The effect of pipe diameter on the structure of gas/liquid flow in vertical pipes

doi:10.1016/j.ijmultiphaseflow.2009.11.010

International Journal of Multiphase Flow

Volume 36, Issue 4, April 2010, Pages 303-313

https://doi.org/10.1016/j.ijmultiphaseflow.2009.11.010 Get rights and content

Abstract

Experimental work on two-phase vertical upward flow was carried out using a 19 mm internal diameter, 7 m long pipe and studying the time series of cross-sectional average void fractions and pressure gradient which were obtained simultaneously. With the aid of a bank of published data in which the pipe diameter is the range from 0.5 to 70 mm, the effect of pipe diameter on flow characteristics of two-phase flow is investigated from various aspects. Particularly, the work focuses on the periodic structures of two-phase flow. Average film thicknesses and the gas flow rate where slug/churn and churn/annular flow transitions occur all increase as the diameter of the pipe becomes larger. On the other hand, the pressure gradients, the frequencies of the periodic structures and the velocities of disturbance waves decrease. The velocity of disturbance waves has been used to test the model of Pearce (1979). It is found that the suggested value of Pearce coefficient 0.8 is reasonable for lower liquid flow rates but becomes insufficient for higher liquid flow rates.

Introduction

For application in a number of industries, from compact heat exchangers to large diameter deep-water risers in hydrocarbon production, extension of the current knowledge on gas/liquid flows in a wider range of pipe diameters is necessary. Especially in gas/oil industry, with the increase of oil demand and major discoveries of hydrocarbon fields becoming rarer in the conventional offshore, (water depth up to 500 m) the deeper water exploration is emerging. Risers employed for deep water are normally operated under friction dominated conditions. To minimise pressure losses they tend to be of diameters larger than those for which research data is available. However, it has been recognised that gas/liquid flow in such larger diameter pipes is different from that in smaller ones. For example, in such large diameter pipes (approximately >100 mm), it has been reported that the conventional Taylor bubble does not appear, Ohnuki and Akimoto (2000) and Omebere-Iyari (2006).

Although there are applications over a wide range of pipe diameters, few publications have reported systematically on the effect of pipe diameter on two-phase flow structures. Sekoguchi et al., 1985, Sekoguchi et al., 1992 and Ide et al. (1993) studied the effect of pipe diameter for annular flow using data taken from pipes of diameter from 0.5 mm to 26 mm. They investigated several parameters such as film thickness, the velocities/frequencies of what they termed liquid lumps, wave length and wave amplitude. For capillary tubes, Ide et al. found that the liquid lump velocity increases with decreasing pipe diameter but decreases suddenly at a pipe diameter of 2 mm for a constant liquid flow rate. They linked this with the change of wave structure having shorter wavelength and lower amplitude in pipes of diameter ⩽1.5–2 mm. Recent investigations by Jayanti et al. (1996) and Vijayan et al. (2001) shows that there is a definite effect of pipe diameter on the conditions at which flooding occurs. They examined pipes of 25, 67 and 99 mm diameter and proposed three mechanisms of flooding condition depending on the pipe diameter: one due to wave transportation for the smallest diameter pipes and the others linked to the transport of entrained droplets or churn-like motion of liquid film for larger ones.

This paper describes the effect of pipe diameter on parameters indicating flow structure by combining the results of time series of cross-sectionally averaged void fraction and pressure gradient from experimental work using a 19 mm internal diameter pipe and a data bank from 5 to 70 mm internal diameter pipes gathered from published work. Focus is on periodic structures in the slug, churn and annular flow patterns.

Section snippets

Flow pattern specific model for annular flow

Published models for predicting film thickness and the velocity of disturbance waves are applied to experimental results in the present work for the purpose of their validation. In a number of empirical equations the film thicknesses are correlated with liquid film Reynolds number as in the following example: $δ_{l}^{+} = A {Re}_{lf}^{B},$ where A and B are constants, ${Re}_{lf} = \frac{{\dot{m}}_{lf} D_{t}}{η_{l}} and$ $δ_{l}^{+} = \frac{δ ρ_{l}}{η_{l}} \sqrt{\frac{τ_{i}}{ρ_{l}}} .$

Here ${\dot{m}}_{lf}$ is liquid film mass flux, D_t is pipe diameter, ρ_l is liquid density, η_l is liquid dynamic viscosity, δ is film

Experimental facility

A schematic diagram of the experimental facility is shown in Fig. 1. This facility is of a ‘Double Closed Loop’ configuration, in which both gas and liquid are recirculated. The facility consists of a liquid ring compressor unit, a centrifugal pump, a heat exchanger, two cyclones, two measuring tanks, a buffer tank and a separator tank. The test section, made of transparent acrylic resin, has an internal diameter of 19 mm and is 6.87 m tall. In the test section, eight ring-type conductance probes

Results

Measurements were made of void fraction and pressure drop for gas superficial velocities of 1–33 m/s and liquid superficial velocities 0.03–0.65 m/s.

The effect of pipe diameter

The data from various pipe diameters have been gathered from sources listed in Table 1. Investigation was focused on the structure of slug and annular flow from the limitation of data bank. The data from much larger pipe diameter, for instance 127 mm employed by Omebere-Iyari (2006), have not been included at this stage since no slug flow was observed. It what follows the data is presented in terms of superficial velocities as the physical properties which appear in dimensionless groups have not

Conclusions

Time series of cross-sectional average void fraction were obtained by ring-type conductance probes mounted on a 19 mm pipe. The velocity of periodic structure was derived by cross correlation using information of two successive probes. The pressure gradient was also obtained simultaneously. Using these experimental results and a published data bank from 5 to 50 mm pipes at dimensionless axial distance >100 pipe diameters, i.e., considered as a fully developed flow, the effect of pipe diameter on

Acknowledgements

This work has been undertaken within the Joint Project on Transient Multiphase Flow (TMF3). The author(s) wish to acknowledge the contributions made to this project by the Engineering and Physical Science Research Council (EPSRC), the Department of Trade and Industry and the following:- Advantica; AspenTech; BP Exploration; Chevron; ConocoPhillips; ENI; ExxonMobil; FEESA; Granherne/Subsea 7; Institutt for Energireknikk; Institut Français du Petrole; Norsk Hydro; Petrobas, Scandpower; Shell;

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The effect of pipe diameter on the structure of gas/liquid flow in vertical pipes

Abstract

Introduction

Section snippets

Flow pattern specific model for annular flow

Experimental facility

Results

The effect of pipe diameter

Conclusions

Acknowledgements

Int. J. Multiphase Flow

Nucl. Eng. Des.

Int. J. Multiphase Flow

Flow Measure. Instrum.

Int. J. Heat Mass Transf.

Trans. Inst. Chem. Eng.

Int. J. Multiphase Flow

Int. J. Multiphase Flow

Int. J. Heat Mass Transf.

Nucl. Eng. Des.

Int. J. Multiphase Flow

Exp. Therm. Fluid Sci.

Int. J. Multiphase Flow

Int. J. Multiphase Flow

Chem. Eng. Sci.

Interfacial drag and film height for vertical annular flow

AIChE J.