U.S. patent application number 12/837654 was filed with the patent office on 2012-01-19 for disc pump.
Invention is credited to Charles David Gilliam.
Application Number | 20120014779 12/837654 |
Document ID | / |
Family ID | 45467117 |
Filed Date | 2012-01-19 |
United States Patent
Application |
20120014779 |
Kind Code |
A1 |
Gilliam; Charles David |
January 19, 2012 |
DISC PUMP
Abstract
A pump is disclosed having one or more rotating discs within a
housing. The discs have a plurality of relatively small surface
perturbations covering at least half of one side of their surface.
The perturbations may be recessed or raised. In operation, a
boundary layer is formed near the surface of the rotating discs.
The fluid within the pump flows in a circular and outward
direction, thus moving fluid from a central coaxial inlet to an
outlet located at the peripheral wall of the housing. The surface
perturbations produce turbulence within the boundary layer during
operation. The pump is suitable for pumping liquids with entrained
gases, liquids with entrained solids, liquids with both gases and
solids, and thick liquids.
Inventors: |
Gilliam; Charles David;
(Baton Rouge, LA) |
Family ID: |
45467117 |
Appl. No.: |
12/837654 |
Filed: |
July 16, 2010 |
Current U.S.
Class: |
415/90 ;
416/4 |
Current CPC
Class: |
F04D 5/001 20130101 |
Class at
Publication: |
415/90 ;
416/4 |
International
Class: |
F01D 1/36 20060101
F01D001/36; F04D 5/00 20060101 F04D005/00 |
Claims
1. A pump comprising, a. a generally cylindrical housing formed by
a front wall, a back wall, and a peripheral wall, wherein the front
wall has a central, coaxial inlet and the peripheral wall has an
outlet; b. a disc positioned within the housing, one side of the
disc having a plurality of surface perturbations, wherein each
surface perturbation covers less than 5% of the surface area of the
side of the disc and the plurality of surface perturbations
collectively cover at least 50% of the surface area of the side of
the disc; and, c. a rotational drive member extending through the
back wall of the housing and connected to the disc.
2. The pump of claim 1, wherein the surface perturbations are
recessed.
3. The pump of claim 2, wherein the depth of the recessed surface
perturbations is no more than 50% of the thickness of the disc.
4. The pump of claim 2, wherein the recessed surface perturbations
are generally hemispherical.
5. The pump of claim 2, wherein the recessed surface perturbations
are generally cylindrical.
6. The pump of claim 2, wherein the recessed surface perturbations
are generally conical.
7. The pump of claim 1, wherein the disc further comprises a second
side having a plurality of surface perturbations, wherein each
surface perturbation covers less than 5% of the surface area of the
second side of the disc and the plurality of surface perturbations
collectively cover at least 50% of the surface area of the second
side of the disc.
8. The pump of claim 1, wherein the plurality of surface
perturbations includes both raised and recessed perturbations.
9. The pump of claim 1, wherein the surface perturbations are holes
extending fully through the disc.
10. The pump of claim 1, wherein the surface perturbations are
raised.
11. The pump of claim 10, wherein the raised surface perturbations
are generally hemispherical.
12. The pump of claim 10, wherein the raised surface perturbations
are generally cylindrical.
13. The pump of claim 10, wherein the raised surface perturbations
extend outward from the surface of the disc a distance no greater
than 50% of the thickness of the disc.
14. The pump of claim 1, wherein the surface perturbations cover at
least 70% of the surface area of one side of the disc.
15. The pump of claim 1, further comprising a second disc
operatively connected to the first disc and having a plurality of
surface perturbations on one side, wherein each surface
perturbation covers less than 5% of the surface area of one side of
the second disc and the plurality of surface perturbation
collectively cover at least 50% of the surface area of one side of
the second disc.
