Apparatus for treating fluids having improved aeration efficiency and operational durability

Abstract

An apparatus for treating fluids having improved aeration efficiency and operational durability has an aerator, an impeller, and a liquid reservoir containing liquid to be treated. The aerator has: a motor rotating the impeller at a blade tip speed less than 1,100 inches/second; an air line having an outlet submerged in the liquid and an inlet adjacent to the motor; and a blower. The blower forces air through the air line to the air line outlet. The impeller two blades extending radially from the hub. Each blade has: a low drag, pressure equalized foil shape absent of rake; a leading edge extending from the hub tangentially; a 0.47-0.55 impeller EAR; 0.59-0.87 Pmean/D; progressive pitch distribution based on radius where from 50% R and out is constant and from 50% R to the hub is reduced; and 60-75 degree skew with a linear distribution from 50% radius to blade tip.

Claims

1. In combination, a blower-assisted aerator, an impeller, and a liquid reservoir containing a liquid, said blower-assisted aerator having: an eight-pole electric motor rotating said impeller fully submerged within said liquid at a blade tip speed less than 1,100 inches per second; an air-line having an air-line outlet submerged in said liquid and distal to said motor and an air-line inlet relatively more adjacent to said motor than said air-line outlet; and a blower having a blower air inlet and an air outlet, said blower forcing air from said blower inlet into said air-line inlet and through said air-line to said air-line outlet; said impeller having: a hub coupled to said electric motor and defining an axis of rotation; and two blades extending radially from said hub, each one of said two blades having a pressure equalized foil shape absent of rake, a leading edge extending from said hub tangentially, an impeller Expanded Area Ratio (EAR) between 0.47 and 0.55, a radius integrated pitch to diameter ratio (P.sub.mean/D) between 0.59 and 0.87, a progressive pitch distribution based on radius where from 50% radius and out is constant and from 50% radius to the hub is reduced, and a skew of between 60 and 75 degrees with a linear distribution from about the 50% radius to a blade tip.

2. The combination blower-assisted aerator, impeller, and liquid reservoir of claim 1, wherein said liquid comprises municipal sewage.

3. The combination blower-assisted aerator, impeller, and liquid reservoir of claim 1, wherein said liquid comprises industrial process water.

4. The combination blower-assisted aerator, impeller, and liquid reservoir of claim 1, wherein said liquid comprises industrial waste water.

5. The combination blower-assisted aerator, impeller, and liquid reservoir of claim 1, wherein said liquid comprises aquiculture water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing and other objects, advantages, and novel features of the present invention can be understood and appreciated by reference to the following detailed description of the invention, taken in conjunction with the accompanying drawings, in which:

(2) FIG. 1 illustrates a preferred embodiment apparatus for treating fluids having improved aeration efficiency and operational durability designed in accord with the teachings of the present invention from a projected view.

(3) FIGS. 2-4 illustrate a preferred embodiment impeller designed in accord with the teachings of the present invention as illustrated in the combination of FIG. 1 from projected, side, and end view showing the aft or pressure generating face of the blade, respectively.

(4) FIGS. 5-8 illustrate an exemplary specific embodiment of the impeller of FIGS. 1-4 showing the impeller in profile view, with pitch distribution, by transverse view looking aft, and by expanded view, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) Manifested in the preferred embodiment, the present invention provides an apparatus for treating fluids having improved aeration efficiency and operational durability. As illustrated in FIG. 1, a preferred combination blower-assisted impeller aerator and impeller 1 is designed to be installed in a partially submerged position within a reservoir 4 filled to a water line 5 with a liquid 6 to be treated. Reservoir 4 may be of any size and geometry suitable to accommodate preferred combination blower-assisted impeller aerator and impeller 1.

(6) A blower 2 is preferably provided outside of the liquid, and draws air from the environment and forces the air into air line 10. Ultimately, the air exits through outlet 14, which is most preferably fully submerged in the liquid 6 to be aerated or otherwise treated. A motor 3, most preferably an eight pole electric motor, in a preferred embodiment is also positioned outside of the liquid being treated. While motor 3 may in some alternative embodiments be fully submerged, as could all but the air inlet for blower 2, such submersion undesirably complicates both installation and maintenance.

