WO1979000958A1

WO1979000958A1 - Aeration propeller and apparatus

Info

Publication number: WO1979000958A1
Application number: PCT/US1979/000224
Authority: WO
Inventors: J De Veau; H Inhofer
Original assignee: Aeration Ind Inc; J De Veau; H Inhofer
Priority date: 1978-04-21
Filing date: 1979-04-10
Publication date: 1979-11-15
Also published as: GB2035823B; JPS55500281A; JPS553891A; CA1110786A; GB2035823A; JPS5820294B2

Abstract

An apparatus (10, 212) for mixing a gas and a liquid is disclosed. The apparatus is comprised of a hollow outer housing (22) and a hollow inner tube (24) received for rotary motion within the outer housing (22). A motor (61) is attached to the outer housing (22) adjacent a first end thereof and is drivingly coupled to a first end of the inner tube (24). The inner tube (24) has a support tube (214) which extends beyond the second end of the outer housing (22). Propeller blades (216) are attached to the support tube (214) for rotation therewith. An inlet (82) is formed in the inner tube (24) for admitting a gas to the hollow interior of the inner tube (24). The support tube (214) has a diffusion section (222) that extends below the propeller blades (216). The propeller mechanism (210), which includes the support tube (214) and the blades (216), is designed to increase the oxygen transfer efficiency of the apparatus (10, 212) over that provided by a standard marine propeller (48). Each propeller blade (216) has an impelling surface (232) with a varying rake which changes to a more positive rake from a leading end (226) to a tail end (228) of each propeller blade (216). Plates (238, 240, 242) are attached to the air outlet end (224) of the support tube (214). Lower portions (250) of the plates (240, 242) are bent backward in the direction in which the propeller mechanism (210) is to be rotated.

Description

AEmiTCN ERCFHIER ND APPARATUS

Technical Field The present invention relates broadly to a pro¬ peller mechanism and apparatus for mixing a gas with a liquid. More particularly, the present invention relates to a propeller mechanism and apparatus for aerating water in a water treatment process. The present invention can be used in municipal and private water treatment facilities.

Background of the Prior Art Aeration apparatus are utilized in the treatment of water for the purpose of increasing the dissolved oxygen (DO) content of the water. A certain amount of dissolved oxygen is required for the life of fish and other aquatic organisms. Dissolved oxygen is also required to prevent the formation of offensive odors and to break down organic matter in water. The biochemical oxygen demand (BOD) is the measure of the amount of oxygen consumed in the biolo¬ gical processes which break down organic matter in water. A high BOD indicates that large amounts of organic waste are present and will use up large amounts of dissolved oxygen. Aeration apparatus are especially useful in in¬ creasing the amount of dissolved oxygen and, hence, are useful in high-BOD situations.

Aerators utilized in waste water treatment can be broadly classified into two types: a diffused air type, and a mechanical type. A diffused air type aerator intro¬ duces air or pure oxygen into water via submerged porous diffusers or nozzles. Mechanical type aerators agitate the water so as to promote solution of air from the atmosphere.

Mechanical type aerators are further classified as either surface aerators or turbine aerators. A surface aerator utilizes a submerged or partially submerged impel¬ ler which agitates the water vigorously to thereby entrain air in the water and cause a rapid change in the air-water interface. Turbine aerators generally utilize a rotating impeller which is disposed a certain distance below the surface of the water being treated. A draft tube is sup¬ ported generally coaxial with the axis of rotation of the impeller and is utilized to supply air to the liquid adja-_ cent the impeller. In U.S. Patent No. 3,465,706 to Gwidt, an app atus for injecting air into the underwater exhaust outboard motors is disclosed. Air is injected into wa through a hollow propeller tube upon which a marine-t propeller is attached. A diff ser assembly comprised o air of U-shaped and crossed plates is attached at outlet end of the propeller tube. The air outlet end disposed relatively close to the marine prop and the dif ser plates have a relatively narrow width. A round disc attached to this lower end of the plates. The round d would apparently inhibit axial flow of water and air b bles.

Summary of the Invention One embodiment of the present invention is d ected to a non-fouling propeller mechanism for use with aeration apparatus. The propeller mechanism is compri of a support tube and a plurality of propeller bla attached thereto. The support tube is adapted to be tached to an end of a rotatable tube of an aeration app atus. The propeller blades are attached to the ou surface of the support tube. Each propeller blade ha leading^' end, a tail end, an outer edge and an impell surface. The outer edge at the leading end extends o wardly from the outer surface of the support tube at angle less than 90°. The impelling surface is adapted move into a liquid in which the support tube is rotat That is, the impelling surface faces in the direction rotation. The impelling surface has a varying rake t changes to a more positive rake from the leading end to tail end.

The support tube preferably has a diffus section which extends below the lowermost extent of propeller blades a sufficient distance such that air b bles which are injected from an open air outlet end of support tube do not intermix with the water through wh the propeller blades are rotated when the support tube held at an acute angle relative to the horizontal. A plurality of plate members are attached to the support tube adjacent its air outlet end and extend a distance below the air outlet end for breaking up air bubbles exiting the air outlet end and for causing a radial flow thereof. The plate members are preferably comprised of a plurality of plates extending in a plurality of planes. At least one of the plates has a lowermost section which is bent backward in the direction of rotation of the propeller member so as to permit or reestablish an axial flow of the gas bubbles and water at the lowermost end of the plate members. The axial flow is reestablished after the portion of the plate members above this lowermost section have established a radial flow.

