Patent Application
20110027076
An embodiment is directed to inducers, and more particularly to a housing for an inducer that incorporates grooves or vanes that are helical in nature and in counter rotation with respect to the rotation of the blades of the inducer, which grooves or vanes capture fluid rotating with the inducer blades and use that rotation to move the fluid up along the grooves or vanes and into an impeller, pump or other device.
Not Applicable.
Not Applicable.
A common problem with spiral inducers used within centrifugal pumps and similar devices is that the fluid in the tank in which the centrifugal pump is installed will begin to rotate in the same direction as, and along with, the inducer blades. When this occurs, the fluid does not move up through the inducer as efficiently. This phenomenon can also result in a change in pressure near the inlet of the inducer and increase the amount of net positive suction head (NPSH) required to make the pump continue to work efficiently or properly.
Net positive suction head required (NPSHR) is a measure of the amount of head or pressure required to prevent the fluid from cavitating, i.e., the formation of vapor bubbles in a flowing fluid. It is desirable to prevent cavitation in devices like inducers, impellers and pumps because the fluid vapor bubbles created by cavitation can generate shock waves when they collapse that are strong enough to damage moving parts around them. While a higher NPSHR is desirable to prevent cavitation in an inducer, impeller and pump, a high NPSHR can also generate cavitation in the tank as the fluid level drops. Hence, a low NPSHR is desirable to enable more fluid to be pumped out of the tank or structure. Accordingly, other solutions are required to reduce cavitation at the inlet of an inducer while not increasing the NPSHR.
Inducers are frequently used in cryogenic systems, including storage tanks, rocket fuel pump feed systems, and other similar uses. Inducers are used in such systems to prevent the fluid being moved from cavitating in the impeller or pump, which can occur when there is not enough pressure to keep the liquid from vaporizing. Non-cavitating inducers are used to pressurize the flow of the fluid sufficient to enable the devices to which the inducer is attached to operate efficiently. An excellent discussion of the fluid dynamic properties of inducers is provided by B. Lakshminarayana, Fluid Dynamics of Inducers—A Review, Transactions of the ASME Journal of Fluids Engineering, December 1982, Vol. 104, Pages 411-427, which is incorporated herein by reference.
The techniques used to improve pump performance relative to the operation of inducers vary significantly. For example, Nguyen Duc et al., U.S. Pat. No. 6,220,816, issued Apr. 24, 2001, describes a device for transferring fluid between two different stages of a centrifugal pump through use of a stator assembly that slows down fluid leaving one impeller before entering a second impeller. A different technique is used in Morrison et al., U.S. Pat. No. 6,116,338, issued Sep. 12, 2000, which discloses a design for an inducer that is used to push highly viscous fluids into a centrifugal pump. In Morrison et al., an attempt is made to resolve the problem of fluids rotating with the inducer blades by creating a very tight clearance between the blades of the auger of the inducer and the inducer housing, and configuring the auger blades in such a way as to increase pressure as fluid moves through the device to the pump.
While grooves have been used in inducer designs in the past, they have not been used to help efficiently move the fluid through the inducer. For example, in Knopfel et al., U.S. Pat. No. 4,019,829, issued Apr. 26, 1977, an inducer is illustrated that has a circumferential groove around a hub at the front of the inducer. This design causes turbulence to develop within the grooves of the inducer hub rather than in the fluid outside of the grooves, thereby reducing the tendency of the fluid to pulsate and generate noise.
Grooves are also illustrated and described in Okamura et al., An Improvement of Performance-Curve Instability in a Mixed-Flow Pump by J-Groves, Proceedings of 2001 ASME Fluids Engineering Division, Summer meeting (FEDSM '01), May 29-Jun. 1, 2001, New Orleans, La. In Okamura et al., a series of annular grooves are formed on the inner casing wall of a mixed-flow water pump to suppress inlet flow swirl and therefore passively control the stability performance of the pump. In particular, the J-grooves of Okamura et al. reduce the onset of back flow vortex cavitation and rotating cavitation that can be induced by the flow swirl at the inlet of the inducer.
Okamura et al. acknowledge, however, that increasing the specific speed of mixed-flow pumps has a tendency to make their performance curves unstable and to cause a big hump at low capacities, thus it is stated that it is doubtful that the illustrated technique would be effective for higher specific-speed (i.e., higher flow rate) pumps.
a is a partially broken, cross-sectional, side view of an impeller, inducer auger and an interior hub of an inducer including a series of imbedded groves in accordance with an embodiment;
b is a partially broken, plan view of inlet vanes for the impeller of
An embodiment is directed to inducers, and more particularly to a housing for an inducer that incorporates grooves or vanes that are helical in nature and in counter rotation with respect to the rotation of the blades of the inducer, which grooves or vanes capture fluid rotating with the inducer blades and use that rotation to move the fluid up along the grooves or vanes and into an impeller, pump or other device.
