Apparatus and method for producing small gas bubbles in liquids Number:7,419,143 from the United States Patent and Trademark Office (PTO) owispatent An apparatus for creating microbubbles of gas in a liquid. A vertical pipe member is adapted to receive a liquid-gas mixture having gas bubbles of larger diameter therein. A series of horizontally-extending apertures are provided to permit the pipe member to expel such liquid-gas mixture radially outwardly from such pipe member. The expelled liquid-gas mixture may contact the sides of a containment vessel. In a refinement of the invention, a specific relationship is further specified between the exit area of the apertures and the interior cross-sectional area of the pipe member, in order to most suitably convert the gas bubbles in such liquid-gas mixture to microbubbles of a desired small size when expelled under pressure from such pipe member via such apertures. A method of converting gas bubbles in such liquid-gas mixture to gas microbubbles is further disclosed.<H producing, Apparatus, Apparatus, and, m, 7419143.html, Patent, pto, 7419143

Title: Apparatus and method for producing small gas bubbles in liquids

Abstract: An apparatus for creating microbubbles of gas in a liquid. A vertical pipe member is adapted to receive a liquid-gas mixture having gas bubbles of larger diameter therein. A series of horizontally-extending apertures are provided to permit the pipe member to expel such liquid-gas mixture radially outwardly from such pipe member. The expelled liquid-gas mixture may contact the sides of a containment vessel. In a refinement of the invention, a specific relationship is further specified between the exit area of the apertures and the interior cross-sectional area of the pipe member, in order to most suitably convert the gas bubbles in such liquid-gas mixture to microbubbles of a desired small size when expelled under pressure from such pipe member via such apertures. A method of converting gas bubbles in such liquid-gas mixture to gas microbubbles is further disclosed.

Patent Number: 7,419,143 Issued on 09/02/2008 to Lee, et al.

Inventors: Lee; Douglas (Calgary, CA), Szilagyi; Dennis Nicholas (Calgary, CA)
Assignee: GLR Solutions Ltd. (Calgary, Alberta, CA)

Appl. No.: 11/882,789

Filed: August 6, 2007

Related U.S. Patent Documents


Application Number	Filing Date	Patent Number	Issue Date
11338784	Jan., 2006	7278630
10795239	Jan., 2007	7159854

Foreign Application Priority Data


Aug 21, 2003 [CA]			2437948
Mar 08, 2004 [CA]			2460123

Current U.S. Class: 261/76 ; 261/115; 261/DIG.75

Current International Class: B01F 3/04 (20060101)

Field of Search: 261/28,29,76,77,115,116,DIG.75

References Cited [Referenced By]

U.S. Patent Documents


4152409	May 1979	Nagao et al.
4313827	February 1982	Ratigan et al.
4735750	April 1988	Damann
4863643	September 1989	Cochran
5015370	May 1991	Fricano
5427693	June 1995	Mausgrover et al.
5961895	October 1999	Sanford
6197206	March 2001	Wasinger
6935624	August 2005	Bellas et al.
7278630	October 2007	Lee et al.
2003/0183584	October 2003	Galatro et al.
2004/0217068	November 2004	Kirby
2005/0077636	April 2005	Bortkevitch et al.

Primary Examiner: Bushey; Scott
Attorney, Agent or Firm: Gowling Lafleur Henderson LLP Horne; D. Doak

Parent Case Text

RELATED APPLICATIONS

This application is a divisional of U.S. Ser. No. 11/338,784 filed Jan. 25, 2006 now U.S. Pat. No. 7,278,630 which is a divisional of U.S. Ser. No. 10/795,239 filed Mar. 9, 2004, published as US 2005/0040548A1, issued on Jan. 9, 2007 under U.S. Pat. No. 7,159,854, claiming priority from CA 2,437,948 filed Aug. 21, 2003 and CA 2,460,123 filed Mar. 8, 2004, and is directed inter alia to subject matter of US publication 2005/0040548A1, which is incorporated herein by reference.

Claims

We claim:

1. An apparatus having means for creating microbubbles in a liquid to permit a selected gas to better react with impurities entrained in said liquid, comprising: means for introducing gas bubbles, the majority of which are of a size greater than 100 microns, into a liquid to form a liquid-gas mixture; elongate, hollow pipe means, substantially symmetrical in cross-section of interior cross-sectional area Ai, positioned substantially vertically, adapted to receive said liquid-gas mixture and supply said liquid-gas mixture under a first pressure to aperture means, said pipe means having plug means situate at a lowermost distal end thereof for preventing egress of liquid-gas mixture vertically downward from said distal end; said aperture means situate on said pipe means and disposed substantially perpendicular to a longitudinal axis of said pipe means and extending from an interior of said pipe means to an exterior of said pipe means, adapted to direct said liquid-gas mixture substantially horizontally outwardly from said pipe means; and said pipe means of uniform wall thickness and having a maximum interior width D.sub.i and a maximum exterior width D.sub.o, having identical moments of inertia about at least two separate axis in a cross-sectional plane through said pipe means; said aperture means comprising at least one or more apertures having a combined exit area A.sub.e; and said combined aperture exit area A.sub.e defined as a function of widths D.sub.i and D.sub.o and said cross-sectional area A.sub.i of said pipe means, wherein A.sub.e is no greater than: A.sub.i.times.D.sub.i/D.sub.o said liquid-gas mixture when directed through said aperture means having said above defined relationship between A.sub.e, A.sub.i, D.sub.i and D.sub.o thereby forming microbubbles in said liquid-gas mixture, the majority of which are of a size less than 100 microns; and wherein said aperture means comprises at least one aperture, and wherein the individual cross-sectional area of each of said at least one aperture is no greater than A.sub.i.times.D.sub.i/2D.sub.o; and wherein said apertures comprise a plurality of horizontally-extending slots in said pipe means.

2. The apparatus as claimed in claim 1, said pipe means having an exterior circumference C, each of said horizontally-extending slots being rectangular and of a horizontal width no greater than said maximum interior width D.sub.i of said pipe means, and each of a vertical depth no greater than A.sub.i/C.

3. The apparatus as claimed in claim 2, comprising a pair of horizontally-extending slots, each of said horizontally-extending rectangular slots of a width substantially equal to said maximum interior width D.sub.i of said pipe means, and of a vertical depth substantially equal to A.sub.i/C.

4. The apparatus as claimed in claim 1, wherein said pipe means comprises a substantially cylindrical pipe member having an exterior circumference C, said maximum interior width D.sub.i equal to an inner diameter of said pipe member, and said maximum exterior width D.sub.o equal to an outer diameter of said pipe member.

