US3685806A

US3685806A - Method of stirring materials and apparatus therefor

Info

Publication number: US3685806A
Application number: US862744A
Authority: US
Inventors: Fritz Schoppe
Original assignee: Individual
Current assignee: Individual
Priority date: 1968-10-07
Filing date: 1969-10-01
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22
Also published as: DE1801626A1; DE1801626C3; CA918144A; FR2020042A1; GB1280869A; DE1801626B2

Abstract

A method of stirring to mix a liquid material with another material, such as another fluid (liquid or gas) or a finely divided solid, in a container. A circulation of the materials is generated within the container between one container end and the other end of the container, which is at least equal to the diameter of the first end. A circulating force is imparted to the materials at the first end of the container to create a limited throughflow with a helical peripheral component creating a negative pressure at the center of the first end of the container producing an external flow of materials in an outer zone rotating along the wall of the container from the first end to the second end of the container. Near the second end a substantial part of the spin from the external flow at the second end is removed to produce a higher static pressure at the center of the second end than at the center of the first end, to establish an internal laminar flow of materials from the second end to said first end, which is substantially parallel to the external flow and exceeds the maximum diameter of the confined material flow path. Between the oppositely moving inner and outer paths of material flow, an annular elongate zone of turbulence is generated to create efficient mixing of the materials. The disclosure shows several embodiments of a stirring container apparatus to accomplish mixing between parallel zones of oppositely moving material; namely a container having a base at one end, a cover closing the other end, a liquid driving or circulating unit including an impeller within the container at one end, e.g. the base end. The impeller is shaped to cause material flow leaving the impeller to follow a path adjacent the base wall to the adjoining container wall and then along the container wall with a spin or spiralling flow to the other end of the container where vanes remove the spin and the material flow is reversed at the cover end to pass back along the center of the container. The diameter of the cover end is at least equal to and preferably greater than the base end and the length of the interior space of the container exceeds the maximum interior diameter of the container. The container walls between the base and cover should be smooth and either cylindrical or frusto-conical, preferably the latter for most efficient operation.

Description

' 22 Filed:

United States Patent Schoppe [54] METHOD OF STIRRING MATERIALS AND APPARATUS THEREFOR [72] Inventor: Fritz Schoppe, 8026 Ebenhausen/ Isartel Max Ruttgers, Strs. 24,

M sh fl y Oct. 1, 1969 [21] Appl. No.: 862,744

[30] Foreign Application Priority Data Primary Examiner-Jordan Franklin Assistant Examiner--Geo. V. Larkin Attorney-Strauch, Nolan, Neale, Nies & Kurz 5 7] ABSTRACT A method of stirring to mix a liquid material with another material, such as another fluid (liquid or gas) or a finely divided s olid, in a container. A circulation of the materials is generated within the container 0 between one container end and the other end of the "[4s1 Aug. 22, 1972 container, which is at least equal to the diameter of the. first end; A circulating force is imparted to the materials at the first end of the container to create a limited throughflow with a helical peripheral component creating a negative pressure at the center of the first end of the container producing an external flow of materials in an outer zone rotating along the wall of the container from the first end to the second end of the container. Near the second end a substantial part of the spin from the external flow at the second end is removed to produce a higher static pressure at the center of the second end than at the center of the first end, to establish an internal laminar flow of materials from the second end to said first end, which is substantially parallel to the external flow and exceeds the maximum diameter of the confined material flow path. Between the oppositely moving inner and outer paths of material flow, an annular elongate zone of turbulence is generated to create efficient mixing of the materials. The disclosure shows several embodiments of a stirring container apparatus to accomplish mixing between parallel zones of oppositely moving material; namely a container having a base at one end, a cover closing the other end, a liquid driving or circulating unit including an impeller within the container at one end, e.g. the base end. The impeller is shaped to cause material flow leaving the impeller, to follow a path adjacent the base wall to the adjoining container wall and then along the container wall with a spin or v spiralling flow to the other end of the container where vanes remove the spin and the material flow is reversed at the cover end to pass back along thecenter of the container. The diameter of the cover end is at least equal to and preferably greater than the base end and the length of the interior space of the container exceeds the maximum interior diameter of v the container. The container walls between the base and cover should be smooth and either cylindrical or frusto-conical, preferably the latter for most efficient operation.

