U.S. patent number 3,860,217 [Application Number 05/354,688] was granted by the patent office on 1975-01-14 for shear mixer.
This patent grant is currently assigned to Kenics Corporation. Invention is credited to Kenneth M. Grout.
United States Patent |
3,860,217 |
Grout |
January 14, 1975 |
SHEAR MIXER
Abstract
A shear mixer for mixing components of a flowing fluid in which
the mixing action is produced primarily, but not solely, by high
internally generated shear forces. The basic element of the mixer
is formed with a plurality of elongated channels, each preferably
having an elliptic transverse cross section. The channels are
disposed about each other in a helical arrangement and communicate
with each other through one or more elongated helical slots formed
in adjacent sides of two or more contiguous channels. The sides of
each slot are cusp-shaped and the end faces of each mixing element
are preferably concave at the ends of said channels with cusps in
the end faces joining the cusps at the slot edges. A mixer may
consist of a single element or of a plurality of such elements
arranged with alternating right and left-handed helix groups, (a
group consisting of one or more of such elements). The element or
elements in one helix group has the transverse axis of each pair of
its channels angularly disposed with respect to such axis of an
adjacent group. Methods of making such mixers are also
disclosed.
Inventors: |
Grout; Kenneth M. (Topsfield,
MA) |
Assignee: |
Kenics Corporation (Danvers,
MA)
|
Family
ID: |
23394496 |
Appl.
No.: |
05/354,688 |
Filed: |
April 26, 1973 |
Current U.S.
Class: |
366/336 |
Current CPC
Class: |
B01F
5/0646 (20130101); B01F 5/0644 (20130101) |
Current International
Class: |
B01F
5/06 (20060101); B01f 005/00 () |
Field of
Search: |
;259/4,18,19,36,37,99,114 ;138/38 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Hornsby; Harvey C.
Assistant Examiner: Pous; Robert
Claims
I claim:
1. A mixer element comprising a body having therein a plurality of
elongated channels extending through said body and displaced with
respect to each other around a longitudinal axis, each of said
elongated channels being disposed along a helix around said
longitudinal axis, the helices of adjacent channels being disposed
in the same sense around said longitudinal axis, the contiguous
inner sides of adjacent channels being provided with at least one
common opening through which said adjacent channels communicate
with each other; said opening comprising an elongated slot
extending throughout the length of said channels.
2. A mixer element according to claim 1 in which at least one end
face of said body is concave at the end of each of said
channels.
3. A mixer element according to claim 1 in which the number of said
channels is at least three.
4. A mixer comprising a plurality of mixer elements according to
claim 2 mounted in end to end relationship with their longitudinal
axes in line with each other.
5. A mixer according to claim 4 in which said mixer elements are
arranged in alternating right and left-handed helix groups.
6. A mixer according to claim 4 in which adjacent mixer elements
are mounted with these ends abutting each other.
7. A mixer according to claim 4 in which adjacent mixer elements
are mounted with their ends spaced from each other.
8. A mixer according to claim 4 in which the transverse axis
through the centers of said channels of each of said units is
angularly displaced with respect to such transverse axis of each
unit adjacent thereto.
9. A mixer according to claim 1 in which each of said channels has
an elliptic cross section.
10. A mixer element comprising a body having therein a plurality of
elongated channels extending through said body and displaced with
respect to each other around a longitudinal axis, each of said
elongated channels being disposed along a helix around said
longitudinal axis, the helices of adjacent channels being disposed
in the same sense around said longitudinal axis, the contiguous
inner sides of adjacent channels being provided with at least one
common opening through which said adjacent channels communicate
with each other, at least one end face of said body being concave
at the end of each of said channels, said concave face having
pointed cusps transverse to the line joining the centers of said
channels at said end face, each of said cusps extending from an
edge of said slot to a point on said end face removed from said
edge.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
Mixers having stationary elements for mixing or otherwise
contacting components of a flowing fluid or fluid-like stream in
order to produce such effects as homogenization of miscible fluids,
mass transfer to reactive components, establishing a uniform
temperature throughout the stream and producing dispersions of
immiscible substances.
2. Nature of the Prior Art
The field of motionless mixers relates to that type of mixing
device designed to mix components of a flowing fluid by causing a
stream of such fluid to pass through a conduit containing within it
stationary structural elements which physically react with said
stream to produce the desired mixing action. An example of this
type of mixer is shown in the U.S. Pat. No. 3,286,992 to Armeniades
et al. Such devices are used for a wide variety of purposes
including the homogenization of miscible fluids, mass transfer of
reactive components, the establishment of a uniform temperature
throughout a flowing fluid mass, and the dispersion of immiscible
substances including generating such fine dispersions as to produce
stable emulsions. While such devices are generally satisfactory for
many purposes, completely satisfactory operation has not yet been
achieved for a variety of objectives.