The present invention is also directed to an improvement of the apparatus as disclosed in United States Patent Application Serial Number 898,983 of Daniel J. Durda on an "Apparatus for Mixing a Gas and a Liquid", which is assigned to the same assignee as the present invention. The apparatus is comprised of a hollow outer housing and a hollow inner tube received within the outer housing. The inner tube is mounted for rotary motion within the hollow interior of the outer housing. A motor is attached to the outer housing adjacent a first end thereof and is drivingly coupled to a first end of the inner tube. The inner tube includes a support tube which extends beyond the second end of the outer housing. An inlet is formed in the inner tube for admitting a gas to the hollow interior of the inner tube. A plurality of propeller blades are attached to the support tube to form a propeller mechanism. The propeller mechanism is adapted to be placed in a liquid and to propel the liquid in which the propeller mechanism rotates. The propeller blades have a maximum transverse dimension in a plane passing through the propeller blades and generally perpendicular through the axis of the support tube. Each propeller blade has a leading end, a tail end, and outer edge and an impelling surface facing in the direction in which the inner tube is rotated. The outer edge at the leading end extends outwardly from the outer surface of

OMPI ^< . 1P0 support tube at an angle less than 90°. The impellin surface has a varying rake which changes to a more positiv rake from the leading end to the tail end. The suppor tube has a diffusion section which extends below the lower most extent of the propeller blades and an open air outle end which forms the second end of the inner tube. Th diffusion section extends a predetermined distance belo the propeller blades such that the propeller blades ca rotate through a liquid substantially free of gas bubble injected into the liquid through the air outlet end whe the axis of the inner tube is disposed at an acute angl relative to the horizontal.

The propeller mechanism also preferably include a plurality of plate members comprised of a plurality o plates for causing the breaking up of air bubbles exitin the air outlet end and for causing a radial flow thereof The plate members also cause a low pressure area in th area of the water in which they rotate. Such a low pres sure area also increases the injection rate of the air int the water. A lower section of at least one of the plate is bent backward from the direction of rotation of th inner tube so as to permit or reestablish an axial flow o gas bubbles and water.

Various advantages and features of novelty whic characterize the invention are pointed out with particular ity in the claims annexed hereto and forming a part hereof However, for a better understanding of the invention, it advantages, and objects obtained by its use, referenc should be had to the drawings which form a further par hereof, and to the accompanying descriptive matter, i which there is illustrated and described a preferred embo diment of the invention.

Brief Description of the Drawings FIGURE 1 is a side elevational view illustratin an apparatus in accordance with the present inventio disposed within a liquid.

FIGURE 2 is a partial side elevational and par tial sectional view of the apparatus.

^"BLT 0 ^~ FIGURE 3 is a sectional view of the lower end of the apparatus on an enlarged scale.

FIGURE 4 is a view illustrating a U-joint at¬ tached to an end of the inner tube on an enlarged scale. FIGURE 5 is an end elevational view of a motor adapter.

FIGURE 6 is a view taken along lines 6-6 of FIGURE 5.

FIGURE 7 is a perspective view illustrating the motor adaptor connected to the outer tube.

FIGURE 8 is a perspective view illustrating the lower end of the apparatus.

FIGURE 9 is a plan view of the lower end of the apparatus-. FIGURE 10 is a fragmentary cross-sectional view of the inner and outer tubes of the apparatus.

FIGURE 11 is a cross-sectional view taken along lines 11-11 of FIGURE 4.

FIGURE 12 is a cross-sectional view taken along lines 12-12 of FIGURE 1.

FIGURE 13 is a perspective view illustrating a prop mechanism in accordance with the present invention attached to an aeration apparatus.

FIGURE 14 is a top plan view of the propeller mechanism itself.

FIGURE 15 is a bottom plan view of the propeller mechanism itself.

FIGURE 16 is a side elevational view on an en¬ larged scale, with portions broken away, of the propeller mechanism.

FIGURES 17, 18 and 19 are sectional views taken generally respectively along lines 17-17,-18-18, and 19-19 of FIGURE 16 illustrating the varying rake of the propeller blades. FIGURE 20 is a side elevational view of another embodiment of the propeller mechanism in accordance with the present invention.

'BUREA U

O PI ^WIP0 FIGURE 21 is a side elevational view illustrati a typical marine prop of the prior art.

