WO2020153898A1

WO2020153898A1 - Method and apparatus for agitating a fluid

Info

Publication number: WO2020153898A1
Application number: PCT/SE2020/050059
Authority: WO
Inventors: Thomas Jemt
Original assignee: Dolprop Industries Ab
Priority date: 2019-01-24
Filing date: 2020-01-24
Publication date: 2020-07-30

Abstract

Method for agitating fluid in a body (12) of fluid, which method comprises the steps of arranging a fluid agitating device (500) in an operating orientation at least partly submerged in the fluid body (12) and connecting the fluid agitating device (500) to a power supply; and operating the fluid agitating device (500) for agitating the fluid in which the fluid agitating device (500) is at least partly submerged; characterised in that the fluid agitating device (500) is provided with a fluke (507), arranged to be completely submerged in the body (12) of fluid when said fluid agitating device (500) is in said operating orientation, in that the method further comprising using said power supply for imparting a reciprocal movement to the fluke (507) and as a result to set fluid locally surrounding the fluke (507) in motion in a direction perpendicular to the said reciprocal movement direction of the fluke (507). The invention also relates to a fluid agitating device.

Description

Method and apparatus for agitating a fluid

The present invention relates to a method and an apparatus for agitating a fluid, in other words for setting a fluid in motion. In particular, the invention relates to such a method for use at a stationary structure in connection to a body of a fluid to be agitated, as well as a system for stationary installation and such use for agitating such a body of a fluid.

In many circumstances, it is desirable to agitate a fluid in a body of fluid. Such a fluid may be a liquid or a gas.

For instance, such agitation of a water body may be used to prevent ice from forming. This may be the case, for example, in the vicinity of a jetty during the cold season. In other examples, it is desired to agitate water in a dam or similar, in order to prevent the water body in question to be overgrown with algae and seaweed. This may, for instance, be the case in dams at zoos and golf courses.

Furthermore, in many industrial processes, such as in the food, chemical and paper production industries, various fluids may have to be agitated, for avoiding the fluid stand ing still in a space. In such industrial processes, energy efficiency is often important. It may also be desired to minimize turbulent flow of the fluid during such agitation, providing a gentle agitation.

Systems for agitating fluids are already known, however using fountains, jets, propellers etc. Such systems are generally complex, expensive, noisy and/or are prone to get entan gled in growing plants and equipment and/or present security hazards.

The present invention solves these problems, and in particular using a stationary mounted but reciprocating fluke for agitating the fluid in question.

It has previously been described, such as in US 8,684,777, how a dolphin fluke-shaped fin can be used to propel a floating vessel. Such a fin, which may be of different sizes and which may be the more or less the shape of a dolphin fluke, is hence herein denoted a "fluke".

Hence, the invention relates to a method for agitating fluid in a body of fluid, which method comprises the steps of arranging a fluid agitating device in an operating orienta tion at least partly submerged in the fluid body and connecting the fluid agitating device to a power supply; and operating the fluid agitating device for agitating the fluid in which the fluid agitating device is at least partly submerged; which method is characterised in that the fluid agitating device is provided with a fluke, arranged to be completely sub merged in the body of fluid when said fluid agitating device is in said operating orienta tion, in that the method further comprising using said power supply for imparting a reciprocal movement to the fluke and as a result to set fluid locally surrounding the fluke in motion in a direction perpendicular to the said reciprocal movement direction of the fluke.

Furthermore, the invention relates to a fluid agitating device for agitating fluid in a body of fluid, which fluid agitating device is arranged to be provided in an operating orientation at least partly submerged in the fluid body and there, when operated, agitate the fluid in which the fluid agitating device is at least partly submerged, which fluid agitating device comprises a power supply connection, which fluid agitating device is characterised in that the fluid agitating device further comprises a fluke, arranged to be completely submerged in the body of fluid when the fluid agitating device is in said operating orientation, in that the fluid agitating device is arranged to, using a power from power supply connected to said power supply connection, impart a reciprocal movement to the fluke and as a result to set fluid locally surrounding the fluke in motion in a direction perpendicular to the said reciprocal movement direction of the flukes.

