Note: Descriptions are shown in the official language in which they were submitted.
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SUBMERSIBLE DISK-TYPE PUMP FOR VISCOUS AND SOLIDS-LADEN
FLUIDS HAVING HELICAL INDUCER
FIELD OF THE INVENTION
[0001] The present disclosure relates to the field of submersible pumps and,
in particular,
to a submersible disk-type pump assembly having a helical inducer for pumping
viscous
and solids-laden fluids.
BACKGROUND OF THE INVENTION
[0002] Submersible pumps, and in particular electrical submersible pump (ESP)
systems,
are known as an effective artificial lift method for pumping production fluids
to the
surface. ESP systems typically include an electric motor and a multi-stage
centrifugal
pump operating in a vertical position and run on a production string,
connected back to a
surface control mechanism and transformer via an electric power cable. The
multi-stage
centrifugal pump typically consists of stages of rotating impellers and
stationary diffusers
mounted on a single shaft. As the impellers are rotated, fluid is passed to
the eye of the
next impeller through the respective diffuser. As the fluid leaves the
impeller, the liquid
kinetic energy and the velocity in it is transformed to static pressure,
leading to an
amplified pressure on the downstream side of the pump. In a multi-stage
system, pressure
is increased as fluid is pumped from one impeller to the next to push the
fluid upwards.
[0003] Viscous and solids-laden fluids present challenges for ESP systems. In
particular,
the high internal friction arising with viscous and solids-laden fluids
typically results in
significant performance inefficiencies. As well, the abrasive materials in
such fluids results
in rapid solids impingement wear and eventual loss of performance. The
development of a
number of modifications to ESP systems have been described for addressing
these
challenges.
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[0004] Commonly invented United States Patent No. 6,227,796 describes a
modification
to the pump impeller that can be used in a multi-stage pump system to
manipulate the flow
patterns at the radial periphery of the impeller so as to significantly reduce
head losses in
the annular flow chamber. Specifically, an impeller comprising a stack of
circular disks is
described that form a frusto-conical profile between the upstream and
downstream ends.
In this way, the disks form a plurality of radial flow passages wherein
incrementally less
fluid issues from each successive radial flow passage between adjacent disks
thereby
reducing head loss in the issuing viscous fluid flow and increasing pumping
efficiency.
Solely by modifying the impeller, fluid flow is manipulated at the impeller
stage to
improve efficiency in a submersible pump system.
[0005] United States Patent Publication No. 2012/0269614 relates to a staged
centrifugal
pump (as opposed to a staged disk-type pump and of the present invention) and
attempts to
improve pump efficiency of such centrifugal pump by manipulating fluid flow at
intake.
In particular, there is described an auger assembly coupled to the shaft
leading to the first
centrifugal pump stage. The auger assembly comprises a helical portion
terminating into a
plurality of radial blades that lead into the multi-stage impellers. The auger
is described as
creating a contained tight vortex of fluid that keeps solids suspended in the
fluid and
increases velocity of the fluid into the eye of a diffuser. The auger further
acts to break up
solids to further facilitate fluid flow. In this way, solids are kept from
accumulating and
"plugging" flow in the lower stages of the multi-stage centrifugal pump stack,
and as a
result, reduce the amount of abrasive wear.
[0006] There continues to be a need for a submersible disk-type pump system
that is
resistant to the abrasiveness of solids-laden fluids, while still able to
achieve flow and
pressure requirements sufficient for efficient production of viscous fluids
comparable to
centrifugal stage pumps.
[0007] This background information is provided for the purpose of making known
information believed by the applicant to be of possible relevance to the
present invention.
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No admission is necessarily intended, nor should be construed, that any of the
preceding
information constitutes prior art against the present invention.
SUMMARY OF THE INVENTION
[0008] Disclosed herein are exemplary embodiments pertaining to a submersible
pump
assembly for viscous and solids-laden fluids. In accordance with one aspect of
the present
disclosure, there is described a submersible pump assembly for pumping a
viscous or
solids-laden fluid upwardly, comprising: a cylindrical housing having an
intake disposed at
an upstream end and an outlet disposed at a downstream end opposite the
intake; a rotating
shaft extending through the cylindrical housing along a center axis of the
housing and
adapted to be driven by a submersible motor; a plurality of successive pumping
stages
disposed along the rotating shaft in a co-axial arrangement, each pumping
stage
comprising a frusto-conical disk impeller and a diffuser; and a helical
inducer coupled to
the shaft at the upstream end disposed between the intake and the plurality of
pumping
stages, the inducer comprising at least a single helical turn that directly
converges into the
plurality of pumping stages.