19 Claims, 9 Drawing Figures PATENTED M1922 I972 SHEET10F3 Fig. I

INVENTOR FRITZ SCHOPPE ATTORN EYS PATENTEDmszz 1972 SHEET 2 [IF 3 INVENTOR FRITZ SCHOPPE ATTORN EYS PATENTED M22 1972 sum 3 or 3 INVENTOR FRITZ SCHOPPE BY f 7.4

ATTORNEYS METHOD OF STIRRING MATERIALS AND APPARATUS THEREFOR Cylindrical stirring apparatus containers are known in which there is situated a stirring tool for mixing a liquid with another substance, and, if desired with the supply and discharge of heat. The stirring tool is driven by a central rotating shaft and has the form of a propeller, or of crossed arms or a similar form suitable for mixing liquids.

Detailed studies, carried out within the course of extensive experiments, of the mixing processes in known stirring apparatus containers have shown that, not only in the case of liquids of low viscosity, but also in the case of liquids of medium or high viscosity, the whirling of the liquid, i.e. the turbulent exchange processes of momentum, matter and heat, have a determining effect even when, in the case of liquids of relatively high viscosity, the final fine mixing is effected only by intermolecular processes, for example diffusion or heat conduction. The method and stirring apparatus can be used to homogenize the water and other chemicals of milk with the fatty materials of cream or to mix the oils and pigments of paints or to mix chemicals for plasticizers as well as mixing many other materials.

Further investigations had the object of finding a direct measure of the effectiveness of a mixing process. It was found that the range of turbulent fluctuation frequencies which arises in a turbulent flow is a direct measure of the mixing performance. By turbulent fluctuation frequencies is meant the following.

In any turbulent flow, there exist large and small vortices. With a given speed of rotation, the large vortices have a low rotational frequency, while the small vortices have a high rotational frequency. If there are many large vortices, the components to be mixed are brought together from a long distance, while the small vortices ensure the final fine mixing. From the viewpoints of measuring technique and mathematics, it is simpler to consider the reciprocal of the vortex diameter, i.e. the whirling frequency. It is therefore obvious that a mixing process proceeds more intensively in proportion as the range of high and low frequencies in the liquid is greater. This range is known as the turbulence spectrum or the range of excited turbulent fluctuation frequencies.

It is also known that this range depends upon the manner in which the turbulence is produced. In. all known stirrers, there are set up, in addition to a rota- ,tion about the axis of the stirrer, rotational movements of the most varied kinds in radial planes. If, for example, the stirrer has the form of a propeller, the propeller will accelerate a liquid stream in an axial direction, for example downwardly. Parts of the liquid consequently flow upwards in the neighborhood of the wall, are reversed inwardly towards the axis of the stirrer at the top and then tend to flow downwards towards the propeller again.

In other stirrer constructions, resistance bodies, for example such as crossed arms, blades or anchor-shaped arms, are moved by the liquid. Beyond these resistance bodies, the flow is detached in known manner and also forms rotating vortices of the most varied forms, which, according to the form of the stirrer, rotate in different planes and may have superimposed upon them other rotational and throughflow motions.

In any case, however, clearly determinable rotating flow elements exist, closer investigations having shown that the velocity distribution in the external regions of the rotating zone corresponds substantially to a potential vortex, while there exist in the interior partly rotational movements having a constant angular velocity,

and partly completely random motions. These zones of rotationgenerally also known as vortices-have only a limited lifetime owing to their flow losses in the internal region and thereafter break up into smaller vortices, whereby they produce the mixing process.

All these flows have like turbulence spectra, assuming comparable dimensions and speeds of flow. More especially, a relatively high Reynolds number is required in order to obtain turbulence at all. As is known, laminar and therefore nonturbulent flow exists below this Reynolds number.- As the Reynolds number increases, the turbulence spectrum initially widens, but thereafter narrows again. At very'high Reynolds numbers, the turbulence spectrum returns towards zero. This fact is also known from the boundarylayer theory.

The aforesaid conditions are always obtained provided that the said rotating individual vortices occur in the flow, and zones of intensive mixing and zones of less intensive mixing are then produced.

The object of the invention is to provide'a method of mixing liquids in a stirring apparatus container,

wherein zones of less intensive mixing are substantially avoided, so that the intensity of the mixing can be considerably increased and the mixing performance thus greatly enhanced.