In the following, the invention will be described in detail, with reference to exemplifying embodiments of the invention and to the enclosed drawings, wherein:

Figure 1 is a perspective view of a first fluid agitating device according to the invention; Figure 2 is a perspective view of a second fluid agitating device according to the invention; Figure 3 is a perspective view of a third fluid agitating device according to the invention; Figure 4 is a perspective view of a fourth fluid agitating device according to the invention; Figure 5 is a simplified side view of a fluid agitating device according to the invention in an operating orientation; and

Figure 6 is a flow chart illustrating a method according to the present invention.

All Figures share the same two last digits of all three-digit reference numerals for same or corresponding parts.

Hence, in Figures 1-5 different respective exemplifying fluid agitating devices 100; 200; 300; 400; 500 according to the present invention are illustrated, each arranged to perform a method according to the invention, for agitating fluid in a body of fluid 12. Figure 6 illustrates such a method. In the following, the method will be discussed in relation to primarily the embodiment illustrated in Figure 5. All which is said regarding this embodi ment illustrated in Figure 5 is also applicable correspondingly to the embodiments illus trated in Figures 1-4, even if not explicitly stated.

In a first step, the method starts.

In a subsequent step, a fluid agitating device 500 of the said type is arranged in an operat ing orientation, at least partly submerged in the fluid body 12, hence at least partly submerged below a fluid body 12 surface 11. In this step, the said fluid agitating device 500 is also connected to a power supply (not shown), using a power supply connection 509. The power supply may be conventional as such, for instance in the form of a perma nently installed electric mains connection or a battery, such as a solar-charged battery.

In a subsequent step, the fluid agitating device 500 is operated for agitating the fluid in which the fluid agitating device 500 is at least partly submerged. According to the invention, the fluid agitating device 500 is provided with (comprises) a fluke 507, arranged to be completely submerged in the body 12 of fluid when the agitating device 500 is in said operating orientation.

More particularly, according to the invention, the method further comprises using said power supply for imparting a reciprocal movement to the fluke 507, and as a result to set fluid locally surrounding the fluke 507 in question in motion in a direction D1 perpendicu lar to a direction D2 of said reciprocal movement of the fluke 507.

The reciprocal movement direction D2 may be vertical, so that the fluke 507 reciprocally moves upwards and downwards. However, the fluke 507 may also be mounted so that it reciprocally moves horizontally, or in any other direction. In general, a main plane of the fluke 507 will be arranged perpendicularly to the reciprocal movement direction D2, so that the reciprocal movement results in the fluke 507 displacing the fluid in the body 512 locally back and forth along the reciprocal movement direction D2 as a result of said reciprocal movement. In the case in which the direction D2 is the vertical, this means that the fluke 507 lifts and lowers the fluid in the fluid body 512. As a result of this raising and lowering, the fluid as a whole will be propelled horizontally, away from the fluke 507 in the direction Dl.

As a result of said reciprocating movement of the fluke 507, a stream of the fluid in question is hence directed in a stream direction, which in the Figures is the same as the direction Dl and which lies in a fluke plane, associated with the fluke 507, in which the said reciprocating movement of the fluke 507 occurs. It is realized that the said fluid may also be set in motion in other directions, apart from the (stream) direction Dl. However, the "stream direction" relates to a general flow direction of the fluid being set in motion as a result of the said reciprocating movement of the fluke 507. This general fluid stream motion will result in global fluid circulation in a larger part of the body 12 of fluid, such as in substantially the whole body 12, achieving the goals of the invention. In Figure 5, the fluke plane is the plane of the drawing. It is especially noted that the "fluke plane" is not a main plane of the (generally flat) fluke, but rather a plane inscribed by the reciprocal movement of pivot rod 504 during operation.

In a subsequent step, the method ends.

In general, the fluke 507 is propelled by a pivot rod 504 undergoing reciprocating move ments bringing the fluke 507 with it. The fluke 507 may be rigidly connected to the pivot rod 504, or may be pivotable, in the said fluke plane, in relation to the pivot rod 504. This pivotable connection may be spring-loaded.

In particular, the pivotable connection between the reciprocating pivot rod 504 and the fluke 507 may be spring-loaded in a way so that more force is required for pivoting the fluke 507 in relation to the pivot rod 504 in a first angular direction in the fluke plane, as compared to pivoting the fluke 507 in a second, opposite angular direction in the fluke plane.

