Note: Descriptions are shown in the official language in which they were submitted.
CA 02937398 2016-07-28
CAVITATION DEVICE
Technical Field
[0001] An axially-oriented inlet feeds fluid directly to the vertex of a
generally conical,
curved profile, or campanulate flow-directing face of a rotor containing
cavities on its
cylindrical surface. The flow director spreads the fluid to a cavitation zone
formed between
the cavity-containing surface and the closely conforming interior surface of a
housing. The
device pumps, heats and mixes the fluid. The device may contain discs to
contribute an
enhanced disc pump effect. The flow patterns of the fluid material to be mixed
and heated
are designed to preheat and may create turbulent flow mixing of the fluid
before it enters the
cavitation zone. Heat generated in the cavitation zone is conducted through
the rotating disc-
like body of the cavitation rotor. The advantages of the central inlet and
flow directing
element may be facilitated by a cantilever construction to alleviate stress on
the bearings.
Background of the Invention
[0002] The phenomenon of cavitation, as it sometimes happens in pumps, is
generally
undesirable, as it can cause choking of the pump and sometimes considerable
damage not
only to the pump but also auxiliary equipment.
[0003] However, cavitation, more narrowly defined, has been put to use as a
source of
energy that can be imparted to liquids. Certain devices employ cavities
deliberately
machined into a rotor turning within a cylindrical housing leaving space for
liquid to pass. A
motor or other source of turning power is required as well as an external pump
to force the
fluid through. The phenomenon of cavitation in all previous devices relevant
hereto is
caused by the rapid passage of the liquid over the cavities, which creates a
vacuum in them,
tending to vaporize the liquid; the vacuum is immediately filled again by the
liquid and
created again by the movement of the liquid, causing extreme turbulence in the
cavities,
further causing heat energy to be imparted into the liquid. Liquids can be
simultaneously
heated and mixed efficiently with such a device. Also, although the cavitation
technique is
locally violent, the process is low-impact compared to centrifugal pumps and
mixing pumps
employing impellers, and therefore is far less likely to cause damage to
sensitive polymers
1
CA 02937398 2016-07-28
used in oilfield fluids. Centrifugal pumps tend also to break large particles
such as drill
cuttings into small, low gravity particles which are more difficult to
separate by
centrifugation. The impeller blades of many types of pumps will fracture and
break solids
into smaller particles which may resist separation by any conventional method.
[0004] Good mixing is especially important in mixing oil field fluids such
as drilling
fluids and fracturing fluids.
[0005] Proper operation of the cavitation device, until now, has generally
required a
separate pump. Liquid must be forced through the existing cavitation devices
to accomplish
substantial heating, mixing, or both. Cavitation devices are excellent for
intimately mixing
gases with liquids, but centrifugal pumps do not handle large volumes of gases
well,
sometimes losing the ability to pump at all when the gas volume is too great.
A disc pump
can easily handle and pump mixtures containing significant volumes of gas.
[0006] Moreover, in the conventional cavitation devices, there is a viscous
or surface
effect drag against the stationary end wall of the cavitation device housing.
[0007] Rotating cavitation devices in the past generally have not been
designed to
optimize the flow of the incoming fluid, which must find its way from an inlet
on one side of
the rotor to and through the cavitation zone between the cylindrical interior
of the housing
wall and the cavities on the periphery of the rotor. Workers in cavitation
mixing and heating
in the past have generally not attempted to analyze and improve the flow
patterns of the
treated material on either the incoming or outgoing sides of the rotor, to
achieve greater
uniformity of heating and mixing. They have tended to concentrate on the
phenomenon of
cavitation at the periphery of the cavitation rotor, after the fluid arrives
there, but have paid
little attention to the heating potential of the body of the rotor or the
effects on flow patterns
of the sides of the rotor for enhancing mixing as well as heating.
[0008] Our invention provides improved heating, improved mixing, and
improved
uniformity of heating and mixing of fluid materials passing through a rotating
cavitation
device.
[0009] Unlike many designs of the prior art, our cavitation device is
"overhung,"
meaning that it is supported on one side only of the housing. Because the
other side of the
housing is unencumbered by a support for the rotating power shaft, we are able
to direct the
2
CA 02937398 2016-07-28
incoming fluid to be mixed toward the center of the spinning rotor. The center
of the
spinning rotor, however, is modified in our invention so that the incoming
fluid impacts on
the vertex of a substantially conical or bell-shaped surface which provides a
tapering,
spreading, path for the fluid toward the side of the spinning rotor. The
materials of
construction of the rotor, and its shape, may also be chosen to transfer heat
efficiently from
the cavitation zone to the body of the rotor and then to the incoming fluid as
it contacts the
rotor. The overhung design is stabilized by at least one bearing on the
rotating power shaft
outside the housing in addition to the bearing in the housing wall.
Beneficially, there are two
additional bearings on the shaft, spaced from the housing wall before it
connects to the
motor.
[0010] In
addition, the gap between the sides of the spinning rotor and the housing can
be
varied to optimize heating and mixing as a function of the assumed, presumed,
or calculated
properties of the treated fluid.
[0011] There is
a need for improvements to overcome the disadvantages of the existing
cavitation devices.
