Note: Descriptions are shown in the official language in which they were submitted.
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SWIRL MIXING DEVICE
BACKGROUND OF THE INVENTION
The presen~ invention relates to a mixing device. More
particularly, I the invention relates to a mixing device for
5 mixing fluid~ such as liquids, gases and fluid suspensions of
particles, by the interaction of counter-rotating flows of
fluids. This type of device is generally known as a swirl
~.ixing device, the term "swirl" being generally used to refer
to the circulating flow of the fluid in a mixing chamber.
Some prior art swirl mixing devices are known. Examples
of such devices are shown in U.S. Patent Nos. 981,098,
3,261,593 and 3,862,907. In these known devices fluids are
clirected into a cylindrical mixing chamber from inlet pipes
having nearly tangetially directed outlets, such that the
15fluids' tend initially to move around the outer wall of the
chamber, and constr~ins (kinematically). eddies that must
occur at the interface of the fluids to be mixed. This results
in significant energy dissipation due to frictional losses as
fluids impinge on the walls of the chamber. The fluids move
20 more slowly as they approach 'the center of the chamber,
resulting in a central 'idead region". These effects reduce the
ability of the fluids to mix thoroughly. '
A swirl mixing device which reduces these effects is
described in my earlier application, Serial No. 205,147, where
25 fluids are injected into a mixing chamber at spaced levels
within the chamber, the' fluids injected at dIfferent levels
being injected in opposite rotational directions. The injection
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inlets are directed at a ~angent to a circle of radius smaller
than that of the mixing chamber, thus reducing the frictional
energy losses due to interaction with the walls of the chamber.
! SUMM~RY OF THE INVENTION
The present invention provides a swirl mixing device
which mixes fluids more efficiently.
The swirl mixing device according to the present inven-
tion basically comprises a container having an exhaust and
at least two adjacent fluid injection chambers. Each injection
chamber has injection means associated with it through which
a respective fluid is'injected into the chamber. The fluids are
directed in opposite rotational directions in adjacent cham-
bers. Passage means between' the chambers allows the fluid in
one chamber to flow into the next chamber and mix with the
fluid there, and further passage means is provided between
the final injection chamber and the exhaust.
The container preferably has a subs~antially cylindrical
inner surface.
The in'jection means are preferably arranged to direct
the fluids at a tangent to an imaginary circle of diameter
less than that of,the respective injection chamber and larger
than a respective passage means. The fluids swirl in opposi~e
directions within their respective chambers. As the fluid in
the first chamber passe,s through the passage means, which
preferably comprises a reduced diameter central circular open-
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ing in a collar separating the two chambers, the fluid will
spin up ( according to the so-called "figure skater effect" )
and thus there will be a relatively large tangential velocity
in opposite dlirections where the two fluids meet. This restllts
5 in radial gradients of swirl velocity which are fluid dynam-
ically unstable, resulting in vigorous growth of small scale
turbulent edclies. This greatly accelerates the mixing process,
and the turbulence will be greater than that produced if both
fluids are introduced into a single cylindrical mixing chamber.
Besides improving the efficiency of the device, the use
cf such collars leads to smooth performance over large ranges
of injection pressure ratios and reduces the tendency to
"chug", compared to other internal mix atomi7ers and mixers.
Accordingly, the collar promotes smooth, efficient mixing/a tom-
15 izin~ away from rigid boundaries.
Any number of fluids may be mixed by the addition of afurther injection chamber for each additional fluid to be
mixed. Each fluid is injected into its injection chamber with
an angular momentum opposite to that of the fluid or fluids
20 circulating in the preceding injection chamber. This is achiev-
ed by suitable seiection of the injection axis and/or velocity.
The fluids are injected with a predetermined angular
momentum such that the resultant angular momentum summed
over all injected fluids is small compared to the angular
25~momentum of an individual injected fluid. The mlxture ejected
from the exhaust therefore has low net angular momentum and
tends to resist dispersion. This concentrates the exhaust and
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tends to produce a relatively high axial velocity near the
center of the exhaust.
