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7/29/2019 Two Phase Flow in Pipeline
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Two Phase Flow in pipelines
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Reasons for Two Phase formation
In pipelines when velocity of liquid is increased
sufficiently or a portion of the pipeline is elevated
(as in the case of siphon) , it causes the static
pressure in the pipeline to decrease.
When this pressure becomes less than the vapor
pressure of liquid vaporization of liquid occurs.
It leads to the formation of two phases(liquid/vapor ) in pipeline
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Types of flow pattern
1.Segregated flow
(i) Stratified
ii) Wavy iii)Annular
2. Intermittent
i )Plug flow ii) Slug flow
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3. Distributed flow
i)Bubble flow
ii) Mist flow
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Stratified flow
At low gas velocities ,complete separation of
two phases occurs.
The gas goes to the top and the liquid to the
bottom of the tube ,separated by an
undistributed horizontal interface .
Hence the liquid and gas are fully stratified in
this regime
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Wavy Flow
Increasing the gas velocity in a stratified flow
leads to the formation of waves on the
interface These waves travel in the direction
of flow.
However this crest do not reach the top of the
tube .
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Annular Flow
At even larger flow rates ,the liquid forms a
continuous annular film around the perimeter
of the tube ,the film is thicker at the bottom
than the top.
The interface between the liquid annulus and
the vapor core is distributed by small
amplitude waves and the droplets may bedispersed in the gas core .
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Intermittent flow
Further increasing the gas velocity ,these
interfacial waves become large enough to wash
the top of the tube .
This regime is characterized by large amplitudewaves intermittently washing the top of the tube
with smaller amplitude waves in between .
Large amplitude waves often contain entrainedbubbles . The top wall is continuously wetted by
large amplitude waves
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Intermittent flow is also a composite of plug
flow and slug flow regimes . These are of
following two types :
I ) Plug flow
Ii)Slug flow
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Plug Flow
This flow regime has liquid plugs that are
separated by elongated gas bubbles.
The diameters of the elongated bubbles are
smaller than the tube such that the liquid
phase is continuous along the bottom of the
tube below the elongated bubbles. (D
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Slug flow
At higher velocities ,the diameter of the
elongated bubbles become similar to the
channel height .(D=H)
The liquid slugs separating such elongated
bubbles can also be described as large
amplitude waves.
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Mist Flow
At very high gas velocities ,all the liquid may
be stripped from the wall and entrained as
small droplets in the new continuous phase .
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