Summary of the Invention
[00121 By the
incorporation of at least one rotating disc having an open center for the
passage of liquid, and with an appropriate housing design for intake and
outflow, we are able
to use the same motor that turns the cavitation device rotor to turn the disc
also, thus utilizing
the disc in combination with the cavitation rotor as a kind of disc pump to
pass the liquid
through the cavitation device. The rotating disc not only facilitates a
pumping effect, but
ameliorates the counterproductive drag imposed by the stationary housing wall
of the unit.
[0013] In this
continuation-in-part, the function and benefits of the central, or coaxial,
inlet which facilitates the flow path through the open center of the disc have
been further
developed. This
continuation-in-part utilizes a tapered flow director aligned with the
rotating shaft and facing the central (coaxial) inlet to enhance the heating,
mixing, and
pumping effects of the device. The flow director is an improvement on the
accelerator seen
in Figure 6. Figures 8-12 relate to the utilization of a flow director
immediately next to the
3
CA 02937398 2016-07-28
coaxial inlet guiding the fluid to distribution over the cavitation surface of
the rotor; In
Figure 13, the flow director receives the incoming fluid through a rotating
disc.
[0014] Our combined disc pump and cavitation device is inherently safer
than the
conventional use of a positive displacement pump to force the mixture through
a separate
cavitation device, in that, if there is a blockage of some sort, excess
pressure will not build up
within the device. Although the disc, or discs, will continue turning, they
will generate only
a relatively low pressure within the device.
[0015] The shaft may pass through both end walls or only one end wall. The
inlet and
outlet may be independently on the respective end wall or on the cylindrical
shell, providing
a flow path for the fluid across the cavitation device ¨ that is, forming an
inlet end and an
outlet end of the device for the flow path.
[0016] The combined device may be immersed in a mixing tank so that its
intake is
below the level of the materials to be mixed; the motor may be above the
liquid level or its
shaft may pass through the wall of the tank.
Brief Description of the Drawings
[0017] Figure 1 is a side sectional view of the cavitation pump.
[0018] Figure 2 is a front view of a pump disc.
[0019] Figure 3 is side sectional view of the cavitation pump employed as a
tank mixer.
[0020] Figure 4 shows a variation of the invention having more than one
disc.
[0021] Figure 5 illustrates a disc having splines.
[0022] Figure 6 shows a variation in which the shaft passes through both
ends of the
cylindrical housing.
[0023] Figure 7 is the face of the disc in Figure 6.
[0024] Figure 8 is a partly sectional view of our cavitation device having
a flow director
oriented toward the inlet.
[0025] Figure 9 is a frontal view of the cavitation rotor with a flow
director, showing the
resulting flow pattern of incoming fluid.
[0026] Figure 10 is an expanded section of the cavitation device showing
flow patterns
in more detail; the outlet is placed near the shaft.
4
CA 02937398 2016-07-28
[0027] Figure 11 shows the cavitation device with recirculation piping to
elevate the
temperature of the fluid and improve mixing.
[0028] Figure 12 illustrates a screw-shaped flow director in our cavitation
device.
[0029] Figure 13 shows the combination of the axially oriented inlet, flow
director, and
shaft with the addition of an axially oriented disc.
Detailed Description of the Invention
[0030] Referring first to Figure 1, the cavitation pump is shown in section
and more or
less diagrammatically. Fluid enters a housing 1 through a conduit 2 passing
through central
hole 4 in solid disc 3. Solid disc 3 is held in place by disc supports 5,
which are attached to
cavitation rotor 6. Cavitation rotor 6 is substantially cylindrical in shape
and has a plurality
of cavities 7 on its cylindrical surface. Housing 1 is also substantially
cylindrical in shape so
that its inside surface can accommodate the cylindrical surface of the
cavitation rotor 6
substantially concentrically and in close proximity. That is, the peripheral
space 8 between
the cavitation rotor 6 and the substantially concentric internal surface of
the housing 1 is
somewhat constricted to enhance the efficiency of the cavitation effects on
the fluid, as will
be explained more fully below. Cavitation rotor 6 is mounted on a shaft 9
which passes
through the end wall 12 of housing 1 by way of a thrust bearing having a seal,
not illustrated.
The end wall 12 of housing 1 is substantial enough to accommodate the thrust
bearing, which
permits rotation of the shaft 9 and its attached cavitation rotor 6 and solid
disc 3, and a
suitable seal to prevent leakage. Suitable fixtures for the conduit 2 may also
be envisioned.
As indicated by the arrows, fluid flows into the housing 1 through conduit 2,
then through the
central hole 4 of solid disc 3; it then fans out 360 degrees in the
distribution space 10
between solid disc 3 and cavitation rotor 6, finally exiting peripherally
through fluid outlet
11. By peripherally, I mean on the rounded, or cylindrical, surface of housing
1 as opposed
to the normally substantially planar end wall 12. It may also be noted that
the cylindrical
housing has an inlet end near solid disc 3 and an outlet end on the opposite
side of rotor 6. In
a variation, the outlet may be located on end wall 12.
[0031] The cavitation rotor 6, acting within a surface-conforming housing
1, acts in a
known manner to simultaneously heat and intimately mix fluids. But unlike
previously
known devices, fluid entering through conduit 2 of the present invention need
not be pumped
or otherwise under positive pressure. Introduction of solid disc 3 provides a
disc pump
action integral to the cavitation device. Various aqueous and nonaqueous
liquids may be
mixed in our invention; solid materials may be dissolved or hydrated, and
gases, including
air, may be introduced to the mix, most conveniently by injecting them into
conduit 2.
