GB2057282A

GB2057282A - Static mixer

Info

Publication number: GB2057282A
Application number: GB8027293A
Authority: GB
Original assignee: MTA MUESZAKI KEMIAI KUTATO INTEZET; Magyar Tudomanyos Akademia Muszaki Kemiai Kutato Intezete
Current assignee: MTA MUESZAKI KEMIAI KUTATO INTEZET; Magyar Tudomanyos Akademia Muszaki Kemiai Kutato Intezete
Priority date: 1979-08-31
Filing date: 1980-08-21
Publication date: 1981-04-01
Also published as: HU179046B; DE3032132A1; GB2057282B; CH653567A5; YU209780A; DE3032132C2

Abstract

A static mixer comprises a casing (1) affording an internal flow passage obstructed by bales (2) arranged to provide a succession of surfaces, in the axial direction of the passage, at different angles ( alpha , beta ) and/or in different planes relative to the axis of the passage so as to sub-divide a flowing stream or streams of material and engender mutual entrainment of one stream by another concomitant with repeated intermingling and resubdivision of the streams in areas of the passage intermediate the baffles. Many different arrangements of various types of baffles are disclosed. The baffles may be constituted by planar or twisted vanes enclosed within the casing (1) or by inwardly projecting protuberances of the casing wall. <IMAGE>

Description

SPECIFICATION Process and apparatus for static stirring This invention relates to a process and an apparatus for static stirring of media flowing in the same direction in a space provided with boundary wall(s) /party/ surrounding said space and divided with separation walls, wherein the rate of flow of one or more media is varied alternately and in opposite senses, while in given periods of the speed variation the media are contacted and by using the flow of media further medium or media is or are induced to floworthe rates of flow thereof are varied.

According to the present invention the apparatus comprises boundarywall/s/surrounding a space containing flowing media and separation wallls/ Ipieces of separation walls positioned in alternately acute and obtuse angles relative to the axis of the apparatus coinciding with the direction of flow dividing the above-mentioned space into sections.

In static stirring the stirring element is stationary and the media flow relative thereto. There are a number of known processes and apparatus realizing static stirring.

In accordance with the United States Patent No.

2.847.649 a helical element is placed in a cylindrical space providing a stirring effect. According to the United States patent No. 2.847.196, a double pulley is used.

In United States patent No.3.286.992 an apparatus is described in which the liquid flowing in a pipe is @orc reed to c. ç dial movement perpendicular to the pipe axis by means of successive oppositaly threade@ helical separation walls dividing the pipe in axial direction into two parts. The edges of the contacting oppositely threaded helical separation wells a.e positioned in angle relative to each other and the set of separation walls divides the pipe always into two channels of equal cross-sections.

According to the United States patent No.

3.871.624 and 3.918.688 both media of different phases flow through channels of equal crosssections created of parallel separation walls of equal lengths and the channels are positioned longitudi wally in the pipe, perpendicularly and ofLet relative to each other. This channel system divides the media continuously into parts and stirs them hereby.

In each process described above the separated space, e.g. pipe in which the media flow are divided into parts of equal cross-sections in the length by means of separation wall/s//positioned in parallel to the pipe axis, and the stirring effect is induced with a forced flowing perpendicular to the axis or witch continuous further division of the media. The separation walls is/are/set up of pieces positioned lengthwise in the pipe, contacting each other.

Said apparatus and stirring processes have disad vantages, as follows: The effective energy used for stirring is relatively small, consequently the length of the pipe and the ratio L/D, i.s. length/diameter will be great, the mixing will be more similar to a "corkscrew"-like flow than to a laminar flow occurring in an empty pipe; however, it is still rather different from the former one. The occurring shearing action is small, therefore, many serially positioned units must be used to achieve the necessary stirring effect. When greater geometric dimensions are wanted, the manufacturing process must be modified to a large extent for producing an insert giving a good static stirring. In a given apparatus the relative input flow-rate of the phases can be varied in a rela-tively small range.Furthermore, especially the apparatus described in United States patent No.

3.871.624 is prone to contamination.