In accordance with the invention, the aforesaid object is achieved by virtue of the fact that, for producing an external flow rotating along the inside walls of the stirring apparatus container from the first end of the latter to the second end, there is imparted to the material to be mixed, in the region of the first end of the container, a limited throughflow and peripheral component with maximum negative pressure in the center of the first container end, and by virtue of the fact that, for producing a higher static pressure at the center of the second endof the container than at the center of the first end of the container, a substantial part of the spin is extracted from the external flow close to the wall, in the region of the second end of the container, there being set up an internal flow which is substantially parallel to the external flow and which extends over a sufficiently long distance of at least 5 to 6 times and preferably 10 to 12 times the thickness of each individual flow layer in the region of the longitudinal axis of the container, from the second end of the latter to the first end thereof, the velocity of the said internal flow being of equal order of magnitude but of opposite direction to the said external flow, while an elongate tubular zone of intensive turbulence is developed between the external flow closed to the wall and the oppositely flowing central internal flow.

Further advantageous developments of the method of the invention will be apparent from the following description and from the claims.

By means of the method of the invention, there is produced in a stirring apparatus container a very particularly flow pattern, in which there exist completely different conditions from those of flow patterns arising in the known stirring apparatus containers. If it is enthe manner of a short circuit.

sured that as far as possible no flow short-circuits are formed in the flow pattern produced in accordance with the invention, i.e. that each flow actually passes through the wholelength of travel, no rotating individual vortices are developed in a stirring apparatus container operated in accordance with the invention,

the entire surface of separation and thus also produces a hitherto unattained intensivemixing,

The turbulence spectrumobtained by the method of the invention is thus of fundamentally different appearance fromthat obtainedin the operation of known stirring apparatus containers.

It is found that the turbulence of the method of the invention commences at a very much lower critical Reynolds number. This Reynolds number is lower substantially by a'factor. of.25 than in the case of the In accordance with the invention, the rotation of the outside flow should be only just sufficiently strong to.

keep the flow against the wall'by'centrifugal force. If the rotation components were too high in relation to the throughflow component, centrifugal effects would be set up asin a cyclone separator, which would be so great as to cause a separation of matter and not an interrnixing.

On the other hand, in order to cause the opposed flow to take place from the second end of the container to the first end thereof along its axis,there must be made available to this flow in accordance with the in- I vention a pressure gradient such as to ensure that it aforesaid containers. With comparableReynolds numbers, the turbulence spectrum obtained in accordance with the invention, i.e. the range of excited turbulent fluctuation motions, and thus also the specific mixing performance, is about 4 to 6 times greater, depending upon the comparison basis. At higher Reynolds numbers, the turbulence spectrum tends towards zero in the known procedures, but in a procedure according to the invention the turbulence spectrum proceeds asymptotically towards a constant value, The turbulence produced in accordance with theinvention occurs even at'low and medium Reynolds numbers and is largely independent of the Reynolds number provided that a very low critical Reynolds number is exceeded.

' The frequency spectrum produced in accordance with the invention results in an increased momentum exchange and thus'in a greater flow friction. However, since any flow tends to proceed along the path of lower resistance, each of the opposed flow. components would initially exhibit a tendency towards flow shortcircuits. Such flow short-circuits may be avoided in accordance with the invention by applying to the two opposed flows additional forces which are sufficiently high in relation to the local pressure heads.

' Y Such additional forces may most simply be produced in a rotationally symmetrical stirring apparatus container.

For example, in an elongate cylindrical or conical container employed in accordance with the invention, there may be produced a flow close to the wall, which proceeds from the first end to the other, second end, while there exists in the region of the axis of the container an opposed flow which proceeds fromthe second end back to the first end. If a certain rotation,

which is as weak as possible, is imparted to the outside flow in accordance with the invention, it in fact travels from the first container end to the second without flowing to the center, immediately after leaving the, first end of the container, and then back to the said' first end in flows from the second end of the container to the first. This pressure gradient may be produced by extracting the spin to the-greatest possible extentfrorn' the flow component close to the wall by means of a guide device as soon as itreaches the second end of the container. lf this were not done, the flow close to the wall would flow inwardly towards the axis at the second end of the container and would acquire a high peripheral velocity in accordance with the spin theorem. According to Bernoullis theorem, the static pressure would thus decrease, and .this is not desired in accordance with the I invention. On the contrary, in accordancewith the invention, a maximum static pressure mustobtain-at the center of the cross-section at the second end of the a container in order that a pressure gradient may be present from the center of the. second end of the container to the center of the first-mentioned end of the container. f

In order to produce a sufficiently high negative pressure at the center of the cross-section of the first endof the container, it is possible in accordance with the invention to provide at the first end of the container an impeller of the type employed in centrifugal pumps, of which thecentral intake aperture is directed towards the second end of the container. The flow is then thrown radially outwards and directed on to the outside wall of the container in order that it-rnay flow -with a moderate peripheral component towards the second endof the container to form a flow pattern according to the invention. r

lnaccordance with the invention, the impeller at the desired course of the flow in the container by providing 1 it with a relatively large intake aperture, while the out-.

let cross-section 'inthe neighborhood of the wall extends only over a relatively small part ofthe external diameter, because the central return flow directed from the second end of the container to the first end thereof advantageously occupies substantially the inner percent of the diameter of the container, while the flow close to the wall from the first-mentioned end of the container to the other end has a layer thickness of only about 10-20 percent of the diameter of the container.