[0032] Cavitation devices are designed deliberately to generate heat by
cavitation.
Cavitation occurs in a fluid when the fluid flows in an environment conducive
to the
formation of partial-vacuum spaces or bubbles within the fluid. Since the
spaces or bubbles
are partial vacuum, they almost immediately implode, causing the mechanical or
kinetic
energy of the fluid to be converted into thermal energy. In many devices, such
as most
pumps, cavitation is an occurrence to be avoided for many reasons, not only
because of
convulsions and disruption to the normal flow in the pump, but also because of
the loss of
energy when the mechanical energy of the pump is converted to undesired heat
instead of
being used to propel the fluid on a desired path. There are, however, certain
devices
designed deliberately to achieve cavitation in order to increase the
temperature of the fluid
treated. Such cavitation devices are manufactured and sold by Hydro Dynamics,
Inc., of
Rome, Georgia, perhaps most relevantly the devices described in US Patents
5,385,298,
5,957,122, 6,627,784 and particularly 5,188,090. These patents may be referred
to below as
the HDI patents.
[0033] The basic design of the cavitation devices described in the HDI
patents comprises
a cylindrical rotor having a plurality of cavities bored or otherwise placed
on its cylindrical
surface. The rotor turns within a closely proximate cylindrical housing,
permitting a
specified, relatively small, space or gap between the rotor and the housing.
Fluid enters at
the face or end of the rotor, flows toward the outer surface, and enters the
space between the
concentric cylindrical surfaces of the rotor and the housing. While the rotor
is turning, the
fluid continues to flow within its confined space toward the exit at the other
side of the rotor,
but it encounters the cavities as it goes. Flowing fluid tends to fill the
cavities, but is
6
Date Recue/Date Received 2021-05-27
CA 02937398 2016-07-28
immediately expelled from them by the centrifugal force of the spinning rotor.
This creates a
small volume of very low pressure within the cavities, again drawing the fluid
into them, to
implode or cavitate. This controlled, semi-violent action of micro cavitation
brings about a
desired conversion of kinetic and mechanical energy to thermal energy,
elevating the
temperature of the fluid without the use of a conventional heat transfer
surface.
[0034] Benefits of the 1 IDI-style cavitation devices include that they can
handle slurries
as well as many different types of mixtures and solutions, and the heating of
the fluid occurs
within the fluid itself rather than on a heat exchange surface which might be
vulnerable to
scale formation and ultimately to a significant loss of energy and reduction
in heat transfer.
[0035] However, the conventional cavitation devices require the use of an
external pump.
Our invention incorporates a disc pump into the housing used by the cavitation
rotor, and
utilizes one side of the cavitation rotor as part of the disc pump. None of
the versatility of the
conventional cavitation devices in handling solutions, mixtures and slurries
is sacrificed by
combining the disc pump action with cavitation in the same housing.
[0036] Referring now to Figure 2, the solid disc 3 is seen from the front.
It has a hole 4
in its center to permit fluid to pass through, and has a plurality of disc
supports 5 (see Figure
1 also) to retain it in place in a plane substantially parallel to that of the
cavitation rotor 6;
thus it rotates with the cavitation rotor 6.
[0037] In Figure 3, the cavitation pump of Figure 1 is set up to mix
materials in tank 13.
Housing 1 is fully submerged in tank 13, in fluid having a fluid level 14. A
motor not shown
is mounted on motor base 15 and stabilized by housing supports 16. Motor shaft
9 passes
below fluid level 14 and through housing 1 as explained in Figure 1, and
rotates cavitation
rotor 6, which has cavities 7. Fluid already in the tank enters through
conduit 2 through
central hole 4 of disc 3 and passes into distribution space 10, through
peripheral space 8, and
out fluid outlet 11 as described with respect to Figure 1. Fluid outlet 11 may
have an
extension or otherwise connect to the open space above fluid level 14 to
reduce back
pressure. As indicated in the discussion above, the cavitation rotor 6 acting
on the liquid
within the confined peripheral space 8 will heat the fluid, which will
facilitate and render
more efficient the mixing of whatever materials are in the fluid. Various
aqueous and
nonaqueous fluids may be mixed, and many different types of solids may be
readily
7
CA 02937398 2016-07-28
dissolved or dispersed with the cavitation pump, which does not require any
pumping or
positive force to cause the fluid to enter. Materials to be mixed are added to
the tank in any
convenient manner.
[0038] Figure 4 is a sectional view similar to Figure 1 except that it
incorporates three
discs 20, 21, and 22. Discs 20, 21, and 22 may be thinner or thicker than disc
3 of Figure 1,
but each has a central hole similar to central hole 4 of disc 3 ¨ central hole
23, for example, is
in disc 20. The cavitation pump of Figure 4 has a cavitation rotor 6 for
rotating with shaft 9
in cylindrical housing 1 as in Figure 1. Disc supports 5 connect cavitation
rotor 6 to disc 22,
disc supports 24 connect disc 22 to disc 21, and disc 21 to disc 20,
maintaining all the discs
in planes substantially parallel to cavitation rotor 6. Cavitation rotor 6 has
cavities 7 also as
in Figure 1.
