EP0137955A2

EP0137955A2 - Method and apparatus for mixing fluids

Info

Publication number: EP0137955A2
Application number: EP84109688A
Authority: EP
Inventors: John R. Weske
Original assignee: Individual
Current assignee: Individual
Priority date: 1983-08-16
Filing date: 1984-08-14
Publication date: 1985-04-24
Also published as: EP0137955A3

Abstract

Method and apparatus are disclosed which are used to mix two fluids, two gases, or a fluid and a gas. The preferred embodiment is useful primarily for the aeration of water but can be used to mix any gas with a liquid. The method involves creating relative movement between an elongate element and a fluid whereby a low-pressure area will be developed on the lee side of the element. The gas is then admitted to the low-pressure area and bubbles are formed. The element is preferably pointed to form a spike, and the bubbles are moved along the spike by a component of the relative motion toward the tip. When the bubble reaches the tip it will be detached and entrained in the fluid. When a plurality of spikes is used, significant efficiencies are observed. One embodiment employs spikes mounted to a rotating body and other embodiments use arrays of parallel spikes.

Description

Technical Field

This invention relates to the art of mixing fluids; particularly, the art of mixing a gas with a liquid. In the preferred embodiment, the invention relates to the art of aeration of a liquid.

Background Art

Many methods and apparatus are known which are employed for mixing two fluids. Many of these methods involve a process wherein a low pressure area is created in a first fluid, and a second fluid is admitted to the low pressure area to be mixed with the first fluid. In processes which relate to gasification of a fluid, one method employs a venturi to create a pressure lower than atmospheric to thereby pull air into a flowing fluid stream.
One such venturi system is shown in U.S. Patent 3,853,271 (Freshour et al). This system includes a plurality of cup-shaped members. A fluid flows through the central portions of the members, and a low pressure area is developed in the fast-flowing fluid so that air is pulled in from the exterior of the cups to mix with the flowing fluid. Another such venturi system is shown in U.S. Patent 4,017,565 (Muller). This patent shows a system for mixing a gas with a liquid wherein a pump circulates a liquid in a container. The liquid is pumped through a cylindrically symmetric baffle which provides an annular constriction for increasing the velocity of the circulating liquid. This increased velocity creates the venturi effect whereby air from a tube aligned with the axis of the baffle is admitted to the flowing liquid.
It is also known to provide a vortex for pulling air into a fluid. U.S. Patent 4,259,267 (Wang) shows an apparatus wherein a single propeller is located in a fluid beneath a plurality of vertical, cylindrical tubes. As the propeller pulls the fluid through the tubes, a vortex develops in each tube thus entraining gas into the center of each vortex.
It is further known to simply pump air under pressure into a body of fluid. U.S. Patent 3,643,403 shows an apparatus wherein air is pumped to a disperser located in the body of the fluid. An impeller is located above the disperser and circulates fluid so that bubbles which are emitted from the disperser flow downwardly with the fluid flow to thereby increase the time of contact of the bubbles with the fluid. U.S. Patent 2,479,403 shows a system wherein aeration of sewage is effected by the action of a submerged water-jet injector. British Patent 1,484,657 shows a system wherein air is injected under pressure into a downwardly flowing stream so that the contact time of air bubbles with the fluid is increased.
The common faucet aerator is also known wherein flowing water is caused to be turbulent so that air is drawn in by a process similar to the venturi effect. U.S. Patent 4,214,702 (Shams et al) shows such a faucet aerator.
Another aerator, shown in U.S. Patent 2,295,391 (Derden, Jr.) uses a pump to circulate fluid between a container and a chamber containing a gas. The fluid flows through a series of openings into the chamber resulting in a turbulent mixing of the fluid with the gas.
Another aeration apparatus is shown in U.S. Patent 3,591,149 (Auler). This apparatus includes a plurality of blades which rotate about a single vertical axis. The blades are elongated and extend into the fluid so that when the blades are rotated, fluid flows in an upward direction along one side of each blade. The resulting turbulence causes aeration of the fluid.