This is due substantially to the fact that, in the first place, the'cross-section depends on the square of the diameter, and in'the second place to the fact that the velocity profile of the flow close to thewall has a somewhat different form from that ,of the central return flow, the flow close to the wall having a somewhat higher maximum velocity value thanthe return flow.

Independently thereof, however, there is formed between the two flows in accordance with the invention a tubular zone of very intensive turbulence, which fills the whole container with the exception of the boundary layer close to the wall. It is only in the boundary layer close to the wall that no turbulence i.e. i.e., no radially directed flow components are present.

In accordance with the invention, it is advantageous to cover the impeller between the intake cross-section and the outlet cross-section in known manner in order thus to effect a better guiding of the flow.

For increasing the pressure gradient of the central return flow, it is desirable in accordance with the invention to widen the container in the direction from the first end of the container to the second end. Due to this widening, the peripheral velocities decrease in accordance with the spin theorem and the static pressures correspondingly increase. The static pressure at the center of the second end of the container also correspondingly increases, whereby the pressure gradient along the axis of the container, from the second end of the latter to the inlet cross-section of the impeller, is increased. In a container thus constructed and employed in accordance with the invention, the mixing performance per unit volume is about 4-6 times as great as in other stirrers known at present. Moreover, the turbulence commences at substantially lower Reynolds numbers, so that it is possible to produce turbulence in substantially more highly viscous liquids than in known stirring apparatus containers. In addition, in the method of the invention, the turbulence spectra, and thus the flow patterns above a certain, relatively low Reynolds number are no longer dependent upon the latter, and the flow patterns become modular with sufficient accuracy for practical purposes. The invention consequently affords the possibility of removing any desired quantities from liquid stirrers and of accurately predetermining the efficiency of the mixing process, as also the necessary driving energies.

The fact that the tubular turbulence zone produced in accordance with the invention has a more or less strong peripheral component superimposed thereon owing to the general rotation of the liquid has only negligible effect on the efiiciency of the mixing process.

A stirring apparatus container for carrying out the method of the invention, consisting of a conical or even cylindrical container having a base and a cover, as also a driving unit rotating about the base is so constructed in accordance with the invention that the driving unit has the form of an impeller of a centrifugal pump, which impeller is provided with conveyor blades which are so shaped that the flow leaving the impeller is adapted to the form of the base and of the adjoining container wall, while the axial length of the container is greater than its maximum diameter.

As preferred embodiments of the apparatus of this invention there are diagrammatically illustrated in FIGS. 1 to 8 of the drawings a number of advantageous forms of construction of the stirring apparatus container according to the invention, which will hereinafter be more fully described and the particular manner of operation of which will be explained. In the drawings:

FIGS. 1 to 4 are longitudinalsections through four different stirring apparatus containers according to the invention.

FIG. 5 is a longitudinal section through a stirring apparatus container (drawn to a larger scale).

FIG. 6 is a longitudinal section through a further stirring apparatus container,

' FIG. 7 is a cross-section through the stirring apparatus container according to FIG. 6 along the line VIIVII,

FIG. 8 is a cross-section through the stirring apparatus container according to FIG. 6 along the line VIII-VIII, and I FIG. 9 is a longitudinal section through a further different shape of stirring apparatus according to the invention.

In the drawings, corresponding parts of the stirring apparatus containers are i denoted by the same reference numerals.

As is apparent from FIG. 1, a stirring apparatus container according to the invention consists of a conical container 1 having a base 2 and an upper cover 3. Rotating in the neighborhood of the base 2 is a centrifugal pumptype impeller consisting of a supporting shell 4 corresponding to the shape of the base, which shell is rotated by means of a shaft 5 and supports known conveyor blades 6. Situated at the opposite end of the container 1 are fixed guide vanes 7 which extract the twist from the flow. The components to be mixed are supplied through connecting

pipes

8 and 9 which may also serve as air extraction and gas extraction pipes. A discharge duct 10 is employed for emptying.