[0039] Fluid enters through conduit 2 as in Figure 1, and passes through
central hole 23
of disc 20. As shown by the arrows, some of the fluid is distributed between
discs 20 and 21;
some continues through the central hole of disc 21 (similar to central hole 23
of disc 20),
where some is distributed between disc 21 and disc 22; some fluid continues
through the hole
in disc 22 and is distributed between disc 22 and cavitation rotor 6. A motor
not shown turns
shaft 9, turning the rotor 6 and all three discs, causing the centrifugal
distribution of the fluid
as indicated by the arrows, acting as a pump to continue the flow of fluid. In
the peripheral
space 8, the fluid continuously flows into cavities 7 and is flung out by
centrifugal force,
thereby creating the alternating vacuum and micro-implosions that effectively
mix and heat
the fluid before it exits at fluid outlet 11.
[0040] A multidisc variant of our invention such as is illustrated in
Figure 4 can be used
in the tank mixing configuration of Figure 3.
[0041] Our cavitation pump can employ several discs aligned in a manner
similar to that
shown in Figure 4; as a practical matter, the strength of the seal and bearing
for the shaft 9 in
end wall 12 may be a limiting factor; otherwise there is no reason not to have
as many as
twelve or more discs.
[0042] Figure 5 shows the face of a disc similar to discs 20, 21, and 22 in
Figure 4
except that it has splines, illustrated as straight radial splines 25 and
curved splines 26. As
with the other illustrated discs, the disc of Figure 5 has a central hole 28
and disc supports 24
8
CA 02937398 2016-07-28
which may be similar to disc supports 5. Splines are ridge-like protuberances
designed to
encourage the flow of the fluid from the center of the disc to its periphery;
hence they are
generally radial. Splines 25 are substantially straight and splines 26 have a
curve which may
be designed to take into account the speed of rotation of the disc. Although
the illustration of
Figure 5 shows both kinds on the same disc, the user may wish to have one or
the other, or
no splines at all. The splines need not extend the entire distance from the
edge of hole 28 to
the rim of the disc, as illustrated. Splines may be included on one or both
sides of the discs,
and may be built into one or both sides of rotor 6.
[0043] Referring now to Figure 6, cylindrical rotor 30 having cavities 31
is mounted on
shaft 32 substantially as previously described. Shaft 32 is connected to a
motor or other
power source not shown. Shaft 32 passes through seal 33 in end wall 34 of the
housing as
well as seal 35 of end wall 36 of the housing. Cylindrical shell 37 is
substantially concentric
to the periphery of rotor 30, forming a cavitation zone 38, similar to
peripheral space 8 in
Figure 1, around rotor 30. Fluid entering inlet 39 encounters disc 40, which
is held in place
by supports 41 connected to rotor 30. Disc 40 has a central hole 44 (see
Figure 7) similar to
central hole 4 in Figure 1. Unlike Figure 1, fluid entering through inlet 39
does not pass
directly into the hole 44 but impacts disc 40 as may be seen also in Figure 7.
Helping to
direct the flow as indicated by the arrows is an optional accelerator 42,
having a slanted or
conical surface around shaft 32. The surface of accelerator 32 may have a
curved profile as
well as the straight profile shown. After passing through the cavitation zone
38 as indicated
by the arrows, the fluid, now well mixed, exits through outlet 43. Outlet 43
need not be on
cylindrical shell 37 as shown, but could alternatively be located in end wall
36. The outlet is
positioned so that the fluid must traverse the full width of rotor 30 before
reaching it. As
seen in Figure 6, inlet 39 and outlet 43 define a flow path half way around
the internal
surface of shell 37 as well as through cavitation zone 38. The invention is
not limited to the
placement of the inlet and outlet 180 degrees apart with respect to shell 37.
They may be
placed at any angular distance from each other with respect to the cylindrical
shell 37.
[0044] The Figure 6 variation of the invention is not limited to the use of
only one disc.
It may have two, three (as seen in Figure 4) or more. Since shaft 32 passes
through both end
walls 34 and 36, the variation of Figure 6 is quite rugged. But it should be
noted also that a
9
CA 02937398 2016-07-28
significant advantage of all variations of our invention is that it can handle
high viscosity
fluids more efficiently than a centrifugal pump.
[0045] Figure 7 shows the face of disc 40, to illustrate that it encircles
shaft 32 while
inlet 39 is not centrally located as inlet 2 is in Figure 1. Fluid entering
inlet 39 will tend to
impact disc 40 and will flow both toward the cylindrical shell 38 (see Figure
6) and through
hole 44, in both cases having to pass through cavitation zone 38 before
arriving at outlet 43.
Disc 40 may have splines as described with respect to Figure 5.
[0046] The variation of Figures 6 and 7 can be immersed in a tank in a
manner similar to
that shown in Figure 3.
[0047] Since our device does not require an external high pressure pump,
high pressure
seals are not needed. They may be desired, however, to protect against the
possibility of a
high pressure backup event or some other unforeseen circumstance.
[0048] The invention includes a technique for starting up wherein the
device is partially
filled with fluid before the rotation is begun ¨ that is, before the motor is
started. The
reduced torque requirements of a partially filled device will enable a smooth
startup.