Summary of the Invention

Apparatus known in the prior art, such as those described above, suffer from several disadvantages. First, they have a low efficiency. That is, a large power input is required to cause a mixing of the air. Efficiency is typically measured in units of kilograms of oxygen transferred per kilowatt hour of input energy. Secondly, the prior art apparatus are complex and require structures which are expensive to produce and to maintain.
The invention is a method and apparatus wherein a plurality of spike-like elements are used to mix two fluid substances, preferably a gas with a flowing liquid, in a highly simple and efficient manner. The spikes are caused to have motion relative to a fluid, and the spike extends at an angle which is transverse to the direction of flow of the fluid. This produces a low-pressure area on the lee, or downstream, side of the spike, and a gas is admitted to this low pressure area. The low pressure area is created since the flow past an immersed blunt body separates from the body and a region of low-speed flow forms immediately downstream of the body. This low-speed region is bounded on both sides by high speed flow. Large fluid shear stresses in the flow cause the pressure on the downstream side of the obstacle to be considerably lower than the free stream static pressure. As the gas is pulled into the low-pressure area, a bubble begins to form. A bubble is formed since the turbulence of the flowing liquid on the lee side of a spike causes the gas-liquid interface to have an irregular curved shape. Surface tension acts to pinch off parts of the gas to create a bubble, and as the bubble forms, it becomes an obstacle to the surrounding flow. Drag forces then act upon the bubble to move it along the spike and to entrain the bubble in the fluid flow. Since the spike is placed at an angle to the flowing liquid, a component of the flow is directed along the spike toward the tip of the spike which extends into the fluid. The bubble is thus pulled along the spike by this component until it reaches the tip of the spike. At this point, the bubble is detached from the spike and becomes entrained in the flowing liquid.
If the flow velocity of the liquid in a downward direction is larger than the upward velocity of the gaseous bubble due to its buoyancy, the bubble will be carried with the flow of the fluid and will dissolve into the liquid. The process is continuous so that a series of bubbles is continuously formed and entrained in the flowing fluid. When the admitted gas is air, about five percent of the oxygen contained in the air is transferred to liquid water. Transfer of oxygen across the air-water interface continues as long as the bubbles are in contact with the fluid and the rate depends upon the relative concentrations. Of course, other constituents of the air bubble also pass across the air-water interface.
The above-described process is very simple and requires very few moving parts. The spike may be placed in a naturally flowing stream, such as in a river or in the outflow of a dam. Alternatively, a pump may be used to circulate the fluid from a stationary pond over the spike to produce aeration. The air introduced by a single spike may be relatively small and, in the preferred embodiment, structures which employ a plurality of spikes are preferred. These structures are easy to produce, are relatively inexpensive and are quite efficient.
In one embodiment, the spikes are provided in parallel rows, and fluid is passed over the spikes. In a second embodiment, the spikes extend outwardly from a central body which is rotated in a stationary fluid.
It is an object of this invention to provide method and apparatus for mixing fluids.
It is a further object of this invention to provide . method and apparatus for mixing a gas with a liquid by the creation of a low pressure area in the liquid whereby gas bubbles are formed and become entrained in a flowing liquid.
It is a further object of this invention to provide method and apparatus for aeration of a flowing liquid wherein a plurality of spikes extend transversely into flow of a liquid, and air is admitted to a low pressure area on the lee side of each spike.

Brief Description of the Drawings

Figure la is a side view illustrating the principle of the invention.
Figure lb is a cross section taken along line lb-lb of figure la.
Figure lc is a plan view of the element shown in figure la.
Figure 2a is a cross section of a first embodiment of the invention.
Figure 2b is a section along line 2b-2b of figure 2a.
Figure 3a is a cross section similar to that shown in figure 2a but showing a different arrangement of spikes.
Figure 3b is a cross section taken along line 3b-3b of figure 3a.
Figure 4a is a cross section of a rotational embodiment of the invention.
Figure 4b is a view taken along line 4b-4b of figure 4a.
Figure 5a is a detail of a rotational embodiment similar to that shown in figure 4a but having a different spike arrangement.
Figure 5b is a plan view of the apparatus shown in figure 5a.
Figure 6 is a side view, having a partially cut-away portion, showing a further modification of the rotational embodiment of the invention.
Figure 7a is a cross section of an embodiment of the invention utilizing a floating structure.
Figure 7b is a view taken along line 7b-7b of figure 7a.
Figure 7c is a cross section taken along line 7c-7c of figure 7a.
Figure 8 is a partially cut away side view of another embodiment of the invention.
Figure 9 is a cross-section of a further embodiment of the invention.
Figure 10 is a cross-section of an embodiment utilizing a cascade of a series of aerators in accordance with the invention.