Nature of Present Invention
The present invention takes a basically new approach to the
solution of the fluid mixing problem by placing a major emphasis
upon increasing the shear forces which interact between different
parts of the fluid stream. While high shear is important in many
mixing processes, it is particularly important where it is desired
to produce a stable emulsion of immiscible fluids. As the viscosity
ratio between the two fluids increases, a higher and higher degree
of shear is required to improve the degree of subdivision of the
fluid particles to the point where a stable emulsion is reached.
Even in those cases where such an emulsion is not required, the
higher shear forces produced by the present invention are very
useful.
BRIEF DESCRIPTION OF THE DRAWINGS
In the annexed drawings:
FIG. 1 is a perspective view of one of the novel mixer
elements;
FIG. 2 is a side view of a simple mixer using one of the mixer
elements of FIG. 1;
FIG. 3 is an enlarged cross-sectional diagram taken along line 3--3
of FIG. 2, illustrating the nature of its operation;
FIG. 4 is a view similar to FIG. 1 but with the sense of the
helical passages reversed with respect to the sense of FIG. 1;
FIG. 5 is a side view of a mixer using multiple mixer elements;
FIG. 6 is a representation of a step in the assembly of two mixer
elements in an arrangement as in FIG. 5;
FIG. 7 is a view as in FIG. 3 showing the effect of the reversal of
the sense of the helical passages in the mixer unit;
FIG. 8 is a partial view, similar to FIG. 4, showing a mixer with
spaced units;
FIG. 9 is a view similar to FIG. 3 but illustrating the effect of
using more than two helical passages in a single mixer unit;
FIG. 10 is a view similar to FIG. 1 showing a form of mixer element
with concave ends;
FIG. 11 is a side view of an arrangement with two elements of the
type of FIG. 8 assembled in end-to-end relationship;
FIG. 12 is an enlarged end view of the upper element taken along
line 12--12 of FIG. 11 with the orientation of the lower element
shown in dotted lines;
FIG. 13 is a perspective view, partly in section, illustrating one
method of making a mixer element;
FIG. 14 is a perspective view of a metal blank illustrating a step
in another method of making a mixer element; and
FIG. 15 is a cross-sectional view of a mixer element made by the
process illustrated in FIG. 14.
The basic component of the mixer of this invention, as illustrated
by way of example in FIG. 1, consists of a body 1 in which is
formed a plurality of elongated channels 2 and 3 each having an
eliptic cross section and each having its longitudinal axis
disposed along a helical path. These channels are interwound with
each other and their cross-sections intersect adjacent the
longitudinal axis of the body 1 so as to produce an elongated
helical opening 4 through which each channel communicates with its
adjacent channel. If we pass along each channel 2 and 3 in FIG. 1
from the top to the bottom, it will be seen that the helices formed
by these channels are left-handed helices. As shown in FIG. 1, a
preferred embodiment of the basic component is one in which each
channel 2 and 3 consists of a 180.degree. helical turn. Variations
in the degree of helical turning in each such unit will be matter
of choice in the design of such mixers. While the longitudinal axis
of the body 1, referred to above, lies along a straight line, it is
to be understood that the term "longitudinal axis," as it applies
to body 1, includes any line, whether or not straight, about which
the channels progress with either right-handed or left-handed
turnings. In addition, although the opening 4 is shown as a
continuous slot extending from the top to the bottom of body 1,
parts of the contiguous sides of channels 2 and 3 could be left
solid so as to provide a plurality of such slots extending
longitudinally of the body 1.
A simple or elementary form of a left hand helix mixer using such a
basic element is shown diagramatically in FIG. 2 in which a fluid
extruder 5 is connected to the input end of a unit 1 and a
discharge nozzle 6 is connected to its output end. The resulting
reaction within the unit 1 is illustrated in FIG. 3. As the fluid
is caused to flow from the extruder 5, it follows a helical path
through each channel 2 and 3. Frictional forces will be set up
between the walls of these channels and the fluid to produce a
counter rotation in each channel at right angles to the direction
of longitudinal flow of the fluid. The direction of such counter
rotation is shown by the arrows in FIG. 3 as a clockwise rotation
of the fluid in each of the channels 2 and 3. This assumes a
counterclockwise progression of the channels into the plane of the
paper and a flow of the fluid into such plane. Therefore, at each
opening or slot 4 between the channels, the fluids flowing in the
channels will be rotating oppositely to each other producing a very
high degree of internal fluid shear. Such high internal shear will
produce a strong mixing action for the various purposes for which
such a device is intended. Where the opening 4 is not continuous
from the top to the bottom of body 1, it is merely required that a
sufficient total length of the common openings between channels 1
and 2 be produced to result in a substantial volume in which the
above-described shear forces may be developed.