The object ofthe present invention is to provide a process and an apparatus for realizing the said process, wherein especially in case of stirring media consisting of gas-liquid phases a stronger stirring effect can be achieved in a smaller length, and wherein the production of the insert element is simple and less costly.

According to the present invention the process and the apparatus are based on the recognition that the stirring effect can be made greater and the phase contacting surfaces can be significally increased in area by varying the rate of flow of the media flowing in parallel but separated by separation wall/s/; on Lhe one hand, the e media or liquid and/or of lumpy solid phases, on the other hand of gas phase - alternatel" in opposite senses, by varying the angles of the separation walls relative eo the pipe axis akernately to acute and obtuse angles, while the medium/media/ of higher rats of flow is /are/ contacted with the medium medial of smaller rate of flow at or through the discontinuity points of the separation wall/s/.In this simple arrangement the sucking affect of teh medium/media/flowing with higher rate results in a surprisingly significantly increased stirring effect.

Namely, a great local turbulency develops, even if the flow of the medium/media/ is laminar. A further recognition of the present invention is that the suck- ing effect of media flowing with high rate is so signif- icant that surprisingly an increased stirring effect is obsenJed, even if the separation walls/s/ positioned at an angle relative to the pipe axis is/arel made simply of flat plates.

Another recognition is that, surprisingly, by var"- ing slowing of accelerating/ the rate of flow of a single medium alternately in opposite senses, a second medium can be induced to flow or the rate of flow thereof can be varied. On the other hand, it means that the rates of flow of different media can be varied even in a given apparatus in a great range.

According to our recognition, it is sufficient to cause two media to flow in the space surrounded by boundary wall/sl, e.g. in a pipe, provided with a single separation wall consisting of a set of epprop- riately positioned plates, in the way that the rate of flow of the medium relative to the second medium increases or decreases alternately, and said medium is contacted with said second medium at or through the discontinuity points of the set of successively placed plates.

In accordance furthermore with our recognition, said advantageous effect can be achieved also when the boundary wall/s/are/not the one/s/ which is larel straight, and the separation walls are not positioned alternately at acute and obtuse angles relative to the longitudinal axis, but on the contrary, the separation walls are positioned in a straight line and the boundary wall/s/ is larel provided with vari ous notches.

The he process according to the present invention consists essentially of the steps, as follows: in a space surrounded with boundary wall/s/and separated with at least one separation well, the rates of flow of one or more media flowing in parallel and in the same direction are varied alternately in opposite senses, while in given periods of the speed varia tions at least two media Bf owing in space sections divided with separation wall/el are contacted and, in a given case, one or more media is or are induced to flow by flowing further one or more media, or the rate and/or the direction of the @e flow is or are varied.

In a preferred embodiment of the process according to t the present invention, in one or more media at least during a part of the alternately opposite speed variation a flow deviating from the he main flow direction along the a:'ie, in the limit apprn"imately perpendicular thereto, is induced.

In a preferred embodiment of the process according to the present invention the flow deviating from the main flow direction along the aris, in the limit approximately perpendicular thereto, is induced at the end of and/or after the alternately opposite speed variation.

Resides the main flow direction, the deviating and in the limit approximately perpendicular radial flow compsnert can be induced in such a way that the bend or curvature of the separation wall according to the present invention induces a radially forced flow.

In this way in a preferred embodiment of the process according to the present invention, the media are forced into a flow deviating from the main flow direction and, in the limit, perpendicular flow by means of the bend of the separation wall dividing the space into sections.

in the process according to the present invention the media are contacted at orthtough the discon tinuity of the separation wall which separates said media. In order to achieve an increased stirring effect, always a medium flowing at higher rate is contacted with one or more media flowing at lower rate, but between the medium flowing at higher rate and the medium flowing at lower rate a contact can be effected in any period of the speed variation /acceleration or slowing douJn/. In a preferred embodiment of the process according rdin g to the present invention, in the periods of the speed variation the media are contacted by interrupting the continuity of the separation walls dividing the space into sections.

