Fluctuation of Air-Water Two-Phase Flow in Horizontal and Inclined Water Pipelines

[+] Author and Article Information
A. R. Kabiri-Samani1

School of Engineering, Civil Engineering Division, ShahreKord University, ShahreKord, Irankabiri@eng.sku.ac.ir

S. M. Borghei

Civil Engineering Department, Sharif University of Technology, P.O. Box 11365-9313, Azadi Avenue, Tehran, Iranmahmood@sharif.edu

M. H. Saidi

Mechanical Engineering Department, Sharif University of Technology, P.O. Box 11365-9313, Azadi Avenue, Tehran, Iransaman@sharif.edu


Corresponding author.

J. Fluids Eng 129(1), 1-14 (Jun 17, 2005) (14 pages) doi:10.1115/1.2375134 History: Revised June 17, 2005; Received May 24, 2006

Air in water flow is a frequent phenomenon in hydraulic structures. The main reason for air entrainment is vortices at water intakes, pumping stations, tunnel inlets, and so on. The accumulated air, in a conduit, can evolve to a different flow pattern, from stratified to pressurized. Among different patterns, slug is most complex with extreme pressure variations. Due to lack of firm relations between pressure and influential parameters, study of slug flow is very important. Based on an experimental model, pressure fluctuations inside a circular, horizontal, and inclined pipe (90mm inside diameter and 10m long) carrying tow-phase air-water slug flow has been studied. Pressure fluctuations were sampled simultaneously at different sections, and longitudinal positions. The pressure fluctuations were measured using differential pressure transducers (DPT), while behavior of the air slug was studied using a digital camera. The objective of the paper is to predict the pressure variation in a pipeline or tunnel, involving resonance and shock waves experimentally. The results show that the more intensive phase interaction commences stronger fluctuations. It is shown, that the air-water mixture entering the pipe during rapid filling of surcharging can cause a tremendous pressure surge in the system and may eventually cause failure of the system (e.g., the maximum pressure inside the pipe would reach up to 10 times of upstream hydrostatic pressure as suggested by others too). Relations for forecasting pressure in these situations are presented as a function of flow characteristics, pipe geometry, longitudinal, and cross-sectional positions and head water.

Copyright © 2007 by American Society of Mechanical Engineers
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Figure 1

Stages of flow from pressurized to free-surface

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Figure 2

Schematic view of the experimental setup

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Figure 3

The arrangement of sensors at a pipe section

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Figure 4

Examples of pressure fluctuation pulses for different conditions in slug flow at different longitudinal positions (x)

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Figure 5

Typical mean pressure distribution on the pipe wall in a horizontal pipe (at x=1.61m)

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Figure 6

Normalized maximum and minimum instantaneous pressure versus mean pressure

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Figure 7

Normalized mean pressure versus the pipe distance

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Figure 8

Dimensionless pressure gradient as a function of (a)Qw∕Qc, and (b)Qa∕Qw

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Figure 9

Dimensionless mean pressure versus air/water flow rates ratio for different pipe inclinations: (a) data; (b) best fit curves

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Figure 10

Dimensionless mean pressure against strouhal number for different pipe inclinations

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Figure 11

The effect of dimensionless parameter Frah∕Fr versus dimensionless mean pressure

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Figure 12

Relation between pipe inclination and dimensionless mean pressure

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Figure 13

Dimensionless parameter Kf=fTPL∕D versus dimensionless mean pressure for different pipe inclinations

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Figure 14

The relation between Ph∕h and dimensionless parameter wfs

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Figure 15

Influence of void fraction on Ph∕h

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Figure 16

Variation of dimensionless mean pressure versus Frc

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Figure 17

Variation of Ph∕h with concentration

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Figure 18

Comparison of present results with Yakubov for zero slope pipe: (a) pressure loss versus water flow rate; (b) dimensionless mean pressure versus water flow

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Figure 19

Comparison of present results with previous works (pressure loss versus air/water rates ratio)

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Figure 20

Comparison of present data with Tarasevich

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Figure 21

Observed versus measured data: (a) Eq. 17; (b) Eq. 18; (c) Eq. 19.

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Figure 22

NRMSE and R2 for presented relations




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