[0049] Our cavitation pump can be used to prepare drilling muds, completion
fluids, and
fracturing fluids for use in hydrocarbon recovery, and to hydrate synthetic
and natural
polymers for use in oilfield fluids. Excellent mixing can be accomplished
without a tank as
shown in Figure 3 ¨ that is, various materials including at least one fluid
can be present in
inlet conduit 2 as shown in Figure 1, and they will be thoroughly mixed by
activating the
motor to turn shaft 9.
[0050] Figures 8-13 are added for this continuation-in-part.
[0051] In Figure 8, cavitation rotor 51 is mounted on a shaft 52 which is
turned by a
motor, not shown, on shaft 52. Shaft 52 is supported by sleeve 58. Shaft 52
passes through
a bearing 65 in wall 59 of housing 53. Cavitation rotor 51 is substantially
cylindrical, and is
situated within housing 53 having a substantially cylindrical interior. The
cylindrical surface
of cavitation rotor 51 contains a plurality of cavities; the cavities are
illustrated as cavities
54a, showing their depth, and cavities 54b, showing their openings; the
cavities may be
referred to below as cavities 54. The cavities 54 (54a and 54b) generally
cover the entire
cylindrical surface of cavitation rotor 51, whose cylindrical surface is
substantially concentric
CA 02937398 2016-07-28
to the interior surface of housing 53, leaving a substantially uniform gap
between the two
cylindrical surfaces; this gap is referred to as the cavitation zone 60
because the flowing
fluid, confined in the gap, is subjected to a powerful cavitation effect to be
explained further
below. The cylindrical surface 51 containing cavities may be referred to
herein as the
"cavitation surface."
100521 It
should be noted that the surface 51 need not be strictly cylindrical. For
example, it may be frusto-conical or partly frusto-conical, with a conforming
surface inside
housing 53, but we prefer cylindrical for the cavity-containing surface
because, with a
conical surface, or any other surface having cavities located on a relatively
short radius from
the shaft, cavities on the short radius will not be as efficient as those on
the full radius of the
rotor 51, primarily because their peripheral velocity will not be as high and
the centrifugal
forces will not be as great as those on the full radius. The term "cavitation
surface" as used
herein nevertheless is intended to include any surface on a rotor which
contains cavities
intended to induce cavitation.
[0053] Housing
53 includes an inlet 55 for incoming material to be mixed, heated, or
otherwise treated, and an outlet 56 for the product. Outlet 56 need not be
exactly where
shown in Figure 8; it could be closer to shaft 52 or could be located on the
upper
(cylindrical) surface of housing 53. Inlet 55 is located centrally with
respect to the axes of
rotor 51 and shaft 52 so that fluid material entering inlet 55 immediately
encounters flow
director 57, which is attached to or integral with the center of cavitation
rotor 51 and
therefore spinning with rotor 51.
100541 The flow
path of the materials to be mixed (or otherwise treated) is indicated by
the arrows, beginning at inlet 55, continuing (in this view) upwardly and
downwardly as the
spinning rotor 51 urges the material to the peripheries of flow director 57
and cavitation rotor
51. The
fluid then proceeds into cavitation zone 60 across the cylindrical surface of
cavitation rotor 51. As is known in the art, a fluid flowing in such a gap
(between a spinning
rotor having cavities and a closely set conforming surface) constantly falls
into cavities 54,
but is almost immediately thrown out by centrifugal force, causing a mini-
vacuum in the
cavities 54, which in turn tends to draw the fluid back into the cavities 54.
This mini-violent
turbulence causes excellent mixing while also generating heat without chance
of scale
11
CA 02937398 2016-07-28
buildup. As is also known in the art, cavitation efficiency is affected by the
velocity of the
rotor's periphery as well as the gap height. Cavitation zone 60, the gap
between the
periphery of cavitation rotor 51 and the cylindrical internal surface of
housing 53, may be
from 0.1 inch to 1.0 inch in height, or as much as 3 inches, in order to
achieve an efficient
cavitation effect within a wide range of peripheral velocities and fluid
properties. The
system can handle a great variety of liquids and gases with or without solid
particles.
Normally a pump, not shown, upstream from inlet 55, will assure passage of the
fluid into the
housing 53.
[0055] From the cavitation zone 60, the fluid passes to outlet 56. Where
the cavitation
device is making drilling fluid for use in well drilling, it may be sent
directly to the well; for
many other purposes it may be sent to storage.
[0056] We may make our cavitation rotor of steel or stainless steel but
alternatively we
may use titanium because of its light weight and resistance to corrosion. Any
material of
suitable strength may be used. Various abrasion-resistant and corrosion-
resistant coatings
may be used on rotor 51 and flow director 57 as well as the interior of
housing 53. Titanium
weighs about 55% less than steel. Lighter weight means the rotor can be larger
than it
otherwise might be. A larger diameter rotor means a higher peripheral velocity
for a given
angular velocity, and the peripheral velocity is an important function in the
cavitation effect.
A larger rotor also means the ability to include more cavities on the rotor's
cylindrical
surface, whether the increased size is realized in a wider cavitation zone or
a larger diameter.
And not least important, a lighter rotor means less stress on the shaft
bearing 65 in housing
wall 59. However, a lighter rotor reduces the flywheel effect compared to a
heavier one of
the same shape and size. All such factors may be considered and varied with
the fluid
processed and the results desired.
[0057] The cavitation rotor 51 is seen to be wider at its periphery than in
its central body.