More particularly, the fluke plane may be oriented so that the said first angular direction pivoting brings the fluke downwards in relation to the pivot rod 504, and so that the said second angular direction pivoting brings the fluke upwards in relation to the pivot rod 504. One example of this is the vertical fluke plane as seen in Figure 5 (and also in Figures 1-4). In this particular example, more force is required to pivot the fluke 507 downwards (at its spring-loaded connection to the pivot rod 504) as compared to pivoting the fluke 507 upwards. This results in that the said reciprocating fluke 507 movement lifts the fluid upwards on each stroke, achieving a very efficient fluid circulation.

In general, the fluke plane may be vertical or at least substantially vertical in said operat ing orientation.

The stream direction may generally be horizontal or at least substantially horizontal in said operating orientation. The fluke 507 may be driven by an electric motor 505, which is powered from said power source via said connection 509. The electric motor 505 may be connected to an eccentric drive means 506, such as a cam wheel, which connects to a link arm 503 in turn being connected to the pivot rod 504 for reciprocally driving the pivot rod 504 as described above. A rigid structure 502 may be provided to fix a different part of the pivot rod 504 so as to achieve said reciprocating movement of the pivot rod 504 when the link arm 503 is driven back and forth by said eccentric drive means 506. This provides a very simple, safe, reliable and sturdy, yet efficient construction. A very simple electric motor may be used, providing cost-efficiency and reliability.

I particular when the fluid is a liquid, the method may comprise providing the electrical motor 505 above the surface 11 of the liquid body 12 of fluid in which the fluid agitating device 400 is partly submerged in said operating orientation. The electrical motor 505 may, in turn, be arranged to impart said reciprocal movement to said fluke 507 via a link arm 503 being connected to a pivot rod 504 on which the fluke 507 is mounted.

The fluid agitating device 500 may be arranged to agitate any fluid in which the fluke 507 is arranged or submerged, such as a gas, for instance air or any industrial processing gas; or a liquid, such as water or any industrially processed liquid.

Particular examples of practical application comprise the agitation of water surrounding a jetty 10 or similar during the cold season, to prevent ice formation; and agitation of water in a small dam, such as at a golf course or fish breeding facility, to prevent fouling and/or for promoting oxygenating of the water.

In some embodiments, the fluke 507 may be provided within a tubular member 510, such as a metal tube. Then, the above discussed stream direction may be defined by said tubular member 510. In other words, as the fluke 507 pivots, it does so in a way so that the fluid surrounding the fluke 507 is set in motion within the tubular member 510, along the tubular member 510, so that a flow (which may be a predominantly laminar flow) forms within the tubular member 510 hence defining said stream direction as a stream direction of a majority of the agitated fluid.

Then, the tubular member 510 may be pivotable in an angular direction perpendicular to the reciprocating movement of the fluke 507, such as in a horizontal plane. As the tubular member 510 is displaced in said angular direction, such as by a separately provided electric motor 411 (see Figure 4), the stream direction may be set or varied as is desired, to provide a broader or suitably directed fluid circulation. The tubular member 510 may also be non-driven, but user adjustable, for offering flexibility as to the current circulation patterns of the fluid.

Alternatively, and as is illustrated in Figures 1-4, the fluke 507 may be freely provided in said body 12 of the fluid in a manner so that the stream direction is defined by the said fluke plane. In Figure 5, the tubular member 510 is drawn using broken lines. This is to show that it may optionally be omitted, in which case the fluke 507 would be freely provided also in Figure 5.

The fluid agitating device 500 also comprises a fastening means 501, such as a metal plate with screw holes, for rigidly fastening the device 500 to a rigid structure, such as the jetty 10, so as to assume said operating orientation of the fluid agitating device 500.

However, in order to increase the reach of the achieved circulation, instead of, or in addition to, the tubular member 510, the present method may also comprise a step in which the fluke plane is reciprocally rotated about an axis, and as a result reciprocally swinging the stream direction back and forth. An exemplifying embodiment of this is illustrated in Figure 4, in which the fluid agitating device 400 comprises a separate recip- rocatingly operating fluke plane swinging electric motor 411, acting on a cog wheel 412 in turn connected to the rigid structure 402 for driving the rigid structure 402 in a rotating, reciprocating manner, back and forth about said axis, which in this case is a main axis of the rigid structure 402. This rigid structure 402 hence forms, or is at least parallel to, an axle which is arranged to rotate about said axis. It is noted that Figure 4 also illustrates the link arm 403; the pivot rod 404; the motor 405; the eccentric means 406; and the fluke 407; as described above.