(7) Motor 3 imparts rotary motion to an impeller 40. Impeller 40 is most preferably fully submerged in liquid 6. Air line 10 is preferably tilted so as to pass from adjacent motor 3 in the air space above the liquid being treated down through the surface intermediate between motor 3 and impeller 40, and finally into the liquid to submerged impeller 40.

(8) Preferably, when blower 2 is turned off air does not aspirate through blower 2 and air line 10 to outlet 14. Instead, the preferred combination blower-assisted impeller aerator and impeller will operate as a mixer when blower 2 is off. A baffle structure 20 configured to improve oxygenation efficiency while preventing the aforementioned aspiration when blower 2 is off preferably comprises a first baffle 21 and a second perforated baffle 22.

(9) In some alternative embodiments, blower 2 will be removed, and replaced with an ambient air inlet. In such embodiments, baffle structure 20 will either be removed or substantially altered to permit ambient air to be aspirated through air line 10 to outlet 14 by the suction created by moving liquid passing outlet 14 under the influence of impeller 40.

(10) Preferred embodiment impeller 40 is illustrated in greater detail in FIGS. 2-4. Hollow center hub 41 is generally cylindrical, though various other options may be incorporated therein, such as the key slot visible in FIGS. 2 and 4. The longitudinal center of hub 41 defines an axis A of rotation, the direction of rotation being designated in the figures by rotation arrow R. Hub 41 supports two blades 42, 43. Blades 42, 43 connect to hub 41 at blade roots 44, 45. Blades 42, 43 taper from blade leading edges 46, 47 to narrow and yet still rounded blade trailing edges 48, 49. Blades 42, 43 are curved and are affixed to hub 41 in a helical manner, running from near the top of hub 41 to near the bottom, thereby defining a blade pitch. Blades 42, 43 are additionally substantially skewed.

(11) In order to accomplish the objectives described herein above, preferred embodiment anti-fouling impeller 40 will preferably be designed using the following two critical criteria: first, a pitch and skew will be used that, when rotating at the desired RPM, is conducive to shedding sinewy debris; second, a dimension and surface area that, when rotating at the desired RPM, maintains required mixing and oxygen transfer rates and combines with pitch and skew to function without undesirable vibration or cavitation.

(12) In a manner similar to other known impellers used in the aeration industry, during operation the preferred embodiment impeller of FIGS. 2-4 swirls the water or other liquid to create a long cone. Air may, for exemplary purposes, be mixed into the center of the cone of water. At the intersection with blade roots 44, 45, leading edges 46, 47 present an obtuse angle approximately tangent with the immediately adjacent hub 41 surface in the direction of rotation. While not limiting the present invention to be bound by any particular theories, preferred embodiment anti-fouling impeller 40 is thought to more readily shed debris such as rags and the like owing to this obtuse angle. In some embodiments where leading edges 46, 47 are entirely tangential with hub 41, there are no surfaces upon which debris can catch, and instead the debris will slide outward away from hub 41, rather than being wrapped in blades 42, 43 or around hub 41.

(13) Preferred embodiment impeller 40 is also thicker than other impellers of equivalent diameter. This is believed to help prevent flexing at the edges of the blade, which would change the flow pattern in the water, and which can generate unwanted vibration and noise. Alternative embodiments may be thinner if a different material with less flexing properties is used, if the pitch or tip speed are reduced, or if the performance is not otherwise sufficiently adversely affected by a thinner impeller.

(14) The dimension and surface area of the preferred blades illustrated in FIGS. 2-4 are chosen to preferably maintain desired mixing and oxygen transfer rates when rotating at the desired rotations per minute. Preferably, the preferred blades is conducive to shedding sinewy debris, such as string or plastic bags, when rotating at the desired rotations per minute. This decreases impeller obstructions and malfunctions, reducing maintenance costs and maintaining higher performance levels.