This is done to reduce the overall mass of the rotor and to enhance the
transfer of heat from
the body surface to material in contact with it and flow director 57. The
cavitation process
constantly generates heat energy which is not only instilled in the fluid by
intimate
cavitation, but also conducted through the metal body of the rotor 51 to its
side surfaces,
including flow director 57, where it is picked up by the fluid being treated.
As a rule of
12
CA 02937398 2016-07-28
thumb, we may reduce the mass of the rotor 51 by "hollowing out" perhaps
twenty percent or
more of the volume of a purely cylindrical shape of the same outer dimensions.
Reducing
the mass means the rotor is less of a heat sink and more of a heat transfer
element. The
somewhat dumbbell shaped profile also means that the mass actually present is
distributed to
provide a noticeable flywheel effect, thus reducing the energy needed to
maintain rotation in
the viscous materials we treat.
[0058] We further reduce stress on the bearing 65 in housing wall 59
through the use of a
cantilever bearing 66 on sleeve 58 and shaft 52, spaced from bearing 65 to
counterbalance
the downward force of rotor 51. That is, to the extent bearing 65 in housing
wall 59 acts
somewhat like a pivot, its stress is relieved by the leverage of the spaced-
apart bearing 66 on
shaft 52. It may be noted, however, that the possible reduction in weight
realized by the use
of titanium in rotor 51 would also reduce stress on bearing 65, as does the
buoyant effect of
rotor 51's total immersion in fluid, which is commonly quite dense in
practice. But density
and viscosity of drilling fluid, for example, places great stress on the
entire device including
the bearings. As a rule of thumb, the cantilever effect may be accomplished by
placing
bearing 66 at least twice as far away from bearing 65 as bearing 65 is from
the cavitation
rotor 51. That is, referring to Figure 8, the distance between bearings 65 and
66 is seen to be
more than twice the distance between rotor 51 and bearing 65 as indicated by
dotted arrow
67. However, persons skilled in the art may wish to refer to the literature on
stabilizing
shafts which considers the shaft shape and diameter, loading forces, rotating
masses, stress
under various conditions, and other factors. See, for example, the MIT on-line
publication
www.mitcalc.com/doc/shafts/help/enshaftxt.htm.
[0059] Flow director 57, sometimes called an accelerator, can have various
profiles, such
as parabolic, elliptical, spiral, hyperbolic or generally campanulate. All of
these have a
vertex and a base, generally a wide circular base. The flow director's shape
and position
with respect to the inlet should assure that the incoming fluid strikes its
highest point (the
vertex) first and, because the flow director 57 is spinning along with the
cavitation rotor 51,
is spread towards its lower regions (that is, the flared or asymptotic base
edge of the conical
or tapering shape) and onto the surface of the body of the rotor 51 before it
reaches the
cavitation gap 60. Flow director 57 can contain ridges, channels, bumps, and
various other
13
CA 02937398 2016-07-28
turbulence-inducing protuberances, or spiral threads, but overall should
exhibit a generally
conical, tapering, or bell-shaped profile.
[0060] Figure 9
shows the flow pattern on and near the flow director 57 and cavitation
rotor 51, from the perspective of the inlet 55 (Inlet 55 is visible in Figure
8). Arrows
indicating the direction of flow of the fluid on the flow director 57 appear
to be headed in a
direction opposite the direction of rotation of the cavitation rotor 51 and
the flow director 57.
This is because the rotation speed of the rotor is normally greater than the
flow rate;
moreover, as is known from the technology of spinning disc reactors, the fluid
tends to
spread towards the periphery of the spinning disc and tends to become a
thinner layer of
material as it is centrifugally forced to the periphery. In the construction
of Figure 8, unlike
on a spinning disc reactor, a thin film is not formed, as the entire volume
within housing 53 is
filled with moving fluid. But the spreading effect caused by the spinning flow
director is
quite uniform in both the dispersion of the fluid to the periphery of the
rotor 51 and in the
establishment of a distinct turbulent regime above the flow director 57, as
will be illustrated
in Figure 10. On reaching the periphery of the cavitation rotor 51, the fluid
to be mixed
enters cavitation zone 60 between cavitation rotor 51 and housing 53 for
processing as
described with respect to Figure 8.
[0061] From
Figure 10, and recalling the spreading and thinning effects near the surface
of flow director 57 depicted in Figure 9, it is seen that a much more
turbulent flow is
achieved in the larger space between housing 53 and rotor 51 as the fluid
moves toward the
cavitation zone 60. The
turbulence is depicted in the form of long coiled arrows. This
turbulence on the sides of the rotor 51, which is a function of the gap
between the housing 53
and rotor 51, combined with the spreading and thinning "spinning disc" effects
seen in
Figure 9, results in a very efficient and uniform heat transfer from the rotor
51 to the fluid.
Heat, constantly generated in the cavitation zone 60, is conducted through the
metal of rotor
51 and is picked up by the fluid at all points on the rotor surface by ever-
changing portions of
the fluid. The fluid is thus substantially uniformly preheated when it enters
the cavitation
zone 60, where it tends to assume a Taylor-Couette flow [see Taylor, G. I
(1923) "Stability
of a Viscous Liquid contained between Two Rotating Cylinders" Phil. Trans.
