Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to equipment for the mi~ing
of fluids. The invention is particularly useful in, for
example, mixing of stra-tified fluids and keeping in uniform
suspension solid-fluid suspensions or solid-liquid slurries.
In-the prior art, numerous devices using oscillating
motion of a perforated plate or conical or various geometry
plates or a diaphragm or piston have been used to either mix
fluids or to pump a fluid in a specific direction.
~urthermore, an extremely large number of rotating or
oscillating blade systems have been developed for mixing
purposes. It has been proposed that vortex ring propagation
can be used to enhance the penetrating effect of stack
emissions to achieve better dispersion of stack emissions.
Also devices employing ultrasonic or high frequency
oscillations have been used to create localized mixing.
However, none of the prior art devices are designed
specifically to create ring or linear vortices for the purpose
of efficient mixing of fluids. A problem with most of the
existing relatively high fre~uency devices is that they
dissipate the majority of the input energy in heat created
from localized turbulence, whereas the present invention is
relatively much more energy efficient while moving and mixing
relatively large volumes of fluid, and is relatively
insensitive to the fluid viscosity compared with most other
devices.
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The present invention generates a ring vortex,
similar to that which occurs in a mushroom cloud associated
with an atomic explosion. The propagation of the ring vortex
results in efficient mixing with low energy losses.
In accordance with one aspect of the invention,
there is provided a vortex ring mixer for mixing fluids, the
mixer comprising an orifice plate adapted to be located in a
fluid to be mixed, the orifice plate having an orifice of
diameter d formed therein. Means is provided for forcing
fluid through the orifice in a direction perpendicular to the
orifice plate, the fluid travelling a distance L relative to
the orifice. The ratio of L/d is between 1.5 and 3.5.
Preferred embodiments of the invention will now be
described, with reference to the accompanying drawings, in
which:
Figure 1 is a diagrammatic view showing the
operation of a vortex ring generator according to the present
invention;
; Figure 2 is a plan view of the vortex ring generator
shown in Figure 2;
Figure 3 is a sectional view taken along lines 3-3
of Figure 2 showing a preferred embodiment of a vortex ring
generator according to the present invention;
Figure 4 is a sectional view of a vortex ring
generator similar to that of Figures 2 and 3, but showing the
generator mounted in an inverted position;
Figure 5 is a sectional view of another embodiment
of a vortex ring generator according to the present invention;
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Figure 6 is a sectional view of the vortex ring
generator of Figure 5, but mounted in an inverted position;
Figure 7 is a sectional view of a floating
embodiment of a vortex ring generator which is similar to the
embodiment of Figure 4;
Figure 8 is a sectional view of a floating
embodiment of a vortex ring generator which is similar to the
embodiment of Fiyure 6;
Figure 9 is a sectional view of yet another
embodiment of a vortex ring generator according to the present
invention;
Figure 10 is a bottom view of the orifice plate of
the embodiment shown in Figure 9;
Figure 11 is a sectional view of yet another
embodiment of a vortex ring generator according to the present
invention;
Figure 12 is a sectional view of a "T" adaptor for
a vortex ring generator according to the present invention;
Figure 13 is a sectional view of an angled adaptor
for a vortex ring generator according to the present
invention; and
; Figure 14 is a sectional view of a right angled
adapter designed to permit a device constructed according to
the present invention to be mounted above a fluid to be mixed.
Referring first to Figure 1, the operation of a
vortex ring mixer or generator according to the present
invention will be described briefly. An orifice plate 3 is
shown, having an opening or orifice 7. The orifice plate 3 is
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disposed in a fluid 25 to be mixed, which in turn is contained
in a container 20. A ring vortex or vortex ring, which is
generally indicated by reference to numeral 5, is formed in
the fluid 25, by moving orifice plate 3 downwardly in the
direction of arrow 22. This causes a slug of fluid to be
forced upwardly through orifice 7 producing ring vortex 5.