It may be that, for some purposes, the elementary form of mixer
shown in FIG. 2, would not be the preferred one. Therefore, a mixer
might comprise a plurality of units 1 in which the helical turns of
channels 2 and 3 would be reversed in each alternate unit. For this
purpose, it is desired to add to the left-hand helical passage
member 1, as shown in FIG. 1, a right-hand helical passage member
1a as shown in FIG. 4.
FIG. 4 illustrates an element 1a with right-hand helical passages
2a and 3a providing a passage 4a between them.
A preferred embodiment of the invention is that illustrated in FIG.
5 in which the mixer would consist of a plurality of basic elements
1b and 1c, 1d and 1e assembled end to end in a series within a
casing 7. Each basic element 1b and 1d is as illustrated in FIG. 1,
while each element 1c and 1e is as illustrated in FIG. 4. Thus, the
direction of the helical passages in each alternate element is of
the opposite sense to the direction of the helical passages in the
adjacent elements.
In addition to the reversal of direction of the helices in
alternate elements, each alternate element also preferably has the
transverse axis joining the centers of the passages angularly
disposed with respect to such axis in each adjacent unit. Thus,
FIG. 6 shows a step in the assembly of two adjacent units wherein
the upper unit 1 is the same as that shown in FIG. 1 while the
lower unit 1a is the same as that shown in FIG. 4 but with the
above described transverse axis rotated through 90.degree. so that
the transverse axes of 1 and 1a are disposed 90.degree. with
respect to each other. This angular relationship is not critical
and may be of any substantial size.
The effect of reversing the direction of the helices is illustrated
in FIG. 7. The clockwise rotation of the fluid for the right-hand
helices of the unit of FIG. 3 becomes a counterclockwise rotation
as shown by the curved arrows of FIG. 7. The same high degree of
internal fluid shear, as in FIG. 3, is also generated at the
opening 4a in FIG. 7. Therefore, in FIG. 5, when the fluid issues
from the first unit 1b and encounters the second unit 1c, the
rotation imparted by unit 1b will be reversed by the action of the
unit 1c, thus increasing the mixing effectiveness of the combined
device. Furthermore, the angular displacement of the transverse
axes of the helices between adjacent elements introduces additional
subdivisions of the fluid stream and increased internal shearing
forces which further enhance the mixing action.
Instead of reversing the direction of the helices in every
alternate mixer element, a plurality of such elements with these
helical elements all in the same sense may be followed by a
plurality of such elements with their helices all in the opposite
sense. Therefore, such elements may be considered broadly as being
arranged in alternating right-handed and left-handed helix groups,
it being understood that a group may consist of one or more
elements.
Also, as illustrated in FIG. 8, instead of the adjacent ends of
successive elements 1b and 1c being in contact with each other,
such ends may be spaced from each other where it is desired to
provide a plenum 8 between successive elements.
The principles of the present invention may be incorporated in
structures in which more than two helical channels are present. For
example, in FIG. 9, three helical channels 9, 10, and 11, similar
to channels 2 and 3 of FIG. 1, are provided in a body 12. These
channels are formed respectively with longitudinal openings 13, 14
and 15, similar to opening 4 of FIG. 1. These openings 13, 14 and
15 merge into a central opening 16 extending the length of the body
12. As described in connection with FIG. 3, when fluid is caused to
flow along each channel 9, 10 and 11, frictional forces between the
walls of the channels and the flowing fluid produce a rotation of
the fluid as indicated by the arrows in FIG. 9. The direction of
such rotation about the opening 16 produces a cumulative
circumferential force around the opening 16 and drives the fluid in
such opening circularly in a direction opposite to the direction of
rotation of the fluid in channels 9, 10 and 11. As shown, the
rotation of the fluid in opening 16 is in a counterclockwise
direction. The resultant of the forces causing the flow of fluid
along the length of the body 12 and the above rotation forces will
cause each particle in the opening 16 to flow in a helical path
along the length of the opening 16 substantially in synchronism
with the helical flow in each of the channels 9, 10 and 11. Not
only will there exist a very effective mixing action, but also the
residence times in the mixer for all particles in the fluid flow
will tend to be equal resulting in a highly uniform product.