16. A pump comprising, a. a generally cylindrical housing formed by
a front wall, a back wall, and a peripheral wall, wherein the front
wall has a central, coaxial inlet and the peripheral wall has an
outlet; b. one or more pairs of discs positioned within the
housing, wherein each disc has a plurality of surface perturbations
on one side of the disc, each surface perturbation covering less
than 5% of the surface area of one side of the disc, and the
plurality of surface perturbations collectively covering at least
50% of the surface area of one side of the disc; and, c. a
rotational drive shaft extending through a central, coaxial opening
in the back wall of the housing and connected to at least one
disc.
17. A pump comprising, a. a generally cylindrical housing formed by
a front wall, a back wall, and a peripheral wall, wherein the front
wall has a central, coaxial inlet and the peripheral wall has an
outlet; b. a disc positioned within the housing, one side of the
disc having a plurality of dimples, wherein each dimple covers less
than 5% of the surface area of the side of the disc, and the
plurality of dimples collectively cover at least 50% of the surface
area of the side of the disc; and, c. a rotational drive member
extending through the back wall of the housing and connected to the
disc.
18. The pump of claim 17, wherein the depth of the dimples is
approximately 50% of the thickness of the disc.
19. The pump of claim 17, wherein the dimples are generally
hemispherical.
20. The pump of claim 17, wherein the dimples are generally
cylindrical.
21. The pump of claim 17, wherein the dimples are generally
conical.
22. A pump impellor, comprising: a. a cylinder having a diameter
and a thickness, wherein the diameter is at least five times larger
than the thickness, the cylinder further having, i. a first
circular surface configured for attachment to a rotational drive
shaft; and, ii. a second circular surface having a plurality of
surface perturbations, wherein each surface perturbation covers
less than 5% of the second circular surface, and the plurality of
surface perturbations collectively cover at least 50% of the second
circular surface.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a pump, and more particularly to a
disc pump wherein the disc or discs have a plurality of surface
perturbations covering at least half the surface area of one side
of the disc or discs.
BACKGROUND OF THE INVENTION
[0002] Boundary layer or bladeless turbines, pumps, and other
related turbo-machinery have been known for 100 years or more.
Nikola Tesla obtain a patent (U.S. Pat. No. 1,061,142) for such a
device in 1913. The Tesla patent disclosed a multiple-disc pump
that utilized rotating flat discs with no blades, vanes, or
propellers. Such pumps have been referred to as disc pumps,
boundary layer pumps, or bladeless pumps.
[0003] In related U.S. Pat. No. 1,061,206, Tesla disclosed a
fluid-driven boundary layer or bladeless turbine which may be
utilized as a prime mover in various applications. The Tesla
bladeless turbine, when used as the driving force for a
hydro-electric generator, could transform the kinetic energy of a
flowing fluid into electrical energy. In U.S. Pat. No. 1,329,559,
Tesla disclosed another application of the bladeless turbine, this
time in an internal combustion engine. The Tesla patents show early
disclosures of rotational machines using bladeless or boundary
layer discs.
[0004] Unlike more traditional centrifugal pumps which utilize
vanes, blades, augurs, buckets, pistons, gears, diaphragms, and the
like, boundary layer pumps, such as those described by Tesla,
typically utilize multiple rotating parallel discs. Disc pumps, as
these machines are sometimes called, utilize the fluid properties
of adhesion and viscosity. These fluid properties combine to create
an interaction between the fluid and the rotating flat discs that
allows the transfer of mechanical energy from the rotating discs to
the fluid.
[0005] Boundary layer or disc pumps (both name are used in the
industry and both will be used interchangeably herein) have been
reported to have advantages over more traditional pumps, especially
when utilized for pumping fluids other than cool, clean, homogenous
liquids. The vanes, buckets, or the like, of traditional pumps wear
and lose effectiveness due to normal friction and/or impingement
with particles such as sand or other abrasives. However, the flat
surfaces of boundary layer pumps are much less susceptible to wear.
It is not unusual for such a pump to show little or no wear even
after extended use.
[0006] Boundary layer pumps have been found to be especially
effective for pumping high viscosity fluids wherein the efficiency
of such pumps may actually increase as the fluid viscosity
increases. Boundary layer pumps have also been reported to be more
cost effective in terms of reliability and decreased downtime for
pumping problematic multiphase fluids, which may comprise gases,
liquids, and/or solid materials. Boundary layer pumps have been
found to greatly reduce maintenance costs and downtime when used to
replace more traditional pumps in these demanding settings.