Ring vortex 5, which is in the form of an oblate
spheroid as indicated by the chain-dotted line 23, moves
upwardly in the direction of arrow 24. Rin~ vortex 5 in
effect rolls through fluid 25, because the layer of fluid at
the outer surface or boundary 27 of the vortex ring travels
with or at the same speed as the adjacent fluid 39, the latter
moving downwardly to be taken up or inducted into the centre
of ring vortex 5. In fact, there is almost no viscous drag at
the outer boundary 27 of the vortex ring 5, with the result
that ring vortex 5 can travel or propagate great dis~ances
through fluid 25, even in very viscous or even non-newtonian
fluids. While some fluid is being inducted into ring vortex
5, there is also some fluid ejeGted from the ring vortex in
the form of a fluid trail or wake 43. This induction, wake,
and the general flow or circulation pattern around the ring
vortex as it moves upwardly creates very efficient mixing or
agitation of fluid 25. In order to produce the type of ring
vortex 5 in ~uestion, however, there is a required
relationship between the diameter of orifice 7 and the travel
of orifice plate 3, as will be described further below.
Referring next to Figures 2 and 3 a portable ring
vortex generator is generally indicated by reference number
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.
45. Generator 45 has three hydraulic or pneumatic actuators
26 which operate a mov~ng orif~ce plate 3 with centrally
located orifice 7. The orifice plate 3 is located in a
cylindrical housing 28, open at one end and having a closed
end or base plate or end wall 21, the housing acting as an
anchor for the moving orifice plate. Piston rods 37 of
actuators 26 are connected to the base plate 21 of housing 28,
and cylinders 38 of actuators 26 are attached to orifice plate
3. Orifice plate 3 moves up and down inside housing 28 in a
controlled motion and generates ring ~ortices 5 as seen in
Figure 1.
The orifice plate 3 is moved by actuators 26 in a
controlled manner to achieve the most efficient results for
various liquids and suspensions. This control is achieved by
the combination of a hydraulic or air valve 29 and electric
control circuit 30. Generator 45 is portable and can be large
or ~uite small. The outer diameter of orifice plate 3
compared with the orifice diameter d is such that the distance
from the centre of orifice 7 to the vertical wall of housing
28 or any other adjacent vertical wall (or the peripheral edge
of orifice plate 3) should bè equal to or greater than twice
the diameter of orifice 7.
Figure 4 shows a ring vortex generator 50 which is
mounted upside down on an adjustable support bar 33 so that
the ring vortices are projected downwardly. Generator 5~ is
kept at or near the liquid surface, but it could be located at
any required depth in the li~uid being mixed or agitated.
Furthermore, by the introduction of a small controlled air
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vent 31, air may be admitted to generator 50 and a highly
aerated vortex ring is emitted from the unit and projected
downwardly into fluid 25. This operation has been tested and
found to result in very efficient aeration of a fluid and
therefore the unit can be used as a very efficient aeration
unit, and could be used for the aeration and destratification
of lakes or large bodies of liquids.
Figure 5 shows another embodiment of a ring vortex
generator 55 in which the cylindrical wall of housing 28 is
removed leaving a base plate 40. This results in radial
discharge of the liquid as well as the projection of a vortex
ring and also gives excellent mixing performance. The
diameter of base plate 40 is larger than that for a generator
having side walls.
Figure 6 shows a ring vortex generator 65 which is
similar to generator 55, but which is inverted and supported
on an adjustable sup~ort bar 33 like generator 50 of Figure 4.
Figure 7 shows a ring vortex generator 70 which is
basically the same as generator 50, but with a flotation tank
32 enclosing actuators 26 therein so that generator 50 floats
on the surface of fluid 25.
Figure 8 shows a ring ~ortex generator 75 which is
basically the same as generator 65, but again with a flotation
tank 32 enclosing actuators 26, so that generator 75 also
floats on the surface of fluid 25.
