US3402917A

US3402917A - Fluid mixer

Info

Publication number: US3402917A
Application number: US679695A
Authority: US
Inventors: Jack A Van Ingen; John C Mcfall
Original assignee: Eastman Kodak Co
Current assignee: Eastman Kodak Co
Priority date: 1967-11-01
Filing date: 1967-11-01
Publication date: 1968-09-24
Anticipated expiration: 1985-09-24
Also published as: FR1590326A; DE1805059A1; GB1244625A

Description

Sept. 24, 1968 J. A. VAN INGEN ETAL FLUID MIXER Filed NOV. 1, 1967 JOHN C M FALL JACK A. V 'UNGEN INVENTORS A onrs United States Patent 3,402,917 FLUID MIXER Jack A. Van Ingen, Webster, and John C. McFall, Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed Nov. 1, 1967, Ser. No. 679,695

11 Claims. (Cl. 259-7) ABSTRACT OF THE DISCLOSURE A fluid mixer which blends two or more viscous fluids without substantial hold-up time in the mixing chamber having an impeller with at least two axially spaced blades. At least one stationary blade extends radially inwardly from the mixing chamber housing bet-Ween the blades of the impeller. Each of the impeller blades has a pitch which varies from near the axis of the impeller to the outer tip of the blade.

Background of the invention Many processes require the intimate and complete mixing of two or more materials and many types of mixing apparatus have been devised in order to accomplish the specific requirements of various processes. It is known that, in mixing together fluids of high viscosity, it is desirable to create high. shear forces within the fluids in order to overcome their viscous nature and permit intimate mixing. Normally, the process of mix-ing together two or more viscous fluids has utilized a mixer incorporating screw-type blades, paddles, pairs of meshing gears rotating in a housing, or one of many other forms of agitators well known in the art.

Mixing apparatus of the prior art includes the batchtype wherein a selectedquantity ofthe various fluids to be mixedare introduced into a large mixing chamber and the mixer agitator is operated until the desired degreeof mixing is achieved. Other forms of mixers include the in-line type, wherein only a very small volume of fluid is contained in the mixer at any one time and .the fluid is constantly discharged therefrom so that there is little or nohold-up time of the mixed fluids within the mixingchamber. Each of these types of mixing operations have their respective advantages and disadvantages.

Batch-type mixers, having relatively low speeds and extended mixing times, are employed when complete mixing of the components is necessary with very little probability of entraining air in the fluid. However, many processes cannot employ such a batch-type mixing operation due to the fact that various characteristics of the mixed fluid change after the components are combined so that prolonged hold-up in a mixing chamber undesirably changes the characteristics of the mixed fluid. Examples of such systems are those utilizing chemical reactions wherein the reaction commences as soon as the elements are brought together and the mixed fluid proceeds to lose its eflicieucy or desirable characteristics with prolonged hold-up.

In-line mixers are used in systems such as the foregoing in an attempt to overcome the problems of extended fluid hold-up in the mixing chamber. Such in-line mixers maybe either of the pump type, or of the fixed orifice type wherein the fluids are passed through an orifice to an expansion chamber. In pump type in-line mixers, problems are encountered ,at high operation speeds due to the fact that cavitation of the fluid results at the pump agitator. In many operations such cavitation is intolerable due to the fact that entrained air is introduced into the fluid which may later negatively affect the quality of the final product. In an attempt to utilize pump-type mixers at high production rates, defbub'bling apparatus has been emice ployed between the outlet of the mixer and the point of fluid application. However, the de-bubbling apparatus generally introduces a substantial hold-up time to the fluid, resulting in the characteristic change problems noted above.

Orifice-type mixers are generally subject to the same problems as the pump-type mixers, with the additional consideration that high throughputs result in excessively high pressure drops and the problems associated therewith.

As a result, it has become increasingly apparent that a mixer capable of thoroughly mixing viscous fluids without introducing entraining air therein and which can be disposed in the system just prior to the utilization of the mixed fluid would be extremely desirable.

Summary of the invention Accordingly, the present invention provides an in-line mixer which can thoroughly mix two or more viscous liquids at substantially greater production rates than has been heretofore possible without generating bubbles or entraining gas in the fluids. Furthermore, the present invention provides a mixer which will thoroughly mix the viscous fluids without requiring a substantially hold-up time in the mixer whereby the fluids can be quickly used after the initial mixing.

More specifically, the present invention provides a mixer comprising a substantially cylindrical housing having an inlet opening substantially radially therein. An outlet from the housing is angularly displaced about the periphery of the mixer housing from the inlet. An impeller is disposed coaxially within the housing and has at least two axially spaced blades, each of which have a pitch which varies from the axis of the impeller to the outer tip of the blade. At least one stationary blade is disposed within the mixer housing and extends inwardly from the inner surface thereof between the axially spaced blades of the impeller.