5. The apparatus as claimed in claim 4, said pipe having an exterior circumference C, wherein said horizontally-extending slots in said pipe member are rectangular, and each of a vertical depth equal to or less than A.sub.i/C.

6. The apparatus as claimed in claim 5, wherein said horizontally-extending slots each extend to a depth within said pipe member substantially equal to 1/2 D.sub.o, and are of a horizontal width substantially equal to D.sub.o.

7. The apparatus as claimed in claim 1, 2, or 4, further comprising a containment vessel, an upper portion adapted to contain quantities of said gas at a second pressure greater than ambient pressure but less than said first pressure, a lower portion adapted to capture said liquid-gas mixture having microbubbles of gas entrained therein and to permit said microbubbles to react with said entrained impurities; and said second pressure being at least 10 psi greater than said ambient pressure.

Description

FIELD OF THE INVENTION

The present invention relates to an apparatus and method for aeration and purification of liquids, and more particularly to an apparatus and method for producing small gas bubbles in liquids for purification and aeration of said liquids.

BACKGROUND OF THE INVENTION

Entrainment of a gas in a liquid is required in numerous industrial processes, typically for the purposes of reacting the gas with such liquid or materials in such liquid, such as dissolved ions or finely dispersed solids, to cause reaction of such gas with materials therein to cause same to be neutralized by, react with, or precipitate or be filtered out of such liquid.

For example, it is known to bubble ozone through water, to allow the ozone to react and combine with dissolved minerals and/or finely dispersed solids within the water, so as to form solid products which may either precipitate out of the liquid or be filtered from the water, so as to thereby purify the water. The ozone may further react with harmful bacteria or the like in the water so as to render them harmless or odorless.

Where a gas is desired to react with a liquid or finely dispersed solids in such liquids, it is widely known that small bubbles of gas immersed in such liquid will have, for the same volume of gas, a greater surface area and thus a greater liquid/gas interface, than the same volume of gas when such gas exists in larger bubbles.

A large gas/liquid interface is a desirable characteristic in instances where the gas is introduced into a liquid for the purposes of reacting the gas with the liquid or dispersed solids in such liquid, since greater surface area of the gas exposed to such liquid and/or finely dispersed solids in such liquid decreases the time it takes for the gas to react with the liquid or finely dispersed solids within such liquids, thus allowing quicker processing. As well, a lesser amount of gas, and smaller containment vessels, can thus be used, resulting in cost savings.

The benefits, therefore, of introducing or entraining very small bubbles of gas, typically in the range of 50 to 100 microns in diameter, into a liquid for the purposes of increasing the surface area of the gas relative to the liquid (and/or finely dispersed solids in such liquid) are known. Small bubbles of this size are generally referred to in the art as microbubbles. For the purposes hereinafter of this disclosure, microbubbles will be referred to and will be understood as meaning gas bubbles of a diameter in the range of 50 to 100 microns, and preferably 5 to 50 microns.

A number of devices and methods for aerating liquids, typically water, with gas bubbles, are known.

For example, U.S. Pat. No. 2,890,838 teaches a device for filter-separating iron from water. Water is delivered via a pipe 13 to an air aspirator 14, and thereafter such water having air entrained therein is delivered via pipe 16 to the upper portion of a tank 10, where it passes vertically downwardly in the tank 10 to a spray valve 19. At the spray valve 19 the water-air mixture flows outwardly through openings 21 into chamber 22 formed in a cylindrical hollow body 23 mounted on valve 19. The upper end of the body 23 is cone shaped, and contacts the mating lower cone-shaped end 25 of valve body 26. The water-air mixture flows upwardly and outwardly through the cone-shaped opening formed between cone-shaped surfaces 24,25 in the form of a vaporized spray S, as shown in FIGS. 2 & 4 thereof, and mixes with the air in the tank 10 as it strikes the underside 27 of the top 28 of the tank 10, thereby introducing air into the liquid which in turn oxidizes metabolic iron present in the water. Iron precipitates then settles out of solution and down through the water contained in tank 10.

U.S. Pat. No. 5,601,724 and U.S. Pat. No. 5,460,731 teach an apparatus and method, respectively of aerating liquids. FIGS. 1 & 2 of each of '724 and '731 show a venturi air injector 10 used to inject air into water in a conduit 12. Such air-water mixture enters the bottom portion of a tower-like pressure vessel 14, where it is directed upwardly via conduit 30, where it is directed through a cylindrical restriction gap 19 formed between the second end 34 of conduit 30 and the top 18 of vessel 14. The gas, being of lesser density, passes more quickly through the restriction, thereby accelerating the liquid. As the liquid exits the restriction gap 19 it pneumatically hammers against the top 18 of pressure vessel 14. Thereafter the liquid stream, by force of gravity, cascades through the gas in pressure vessel 14 downwardly to further impact plate 35. Thereafter the liquid stream then passes through openings 37 in plate 35 and by force of gravity cascades through the gas in pressure vessel 14 to further impact on liquid at the bottom of the vessel. Thereafter such liquid, having small bubbles of air entrained therein, is removed via a conduit from the bottom of vessel 14.

U.S. Pat. No. 5,096,596 to a "Process and Apparatus for Removal of Mineral Contaminants from Water" teaches a pressurized aeration tank 24 having a tube 26 located within said tank 24 which supplies the tank 24 with raw water, which is introduced to the tank 24 via the tube 26 via a plurality of holes 28 in the tube (ref. col. 2, lines 49-54 and FIGS. 1-7). The tube 24 only supplies "raw water" and not water having air bubbles entrained therein, and is not for the purpose of providing gas microbubbles of a range of 5-50 microns. Most importantly, no relationship regarding the size of the holes 28 in the tube 24 is specified to attempt to attain microbubbles, even if the patent further provided for the raw water to first have bubbles introduced therein.

U.S. Pat. No. 4,556,523 teaches a microbubble injector usable to separate material of different density by flotation, wherein microbubbles of gas are introduced into a chamber 14 containing a liquid mass 16. As may be seen from FIG. 1 of U.S. '523, a gas admixture device 4 receives air through an inlet 6 and ordinary water through an inlet 8. The resulting air-water mixture is supplied by a conduit to the bottom of chamber 14, where it passes through an injector wall 10 via an injector hole 12 to procure a high velocity jet of air water. A deflector wall 18 is disposed over such injector hole, so as to create a narrow gap around the injector hole, which the water/air mixture must pass through. The injector hole is preferably substantially circular, and the height of the passage between the injector and deflector wall at the edge of the injector hole is less than one quarter of the diameter of the injector hole in the injector wall.