If it is required that the ring vortices travel
large distances, then the sidewall configurations as in
Figures 2, 4 and 7 are used to induce a high energy to the
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vortex ring. ~owever, if there is need for considerable
agitation in the vicinity of the orifice plate 3, then the
side wall is removed as in Figures 5, 6 and 8 to permit some
radial flow of the fluid.
Another vortex ring generator 80 is shown in Figures
9 and 10 and has a vortex generating orifice plate 3 which is
activate by two rods 3g, which are in turn actuated by a
single rod 35 from a pneumatic actuator 36 mounted on support
bar 33. Actuator 36 has an associated air valve 29 and
control circuit 30. If generator 80 is to be used for an
explosive or flammable liquid and an electrical control system
is used, the electrical controller can be located in a
separate control box located remote from the mixer. However,
a totally pneumatic control system is normally employed for
flammable or explosive fluids. In generator 80, both the
pressure and therefore the force of the agitation and also the
frequency of the agitative cycle can be varied. Generator 80
can be used in a similar manner to conventional mixers, that
is with the primary energizing unit located outside the mixing
vessel as compared with the immersed units described above.
Yet another embodiment oE a ring vortex generator 85
is shown in Figure ll. A prime mover 8 reciprocates a rod 9,
which in turn operates a driver 10, in the form of a diaphragm
or a piston located in a primary fluid chamber 13 located
adjacent to orifice 7. When driver 10 is pulled away from the
orifice 7, a return spring 12 is compressed. Rod 9 is then
instantly released causing the spring 12 rapidly to force the
dri~er 10 upwardly to force the fluid in the primary chamber
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13 through the orifice 7 and create ring vortex 5. In this
case, the bottom wall of container or tank 20 forms the
orifice plate 3. The velocity and stroke of driver 10
indicates the velocity of propagation and volume of the ring
vortex 5 in much the same manner as in the previously
described embodiments.
The stroke of rod 9 and therefore the volume of
fluid discharged during each stroke is controlled using an
adjuster 14. The stroke length of rod 9 is the difference
between the stroke length created by prime mover 8 and the
non-contact dwell created by adjuster 14 during each stroke
cycle. A spring pre-tensioning nut 15 is used to balance the
forces on driver 10 especially where generator 85 is used with
a pressurized tank or is located at the bottom of a tank
filled with a relatively dense fluid or large quantity of
fluid.
Various configurations and geometries can be used
for orifice 7 in all of the embodiments described above, but
the optimal shape is circular.
Optionally, extension tube or tubular adapters 17
can be used, as shown in Figures 12 and 13. Adapters 17 act
as orifice extensions and can be employed with any of the
embodiments described above. Adapters 17 are used to control
the direction of propagation of the vortex ring. They may
also be used to give considerable flexibility in the use and
location of the ring vortex generator in a particular ~luid
field, such as the location of a de~ice in the side wall,
bottom or top of a mixing tank.
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Multiple hole extension tubes 17 can be used to
generate more than one vortex from one unit, which can be
projected at various directions into the fluid media, as shown
in Figure 12. This permits agitation and mixing in various
directions and locations at the same time. Extension tube 17
permits control of the direction of the vortices without undue
intrusion into the mixing vessel or angular positioning of the
mixer unit, as shown in Figure 13. The extension piece 17 can
also be used to permit positioning of the mixer above a fluid,
as shown in Figure 1~. This permit the mixer unit to be
located in the top of the fluid mixing vessel tank of
reservoir and avoids the need for pressure seals between the
fluid reservoir and the mixer unit.