Hence, the said reciprocal rotation of the said fluke plane may be a reciprocal rotation imparted by the fluid agitating device 400 to an axle connected to the pivot rod 404 to which the fluke 407 is mounted, which axle is vertical or at least substantially vertical in said operating orientation. This may also imply that the link art 403 moves as a result of said fluke plane rotation.

In an optional embodiment the fluid agitating device comprises several axles of said type, as is illustrated as such in Figure 3, and also several flukes. Each of the said axles is con nected to at least a respective one of several flukes comprised in the fluid agitating device and each of the several flukes is arranged to be completely submerged in the body 12 of fluid when the fluid agitating device is in said operating orientation. As has been described above, the fluid agitating device is arranged to, using said power supply, impart a recipro cal movement to each of said several flukes. In this optional embodiment, the said several axles are further interconnected via a link arm power transfer system, in turn arranged to force synchronization between the said several axles of said reciprocal rotation. The link arm power transfer system may be, for instance, a horizontally arranged link arm (not shown in the Figures) arranged to interconnect several of said axles and to be displaced horizontally as a result of each one of the axles rotating, with the result that the reciprocal rotation of all interconnected axles (fluke planes) is synchronized. This way, only one motor for imparting reciprocal axle rotation is required to drive several interconnected axles to reciprocally rotate several fluke planes in synchrony.

As opposed to the embodiment illustrated in Figure 4, which has a separate motor 411 for imparting said reciprocal rotation, the said reciprocal rotation may also achieved using the said electric motor 405, via a separate mechanical gear drive. In this and other cases, the reciprocal movement of the fluke plane in general has a frequency which is at least 10 times smaller than a fluke reciprocation frequency. Figure 1 illustrates a practical example of a fluid agitating device 100 according to the invention, corresponding to the device 500. The device 100 also comprises the fastening means 101; the rigid structure 102; the link arm 103; the pivot rod 104; the motor 105; the eccentric means 106; and the fluke 107.

Turning to Figures 2 and 3, respective fluid agitating devices 200; 300 are shown having more than one respective fluke 207; 307, each such fluke 270; 307 being agitated by a respective pivot rod 204; 304. Each pivot rod 204; 304 is rigidly connected to the fastening means 201; 301 via a structure comprising the rigid structure 202; 302, so that the respec tive pivot rod 204; 304 can be driven via a respective link arm 203; 303 via the motor 205; 305 and eccentric means 206; 306.

As shown in Figure 2, several flukes 207 can be reciprocally driven by one and the same motor 205 and one and the same link arm 203, acting on all fluke 207 pivot rods 204. In Figure 3, several motors 305, with respective eccentric means 306, are used to reciprocally drive one respective fluke 307 each. These two variants can also be combined, so that more than one motor may drive more than one fluke, but so that there are more flukes than motors.

In particular, the method may comprise providing the fluid agitating device 200 with several flukes 207, each of which several flukes 207 is arranged to be completely sub merged in the body 12 of fluid when said agitating device 200 is in said operating orienta tion. Then, the method may further comprise using said power supply for imparting a reciprocal movement to each of said several flukes 207 via a link arm power transfer system (in Figure 2 illustrated by the link arm 203) interconnecting the said several flukes 207 for synchronized reciprocating movement, such as via their respective link arms 203 (as is illustrated in Figure 2).

In particular, the said several flukes 207 may then be vertically arranged one in relation to the other in a liquid fluid in which the fluid agitating device 200 is at least partly sub merged, hence imparting liquid circulation from different depths. For the case of water as the liquid, suitable fluke 507 lengths vary between 0.5 and 2.0 meters, and suitable widths vary between 0.2 and 0.5 meters. Each fluke 507 is preferably made from a flexible material, such as a flexible plastic or rubber material. It may incorpo rate metal inlays, such as made from spring steel material, to increase fluke stiffness locally. In general, each fluke 507 has a stiffness which varies from stiffer to less stiff towards its distal end away from the respective pivot rod 504, causing it to move in a way similar to a dolphin fluke as used for propulsion.

Each fluke 507 may be reciprocally driven at a full cycle frequency of about 0.2 - 2 Hz.

Above, preferred embodiments have been described. However, it is apparent to the skilled person that many modifications can be made to the disclosed embodiments without departing from the basic idea of the invention.

For instance, the fastening means 501 may have any suitable shape or form, and be arranged to be fastened to any type of standard equipment fastening socket on a struc ture onto the device is to be mounted for use.