[0007] Typical vaned centrifugal pumps often require precise gaps
between the impellors and the pump housing. When the impellor vanes
or blades of such a pump begin to wear, the pump becomes less
efficient and may either pump less fluid or produce less outlet
pressure, depending upon the application. Disc pumps, on the other
hand, are not as dependent upon spacing of the discs. This
characteristic is yet another advantage provided by disc pumps over
traditional bladed-impellor centrifugal pumps.
[0008] Due to the absence of spinning blades or impellers, boundary
layer pumps are more gentle on sensitive fluids than are
traditional centrifugal pumps. Shear-sensitive fluids or fluids
containing fragile or delicate solids may be safely pumped with
boundary layer pumps. For example, boundary layer pumps have been
used to pump water containing live fish without harming the
fish.
[0009] Cavitation is another problem that sometimes arises with
traditional axial, bladed, centrifugal, and mixed-flow pumps
Cavitation describes a vacuum-like condition in the pump which can
occur when liquid in the low-pressure area of the pump vaporizes.
Vapor bubbles collapse or implode when they reach the high pressure
area within the pump. This result can occur due to vapor bubbles
formed within the pump, as described above, or due to a mixed-phase
fluid entering the pump (i.e. a liquid with entrained gas).
Cavitation can create a shock wave powerful enough to damage a
pump, other equipment, or connections to the pump or other
equipment.
[0010] Cavitation is less likely in a disc pump, because the fluid
flow changes are more gradual. Much of the flow within a disc pump
is laminar, rather than turbulent, which also tends to reduce the
risk of cavitation. The pressure differences within a disc pump are
typically lower than those seen in bladed-impellor centrifugal
pumps, which further reduces the risk of cavitation.
[0011] One of the most important advantages of the disc pump is the
greatly reduced wear. This advantage is of particular importance
when the fluids being pumped contain sand, grit, or other small,
abrasive particles. Such a fluid can quickly wear down the impellor
blades in a typical centrifugal pump, while the same fluid may
cause little or no damage to a disc pump. Another way to explain
this distinction is to consider the angle of impingement between
the solid particles and the rotating impellor. The higher the angle
of impingement (i.e., the closer to 90.degree.) between the
particle and the impellor, the greater the damage. In a traditional
bladed impellor centrifugal pump, the solid particles impinge the
vanes or blades of the impellor at large angles, often close to
90.degree.. In a disc pump, if the solids reach the disc at all,
the angle of impingement will be quite low. Because a rotating disc
within a disc pump creates a boundary layer, and because the flow
in the inner sections of the pump housing is primarily laminar,
entrained solids rarely reach the discs, but will instead be gently
moved from the inlet to outlet of the pump.
[0012] Other problems related to more traditional pumps include
vapor lock problems, and pump efficiencies being limited by
affinity laws. The flow to head ratio is often restricted by design
limitations in traditional pumps. Turbulent flow in the stage to
stage transition can be problematic as well.
[0013] Traditional centrifugal pumps also produce large axial
thrusts. Radial and side loading thrust is often inconsistent
relative to rotational speed. Upon startup, up thrust can be
detrimental to the ultimate balance of the pump. Not only do these
large thrust issues require substantial thrust bearings, but these
forces produce wear that leads to greater vibration over time.
[0014] Traditional centrifugal pumps are highly subject to
vibrations as a natural result of impact of the vanes and blades
with the fluids pumped. This vibration problem is highly
exacerbated when multiphase fluids are pumped that may include
solids, liquids, and gases. Accordingly, the shaft rotation speed
of traditional pumps, especially those used for pumping multiphase
fluids, is limited to avoid destroying the pump due to vibration
damage. The limited shaft rotational speeds result in lower pump
output, limited horsepower, and generally less pumping
capability.