In some cases, it may be desirable to use two or
more orifices, in orifice plate 3. In this case, the orifices
must be spaced apart or the respective vortices generated can
collide with each other before they have travelled any
appreciable distance. A semi-empirical analysis found that
the minimum reasonable distance between the centres of
adjacent orifices to be given by:
X~d 2 2.5
where X is the centre to centre distance between the orifices
and d is the orifice diameter. In other words, khe distance
from the centre of one orifice to the peripheral edge of an
adjacent orifice (or the peripheral edge of orifice plate 3
which is equivalent for the purposes of this disclosure)
should be greater than twice the diameter of the first
o~ifice.
g
:
As mentioned above, there is a desirable
relationship betwee~ the diameter d of orifice 7 and the
stroke L (see Figure 2) of orifice plate 3 in order to produce
the ring vortices according to the present invention. This
relationship refers to the ratio of the equivalent plug length
to the diameter of the orifice and may be expressed as
follows:
1.5 ~ L/d ~ 3.5
where d is the orifice diameter and L is the equivalent plug
len~th which is the distance travelled by orifice plate 3 or
the length of the fluid plug passing through orifice 7 (such
as in the Figure 11 embodiment) in generating ring vortex 5.
The optimal value based on experimental data appears
to be given bY:
L/d ~ 2.~
At the instant and immediately after the generation
of a ring vortex, the ratio of the translational velocity of
the vortex ring Uv to the mean velocity of the slug of fluid
passing through the orifice Um is given by:
Uv /U~ 0.6
For relatively small distances, Un~ can be considered to be
constant, and therefore the time t for a vortex ring to reach
the surface or travel a distance H is:
: t = H/U~
To mix a fluid in a container 20, repeated strokes
of orifice plate 3 may be used to produce repeated or
successive ring vortices 5. The frequency required to mix or
maintain a mixed condition obviously depends on the type of
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material(s) beiny mixed. However, in a simple two fluid
system in which the density difference is relatively small
(that is, a density ratio of less than 1.1), it has been found
that a frequency of 0.25 Hz was quite adequate. However for
slurries such as line, in which the density ratio between the
particles and the fluid can be as high as 3.0, a higher
fre~uency should be used. It was found that a frequency of
about 0.4 Hz was adequate for a lime slurry with a weight
concentration of 24% ana a density ratio of 2.29.
Frequencies of greater than about 0.6 Hz may result
in the ingestion of secondary vortices into the orifice and
excessive localized turbulence which results in the generation
of a weak primary vortex ring. This to a large extent can be
controlled by the use of a stroke characteristic such that
there is a relatively fast vortex generation stroke of orifice
plate 3 or driver 10 followed by a slow return stroke, or by
introducing a dwell period after the return stroke. ~or these
reasons, a sinusoidal motion of orifice plate 3 or driver 10
has been found not to be desirable for the efficient
generation of vortices. It also causes excessive genera~ion
of localized turbulence which can affect the efficient
generation of vortex rings.
The preferred stroke frequency of orifice plate 3 is
between 0.25 Hz and 0.6 Hz.
It is difficult to predict the distance that a
vortex will travel before it disintegrates, and it depends on
a number of factors, such as whether it is initially stable or
unstable, laminar or turbulent. It also depends on the
.
initial velocity of the vortex Uv , and any density
differences or density strati~ication in the fluid initially
in the ring at its formative stages and the ambient or bulk of
the fluid to be mixed, but it is relatively insensitive to the
fluid's viscosity or wether the fluid is Newtonian or non-
New-tonian, since the shear and drag forces are relatively
insignificant in the motion of a vortex ring. However,
vertical distances of 2m in a 51% by weight aqueous lime
suspension were achieved with the ring still very energetic
when it broke the liquid surface, and in water solutions
vortices travelled vertically 1.3m and then continued to
travel in the air over lm after leaving the surface of the
water. On the basis of ~ualitative observations it is felt
that distances of over 10m or 100 x diameter of the orifice
would not be unreasonable when the density difference is not
too great, such as ~ 1.1. Smaller d/D ratios (see Figure 3)
tend to produce vortex rings that travel longer distances.
It will be appreciated that the above description
relates to the pre~erred and alternative embodiments by way of
example only. Many variations on the invention will be
obvious to those skilled in the art, and such obvious
variations are within the scope of the invention as described
and claimed, whether or not expressly described.
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