The contact between the media can be effected not only with interrupting the separation wall, but e.g. by means of a perforation or screen wall, etc. made on the separation wall. In a preferred embodiment of the process according to the present invention the media are therefore contacted in the periods of the speed variation through a screen wall.

The increased stirring effect achieved by the process according to the present invention can be further increased, when simultaneously with the contacting of the media by interrupting the continuity of the separation wall, the given medium is also divided into parts by means of the edge of said separation wall opposite to the flow. With this measurement a given medium can be divided into parts ate given point going on in the flow direction.

The media flowing in parallel can be divided into parts at the same given point, although in the various parallel-flowing media the division into parts can be effected at different points shifted in the flow direction. Also, in a preferred embodiment of the process according to the present invention the media separated by means of separation wall/s/and flowing in parallel are divided into parts simultaneously or shifted in the flow direction at the discontinuity of the separation walls by means of the edges opposite to the flow direction of the separation well In another preferred embodiment of the process according to the present invention the parallei-flowing media are divided into parts after the discon tinuity of the separation wall/s/ by means of turning the edge/s/ the continuation of the separation wall/s/ being opposite to the flow in a given angle relative to the preceding separation wall end.

The apparatus according to the present invention is based on that the apparatus comprising walls around the longitudinal axis comprises separation walls which include at least partly alternately acute or obtuse angles with the longitudinal axis and/or with some predetermined plane/a-b/laid across the longitudinal axis or with the boundary wall/s/ around the longitudinal axis, comprises piece/s/of separation wall/s/, and spaces consisting of at least some alternately expanding or contracting space sections surrounded by boundary walls and separation wall/s/ and in certain cases surrounded bathe boundary wall/s/.

The apparatus according to the present invention is not affected in essentials by the fact that not all of the separation walls include alternately acute or obtuse angles with the longitudinal axis and/or with some predetermined plane/a-b/laid across the longitudinal axis or with the boundary walls around the longitudinal axis, it is sufficient if at least a part of the separation walls include an acute or obtuse angle therewith.

The plane/a-b laid across the longitudinal axis should be predetermined, and at least a part of the separation walls should be positioned alternately ae acute or obtuse angles relative thereto. With the separation walls positioned in the said way, a second plane can be found in general which can be laid across the longitudinal axis, with which the half of the separation walls including an acute or obtuse angle with said plane/a-b/include a right angle, the other half of the separation walls include either always acute angles or always obtuse angles with said second plane.

In a preferred embodiment of the apparatus according to the present invention the separation walls include always equal acture angles or always equal obtuse angles with the longitudinal axis, with the plane/a-b/or with the boundary wall/s/. In another embodiment of the apparatus according to the present invention the acute or obtuse angles may be of different values (magnitudes). The values of the angles may be different in such a way that the successive acute angles or the successive obtuse angles along the longitudinal axis are of different values, but the expression "different values of angles" means as well that the angles between the separa tion wall/s/and/or the boundary wall/s/forming a single contracting or expanding space vary continuously.An embodiment of the apparatus according to the present invention comprises also separation wall/s/including alternately acute or obtuse angles with the longitudinal axis and/or with a predetermined plane/a-b/laid across the longitudinal axis or with the boundary wall/s/ around the longitudinal axis, furthermore, said apparatus comprises separation wall piecelsl.

In a preferred embodiment of the apparatus according to the present invention the separation wall/s/ has /have/ discontinuities.

In a preferred embodiment of the apparatus according to the present invention the discontinuities of the separation wall/s/are perforated holes.

In another embodiment of the apparatus according to the present invention the discontinuities are holes of a screening cloth.

A preferred embodiment of the apparatus according to the present invention comprises separation wall/s/ of helical form including alternately acute or obtuse angles with the longitudinal axis, including continuously varying angles with some predetermined plane/a-b/laid across the longitudinal axis.

Another preferred embodiment of the apparatus according to the present invention comprises oppositely threaded successive helical separation walls.

Another preferred embodiment of the apparatus according to the present invention comprises a few or all of the successive separation walls turned by a given angle on the tail relative to the preceding end.

