5.
Conclusions
The experimental data provided a comprehensive overview of pressure drop
in small pipes with 0, 50% and 100% hydrophobic coating of inner pipe
surface over the Reynolds range from 150 to 10000. The main findings can
be summarized as:
- The hydrophobic coating reduce the drag for laminar flow in small
pipes of 1 and 2 mm by around 10% but increase the drag by around
10% in transition and turbulent flow in the larger pipes of 4 and 5
mm. This behaviour may attributed to the change from the liquid-air
wetting surface condition to the liquid wetting surface of the pipes
used in this paper.
- The increase of drag in transition and turbulent flow may be
attributed to the very smooth surfaces of the pipes used in present
work. This minimized/ eliminated any slip velocity at the wall which
depend on the surface topology.
- There is a correlation between the percentage of surface coating and
the drag reduction/increase. This correlation is not linear due the
additional effect from the possible generation of vortices in the flow
due to unbalanced shear forces on the walls.
- The data from 3mm pipe indicating a transition from small pipes where
the viscosity have a significant influence on the velocity profiles to
large pipes when momentum have more influence on velocity profiles.
- The high definition imagery has presented some interesting and
intriguing information, in particular on the half-coated bubble
trajectories. The complex interactions between fully coated and
non-coated pipe walls will be invaluable to industry. The data
provided within this article will present microfluidics and biometrics
with opportunity to maximize the efficiency and reduce maintenance of
any system which operated under hydrophobic conditions in small pipes.