Disadvantageously, none of the aforementioned patents teach or disclose any specific design interrelation between the dimensions of the injector holes/parts/or gaps and the conduit outer dimensions which will best produce microbubbles in the liquid.

For example, U.S. '838 simply provides a nut 23 on the end of the valve 24 to adjust the size of the aperture between cone surfaces 24,25 through which the water must pass. No gap dimension is ever specified which best provides bubbles of a desired small size.

Similarly, each of U.S. '724 and '731 simply disclose that the size of the restriction gap 19 required is dependent upon the size of the bubbles that are produced, with no direction as to what gap size will produce microbubbles in the range of less than 100 microns. These two patents each go on to note that (at col. 6, lines 44 to 47) that the greater the diameter of the cylindrical edge, the closer the end of conduit 30 had to be positioned to the top 18 of the pressure vessel 14 (i.e. the smaller the restriction gap had to be) in order to form bubbles of the desired size. No desired size of bubbles was ever identified, nor was there ever any relationship specified between the gap size and the diameter of the pipe, which would produce the smallest bubbles, namely microbubbles of diameter in the 5-100 micron range.

U.S. Pat. No. 4,556,523 perhaps comes closest to specifying an interrelation between the components in order to achieve desired small microbubble size in the range of 50 to 100 microns, specifying as noted above that the passage between the injector and deflector wall at the edge of the injector hole is less than one quarter of the diameter of the injector hole in the injector wall. No specific optimum size was specified. Moreover, the particular manner by which the microbubbles are created, namely requiring an injector wall 10 and deflector wall 14, requires substantial quantity of material, and is thus a particularly material-intensive design and thus relatively costly.

Accordingly, a clear and real need exists for an aeration apparatus of simple and relatively inexpensive design having a configuration wherein the size of the flow aperture(s) through which a gas/liquid mixture flows can be accurately designed so as to give microbubbles of the desired small size.

SUMMARY OF THE INVENTION

In order to meet the above need for a device of simple and relatively inexpensive design able to introduce gas microbubbles into a liquid, in a broad aspect of the present invention such invention comprises an apparatus having means for creating microbubbles in a liquid, comprising:

means for introducing gas bubbles, the majority of which are of a size greater than 100 microns, into a liquid to from a liquid-gas mixture;

elongate, hollow pipe means, substantially symmetrical in cross-section of interior cross-sectional area, positioned substantially vertically, adapted to receive said liquid-gas mixture under first pressure and supply said liquid-gas mixture to aperture means, said pipe member having plug means situate at a lowermost distal end thereof for preventing egress of liquid vertically downward from said distal end;

said aperture means situate on said pipe means and disposed in one or more planes each substantially perpendicular to a longitudinal axis of said pipe means and extending from an interior of said pipe means to an exterior of said pipe means, each adapted to direct said liquid substantially horizontally outwardly from said pipe means; and

a containment vessel, to capture said liquid-gas mixture having microbubbles of gas entrained therein.

Importantly, however, and quite surprisingly, it has been further discovered that for an apparatus of the above design, that in the case of a pipe member that has a symmetric cross-sectional area and a uniform pipe wall thickness, and a maximum interior width Di and a maximum exterior width Do, a specific inter-relation need exist between the aperture exit area A.sub.e of the aperture(s), and the interior cross-sectional area A.sub.i of the pipe means, in order to achieve creation of microbubbles of the desired small size, namely in the range of 50-100 microns and preferably in the range of 5-50 microns.

Accordingly, in a highly preferred embodiment, where the aperture means consists of at least two apertures, the pipe means is symmetric and has substantially identical moments of intertia about two axis in a plane of cross-section through said pipe, wherein the combined aperture exit area A.sub.e of the apertures is a function of widths D.sub.i and D.sub.o, namely A.sub.e is no greater than A.sub.i.times.D.sub.i/D.sub.o.

Where only a single aperture is used, it has been found that Ae must not be any greater than Ai.times.Di/2Do.

While the above interrelation, namely for a plurality of apertures where Ae.ltoreq.Ai.times.Di/Do and for a single aperture Ae.ltoreq.Ai.times.Di/2Do, means it is possible to utilize apertures whose total combined cross-sectional area Ae is less than Ai.times.Di/Do or Ai.times.Di/2Do, typically, due to the desire to utilize an apparatus which utilizes the largest flow rate possible, it is usually greatly preferred that the greatest possible aperture exit area be used. Accordingly, more than one aperture will typically be desired to be used (thus the aperture exit area Ae may be twice as large than if only one aperture were used), and further that the aperture exit area Ae equal Ai.times.Di/Do, as such will give the greatest "throughput" of liquid which can be provided with gas microbubbles over a given time.

Accordingly, in a highly preferred embodiment, the pipe means will possess more than one aperture, and the exit area of each of the apertures will be equal to Ai.times.Di/Do.

In order for the above formula of Ae.ltoreq.Ai.times.Di/Do apply for pipe members having more than one aperture, it is necessary that the pipe member be not only symmetric in cross-section, but further it have substantially identical moments of inertia about two axis in a plane of cross-section through said pipe. This encompasses pipes having circular, square, hexagonal, octagonal and the like having uniform cross-sectional shape, but not to pipes having, for example, a rectangular cross-section. As more fully explained in this disclosure, for geometric cross-sectional areas which although symmetric but which do not have identical moments of inertia about at least two axis of a plane of cross-section, such as for rectangular pipe, such formula does not hold true, and other inter-relations may apply. However, in the case of rectangular pipe of uniform thickness, as is more fully explained below, it has been discovered that the required interrelation between exit areas of the apertures Ae, the dimensions of the pipe, and the cross-sectional area Ai of the pipe for microbubbles of the desired size to be produced be defined as: Ae.ltoreq.A.sub.i.times.[D.sub.3+D.sub.4]/[D.sub.1+D.sub.2] where D.sub.1 is the major exterior side length, D.sub.2 is the minor exterior side length, D.sub.3 is the major interior side length, and D.sub.4 is the minor interior side length. However, as rectangular pipe is difficult to acquire, the more common application of this invention will be to pipe members having circular or square profiles which have identical moments of inertia about two or more axis in the plane of cross-section.