Everything which has been said about the present method is correspondingly applicable to the present device, and vice versa.

Hence, the invention is not limited to the described embodiments, but can be varied within the scope of the enclosed claims.

Claims

C L A I M S

1. Method for agitating fluid in a body (12) of fluid, which method comprises the steps of

arranging a fluid agitating device (100;200;300;400;500) in an operating ori entation at least partly submerged in the fluid body (12) and connecting the fluid agitating device (100;200;300;400;500) to a power supply; and

operating the fluid agitating device (100;200;300;400;500) for agitating the fluid in which the fluid agitating device (100;200;300;400;500) is at least partly sub merged;

c h a r a c t e r i s e d i n that the fluid agitating device (100;200;300;400;500) is provided with a fluke (107;207;307;407;507), arranged to be completely submerged in the body (12) of fluid when said fluid agitating device (100;200;300;400;500) is in said operating orientation, in that the method further comprising using said power supply for imparting a reciprocal movement to the fluke (107;207;307;407;507) and as a result to set fluid locally surrounding the fluke (107;207;307;407;507) in motion in a direction perpen dicular to the said reciprocal movement direction of the fluke (107;207;307;407;507).

2. Method according to claim 1, c h a r a c t e r i s e d i n that a stream of the fluid, as a result of said reciprocating movement of the fluke (107;207;307;407;507), is directed in a stream direction (Dl) lying in a fluke (107;207;307;407;507) plane in which the said reciprocating movement of the fluke (107;207;307;407;507) occurs.

3. Method according to claim 2, c h a r a c t e r i s e d i n that the fluke (107;207;307;407;507) is provided within a tubular member (510), and in that said stream direction (Dl) is defined by said tubular member (510).

4. Method according to claim 2, c h a r a c t e r i s e d i n that the fluke (107;207;307;407;507) is freely provided in the said body (12) of the fluid in a manner so that the stream direction (Dl) is defined by the said fluke plane.

5. Method according to any one of claims 2-4, c h a r a c t e r i s e d i n that method comprises reciprocally rotating the fluke plane about an axis (102;202;302;402;502), and as a result reciprocally swinging the stream direction (Dl) back and forth.

6. Method according to any one of the preceding claims, c h a r a c t e r i s e d i n that the method comprises providing the fluid agitating device (100;200;300;400;500) with several flukes (107;207;307;407;507), each of which several flukes (107;207;307;407;507) being arranged to be completely submerged in the body (12) of fluid when said agitating device (100;200;300;400;500) is in said operating orientation, and in that the method further comprises using said power supply for imparting a recipro cal movement to each of said several flukes (107;207;307;407;507) via a link arm power transfer system interconnecting the said several flukes (107;207;307;407;507).

7. Method according to any one of the preceding claims, c h a r a c t e r i s e d i n that the fluid is a liquid, and in that the method comprises providing above a liquid surface (11) an electrical motor (105;205;305;405;505) arranged to, using said power source, impart said reciprocal movement to said fluke (107;207;307;407;507) via a link arm (103:203;303;403;503) being connected to a pivot rod (104;204;304;404;504) on which the fluke (107;207;307;407;507) is mounted.

8. Fluid agitating device (100;200;300;400;500) for agitating fluid in a body (12) of fluid, which fluid agitating device (100;200;300;400;500) is arranged to be provided in an operating orientation at least partly submerged in the fluid body (12) and there, when operated, agitate the fluid in which the fluid agitating device (100;200;300;400;500) is at least partly submerged, which fluid agitating device (100;200;300;400;500) comprises a power supply connection (509), c h a r a c t e r i s e d i n that the fluid agitat ing device (100;200;300;400;500) further comprises a fluke (107;207;307;407;507), arranged to be completely submerged in the body (12) of fluid when the fluid agitating device (100;200;300;400;500) is in said operating orientation, in that the fluid agitating device (100;200;300;400;500) is arranged to, using a power from power supply connected to said power supply connection (509), impart a reciprocal movement to the fluke (107;207;307;407;507) and as a result to set fluid locally surrounding the fluke (107;207;307;407;507) in motion in a direction perpendicular to the said reciprocal movement direction of the fluke (107;207;307;407;507).

