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Research Papers: Petroleum Wells-Drilling/Production/Construction

Simultaneous Investigation of Entrained Liquid Fraction, Liquid Film Thickness and Pressure Drop in Vertical Annular Flow

[+] Author and Article Information
M. B. Alamu

 Floxpat Petroleum and Energy Services, 145-157 St. John Street,London EC1V 4PW, UKmhunir.alamu@floxpat.com

B. J. Azzopardi

 Chemical Engineering Department, University of Nottingham, University Park, Nottingham NG7 2RD, UKbarry.azzopardi@nottingham.ac.uk

J. Energy Resour. Technol 133(2), 023103 (Jun 27, 2011) (10 pages) doi:10.1115/1.4004265 History: Received March 11, 2010; Revised May 10, 2011; Published June 27, 2011; Online June 27, 2011

The mechanism of atomization of part of the liquid film to form drops in annular two-phase flow is not entirely understood. It has been observed that drop creation only occurs when there are large disturbance waves present on the film interface. (Woodmansee and Harrantty, 1969, “Mechanisms for the Removal of Droplets From a Liquid Surface by a Parallel Air Flow,” Chem. Eng. Sci., 24 , pp. 299–307) observed that ripples on these waves were precursors to drops. Though it has been reported that drops occur in bursts by (Azzopardi, Gas-Liquid Flows Begell House Inc., New York, 2006), all previous drop size or concentration measurements have always been time integrated to simplify data analysis. Dynamic time averaged drop size measurements are reported for the first time in annular flow. Experiments were carried out on a 19 mm internal diameter vertical pipe with air and water as fluids. Spraytec, a laser diffraction-based, drop size measurement instrument, was used in the drop related data acquisition. Simultaneous time-resolved measurements were carried out for drop, film thickness, and pressure drop. Film thickness has been measured using the conductance probes employing a pair of flush mounted rings as electrodes. Pressure drop was logged using differential pressure cell connected to two pressure taps located within the test section. The gas superficial velocity was varied systematically from 13 to 43 m/s at fixed liquid superficial velocities of 0.05 and 0.15 m/s, respectively. Additional tests were carried out with the gas velocity fixed at 14 m/s while the liquid superficial velocity was varied from 0.03 to 0.18 m/s. Signal acquired are presented in form of time series to permit data analysis at different levels. Based on signal analysis, interrelationships between liquid film where the drops are sourced and the contribution of the entrained liquid droplets to the overall pressure drop in the system has been elucidated. Though structures are not clearly visible in the signals acquired, the time series have been analyzed in amplitude space to yield probability density function (Pdf). Beyond gas superficial velocity of 30 m/s, Pdf of drop size distribution becomes monomodal or single-peaked marking transition to mist annular flow.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic flow diagram of the rig used in the present study

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Figure 2

Schematics of the test section

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Figure 3

Cross sectional view of ring-type conductance probes as used to measure void fraction

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Figure 4

Schematics of annular two-phase flow

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Figure 5

Film thickness time series. Inlet conditions: VSG  = 14 m/s and VSL  = 0.15 m/s.

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Figure 6

Entrained fraction time series. Inlet conditions: VSG  = 14 m/s and VSL  = 0.15 m/s.

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Figure 7

Pressure drop time series. Inlet conditions: VSG  = 14 m/s and VSL  = 0.15 m/s.

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Figure 8

Film thickness variation with gas superficial velocity for liquid superficial velocities of 0.05, 0.10, and 0.15 m/s. Data for VSL  = 0.10 m/s were interpolated linearly between liquid superficial velocities, VSL  = 0.05 m/s and VSL  = 0.15 m/s.

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Figure 9

Variation of standard deviation of mean film thickness as gas superficial velocity increases. Liquid superficial liquid velocities were fixed at VSL  = 0.05 m/s and VSL  = 0.15 m/s, respectively.

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Figure 10

Variation in drop concentration with increase gas superficial velocity at fixed liquid superficial velocities

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Figure 11

Dispersed phase pressure drop as a function of gas and liquid superficial velocities

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Figure 12

Entrained liquid fraction in the gas core as a function of gas and liquid superficial velocities

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Figure 13

Relationship between entrained liquid fraction and the dispersed pressure drop in vertical annular flow

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Figure 14

Comparison of present data with measurement of (Azzopardi [12])

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Figure 15

Relationship between pressure drop and entrained fraction. The relationship reveals three different flow regimes usually encountered in annular flow- wispy, co-current, and mist flow.

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Figure 16

Normalized drop size as a function of gas superficial velocity

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Figure 17

Changes in drop size distribution based on characteristic shape of the probability density function. There is a change from multiple to single peak after gas superficial velocity of 30 m/s is exceeded. This change marks transition to annular mist. The data considered were taken at a fixed superficial liquid velocity of 0.05 m/s.

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