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.

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.

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.