[0015] On the other hand, boundary layer pumps with flat, smooth
discs which may be easily balanced and produce little or no
vibration when spinning within a fluid even at relatively higher
rotational speeds. Typical boundary layer pumps do not utilize
lifting surfaces on the rotating elements. Higher rotational speed
is directly related to pump flow rates in boundary layer pumps,
thus permitting significantly increased pump rotation speeds when
pumping multiphase fluids which may contain solids, liquids, and
gases. Moreover, boundary layer pumps have been found to not only
increase the output under these difficult pumping conditions as
compared to traditional pumps, but also have been found to be much
more reliable.
[0016] Despite the many advantages of boundary layer pumps over
more traditional pumps, there remains room for improvement. Many of
the disc pumps in use today differ little from the designs
disclosed by Tesla over 100 years ago. Flat, smooth discs are
typically used. While such discs provide the advantages described
above, even greater pump efficiency could be obtained if the
boundary layer near the rotating discs were larger or more
turbulent. Some variations on flat discs have been disclosed,
including ribs or waves extending radially outward on the surface
of the discs. These designs may increase the turbulence in the
boundary layer, and thus may increase pump efficiency. But these
changes tend to move the disc pump closer to the design of the
traditional, bladed-impellor centrifugal pump. Adding the
equivalent of small blades or vanes on the surface of the discs may
improve pump performance in some situations, but it may come at the
expense of reliability and longevity. These design variations may
also produce a pump less gentle on delicate fluids.
[0017] A boundary layer pump that retains the benefits described
above while also increasing the pump's efficiency would be a
desirable advance over the existing state of the art. To accomplish
this result, more turbulence is needed in the boundary layer
without significantly changing the low-wear and low-thrust
characteristics of the existing boundary layer pump design. The
present invention provides such a solution.
SUMMARY OF THE INVENTION
[0018] The present invention utilizes a unique design for the discs
that makes the pump particularly suited handling multiphase fluids
with solids, liquids, and gases. Such fluids are typical of oil and
gas wells, geothermal energy production and tar sands oil
extraction applications. The invention provides improved pump
performance without reducing the long-wear and high-reliability
attributes described above. These benefits may be of value in many
industrial settings.
[0019] The present invention utilizes discs having a plurality of
surface perturbations covering more than half the surface of one
side of the disc. These surface perturbations may be recessed
(e.g., dimples) or raised (e.g., bumps). Each perturbation is small
relative to the size of the full disc and is recessed or raised
only a small distance. In the embodiments where raised surface
perturbations are used, the perturbations protrude only a short
distance away from the disc surface and should not, under most
operating circumstances, extend beyond the surface boundary layer.
Many distinct, yet small, surface perturbations are used to
increase the turbulence in the boundary layer near the disc surface
and thus increasing pump performance.
[0020] In a preferred embodiment, the invention has a generally
cylindrical housing formed by a front wall, a back wall, and a
peripheral wall, wherein the front wall has a central, coaxial
inlet and the peripheral wall has an outlet; a disc having a
plurality of surface perturbations, wherein each surface
perturbation covers less than 5% of the surface area of one side of
the disc and the plurality of surface perturbation collectively
cover at least 50% of the surface area of one side of the disc;
and, a rotational drive member extending through the back wall of
the housing and connected to the disc. Multiple discs having the
same or similar surface perturbations may be used, or a single disc
may be used.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a cross-sectional view of a disc pump showing
multi-phase flow.
[0022] FIG. 2 is a perspective, cut-away view of a preferred
embodiment of the present invention.
[0023] FIG. 3 is a perspective view of a disc having recessed
surface perturbations.
[0024] FIG. 4 is a cross-sectional view of the disc shown in FIG.
3.
[0025] FIG. 5 is a perspective view of a disc having raised,
cylindrical surface perturbations.
[0026] FIG. 6 is a cross-sectional view of the disc shown in FIG.
5.
[0027] FIG. 7 is a perspective view of a disc having raised,
hemispherical surface perturbations.
[0028] FIG. 8 is a cross-sectional view of the disc shown in FIG.
7.