(15) The increased ability to maintain function even in areas with high debris content expands the range of applications for preferred embodiment anti-fouling impeller 40, making the preferred embodiment ideal for containment areas that are not pre-filtered.

(16) FIGS. 5-8 illustrate a most preferred but also exemplary specific embodiment of impeller 40 of FIGS. 2-4 showing impeller 40 in profile view, with pitch distribution, by transverse view looking aft, and by expanded view, respectively. In association with the present text, these Figures help to illustrate one preferred embodiment impeller, though it will be understood from the text that the geometry of a preferred embodiment impeller may vary from that illustrated in FIGS. 5-8 owing to particular horsepower ratings and other design considerations.

(17) In accord with the teachings of the present invention, a preferred motor 3 comprises an eight pole electric motor, which has an ideal unloaded rotational velocity of 900 RPM when operated on 60 Hz AC power. In alternative embodiments, gearing, electronic motor controllers, or other apparatus and techniques may be used to adjust the rotational speed of motor 3. However, such extra apparatus adds cost and can interfere with other aspects of the present invention and embodiments thereof. As a corollary thereto, desirably the tip speed of the blade, which is determined by the rotation rate and impeller diameter, will remain below approximately 1,100 inches/second. In a most preferred embodiment, the tip speed will be between 750 and 1,060 inches/second.

(18) Also in accord with the teachings of the present invention, a preferred impeller 40 will have two blades, each with a skew between approximately 50 and 100 degrees. For those artisans skilled in impeller design, this will be understood to be unusually highly skewed. In a most preferred embodiment, the skew will be between 60 and 75 degrees. In addition, there will be a linear distribution from about the 50% radius to the tip, such as illustrated in FIG. 7. Nevertheless, and as evident from preferably when viewed along the axis of rotation A, in the preferred embodiment the blades do not overlap, and the gap between blades generally increases with an increase in radius from the hub. Preferred embodiment impeller 40 will additionally have no rake.

(19) A preferred embodiment impeller 40 will additionally have an EAR (Expanded blade Area Ratio) within the range of 0.4-1.0. In a most preferred embodiment, the EAR will be between 0.47 and 0.55.

(20) In some embodiments, an impeller 40 will also preferably have a P.sub.mean/D below 0.9, where P.sub.mean is the cord/radius integrated pitch and D is diameter. In a most preferred embodiment, the P.sub.mean/D will be between 0.59 and 0.87.

(21) In some embodiments, an impeller 40 will also have a progressive pitch distribution from A leading edge to trailing edge.

(22) In some embodiments, this progressive pitch distribution may also be based on radius, where from 50% radius and out is constant, while from 50% radius to the hub is reduced.

(23) In some embodiments, an impeller 40 will also have a low drag, pressure equalized foil shape, commonly referred to as a wake-adapted propeller design. While there a wide variety of known foil shapes that may be suitable for various applications, one exemplary embodiment is known as a NACA 16 with an a=0.8 mean line camber distribution. One exemplary article discussing NACA 16 hydrofoils is entitled “Designing for Cavitation-Free Operation on Hydrofoils with NACA 16-Series Sections by Alan C. Connoly, J. Aircraft, November-December 1966, pp. 598-605, the teachings which are incorporated herein by reference.

(24) From the foregoing figures and description, several additional features and options become more apparent. Preferred embodiment impeller 40 may be manufactured from a variety of materials, including metals, resins and plastics, ceramics or cementitious materials, or even laminations, combinations or composites of the above. Nevertheless, for most applications metals may be preferable given the high forces, and the metals will preferably be intrinsically corrosion resistant, such as is the case with stainless steel.

(25) While aeration apparatuses are the focus of the present invention, preferred embodiment impeller 40 may also be used with other units that operate with the same or similar conditions and objectives as aeration units, such as mixers and related apparatus.

(26) While the foregoing details what is felt to be the preferred embodiment of the invention, no material limitations to the scope of the claimed invention are intended. Further, features and design alternatives that would be obvious to one of ordinary skill in the art are considered to be incorporated herein. The scope of the invention is set forth and particularly described in the claims herein below.