There may be a final mixing chamber between the
injection chambers and the exhaust, or alternatively the
5 exhaust may I comprise an exit opening from the final injection
chamber. The passage means comprise generally circular open-
ings in walls separating the chambers, in a preferred embodi-
ment, the openings being centered on the axis of the contain-
er. The openings are preferably of progressively increasing
10 size towards the exit end of the container.
Each injector means is orientated to inject fluid into its
associated chamber at such an angle that it tends to move
initially in a circular path of radius less than that of the
chamber and greater than that of the opening or passage into
15 the next chamber.
The use of multiple symmetrically spaced injectors within
a given a injection chamber promotes more uniform and
efficient mixing/atomization, and such is within the scope of
this invention.
The separating walls preferably comprise removably
mounted collars, such that the size and shape of the injection
chambers and the openings can be adjusted by the use of
different shapes and sizes of collar. Thus the mixing device
can be easily altered for the mixing of materials of various
25 viscosities, for example.
Accordingly, in view of the above, it is an object of
this invention to provide a swirl mixing device which enables
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thorough mixing of a plurality of reagents through the
interactions of counter swirling flows. It is a further object
of this invention to provide a swirl mixing device which can
be used as la sprayer for atomizing a liquid with a gas and
have the li~uid dispersed in small uniform droplets with a
full cone dispersion pattern.
It is another object of this invention to provide a swirl
~ixing device which is easy to fabricate and readily adapt-
able to a variety of materials and viscosities.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The following is a brief description of the acccmpanying
drawings;
Figure 1 is a perspective view of a swirl mixing device
~ccording to the present invention;
Figure 2 is a front elevational view of the mixing
device of Figure 1;
Figure 3 is a top plan view of the mixing device of
J:igures 1 and 2;
Figure 4 is a vertical cross section along lines 4-4 of
Figure 3;
Figure 5 is a horizontal cross section along lines 5-5 of
Figure 2;
Figure 6 is a vertical cross sectional view of a second
embodiment of the mixing device according to the invention;
Figure 7 is a vertical cross section through a third
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embodiment of mixing device in which three fluid injection
chambers are provided;
Figure 8 is a vertical cross section through a fourth
embodiment ofl the invention in which the chamber walls are
contoured; anl
Figure 9 is a vertical cross section through a further
embodiment of the invention showing another type o.f contour
to the chamber walls;
Figure 10 is a horizontal cross section of through a
further embodiment of the invention showing symmetrically
spaced injectors within a given injection chamber.
DESCRIPTION OF THE PREFERRED EMBQDIMENT
Figures 1 to S show a ~irst embodiment of a swirl
mixing device 10 according to the present invention. The
device comprises a cylindrically shaped container 12 closed at
one end 14 and with an exhaust opening 16 at the opposite
end.
Fluids to be mixed together in the container 10 are
sto~ed in conventional storage means, as shown by way of
example at 36 and 38. The storage means 36 and 38 are
connected to the respective fluid injection pipes 32 and 34 via
piping 40, 42 and pressure control valves 44 and k6.
As shown in Figure 4 the interior of the container is
divided by separating collars 18 and 20 into a first fluid
injection chamber 22, a second fluid injection chamber 24 and
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a final mixing chamber 26. The collars 18 and 20 are
plate-like members having openings or passages 28 and 30
that connect the first chamber 22 to the second chamber 24,
and the second chamber 24 to the mixing chamber 26,
respectively.
A fi~st fluid injection pipe 32 communicates with
the first injection chamber 22, and a second fluid injection
pipe 34 communicates with the second injection chamber 24.