[0009] In accordance with another aspect, there is described a submersible
pump
assembly for pumping a viscous or solids-laden fluid upwardly, comprising: a
cylindrical
housing having an intake disposed at an upstream end and an outlet disposed at
a
downstream end opposite the intake; a rotating shaft extending through the
cylindrical
housing along a center axis of the housing and adapted to be driven by a
submersible
motor; a plurality of successive pumping stages disposed along the rotating
shaft in a co-
axial arrangement, each pumping stage comprising a frusto-conical disk
impeller and a
diffuser, the frusto-conical disk impeller comprising a stack of axially
spaced apart circular
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disks of progressively decreasing radii towards the downstream end, each disk
extending
radially and concentrically from a cylindrical core for receiving the rotating
shaft
therethrough, the cylindrical core comprising a plurality of parallel flow
passages spiraling
axially about the cylindrical core and communicating with a plurality of
radial flow
passages formed between the disks, wherein fluid flows from the upstream end
of the
impeller through the axial flow passages and into the radial flow passages
between disks;
and a helical inducer coupled to the shaft at the upstream end disposed
between the intake
and the plurality of pumping stages, the inducer comprising at least a single
helical turn
that directly converges into the plurality of pumping stages.
[0010] In accordance with a further aspect, there is described a method for
pumping a
viscous or solids-laden fluid upwardly, comprising: providing the submersible
pump
assembly according to embodiments described herein, and a motor configured to
drive the
pump assembly; positioning the submersible pump assembly in a wellbore;
activating the
motor to actuate the submersible pump assembly; wherein viscous or solids-
laden fluid
enters the submersible pump assembly to be homogenized by the helical inducer
to break
up any solids in the fluid while accelerating and directing the fluid into the
plurality of
successive pumping stages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] These and other features of the invention will become more apparent in
the
following detailed description in which reference is made to the appended
drawings.
[0012] Figure 1 is a cross-sectional view of a pump assembly, according to
embodiments
of the present disclosure;
[0013] Figures 2A and 2B are cross-sectional and perspective views of a prior
art conical
impeller shown as part of the pump assembly illustrated in Figure 1, according
to
embodiments of the present disclosure;
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[0014] Figures 3A and 3B are partial cross-sectional and top views of the
prior art
conical impeller shown in Figures 2A and 2B, according to embodiments of the
present
disclosure;
[0015] Figures 4A and 4B are perspective views of a single helix inducer,
according to
embodiments of the present disclosure;
[0016] Figures 5A and 5B are top and cross-sectional views of the single helix
inducer
shown in Figures 4A and 4B, according to embodiments of the present
disclosure;
[0017] Figures 6A and 6B are perspective views of a double helix inducer,
according to
embodiments of the present disclosure;
[0018] Figures 7A and 7B are top and cross-sectional views of the double helix
inducer
shown in Figures 6A and 6B, according to embodiments of the present
disclosure;
[0019] Figure 8 is a graphical representation of the effect of an inducer at
intake on
performance and system efficiency of a prototype frusto-conical stage disk-
type pump,
according to embodiments of the present disclosure, with water, at 25 C, 3500
RPM, no
charge pump (200 - Performance with Inducer, Standard Diffuser; 210 ¨
Performance with
Inducer, Modified Diffuser; 220 ¨ Performance with No Inducer, Standard
Diffuser; 400 ¨
Efficiency with Inducer, Standard Diffuser; 410 ¨ Efficiency with Inducer,
Modified
Diffuser; 420 ¨ Efficiency with No Inducer, Standard Diffuser); and
[0020] Figure 9 is a graphical representation of the effect of rotation
direction on
performance and system efficiency of a prototype frusto-conical stage disk-
type pump,
according to embodiments of the present disclosure, with water, at 25 C, 3500
RPM, no
charge pump, and with a standard diffuser (500 - Performance with Clockwise
Rotation;
510 ¨ Performance with Counter-Clockwise Rotation; 600 ¨ Efficiency with
Clockwise
Rotation; 610 - Efficiency with Counter-Clockwise Rotation).
