For vertical pipes, there are four main regimes, shown in Figure 1, and which occur successively at ever-increasing gas flow rates:
(a) Bubble flow: There is a continuous liquid phase, and the gas phase is dispersed as bubble within the liquid continuum. The bubble travel with a complex motion within the flow may be coalescing and are generally of non-uniform size.
(b) Slug flow: This flow regime occurs when the bubble size tends toward that of the channel diameter, and characteristic bullet-shaped bubbles are formed.
(c) Annular flow: This configuration is characterized by liquid travailing as a film on the Channel walls, and gases flowing through the center. Part of the liquid can be carried as droplets in the central gas core.
(d) Mist flow: in which the velocity of the continuous gas phase is so high that it reaches as far as the tube wall and entrains the liquid in the form of droplets.
Figure 1 Two-phase flow regimes in a vertical tube: (a) bubble, (b) slug, (c) annular, and (d) mist flow. In each case, the gas is shown in red, and the liquid is shown in blue.
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