Detailed Description of the Invention

One basic principle of hydrodynamics on which the invention relies may be described with respect to figure la. A spike 2 is located in a stream of flowing liquid 4. A low pressure develops in the downstream, or lee, portion 6 of the spike 4. A gas (such as air) is drawn into the fluid at the low pressure area 6 since the hydrostatic pressure in the area 6 is less than the pressure of the gaseous region 8 adjacent the flowing liquid 4.
The direction of flow of fluid 4 is indicated by arrow 10 and it will be appreciated that since the spike 2 is transverse to the direction of flow, there will be a component of the flow velocity normal to the spike and a component along the spike. The component of flow normal to the spike causes the development of the low pressure area 6, and the component of the flow along the spike causes the air which has been drawn into the low pressure area to move along the spike. As the air moves along the spike, it forms bubbles 12, and these bubbles are swept off the end of the spike and into the flowing liquid 4. While the bubbles are carried along by the liquid, transfer of the gas which forms the bubble takes place across the gas-liquid interface as dictated by the concentration gradient.
Figure lb shows a cross section of the spike 2 taken along the line lb-lb of figure la. This illustrates how the liquid 4 flows around the spike and creates a low pressure area 6.
A preferred form of the spike is shown in plan view in figure lc. The spike shown there is longer than it is wide, the preferred ratio being about 5:1, and it narrows to a point 14. This preferred shape of the spike 2 allows the bubbles to be easily discharged from the end of the spike. The spike is preferably about one inch in length or longer.
Practical embodiments for employing the above-described principle to gasify fluids are shown in the remaining figures.
Figure 2a shows an embodiment wherein fluid 4 flows downwardly through a channel 16. The channel may be a variety of shapes, but preferably has at least two side walls which are parallel. A first array 18 of spikes is placed on one side of the channel, and a second array 20 is placed on an opposed side of the channel. The spikes extend in a plurality of parallel directions. As the fluid 4 flows through the channel 16, it encounters the first and second arrays of spikes 18, 20 and a low pressure area 6 is developed in the lee of each spike of each array. The spikes extend outwardly from the channel so that they form an angle of 30 to 45 degrees with the direction 10 of the flow of the liquid. This angle is preferably 35 to 36 degrees.
A first manifold 22 allows the passage of gas therethrough, and a passage 24 in the channel 16 allows the manifold 22 to communicate with the lee side of each of the spikes in array 18. A similar manifold 26 is located on the opposed side of the channel 16 and communicates with the lee side of the spikes in the array 20 by way of passage 28. The manifolds 22 and 26 may be connected to a common source of gas.
It will thus be appreciated that as the fluid 4 flows through the channel, gas is drawn through the manifolds 22 and 26, passages 24 and 28, and into the low-pressure areas 6 on the lee side of each spike in the arrays 18 and 20. Bubbles 12 are formed in the manner described above with respect to figure la, and these bubbles are swept off the tips of the spikes and into the flowing liquid 4.
Since the bubbles have buoyancy, they will tend to rise in the fluid 4. The downward velocity of flow of the fluid is preferably greater than the upward velocity of the bubbles whereby the bubbles are carried into the liquid 4. This provides contact between the air in the bubbles and the fluid for a substantial period of time and thus allows the gas to pass through the air-liquid interface and into the fluid 4.
Figure 2b shows a cross section taken along line 2b-2b of figure 2a. The plurality of spikes 2 in each array can be seen from this figure. It is also seen how a plurality of passages 24 and 28 provide communication with each of the spikes so that air is drawn into the lee side of each spike and each spike forms bubbles as described with respect to figure la. The spikes are preferably slightly curved in the cross-section transverse to their length to present a convex face to the upstream side of the flowing liquid, and a concave face to the downstream side. They are preferably flat at their tips.