Accordingly, in a highly preferred embodiment, the pipe means of the present invention is of uniform wall thickness and has a maximum interior width D.sub.i and a maximum exterior width D.sub.o, further having identical moments of inertia about at least two separate orthogonal axis in a cross-sectional plane through said pipe means; said apertures having a combined cross-sectional exit area A.sub.e defined as a function of widths D.sub.i and D.sub.o and said cross-sectional area A.sub.i of said pipe means, wherein A.sub.e is substantially equal to A.sub.i.times.D.sub.i/D.sub.o.

It is highly preferred, although not absolutely necessary, that there be a vertical surface which created jets of gas/liquid mixture which exit from such apertures may impact against, in order to assist in the creation of microbubbles of gas within the liquid.

Accordingly, in a further refinement of the apparatus of the present invention, such apparatus further consists of substantially vertical surface means adapted to be impacted by said liquid when said liquid is directed horizontally outwardly from said pipe means by each of said apertures.

It is further preferred, although not absolutely necessary, that the collection vessel for containing the resultant liquid having microbubbles contained therein form part of an integral structure with the pipe means and together form a single containment vessel in which the pipe means is located. While there are a number of advantages to using an integral containment vessel having the pipe member therewithin as explained later within this specification, including the ability to create microbubbles within the gas/liquid mixture under an ambient gaseous pressure within such containment vessel, one particular advantage is that, if desired, and if the gas/liquid mixture in the pipe means is expelled from the apertures under sufficient pressure, the sides of the containment vessel may be used as the vertical surface against which the horizontal streams of gas/liquid which exit the apertures may be directed.

Accordingly, in a further broad embodiment of the present invention, the apparatus of the present invention comprises a vessel adapted to be positioned substantially vertically and adapted to contain a volume of gas in an upper portion thereof; means for introducing gas bubbles, the majority of which are of a size greater than 100 microns, into a liquid to form a liquid-gas mixture; elongate, hollow pipe means within said vessel of interior cross-sectional area A.sub.i, for conveying said liquid when in a pressurized state to an interior of said vessel, substantially symmetrical in cross-section, situate centrally in said vessel and proximate said upper portion of said vessel and extending substantially vertically downwardly within said vessel from said upper portion thereof, and having plug means situate at a lowermost distal end thereof for preventing egress of liquid vertically downward from said distal end; and at least two apertures situate on said pipe means and disposed in one or more planes each substantially perpendicular to a longitudinal axis of said pipe means, extending from an interior of said pipe means to an exterior of said pipe means, each adapted to direct said liquid under pressure substantially horizontally outwardly from said pipe means.

Again, in a preferred embodiment, where symmetrical pipe means such as a cylindrical, square, hexagonal, octagonal, or even a triangular (equal sided) pipe member is used, the apparatus of the present invention comprises: i) a containment vessel adapted to be positioned substantially vertically and adapted to contain a volume of gas in an upper portion thereof; ii) elongate, hollow pipe means for providing said liquid to an interior of said vessel, having a longitudinal axis and substantially symmetrical in cross-section so as to have identical moments of inertia about at least two separate axis in a cross-sectional plane through said pipe means, of uniform wall thickness, and having a maximum interior width D.sub.i and a maximum exterior width D.sub.o and an interior cross-sectional area A.sub.i, said pipe means situate substantially centrally in said vessel and proximate said upper portion of said vessel and extending substantially vertically downwardly within said vessel, adapted for supplying a pressurized liquid to an interior of said vessel, and having plug means situate at a distal end thereof for preventing egress of liquid vertically downward from said distal end; iii) at least two apertures situate in said pipe means and disposed in one or more planes each substantially perpendicular to a longitudinal axis of said pipe means, each extending from an interior of said pipe means to an exterior of said pipe means, each adapted to direct said liquid substantially horizontally outwardly from said pipe means, of combined cross-sectional exit area A.sub.e; and iv) said combined aperture exit area A.sub.e of said apertures, defined as a function of widths D.sub.i and D.sub.o and said cross-sectional area A.sub.i of said pipe means, wherein A.sub.e is no greater than, and preferably equal to, A.sub.i.times.D.sub.i/D.sub.o

The aperture(s) may be of any geometric shape in cross section, such as circular (ie cylindrical apertures), provided the exit area of such aperture(s) in such pipe member meets the requirement for exit area Ae as discussed above in order to create microbubbles of a size in the range of 50 to 100 microns, and preferably 5-50 microns. In particular, the apertures may be one or more narrow horizontally-extending rectangular slots, or alternatively one or more vertical slots in such pipe member, all of which are easy to manufacture, either by drilling in the case of cylindrical apertures, or cutting/milling in the case of vertical or horizontal slots.

Importantly, it has further been discovered that apertures in the pipe member of a maximum dimension in excess of a certain amount may not form microbubbles of the required small size (5-50 microns).

In particular, the maximum gap "G", namely the maximum cross-sectional dimension that the aperture may possess is a function of the inner cross-sectional area of the pipe member divided by the outer circumference of the pipe member.

Accordingly, in such cases, where the aperture(s) are of a horizontally extending rectangular slot, of vertical depth G, where the pipe member has an exterior circumference C, G should preferably be no greater than Ai/C in order to form microbubbles when said liquid-gas mixture is expelled from the pipe member via such aperture(s).

Likewise, where the aperture(s) are of a circular cross-section (ie cylindrical), the diameter of such aperture should preferably be no greater than Ai/C.

Again, it is possible to utilize apertures of maximum dimension (or diameter, as the case may be) less than Ai/C, and still create gas microbubbles of the desired size of 5-100 microns. Accordingly, a large number of small apertures, where the total combined aperture area Ae adds up to the maximum aperture area [Ai.times.Di/Do] may be used, in order to introduce microbubbles in as great a quantity of liquid over a given time. However, having to drill large numbers of small apertures adds to the cost and time in the manufacture of the pipe member and thus of the apparatus of the present invention. It is much less expensive and less time-consuming to drill/mill as few a number of apertures as possible (see discussion below as to what the minimum number of apertures may be for a circular pipe).

The above relationship for the aperture exit area A.sub.e is derived from the surprising observation that the maximum aperture dimension (i.e. the "gap" ) through which the gas/liquid mixture must pass is determined from the experimentally-derived observation that the aperture dimension, hereinafter referred to as the "gap", which best creates microbubbles of the desired small size, is determined by the relationship gap "G"=A.sub.i/(pipe outer circumference).