DETAILED DESCRIPTION OF THE INVENTION
[0029] A cross section of a typical boundary layer or disc pump 10
is shown in FIG. 1. The portion of interest for this description is
seen on the right end of the drawing. A pump housing 12 is formed
by a front wall 14, a back wall 18, and a peripheral wall 20. These
three walls may be distinct pieces or two or more of the walls may
be a single part. The three walls are defined in this way based on
the physical configuration of the pump housing. This definitional
choice is not meant to limit the type of housing in any way. It is
for convenience only.
[0030] The pump 10 has a inlet 16 located near the center of the
front wall 14. The inlet 16 is aligned with the longitudinal axis
of the pump drive shaft 32. The inlet 16, therefore, can be
described as a central, coaxial inlet. The inlet 16 can take
various forms. It can supply feed flow from one side of the housing
12 or from both sides of the housing. A design showing dual inlet
flow from both sides of the housing is disclosed in U.S. Pat. No.
4,403,911, which is hereby incorporated by reference. FIGS. 16 and
17 of the '911 patent, and the accompanying description, show a
central, coaxial inlet attached to both sides of a pump housing.
The only limitation on the inlet is that it be a central, coaxial
inlet. One means of providing such an inlet is shown in FIG. 1.
Another is shown in the '911 patent.
[0031] The housing 12 has an outlet 22 that is positioned on or
within the peripheral wall 20. The housing 12 is of a generally
cylindrical shape, and the peripheral wall 20 forms the outer
surface of the cylinder. In general, the peripheral wall 20 is at a
fixed radius from the axial center of the housing 12. The outlet 22
may be formed in a variety of ways, but must be located at or near
the radially outermost region of the housing 12. The reason for the
locations of the inlet 16 and outlet 22 will be explained in more
detail below.
[0032] A first disc 26 and a second disc 28 are also shown in FIG.
1. The first disc 26 is shown near the back wall 18 and is
operatively connected to the drive shaft 32. Any type of rotational
drive member may be used to rotate the discs. A drive shaft 32 is
perhaps the most common type of rotational drive member and is,
therefore, shown in FIG. 1. A cylindrical drive member or any other
type of rotational driving structure may be used. The drive shaft
32 in FIG. 1 is shown threaded into the first disc 26. No
particular connection means is required. All that is required is
that the rotational driving member be operatively connected to the
first disc 26 such that the disc may rotate within the housing
12.
[0033] The second disc 28 is shown near the front wall 14. The two
discs are connected by pins 30, though other connections are also
contemplated. The connecting members between the discs must be of
sufficient strength to allow the first disc 26 to cause the second
disc 28 to rotate. If additional discs, or additional pairs of
discs, are used, similar connections would be required between
those discs. Only the first disc 26 is directly connected to the
rotational drive member in FIG. 1, though it is contemplated that
in some embodiments the rotational drive member may extend into the
housing and be directly connected to other discs, as well.
[0034] The pins 30 or other members used to connect the discs to
each other should be of relatively small cross section in order to
reduce the turbulence caused by the rotation of such members
through the housing 12 during operation of the pump. To reduce the
turbulence induced by such rotation of the connecting pins 30, the
pins could be formed in a tear drop or other more aerodynamic form
that would reduce the fluid turbulence caused when the pins 30 are
rotated through the fluid to be pumped.
[0035] To be clear, the front wall 14, back wall 18, and peripheral
wall 20 need not be physically distinct components or pieces. For
example, the pump 10 of FIG. 1 could be constructed such that the
back wall 18 is part of the main body of the pump, with the
threaded end of the drive shaft 32 extending through a central
opening in the back wall 18. The first disc 26 (or a pair of
preconnected discs 26, 28) could then be threaded onto the drive
shaft 32. A single physical piece--i.e., a piece comprising the
front wall 14, inlet 16, peripheral wall 18, and outlet 22--could
then be connected to the back wall 18, thus forming the housing 12
around the discs 26, 28. Alternatively, the back wall 18,
peripheral wall 20 and outlet 22 might be a single physical piece,
allowing for disc installation, followed by installation of the
front wall 14, with inlet 16, to complete the formation of the
housing 12. Gaskets or other material to ensure the housing 12 is
watertight are not shown, but may also be used as needed. These and
other variations are within the meaning of the housing and its
three walls as described herein.