Figure 3a shows a modification of the apparatus described in figure 2a. The spike arrays used in figure 3a provide a plurality of spikes at different angles to increase the rate of bubble formation. A first array 30 is placed on one side of the channel 16 and a second array 32 is placed on an opposite side. Some of the spikes are located at a first angle with respect to the direction of flow 10 of the liquid and other spikes are located at a different angle. This arrangement provides twice as many spikes as in the embodiment shown in figures 2a and 2b, and the angles at which the spikes extend into the flow are such that efficient operation of the apparatus for each spike array is maintained. That is, the arrays form an angle with the direction of flow of between 30 and 45 degrees.
Figure 3b shows how the spikes 2 are interleaved to provide an increased number of spikes, thus providing increased efficiency.
The flow of fluid 4 may be provided by any known means. For example, a pump may raise a fluid from a tank and direct it through the channel 16. Alternatively, the channel 16 may be placed in a naturally flowing stream, such as an outlet from a dam so that water will fall by the force of gravity through the channel 16 and become aerated.
Figures 4a, 4b, 5a, 5b, and 6 show a rotational embodiment of the invention which employs the principles described above. An axially symmetric body 34 is mounted to a shaft 36 for rotation. The shaft 36 is rotated, for example, by a motor 38. A plurality of spikes 2 is attached to the perimeter of body 34 at equal spacings and extend outwardly therefrom. The spikes also slant downwardly at an angle of about 45 degrees with respect to the axis of rotation. The spikes are curved backwardly with respect to the direction of rotation of the body 34 so that a tangent of the curved spike at any point forms an angle of 30 - 45 degrees with the tangent of a circle through that point and concentric with body 34. As the body 34 rotates, the spikes move with respect to the fluid 4, and the fluid between the spikes begins to rotate in the direction of rotation of the body. This implies that a low pressure area exists on the lee, or concave, side of each spike 2. A collar 40 is mounted for rotation with the body 34 and provides an open channel for gas to be admitted to the lee side of each of the spikes 2. Thus, as the body 34 is rotated, air is drawn in through the collar 40 and passes along each spike where bubbles are formed and dispersed into the fluid 4.
It will be appreciated that the rotational embodiments provide spikes in series, whereas the other embodiments provide spikes in parallel. As the body 34 rotates, liquid is displaced toward the tips of the spikes by centrifugal force. As the pressure on the lee side of the spikes decreases below the pressure in the area within collar 40, gas flows into the lee side of each spike.
Liquid is also.pulled into the spaces between the spikes from above and below the spikes. This creates two toroidal systems of circulation as indicated by arrows C in figure 4a.
Bubbles are formed and are swept into the stream of circulating water until they rise to the surface of the liquid. The gaseous constituents of the bubbles pass through the gas-liquid interface as a function of contact time and relative concentrations.
Tests have shown that the rotational embodiment is capable of producing a reduction in pressure, measured in inches of water, which is approximately equal to the velocity head of the tips of the spikes. For example, in one test a tip velocity of about 4 feet per second produced a pressure reduction of about 3 inches of water.
If the collar.40 is supplied with gas at a pressure higher than atmospheric, the rotor may be immersed in a tank. This would be useful if it were desired to aerate a deep tank by placing the rotor near the bottom of the tank and connecting the collar to a high-pressure hose.
Figure 4b shows a view taken along line 4b-4b of figure 4a. This figure shows how the spikes 2 are curved to provide the angular relationship with respect to the fluid 4 which was described above with respect to figure la: that is, the fluid preferably meets the spike at 30 - 45 degrees. As the body 34 rotates, there will be relative motion between the spikes 2 and the fluid 4, and the low pressure area 6 will develop. Gas will then be drawn in through the collar 40 and into the fluid.
Figure 5a shows a spike rotor wherein two rows of spikes 2 extend from the rotating body 34 at different angles. This doubles the number of spikes mounted to the body 34 and thus increases the efficiency of aeration since the number of sources is doubled without a correspondingly large increase in the required input power.
Figure 5b shows a plan view of the embodiment shown in figure 5a and shows the interleaving of the spikes 2.
