Slug flow in vertical tubes

This is not true because the slug is found to rise with a velocity 0.35VigDp) relative to the centre-line velocity of the liquid. The liquid flow will be turbulent and its centre-line velocity therefore approximately 20 per cent greater than its average velocity. Thus the correct expression for the slug s velocity is 

This equation has been verified by many investigators for well-spaced 

Plot ofk, against Eotvos number for slug flow 

Source E. T. White and R. H. Beardmore, Chemical Engineering Progress 17, pp. 351-361 (1962) 

When the slugs are not well spaced, the slug following in the wake of another slug rises more quickly and after some distance the two slugs will coalesce. Moissis and Griffith (1962) have given a correlation to account for this  

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Slug Flow in Vertical Tubes of Cylindrical Cross Section... 

Unstable Slug Flow Froth, Turbulent, Semi-Annular) in Vertical Tubes... 

Vertical Ducts. Typical flow patterns in upward vertical two-phase flow in a tube are presented in Fig. 17.48a. At low vapor qualities and low mass flow rates, the flow usually obeys the bubbly flow pattern. At higher vapor qualities and mass flow rates, slug or plug flow replaces the bubbly flow pattern. Further increase in vapor quality and/or mass flow rates leads to the appearance of the churn, annular, and wispy annular flow patterns. 

Two-phase flow patterns in vertical tubes. The liquid flow rate is upward at a small, constant velocity. The gas flow rate upward increases steadily from left to right. The annular pattern shown is often referred to as climbing film flow. [From D. J. Nicklin and J. F. Davidson, The onset of instability in two-phase slug flow, in Symposium in Two-Phase Flow, Institution of Mechanical Engineers, London, 1962. Reproduced by permission j of the publisher.]... 

In this chapter, the work published by the authors is reviewed. The importance of the wakes of slugs as the primary agent in promoting mixing is considered first. Next, the problem of Taylor dispersion for laminar liquid flow along a tube is briefly outlined, and, finally, the analysis of dispersion in co-current flow of gas slugs and liquid in vertical tubes is presented. 

The flow regime maps shown in Fig. 5.16a,b indicate that typical flow patterns encountered in the conventional, large-sized vertical circular tubes, such as bubbly flow, slug flow, churn flow and annular flow, were also observed in the channels having larger hydraulic diameters ([Pg.216]

As depicted in Figure 8.34, the flow patterns formed in a vertical tube follow a trend with increasing gas flow of bubble flow, slug flow, chum flow, and annular flow. These regimes are described briefly below. 

Fig. 5 Boiling in a narrow vertical tube. (A) Boiling suppressed by head, natural convection is shown (B) bubble formation (C) slug formation due to bubble coagulation (D) fully developed slug flow (E) breakdown of slugs at high vapor rates (F) annular-flow-climbing film.

Slug flow Where the bubbles coalesce to form slugs of vapor, which may occupy the cross section of the tube. Slug flow is similar to the flow pattern in a percolating coffee pot and is the predominant flow pattern in vertical thermosiphon reboilers. 

Outlet line This line is usually sized so that its cross-sectional area is at least the same as the total cross-sectional area of the reboiler tubes (253, 358, 360). Excessive pressure drop in this line promotes oscillations and elongates the preheat zone. Excessive velocity in this line may also be undesirable at the column inlet (see Sec. 4.1, guideline 5). On the other hand, if the outlet line rises vertically before bending toward the column, velocities should be kept above 15 ft/s (237), or slug flow may result. 

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