Propeller, Propellor, or PR
|
Impeller courtesy of K.
McDermott
 
Impellers courtesy of P. Csiszar
down- and up-pumping orientations |
The propeller was probably the first axial flow impeller. Most
propellers are designed with a near perfect pitch. Because of
this, most propellers are castings. This makes them very heavy and
expensive. The pitched blade turbine, PBT,
took over as the next axial flow impeller, because it is made of flat
stock material and is easy to build. It is much lighter, too,
making it easier for mixing companies to design.
Turbulent Power Numbers and Flow Numbers
 | Np=0.32 for 1.0
pitch, D/T=0.35, wB/T=0.1 |
| Np=0.36 for 1.0
pitch, D/T=0.22, wB/T=0.1 |
| Np=0.62 for 1.5
pitch, D/T=0.22, wB/T=0.1 |
| Np=1.00 for 2.0
pitch, D/T=0.31, wB/T=0.1 |
| Np=1.35 for 2.5
pitch, D/T=0.22, wB/T=0.1 |
| Note: Subtract 0.01 from Np for wB/T=1/12 |
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| The pitch of the impeller describes the
distance a tip on the blade travels in the axial direction for one
revolution of the impeller. A 1:1 pitch of a 1 meter diameter
propeller means that point would travel 1 meter out for each
revolution. A 1.5:1 pitch propeller would travel 1.5 meters for
each revolution.
A 1:1 pitch propeller is often referred to as a square pitch
propeller. A 1.5:1 pitch propeller is often called a super pitch
or a steep pitch propeller. They can obtain 50-70% more flow than
a square pitch propeller. As you can see above, the power is
75-100% higher, too.
As you can see from the two pictures to the left, propellers come in
many shapes. It is difficult and almost impossible to
pre-determine the Np and Nq numbers of them, because the shape of the
blades have a great impact. |
| We plan on compiling Np and Nq numbers of all
propellers we can find out there soon. Bookmark this page if you
are interested and come back again later.
The reason we have various spellings for this impeller type is
because they seem to be common. |
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