Wispy annular flow

Fig. 4.44 Flow types in a vertical, unheated tube with upward flow, a bubble flow b plug flow c churn flow d wispy-annular flow e annular flow f spray or drop flow...

The wispy-annular flow, Fig. 4.44 d, consists of a relatively thick liquid film at the wall, even though the liquid fraction in the vapour or gas core of the flow is still large. The film is interspersed with small bubbles, and the liquid phase in the core flow is mainly made up of large drops that sometimes coalesce into liquid strands. This type of flow pattern is normally observed when the mass flux is large. 

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. 

Wispy annularflow As the liquid flow rate is increased in annular flow, the concentration of drops in the gas core increases ultimately, droplet coalescence in the core leads to large lumps or streaks (wisp) of liquid in the gas core. 

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