The first and second fluid injection pipes 32 and 34 may
include injection nozzles structure~ as the swirl mixing
device 10 described in this application~
The body of the container is seen to comprise an
open-ended sleeve 48 with screw-threaded portions 50 and
52 on its inner surface at each end. The threaded portion
50 at the exhaust end of the cohtainer is in threaded
engagement with an exhaust head 54 in which exhaust opening
16 is located. The head 54 has a conical internal surfaee
56 leading to opening 16.
The threaded portion 52 at the bottom end of the
container is in threaded engagement with a base plate 58.
The interior of sleeve 48 has three portions 60,
62 and 64 of progressively stepped diameter defining the
respeetive ehambers 22, 24 and 26. An O-ring seal 66 is
compressed between a first step 68 and base plate 58 to
prevent leakage from the bottom end of the container.
The collars 18 and 20 are removably mounted against
steps 70 and 72, respectively.
This construction allows removal and replacement
of the
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head 53, the base plate 58, and collars 18 and 20, for
example to replace worn parts or to use parts of different
shapes and sizes in order to modify the flow configurations
within the c jhambers for different applications of the device.
5 Thus, for exlmple, an exhaust head with a different internal
shape or different size exhaust opening could be used, to
change the characteristics of the exhaust mixture. Collars
with different shapes or different size openings could be
substituted, for example to accommodate flulds of different
10 viscosities. Although circular openinl3s are preferred, slit or
cross openings may also be used. The collar themselves need
not be separate structures, but may be contoured portions of
the inner surface of the sleeve.
It is therefore clear that this device has considerable
15 versatility and some of the possible alternative configurations
are described below in connection with other embodiments.
Returning to the present embodiment, Figure 5 shows the
entry direction of injection pipe 34 into injection chamber 24.
Injection pipes 32 and 34 are oriented so as to direct the
20 injected Muids in opposite directions of swirl in their respec-
tive chambers 22 and 24. The injection axis 74 of pipe 34 lies
on a tangent to an imaginary circle in a plane perpendicular
to the container axis. The circle is of diameter less than that
of chamber 24 but greater than that of opening 30 in collar
25 20. Fluid injected into this chamber will tend to move in a
counter-clockwIse direction inwardly from this circle. Similar-
ly, the in jection axIs of pipe 32 wiIl be a tangent to a circle
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of diameter less than that of chamber 22 but greater than
that of opening 28, and it will direct fluid entering the
chamber in a clockwise direction. Opening 30 is larger than
cpening 28, ! and exhaust opening 16 is smaller than the
5 openings betwlleen the chambers (see Figure 4).
The counter swirling fluids will meet in the vicinity of
opening 28 and thorough mixing will take place in chambers
24 and 26. The relatively large tangential velocities in
opposite directions where the two fluids meet result in vigor-
10 ous growth of small scale turbulent eddies. This is known as"centrifugal" or Taylor instability. It results in rapid mixing
of the materials in jected with opposing swirls, the reduced
diameter opening where they meet enhancing the turbulerit
effect .
In this device relatively little pumping is required to
achieve a given degree of mixing. When a mixing device
according to the invention was used as a water spray nozzle ~
the nozzle was found to atomize 9 gallons per hour of water
to a volume median diameter of 113 microns droplet size with
20 cnly 2.5 psi air pressure at the rate of 1.7 standard cubic
feet of air per minute. The nozzle was found to have a stable
performance over a wide range of air to water injection pres-
sure ratics.
The structure of the mixing of the present invention
25 results in a high pressure region towards the outside of the
chambers 24 and 26, caused by the fluid - circulation. This
high pressure causes a secondary flow of that fluid which has
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less swirl, i.e. angular momentum, towards the center of
chambers 24 and 26. This effect is analagous to the "teacup
effect" where tealeaves gravitate towards the center of the
cup when thle tea is stirred. Accordingly, that portion of the
5 fluid which I has low angular momentum and centrifugal ac-
celeration is forced towards the center of chambers 24 and 26.
