Centrifugal pump with serrated impeller

A centrifugal pump and an impeller thereof are provided. The impeller defines an outer peripheral edge which includes a plurality of serrations circumferentially thereon. The plurality of serrations are configured such that additional power and momentum are transferred to a working fluid of the pump, which results in an additional pressure rise in the working fluid at relatively low flow rates of the centrifugal pump.

FIELD OF THE INVENTION

This invention generally relates to centrifugal pumps and their associated componentry, and more particularly to the impeller of a centrifugal pump.

BACKGROUND OF THE INVENTION

An impeller is a rotating component of a centrifugal pump which transfers energy from the power source that drives the pump to the fluid being pumped by accelerating the fluid outward from the center of rotation. The velocity of the impeller translates into pressure when the output movement is confined by the pump casing. Typically, an impeller includes a central hub or eye which is positioned at the pump inlet, and a plurality of vanes to propel the fluid radically. The central hub typically includes an axial bore or opening which may be splined to accept a splined driveshaft.

One of the challenges of centrifugal pumps is providing a generally constant pressure rise at the output of the pump across varying flow rates of the pump. This generally constant pressure rise is desirable for improving a dynamic stability of the system. Indeed, many contemporary high efficiency pumps, despite their high efficiency, have an appreciably lower pressure rise at low flow rates than at higher flow rates. To address this problem, a common solution is to use a less efficient centrifugal pump which does not exhibit as drastic of a pressure rise differential at low flow rates by increasing pump internal leakages. While such a solution has proven to be effective, it is not desirable in many cases, especially those applications where good thermal efficiency and low power consumption is a requirement.

Another approach to maintain a generally constant pressure rise across differing flow rates is to incorporate a stability valve into the system that effectively acts as a fixed orifice at any given flow. Unfortunately, this stability valve consumes extra power and reduces the pressure output of the pump. Further, with such a configuration, the overall size, weight, and cost of the system is increased.

Accordingly, there is a need in the art for a centrifugal pump which provides for a reduced amount of pressure rise variation across varying flow rates. The invention provides such a centrifugal pump. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.

BRIEF SUMMARY OF THE INVENTION

In one aspect, embodiments of the invention provide an impeller for a centrifugal pump. An impeller according to such an embodiment includes a disc-shaped shroud which has a central axis and a central hub circumscribing the central axis. The impeller also includes a disc shaped baseplate having a central axis coaxial with the central axis of the shroud. The baseplate has a plurality of vanes extending from a first surface of the baseplate. The shroud includes a plurality of serrations formed circumferentially along a periphery of the shroud. The baseplate includes a plurality of serrations formed circumferentially along a periphery of the baseplate. The shroud is mounted against the baseplate.

The central hub of the shroud has a first outer diameter. The baseplate includes a central hub extending axially from the first surface of the baseplate. The central hub of the baseplate has a second outer diameter which is less than the first outer diameter. A portion of the central hub of the baseplate extends axially into an opening defined by the central hub of the shroud.

The plurality of serrations of the baseplate includes a plurality of major teeth and a plurality of minor teeth arranged such that multiple minor teeth are arranged between adjacent ones of the plurality of major teeth. Each one of the plurality of major teeth has a thickness measured in the circumferential direction. Each one of the plurality of minor teeth has a thickness measured in the circumferential direction. The thickness of each of the plurality of major teeth is greater than the thickness of each of the plurality of minor teeth, respectively.

The plurality of vanes are aligned with the plurality of major teeth such that a radially outer facing surface of each vane is coplanar with a radially outer facing surface of each major tooth, respectively. A combined thickness of each one of the aligned plurality of vanes and plurality of major teeth measured circumferentially is variable in the axial direction.

The plurality of serrations of the shroud includes a plurality of major teeth and a plurality of minor teeth such that multiple minor teeth of the plurality of minor teeth are interposed between adjacent ones of the plurality of major teeth. The plurality of major teeth of the shroud are aligned with the plurality of major teeth of the baseplate. The plurality of minor teeth of the shroud are aligned with the plurality of minor teeth of the baseplate.

Each one of the plurality of serrations of the shroud has a first width measured axially and each one of the plurality of serrations of the baseplate has a second width measured axially. The first width is less than the second width.

In another aspect, embodiments of the invention provide an impeller for a centrifugal pump. An embodiment of a centrifugal pump according to this aspect includes a shroud and a baseplate. The shroud is mounted to the baseplate. A plurality of vanes are formed on the baseplate and are axially interposed between a portion of the baseplate and the shroud. The shroud and baseplate define an outer peripheral edge of the impeller. The outer peripheral edge includes a plurality of serrations formed circumferentially thereon.

Adjacent ones of the plurality of serrations are separated by gaps such that the plurality of serrations project radially outward. Each one of the plurality of serrations has a generally rectangular cross-sectional shape in the radial direction. The plurality of vanes project radially outward to the outer peripheral edge of the impeller. The plurality of serrations are formed by a plurality of serrations formed on the shroud and a plurality of serrations formed on the baseplate. The plurality of serrations on the shroud are aligned with the plurality of serrations on the baseplate.