Detailed Description of the Invention Referring to the drawings in detail, wherein li numerals indicate like elements, there is shown in FIGURE an apparatus in accordance with the present inventi designated generally as 10. The apparatus 10 as shown FIGURE 1 is disposed within a liquid 12. The liquid 12 generally waste water or sewage to which oxygen must injected. A gas, generally ambient air, is shown enteri the liquid 12 as a plurality of bubbles 14. The apparat 10 is designed to be portable and is shown supported on platform 15 by means of a suitable fastener ^"16 which attached to an arm 18 extending from the apparatus 10. T apparatus 10 is shown supported in the liquid 12 at angle 20 relative to the horizontal. The angle 20 between the horizontal and the vertical. An angle approximately 22° below horizontal has been found especia ly efficient for use in the treatment of shallow lagoons. The apparatus 10 includes an outer tube means housing 22 and an inner tube means 24. The outer housi 22 is comprised of a central tube 26, a motor adaptor attached to a first or upper end of the central tube 2 and a bearing housing 30 attached to a second or lower e of the central tube 26. The inner tube means 24 includes longitudinally extending tube 32, a propeller tube 34, a a diffusion tube 36.

The propeller tube 34 has a first end 38 who outer diameter is less than the inner diameter of an end of the tube 32. The end 38 thus can be received within t tube 32 and secured thereto by suitable means such welding. The propeller tube 34 has a second end 42. best seen in FIGURE 3, the second end 42 has an out diameter which is less than the outer diameter of a medi section 44 of the propeller tube 34. A shoulder 46 is th formed at the juncture between the second end 42 and t medial section 44. A propeller 48 can thus be receiv about the second end 42 and abut against the shoulder 4 The lowermost portion of the second end 42 has a threaded exterior. The interior of one end of the diffusion tube 36 is threaded to mate with the threads of the diffusion tube 36. The propeller 48 can thereby be held on the propeller tube 34 by threading the diffusion tube 36 onto the propel¬ ler tube 34 so that the propeller 48 is frictionally en¬ gaged between the shoulder 46 and the diffusion tube 36.

The motor adaptor 28 includes a cylindrical section 50 and a truncated cone section 52. The truncated cone section 52 is divided into a first section 54 and a second section 56. A plurality of ribs 58 are formed in the second section 56. A plurality of support arms 60 extend radially outward from the ribs 58. A handle 62 also ex¬ tends outwardly from the motor adaptor 28. The handle 62 is used as a grip to either carry or adjust the position of the apparatus 10.

A motor 61 is secured to the innermost holes 64 in the arms 60. A casing or housing 66 is attached to the outer holes 68 in the arm 60. The housing 66 includes a circumferential wall 70 which completely encircles the motor 61 and a top wall 72. The top wall 72 has a plurality of holes or slots 74. The slots or holes 74 provide an air inlet for air to be drawn into the interior of the housing 66. The housing 66 forms a plenum 78 around the motor 61. The motor 61 has a fan section 80 which includes a fan for drawing air across the outer surface of the motor 61 in order to keep the motor 61 cool. The movement of the air into and through the plenum 78 is illustrated by arrows 76.

Air as it passes through the plenum 78 is heated by the motor 61. The air passes through the plenum 78 to the hollow interior of the motor adaptor 28. The motor adaptor 28 also forms an enclosed plenum so that the air is confined to move down the hollow interior of the outer tube means 22. Inlet means, such as air inlet slots 82, are formed in the tube 32 adjacent its first or upper end. As shown by arrows 84, the heated air which is moving down the hollow interior of the outer tube means 22 passes into the hollow interior of the inner tube means 24 via the air inlet slots 82. Only one air "inlet slot 82 is shown FIGURES 2 and 4, however, preferably at least two air i slots 82 are formed in the tube 32. As will be expla more fully hereinafter, the heated air thereafter pa downwardly through the tube 32 and out the open end of diffusion tube 36.

The inner tube means 24 is supported within outer tube means 22 at one of its ends by a flexible c ling, such as a U-joint 86. The other end of the i tube means 24 is supported in a water bearing 88 whic secured within the bearing housing 30. The U-joint couples one end of the tube 32 to a rotary-driven d shaft 90 of the motor 61, while the water bearing 88 mits the rotation of the entire inner tube means 24. axis of the inner tube means 24 is shown as arrow 92.

The U-joint 86 includes an upper yoke 94 coup to a lower yoke 96 by means of a crosshead 98. The up yoke 94 has a head section 100 with a central bore extending therein. The drive shaft 90 of the motor 61 secured within the bore 102 to transmit the rotary mo of the drive shaft 90 to the U-joint 86. The upper yoke also includes a pair of opposing arms 104, 106. The 104 has a hole 109 extending through it and the arm 106 a hole 111 extending through it. The crosshead 98 inclu a first fin 108 with opposite ends 113, 115. The end 113 pivotably supported in the hole 109 and the end 115 pivotably supported in the hole 111. The lower yoke 96 a head section 110 with a bore 112 extending therein. upper end of the tube 32 is secured within the bore 112 that the rotation of the yoke 86 is transmitted to the t 32. The yoke 96 also includes a pair of opposing arms 1 116. The arm 114 has a hole 118 extending through it the arm 116 has a hole 120 extending through it. crosshead 98 includes a second pin 126 with opposite e 122, 124. The end 122 is pivotably supported in the h 118 and the end 124 is pivotably supported in the hole 1 Clips 128 hold the ends 113, 115, 122, 124 in the respe ive holes 109, 111, 118, 120. The lower yoke 96 and upper end of the tube 32 attached thereto are thus capable of pivoting about transverse axes 130, 132 of the pins 108, 126. The U-joint 86 permits universal motion of the first or upper end of the tube 32 while transmitting rotary motion from the drive shaft 90 to the tube 32.