In a preferred embodiment of the apparatus according to the present invention a part of the separation walls are of form as described before, another part thereof are of self-contained form, hence bounding separated space sections. In an advantageous way said separation walls of selfcontained form intercept the other said separation walls. A preferred embodiment of the apparatus according to the present invention comprises therefore separation walls of self-contained form bounding a contracting or expanding space section, said separation walls intercept separation walls including at least in part alternately acute or obtuse angles with the longitudinal axis and/or with some predetermined plane/a-b/laid across the longitudinal axis or with the boundary walls around the longitudinal axis.

Figures 1-7 show the embodiments of the apparatus according to the present invention in sectional views.

Referring to Figures lie, ib 1 b and ic, a boundary wall 1 of circular section around the vertical longitudinal axis and separation walls 2 are shown, said separation walls 2 include with the longitudinal axis an acute angle a and an obtuse angle p alternating with the direction of arrow AB. In the embodiment of the example a and,3 are complementary angles.The space section I contracts along the longitudinal axis /that is, in the direction of arrow AB/, while simultaneously the space section II expands and the space section III surrounded by boundary wall 1 of circular section is of equal cross-section, the space section IV expands in the direction ofthe longitudinal axis and at the same time the space section V contracts. In this way the space section I and the space sections IV and VII following said space section I and the space sections 11, V and VIII etc. respectively contract and expand alternately, and said space sections 1, IV and VII contract and expand alternately in a similar way.

In a preferred embodiment of the apparatus according to the present invention said space sections 1, IV, VII, etc. contract and expand alternately, while said space sections II, V, VIII, etc. are of equal crosssections. The separation walls 2 in Figure 1 can be regarded as a single separation wall having discontinuities at places 5. In Figure 1 arrow A represents the input point of the first medium, and arrow B represents the input point of the second medium. Arrow AB represents the mixed medium outputting (exiting) from the apparatus.

Referring to Figure 1.a, a section taken up in Figure 1 through C-C is shown, where inside the boundary wall 1 of circular section a single separation wall 2 is placed, and said separation wall 2 divides the space into two parts. In Figure 1.three in angle assembling separation walls 2 are shown which divide the space inside the boundary wall 1 into three space sections. Referring to Figure 1 .c, six separation walls 2 assemble in the axis and thereby the space inside the boundary wall 1 is divided into six sections.

Referring to Figures 2 and 2a, the longitudinal axis ofthe apparatus is horizontal, said boundary well 1 is of rectangular section, the separation walls 2, 3 and 4 are of different lengths. Said separation wall 3 extends up to said boundary wall 1, thereby providing a side inlet for said phase B. Said separation walls 2 and 4form a single continuous separation wall provided with discontinuities at place 5. In Figure 2 said discontinuity 5 is a hole or a screening cloth, and the angles a and jS are not complementary angles.

Referring to Figure 3.a and 3.b, said separation walls 2 including alternatively bevel or obtuse angles with some plane/a-b/laid across the longitudinal axis are shown. In Figure 3.a the predetermined plane/a-b/is perpendicular to the plane of the figure.

Said separation walls 2 include alternatively bevel or obtuse angles with said plane la-bl, and at the same time include bevel or obtuse angles with the longitudinal axis as well. In Figure 3.b an extreme case is shown for the arrangement of Figure 3.a, wherein an example is shown for the apparatus according to the present invention, where said predetermined plane la-bl may include an arbitrary angle with the plane of the figure, and said separation wells 2 include alternatively bevel or obtuse angles with said plane la-bl. When said plane la-bl is turned in the plane of the figure, half of the separation walls include a right angle, that is, these are perpendicular to this turned plane la-bl.

Referring to Figures 4 and 4a, the separation walls 2 do not include angles, these separation walls 2 are placed in a plane. Said separation walls 2 can also be regarded as a single separation wall 2 provided with discontinuities. On said boundary wall 1, which is in the example of rectangular cross-section, narrowings formed by neckings or notches 6 of arcuate or angled form and by notches or neckings 7 or circular form are provided. In the direction of the flow, said notches form together with said separation wall 2 a contracting, then expanding space. In Figures 5 and 5a an apparatus is shown, wherein two, each other perpendicularly crossing separation walls 2 divide the space into four sections.