DETAILED DESCRIPTION OF THE INVENTION
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[0021] The submersible disk-type pump assembly according to embodiments of the
present disclosure is configured to manipulate the flow of fluids to achieve
sufficient flow
rate and fluid pressure to efficiently pump viscous or solids-laden fluid
upwardly, while
minimizing the risk of pump clogging and/or damage due to the solids content
of the fluid.
The submersible pump assembly of the present disclosure, provides a coupled
approach to
addressing the particular challenges presented by viscous or solids-laden
fluid. According
to embodiments described herein, the submersible pump assembly is configured
to
manipulate fluid flow at fluid intake into the pump assembly as well as
through the
pumping stages of the assembly. In this way, pumping efficiency of viscous or
solids-laden
fluid can be maximized as well, according to certain embodiments, the coupled
operation
of the pump assembly allows the configuration of the pump assembly to be
adjusted either
at intake and/or in the pumping stages to optimize performance for the
particular fluids
being pumped.
[0022] In particular embodiments, the submersible pump assembly comprises
successive
pumping stages made up of frusto-conical disk impellers separated by a
diffuser to
manipulate fluid flow in such a way as to generate sufficient fluid flow and
pressure to
pump viscous or solids-laden fluid upwardly. The pump assembly can be adjusted
to
accommodate the properties of the fluids being pumped. For example, the number
of
stages of frusto-conical disk impellers included in the pump assembly can be
adjusted
according to the viscosity of the fluid being pumped. Specifically, according
to
embodiments, the number of stages can be increased to accommodate increasing
viscosity
of the fluid.
[0023] The pump assembly further comprises a helical inducer coupled to the
shaft at the
upstream end disposed between the intake and the plurality of pumping stages.
The helical
inducer comprises at least a single helical turn that directly converges with
the plurality of
pumping stages. This configuration, according to the embodiments described
herein,
causes solids at the intake of the fluid to be homogenized and the homogenized
fluid to be
directed into the pumping stages. Specifically, the helical inducer breaks up
any solids in
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the fluid while accelerating and directing the fluid into the plurality of
successive pumping
stages. According to preferred embodiments, the helical inducer directs the
fluid into the
eye of the impeller. The helical inducer can further be adjusted to
accommodate the fluids
being pumped. Specifically, the number of helical turns in the inducer can be
adjusted to
increase or decrease the vortical force generated by the inducer. According to
certain
embodiments, the number of helical turns in the inducer may be adjusted to the
number of
stages in order to achieve sufficient fluid flow and pressure.
Definitions
[0024] Unless defined otherwise, all technical and scientific terms used
herein have the
same meaning as commonly understood by one of ordinary skill in the art to
which this
invention belongs.
[0025] As used herein, the term "viscous and/or solids-laden fluid" refers
generally to
fluids containing solid particles. The term, in particular embodiments, refers
to fluids
produced from an underground reservoir such as heavy oil bitumen which
typically will
include other liquids, gases, and solid particles in fluid admixture with the
bitumen.
According to certain embodiments, viscous fluids includes fluids having a
viscosity of
1000 cp or greater. According to other embodiments, solids-laden fluid
includes fluids
having a solids content of greater than trace levels of solids such as sand,
for example.
[0026] As used herein, the term "about" refers to an approximately +/-10%
variation
from a given value. It is to be understood that such a variation is always
included in any
given value provided herein, whether or not it is specifically referred to.
Submersible Pump Assembly ¨ Coupled Control
[0027] Embodiments of the present disclosure will now be described by
reference to
Figs. 1 to 7B, which show representations of the submersible pump assembly 50
according
to the present disclosure. For convenience and ease of reference, the
orientation of the
pump assembly 50 is referred to as being vertically arranged with the fluid
moving
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upwardly. It will be understood, however, that the pump assembly 50 may also
be
positioned in other orientations without limiting the scope of the invention.
[0028] Referring to Fig. 1, a submersible pump assembly 50 of the present
disclosure is
configured for coupled operation of successive pumping stages 95 with a
helical inducer
110 that together operate to create sufficient fluid flow and pressure to
upwardly pump a
viscous or solids-laden fluid. According to certain embodiments, the dual
configuration
allows the pump assembly 50 to be adjusted at fluid intake and/or during the
pumping
stages to optimize performance for the particular fluids being pumped.