As best seen in FIGURE 12, the water bearing 88 includes a plurality of bearing bars 134 extending along its length. The bearing bars 134 are so disposed that a gap 136 exists between adjacent bars 134. When the water bearing 88 is placed in a liquid such as water, the water is permitted to flow in the gaps 136- and also between the outer circumference of the propeller tube 34 and the bars 134. Water thus acts as a lubricant between the propeller tube 34 and the bearing 88. The tube 32 is mechanically straightened to exact tolerances. The tube 32 is straightened so that the cylin¬ drical wall 138 of the tube 32 is aligned about the axis 92 a certain distance 140 to a tolerance of better than fif¬ teen thousandths of an inch. That is, the distance 140 is the same throughout the entire length of the tube 32 to a tolerance better than fifteen thousandths of an inch. Applicant has discovered that when the tube 32 is straigh¬ tened to a tolerance of only fifteen thousandths of an inch, vibration and whipping of the tube 32 occurs such that early breakage of the tube 32 results. Applicant has discovered that straightening the tube 32 to a tolerance of ten thousandths of an inch, that is, dynamically balancing the shaft to one ounce-inch at 3,450 r.p.m., essentially eliminates the problem of vibration of the tube 32. Appli- cant, however, believes that straightening the tube 32 to a tolerance better than fifteen thousandths of an inch would also essentially eliminate or alleviate the problem of vibration. The use of a flexible coupling, such as U-j.oint 86, together with the above critical tolerances, further aids in eliminating vibration. The problem of vibration in aeration apparatus of the type disclosed herein results in shearing or breaking of an inner tube means after only a relatively short period of operation. A plurality of fins 142 extend radially outw from the bearing housing 30. Each fin 142 has a distal 144. A vortex shield 146 is attached to a number of distal ends 144. The shield 146 has a lengthwise dimens extending generally parallel to the axis 92 and a circ ferential dimension extending in an arc less than 360°. best seen in FIGURE 8, the shield 146 has a lower end in a generally truncated-V configuration. A portion of lower end 148 extends above the propeller 48. The shi prevents the formation of a vortex adjacent the propel in the liquid in which the propeller is driven. With the shield 146, a vortex of liquid may form at the prop ler and, hence, decrease the efficiency at which the p peller moves the liquid. The apparatus 10 operates in the following m ner. The apparatus 10 is disposed in a liquid 12 at angle 20 relative to the horizontal. The liquid 12 generally sewage or waste water which contains orga materi _al and which requires a high level of dissol oxygen. The motor 61 is driven preferably by an electri source (not shown). The drive shaft 90 of the motor 61 thereby rotated and the rotary motion is transferred to inner tube means 24. The propeller 48 rotates in liquid 12 and propels the liquid 12 by the open end of diffusion tube 36 creates a venturi or suction effect whi draws air down through the hollow interior of the in tube means 24. The air which is drawn through the holl interior of the inner tube means 24 was preheated whi passing through the plenum 78. The preheating of the air desirable when the apparatus 10 is used as an aerator bodies of water in northern climes wherein the body water generally freezes over in the winter. By utilizi the preheated air, at least a portion of the body of wa can be kept unfrozen or open. The unfrozen portion of water thus provides a contact surface with the ambient a wherein the air can dissolve into the water. If the bo of water is completely frozen over, such an open air-wa contact at the surface of the water is lost.

'ζϋ ^ The diffusion tube 36 has a length which is at least fifty percent of the transverse dimension of the propeller 48. The transverse dimension of the propeller 48 is indicated as line 150 which lies in a plane passing through the propeller and perpendicular to the axis 92. By utilizing a diffusion tube 36 that extends below the pro¬ peller by a length of at least fifty percent of the trans¬ verse dimension 150 of the propeller 48, the air bubbles 14 are released into the liquid 12 a sufficient distance away from the propeller 48 so that the propeller 48 moves through liquid which does not contain bubbles 14. This increases the efficiency with which the propeller 48 pro¬ pels the liquid 12. If the diffusion tube 36 were too short, the bubbles 14 would be released too close to the propeller 48 and thereby become intermixed with the liquid through which the propeller 48 was being driven. In such a condition, less liquid would be moved by the end of the diffusion tube 36 and the efficiency of the aeration pro¬ cess would be decreased. A three-inch diffusion tube used with a five-inch propeller has been found satisfactory.