For example, for a circular conduit/pipe of minor diameter D.sub.i, outer diameter D.sub.o, and cross-sectional area Ai=.pi.D.sub.i.sup.2/4 it has been found that for a rectangular aperture cut perpendicularly into the side of the pipe, to a depth of 1/2 the pipe diameter, so as to create an aperture to allow egress of a gas/liquid mixture under pressure therethrough, the maximum permissible "gap" G , namely the maximum vertical height of such horizontal slot, is: A.sub.i/(pipe outer circumference)=.pi.D.sub.i.sup.2/(4.sub.--.pi.D.sub.o)=D.sub.i.sup.2/4D.s- ub.0 (Eq'n #1)

The surface exit area Ae of two slots each formed over 1/2 the inner diameter of the pipe D.sub.i is calculated as follows: A.sub.e=2.times.gap.times.1/2.pi..times.D.sub.i Thus the maximum exit area A.sub.e of such apertures for a circular pipe member is thus equal to: Ae=2.times.D.sub.i.sup.2/4D.sub.o.times.1/2.pi..times.D.sub.i=.pi.D.s- ub.i.sup.3/4D.sub.o. (Eq'n. #2)

Accordingly, Ae stated more generally in terms of A.sub.i, where Ai=.pi.D.sub.i.sup.2/4 may be stated as follows:

.pi..times..times..times..pi..times..times..times..times. ##EQU00001##

Where only one exit aperture is utilized, maximum exit area is=.pi.D.sub.i.sup.3/8D.sub.o, and stated in terms of Ai is equal to: Ai.times.Di/(2Do)

In view of the above, the minimum number of apertures in a circular pipe may be determined. In this regard, in a preferred embodiment of the apparatus of the present invention, for the reasons discussed above, namely the desire to use the greatest amount of "throughput" for the apparatus with the least number of holes/apertures, and thus introduce microbubbles into the greatest volume of liquid in the shortest time, the largest-sized aperture utilizable equals Ai/C. In order to achieve as much throughput of liquid which has microbubbles introduced therein, the apparatus in a preferred embodiment will not only possess apertures of maximum size, but also the combined exit area Ae of such apertures will equal the maximum permissible area in order that the apparatus be able to process (ie introduce gas microbubbles) into as much liquid as possible for a given time.

Accordingly, in the case of cylindrical pipe, having circular (cylindrical) apertures, the minimum number of holes (apertures) which can be used is determined by reference to Eq'n. #2, which defines the maximum exit area for a circular pipe member, namely: Ae=.pi.D.sub.i.sup.3/4D.sub.o

Although the surface exit area of a circular hole in a cylindrical pipe forms a "saddle-like" exit area on the surface of the pipe, for small diameter apertures relative to the diameter of the pipe, the combined surface exit area of all apertures is approximately equal to the number of apertures multiplied by the exit area A.sub.aperture of each aperture: Ae(max)=n.times.A.sub.aperture(max)=n.times.(.pi..times.Da.sup.2/4) As discussed, Da is preferably no greater than Ai/C. Accordingly, substituting Ai/C for Da produces the following:

.function..times..times..pi..times..times..pi..times..times..times..pi..ti- mes..pi..times..pi..times. ##EQU00002##

The above equation for Ae(max) can be equated to Eq'n. # 2 for the Ae(max) of a circular pipe, and solved for "n" as follows:

.function..times..times..pi..times..pi..times..pi..times..times..pi..times- ..times..times..times..times..times..times. ##EQU00003## Accordingly, since Eqn. 6 may, depending on the ratio of Do/Di, produce a fractional value for the number of holes "n", in a preferred embodiment, the minimum number of circular apertures in a circular pipe member for maximum flow of liquid is defined by the following expression, namely: n=nearest whole integer to [16.times.D.sub.o/D.sub.i] (Eq'n. 6A). It is noted that since the maximum combined aperture exit area Ae for cylindrical pipe is Ai.times.Di/Do, for apertures of small diameter D.sub.A relative to the diameter of the cylindrical pipe, the following is true: Ae.sub.max=n.times..pi.D.sub.A(Max).sup.2/4 and thus Ai.times.Di/Do=n.times..pi.D.sub.A(Max).sup.2/4 The above allows us to solve for the maximum diameter of the apertures D.sub.A(max), where for circular pipe,

.pi..times..times. ##EQU00004## follows: .pi..times.Di.sup.2/4.times.Di/Do==n.times..pi..times.D.sub.A(Max).sup.2/- 4 thusD.sub.A(MAX)= {square root over (Di.sup.3/[n.times.Do)}] stated alternatively, D.sub.A(MAX)= {square root over (4.times.Ai.times.Di/[n.times..pi..times.Do)}]

It is usually the case for most cylindrical pipe having diameters Di and Do that "n" must be greater than 2 for most pipe, namely there must usually be a plurality of apertures, since otherwise the calculated diameter D.sub.A results in a diameter greater than both the interior diameter Di and the exterior diameter Do, which is a physical impossibility, as diameter D.sub.A can only be as large as, or smaller than, Di and Do.

The above value D.sub.A(MAX) for a circular pipe having cylindrical apertures may, in instances where there are relatively few number of apertures (ie n is a low number, but greater than one as per the above) give values of D.sub.A which are higher than Ai/(outer circumference of pipe) and which are too high and which will generally not produce microbubbles of desired size (ie less than 50 microns). Accordingly, the two criteria which are preferably satisfied in order to form microbubbles of the desired size are that Ae(max)=Ai.times.Di/Do, and D.sub.A(MAX).ltoreq.Ai/(Circumference of Pipe).

For a square conduit of inner dimension D.sub.i and outer dimension D.sub.o, having inner flow area A.sub.i=D.sub.i.sup.2 and outer circumference 4 Do, for a horizontally extending slot of Gap "G", it has been found that the maximum gap is likewise the flow area through the pipe Ai divided by the exterior circumference of the (square) pipe, being 4Do. Accordingly, the maximum vertical slot depth "G" for a square pipe may be stated as follows:

.times..times."".times..times..times. ##EQU00005##

The exit area A.sub.e for a plurality apertures in a square pipe may thus be calculated, knowing such maximum Gap "G". Accordingly, where the apertures comprise a pair of rectangular slots of vertical depth equal to the above Gap (Max), the exit area Ae for the apertures may be calculated as: A.sub.e=2.times.Gap(max).times.(1/2 D.sub.i+D.sub.i+1/2 D.sub.i)

Accordingly, expressed in terms of inlet area Ai for the square pipe, Ae may be stated as follows:

.times..times..times..times..times..times..times..times..times. ##EQU00006##

Again, where there is only one aperture in such square pipe, Ae is thus: A.sub.e=Gap(max).times.(1/2 D.sub.i+D.sub.i+1/2 D.sub.i) and thus, expressed in terms of Ai, is thus: Ae=Ai.times.Di/(2.times.Do)

As in the case of circular apertures in circular pipe, where there are circular apertures in square pipe, the diameter D.sub.A(MAX) may be solved for as follows: Ae=Ai.times.Di/Do (1) Ae=n.times..pi..times.D.sub.a.sup.2/4 (2) where `n` is the number of apertures Equating (1) with (2) allows for the diameter D.sub.A(Max) to be solved for as follows: Ai.times.Di/Do=n.times..pi..times.D.sub.a.sup.2/4 D.sub.A(MAX)= {square root over (4.times.Di.sup.3/[n.times..pi..times.Do])}== {square root over (4.times.Ai.times.Di/[n.times..pi..times.Do])}

Again, it is usually the case for most square pipe having interior width Di and exterior width Do that "n" must be greater than 2 for most pipe, namely there must usually be a plurality of apertures, since otherwise the calculated diameter D.sub.A of the cylindrical aperture results in a diameter greater than either the interior width Di or the exterior width Do, which is a physical impossibility, as diameter D.sub.A can only be as large as, or smaller than, Di and Do.

Again, the above value D.sub.A(MAX) for a square pipe having cylindrical apertures may, in instances where there are relatively few number of apertures (ie n is a low number, but as per the above, greater than one) give values of D.sub.A which are higher than Ai/(outer circumference of pipe) and which are too high and which will generally not produce microbubbles of desired size (ie less than 50 microns). Accordingly, the two criteria which are preferably satisfied in order to form microbubbles of the desired size are that Ae(max)=Ai.times.Di/Do, and D.sub.A(MAX)=Ai/(Circumference of Pipe).

It has been discovered that the above relationship(s) hold true for any pipe of symmetrical cross-sectional area and having at identical moments of inertia about at least two axis in a plane of cross-section through such pipe.

For example, for a triangular pipe member (of equal interior side length Di and equal exterior side length Do so as to be symmetrical and have identical moments of inertia about at least two axis in a plane of cross-section through such pipe member), the interior cross-sectional area Ai of such pipe member of interior side length Di is:

.times. ##EQU00007##

For two identical horizontal slots (apertures) cut into such pipe to form a "gap" of vertical height "G", where such slots to a depth so as to provide access to one-half of the interior area Ai of such pipe member, the maximum gap (ie vertical depth of each slot) is again determined by the relationship:

.times..times..times..times..times..times..times..times..times..times..tim- es..times..times. ##EQU00008##

The exit area of such two apertures is accordingly determined as the product of the gap multiplied by the perimeter of the gap. Accordingly,

.function..times..times..times..times..times..times..times..times..times..- times..times..times. ##EQU00009## Expressed in terms of Ai,

.function..times..times..times. ##EQU00010##

The present invention, in a further of its broad aspects, relates to a method for creating microbubbles of gas in a liquid and exposing them to matter entrained in said liquid. Accordingly, in one broad aspect of the method of the present invention, such method comprises the steps of:

providing gas to said liquid to form a gas/liquid mixture;

directing said gas-liquid mixture into a hollow pipe member, said pipe member having a maximum interior width D.sub.i and a maximum exterior width D.sub.o, said pipe member situate proximate an upper portion of a containment vessel and extending into an interior of said containment vessel, said upper portion of said containment vessel containing said gas being under pressure, and a bottom portion of said containment vessel substantially containing said liquid;

injecting said gas-liquid mixture under pressure via said pipe member, into said containment vessel;

spraying substantially radially outwardly from said pipe member said gas-liquid mixture into said upper portion of said containment vessel via at least two apertures in said pipe member;

said at least two apertures in said pipe member in communication with said gas-liquid mixture in said pipe member and having a combined area A.sub.e sized as a function of a maximum interior widths D.sub.i and maximum outside width D.sub.o and a cross-sectional area A.sub.i of said pipe member, wherein A.sub.e is substantially equal to: A.sub.i.times.D.sub.i/D.sub.o and

removing from said bottom portion of said containment vessel said liquid which has been exposed to said microbubbles.

In yet another aspect of the method of the present invention, such method comprises a method for converting a liquid-gas mixture having bubbles of gas therein the majority of which are greater than 5-100 microns in size to a liquid-gas mixture having microbubbles of gas therein the majority of which are of a size between 5-100, comprising the steps of:

directing said gas-liquid mixture having bubbles of gas therein the majority of which are greater than 5-100 microns in size into a hollow, substantially vertical pipe member, having a maximum interior width D.sub.i and a maximum exterior width D.sub.o;

spraying said gas-liquid mixture substantially radially outwardly from said pipe member via a plurality of apertures in said pipe member, so that said gas-liquid mixture contacts a vertically extending surface;

said plurality of apertures in said pipe member in communication with said gas-liquid mixture in said pipe member and having a combined area A.sub.e, said apertures sized as a function of said maximum interior width D.sub.i and said maximum outside width D.sub.o and a cross-sectional area A.sub.i of said pipe member, wherein A.sub.e is no greater than, and preferably equal to: A.sub.i.times.D.sub.i/D.sub.o

collecting a resulting gas-liquid mixture having microbubbles of gas entrained therein in a vessel; and

removing said gas-liquid mixture from said vessel.

In a further refinement of the methods of the present invention, one such method further comprises the step of collecting within said bottom portion of said vessel said liquid with microbubbles entrained therein and withdrawing said liquid from said bottom of said vessel at a rate approximately equal to a rate at which said liquid is introduced into said containment vessel.

In yet a further refinement of the aforesaid methods, the rate of withdrawing the liquid from the bottom of the vessel is substantially at a rate which microbubbles entrained in said liquid rise in the vessel, so that at a time when liquid is removed from said bottom of said vessel said microbubbles will have traveled upwardly a distance through said liquid equal to a depth of liquid in the bottom of the vessel.

In yet a further aspect of the method of the present invention, the liquid-gas mixture sprayed from said pipe member may be passed through a baffle plate member positioned in the containment vessel below said pipe member and intermediate said upper portion and said bottom portion of said containment vessel, and the rate of injection and removal of gas-liquid from the vessel adjusted so that baffle plate member is positioned above the level of the liquid in the vessel.