[0036] The pump 10 shown in FIG. 1 is of a type known in the art.
The first disc 26 and second disc 28 are flat and smooth. In
operation, the drive shaft 32 is rotated by some driving force, and
thereby rotates the discs 26, 28 within the housing 12. For
purposes of explaining the operation of the pump, assume the
housing 12 is filled with water. When the discs 26, 28 begin to
rotate, a thin boundary layer of water near the outer surface of
the discs 26, 28 will also begin to rotate. The adhesion of the
water (or other liquid) to the solid surface of each disc creates
drag, and that tends to pull a thin boundary layer of water along
with the disc as it rotates. The two discs 26, 28 shown in FIG. 1,
therefore, each cause a thin boundary layer of water to begin
rotating in the same direction as the discs.
[0037] In the region between the discs, it is the viscosity of the
fluid that accounts for the generation of flow. The liquid between
discs 26, 28 of FIG. 1 may be understood as many thin sheets of
liquid, where each thin sheet is parallel to the two rotating
discs. Moving away from the discs 26, 28 and toward the center of
the housing 12, we first encounter the thin boundary layers that
are rotating in the same direction as the discs 26, 28 due to the
adhesion forces between the discs 26, 28 and the boundary layers.
The next thin layers of water are in contact with the boundary
layers, and due to the viscosity of the water, these next layers of
water will begin to rotate with the boundary layers. Each thin
layer of water begins to rotate because the water immediately
around it is rotating. This process continues until all the water
in the housing 12 is rotating in the same direction as the discs
26, 28.
[0038] The pump 10, thus produces primarily laminar liquid flow.
The boundary layer will experience some turbulent flow due to minor
irregularities upon the surfaces of the discs 26 and 28, but the
many thin layers of water (as described above) will each rotate
primarily in a laminar matter. This is important, because it
results in minimal mixing of the liquid within the housing. If
there were perfectly laminar flow within the housing, there would
be no impingement of solid particles with the discs, because such
particles would remain fixed within their respective layer of
laminar flow. Though this ideal scenario does not occur in
practice, the prevalence of laminar flow does greatly reduce the
impingement of particulates with the discs.
[0039] As the water in this example rotates with the discs, the
water experiences centrifugal forces which tend to force the water
radially outward from the axial center of the housing 12. The
water, therefore, moves in a generally outward spiral from the
axial center to the outer peripheral region of the housing 12,
where the outlet 22 is positioned. Because of the process described
above, the water (or other liquid) is pumped from the central,
coaxial inlet 16 to the outlet 22. In FIG. 1, the liquid entering
the pump 10 has entrained gas or solid particles 24, which are
moved in the same outward spiral pattern as the liquid. The
entrained matter 24 moves through the pump housing 12 with little,
if any, contact with the rotating discs 26, 28.
[0040] The disc pump 10 described above may use a single rotating
disc, a pair of discs (as shown in FIG. 1), or a larger number of
discs, which may be arranged in pairs or as a series of individual
discs. If a single disc is used in a relatively large housing, the
pump will not generate as large a pump head as it would if multiple
discs are used. For example, if only the first disc 26 of FIG. 1
were used, the pump would work, but the liquid nearest the front
wall (i.e., the farthest from the first disc 26) would receive the
least rotational force. The single disc pump may produce a lower
pump head, lower flow rate, or both. Use of a pair of discs, as
shown in FIG. 1, or use of even more discs, is generally preferred
to use of a single disc if a large flow rate or pump head are
required.
[0041] On the other hand, a single disc pump is the most gentle
embodiment of the present invention. When two or more discs are
used, connecting pins 30, or some other connecting members, may be
used to connect the discs together. These pins 30 or other
connecting members rotate with the discs, causing some turbulence
within the housing 12. Moreover, the rotation of connecting pins 30
can result in damage to particles or other materials impacted by
the pins 30 as the discs 26 and 28 rotate. When the most gentle
pumping is required, a single disc pump may be the best option.