9. Fluid agitating device (100;200;300;400;500) according to claim 8, c h a r a c t e r i s e d i n that the fluke (107;207;307;407;507) is associated with a fluke plane in which the said reciprocating movement of the fluke (107;207;307;407;507) occurs, as well as a stream direction (Dl) in which a stream of the fluid is directed as a result of said reciprocating movement of the fluke (107;207;307;407;507).

10. Fluid agitating device (100;200;300;400;500) according to claim 9, c h a r a c t e r i s e d i n that the fluke plane is vertical or at least substantially vertical in said operating orientation.

11. Fluid agitating device (100;200;300;400;500) according to claim 9 or 10, c h a r a c t e r i s e d i n that the stream direction (Dl) is horizontal or at least substan tially horizontal in said operating orientation.

12. Fluid agitating device (100;200;300;400;500) according to any one of claims 8-11, c h a r a c t e r i s e d i n that the fluke (107;207;307;407;507) is arranged within a tubular member (510), arranged to define said stream direction (Dl).

13. Fluid agitating device (100;200;300;400;500) according to any one of claims 8-12, c h a r a c t e r i s e d i n that fluid agitating device (100;200;300;400;500) comprises an electric motor (105;205;305;405;505) arranged to be located above a surface (11) of the body (12) of a liquid fluid in which the fluid agitating device (100;200;300;400;500) is partly submerged in said operating orientation, which motor (105;205;305;405;505) is arranged impart said reciprocal movement to the fluke (107;207;307;407;507) via a link arm (105;205;305;405;505) being connected to a pivot rod (104;204;304;404;504) on which the fluke (107;207;307;407;507) is mounted.

14. Fluid agitating device (100;200;300;400;500) according to any one of claims 8-13, c h a r a c t e r i s e d i n that the fluid agitating device (100;200;300;400;500) is also arranged to reciprocally rotate the fluke plane about an axis, and as a result recip rocally swing the stream direction (Dl) back and forth.

15. Fluid agitating device (100;200;300;400;500) according to claim 14, c h a r a c t e r i s e d i n the said reciprocal rotation of the said fluke plane is a reciprocal rotation imparted by the fluid agitating device (100;200;300;400;500) to an axle (102;202;302;402;502) connected to a pivot rod (104;204;304;404;504) to which the fluke (107;207;307;407;507) is mounted, which axle (102;202;302;402;502) is vertical or at least substantially vertical in said operating orientation.

16. Fluid agitating device (100;200;300;400;500) according to claim 15, c h a r a c t e r i s e d i n that the fluid agitating device (100;200;300;400;500) comprises several axles (102;202;302;402;502) of said type, and also several flukes (107;207;307;407;507), each of which axles (102;202;302;402;502) being connected to a respective one of several flukes (107;207;307;407;507) comprised in the fluid agitating device (100;200;300;400;500), each of which several flukes (107;207;307;407;507) is arranged to be completely submerged in the body (12) of fluid when said agitating device (100;200;300;400;500) is in said operating orientation, in that the fluid agitating device (100;200;300;400;500) is further arranged to, using said power supply, impart a reciprocal movement to each of said several flukes (107;207;307;407;507), and in that the said several axles (102;202;302;402;502) are interconnected via a link arm power transfer system in turn arranged to force synchronization between the said several axles (102;202;302;402;502) of said reciprocal rotation.

17. Fluid agitating device (100;200;300;400;500) according to claims 13 and any one of claims 14-16, c h a r a c t e r i s e d i n that the said reciprocal rotation is achieved using the said electric motor (105;205;305;405;505), via a mechanical gear drive.

18. Fluid agitating device (100;200;300;400;500) according to any one of claims 8-17, c h a r a c t e r i s e d i n that the fluid agitating device (100;200;300;400;500) comprises several flukes (107;207;307;407;507), each of which several flukes (107;207;307;407;507) is arranged to be completely submerged in the body (12) of fluid when said agitating device (100;200;300;400;500) is in said operating orientation, and in that the fluid agitating device (100;200;300;400;500) is further arranged to, using said power supply, imparting a reciprocal movement to each of said several flukes (107;207;307;407;507) via a link arm power transfer system interconnecting the said several flukes (107;207;307;407;507).

19. Fluid agitating device (100;200;300;400;500) according to claim 18, c h a r a c t e r i s e d i n that the said several flukes (107;207;307;407;507) are vertically arranged on in relation to the other in the body (12) of liquid fluid in which the fluid agitating device (100;200;300;400;500) is at least partly submerged.