[0029] As illustrated in Fig. 1, a submersible pump assembly 50 of the present
disclosure
comprises a cylindrical housing 60 having an intake disposed at an upstream
end for
receiving viscous and/or solids-laden fluid and an outlet disposed at a
downstream end
opposite the intake for discharging the fluid to the surface, for example. A
rotating shaft
80 extends through the cylindrical housing 60 along a center axis of the
housing 60 and is
adapted to be driven by a submersible motor (not shown). A plurality of
successive
pumping stages 95 is disposed in a co-axial arrangement along the rotating
shaft 80.
Positioned at the upstream end, disposed between the intake and the plurality
of pumping
stages 95, is a helical inducer 110 coupled to the shaft 80. The helical
inducer 110
comprises at least a single helical turn that directly converges into the
plurality of pumping
stages 95. In contrast to prior art assemblies, it has been found that direct
convergence of
the helical inducer 110 with the downstream plurality of successive pumping
stages 95
allows solids-laden fluid to be homogenized and accelerated into the intake of
the pumping
stages 95 with a reduced risk of the solids being propelled to the outer
circumference of the
inducer 110 causing jamming or clogging of the pump 50. According to certain
embodiments, the direct convergence of the helical inducer 110 with the
downstream
plurality of successive pumping stages 95 allows solids-laden fluid to be
homogenized and
accelerated into the eye of the diffuser and/or impeller of the pumping stages
95.
[0030] The helical inducer 110 may be coupled to the shaft 80 in any suitable
manner so
as to rotate with the shaft 80. As illustrated in Figs. 4B and 6B, the helical
inducer 110 can
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comprise a cylindrical axis 150 having a central bore 130 sized to fit onto
the rotating shaft
80 of the pump assembly 50. In this way, the helical inducer 110 can be co-
rotated with
the pumping stages 95 disposed downstream from the helical inducer 110. The
helical
inducer 110 is positioned below the first impeller 90 at the upstream end of
the pumping
stages 95 and directly above the housing intake. According to certain
embodiments, as
illustrated in Fig. 1, the helical inducer 110 may be disposed within a spacer
100 that
extends along the length of the housing 60 to form an annulus for fluid flow.
[0031] Helical inducers 110, according to embodiments of the present
disclosure, may
comprise multiple helical turns. As illustrated in Figs. 4A, 4B, 5A, and 5B,
the helical
inducer 110 may comprise a single helical turn 120 or more than one helical
turn as shown
in Figs. 6A, 6B, 7A, and 7B which illustrate a double helical turn 160. The
number of
helical turns in the helical inducer 110 can be adjusted as required by
design/implementation requirements. For example, according to certain
embodiments, the
number of helical turns in the helical inducer 110 will be adjusted in
accordance with the
properties of the fluid being pumped. According to other embodiments, the
number of
helical turns in the helical inducer 110 will be adjusted to the number of
impellers 95 in the
pumping stages 95 in order to achieve the desired fluid flow and pressure for
the particular
fluid being pumped. According to certain embodiments, the helical inducer 110
comprises
a plurality of helical turns. In other embodiments, the helical inducer 110
comprises at
least a double helical turn. In further embodiments, the helical inducer 110
comprises a
single helical turn.
[0032] The helical inducer 110 may have varying pitches and inducer vane
lengths 140
which may vary depending on varying well conditions and implementations.
According to
certain embodiments, the helical inducer 110 can comprise a pitch to diameter
ratio
ranging from about 1:0.30 to about 1:0.95. According to other embodiments, the
helical
inducer 110 can comprise a pitch to diameter ratio of about 1:0.45 to about
1:0.85.
According to further embodiments, the helical inducer 110 can comprise a pitch
to
diameter ratio of about 1:0.55 to about 1:0.80. According to other
embodiments, the
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helical inducer 110 can comprise a pitch to diameter ratio of about 1:0.65 to
about 1:0.75.
According to further embodiments, the helical inducer 110 can comprise a pitch
to
diameter ratio of about 1:0.8.