Referring to Figures 6 and 6a the separation walls are positioned in a helical form threaded around an axis including angle with the longitudinal axis. In this way said separation walls include continuously varying angles with some predetermined plane la-bl laid across the longitudinal axis. The successive separation walls 2 are threaded oppositely, and each separation wall tail is positioned in a certain angle relative to the preceding separation wall end. The cross-sections of the space formed by the separation walls 2 vary continuously relative to each other.

Referring to Figure 7, separation walls 8 are shown, said separation walls 8 are of self-contained form penetrating through said separation walls 2 positioned alternately at acute or obtuse angles, and said separation walls 8 form contracting or expand ing space sections. Said separation walls 8 are positioned oppositely at obtuse or acute angles with said separation walls 2.

The elements of the apparatus according to the present invention do not move in action. In general at least two media flow through the apparatus; however, these two media may be of the same material in which case there is a difference in one of its physical characteristics /e.g. in temperature/. In the Figures in general two media are shown referred with A and B. The media A and B flow into separate space sections of the apparatus in the direction shown by the arrows, and on the other end of the apparatus a fully mixed medium AB comes out The process and apparatus according to the present invention are explained in the following non limiting examples.

Example 1 Air of temperature 25oC containing ammonia of 4 per cent by volume and ammonia liquid of temperature 20"C and of concentration 0.05 kmol/m3 are fed into the apparatus according to the present invention, under atmospheric pressure. Air containing ammonia of 0.8 percent by volume and aqueous ammonia solution of concentration 0.25 kmol/m3 leave the apparatus.

In the apparatus according to the present invention a quantity 1 of the input aqueous solution is equal to the theoretical value 1 min according to the material balance multiplied by 1.3, the mean motive force is c = 2 100 Pa, and the material transfer factor p, is, in case of a gas flow rate of v = 2 m/s, equal to 1.7 to 1.75 kmol/m2h. The temperature of the output gas is 25"C and the temperature of the output water is 21 C.

Under identical circumstances, on a Raschig ring with charge the input solution is of quantity 1 = 2.17 1 mix, the mean motive force is c = 1 400 P,, the material transfer factorp, in case of a gas flow rate of v = 2 m/s, is 0.9-1 kmol/m2, and the temperature of the output gas is 32"C.

In an apparatus with Sulzer-packing also under identical circumstances 1 = 1 to 6 1min, c = 1700 P, p = 1.2 kmol/m2h,TgasO, = 31-32 C.

In the case of constant solution-gas mixture volume flow, the comparison for values of the absorption factor in case of input concentrations, temperature and pressure identical with the afore-said values, results in the following values: In an apparatus with Raschig ring charge ç = 75 to 76% in an apparatus with Sulzer-packing cp = 84 to 85% in the apparatus according to the present invention cp = 91 to 92% Example 2 Cylinder oils of density ç = 920 to 940 kglm3, of viscosity rl = 17 to 18 kp/mp originating from two or three containers are homogenized in an apparatus according to the invention, e.g. as shown in Figures 1,2 or 4, wherein the arrangement of the separation walls corresponds to e.g.Figures 1.a or 1 .b.

In order to achieve a given homogeneity, in case of stirring media in an empty pipe-line, a given quantity of media requires a power of 5 W by a pipe length of 1 m, in a static stirring apparatus according to the United States patent No. 3.286.992 the power consumption by pipe length of 1 mis between 1 and 1.1 W, while in the apparatus shown in the example the power consumption is 0.7 W/m.

Example 3 In order to manufacture cosmetic creams, a stable emulsion is made of an aqueous solution of viscosity 71 = 1.1 cp, temperature T = 30"C with fatty phase of viscosity 71 = 70 cp, of temperature T = 70"C, and with an additive which is solid at room temperature, and the latter is mixed in at a temperature of 90"C in a molten state. The viscosity of the melt on this temperature is 138 cp.