Royal Society
A223 (605-615); Gollub, J.P.; Swinney, H.L. (1975) "Onset of Turbulenbce in a
rotating
14
CA 02937398 2016-07-28
fluid" Physical Review Letters 35 (14): 927-930]. Taylor-Couette flow occurs
between a
rotating surface and one which is not rotating, or between other parallel or
concentric
surfaces, both of which are rotating at different rates or in different
directions. Significant
factors for turbulence in a Taylor-Couette setting are the viscosity of the
fluid and the gap
between the two surfaces. We have found, as indicated elsewhere herein, that
the cavitation
zone 60 gap should be between 0.1 inch and 1.0 inch and may be as much as 3
inches or
more. Although the cavitation process is highly significant in our device, it
does not
neutralize the manifestation of Taylor-Couette principles.
[0062] It should be noted in Figure 10 that, while inlet 55 sends incoming
fluid toward
the center of flow director 57 as in Figure 8, the outlet 62 in Figure 10 is
much closer to
shaft 52 than outlet 56 of Figure 8. Placing the outlet closer to shaft 52
than the internal
cylindrical surface of the housing 53 permits considerably more mixing on the
outlet side of
rotor 51, reduces the likelihood of relatively quiescent areas within housing
53, and permits
more contact by the fluid with the heated body of rotor 51 before it exits.
Note also that flow
director 57 has a more tapering, flattened bell shape than flow director 57 of
Figure 1. As
discussed elsewhere herein, the flow director may assume various shapes; in
the case of
Figure 10, flow director 57 flares around its perimeter, permitting an even,
smooth
distribution over the side of rotor 51 somewhat more consistent with "spinning
disc"
principles. [see Brian Launder, Sebastien Poncet, Eric Serre: Laminar,
Transitional, and
Turbulent Flows in Rotor-Stator Cavities. Annual Review of Fluid Mechanics,
Annual
Reviews, 2010, 42 (1), pp.229-248. <10.1146/annurev-fluid-121108-145514>. <hal-
00678846> 1
[0063] Our device is useful for many different processes including mixing
and heating,
but it is especially useful for viscous materials, such as drilling muds and
polymer solutions.
It can heat and mix a wide variety of combinations of liquids, solids and
gases having a wide
range of composition, viscosities and other physical properties. Drilling muds
and oil field
polymer solutions have been very difficult to handle in the past, but we have
found that our
invention is very useful for them. By adjusting the gap 63 between housing 53
and the left
(incoming) side of rotor 51 in reference to the expected physical
characteristics of the fluid,
CA 02937398 2016-07-28
particularly the viscosity, we can optimize both the "spinning disc" effects
and the turbulence
indicated by the arrows in Figure 10.
[0064] The gap 63 between cavitation rotor 51 and housing 53 may be varied
by shifting
the entire assembly of shaft 52, rotor 51, and flow director 57 to the right
or left, as depicted,
and securing it in its new position. If shifting the assembly of shaft 52,
rotor 51 and flow
director 57 closer to inlet 55 is deemed to widen gap 64 on the outlet side of
housing 53 too
much, one or more spacer discs may be placed directly on the outlet side of
rotor 51 to
compensate. Alternatively, gap 63 may be changed by adjusting the location of
rotor 51 on
shaft 52 in either direction, or by replacing flow director 57 with a flow
director of a different
thickness.
[0065] Referring now to Figure 11, a recirculation loop is shown in outline
form. A
fluid to be mixed and heated is sent through inlet 71 to the interior of
housing 72 where it
encounters flow director 73 on cavitation rotor 74, being spun by shaft 75
connected to a
motor not shown. The fluid is distributed by flow director 73 as explained in
Figures 8, 9,
and 10, subjected to turbulence-inducing motion of rotor 74 acting within the
walls of
housing 72, passed through the cavitation zone 76 where it is subjected both
to Taylor-
Couette effects and cavitation, and then passed to housing outlet 77. Using
appropriate
valves not shown, a portion of the mixture from housing outlet 77 is diverted
through conduit
78 to pump 79 and directed back to inlet 71, where it mingles with the
incoming fluid and is
sent through the unit again. A recirculation mode could, for example, feed 1/4
barrel per
minute (bpm) to inlet 71, remove 1/4 bpm from exit 80, and divert one bpm from
outlet 77 for
immediate recirculation. It should be noted that results more or less
equivalent to recycling a
portion of the fluid can be obtained simply by reducing the rate of flow of
fluid through the
device.
[0066] Figure 12 is similar to Figure 8, but illustrates a screw-shaped
flow director 85.
As with the other variations of the flow director of our invention, flow
director 85 has a
vertex 86 oriented directly into the flow of fluid entering the device through
inlet 55,
normally assured by a pump (not shown) sending fluid to inlet 55. Flow
director 85 may be
longer and more tapering, or its generally circular base 87 may be smaller,
not necessarily
covering the entire shoulder 88 of rotor 51. A screw-shaped flow director such
as flow
16
CA 02937398 2016-07-28
director 85 will very efficiently spread the incoming fluid to its generally
circular base 87
and then to the periphery of rotor 51 for entry into cavitation zone 60 around
the entire
periphery of rotor 51. We believe that, as with the other shapes of flow
directors illustrated
and described herein, although the fluid is spread more or less evenly over
the flow director
85, there is also a degree of turbulence generated which enhances the ability
of the device to
preheat the incoming fluid to an extent before it enters the cavitation zone
60.
