comparisons showed good concurrence between the measured and predicted results. Furthermore, the influence of the wall inclination angle on the flow regions, the predicted critical height, and the location of the gas entrainment are presented and discussed at different values of independent variables.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 1

Geometry and the coordinate system for finite-branch analysis

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Figure 2

Influence of the wall inclination (α) on the critical Froude number for a single branch

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Figure 3

Influence of Fr2 on the critical value of Fr1 at L∕d=1.5 and α=30deg

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Figure 13

(a) Comparison between predicted and experimental results at L∕d=1.5 and α=0 under the upper figure as shown on the web ready text file. (b) Comparison between predicted and experimental results at L∕d=1.5 and α=0 when shifting the onset point under the lower figure as shown on the web ready text file.

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Figure 12

Comparison between predicted and experimental critical height at different values of Fr2, for L∕d=4.5

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Figure 11

Comparison between predicted and experimental critical height at different values of Fr2, for L∕d=1.5, and (a) Fr2=31.43 and (b) Fr2=43.99

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Figure 10

Variation the critical height versus the wall inclination for Fr2=60 at different values of L∕d: (a) L∕d=1.5 and (b) L∕d=4

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Figure 9

Influence of the wall inclination angle on the critical height

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Figure 8

Influence of the wall inclination angle (α) on flow regions at L∕d=1.5 for (a) α=0.1deg, (b) α=45deg, and (c) α=90deg

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Figure 7

Influence of the wall inclination angle on the variation of the absolute value of (VA∕Vd) versus Fr

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Figure 6

Influence of the wall inclination angle on the variation of (h∕H) versus Fr

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Figure 5

Comparisons between predicted and measured critical height at different values of α (0deg and 90deg)

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Figure 4

(a) Variation of the critical Froude number (Frcritical) versus the wall inclination under the upper figure as shown on the web ready text file. (b) Variation of the critical height (HOGE∕d) versus the wall inclination angle α in the case of a single discharge under the lower figure as shown on the web ready text file.

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