Affiliation:
1. Inst. de Mecanique des Fluides
Abstract
Abstract
Since it was presented by Wallis1 the unit cell model for slug flow has proved its superiority in predicting the phase fractions and pressure gradient with a reasonable accuracy. However it relies on some crucial assumptions and on the choice of four closure laws. These fundamental issues are addressed in the present paper.
On the one hand, the closure laws guarantees the accuracy of the model. The scientific papers provide abundance of these laws whose physical value is unequal. The effectiveness and weakness of some of these laws are discussed from a comparison with existing data. Their critical role for certain ranges of flow rates is emphasised.
On the other hand, some specific assumptions limit the potentiality of the model. In particular the fully developed flow assumption in long bubble and liquid slug is discussed. A route to improve the model is explored.
Introduction
When gas and liquid flow in a pipe the interface between the phases may take a variety of different patterns. the most fascinating and misunderstood being probably slug flow. The primary characteristic of slug flow is its inherent unsteadiness. An observer looking at a fixed position along the axis would see the passage of a sequence of slugs of liquid containing dispersed bubbles. each looking somewhat like a length of bubbly pipe flow. alternating with sections of separated flow (Fig. 1). These two states follow in a random-like manner. inducing pressure. velocity and phase fraction fluctuations.
As this kind of flow occurs over a wide range of intermediate flow rates of gas and liquid. it is of interest for many industrial processes like:oil and gas and geothermal steam production and pipeline transportpipeline chemical reactors
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