The open end of the diffusion tube 36 has a curved inner circumferential surface 39. See FIGURE 3. For reasons unknown, it has been found that the air bubbles 14 disperse over a larger area when the inner circumferen- tial surface of the open end of the diffusion tube 36 is curved than when the inner circumferential area is straight. It has been found that while the curved surface 39 of the diffusion tube 36 increases the dispersion of air bubbles when the marine propeller 48 is used, such a curved surface does not aid the operation of the aeration appara¬ tus when the propeller mechanism illustrated in FIGURES 13-20 is used. As mentioned above, the shield 146 prevents the formation of a vortex of liquid at the propeller 48 and, hence, also increases the efficiency of the apparatus. When the apparatus 10 is disposed at an angle 20 within the liquid 12 the liquid 12 moved by the propeller 48 also aids in dispersing the air bubbles 14 over a large area in the liquid 12

"BUKt4i

OMPI There is shown in FIGURES 13-19 a propell mechanism 210 in accordance with the present inventio The propeller mechanism 210 is shown in FIGURE 13 attach to a portion of an aeration apparatus 212. Only a porti of the apparatus 212 is shown in FIGURE 13. The structu of the apparatus 212 is the same as the apparatus disclos in FIGURES 1-12 except for the propeller mechanism.

The propeller mechanism 210 includes a suppo tube 214 and a plurality of propeller blades 216 attach to the outer surface of the tube 214. The support tube 2 has an inlet end 218 which is attached in any suitab manner to an end of an inner tube 220 of the aerati apparatus 212. The support tube 214 has a diffusion se tion 222 which extends below the lowermost extent of t propeller blades 216. The support tube 214 also has open air outlet end 224 through which gas or air can injected into the liquid in which the propeller mechani 210 is disposed. As with the diffusion tube 36, the diff sion section 222 extends a sufficient distance below t propeller blades 216 such that air ejected from the a outlet end 224 does not intermix with the liquid throu which the propeller blades 216 are rotated when the axis the inner tube 220 is disposed at an acute angle relati to the horizontal, for example at approximately 25°. Each propeller blade 216 has a lead end 226, tail end 228, an outer edge 230 and an impelling surfa 232. The outer edge 230 extends outward from the out surface of the support tube 214 at the lead end 226 at angle less than 90°, and preferably less than 45°. having the outer edge 230 extend from the support tube 2 at such an angle, fouling of the propeller mechanism 210 prevented. When a normal marine prop is utilized, flexib solid material, such as rags, tend to become entangled the prop. Prop blades 216 tend to prevent such fouli under most water treatment conditions.

Each propeller blade 216 is preferably made of flat piece of rigid material and one flat major surface the material forms the impelling surface 232. The impe ling surface 232 faces in the direction in which the pro¬ peller mechanism 210 is designed to rotate. As seen in FIGURE 17, the impelling surface 232 has a slightly nega¬ tive rake adjacent the lead end 226. That is, the impel- ling surface 232 is bent slightly back or away from a radius 233 extending from the rotational axis. As seen in FIGURE 18, which is a sectional view taken farther along the length of the propeller blade 216, the rake of the impelling surface 232 has changed to a slightly positive rake. That is, the impelling surface 232 is leaning in towards a radius 235 extending from the rotational axis. As seen in FIGURE 19, the rake of the impelling surface 232 is even more positive, i.e. the impelling surface 232 is slanted in towards a radius 237 at an even greater angle. While FIGURES 17-19 illustrate the rake going from a nega¬ tive rake to a positive rake, it should be understood that the rake of the propeller blades 216 need not start at a negative rake, but merely that the rake increase to a more positive rake from the lead end 226 to the tail end 228. In this manner, water is impelled from the impelling surface 232 at various velocities along the length of an impelling surface 232. Thus, while the blades 216 create an axial flow, they create a turbulent axial flow. This is contrary to the purpose and function of a typical marine propeller 234, such as illustrated in FIGURE 21. The angle of at¬ tack, pitch or rake of propeller blades 236 on typical marine propeller 234, as illustrated in FIGURE 21, gradual¬ ly increases to a more negative rake. The pitch of the blades 236 changes in this manner because even velocities or laminar flow are desired in a typical marine propeller in order to attain maximum thrust. Applicants have found that such uniform velocity or laminar flow is not desirable in an aeration apparatus. While a strong axial flow is desirable for mixing purposes, a more turbulent flow is also preferable. Varying the rake in the positive direc¬ tion as disclosed above has been found especially useful in increasing the air injection capability of an aeration apparatus. A plurality of plates^"238, 240, 242 are attac to the support tube 214 at its air outlet end 224. plate 238 is preferably a flat plate which passes genera through a first plane. The second and third plates 2 242, or at least a portion of each of these plates, pas generally through a second plane transverse or perpendi lar to the first plane. In this manner, the plates 238- are connected in a crossed manner. The upper end of e plate 238-242 is fitted within a slot 244 formed in support tube 214. In this manner, the area at which plates 238-242 cross is disposed within the hollow inter of the support tube 214. The portions of the plates 2 242 which are disposed within the hollow interior of support tube 214 are thus in an area where only air present when the aerator is operating. Thus, the foul of the plates 238-242 at their crossed intersection prevented. If the area where the plates 238-242 cros were located at the air-water interface, solid materi would tend to gather at the intersection of the pla 238-242. In order to prevent fouling of the propel mechanism 210 at the point where the plates 238-242 int sect with the outer surface of the support tube 214, plates 238-242 have tapered ends 255 that extend from support tube 214 with a gradually increasing transve dimension.

