Rotary kinetic fluid motors or pumps – Including casing part selectively movable relative to fixed... – Separate liner portion
Reexamination Certificate
2002-06-27
2004-05-18
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Including casing part selectively movable relative to fixed...
Separate liner portion
C415S173100, C415S221000
Reexamination Certificate
active
06736594
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an axial-flow type hydraulic machine, having an impeller of non-voluminous type therein, and in particular, to the machine being able to avoid falling into instability in flow, by suppressing pre-swirl generating in main flow of re-circulating flow at an impeller blade inlet and stalls due to blade swirls, thereby being suitable to be applied into an axial-flow pump and/or a reversible pump-turbine.
Rotation machines, being called by turbo-machines, can be classified into the followings, from viewpoints of the fluid, which is deal with therein, and the types thereof:
1. Fluid, which is deal with:
Liquid, and Gas.
2. Types:
Axial flow, Diagonal flow, and Centrifugal types.
The pump, which is mainly used at present, comprises a bell mouth, a casing, a pump, and a diffuser, etc.
An impeller rotating within the pump casing is rotationally driven by means of a rotation shaft thereof, thereby giving energy to liquid, which is sucked from a suction casing. The diffuser has a function of converting a portion of velocity energy of the fluid into static pressure.
FIG. 12
shows a characteristic curve between pump head and flow rate (i.e., pump head-flow rate characteristic curve), being typical to such the turbo-machine as shown in
FIG. 2
, wherein the horizontal axis is a parameter indicative of the flow rate while the vertical one that indicative of the pump head. As is shown in this figure, the pump head comes down as the flow rate rises up, within a low flow rate region, however it shows a so-called right-uprising property (i.e., property of rising up at the right-hand side), in which the pump head rises up in proportion to rising-up of the flow rate, during when lying within S region. Further, when coming up to be more than the right-uprising property region, then the pump head falls down as the flow rate rises up, again.
When the turbo-machine is operated with the flow rate within the right-uprising property region S, mass of liquid generates the so-called surging phenomenon, where it oscillates or vibrates by exiting by itself within conduit lines. Re-circulation flow is generated at an outer periphery of the impeller inlet, when the flow rate of liquid flowing through the turbo-machine comes down, however swirl is generated in the liquid through narrowing in flow channel for the liquid entering into the impeller blades or vanes, therefore the right-uprising property is caused (see FIG.
2
).
The surging gives damages, not only upon the turbo-machine, but also on the pipes, which are connected with in an upper stream and a down stream, therefore the turbo-machine is inhibited from operating stably in that low flow-rate region. Also, for enlarging the operation region of the turbo-machine, various methods are proposed for suppressing the surging, as described below, other than improvements of profile of the impeller blade:
1. Casing Treatment:
This is for the purpose of improvement in stall margin, by forming thin grooves at 10-20% of chord length of the impeller blade. Namely, with the casing treatment being proposed previously, the grooves are formed on the casing inner wall, within the region where the impeller blades lie or reside, in an axial direction, in peripheral direction (i.e., on the periphery thereof) or an oblique direction, while directing in a radius or slantwise.
2. Separator:
This is for the purpose of preventing the re-circulation flow from being enlarged therein, wherein a separator is disposed for separating a reverse-flow portion of the re-circulation flow from a down-stream portion thereof, which is generated at an outer edge of the impeller blade inlet within the low flow rate region.
As examples of the separators, which are applied into an axial-flow type hydraulic machine (one of the turbo-machines), include a suction-ring method, a blade-separator method, and an air-separator method.
With the suction-ring method, the reverse-flow is enclosed within an outside of the suction-ring, and with the blade-separator method, a fin is provided between the casing and the ring. Also, with the air-separator method, moving blades or vanes are opened at tip portions thereof, to guide the reverse-flow into an outside of the casing, thereby preventing the reverse-flow from revolution thereof by means of the fin, and this is large in effect, comparing to both of the two mentioned above, however it comes to be large in scale of the apparatus.
As the conventional art for obtaining such the right-uprising pump head, enabling the stable operation, the provisions of such the casing treatment and the separators are already known, as was mentioned in the above. The prior art of such kind is described in the specification of, for example, U.S. Pat. No. 4,212,585, etc.
Other than this, as is described in Japanese Patent Laying open No. 2000-303995 (2000), also a pump is proposed, which comprises a plural number of grooves are formed upon the inner case surface of a diagonal flow pump, connecting the impeller blade inlet side to within a region on an inner case surface where the blades lies, to suppress the revolution or swirl in an inlet, thereby obtaining a pump head curve having no such the right-uprising property thereon.
With such the casing treatment and the separators of the conventional art mentioned above, it is possible to shift the right-uprising property of the pump head curve into the lower flow rate side, so as to enlarge the stable operation region, however the axial-flow type hydraulic machine is lowered in the efficiency thereof, by 1% for each increase of 10% in the loss margin, with the casing treatment.
Also, with the machine, in which the grooves are formed connecting between the impeller blade inlet side and the region on casing inner surface where the blades lie or reside, the grooves can be formed easily, and the decrease in the efficiency is small, and further it is possible to obtain the pump head curve of no such the right-uprising property. However, no consideration was paid upon the fact that pulsation occurs in pressure due to interference between the flow from the blades and the grooves, when the blades pass by the plural number of grooves formed on the casing inner surface, therefore there is a probability of increasing the vibrations and/or noises.
Further, in the turbo-machine, such as the axial-flow type hydraulic machine, cavitations may occur in the vicinity of the impeller blade inlet thereof. The cavitations are phenomena of generating a large number of bubbles in a liquid due to vaporization when pressure comes down to the vicinity of saturation vapor pressure of the liquid, which flows into the pump, and the generated bubbles flow within an inside of the pump and collapse accompanying with pressure recovery therein. The generation of cavitations may brings about harmful effects, such as, an increases of vibration or/and noises and a low performance sometimes, as well as, injuring the impeller and the wall surface of the casing.
NPSH is called by “Re. NPSH”, being necessary for the pump to generate no such cavitations therein under a certain operation condition thereof. The NPSH means the available head (i.e., the net positive suction head), and indicates the height of total pressure of the liquid above the reference level of the impeller, comparing to the saturation vapor pressure of the liquid under that temperature. The lower the NPSH, the nearer to the saturation vapor pressure: thus, in the condition where the cavitations can be generated easily. Namely, it can be expressed that, the lower the “Re. NPSH”, the more difficult the cavitations to be generated in the pump.
Though the situations or conditions of generating the cavitations are various depending upon the operating condition thereof, however in the axial-flow and/or the diagonal-flow pump, the “Re. NPSH” has a tendency to be high in the small flow-rate where the right-uprising property appears. Namely, it is in the condition where the cavitations can be easily generated.
SUMMARY OF THE INVENTION
An object, therefore a
Anzai Yoshio
Irie Kouichi
Kurokawa Junichi
Okamura Tomoyoshi
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Look Edward K.
White Dwayne J.
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