We were discussing the pumps and
basic pumping system, total
head developed by the centrifugal pump, parts
of centrifugal pump and their function, heads
and efficiencies of a centrifugal pump, work
done by the centrifugal pump on water, expression
for minimum starting speed of a centrifugal pump, multistage
centrifugal pumps, cavitation
in hydraulic machine, specific
speed of a centrifugal pump, cavitation in hydraulic turbines, cavitation in centrifugal pumps, maximum
suction lift of centrifugal pump and net positive suction head of centrifugal pump in our previous post.
Today, we will
find out here a new topic i.e. axial flow pump working principle with the help
of this post. We will find out here the basics behind the axial flow pump,
components of axial flow pump and further we will see the working principle of
axial flow pump.
Axial flow pump working principle
Axial flow pump
could be defined as a pump where liquid i.e. water will flow in axial
direction. Here we have used one term i.e. axial direction. Axial direction means
liquid will flow in the direction of axis of rotation.
In case of axial
flow pump, inlet and outlet of fluid will not vary in radial location from its
axis of rotation.
Axial flow pump
could be considered as the converse of an axial flow reaction turbine.
Axial flow pumps
will be used when we need to deliver the higher flow rate and relatively lower
head.
Axial flow pump: Components and their function
Following figure
shows here the basic schematic view of an axial flow pump.
There will be a
central hub in an axial flow pump as shown in figure and a number of vanes or
blades will be mounted over this central hub of axial flow pump. Therefore, the
central hub with a number of vanes or blades will be called as the rotor or
impeller of the axial flow pump.
Impeller blades will
be mounted over the central hub of axial flow pump in such a way that liquid
i.e. water may flow axially through these impeller blades.
Impeller will be
rotated within a cylindrical housing as displayed in above figure. There will
be a clearance between impeller and cylindrical housing and this clearance
should be as less as possible in order to avoid the leakage.
Now we will see
here the stationary inlet guide vanes of an axial flow pump as shown in above
figure. These stationary guide vanes are provided at inlet of an axial flow
pump in order to direct the liquid i.e. water in correct way to the impeller
blades without any shock.
There will also be
some stationary outlet guide vanes at the outlet of an axial flow pump as shown
in above figure. Stationary outlet guide vanes are basically provided at the outlet
of an axial flow pump in order to change the direction of motion of liquid
coming from the outlet of impeller.
When liquid will
come from the impeller outlet, it will have whirling component of velocity along
with the axial component of velocity. Stationary outlet guide vanes will reduce
this whirling component of velocity. After passing through the stationary
outlet guide vanes, liquid will flow almost in axial direction i.e. in a
direction parallel to the axis of rotation.
We must note it
here that the number of impeller blades will vary from 2 to 8 in an axial flow
pump.
Ratio of hub
diameter to the rotor diameter for an axial flow pump will be in the range of
0.3 to 0.6.
Therefore, we have
seen here the basics of axial flow pump. We have also discussed here the
various important components of axial flow pump and their function too with the
help of this post.
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Further we will find out, in our next post.
Reference:
Fluid mechanics, By R. K. Bansal
Fluid Machines, By Prof. S. K. Som
Image courtesy: Google
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