In yet another aspect, embodiments of the invention provide a centrifugal pump. An embodiment of such a centrifugal pump includes a pump casing that defines an inlet, an outlet, and an internal cavity disposed between the inlet and the outlet. The pump also includes a drive shaft. A portion of the drive shaft is rotatably disposed within the internal cavity. The pump also includes an impeller disposed within the internal cavity. The impeller is mounted to the drive shaft such that it is rotatable with the drive shaft. The impeller is disc shaped and defines an outer peripheral edge. A plurality of serrations are formed on the outer peripheral edge.

The impeller also includes a shroud and a baseplate. The shroud is mounted to the baseplate. The plurality of serrations are formed on each of the shroud and the baseplate. The impeller also includes a plurality of vanes formed on the baseplate. The plurality of vanes extend radially outward to the outer peripheral edge of the impeller such that the radial extents of the plurality of vanes are adjacent select ones of the plurality of serrations. The plurality of serrations have a generally rectangular cross-section in a radial direction.

DETAILED DESCRIPTION OF THE INVENTION

Turning now to the drawings, an embodiment of a centrifugal pump and its associated serrated impeller according to the teachings of the present invention are illustrated. As will be explained in greater detail below, the serrated impeller overcomes problems with existing impeller designs by reducing the variance of pressure rise across differing flow rates. Indeed, the serrated impeller imparts additional momentum and velocity to a working fluid of the pump at low flow rates such that, even at such low flow rates, there is a satisfactory pressure increase in the working fluid. At higher flow rates, the velocity of the working fluid approaches that of the impeller itself, and as such, the serrated impeller has less of an impact on the pressure rise of the working fluid. As a result, the pump maintains a significantly “flatter” pressure rise characteristic of the working fluid across a broad spectrum of flow rates. As a result, the need for a stability valve as well as the need to utilize a less efficient pump is eliminated.

With particular reference toFIG. 1, a centrifugal pump20incorporating the aforementioned impeller is illustrated. More specifically,FIG. 1illustrates a 3-stage centrifugal pump. Two of the stages employ serrated impellers according to the teachings of the present invention. While a 3-stage centrifugal pump is illustrated, it will be readily recognized that the advantages of the serrated impeller as described herein may be employed in other embodiments of centrifugal pumps, e.g. a single stage centrifugal pump.

Centrifugal pump20includes an outer casing22. Centrifugal pump20also includes a number of inlets and outlets for each of its respective stages. Indeed, for one of the aforementioned stages, there is an inlet24and an outlet26. An internal cavity28is defined between inlet24and outlet26. A serrated impeller30is situated within internal cavity28. Impeller30is utilized to pump or convey a working fluid from inlet24to outlet26. In another one of the stages of centrifugal pump20, there is another inlet34and outlet36. Another internal cavity38is positioned between inlet34and outlet36. A serrated impeller40is situated within internal cavity38. This second serrated impeller40is identical to serrated impeller30, except that it is a mirror image.

Turning now toFIG. 2, a cross-section of centrifugal pump20is shown taken through the plane extending through outlet26. This cross-section illustrates the relative positioning of impeller30within internal cavity28. Impeller30is mounted on a shaft32(See alsoFIG. 1). Rotation of shaft32results in a like rotation of impeller30. A peripheral edge42of impeller30includes a plurality of serrations44as shown.

In the particular configuration shown inFIG. 2, as impeller30rotates clockwise relative to a working fluid disposed within internal cavity28, the plurality of serrations44impart extra momentum and power to the fluid causing the fluid to locally spin in a direction opposite to the rotation of impeller30, i.e. counterclockwise. At low flow rates, this results an additional pressure rise. As a result, the relatively small pressure rise at low flows of existing designs is overcome by such a configuration.

As the flow rate is increased, the impeller circumferential velocity and the velocity of the working fluid within the internal cavity28approach one another. As a result, there is less momentum and power transfer to the working fluid from the plurality of serrations44. Accordingly, the pressure rise of the working fluid at a low flow rate is closer to the pressure rise at a high flow rate than in non-serrated impeller designs. Therefore, the undesirable variance of pressure rise across varying flow rates is substantially reduced with such a configuration.

With reference now toFIGS. 3-7, the structural attributes of impeller30will be described in greater detail. As discussed above, but for being a mirror image, impeller30is identical to impeller40shown inFIG. 1. Therefore, the description provided for impeller30applies equally well to impeller40introduced above.

With particular reference toFIG. 3, impeller30includes a shroud50and a baseplate52. Shroud50is mounted directly to baseplate52. This mounting may be achieved by any mechanical connection. Shroud50and baseplate52are concentrically arranged about an axis54of impeller30passing through a center thereof. As can also be seen inFIG. 3, the plurality of serrations44extend radially outward and define the outer periphery of impeller30. As will be understood from the following, both shroud50and baseplate52include their own serrations which are aligned with one another such that when fully assembled they form the aforementioned plurality of serrations of impeller30. It will be recognized, however, that such an alignment is not necessary. In other embodiments, the plurality of serrations on shroud50may be misaligned with the plurality of serrations of baseplate52.