Figure 6 shows an embodiment similar to that shown in figure 4a, but wherein an impeller is combined with body 34. The spikes 2 serve to entrain air bubbles into a downwardly flowing stream, and the impeller conveys this stream to a greater depth by adding a downward velocity. This increased downward velocity prolongs the time of contact of the bubbles 12 with the fluid 4 to increase the amount of gas which is dissolved into the fluid 4. An impeller 42 is connected to the shaft 36 below the rotating body 34 so that impeller 42 rotates with body 34. The impeller includes a plurality of impeller blades 44 which receive fluid flow from the spikes 2, and rotating impeller blades 44 causes the fluid 4 and the entrained bubbles 12 to continue their flow downwardly and outwardly after leaving spikes 2. The impeller is advantageous because it is more efficient at only pumping fluid than are the spikes.
Figure 7a shows another practical embodiment of the invention. This embodiment is useful for aeration of a pond, and it employs a floating structure 46. A first cylindrical duct 48 is supported by flotation elements 50 which causes the entire structure 46 to float. A motor 52 is secured to a mount 54 which is in turn secured to the duct 48 and flotation elements 50 so that it rigidly supports motor 52. A shaft 56 extends downwardly from the motor 52 and is connected to a pump impeller 58. A second duct 60 is attached to the floatation structure and extends downwardly from the pump impeller to direct fluid 4 from the lake or pond to the impeller 58. The cylindrical duct 48 is surrounded by a third duct 62, and the upper edge of duct 48 is below an upper edge of the duct 62. When the motor 52 is activated, the pump impeller 58 draws water in through the duct 60 and creates a body of water 64 which has an upper surface 66 which is above the upper surface 68 of the pond 4.
Between the duct 48 and the duct 62 is a channel 70 through which fluid falls due to the fact that upper surface 66 is above upper surface 68.
A plurality of spike arrays 72 are located in the channel 70 to cause aeration in accordance with the principles described above in connection with figure la. Tubes 74 provide an air channel to supply the spike arrays 72 with air.
Figure 7b shows a view taken along line 7b-7b of figure 7a and the spike arrays 72 are more clearly visible in this figure. Also, a manifold 76 connected to tubes 72 is more clearly shown. This manifold 76 may be formed as a part of duct 62 or may be a separate element.
Figure 7c is a cross section taken along line 7c-7c of figure 7a and shows how the spike arrays 72 are arranged. Each of the spike arrays 72 comprises a plurality of spikes 2 which are similar to those described above with respect to the other embodiments. The spikes are attached to peaked manifolds 78 which communicate with manifold 76. Each manifold 78 is mounted to a channel-defining plate 79 which extends between ducts 48 and 62. Passages 80 permit the interiors of the manifolds 78 to communicate with the low pressure areas on the lee side of the spikes 2 whereby air will be drawn in through the tubes 74, the manifold 76, the manifold 78, and into the flowing fluid 4. Bubbles 12 are formed and are dispersed into the fluid 4 for gasification or aeration of the fluid.
The embodiment shown in figures 7a through 7c may float in a pond and may be anchored to the floor of the pond or to the shore.
Figure 8 shows an embodiment which is adapted to be mounted in a body of liquid 4. This embodiment employs a motor 80 to drive a shaft 82 which, in turn, rotates a pump impeller 84. An inner cylindrical body 86 has a shaft 82 passing therethrough. An outer cylindrical body 88 surrounds the body 86 and is rotationally fixed thereto to form an annular channel 90 between the inner and outer bodies. A first conical array 92 of spikes is connected to an inner surface outer body 88 and a second conical array 94 of spikes is connected to an outer surface of the inner body 86. The arrays preferably extend completely along the annular channel 90.
As the impeller 84 rotates, fluid is pulled through the channel 90 by the impeller blades 96. The fluid flows through the channel 90 and a low pressure area is developed on the lee side of each of the spikes of the arrays 92 and 94. Tubes 98 are attached to outer body 88 and communicate with a manifold 100 which is shown integral with the outer body. The manifold may be separate from the body. Manifold 100 is located in the upper edge of the outer body 88 and a plurality of passages 102 communicate with the lee side of each of the spikes in the array 92 so that as fluid flows through the channel 90, air is drawn in through the tubes 98 and is mixed with the fluid 4. Tubes 104 communicate with the interior of inner cylindrical body 86 and a plurality of passages 106 allow air which is drawn in through the tubes 104 to communicate with the lee side of each of the spikes in array 94.