It is to be understood that, although the cross section of each
channel has been illustrated as a circle, such cross section may be
elliptic, a circle being one form. By the term "elliptic" is meant
any closed planar curve along which there is no reversal of
curvature, but along which there may be changes in the radius of
curvature. Such definition is not to be interpreted as excluding
gaps such as those due to openings 4, 13, 14 and 15.
While channels with elliptic cross sections may be preferred, such
channels may have any type of cross section. As long as such cross
section defines a closed figure (except for a gap due to the
opening in its side) and the channel progresses along a helical
path, as described above, a counter rotation of the fluid in
adjacent channels will be produced and the effects of the present
invention will be generated.
However, the elliptic form of mixer element eliminates all corners
which could create dead areas in which parts of the fluid might
remain for substantially longer periods than the rest of the
flowing fluid. The existence of such corners in prior art devices
are responsible for the fact that it has been virtually impossible
to obtain anything approaching completely uniform residence time
for fluids flowing through such mixers. The present invention makes
possible a much closer approximation of such uniform residence time
than has been possible heretofore.
In order further to enhance the uniformity of residence time and to
increase the mixing action of this invention, the embodiment of
FIGS. 10 and 11 have been devised. In FIG. 10, the unit 18 is
substantially like the unit 1 of FIG. 1 and is formed with channels
19 and 20 corresponding to channels 2 and 3 of FIG. 1. However, in
FIG. 10, the end of each unit is dished with concave surfaces 21
and 22 at the ends of the channels 19 and 20. Such concave surfaces
meet along substantially horizontal cusp edges 23 which terminate
along a circular border 24 which defines the outer limits of the
concave surfaces 21 and 22. This form of the end of each unit may
be more readily seen in FIG. 12. The dotted lines show the
orientation of the end face of an adjacent unit assembled as will
be described below for FIG. 11.
As shown in FIG. 11, a plurality of such units 18a and 18b are
assembled in end to end relation with the direction of the helical
turning of the passages in each unit being reversed with respect to
the direction such turning in an adjacent unit, as described in
connection with FIG. 5. Further, as described in connection with
FIG. 5, the transverse axes are angularly disposed. Thus the edges
23a on the lower face of 18a will be angularly displaced with
respect to the edges 23b on the upper face of 18b. Therefore, any
fluid which passes from the channels of 18a to the channels of 18b
will encounter the sharp edges 23b which will exert additional
shear forces to further enhance the operation of the device.
Each of the units of the type described may be made of any suitable
material and may be manufactured by any suitable process. For
example, the unit may be made of a plastic or metal cast in a
lost-wax type of mold, as shown in FIG. 13. Two cylindrical lengths
of casting wax 25 and 26 are pressed together along their lengths
to form the central portion 27 which is to define the central
opening 4 of the resulting unit. The members 25 and 26 are then
twisted with the desired degree of turning of the channels 2 and 3.
The members 25 and 26 are then placed in a cylindrical mold 28
having a bottom 29 and a cylindrical side wall member 30, shown cut
away in FIG. 13. The mold is then filled with the desired plastic
material and caused to set into a solid form by any well known
process. Thereupon, the plastic body is removed from the mold 28
and the casting wax core 25-26 is dissolved or melted out to leave
the unit substantially as shown and described in FIG. 1. Of course,
the unit of FIG. 4 may be made in the same way with the members 25
and 26 twisted in a direction opposite to that in FIG. 13. Where
desired, the concave surfaces 21 and 22, as described in FIGS. 10,
11 and 12 may be machined out by any well known machining
method.
Other methods of making the units may be used. For example, as
shown in FIG. 14, a sheet of metal 32 may be formed with two
longitudinal channels 33 and 34. Thereupon the sheet 32 may have
its ends twisted in opposite directions so that one end wall
occupies the position as shown in the dotted lines at 35 with
respect to the other end shown in full line at 36. Of course, the
metal would have to be sufficiently malleable to accommodate such
twisting. Two members 37 and 38 so formed may then be assembled
with abutting longitudinal edges 3a as shown in FIG. 15. The shapes
shown in FIGS. 1 and 4 might be made by extruding plastic or
malleable metal through an appropriate die while twisitng the
extruded material with respect to such die. Various other methods
of fabricating these units will suggest themselves to those skilled
in the art.
* * * * *