In order for the apparatus and method of the present invention to form microbubbles, the pressure of the gas in the upper portion of the vessel (back pressure) need be of a pressure of at least 10 psig to 15 psig, and preferably at least 20 psig to 30 psig. The initial-gas liquid mixture, in order to be provided to the apertures and sprayed therefrom, must necessarily, due to a small pressure drop across the apertures, be supplied at a slightly higher pressure than the pressure of the gas within the upper portion of the vessel (i.e. back pressure), in order to be effectively sprayed into the interior of the vessel. The step of spraying the liquid-gas mixture substantially radially outwardly via the apertures may further in a preferred embodiment be adapted to spray such liquid-gas mixture against the sides of the containment vessel.

From another perspective, the invention in a preferred embodiment comprises a method for continuously purifying a liquid containing impurities by exposing the liquid and impurities for a time in a substantially vertically containment vessel to microbubbles in the range of 5-100 microns in diameter, comprising the steps of:

directing a gas-liquid mixture containing impurities and bubbles of gas the majority of which are in excess of 100 microns in diameter into a hollow pipe member, said pipe member of uniform thickness and having a maximum interior width Di and a maximum exterior width Do and identical moments of inertia on two axis in a plane of cross-section through said pipe means, said pipe means situate proximate an upper portion of said containment vessel and extending vertically downwardly in an interior of said containment vessel, said upper portion of said containment vessel containing said gas, and being under pressure of at least 10 psig and preferably 15 psig or higher;

injecting said gas-liquid mixture, under a pressure of at least 5 psig higher than said gas in said containment vessel, into said vessel via said pipe member;

spraying said gas-liquid mixture substantially horizontally outwardly from said pipe member into said upper portion of said containment vessel via a plurality of apertures in said pipe member so that said gas-liquid mixture contacts interior sides of said vessel;

said plurality of apertures in said pipe member in communication with said gas-liquid mixture in said pipe member and having a combined area A.sub.e, said apertures sized as a function of said maximum interior width D.sub.i and said maximum outside width D.sub.o and a cross-sectional area A.sub.i of said pipe member, wherein A.sub.e is no greater than: A.sub.i.times.D.sub.i/D.sub.o collecting said gas-liquid mixture, now having microbubbles of gas entrained therein the majority of which are now of a size less than 100 microns in diameter, in a bottom portion of said containment vessel;

removing, from said bottom portion of said vessel, said liquid with gas microbubbles entrained therein at a rate which said microbubbles entrained in said liquid rise in said vessel so as to permit said gas microbubbles time to react with impurities in said liquid; and

supplying said liquid-gas mixture to said pipe member substantially at a rate at which said liquid-gas mixture having gas microbubbles entrained therein is removed from the bottom of said vessel.

Advantageously, the present invention in a particular refinement of both of one of the method and apparatus of the present invention, makes use of a sorting phenomenon in order to obtain microbubbles of the desired size.

Specifically, in a particular embodiment where a gas-liquid mixture having gas bubbles of substantially large size (>100 microns) entrained therein is sprayed outwardly from a pipe member and captured in a containment vessel, liquid having some large (>100 microns) as well as small (<100 micron) gas bubbles (but preferably a preponderance of small gas bubbles) is collected in said vessel. However, gas bubbles in said liquid which fall vertically down in said vessel when expelled from said aperture tend to fall to various depths in said containment vessel, before starting to rise in such vessel, depending on the size of the gas bubble entrained in surrounding liquid. Specifically, larger gas bubbles within the liquid tend to fall a lesser distance downwardly in liquid collecting at a bottom portion of the containment/collection vessel than smaller gas bubbles.

Accordingly, by proper vertical positioning of a liquid-withdrawal tube from the containment vessel this "sorting" of bubbles within the liquid collecting in the bottom portion of the vessel can be taken into account in obtaining liquid having gas bubbles of the lesser (more desirable) smaller diameter. Specifically, positioning of such withdrawal tube on such vessel at a position somewhat above a lowermost portion of said vessel and immediately below a lowermost level in said vessel which bubbles of a size larger than 100 microns initially fall to before rising in said vessel, and at a level within said bottom portion of said vessel which bubbles of a size less than 100 microns initially fall to before rising in said vessel, will allow the withdrawal tube to withdraw from said vessel only a gas-liquid mixture having smaller (ie <100 micron) bubbles.

Accordingly, in a preferred method of the present invention taking advantage of the above "sorting" principle in order to obtain gas microbubbles of a size less than 100 microns, such method comprises a method for producing a liquid having gas microbubbles therein the majority of which are of a size less than 100 microns, comprising the steps of:

providing gas to said liquid to form a gas/liquid mixture;

directing said gas-liquid mixture into a hollow pipe member, said pipe member having a maximum interior width D.sub.i and a maximum exterior width D.sub.o, said pipe member situate proximate an upper portion of a containment vessel and extending into an interior of said containment vessel, said upper portion of said containment vessel containing said gas being under pressure, and a bottom portion of said containment vessel substantially containing said liquid;

spraying substantially radially outwardly from said pipe member said gas-liquid mixture into said upper portion of said containment vessel via at least two apertures in said pipe member;

and

removing from said bottom portion of said containment vessel, at a position somewhat above a lowermost portion of said vessel, said gas-liquid mixture;

said position being a position immediately below a lowermost level in said vessel which bubbles of a size larger than 100 microns initially fall to before rising in said vessel, and at a level within said bottom portion of said vessel which bubbles of a size less than 100 microns initially fall to before rising in said vessel.

In a further embodiment the invention consists of an apparatus for making use of the "sorting" phenomenon.

Accordingly, in such refinement of the apparatus of the present invention, the containment vessel of the present invention comprises gas-liquid withdrawal means, such withdrawal means in communication with an interior of the vessel proximate a bottom portion thereof, vessel, adapted to withdraw a gas-liquid mixture having microbubbles of entrained gas therein from said interior of such vessel, such withdrawal means situate on said vessel at a position, said position being at a level on said vessel below a lowermost level within said vessel which bubbles of a size larger than 100 microns fall to before rising in liquid in said vessel, and at a level which bubbles of a size less than 100 microns fall to before rising in said vessel.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings, showing selected embodiments of the invention, are non-limiting and illustrative only. For a complete definition of the scope of the invention, reference is to be had to the summary of the invention and the claims.