The emulsification is performed in an apparatus according to the invention shown in e.g. Figures 6 and 6a, the arrangement of the separation walls corresponds to e.g. Figure 1.c. According to the quantitative ratios, in the first, third and fifth sections and in the second, fourth and sixth sections respectively the aqueous and the fatty phases are fed. In order to achieve an emulsion of equal homogeneity and sta bility, in an empty pipe Re = 1000 should be reached, in the apparatus according to the United States patent No.3.871.624, in case of equal pipe length it is sufficient to reach a value of Re = 10 to 20, and finally in the apparatus according to our example a value of Re = 6 to 10 should be reached.

When using a constant Re number of 1000, in contrash to the length of 4 m of an empty pipe, using the apparatus according to the present invention a pipe length of 0.8 to 1 m meets the requirements. The same effect can be achieved by using the apparatus according to the example with 8 to 10 elements, as for example by using the apparatus according to the United States patent No. 3.912.688 with 10 to 12 elements.

In case of a Re value of 1000, the number Nu typical forthe heat-transfer in an empty pipe is Nu = 6to 7, in the known static stirring apparatus Nu = 30, while in the apparatus according to our example Nu = 36 to 40.

Example 4 From 50% aqueous acetone solution, acetone is extracted with chloro-benzene e.g. in the apparatus shown in Figure 3 or 7, applying a rate of flow of 0.1 to 1.3 cm/sec. The concentration of the acetone at the output is 20%.

In a column filled with Raschig rings the value of the material transfer factor is 0.5 to 1.0 cm/sec, in the apparatus according to the example, however, this value is between 2.2 x 10-3 and 5.6 x 10 3 cm/sec.

The latter value can be achieved e.g. in the apparatus shown in Figure 7.

Example 5 In the apparatus according to the present invention shown in Figures 5 and 5a water flows at a rate of flow of 0.5 to 2 m/sec. In the outer jacket, not shown in the figure, steam flows at a rate of 5 to 10 m/sec. In a conventional pipe-in-pipe system a heattransfer factor of K = 200 to 600 Kcal/m2h0C can be achieved, in the known static stirring apparatus values of K = 1000 to 1200 Kcal/m2h0C can be realized, while in the apparatus according to the example K = 1200 to 1500 Kcal/m2h0C can be measured.

By flowing steam in the apparatus and air in the outer jacket on a ribbed heat exchanger, a heat transferfactorof K = lotto 50 Kcal/m2h0C can be achieved, in the known static stirring apparatus a value df K = 80 to 150 Kcal/m2h0C is measured, while in the apparatus according to the example this value is K = 80 to 225 Kcal/m2h0C.

The manner of applying the process and apparatus according to the present invention is made clear with the examples. There are many and various possibilities and areas for using the presented process and apparatus, it is not, of course, restricted to the cases presented in the examples and in the figures.

Our process and apparatus is - even on the basis of the presented data - more advantageous and cheaperthan hitherto known static stirring processes and apparatus. By using these, an increased stirring effect and in connection with this bigger contacting surfaces, an increased heat-transfer and an increased shearing effect can be achieved. Consequently, in order to achieve the same result it is sufficient to use a shorter pipe. In the apparatus no contamination appears on the boundary and separation walls or the measure thereof is much smaller.

Claims

1. A process for the static stirring of media in a space defined by boundary wall(s) divided by at least one separation wall, characterised in that the rate of flow of one or more flowing medium or media, flowing in parallel and in the same direction, is varied alternately in opposite senses, while in given periods of the rate variation at least two media flowing in sections of said space are contacted with each other and in given cases one or more medium or media is or are induced to flow by causing other medium or media to flow, or by varying the rate and/or the direction ofthe flow.

2. A process for the static stirring of media as claimed in claim 1, wherein one or more media, at least during a part of the alternately opposite variation of the rate of flow, is or are induced to flow in a direction deviating from the main flow direction along the axis, in the limit, flow approximately per pendicularly thereto.