Examples of situations where this may be appropriate might include
pumping of live fish or fragile solids suspended in a liquid.
[0042] A preferred embodiment of the present invention is shown in
FIG. 2, which is a perspective view of a cut-away of a disc pump
10. There is a housing 12 formed by a first wall 14, second wall
18, and peripheral wall 20, just as explained above with respect to
FIG. 1. The central, coaxial inlet 16 and the outlet 22 are also
shown in a manner similar to the configuration of FIG. 1. A first
disc 26, second disc 28, and connecting pins 30 are also shown, as
is a drive shaft 32. A thrust bearing assembly 34 and a shaft seal
assembly 36 are also shown for illustration purposes.
[0043] The inner surface of the first disc 26, as shown in FIG. 2,
is covered with small, recessed dimples 38. These dimples 38 are
also present on the inner surface of the second disc 28, but cannot
be seen due to the perspective presented in FIG. 2. The dimples 38
create a markedly different result when the discs rotate, as
compared to the description provided above.
[0044] When the dimpled discs shown in FIG. 2 rotate through the
liquid, the many dimples create small surface disturbances in the
liquid near the disc surfaces. Small eddy currents are formed as
liquid enters and leaves the many dimples 38. Each dimple 38 is
small and shallow, and thus creates only a very small disturbance
to the liquid near the disc surface. The collective impact,
however, of many such small disturbances is a substantially more
turbulent flow within the boundary layer. This turbulence may also
produce a thicker boundary layer.
[0045] The more turbulent boundary layer is more adherent to the
disc surface, and this increase in the adhesion force results in
more rotational movement of liquid within the boundary layer. As
the boundary layer rotates faster, each thin layer of water moving
toward the center of the housing 12 also rotates faster. When a
thicker boundary layer is formed, more liquid is impacted by the
adhesion force, and thus more liquid movement results. By creating
a more turbulent boundary layer, the discs of the present invention
create more flow and a larger pump head as compared to a
traditional disc pump with smooth flat discs.
[0046] Recessed dimples 42 are shown in more detail in FIGS. 3 and
4. More than half of the surface of the disc 40 is covered with
dimples 42 in FIG. 3. In a preferred embodiment, 70% or more of the
disc surface 40 is covered. Each dimple 42 is small relative to the
full disc surface 40. Indeed, each dimple 42 covers an area that is
less than 5% of the surface of the side of the disc. Many dimples
42 are needed to cover at least half (i.e. 50% or more) of the
surface of one side of the disc. In a preferred embodiment, the
dimples 42 are only on one side of the disc, though a disc
positioned at an intermediate point within the housing 12 might
have dimples on both sides and thus be used to produce flow on both
sides of the disc.
[0047] FIG. 4 shows a cross section of the disc surface 40. Many
dimples 42 are shown. In a preferred embodiment, the dimples 42
have a depth 44 equal to roughly (i.e., approximately)50% of the
thickness of the disc. This depth 44 is not critical to the
performance It does provide, however, for a deep enough dimple to
produce surface turbulence while also allowing the disc to retain
structural strength. The benefits of the present invention,
however, are not dependent upon the precise depth of the dimples.
As long as there are enough dimples, and each dimple is deep enough
to create a small area of turbulent flow, the benefits of the
present invention will be attained. The roughly 50% preference is
not a strict or precise figure, and it is not anticipated that
precise depth measurements would be made of each dimple 42.
[0048] The dimples 42 shown in FIGS. 3 and 4 are not the only type
of surface perturbation contemplated by the present invention.
Recessed dimples 42 may be used, but raised perturbations also may
be used. One example of a pattern of raised surface perturbations
is shown in FIGS. 5 and 6. A disc surface 46 is shown with a
plurality of raised surface perturbations 48. The raised surface
perturbations 48 shown in FIGS. 5 and 6 are cylindrical. As shown
in FIG. 6, the height of the raised, cylindrical surface
perturbations is roughly comparable to the depth of the recessed
dimples 42 shown in FIG. 4. The height 50 of the cylinders 48 is
about 50% of the disc thickness.