While the details regarding the means for securing the apparatus of figure 8 in the liquid and for mounting the motor 80 have not been shown, those of ordinary skill in the art will appreciate that many known techniques will accomplish this. The embodiment shown in figure 8 has many advantages in that the impeller is quite-efficient, and since it is located at some depth, the bubbles 12 have a prolonged contact time with the fluid 4 before they rise to the surface of liquid 4. The bottom surface of the impeller forms a cavity and, it has been observed in experiments that air forms under the impeller in this cavity thus reducing friction and increasing efficiency.
Figure 9 shows an embodiment which is useful for a flowing stream. A box 106 is open at a first, upstream end (not shown), and closed at a second, downstream end 108; the direction of flow is shown by the arrow. A channel 110 is formed between an upstanding edge 112 and the downstream end 108 of the box. An outlet channel is formed by portions 109 and 113. The box 106 may rest on the bottom 114 of a stream or may alternatively be secured in some other manner, such as by anchoring the box to the shore of the stream.
The upstanding edge 112 and the downstream end 108 each have a manifold 116 therein which communicates with a tube 118. A first spike array 120 extends outwardly from the upstanding edge 112, and a second spike array 122 extends outwardly from the downstream end 108.
The box 106 is placed in a stream so that it fills with fluid 4 such that the upper surface 124 of the fluid in the box is above the upper surface 126 of the fluid 4 in the river. The hydrostatic head created by this difference in height between surface 124 and surface 126 causes fluid to flow through the channel 110 thus creating low pressure areas on the lee side of the spikes in the arrays 120, 122 and thus drawing air through the tubes 118 and manifolds 116 as described above with respect to the other embodiments. Bubbles 12 are drawn off the spikes 2 in the arrays 120, 122, thus aerating the flowing stream.
Figure 10 shows an embodiment whereby a cascade arrangement permits an efficient use of a natural drop in a stream or the full head created by a pump. A first dam 128 is placed in a flowing stream 4 and a first array of spikes 130 extends outwardly from the dam 128. A manifold is formed along an upstream face of the dam 128 by plate 132 and adjacent portions of dam 128. The spike array 130 communicates with the manifold, and a tube 134 communicates with the manifold to supply fresh air thereto.
A series of these arrangements is provided along the stream, and similar elements have been identified by primed and double primed numbers.
It will be seen that the upper edge of each dam 128, 128' and 128" is arranged so that a hydrostatic head 135 is developed between the surface level of the fluid behind each of the dams and the level downstream of the dam. As fluid flows through a channel between the stream bed and the dam 128, air is pulled in through tube 134 and manifold 132 because of the low pressure area developed on the lee side of the spikes in the arrays. Bubbles 12 are thus formed to cause gasification or aeration of the fluid.
The arrangement shown in figure 10 also illustrates a U-shaped channel formed between the streambed 136 and the lower portion of the dam 128. This arrangement provides increased contact time of the bubbles 12 with the fluid 4 as the fluid flows under the bottom portion 138 of the dam 128. This arrangement is quite efficient since it employs a syphon-like process to draw the fluid along the extended channel between the stream bed and the dam 128. As the air bubbles are conveyed downwardly, work is expended equal to the product of the depth of immersion and the weight of an equal volume of water. When the bubbles rise in the upward part of the channel, some of this work is recovered. This permits prolonged contact time without expenditure of power.
The efficiency of the invention when used as an aerator is estimated to be 3 Kg0_2/KWH for a single stage fixed embodiment and 3.5 Kg0_2/KWH for the rotational embodiment. These estimates are based on test measurements using atmospheric air and a shallow draft. The mean bubble immersion was one-half foot and the specific oxygen input was related to the specific air input by the measured ratio of oxygen uptake to oxygen intake .=0.052.
While the invention has been described with respect to aeration and gasification, it will be apparent to those of ordinary skill in the art that several of the principles described may be employed with respect to mixing of two liquids, or two gases. Other modifications within the scope of the invention will be apparent to those of ordinary skill in the art.