As is best seen in FIGURE 15 the propeller bla 216 have a maximum transverse dimension indicated by a l 246. The first plate 238, as seen in FIGURE 15, ha maximum transverse dimension approximately the same as maximum transverse dimension of the propeller blades 2 As seen in FIGURE 16, the maximum transverse dimension the plate 238 extends over a large portion of the longi dinal or axial dimension of the plate 238. Similarly, maximum transverse dimension of the combined second third plates 240, 242 is also approximate to the maxi transverse dimension of the propeller blades 216. The m function of the plates 238-242 is to increase the amount air injected into water by the aeration apparatus has been found that if the maximum transverse dimension of the plates 238-242 is too narrow, i.e. substantially smal¬ ler than the transverse dimension of the propeller blades 216, the amount of air injected does not increase appreci- ably. By increasing the transverse dimension of the plates 238-242, the amount of air injected into the water by apparatus 212 increases. It has been found that an optimum or satisfactory level of air injection to power consumption results when the transverse dimension of the plates 238-242 approximates the transverse dimension of the propeller blades 216.

The entire plate 238 lies in a single plane and an upper portion 248 of the second and third plates 240, 242 lies in a single plane transverse to the plane of the first plate 238. However, a lower portion 250 of each plate 240, 242 is bent backward or away from the direction of rotation of the propeller mechanism 210. As discussed above, the plates 238-242 function to increase the amount of air injected into the water. The propeller mechanism 210 in addition to increasing the amount of air which is injected into the water, also increases the percentage of oxygen which dissolves in the water. Applicants believe that the increase in the amount of dissolved oxygen is caused by the action of the plates 238-242. The plates 238-242 cause the air bubbles which exit the air outlet end 224 to be broken up into fine bubbles and cause the bubbles to flow radially outward. Applicants believe that breaking the bubbles down into smaller air bubbles decreases the reliance upon "hang time" to cause the dissolving of oxygen into the water. Since the bubbles are broken into fine bubbles which have a smaller diameter, the interface area between air and water for a given volume of air is in¬ creased and thus dissolving of oxygen occurs more rapidly. The time element which is required for oxygen transfer is reduced. The shortening of this time element is especially useful where the aeration is required in a shallow area in which hang time would be minimal.

OMPI The lower bent portions 250 of the blades 240-2 tend to reestablish an axial flow of the air bubbles water at the lowermost end of the propeller mechanism 21 The reestablishment of the axial flow is desirable so t the mixing of the air bubbles and the inducement of a fl in the water can be optimized. If all of the plates 238-2 were completely flat, too great a radial flow would established.

The prop mechanism 210 thus provides broad vers tility in designing a prop mechanism for various wat treatment conditions. When the water or sewage being trea ed requires a high amount of dissolved oxygen, but does n require a large amount of mixing, i.e. in very small pond the lower portions 250 can be made relatively small compared to the remaining portion of the plates 240, 24 The oxygen injection is thus increased, while the axi flow is decreased. Also, the amount of power which is p into air injection is increased over the amount of pow that is placed into mixing. On the other hand, whe mixing is more important than the amount of oxygen which to be injected, the length of the lower portion 250 can increased so that more axial flow for mixing is utilized.

Where the requirement for dissolved is not hi and the requirement for mixing is, the alternate embodime shown in FIGURE 20 can be utilized. There is illustrat in FIGURE 20 an alternate embodiment of a propeller mech nism, designated generally as 210'. The propeller mech nism 210' is comprised of a support hub 214' and a plura ity of propeller blades 216' attached to the outer surfa thereof. The propeller blades 216' are constructed t same as the propeller blades 216. The propeller mechani 210' does not utilize any plates at its air outlet end 22 to cause a radial flow of gas bubbles and water. Ev though no plates are utilized, applicants have found th the propeller mechanism 210' results in higher air inje tion rates than are found in the use of standard mari props. Applicants believe that this is due to the turb lent flow created by the varying rake of the propell blades 216• . Numerous characteristics and advantages of the invention have been set forth in the foregoing description, together with details of the structure and function of the invention, and the novel features thereof are pointed out in the appended claims. The disclosure, however, is illus¬ trative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts, within the principle of the invention, to the full extent extended by the broad general meaning of the terms in which the appended claims are expressed.

Claims

WHAT IS CLAIMED IS:

1. A propeller mechanism for use with an aera apparatus comprising: a support tube for attachment to an end o rotatable tube of an aeration apparatus; a plurality of propeller blades attached to outer surface of said support tube; each propeller blade having a leading end, a end, an outer edge and an impelling surface, the outer at the leading end extending outwardly from the o surface of said support tube at an angle less than 9 said impelling surface facing in the direction in w said propeller mechanism is adapted to rotate, said imp ling surface having a varying rake which changes to a positive rake from the leading end to the tail end.

2. A propeller mechanism in accordance with clai wherein said support tube includes a diffusion sec extending a„ distance below the lowermost extent of s propeller blades and having an open air outlet end whe air bubbles ejected from said outlet end do not inte with water through which said propeller blades are rotate

3. A propeller mechanism in accordance with clai including plate members extending below said air outlet for breaking up air bubbles exiting said air outlet end for causing a radial flow thereof, said plate memb including a first plate extending generally in a fi plane and second and third plates extending generally i second plane transverse to said first plane.