On rotation of the

impeller

4,5,6, it acts as a centrifugal pump and conveys the flow with a moderate twist along the walls of the container 1 to the opposite end of the container. At this end, the fixed guide vanes 7 extract the spin from the rotating flow, whereby a substantially equal static pressure is set up over the whole cross-section in the region of the guide vanes 7. From here, the impeller sucks in its throughflow along the axis of the container 1, so that two flow components are set up, namely one flow from the region of the center of the guide vanes 7 along the chamber axis to the inlet of the impeller, and a second flow, on which a weak rotation is superimposed, from the outlet of the conveyor blades 6 into the guide vanes 7. This flow pattern according to the invention has in fact theoretically predicted properties of increased specific mixing performance.

FIG. 2 illustrates a second form of construction of the stirring apparatuscontainer according to the invention, wherein the shaft 5 does not extend from the bottom through the base 2, but is introduced into the container from the top through the cover 3. This may af-- ford advantages when solids or other corrosive components may impair the stufling box for the passage of the shaft 5 through the base 2.

FIG. 3 illustrates a further variant of the stirring apparatus container according to the invention, in which there are provided instead of simple radial guide vanes 7, guide vanes having a flow-favoring form, which extend around the ring 11 of packing material in order that an orderly flow may take place around the latter. With such a device, and with an appropriate form of the guide vanes 7 in accordance with the known rules of centrifugal pump construction, additional economies in driving energy may be effected.

FIG. 4 illustrates another form of construction of the container 1, which in this case is not conical, but cylindrical. This has the advantage of simplifying manufac- -ture, but it has the disadvantage that the pressure gradient of the return flow from the guide vanes 7 to the impeller at the opposite end is weaker. The specific mixing performance is also correspondingly lower..

apertures 12 which efiect a certain throughput of liquid through the clearance between the supporting shell 4 and the base 2, which is thereby flushed clear.

In addition, the conveyor blades 6 may be covered by a ring-shaped guide body 13 which imparts to the issuing flow a direction corresponding to the adjoining out side walls and on the other hand directs the axial return flow to the inlet edge of the conveyor blades 6.

vWhen the container is sufficiently filled, it' is immaterial in what position the apparatus is disposed. Thus, it may lie on its side or it may be inverted. The functions of the air extraction ducts, the supply pipes and the discharge pipes are then changed accordingly.

The invention covers all of the constructional features referred to. i

The flow pattern in a stirring apparatus container according to the invention is independent of the Reynolds number, i.e. independent of the-dimensions, the flow velocity and the viscosity of the liquid, provided that the Reynolds number exceeds certain minimum values. The specific mixing performances of small and large apparatus are therefore equal. For this' reason, only relative particulars need be given for opt mum configurations. i

It has proved particularly desirable to make the container .l conical, in which-case the larger diameter of the container 1 is twice as large as the small diameter of the conical container 1, whilethe axial length of the container 1 is 3.5 times the small diameter. This corresponds to a configuration according to FIG. 1. a In the case of a cylindrical construction according to mixing performance is low. On deviation from the op I timum values-of the ratio of length to diameter towards the value 121, the specific mixing performance correspondingly decreases, whilethe energy consumption and the mixing time increase. V

The base 2 and theother end or cover 3 have in the optimum case the form of a segment of a sphere or of a basket-handle or segmental arch. Somewhat less favorable is the shape of a cone, which in the boundary case may degenerate to a flat base, but this is the least favorable from the viewpoint of strength and flow technique.

. The final conceivable configuration in which the base 2 has a largerdiameter thecov er 3, i.e. in which the container 1 has the inverse conicityof that'in FIG. 1, is evenless favorable from the viewpoint-of mixing efficiency than the cylindrical shape according to FIG. 4. In the case of the inverted conicity, the

diameters decrease with increasingdistance fro'm'the I impeller; according to thespin. theorem, the peripheral components of the flow correspondingly increase. Ac-

FIG. 4, which represents the limit case of the conical not well be utilized, because the velocities in that part;

of the container which is at the opposite end to the impeller are low and the mixing thereat is correspondingly lower; t

. 'Whenthe optimum ratio of length to diameter is exceeded, the intensity of the tubular turbulence zone constantly decreases; as theorder of magnitude of the ratio of length to diameter 1:1 is approached, the

throughfiow components form a toroidal vortex ring,

.' the tubularturbulence zone becoming a torus whose cording to Bemoullis theorem, the static pressures thus decrease, and hence the-pressure gradient which drives the return flow is weakened along the axis of the,

container 1 in the direction of the impeller. As. the return flow becomes weaker, the mixing also becomes less efficient. i l