Claims

1. A method for mixing a first fluid with a second fluid comprising providing an array of elongate elements, causing a flow of said first fluid substance across said array such that a low pressure area is formed on a downstream side of at least a plurality of said elongate elements, and admitting said second fluid to said low pressure area whereby said second fluid is mixed with said first fluid.

2. The method of claim 1 wherein each of said elongate elements extends in a direction transverse to a direction of flow of said first fluid.

3. The method of claim 2 wherein said flow includes a component in said transverse direction large enough to cause discrete parts of said second substance to be entrained in said flow of said first fluid.

4. The method of claim 3 wherein said first fluid contains water and said second fluid is gaseous and contains oxygen.

5. The method of claim 3 wherein said elongate elements form an angle of between 30 and 45 degrees with said direction of flow.

6. The method of claim 5 wherein said angle is between 35 and 36 degrees.

7. The method of claim 4 wherein said flow is in a substantially vertical direction and said transverse direction forms an acute angle with said flow.

8. The method of claim 4 wherein said flow is in a circular direction and said transverse direction forms an acute angle with said circular direction.

9. Apparatus for mixing a first fluid with a second fluid comprising a plurality of elongate elements, means for causing relative motion between said elongate elements and said first fluid whereby a plurality of low pressure areas will be developed in said first fluid on one side of each elongate element and means for supplying a second fluid to said one side of each of said elongate elements, whereby said second fluid will be mixed with said first fluid.

10. The apparatus of claim 9 wherein each of a first group of said elongate elements extends outwardly from a base in one of a plurality of first parallel directions and is narrower at its outward tip than at its base.

11. The apparatus of claim 10 wherein said means for causing relative motion comprises a tubular channel, and said elongate elements extend from a first sidewall of said channel toward the interior thereof.

12. The apparatus of claim 11 wherein said first parallel directions form an angle with respect to a direction of flow of said first fluid in the range of 30 to 45 degrees.

13. The apparatus of claim 12 wherein said tubular channel is substantially vertical and said means for supplying comprises a portion of said channel having a plurality of apertures therein.

14. The apparatus of claim 13 wherein each of a second group of elongate elements extends outwardly from a base in one of a plurality of second parallel directions.

15. The apparatus of claim 14 wherein said second group of elements extends outwardly from an opposed sidewall of said channel and said second parallel direction forms an angle with said first parallel direction of between 60 and 90 degrees.

16. The apparatus of claim 14 wherein said second group of elongate elements extends outwardly from said first sidewall and wherein said second parallel directions form an acute angle with said first parallel directions.

17. The apparatus of claim 9 wherein each of said elongate elements is convex to a direction of flow of said first fluid.

18. The apparatus of claim 17 wherein said elongate elements are concave to said one side.

19. The apparatus of claim 9 wherein each of said elongate elements extends outwardly from a body which is adapted to rotate in said first fluid.

20. The apparatus of claim 19 wherein said means for supplying said second fluid is a cylindrical collar mounted to said body, the interior of said collar means communicating with said elongate elements.

21. The apparatus of claim 20 wherein each of said elongate elements extends outwardly and is curved in a direction opposite the direction of rotation.

22. The apparatus of claim 15 further comprising an impeller means mounted for rotation with said body for propelling said first fluid away from said body.

23. The apparatus of claim 20 wherein said collar is adapted to receive a gas under a pressure which is greater than atmospheric pressure.

24. The apparatus of claim 9. wherein said means for causing relative motion comprises an outer duct means which surrounds an inner duct means to form an annular channel therebetween, and wherein said plurality of elongate elements project outwardly into said channel and are adjacent a manifold means for supplying gas to said elongate elements, said manifold extending between said first and second duct means.

25. The apparatus of claim 24 further comprising flotation means for causing said apparatus to float in a body of water and pump means for pumping said water into a reservoir formed by said outer duct so that the upper surface of said water in said reservoir will be above the upper surface of said body of water.

26. The apparatus of claim 24 wherein said manifold has a peaked upper surface.

27. The apparatus of claim 9 comprising an outer body which surrounds an inner body to form an annular channel therebetween, said elongate elements projecting into said channel from said first and second bodies.

28. The apparatus of claim 27 comprising an impeller for causing flow of said first fluid through said channel.

29. The apparatus of claim 9 comprising a container means for providing a reservoir and having sidewalls and an end wall extending between adjacent ends of said sidewalls, channel means forming a channel adjacent said endwall, wherein said elongate elements extend into said channel, whereby said container means may be placed in a flowing stream and said sidewalls and end wall will enclose a reservoir having an upper surface above the upper surface of said stream.

30. The apparatus of claim 9 further comprising dam means for restricting flow of a stream and forming an outflow channel, said elongate elements extending from said dam means into said channel.

31. The apparatus of claim 9 comprising a U-shaped channel through which said first fluid flows, said elongate elements being located in an inlet of said channel and the outlet of said channel being below said inlet.

32. Apparatus for mixing a gas with a liquid comprising means for establishing relative movement between said liquid and an elongate element whereby a low-pressure area will be developed on a downstream side of said element, and means for admitting said gas to said low-pressure area.