Furthermore, the mixer of the present invention is provided with an impeller having at least two sets of blades, with one set of blades being axially spaced from the other set, and with the roots of all of the impeller blades lying in a common diametral plane of the impeller.

Moreover, the mixer of the present invention is arranged so that the tips of one set of impeller blades lead the roots thereof and the tips of the other set of blades trail the roots thereof.

Also, the blades of the impeller of the present invention are arranged so that the pitch of the blades having the leading tips is arranged to direct fluid toward the blades having the trailing tips, and the pitch of the blades having the trailing tips is arranged to direct the fluid away from the blades having the leading tips.

The various features of novelty which characterize the present invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and the specific objects obtained by its use, reference should be had to the accompanying drawings and descriptive matter in which the preferred embodiments of the present invention are illustrated and described.

Brief description of the drawings FIG. 1 is a plan view of a preferred embodiment of the mixer of the present invention, with the upper side thereof removed;

FIG. 2 is an elevation view of the mixer of the present invention taken along line 22 of FIG. 1; and

FIG. 3 is an elevation view of a preferred embodiment of an impeller of the present invention.

Description of the preferred embodiment The preferred embodiment of the present invention is illustrated in FIGS. 1 through 3, and comprises a substantially cylindrical housing having

circular end walls

12 and 14. One end wall, 12 can be provided with an axial opening therethrough and a bearing 16 to accommodate a drive shaft 18. The opposite end 14 of the housing may be boltably connected to the cylindrical housing 10 and may be provided with an O-ring seal 20, in a manner well known in the art. A plurality of inlet connections 22 extend radially inward through the cylinder wall 10 of the housing and an outlet 24 extends radially outward from the cylinder wall of the housing. As shown in FIG. 2, the inlets and outlet are substantially axially central of the housing. The relative spacing of the inlets and the outlet will be more thoroughly described hereinafter.

An impeller, generally indicated at 26, is disposed coaxially within the housing 10 and comprises a central hub 28 arranged to be fixed to the end of the drive shaft 18 in a manner well kown in the art. The impeller is rotated by a power source (not shown) through drive shaft 18 in the direction of arrow 36. The impeller is provided with at least two axially spaced blades and, as shown in the preferred embodiment, two sets of axially spaced blades, 30 and 32, which extend substantially radially outward from the hub to close proximity of the inner surface of the housing 10. In the preferred embodiment each set of blades consists of a pair of blades extending from opposite sides of the hub. More specifically, all of the impeller blades may be arranged so that the roots thereof all lie in a common diametral plane of the hub, substantially as shown. Each of the

blades

30 and 32 curves from the root, or point where it joins the hub 28, to the tip. The blade angle; i.e., the angle produced between a line tangent to the blade tip and a line connecting the blade tip with the axis of the impeller, is between 30 and 45. Each of the leading and trailing surfaces of the

impeller blades

30 and 32 has a pitch which varies from a maximum at the root of the blade to a minimum at the tip of the blade. A plurality of stationary blades 34 are connected to the inner periphery of housing 10 and extend radially inward therefrom between the two pairs of

impeller blades

30 and 32. As will be seen in FIG. 2, the stationary blades 34 are disposed in the space between the two sets of impeller blades.

It has been found that the specific configuration of the impeller blades, in cooperation with the stationary blades extending inwardly from the housing, produce the desired high-speed uniform mixing of viscous fluids without undesirable cavitation. Specifically, the impeller blades of I the preferred embodiment of the present invention are arranged so that the tips of one set of blades 30 lead the roots thereof, and the tips of the other set of blades 32 trail the roots thereof. The leading and trailing surfaces of each blade have a pitch which decreases from the root to the tip. The pitch of the blades having the leading tips 30 is such that fluid is directed therefrom past stationary blades 34 toward the opposite blades 32. At the same time, the pitch of the blades 32 having the trailing tips is arranged to direct fluid away from blades 30.

Furthermore, the end walls, 12 and 14, are arranged to be substantially contiguous to the impeller 26 to minimize the mixing chamber volume, and thus the fluid hold-up time, and also to improve the blending capabilities of the mixer. Moreover, it has been found that less cavitation or air entrainment is encountered with the present mixer when it provides no pumping action to the mixed fluids.

Another feature which is important to the successful operation of the present invention is the arrangement of inlets 22 downstream, in the direction of impeller movement, from the outlet 24. It has been found that it is necessary to locate the inlets with an angle of approximately 270 measured from the outlet in the direction of movement of the impeller. Moreover, it has been found that mixing of fluids having higher viscosities requires that the inlets be placed within a smaller angle than the foregoing.