Intermediate forms between the conical form according to FIG. 1 which is most favorable for the'flow,

and the simplified cylindrical form according to FIG. 4

are also conceivable, e.g., assho'wn in FIG. 9 wherein the internal contour 31 is' composed of at least one conical part 32 and one cylindrical part 33, which, in-

volves lower manufacturing cost than a purelyconical container, but the specific'mixing performance of which lies between that of the purely conical form and that of the purely cylindrical form. In. the intermediate form of "FIG. 9 the shaft 34 is shown extending through the cover 35 down to the impeller constituting support shell 36 and impeller vanes 37 located at the base end 38 in a manner like that described for FIG. 2. Other components, such as the pipes 8 and 9', the fixed stationary) guide vanes 7' and the discharge duct 10' are similar in locationgand function. to the corresponding components described for FIGS. 1-4.

FIG. 6. illustrates in greater detail a stirring apparatus container according to the invention which consists of f a conically widening container part 1, a flanged-on lower base portion 2 and an upper cover 3, which is fix-- edly connected to a connecting pipe 8 which extends centrally into the container 1 substantially to the level of the fixed guide vanes 7. The guide vanes 7 consist of radial sheet-metal sections (FIG. 7) which arewelded to aring-shaped body 7 disposed centrally in'the con tainer l and extend as far as and are fixed to the inside wall of the container 1, which extends inwards in pear l shape above the guide vanes and adjoins a centrally situatedcylindrical end portion 14 with a flange 15 for receiving the cover 3. A connecting pipe 9, which may serve as an air extraction and gas extraction pipe, opens into the end portion 14 i There extends into the base portion 2 an blades 6, which are covered by a ring-shaped guide being welded to the conveyor blades.

impeller which consistsof a supporting shell 4 having conveyor The radially outwardly extending conveyor blades 6 are bent over out of their radial direction in scoop-like form in the region of the guide body (FIG. 8). Engaging centrally with the base of the supporting shell 4 is a tubular-shaft 16 which serves for connection of the impeller to a shaft 17, which is adapted to be driven by a motor 19 through gearing (not shown) in a housing 18. The shaft 17 with the tube 16 engaging around it is covered by a cylindrical intermediate housing member 20, which is flanged on the one hand to the gear housing 18 and on the other hand to the container base portion 2. The upper end of housing member 20 is shaped as a stepped flange ring 21 which fits into the container base portion 2 and comprises at its forward end, conically inwardly extending inclined surfaces 22 with packing rings 23. When the apparatus is ready for operation, bevelled shoulders 24 on the rear face of the dished supporting plate are lifted from the inclined surfaces 22. For packing the passage of the shaft 17 through the bottom of the base portion 2, there are provided a packing ring 25 and an adjoining stuffing box 26, which is held in its packing position by an assembly ring 27. The packing ring 25 and a portion of the stuffing box lie between the inside surfaces of the flange ring 21 and the outside surfaces of the tube 16. For removing the packing 25,26, the motor 19 can be downwardly withdrawn with the gearing l8 and the shaft 17. The supporting plate.4 of the impeller thus bears in fluid-tight manner at its shoulders 24 on the packing rings 23 at the inclined surfaces 22 of the flange 21, so that on replacement of the packing 25,26 the liquid need not be drained from the container.

For draining off the liquid, the base portion 2 is provided in its lower region with a branch pipe 28. The guide body 13 may consist of a hollow ring-shaped body.

I claim:

1. A method of mixing a liquid material with another material, such as another liquid, a gas, or a particulate solid, in a container in which the materials are circulated between a first end of the container and a second end of the container, the diameter of the second end being at least equal to the diameter of the first end, comprising: imparting to the materials within the container and at the first container end a limited throughflow with a peripheral spin component and having a maximum negative pressure at the center of the first end of the container so as to produce an outer flow path zone of materials rotating along the inside surface of the wall of the container from the first end to the second end of the container, extracting a substantial part of the spin from the outer zone of flow at the second end providing a substantially straight nonspinning flow to produce a higher static pressure at the center of the second end than said maximum negative pressure at the center of the first end, thereby establishing an inner flow path of materials within said outer zone passing from said second end to said first end which is substantially parallel to the outer zone of flow, the interface between the opposite flow paths creating an annular turbulent elongate zone of mixing of the materials.