FIG. 1 shows a front view of one embodiment of the apparatus of the present invention for creating microbubbles of gas, said apparatus in the embodiment shown using a cylindrical pipe member and a plurality of horizontally-extending cylindrical apertures;

FIG. 2 is an enlarged view of area "A" of FIG. 1;

FIG. 3 is an enlarged perspective view of items 24 and 25, area "B" of FIG. 2, showing in a particular embodiment of the invention wherein item 24 (pipe member) is cylindrical having circular apertures 32 therein;

FIG. 4 is a view of an alternative embodiment of the present invention, similar to that shown in FIG. 1, showing utilization of an inclined but substantially vertical baffle member;

FIG. 5 is an enlarged view of a particular embodiment showing of a pipe member of the present invention of circular cross-section, further showing an embodiment of the pipe member having horizontally-extending rectangular slots formed in such pipe member for acting as apertures to permit the expulsion of a gas-liquid mixture from such pipe member;

FIG. 5A is a section through the pipe member of FIG. 5, taken along plane X-X;

FIG. 5B is a section through the pipe member of FIG. 5, taken along plane Y-Y;

FIG. 6 is an enlarged view of a particular embodiment showing of a pipe member of the present invention of square cross-section, further showing an embodiment of the pipe member having horizontally-extending rectangular slots formed in such pipe member for acting as apertures to permit the expulsion of a gas-liquid mixture from such pipe member;

FIG. 6A is a section through the pipe member of FIG. 6, taken along plane X-X;

FIG. 7 is an enlarged view of a particular embodiment showing of a pipe member of the present invention of triangular (equal sided) cross-section, further showing an embodiment of the pipe member having horizontally-extending rectangular slots formed in such pipe member for acting as apertures to permit the expulsion of a gas-liquid mixture from such pipe member;

FIG. 7A is a section through the pipe member of FIG. 7, taken along plane X-X;

FIG. 8 is an enlarged view of a particular embodiment showing of a pipe member of the present invention of rectangular cross-section, further showing an embodiment of the pipe member having horizontally-extending rectangular slots formed in such pipe member for acting as apertures to permit the expulsion of a gas-liquid mixture from such pipe member;

FIG. 8A is a section through the pipe member of FIG. 7, taken along plane X-X

FIG. 9 is a side view similar to FIG. 1 showing another embodiment of the apparatus of the present invention, wherein the apertures for forming the microbubbles are situate in a plug member which is itself situated at the extreme lowermost distal end of the plug member;

FIG. 10 is an enlarged view of area "A" of FIG. 9;

FIG. 11 is yet a further side view similar to FIGS. 1 and 9, showing yet another embodiment of the apparatus of the present invention, in this case having circular apertures situate in the plug member at the extreme lowermost end of the pipe member;

FIG. 12 is an enlarged view of area "A" of FIG. 11;

FIG. 13 is an enlarged view of the baffle plate member shown in FIGS. 1, 9, and 11;

FIG. 14 is a cross-sectional view of a particular embodiment of the apparatus of the present invention which was selected to conduct tests on;

FIG. 15 is schematic view of additional test apparatus used to test the operability of the apparatus and method of the present invention;

FIG. 16 is a table setting out test data obtained using the test apparatus of FIGS. 14 and 15; and

FIG. 17 is a graph showing a plot of aperture exit area Ae as a function of bubble diameter, such data obtained from data using the test apparatus shown in FIGS. 14 and 15; and

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows one embodiment of the apparatus 10 of the present invention for producing microbubbles 12 in a liquid 14.

A means 16 for introducing gas bubbles 20 into such liquid 14 flowing in pipe 9 is provided. Means 16 may be a venturi, namely a converging-diverging nozzle, as known in the art, having at the converging portion an aperture 17 through which gas, typically although not always air, is drawn and flows in the form of bubbles 20 into the liquid, to form a gas-liquid mixture 22. Alternatively, and more typically, means 16 is simply an orifice to permit the injection of gas under pressure into said liquid 14 in pipe member 12, resulting in formation of gas bubbles 20 within liquid 14, which is under a resulting pressure.

The supply of gas may be from ambient air, if air is the desired gas to be introduced, as shown in FIG. 1, or alternatively may be from a pressurized tank of gas (not shown), if some other form of gas (such as H.sub.2 or CO.sub.2) is desired to be introduced.

Gas bubbles 20 entrained in such gas-liquid mixture 22 in the above manner are typically of a size greater than 100 microns, or at least a majority of gas bubbles 20 entrained in such gas-liquid mixture 22 are of a size greater than 100 microns, at typical ambient temperature and pressure (22.degree. C. and 1 atmosphere).

One of the purposes of the apparatus 10 of the present invention is to reduce the bubble size of the gas bubbles 20 within the gas-liquid mixture 22 to a size less than 100 microns, and preferably to a size in the range of 5-50 microns, in order to increase the ability of the gas in the gas-liquid mixture 22 to react with materials or substances entrained in the gas-liquid mixture 22, for the purposes of purifying and/or causing certain entrained substances in such liquid 14 to precipitate out of such gas-liquid mixture 22, thereby ridding such liquid 14 of such substances.

The gas-liquid mixture 22, having gas bubbles 20 therein the majority of which are of a size greater than 100 microns, is thereafter conveyed typically by means of a hollow pipe or conduit 24 to an elongate, hollow pipe member 24, typically although not necessarily, situate within a containment vessel 40, as shown in FIG. 1.

Pipe member 24 contains aperture means consisting of a one or more apertures 32, extending from an interior 33 of such pipe member 24 to an exterior 37 of pipe member 24 (see enlarged view of one embodiment of pipe member 24 shown in FIG. 3, wherein pipe member 24 is cylindrical in cross-section, having a plurality of cylindrical apertures therein). Each of apertures 32 may be of any geometric shape, but preferably are of a cylindrical shape as shown in FIG. 3, a cylindrical aperture being the resultant shape that results from drilling of such aperture 32 during manufacture using a circular drill bit, drilling being one of the easiest means of forming such apertures 32. Each of said apertures 32 extend horizontally outwardly and substantially perpendicular to a longitudinal axis of the pipe member 24. Pipe member 24 is positioned substantially vertically, as shown in FIG. 1, and is adapted to receive the liquid-gas mixture 22 and supply same under pressure to apertures 32. Each of apertures 32 extend horizontally outwardly from interior 33 of pipe member 24 to exterior 37 of pipe member 24. Pipe member 24 further possesses a plug member 25, situate at a lowermost distal end thereof for preventing egress of liquid-gas mixture 22 from said pipe member 24.

As hereinafter explained, the size (both width and cross-sectional area) of such apertures 32 is dependent in a preferred embodiment on certain formulae which are preferably maintained to allow formation of microbubbles 12 of a desired size, namely less than 100 microns, and preferably 5-50 microns, when the gas-liquid mixture 22 is expelled under pressure from the pipe