Study on Commissioning Techniques for Oil Transportation Pipeline
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Where, ρ g - the density of the gas in the air mass, kg/m 3 ; L - density of liquid, kg/m 3 ;
Ag - cross sectional area of air mass, m 2 ; τ i - air mass by fluid shear stress, Pa. Si -
perimeter length between liquid and air mass, m;
The first term in Eq. (3) represents the component force of air mass gravity along the
pipeline direction. The second term represents the component of air mass buoyancy along
the pipeline direction. The third term is the force between the air mass and the liquid.
Since the length of the air mass is very small, its internal pressure can be considered to
be consistent, and there is no pressure gradient.
(2) Air bubble section
Fig. 5. Schematic diagram of bubble aggregation process
Under the inter-phase friction force and the liquid phase turbulence impact force, the
air mass will break up and disperse into the liquid in the form of small bubbles (downslope
section in Fig. 4), which will be carried by the liquid to flow downstream (upslope section
in Fig. 5) until it reaggregates in the upslope section. During commissioning, due to the
repeated occurrence of air mass fragmentation and aggregation, the flow in most pipelines
is not the single-phase flow of pure liquid, but the bubble flow in the multi-phase flow.
According to the relation proposed by Gregory [2], after the air mass is broken into
bubbles, the calculation formula of liquid holdup in the pipe segment is,
H l =
1
1 +
v s
8.66
1.39
(4)
Where, v s —The velocity of the gas-liquid mixture, m/s;