2. A method according to claim 1, wherein the inner flow path extends over a sufficiently long distance of at least five times the thickness of each individual flow layer adjacent the longitudinal axis of the container,

- rotating centrifugal-type pump impeller disposed cenand the velocity of said inner flow is of equal order of magnitude but of opposite direction to the velocity of the outer zone of flow.

3. The method according to claim 2, wherein the inner flow extends over a distance of about ten to twelve times the thickness of each individual flow layer in the region of the longitudinal axis of the container.

4. The method according to claim 1,- wherein the diameter of the second container end is greater than the diameter of the first container end and the outer zone of flow of materials moves in a conically widening path from the first end to the second end.

5. A method according to claim 1, wherein material from the inner flow is sucked into the inlet opening of a v cover at itsother end; and a liquid and material driving unit including a rotating impeller means positioned closely adjacent said base end; said impeller means having blade support means and a plurality of radially directed blade means secured to saidblade support means, said blade means having outlet portions disposed in a direction away from said base end and with said support means enabling flow of material leaving said impeller means, when rotating, to flow outward at the base end and directed toward and along the adjoining container wall toward said other' end while providing a rotational component in the flow path along the container wall, .and stationary guide vane means located at said cover end and internally of said container disposed to substantially redirect the rotational component of flow in a direction to extract a substantial part of the rotational component of the flow of materials passing therethrough, the diameter of the wall at the cover end of said container being at least equal to the diameter of the wall at the base end and the axial length of the container exceeding its maximum diameter.

7. Stirring apparatus according to claim 6, said liquid driving unit comprising a shaft extending through said base and drive connected to said impeller means.

8. Stirring apparatus according to claim 6, said liquid driving unit comprising a shaft extending through said cover and drive connected to said impeller means.

9. Stirring apparatus according to claim 6, wherein said guide means includes a plurality of fixed vanes which are radial sheet-metal sections.

10. Stirring apparatus accordingto claim 6, wherein said stationary guide vane means includes a ring-like member and a plurality of fixed guide vanes extending radially from said ring-like member.

11. Stirring apparatus according to claim 6, wherein said impeller means comprises a supporting shell spaced from but closely adjacent said base and'said plurality of blades is fixed to said shell, said shell having aperture means through which liquid may pass to flush out the space between said shell and said base.

12. Stirring apparatus according to claiml 1, said impeller means including a cover guide ring having an inlet opening for said impeller means, said blades being disposed between said cover guide ring and said shell.

13. Stirring apparatus according to claim 6, wherein the diameter of the cover end of said container is greater than the diameter of the base end, and the wall of the container is frusto-conical in shape.

v 14. Stirring apparatus according to claim 13, wherein the diameter of the cover end of said container is approximately twice the diameter of the base end, and the axial length of the container is approximately 1 56 to 2 times the largest diameter of the container.

15. Stirring apparatus according to claim 6, the container is cylindrical and the ratio of its length to its diameter is greater than 1:1;

16. Stirring apparatus according to claim 15, wherein the ratio of the length of the container to its diameter is preferably 1 .4-l .8: l.

17. Stirring apparatus accordingto claim 6, wherein the container base and cover a're'curved to provide a smooth flow path direction change at both ends.

18. Stirring apparatus according to claim 6, wherein 1 UNITED S ATES PATENT OFFICE CERTIFICATE OF CORRECTION.

Patent No. 3,685,806 Dated Aug. 22, 1972 Inventor) Fritz Schoppe It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 27, after "aforesaid" insert tubulence spectrum in the know stirring apparatus Column 5, line 6, change "i.e." (first occurrence) to occurs Column 7, line 51, change "not" to now Column 9, line 31, after "flange" insert rings Signed and sealed this 30th day of January 1973.

(SEAL) Attest:

EDWARD M.FLETCHER, JR. ROBERT GOT'ISCHALK Attesting Officer Commissioner of Patents 0.5, GO ERNMENT PR NTING OFFICE Hi9 0-366-334 UNITED STATES PATENT OEFICE CERTIFICATE OF CORRECTION Patent NO. 3,685,806 Dated August 22', 1972 Inventor(s) Fritz SChOppe it is certified that error appears in the above-identified patentand that said Letters Patent are hereby corrected as shown below:

Column 3, line 27, after "aforesaid", insert turbulence spectrum in the known stirring apparatus Column 5, line 6, change "i.e." (first occurrence) to occurs Column 7', line 51, changef'not" to now Column 9, line Z51, after "flange", insert rings This certificate supersedes Certificate of Correction issued Januar 30, 1973".