4. A propeller mechanism in accordance with clai 2 or 3 wherein the rake of each propeller blade is nega at the leading end and changes to a positive rake at tail end. y

5. A propeller mechanism in accordance with claim 3 wherein said first plate has an axial dimension extending generally parallel to the axis of said support tube and a transverse dimension extending generally perpendicular to said axis, said transverse dimension of said first plate along a major portion of said first plate being approxi¬ mately the same as a transverse dimension extending between the widest extent of said propeller blades.

6. A propeller mechanism in accordance with claim 3 or 5 wherein said second plate extends perpendicularly front one side of said first plate and said third plate extends perpendicularly from a second side of said first plate.

7. A propeller mechanism in accordance with claim 6 wherein said second and third plates each have a lower end spaced from the air outlet end of said support tube, said lower end being angled backward away from the direction in which said propeller mechanism is adapted to be rotated whereby an axial flow of liquid and air bubbles is permit¬ ted off said lower end.

8. A propeller mechanism in accordance with claim 3 or 5 wherein said first, second and third plates are at¬ tached within slots formed in said support tube at said air outlet end whereby a portion of said first, second and third plates is disposed within the hollow interior of said support tube.

9. A propeller mechanism in accordance with claim 1 wherein each propeller blade has a flat major surface which forms said impelling surface for contacting a liquid in the rotative direction, said flat surface being slanted away from a radius line extending from the axis of said support tube adjacent the leading end of a respective propeller blade and said flat surface slanting toward a radius line extending from the axis of said support tube adjacent the tail end of a respective propeller blade whereby water is driven off of a rotating propeller blade at differ velocities at different locations along the length thereo

10. A non-fouling propeller mechanism for use with aeration apparatus comprising: a support tube for attachment to an end o rotatable air injection tube of an aeration apparatus; a plurality of propeller blades attached to outer surface of said support tube; each propeller blade having a leading end, a t end, an outer edge, and an impelling surface, the ou edge at the leading end extending outwardly from the ou surface of said support tube at an angle less than 4 said impelling surface facing the direction in which s propeller mechanism is adapted to rotate, said impell surface having a varying rake which changes to a m positive rake from the leading end to the tail end; said support tube having a diffusion sect extending below the lowermost extent of said propel blades a predetermined distance sufficient that air bubb ejected from and open outlet end of said support tube not intermix with the water through which said propel blades are rotated; and a plurality of plate members extending below s air outlet end for breaking up air bubbles exiting said outlet end and for causing radial flow thereof.

11. A propeller mechanism in accordance with claim wherein said plate members include a first plate extend generally in a first plane and having a transverse dim sion along a portion thereof approximately the same as transverse dimension of the widest transverse extent said propeller blades, a second plate extending genera perpendicularly from a first major face of said fi blade, and a third plate extending generally perpendi larly from a second major face of said first plate, s second and third plates having lower ends bent away f the direction in which the propeller mechanism is adap to rotate. _/-"

12. A propeller mechanism in accordance with claim 11 wherein each of said plates is received within a slot formed in said support tube at the air outlet end and wherein each plate has a tapered end extending gradually radially outward from a respective slot.

13. A propeller mechanism in accordance with claim 10 wherein said first plate has a maximum transverse dimension perpendicular to the axis of said support plate approxi¬ mately the same as the maximum transverse dimension of said prop blades.

14. A propeller mechanism in accordance with claim 10, 11, 12 or 13 wherein the rake of each propeller blade is negative at the leading end and changes to a positive rake at the tail end.

15. A propeller mechanism in accordance with claim 14 wherein each propeller blade is comprised of a flat plate.

16., A propeller mechanism for use with an aeration apparatus comprising: a support tube for attachment to an end of a rotatable air injection tube of an aeration apparatus; means for inducing a turbulent axial flow of liquid in which said propeller is rotated, said inducing means including a plurality of propeller blades attached to an outer surface of said support tube and having an impel- ling surface with a varying rake which changes to a more positive rake from a leading end to a tail end of each respective propeller blade; means for injecting air bubbles a sufficient distance below said propeller blades such that said propel- ler blades rotate in water free of air bubbles when said support tube is held at an acute angle relative to the horizontal, said air injection means including a diffusion section of said support tube extending a predetermined distance below a lowermost extent of said propeller blades and having an open air outlet end;

^{^} means for breaking up air bubbles exiting s air outlet end and for causing a radial flow of said bubbles and water, said last-mentioned means includin plurality of plates extending axially below and radia outward from said support tube; and means for reestablishing an axial flow of bubbles and water, said last-mentioned means includin lowermost portion of at least one of said blades being b backward in the direction in which said propeller mechan is intended to rotate.