A series of helical grooves 24 are machined or formed into the circular interior wall 28 of the outer housing 18, either after the inlet (such that they start at the interior wall 28) or starting at a transition area 26 between the inlet 20 and the interior wall 28. The grooves 24, for example, can start out in the transition area 26 with a tapered section 30 and then form one or more semi-circular grooves 24 within the interior wall 28. As noted, the grooves 24 have a substantially helical shape that spirals in a second direction that is counter rotation to the first direction of the blades 17 of the auger 12. The grooves 24 can vary in depth and width, and the number of grooves 24 is dependent upon the fluid in the tank or structure and the process conditions.
Accordingly, as noted above, the number of grooves 24 can range from one groove 24 to as many grooves 24 as are necessary to maintain a lower NPSHR in the tank or structure. In particular, the one or more grooves 24 move fluid that is not being propagated up through the inducer 10 by the blades 17 because the fluid is rotating with the blades 17. More efficiently moving the fluid up through the inducer increases the NPSH (head) so, for example, a pump attached to the inducer 10 can pump the fluid to a lower level within the tank or structure and thus increase the capability and efficiency of the pump. The lowest fluid level a tank or structure can be pumped to is related to the point at which cavitation can occur because there is not enough NPSHA to prevent a vacuum. However, stopping cavitation from occurring is not a purpose of the grooves 24, since it will occur in any tank when the level of the fluid is pumped to the point where NPSHA cannot prevent a vacuum. Hence, a purpose of the present invention is to increase the efficiency of the pump so that the fluid in the tank or structure can be pumped to a lower level.
The grooves 24 can extend all of the way into the outlet 32 of the inducer 10. The counter rotation of the grooves 24 captures at least a portion of the fluid that is rotating with the blades 17 by pushing it into the grooves 24 and then uses that counter rotation to move the fluid up a path formed by the grooves 24 to the outlet 32 and into the structure above the inducer 10, such as an impeller. Since the helical pattern of the grooves 24 is counter to the helical pattern of the blades 17, the portion of the fluid pushed into the grooves 24 readily follows the path formed by the grooves 24 up the sides of the wall 28. If the grooves 24 had a helical pattern that was not counter to blades 17, the blades would be constantly cutting across the path of the grooves 24 and the fluid would not be able to follow the path. The blades 17 need to be positioned sufficiently so that fluid cannot readily escape between the wall 28 and the blades 17.
Although the grooves 24 and blades 17 are shown following an even spiral pattern, other patterns could also be used, as long as the pattern for the blades 17 matches the reverse pattern for the grooves 24. Hence, if the pattern of the blades became tighter as it progressed toward the outlet 32, the pattern for the grooves 24 would also have to become tighter, by an equal degree, as the grooves 24 moved up the interior wall 28, so as to prevent the blades 17 from cutting across the grooves 24 instead of allowing fluid around the blades 17 to follow the path of the grooves 24.
The inducer 60 of
a illustrates an embodiment of the inducer assembly 80 where the grooves 82 are formed within an interior wall 84 of an interior hub 86, instead of in the exterior housing 88. The grooves 82 are helical shapes that spiral in the second direction, which is counter rotation to the first direction. The auger 90 has blades 92 which are positioned sufficiently close to the interior wall 84 to push at least a portion of the fluid into the grooves 82 and guide fluid rotating with the blades 92 along a second path formed by the grooves 82. The grooves can have any of the shapes described above, or other shapes as may be appropriate.
a also illustrates how the auger 90, with blades 92, is mounted to the shaft 94 with a mounting assembly 96, such as a shaft bolt, a weld, a clamp, a cap or other suitable fastening mechanism that will mount the auger 90 to the shaft 94. The auger 12 would be mounted to the shaft 14 of
In
Hence, while a number of embodiments have been illustrated and described herein, along with several alternatives and combinations of various elements, for use in an inducer to a pump or impeller, it is to be understood that the embodiments described herein are not limited to inducers only used with pumps and impellers and can have a multitude of additional uses and applications. Accordingly, the embodiments should not be limited to just the particular descriptions, variations and drawing figures contained in this specification, which merely illustrate a preferred embodiment and several alternative embodiments.
This is a non-provisional, utility patent application, taking priority from provisional patent application Ser. No. 61/273,376, filed Aug. 3, 2009, which application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61273376 | Aug 2009 | US |