[0033] Similarly, the helix angle of the helical inducer 110 can vary
depending on
varying well conditions and implementations. According to certain embodiments,
the
helical inducer 110 can comprise a helix angle of between about 15 to about
45 .
According to other embodiments, the helical inducer 110 can comprise a helix
angle of
between about 18 to about 35 . According to further embodiments, the helical
inducer
110 can comprise a helix angle of between about 20 to about 30 . According to
other
embodiments, the helical inducer 110 can comprise a helix angle of about 20 .
[0034] Directly downstream from the helical inducer 110 is disposed the
pumping stages
95. According to preferred embodiments, each pumping stage comprises a frusto-
conical
disk impeller 90 and a diffuser 70. In particular, the inventor's prior art
frusto-conical disk
impeller 90 (described in United States Patent No. 6,227,796) is positioned
within the
pumping stages 95 of the present disclosure. As shown in Figs. 2A and 2B, the
frusto-
conical disk impeller 90 comprises a stack of axially spaced apart circular
disks 13 of
progressively decreasing radii towards the downstream end. Each disk 13
extends radially
and concentrically from a cylindrical core 11 having a central bore 14 for
receiving the
rotating shaft 80 therethrough. The cylindrical core 11 comprises a plurality
of parallel
flow passages 17 spiraling axially about the exterior of the cylindrical core
11 which
communicate with a plurality of radial flow passages 26 formed between the
disks 13.
[0035] As further illustrated in Figs. 3A and 3B, a plurality of parallel
spiralling slots 17
are formed in the annular wall 16 of the cylindrical core 11 to form the axial
fluid flow
passages. The slot's inside radius 18 is closed at the cylindrical core and
the slot's outside
radius 19 is open. The slots 17 are open at the lower end of the cylindrical
core 11 to form
fluid intakes 20. The slots 17 are blocked at the core's upper end 21 so as to
prevent axial
exit of fluid from the axial flow passages 17. The number of slots 17 (seven
slots shown in
Figs. 3A and 3B) and angle of advance from the axis can be varied in response
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viscosity of the fluid being pumped. For example, flatter angles (greater
angle measured
from the axis) are used in the case of more viscous fluid.
[0036] Each stage is separated by a diffuser 70 positioned between stages to
direct fluid
into the frusto-conical disk impeller 90 of the next stage. As generally shown
in the
exemplary embodiment illustrated in Fig. 1, each diffuser 70 comprises a
stationary and
inwardly spiraling vane located between top 31 and bottom 32 plate structures.
The bottom
plate 32 has a lesser diameter than the housing 60 to allow fluid intake at
its outer
circumference. Fluid is constrained by the top plate 31, engages the diffuser
70 and is
driven spirally inwardly. The top plate 31 has a concentric hole at its center
for discharging
the re-directed fluid at the cylindrical core 11 of the next stage. In this
way, fluid is drawn
from the outer circumference of the pumping stages 95 and is driven radially
inwardly to
the intake of the next stage. By manipulating the flow of fluid through the
successive
pumping stages 95, kinetic energy of the fluid is exchanged for static
pressure.
Operation ¨ Directed Fluid Flow
[0037] The pump assembly 50 according to embodiments described herein provides
a
coupled approach to manipulating fluid flow in order to generate sufficient
fluid flow and
pressure to pump viscous or solids-laden fluid. Specifically, fluid flow is
manipulated at
intake as well as through the pumping stages of the assembly.
[0038] In operation, the helical inducer 110 breaks up solids contained in the
solids-laden
fluid to homogenize the fluid to facilitate intake. As the shaft 80 is
rotated, the helical
inducer 110 creates vortical forces in the fluid that allow suspension of the
solids in the
fluid to be maintained. The vortical forces further create a whirlpool effect
in the fluid that
directs the homogenized fluid into the eye of the impeller 90. Direct
convergence of the
helical inducer 110 with the upstream end of the pumping stages 95 ensures
that the fluid
remains homogenized when entering the eye of the impeller 90. Furthermore, the
helical
inducer 110 accelerates the velocity of the fluid entering the pump assembly
50 to provide
additional pressure at intake.
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[0039] The impeller 90 is disposed on the same rotating shaft 80 as the
helical inducer
110 and, therefore, co-rotates with the helical inducer 110. Rotation of the
impeller 90
further imparts energy into the fluid as it is further driven into the pumping
stages 95.
