Two Phase Flow in Pipe

1. Annular Flow

   -. Once the interfacial shear of the high velocity gas on the liquid film becomes dominant over
      gravity, the liquid is expelled from the center of the tube and flows as a thin film on the wall
      (forming an annular ring of liquid) while the gas flows as a continuous phase up the center of
      the tube. The interface is disturbed by high frequency waves and ripples. In addition, liquid may
      be entrained in the gas core as small droplets, so much so that the fraction of liquid entrained
      may become similar to that in the film. This flow regime is particularly stable and is the desired
      flow pattern for two-phase pipe flow.


2. Bubby Flow

   -. Numerous bubbles are observable as the gap is dispered in the form of discrete bubbles in the
      continuous liquid phase. The bubbles may vary widely in size and shape but they are typically
      nearly spherical and are much smaller than the diameter of the tube itself.


3. Slug Flow

   -. With increasing gas void fraction, the proximity of the bubbles is very close such that bubbles
      collide and coalesce to form larger bubbles, which are similar in dimension to the tube diameter.
      These bubbles have a characteristic shape similar to a bullet with a hemishperical nose with a
      blunt tail end. They are commonly refered to as Taylor bubbles after the instability of that name.
      Taylor bubbles are separated from one another by slugs of liquid, which may include small
      bubbles.
      Taylor bubbles are surrounded by a thin liquid film between them and the tube wall, which may
      flow downward due to the force of gravity, even though the net flow of fluide is upward.


4. Comparision