17. An apparatus for mixing a gas and a liquid c prising: an outer housing having a hollow interior, op site first and second ends, and a longitudinal dimens extending between the ends; inner tube means for defining an air inlet p sage; said inner tube means being mounted for rot motion about its axis within the hollow interior of s outer housing; motor means attached to said outer housing ad cent the first end thereof and drivingly coupled to a fi end of said inner tube means for rotating said inner t means; said inner tube means including a support t extending beyond the second end of said outer housing; a plurality of propeller blades attached to s support tube for rotation therewith, said propeller bla having a maximum transverse dimension in a plane pass through said propeller blades and generally perpendicula through the axis of said support tube, said propel blades being adapted to be placed in a liquid and to pro the liquid in which the propeller rotates; each propeller blade having a leading end, a t end, an outer edge and an impelling surface facing direction in which said inner tube means is rotated, outer edge at the leading end extending outwardly from outer surface of said support tube at an angle less than 90°, and said impelling surface having a varying rake changing to a more positive rake from said leading end to said tail end; inlet means for admitting a gas to the hollow interior of said inner tube means, said inlet means being formed in said inner tube means; and said support tube having a diffusion section extending below the lowermost extent of said propeller blades, said support tube having an open air outlet end at the second end of said inner tube means for injecting a gas passing through the hollow interior of said inner tube means into a liquid in which the support tube is placed, said diffusion section extending a predetermined distance below said propeller blades such that said propeller blades can rotate through a liquid substantially free of gas bubbles injected into the liquid through said air outlet end when the axis of said inner tube means is disposed at an acute angle relative to the horizontal.

18. A propeller mechanism in accordance with claim 17 including plate members extending below said air outlet end for breaking up gas bubbles exiting said air outlet end and for causing a radial flow thereof, said plate members including a first plate extending generally in a first plane and second and third plates extending generally in a second plane transverse to said first plane.

19. A propeller mechanism in accordance with claim 18 wherein said first plate has an axial dimension extending generally parallel to the axis of said support tube and a transverse dimension extending generally perpendicular to said axis, said transverse dimension of said first plate along a major portion of said first plate being approxi¬ mately the same as the maximum transverse dimension of said propeller blades.

20. An apparatus in accordance with claim 17, 1 19 wherein the rake of the impelling surface of each peller blade is negative at the leading^* end and change a positive rake at the tail end.

21. A propeller mechanism in accordance with clai or 19 wherein said second plate extends perpendicul from one side of said first plate and said third p extends perpendicularly from a second side of said f plate.

22. A propeller mechanism in accordance with clai wherein said second and third plates each have a lower spaced from the air outlet end of said support tube, lower end being angled backward away from the directio which said propeller mechanism is adapted to be rot whereby an axial flow of liquid is permitted off said l end.

23. A propeller mechanism in accordance with clai or 19 wherein said first, second and third plates are tached within slots formed in said support tube where portion of said first, second and third plates is disp within the hollow interior of said support tube.

24. A propeller mechanism in accordance with clai wherein each propeller blade has a flat major sur forming said impelling surface for contacting a liqui the rotative direction, said flat surface being sla away from a radius line extending from the axis of support tube adjacent the leading end of a respec propeller blade and said flat surface slanting towar radius line extending from the axis of support tube a cent said tail end of a respective propeller blade whe liquid is driven off of a rotating propeller blade different velocities at different locations along length thereof.

25. An apparatus in accordance with claim 17 in¬ cluding a plurality of arms extending radially from said outer housing at its first end, said motor means including a motor and a drive shaft extending from said motor, means for attaching said motor to said arms, said drive shaft having an axis substantially in alignment with the axis of said inner tube means, said motor being adapted to rotate said drive shaft about its axis, coupling means drivingly coupling said drive shaft to said inner tube means for transferring the rotary motion of said drive shaft to said inner tube means while permitting universal motion of the first end of said inner tube means.

26. An apparatus in accordance with claim 25 in¬ cluding a motor housing attached to said outer housing adjacent its first end, said motor housing encircling said motor, said motor housing forming an inlet plenum around said motor, inlet apertures formed through said motor housing to allow gas surrounding said motor housing to enter said inlet plenum, said inlet plenum being in commu- nication with the hollow interior of said outer housing and with said inlet means of said inner tube means whereby the gas passing through said inlet plenum is heated by said motor and thereafter enters the hollow interior of said inner tube means.

27. An apparatus in accordance with claim 24 in¬ cluding a shield attached to an outer surface of the outer tube means adjacent its second end for preventing the formation of a vortex in the liquid adjacent the propeller blades.

28. An apparatus in accordance with claim 27 in¬ cluding a plurality of fins extending radially from the outer surface of said outer housing adjacent its second end, each fin having a distal end, said sheild having a curvilinear configuration and an inner surface attached to distal ends of said fins to hold said shield in a spaced relationship from said outer housing, said shield ha opposite ends and a lengthwise dimension extending bet the ends generally in the direction of the longitud dimension of said outer housing and a circumferen dimension extending in an arc less than 360° gener around the longitudinal axis of said inner tube means, of the ends of said shield extending over said prope blades.

29. An apparatus in accordance with claim 17, 1 24 wherein said inner tube means includes a cylindr wall aligned along the axis of the inner tube means within a tolerance of ten thousandths of an inch along entire length, said cylindrical wall extending alon major portion of the length of said inner tube means, motor means includes a motor attached to said outer hou adjacent the first end thereof and a drive shaft exten from said motor, and a U-joint drivingly coupling drive shaft to the first end of said inner tube means w permitting universal motion of the first end of said i tube means at said coupling.