Within the pumping stages 95, fluid continues to flow generally upwardly
through the
annular flow passage 16. Between stages, fluid flow is redirected radially
inwardly again
to reach the fluid inlets 20 of the next stage immediately above. In this way,
head losses
caused by turbulence and rising back-pressure in the annular flow passage 16
is reduced as
fluid pressure accumulates with each successive pump stage.
[0040] In this way, the fluid flow is manipulated at two points of operation
in the
submersible pump assembly of the present disclosure, at intake and through the
pumping
stages of the assembly to provide a coupled approach to generating sufficient
fluid flow
and pressure to pump viscous or solids-laden fluid.
[0041] To gain a better understanding of the invention described herein, the
following
examples are set forth. It will be understood that these examples are intended
to describe
illustrative embodiments of the invention and are not intended to limit the
scope of the
invention in any way.
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EXAMPLES
EXAMPLE 1: PROTOTYPE STUDIES
[0042] Quantitative tests of a prototype of the frusto-conical disk pump with
inducer
were conducted at the Borets-Weatherford test facility in Nisku, Alberta, in
order to
demonstrate the effectiveness of the pump design.
[0043] The design of the frusto-conical disk pump with inducer is centrifugal,
bottom
driven with ESP motors, and can be staged to increase the lift. The pump was
designed to
keep the fluid in the laminar flow regime and thereby pump viscous and sand-
laden fluids.
By keeping the fluid in the laminar flow regime, a decrease in the erosion of
the impellers
due to sand is expected.
[0044] A cross section of the prototype pump is shown in Fig. 1. The non-
directional
design of the disk impellers allow the pump to be operated in both directions.
The spacing
between the individual disks in the impeller can be modified to suit the
viscosity of the
fluid being pumped. For example, larger spacings can be designed to
efficiently move
higher viscosity fluids.
[0045] The disk spacing of the prototype was designed for an elevated
viscosity fluid.
The pump was tested with and without an inducer at the intake of the pump
(Fig. 1),
wherein the design of the inducer resembles a machined auger attached to the
pump shaft.
The inducer was designed to ensure that the first stage of the pump would not
have intake
flow restrictions. The effect of the inducer was tested in combination with a
standard
diffuser and with a modified diffuser that had larger openings in the vanes.
[0046] The prototype pump was tested with water on a 250 hp test bench in the
Borets-
Weatherford ESP test facility in Nisku, Alberta. The prototype pump comprised
8 stages
and was expected to produce 11-15 feet of lift per stage with water. An
increase in lift was
expected when pumping viscous fluids. The pumps were tested at a standard
speed of 3500
RPM.
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Results
Performance and Efficiency ¨ Effect of Inducer at Intake
[0047] Performance curves for the three pump configurations studied are shown
in Fig.
8; namely, (1) disk pump with an inducer and a standard diffuser 200, 400, (2)
same disk
pump without said inducer 220, 420; and (3) same disk pump with said inducer
and a
modified diffuser 210, 410.
[0048] The disk pump configuration having (1) the inducer and the standard
diffuser
appears to be the preferred design since it demonstrated higher lift and flow
rates, as well
as better system efficiencies, under the same conditions, as compared to
configurations (2)
and (3). Although issues with a back pressure valve on the test bench
prevented this
particular configuration from being tested at no load conditions, it is
expected that in a no
load situation, this configuration could produce up to 180-190m3/D (1160BPD).
[0049] Because the spacings between the disks on the impeller were sized for
viscous
fluids and not ideal for pumping water, which was used in these tests, the
maximum
system efficiency was relatively low at approximately 13%. System efficiency
is expected
to be better with viscous fluids. The head of 15-20 feet per stage with water
with regard to
configuration (1) was better than predicted.
Performance and Efficiency ¨ Effect of Rotation Direction
[0050] While the disk impeller can be operated in both directions, it was
demonstrated that
there is some directionality to the pump design (1) (Fig. 9), wherein the pump
includes an
inducer and a standard diffuser. As such, the performance suffers when running
one
direction over the other. In this case, spinning clockwise 500, 600 from the
intake produces
better performance.
[0051] The scope of the claims should not be limited by the preferred
embodiments set
forth in the foregoing examples, but should be given the broadest
interpretation consistent
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with the description as a whole.
,
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