With reference now toFIG. 4, shroud50includes a central hub56defining a central opening58. A plurality of serrations64define the outer periphery of shroud50. This plurality of serrations64includes a number of major teeth80and minor teeth82, as will be discussed in greater detail below.

Baseplate52also includes a central hub66with an opening68therethrough. Openings58,68are sized such that shaft32(SeeFIG. 1) may extend therethrough. Additionally, opening58is also sized such that the working fluid flows from internal cavity28and subsequently contacts baseplate52.

A plurality of vanes72extend axially outward from a first surface70of baseplate52. As can be seen from inspection ofFIG. 4, these vanes are arcuate in shape and extend from a diameter which is greater than an outer diameter of central hub66to an outer periphery of baseplate52. In other embodiments, vanes72may extend radially inward such that they contact central hub66. Also in other embodiments, vanes72may not extend radially to the outer periphery of impeller30, but instead may stop short of this outer periphery.

As was the case with shroud50, baseplate52also includes a plurality of serrations74. As can also be seen inFIG. 4, each one of the plurality of vanes72includes a radially outer facing surface which is generally coplanar with a radially outer facing surface select ones of the plurality of serrations74. As discussed in greater detail below, this plurality of serrations74includes a number of major teeth90and a number of minor teeth92.

Turning now toFIG. 5, an additional hub76extends axially outward from a second surface78of baseplate52for the reception of shaft32(SeeFIG. 1). Although not shown, hub56as well as hub76may also include dynamic seals mounted thereon to sealingly engage an interior surface of pump casing22.

With reference now toFIG. 6, the particular structural details of the aforementioned plurality of serrations will be discussed. Turning first to the plurality of serrations of shroud50, the same includes a number of major teeth80and minor teeth82. Major teeth80are distinguishable from minor teeth82in that they have a thickness t1measured in the circumferential direction which is greater than a thickness t2measured in the circumferential direction of minor teeth82. As can also be seen in this view, major and minor teeth80,82have a uniform width measured in the axial direction.

In a similar manner, the plurality of serrations of baseplate52include a number of major teeth90and minor teeth92as shown. Major and minor teeth90,92, are distinguishable in that a thickness t3measured in the circumferential direction of major teeth90is greater than a thickness t4measured in the circumferential direction of minor teeth92. It will also be recognized from inspection ofFIG. 6that thickness t1is equal to thickness t3and thickness t2is equal to thickness t4. As such, when the respective plurality of serrations of shroud50and baseplate52are aligned as shown they generally form a combined plurality of serrations with a number of major teeth and minor teeth. As described above, however, such an alignment is not necessary.

Another distinguishing factor between the major teeth80,90and minor teeth82,92is that between each major tooth80,90an end of one of the aforementioned vanes72is disposed. As introduced above, each vane72includes a radially outer facing surface which is generally coplanar with a radially outer facing surface of each major tooth90on baseplate52. The same holds true for each major tooth80of shroud50. From inspection ofFIG. 6, however, it will be recognized that the aforementioned radially outer facing surfaces of vanes72and major teeth90form a generally continuous and uninterrupted radially outer facing surface94.

It will also be recognized from inspection ofFIG. 6that major teeth80,90are annularly spaced apart at an angle θ1which is greater than an angular spacing between θ2between adjacent minor teeth82,92. In the particular configuration shown inFIG. 6, there are two minor teeth82,92positioned between adjacent major teeth80,90. Further, the spacing or gaps formed between adjacent ones of major teeth80and minor teeth82as well as adjacent ones of minor teeth82is constant. The same holds true for major and minor teeth90,92of baseplate52. It will be recognized from the teachings herein that any number of teeth may be utilized. Further, it is also contemplated that rather than using major teeth and minor teeth of differing thicknesses taken in the circumferential direction, all teeth may have a uniform thickness.

Turning now toFIG. 7, a cross-section of impeller30is illustrated. The aforementioned concentric alignment of shroud50and baseplate52is shown. Hub66of baseplate52extends axially into opening58of hub56of shroud50. Working fluid enters opening58as illustrated generally by flow directional arrows, and then encounters vanes72as it is propelled radially outward to the outer periphery of impeller30.

As discussed above, the plurality of serrations of impeller30are configured to impart additional momentum and power to the working fluid at lower flow rates. Indeed,FIG. 9illustrates a comparative example of a centrifugal pump employing a serrated impeller and a centrifugal pump which does not include a serrated impeller, i.e. a baseline impeller.

As can be seen from this graph, the difference in pump pressurize at a low flow rate of 10 gpm and a high flow rate of 50 gpm for a pump employing a serrated impeller is considerably less than a baseline impeller. As a result, the system produces a more desirable pressurize across low flow rates. This advantageously reduces or entirely eliminates the need to use a less efficient pump, or additionally or in the alternative, a stability valve to ensure that there is a sufficient pressurize at lower flow rates.