A specific example of a mixer of the present invention is one having an inside diameter of approximately 4 inches and a depth of 2 inches, with a capacity of approximately 0.5 pound of fluid. The inner surface of the mixing chamber is provided with a Teflonf lining. This mixer, driven at a speed of 1800 rpm. by a one horsepower motor, successfully mixed a multiple component solution having a viscosity of 400 centipoises with substantially no bubble generation at a throughput of 8 to 10 times greater than that possible with gear-type mixers of the prior art.

While the preferred embodiment illustrates two sets of blades each having two blades, it will be appreciated that an impeller having sets of blades, each having three or four blades, could be employed.

The present invention provides a mixer arrangement which generates a combined axial and radial flow pattern wherein the fluid being mixed is forced outward toward the blade tip and the stationary blades with increasing velocity as it moves toward the periphery of the blade. The stationary blades appear to help eliminate cavitation problems and create complex turbulent flow within the mixing fluid.

Accordingly, the present invention provides a mixer capable of blending viscous fluids at relatively high production rates with minimal air entrainment from cavitation of the fluid at the impeller. As a result, the present mixer may be utilized in-line directly before utilization of the mixed fluid with little or no hold-up so that the quality of the mixed fluid is optimized.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A mixer comprising a substantially cylindrical housing, an inlet opening substantially radially into said housing, an outlet angularly displaced from said inlet and opening substantially radially outwardly from said housing, an impeller disposed coaxially within said housing and having at least two axially spaced blades, each of said impeller blades having a pitch varying from near the axis of the impeller to the outer tip of the blade, a stationary blade connected to the inner surface of said housing and extending radially inward between the axially spaced blades of said impeller, and means for rotating said impeller about its axis within said housing.

2. The invention according to claim 1 wherein the inlet and outlet open into said housing between said axially spaced impeller blades.

3. The invention according to claim 1 wherein the impeller comprises at least two sets of blades extending radially therefrom with one set of blades being axially spaced from the other set.

4. The invention according to claim 3 wherein the roots of all impeller blades lie in a common diametral plane of the impeller.

5. The invention according to claim 3 wherein the tips of one set of impeller blades lead the roots thereof and the tips of the other set of blades trail the roots thereof.

6. The invention according to claim 5 wherein the pitch of the blades having leading tips is arranged to direct fluid toward the blades having the trailing tips, and the pitch of the blades having the trailing tips is arranged to direct fluid away from the blades having the leading tips.

7. A mixer comprising a substantially cylindrical housing forming a substantially cylindrical mixing chamber, an impeller disposed coaxially within said'housing and having at least two axially spaced sets of blades, each of said impeller blades having a pitch varying from the axis of the impeller to the outer tip of the blade, an inletopening substantially radially into said housing between th axially spaced blades of said impeller, an outlet angularly displaced from said inlet and opening substantially radially outwardly from said housing between the axially spaced blades of said impeller, a stationary blade connected to the inner surface of said housing and extending radially inward between the axially spaced blades of said impeller, and means for rotating said impeller about its axis within said housing.

8. A mixer comprising a substantially cylindrical housing forming a substantially cylindrical mixing chamber, an impeller disposed coaxially within said housing and comprising a hub having at least two sets of blades radiating therefrom, one set of blades being axially spaced from the other set of blades, the tips of one set of blades leading the roots thereof and the tips of the other set of blades trailing the roots theref, the leading and trailing surfaces of each blade having a pitch which decreases from the root to the tip, the pitch of the blades having the leading tips arranged to direct fluid toward the blades having the trailing tips, and the pitch of the blades having the trailing tips arranged to direct fluid away from the blades having the leading tips, a plurality of inlets opening substantially radially into said housing between the axially spaced blades of said impeller, an outlet angularly displaced from said inlet and opening substantially radially outwardly from said housing between the axially spaced blades of said impeller, a plurality of stationary blades connected to the inner surface of said housing and extending radially inward between the axially spaced sets of blades of said impeller, and means for rotating said impeller about its axis within said housing, said inlets opening through the cylindrical housing into said mixing chamber within an angle of 270 measured from the outlet in the direction of movement of said impeller.

9. The inventtion according to claim 8 wherein the inlets and the outlet are disposed substantially axially centrally of said mixing chamber.

10. The invention according to claim 8 wherein each set of blades consists of a pair of blades each of which extend from opposite sides of the hub.

11. The invention according to claim 10 wherein the roots of all blades lie in a common diametral plane of the hub.

References Cited UNITED STATES PATENTS 2,538,466 1/1951 Marco 2599 WILLIAM I. PRICE, Primary Examiner.

JOHN M. BELL, Assistant Examiner.