Signed and sealedth'islst day of'January 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. Y jRENE D., TEGTMEYER Attesting Officer v Acting Commissioner of Patents USCOMM-DC compeg FORM Po-mso (10-69) a as. eovsnunzm nglygnue d nes =0" o-a e-Jgr,

Claims

1. A method of mixing a liquid material with another material, such aS another liquid, a gas, or a particulate solid, in a container in which the materials are circulated between a first end of the container and a second end of the container, the diameter of the second end being at least equal to the diameter of the first end, comprising: imparting to the materials within the container and at the first container end a limited throughflow with a peripheral spin component and having a maximum negative pressure at the center of the first end of the container so as to produce an outer flow path zone of materials rotating along the inside surface of the wall of the container from the first end to the second end of the container, extracting a substantial part of the spin from the outer zone of flow at the second end providing a substantially straight non-spinning flow to produce a higher static pressure at the center of the second end than said maximum negative pressure at the center of the first end, thereby establishing an inner flow path of materials within said outer zone passing from said second end to said first end which is substantially parallel to the outer zone of flow, the interface between the opposite flow paths creating an annular turbulent elongate zone of mixing of the materials.

2. A method according to claim 1, wherein the inner flow path extends over a sufficiently long distance of at least five times the thickness of each individual flow layer adjacent the longitudinal axis of the container, and the velocity of said inner flow is of equal order of magnitude but of opposite direction to the velocity of the outer zone of flow.

4. The method according to claim 1, wherein the diameter of the second container end is greater than the diameter of the first container end and the outer zone of flow of materials moves in a conically widening path from the first end to the second end.

5. A method according to claim 1, wherein material from the inner flow is sucked into the inlet opening of a rotating centrifugal-type pump impeller disposed centrally within said container adjacent said first end, the impeller imparting the limited throughflow and peripheral component to the materials to develop the outer flow of material adjacent the wall of the container.

6. Stirring apparatus for mixing a liquid material with another material such as another liquid, a gas, or a finely divided solid, comprising: a container of circular transverse cross-section having a base at one end and a cover at its other end; and a liquid and material driving unit including a rotating impeller means positioned closely adjacent said base end; said impeller means having blade support means and a plurality of radially directed blade means secured to said blade support means, said blade means having outlet portions disposed in a direction away from said base end and with said support means enabling flow of material leaving said impeller means, when rotating, to flow outward at the base end and directed toward and along the adjoining container wall toward said other end while providing a rotational component in the flow path along the container wall, and stationary guide vane means located at said cover end and internally of said container disposed to substantially redirect the rotational component of flow in a direction to extract a substantial part of the rotational component of the flow of materials passing therethrough, the diameter of the wall at the cover end of said container being at least equal to the diameter of the wall at the base end and the axial length of the container exceeding its maximum diameter.

10. Stirring apparatus according to claim 6, wherein said stationary guide vane means includes a ring-like member and a plurality of fixed guide vanes extending radially from said ring-like member.

11. Stirring apparatus according to claim 6, wherein said impeller means comprises a supporting shell spaced from but closely adjacent said base and said plurality of blades is fixed to said shell, said shell having aperture means through which liquid may pass to flush out the space between said shell and said base.

12. Stirring apparatus according to claim 11, said impeller means including a cover guide ring having an inlet opening for said impeller means, said blades being disposed between said cover guide ring and said shell.

14. Stirring apparatus according to claim 13, wherein the diameter of the cover end of said container is approximately twice the diameter of the base end, and the axial length of the container is approximately 1 1/2 to 2 times the largest diameter of the container.

15. Stirring apparatus according to claim 6, the container is cylindrical and the ratio of its length to its diameter is greater than 1:1.

16. Stirring apparatus according to claim 15, wherein the ratio of the length of the container to its diameter is preferably 1.4-1.8:1.

17. Stirring apparatus according to claim 6, wherein the container base and cover are curved to provide a smooth flow path direction change at both ends.

18. Stirring apparatus according to claim 6, wherein the inner contour of the container comprises at least one conical part and one cylindrical part.

19. Stirring apparatus according to claim 6, wherein said driving unit comprises a rotating centrifugal pump-like impeller located adjacent said base end with its axial inlet positioned substantially coaxial with the longitudinal axis of said container and its radial outlet from its radially directed blades adapted to discharged a spinning flow of materials in an outer annular zone along the container wall from said base end to said cover end.