[0049] FIGS. 7 and 8 shown another type of raised surface
perturbation, this time a hemispherical protrusion 54 on the
surface of the disc 52. As in the prior examples, the surface
perturbations cover most of the disc surface 52. Also, the raised,
hemispherical perturbations have a height 56 of about 50% of the
disc thickness. This measurement is not critical. It is chosen to
allow the raised protrusions 54 to extend far enough from the disc
surface 52 to produce surface turbulence, while not extending much,
if any, beyond the boundary layer created when the disc
rotates.
[0050] In a preferred embodiment, more than 70% of one side of the
disc surface is covered by surface perturbations, either recessed,
raised, or some combination of the two. Various shapes may be used
for the perturbations, as illustrated, to an extent, in the
figures. In addition to the shapes shown, conical surface
perturbations (either recessed or raised or a combination) could be
used. A mix of different shapes, together with a mix of recessed
and raised surface perturbations could be used, though this is not
preferred because it might unduly increase manufacturing
complexity.
[0051] The circular ends of the cylindrical discs of the present
invention are large relative to the thickness of the discs. These
proportions are illustrated in FIGS. 3-8. In a preferred
embodiment, the diameter of the cylindrical discs is at least five
times larger than the thickness of the disc. In some
configurations, this ratio may be much larger, with the disc
diameter sometimes being more than ten times larger than the disc
thickness. This type of construction is preferred because it is the
large, circular surface area of the disc that contributes to pump
performance.
[0052] The present invention uses many, discrete surface
perturbations, rather than a few long radial ribs or waves. The
surface perturbations of the present invention are not arranged in
any particular pattern, and do not form radial ridges or rows.
Instead, the surface perturbations are spread across the discs in a
manner designed to create numerous small areas of turbulence that
will collectively create a more adherent, turbulent boundary layer.
This result alters the pumping performance of the disc pump.
[0053] It should be noted that the first disc 26 differs from the
second disc 28, and any other additional discs used, in an
important respect. Only the first disc 26 is a full disc. Each
additional disc (e.g., the second disc 28 shown in FIGS. 1 and 2)
must have a central, coaxial opening to allow flow within the
housing 12. The need for such a central, coaxial inlet flow path is
what requires the use of connecting pins 30 or other connecting
means between the discs. It is possible to make the pump such that
the second disc 28 (and additional discs) is attached directly to
the drive shaft, but some type of central, coaxial flow path still
must be provided through the second disc 28 (or any other
additional discs). That result might be achieved by using a series
of spokes between a central drive shaft an the main body of the
disc, or any other physical configuration that securely connects
the disc to the drive shaft while allowing flow along the central,
axial direction. The means of connecting the second disc 28 and
other discs to the rotational driving force is not critical to the
present invention.
[0054] Because discs beyond the first disc 26 require some central,
coaxial opening, it should be understood that the discs shown in
FIGS. 3, 5, and 7 are all first discs 26. These discs are full
discs, and are, therefore, configured to be attached directly to
the rotational driving member. Second disc 28 (and any other discs
that may be used) would have some type of opening, or group of
openings in the center of the disc surface. In the configuration
shown in FIGS. 1 and 2, the second disc 28 has a central, coaxial
opening aligned with the inlet 16. If such a disc were shown
standing alone (i.e., in the manner of FIGS. 3, 5, and 7), it would
look like an annulus, and not like the solid cylinder of the actual
figures. The annulus form of the second disc 28 is not explicitly
shown in FIG. 3, 5, or 7, but is a well understood characteristic
of existing disc or boundary layer pumps.
[0055] While the preceding description is intended to provide an
understanding of the present invention, it is to be understood that
the present invention is not limited to the disclosed embodiments.
To the contrary, the present invention is intended to cover
modifications and variations on the structure and methods described
above and all other equivalent arrangements that are within the
scope and spirit of the following claims.
* * * * *