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"Shearforce" Rotor : Unique
Concept in Pumping Fluids
Guest article by Frank Tybor of Shearforce Ltd. Company
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Shearforce pumps utilize the
patented "Shearforce" rotor which is a vane less impeller with
non-parallel shrouds. These rotors improves the Shearforce
pumpís capability of pumping certain applications which are not
suitable for standard vane type impellers. Applications include
entrained gas (air), high solid content, viscous and shear
background of shear force pumps is as old as the Egyptians when
it was used to remove water from the Nile River. The Archimedes
pump used a screw (auger) to move material down a cylinder. The
rotation of the screw creates a shearing force on the material
which drives it down the threads of the screw.
Figure 1: Shearforce rotor
The Shearforce pump or vane less
centrifugal pump utilizes the fluid viscosity to generate the
necessary forces required to sustain a pressure differential and
corresponding flow. As the rotor is spinning, fluid is
introduced through the central region where it is drawn in a
radial direction through the rotor spaces. Due to the fluidís
viscosity, the fluid is accelerated by the shear forces and
assumes a tangential velocity. As the fluid progresses
outwardly, the body forces continually develop, sustaining the
pressure gradient and flow in the radial direction.
Boundary condition states that
the normal component of the velocity at a boundary is zero in
steady flow. With the Shearforce pump, the boundary layer (layer
closest to the rotating shroud) is stationary, relative to the
shroud. As the shrouds rotate, energy is transferred to
successive layers of molecules in the fluid between the shrouds
via viscous drag. This generates velocity and pressure gradients
between the shrouds.
The basic principal is well
studied in physics and fluid flow. When a fluid flows between
flat plates or through a tube, under certain conditions, the
flow pattern assumes that of thin layers or laminae which slide
past one another. If there is a friction force along the surface
of contact between the layers a force must be exerted to cause
one layer of the fluid to slide past another.
The friction force arises from a
property of the liquid called viscosity and the flow is said to
be viscous, laminar, or in streamlines. To obtain a quantitative
definition of viscosity, we shall consider the laminar flow of a
fluid between two parallel flat plates, as show below. The upper
plate moves to the right with velocity V due to the force F
which is also to the right. The lower plate is stationary. The
thin layer of fluid in contact with the moving plate is found to
have the same velocity as that of the plate.
Figure 2: Intermediate
layers of fluid
thin layer adjacent to the stationary plate is at rest. The
velocities of the intermediate layers of fluid increase
uniformly from the stationary to the moving wall, as shown by
the arrows. The layers of fluid slide over one another as do the
leaves of a closed book when it is placed flat on a table and a
horizontal force is applied to the top cover. As a consequence
of this motion, a portion of the fluid which at some instant has
the shape abcd, will a moment later take the shape abc'd' and
will become more and more distorted as the motion continues, In
short, the fluid is in a state of continually increasing
To maintain motion it is
necessary that a force F be continually exerted to the right of
the moving plate, and hence on the upper surface of the fluid.
This force tends to move the liquid and the stationary plate as
well to the right. Therefore an equal force F must be exerted to
the left on the lower plate in order to hold it stationary. If A
is the area of the fluid over which these forces are applied,
the ratio F/A is the shearing stress exerted on the fluid. See
our whitepaper on website for more details.
The primary difference in the
Shearforce rotor compared to other impellers or rotors is the
lack of vanes or a vane less impeller. This results in very
little impingement on the fluid since very little fluid comes
into contact with the rotor. The fluid that does come into
contact with the rotor remains stationary relative to the rotor
due to the boundary lawyer of the fluid with the rotor. The
remaining fluid passes through the rotor due to the friction
created by each progressive layer of fluid from the boundary
layer to the center of the rotor. A high pressure area is
created at the boundary layer closes to the outer shrouds with a
resultant lower pressure area in the center of the rotor.
This enables the Shearforce pump
to pump fluids with low shear and without impingement. The low
pressure area in the center of the rotor which is a conduit for
solids and gas to pass through the rotor without impingement.
Since the Shearforce Rotor is utilizing the fluid viscosity to
move the fluid, higher fluid viscosities such as sludge are no
problem for the Shearforce rotor.
Specific Installations : DAF
installations which have demonstrated the advantage of the
Shearforce Rotors are DAF (dissolve air floatation) systems.
A DAF system developed by Water Resources known as the DAF
Whitewater System which utilizes the patented Shearforce
technology. The heart of the system is the ability of the
Shearforce pumps to pump air which has been injected into the
suction of the pumps.
Figure 3: Installation of
Shearforce Pumps installed in DAF application.
The injection of air results in
Whitewater which is pumped through the innovative Pipe
Flocculator. The Whitewater contains millions of microscopic
tiny air bubbles. Extensive laboratory evaluation on the size of
the air bubble and effective liquid-solid separation,
overwhelming demonstrate that the smaller the air bubble, the
more efficient the separation.
specific application which benefits from the Shearforce Rotor is
sludge. Pumps typically used for this application are
progressive cavity pumps. The screw type rotor of these pumps
are subject to high wear due to the abrasive quality of the
sludge. The pump equipped with the Shearforce Rotors are capable
of passing the sand with minimal impingement and therefore wear.
Figure 4: Result of
injecting air into the suction of the Shearforce rotor
Installation showing P.C. type
pump on left being replaced with Dry Pit type pumps without need
for piping modification.
- DAF and Ozone Applications:
Air can be injection into suction of Shearforce rotor
creating millions of tiny air bubbles improving the
efficiency of any DAF or ozone processes.
- Entrained Chemical Gas:
Shearforce rotor can pump up to 20% entrained gas without
effecting pump performance thus eliminating the need to
remove gases produced in chemical processes.
- Latex Paint:
Shearforce rotor will not shear the latex products producing
a better product.
- Oil Sludge: Shearforce
rotor can handle high viscosity and solid content.
- Oil Tank Loading:
Shearforce rotor will not emulsify the crude oil saving in
- Pharmaceutical Crystals:
Shearforce rotor will not damage the crystals used in
producing many pharmaceutical products.
- Plankton: Shearforce
rotor will not damage the living organisms.
- Food Industry:
Shearforce rotor can be installed in A3 pumps for shear
sensitive foods such as milk, grape juice and wine.
Shearforce Rotors have also been
used successfully to pump oil sludge from sludge pits. The
process includes modification. Shearforce Rotors have also been
used successfully to pump oil sludge from sludge pits. The
process includes the liquidizing of the sludge and the
separation of the oil from the sand.
About our author
You can contact our author at
Mr. Frank Tybor
Shearforce Ltd. Company
5510 South Westmoreland, 300
Dallas, TX 75237
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