[0067] Figure 13 is described with many of the same reference numbers as
Figure 1, as
it is similar in all respects except that it includes a flow director 90 which
is not present in
Figure 1 and which differs somewhat in design from other flow directors
described herein.
The housing 1 has an inlet conduit 2 and outlet 11. Cavitation rotor 6, having
a plurality of
cavities 7, is mounted on shaft 9, turned by a motor not shown. Solid disc 3,
which has a
central hole 4, is fixed to cavitation rotor 6 by disc supports 5 so the disc
3 will rotate with
rotor 6. See Figure 2 for a frontal view of disc 3. Fluid enters through
conduit (inlet) 2,
passes through hole 4, and immediately strikes the vertex 91 of flow director
90. It is then
spread in all directions in distribution space 10 between disc 3 and rotor 6
as indicated by the
arrows, continuing into peripheral space 8, which is a cavitation zone. The
fluid, now
thoroughly mixed and heated, passes through outlet 11 to be conducted to its
purpose or
storage. Although outlet 11 is vertical as depicted, it may alternatively be
oriented
tangentially in the direction of flow in peripheral space 8, to reduce
possible resistance to the
exiting fluid. As implied with respect to Figure 4, more than one disc may be
used in the
configuration of Figure 13. Nevertheless, as with all the other variations of
the invention
shown herein, conveyance of the fluid to be treated may be assured or assisted
by use of a
pump upstream of inlet conduit 2.
[0068] The use of both a disc (or more than one), to provide a pumping
effect, and a flow
director oriented toward the incoming fluid, to eliminate the resistance to
flow caused by
impact on a flat rotor face, and to spread the fluid immediately to the
cavitation zone (as
illustrated in Figure 13, results in a highly efficient heating and mixing
device.
[0069] Thus, our invention includes a cavitation device comprising (a) a
cavitation rotor
(b) a housing for said cavitation rotor, said housing including an internal
surface forming a
cavitation zone with said cavitation rotor, (c) a shaft for turning said
cavitation rotor, said
17
CA 02937398 2016-07-28
shaft passing through a wall bearing in an outlet wall of said housing, (d) an
inlet in said
housing for passing fluid into said housing, said inlet being located in an
inlet wall of said
housing, to pass said fluid toward the center of said cavitation rotor, (e) a
flow director fixed
to the center of said cavitation rotor and facing said inlet, said flow
director having a profile
high in its center and gradually receding therefrom, and (f) an outlet for
product, said outlet
being located on or near said outlet wall of said housing.
[0070] Also, our invention includes a method of heating and mixing fluid in
a cavitation
device, said cavitation device comprising a cavitation rotor within a housing,
a shaft
connected to said rotor for turning said rotor, an inlet for introducing fluid
into said housing
and an exit for delivering mixed and heated fluid product from said cavitation
device,
comprising (a) feeding fresh fluid to be mixed and heated through said inlet
and into said
housing to fill up said housing (b) continuing feeding fresh fluid through
said inlet and into
said housing at a known rate, (c) removing mixed and heated fluid from said
exit at said
known rate (d) diverting mixed and heated fluid from an outlet between said
housing and
said exit, at a rate greater than said known rate, and introducing said
diverted mixed and
heated fluid to said inlet at said rate greater than said known rate.
[0071] Our invention also includes an overhung cavitation device comprising
(a) a
cylindrical rotor having cavities on its periphery (b) a housing for said
cylindrical rotor, said
housing including an inlet wall, an outlet wall, and an enclosure forming a
cylindrical
internal surface slightly larger than said cylindrical rotor and forming a
cavitation zone
therewith, and (c) a shaft for turning said cylindrical rotor, said shaft (i)
fixed to said rotor,
(ii) passing through a bearing in said outlet wall, and (iii) passing through
a cantilever
bearing spaced from said outlet wall
[0072] The invention also includes a cavitation device comprising (a) a
housing defining
an internal cylindrical surface, said housing also having an inlet side and an
outlet side (b) a
cavitation rotor having a cylindrical cavitation surface, said cavitation
rotor residing within
said housing to form a cavitation zone with said internal cylindrical surface,
(c) a shaft for
turning said rotor, said shaft passing through a bearing in said outlet side,
(d) a flow director
on said cavitation rotor, said flow director having a central vertex and a
generally circular
18
CA 02937398 2016-07-28
base, and (e) a fluid inlet located on said inlet side, said fluid inlet
axially aligned with said
central vertex and said shaft.
[0073] Our invention also includes an overhung cavitation device comprising
(a) a rotor
having cavities on its periphery (b) a housing for said rotor, said housing
including an inlet
side having a fluid inlet, an outlet side, and an enclosure having an internal
surface
concentric with said rotor and forming a cavitation zone therewith, (c) a flow
director on said
rotor, said flow director having a vertex and a base on said rotor, said
vertex oriented toward
said inlet, and (d) a shaft for turning said rotor, said shaft (i) fixed to
said rotor, (ii) passing
through a bearing in said outlet side, and (iii) passing through a stabilizing
cantilever bearing
spaced from said outlet side.
[0074] And, our invention includes a method of heating and mixing a fluid
comprising
(a) passing said fluid onto the vertex of a rotating tapered flow director and
(b) passing said
fluid from said tapered flow director into a cavitation zone between a
rotating surface
containing cavities and a substantially concentric interior surface of a
housing.
19