Thus there is a selective movement of well-mixed (and hence
low angular momentum) portions of the fluids towards the
center of the chambers. Thus fluids entering chamber 26
10 through central opening 30 are relatively well mixed, and the
same effect in mixing chamber 26 ensures even more thorough
mixing prior to exhaust of fluids through opening 16.
The structure of this device substantially reduces or
eliminates the centrifugal tendency of the fluids which are
15 mixed and ejected from the container. Accordingly, the ejected
mixture has relatively low dispersion characteristics and has
a full cone exhaust pattern. "Full cone" exhaust means that
the radial profile of the ejected mixture ' s axial velocity
component has relatively high values near the center, as
20 opposed to the low values occurring in rapidly swirling "hol-
low cone" exhaust paiterns that occur when the angular
momentum injection rates are not counter balan~edO
The injection pipe 32 may be choked, for example by
means of a nozzle or, alternatively, a flow restricting washer
25 at the opening of the injection pipe 32 and 34 (not shown) to
allow adjustment of the relative velocities, mass flow rates
and angular momentum injection rates of the fluids. The
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injection axis is also adjustable whereby to adjust the
angular momentum inparted to a fluid as it is injected into
the chambers 24 and 26.
Figure 6 shows a second embodiment of the swirl mixing
device acco~ding to the invention. In this embodiment the cone
shaped exhaust head 54 of the first embodiment, the cone
shaped exhaust head 54 and the mixing chamber 26 and the
upper portion 6~ of the interior sleeve 48 have been removed
leaving only a flat open exhaust head 78 and a single
10 interior collar 80 to divide the container 12 into a first and
second injection chamber 22 and 24. Thus the final mixing
chamber is eliminated in this embodiment.
As in the first embodiment, fluids are introduced into
the respective chambers via injection pipes 32 and 34 which
are arranged to direct the fluids with opposin~ swirls. Mixing
occurs in the second injection chamber 24 prior to exhaust
through circular exhaust opening 32 in flat exhaust head 78.
Openlng 82 is of larger radius than that of opening 84 in
collar 80.
Other parts of this embcdiment are analagous tc parts
in the first embodiment and have been given like reference
numerals. Parts 58, 78 and 80 are removable and can be
replaced by parts of different shapes and sizes, as in the
first embodiment.
Figure 7 shows another embodiment of the mixing device
in which a third fluid injection chamber 86 is provided
between the first two injection chambers 22 and 24, and the
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final mixing chamber 26. A third fluid injection pipe 88 leads
into chamber 86 from suitable fluid storage means (not
shown). In the preferred embodiment, the injection pipes 32,
34 and 88 are of suitable relative orientations and/or sizes
such that thl fluid in each chamber tends to swirl in opp,osite
direction to that of the fluid in the next adjacent chamber.
However, within the scope of this invention adjacent injection
pipes may inject fluids into adjacent chambers in 'the same
direction provided that the net angular momentum of all
injected fluids is small.
Thus, in the preferred embodiment, the fluids entering
chambers 32 and 34 swirl in opposite directions, and when the,
mixture of fluid leaves chamber 34 it will swirl in a direction
determined by the relative magnitudes of the angular momen-
tum of the first two injection fluids. The fluid enteringchamber 86 via injection pipe 88 is arranged to swirl in the
opposite direction to that of the mixed fluids in chamber 34.
The angular momentum of each fluid is such that the
resulting angular momentum summed over all injected fluids is
small ccmpared to the angular momentum of a sIngle injected
fluid'.
Clearly any number of fluids can be mixed together in
this way,, by the addition of extra injection chambers and
suitably arranged injection pipes.
The construction in Figure 7 is otherwise analagous to
that of the first embodiment, and like reference numerals have
been used where àppr,opriate.