3. A process for the static stirring of media as claimed in claim 2, wherein a flow deviating from the main flow direction along the axis, in the limit approximately perpendicularly thereto, is induced at the end of and/or afterthe alternately opposite sensed speed (rate) variation.

4. A process forthe static stirring of media as claimed in claim 2 or 3 wherein the media are forced to flow in deviation from the main flow direction, in the limit approxmately perpendicularly thereto, by means of a bend or curvature of said separation wall dividing the space into sections.

5. A process for the static stirring of media as claimed in any of Claims 1 to 4 wherein the media are contacted in the periods of the speed variation by interrupting the continuity of the separation walls/ dividing the space into sections.

6. A process for the static stirring of media as claimed in any of Claims 1 to 5 wherein the media are contacted in the periods of the speed variation through a screen well.

7. A process for the static stirring of media as claimed in any of Claims 1 to 5 wherein the parallel flowing media separated with separation wall/s/ are divided into parts at the dicontinuities of the separation walls by means of the edge/s/of said separation walilsl opposite to the flow simultaneously or shifted in the direction of the flow.

8. A process for the static stirring of media as claimed in any of Claims 1 to 7 wherein the parallelly flowing media are divided into parts afterthe discontinuities of said separation wall/s/ by turning the edges of the continuation of said separation wall/s/ opposite to the flow by a given angle relative to the preceding separation wall end/s/.

9. An apparatus for realizing the process as claimed in any of Claims 1 to 8 comprising boundary wall/s/around the longitudinal axis and separation wall/s/; the boundary wall/s/ /1/ including at least partly acute or obtuse angles with the longitudinal axis and/or with some predetermined plane extending across the longitudinal axis or with the boundary wall/s/ /1/ around the longitudinal axis, and further including pieces or parts of separation walls and, in given oases, spaces surrounded by boundary walls and consisting of longitudinally at least partly alternately expanding or contracting cross sections.

10. An apparatus as claimed in Claim 9 comprising separation walilsl including varying acute or obtuse angles with the longitudinal axis and/or with some predetermined plane extending across the longitudinal axis or with said boundarywall/s/ around the longitudinal axis, comprises furthermore separation wall members.

11. An apparatus as claimed in Claims 9 or 10 comprising discontinuities in said separation wall or wals.

12. An apparatus as claimed in Claim 11 wherein said discontinuities of said separation wall/s/ are perforated holes.

13. An apparatus as claimed in Claim 11 wherein said discontinuities of said separation wall/s/ are holes of a screening cloth.

14. An apparatus as claimed in any of Claims 9 to 13 comprising separation wall/s/ of helical form including alternately acute and obtuse angles with the longitudinal axis, and including continuously varying angles with a predetermined plane extending across the longitudinal axis.

15. An apparatus as claimed in Claim 14 comprising oppositely threaded successive separation walls.

16. An apparatus as claimed in any of Claims 9 to 11 and 14 to 15, comprising separation walls turned on the tail by a given angle relative to a few or all of the separation wall ends.

17. An apparatus as claimed in any of Claims 9 to 16 comprising in part-contained separation wall/s/ each separating one space section.

18. An apparatus as claimed in Claim 17 comprising self-containing separation walls forming contracting or expanding space sections, said separation walls intercepting separation wall/s/including at least alternately acute or obtuse angles with the longitudinal axis and/or with some predetermined plane extending across the longitudinal axis or with the boundary wall around the longitudinal axis, said separation walls including oppositely to said separations wall/s/ obtuse or acute angles.

19. A process for stirring materials substantially as herein described with reference to and as shown in Figure 1 to Figure 1c, or Figures 2 and 2a or Figure 3a or Figure 3b or Figures 4 and 4a or Figures 5 and 5a or Figures 6 and 6a of the accompanying drawing.

20. Apparatus for stirring materials substantially as herein described with reference to and as shown in Figures 1 to lo, or Figures 2 and 2a, or Figures 3a or 3b or Figures 4 and 4a or Figures 5 and 5a or Figures 6 and 6a of the accompanying drawings.