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The openings 28, 30 and 90 in collars 18, 20 and 92,
respectively, which separate the chambers, are of progressive-
ly increasing radius towards the exhaust. The final mixing
chamber maylbe eliminated as in the Figure 6 embodiment so
that the mixeld fluids exhaust from the third injection chamber
86. The collars 18, 20 and 92 are removable as described in
connection with the first embodiment.
In Figure 8 the use of a shaped end plate 94 and
shaped collars 96 and 98 to change the shapes of chambers 22
and 24 is shown. Other parts in this embodiment are anala-
gous to parts in the first embodiment and have been given
corresponding reference numerals.
End plate 94 has a central projection boss 100 and the
two collars 96 and 98 are thickened at 102 and 104, respective-
ly, adjacent their central openings. Thus each injectionchamber has a depth which decreases t6wards the central
line. This tends to produce nearly axisymmetric flow of the
fluids near the shallowest point in their respective chambers,
if the injection pipe openings are relatively large as compar-
ed to the minimum depth areas of the injection chambers. Thisallows efficient and substantially axisymmetric mixing even if
relatively large amounts of fluids are used.
If significantly less of one fluid than the other is to be
used, its injection chamber can be of uniform depth while the
cther in]ection chamber is of reduced depth near its opening.
This can be acheived by replacing collar 98 by a flat collar
and by repIacing collar 96 with a collar having a flat upper
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face, for example.
Figure ~ shows another modified embodiment. A shaped
end plate 106 and shaped collars 108 and 110 are again used,
and a further modification is introduced in that the final
mixing chamb~er 26 has an hourglass shaped inner contour
havin~ its narrowest point at 112. The hourglass contour is
shown by way of example only as all surface contours are
considered within the scope of this invention.
Because of the contoured mixing chamber shown in
Figure 9, the fluids will spin up at the narrowes~ point 112
(due to the so-called "figure skater effect") and this promGtes
more thorough mixing.
Figure 9 also shows the exhaust opening 6 as wider
than in previous embodiments. The exhaust opening is indepen-
dent of other structural limitations shown in Figure 9. Accord-
ingly, all adjustments to the si~e of the exhaust opening are
considered within the scope of the invention.
The shapes of plate 106 and collars 108 and 110 are
such that opposed axial flow components are introduced to the
fluid in chambers 22 and 24 as they are forced along conical
surfaces 114 and 116, respectively. Accordingly, from the
above, it can be seen that by structuring the contoured
shapes of plate 106 and collars 108 and 110, a variety of
axial components can be imparted to the fluid entering cham-
bers 22 and 24. The adjustments of such contours are indepen-
dent of other structural limitations of Figure 9 and all
variations thereof are considered within the scope c,f this
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invention .
Figure 10 shows another modified embocliment of the fluid
mixing device wherein the injection chamber 24 includes oppos-
ed injection I pipes 34 and 34A. The opposed injection pipes 34
5 and 34A ar~ structured to inject fluids into injection chamber
24 with the same angular momentum thereby promoting sym-
metrical injection of the in jected fluid . Accordingly, it is
within the scope of this invention to provide for multiple
injection pipes within a given injection chamber.
The examples given above provide some, indication of
ways in which the various adjustable features of the mixing
device can be changed to satisfy the requirements of various
applications. These and other variations in the structure of
the mixing device are within the scope of the invention.
Some examples of applications to which this mixing
device can be adapted are: as a low pressure' mixing vessel;
as a vat for mixing fluidized reagents; as a combustion
chamber; as a spray nozzle for producing an atomized spray
of fluid droplets, e . g . for paint spraying, water spraying,
20 insecticide sprays, and the like; or as a chemical reaction
chamber.
The mixing device of this invention is des'igned to
promote smooth efficient mixing and/or atomization and the
selective exhaust of only well mixed and/or atomized ma-
25, terials. The mixing occurs in areas well spaced from thechamber walls, thus allowing more freedom for the turbulent
eddies to mix the flulds. This also reduces the tendency for
abra,sive or reactive fluids to damage the' chamber walls.
