Centrifugal type fluid machine

Details Centrifugal type fluid machine Centrifugal type fluid machine

1997-09-10

2000-12-19

Look, Edward K.

Rotary kinetic fluid motors or pumps

Working fluid passage or distributing means associated with...

Plural rigidly related blade sets

4152083, 4152111, 4151993, F04D 2902

Patent

active

061620157

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a multi-stage or single-stage centrifugal type fluid machine in which diffuser vanes are formed on a diffuser on the outer periphery of an impeller and, more particularly, to a centrifugal type fluid machine preferable for a boiler feed water pump and the like installed at a thermal power plant.


BACKGROUND ART

A diffuser having diffuser vanes is constituted by a side wall at a side plate end and another side wall at a core plate end of a radial impeller (hereinafter referred to simply as "impeller") and diffuser vanes. In a centrifugal type fluid machine having diffuser vanes, the diffuser is disposed such that the foregoing both side walls of the diffuser lie in a surface nearly perpendicular to a main shaft; and a radial diffuser is generally used, the radial diffuser allowing a high-velocity, radial, outward fluid which flows out of the impeller to flow out as it is in the radial direction. As the diffuser vanes, there are so-called "two-dimensional vanes" which have the same sectional shape from the side wall at the side plate end to the side wall at the core plate end constructing the diffuser. Ideally, a bent passage for guiding the fluid on the downstream side of the diffuser to a radial flow is formed to have a large radius of curvature. In a multi-stage centrifugal type fluid machine, however, allowing a large radius of curvature is disadvantageous in reducing the size of the machine in the direction of the radius and in the direction of the main shaft; therefore, the bent passage is composed of a rectangular passage which hardly has a radius of curvature.
The diffuser and the bent passage are good in the aspect of size reduction and economy of a fluid machine; on the other hand, however, a passage having an acute curve is disposed in the vicinity of an outlet of the diffuser and therefore, a force is applied to the curved portion in an oblique outward direction due to a change in the momentum which takes place when the upward flow in the radial direction is switched to a flow in the direction of the main shaft at the inlet of the bent passage. Hence, the flow in the vicinity of the outlet of the diffuser becomes a flow inclined toward the core plate rather than in the radial direction. As a result, the boundary layer of the surface along the side wall at the side plate end markedly develops, while the development of the boundary layer of the surface along the side wall at the core plate end becomes small because a main current approaches thereto. This trend becomes so marked that a handled flow rate is decreased below a design point, causing unstable characteristics (a drop in head-discharge curve) of a pump in a low flow rate zone. For this reason, a diffuser having so-called three-dimensional vanes has been developed to improve the unstable characteristics, to prevent a pump from becoming larger, and also to prevent pumping efficiency from being reduced, the diffuser having been disclosed in Japanese Patent Unexamined Publication No. 61-258998.
The diffuser vanes are shaped so that the spreading angle between the vanes is made smaller in a portion near the side wall at the side plate end, while the spreading angle between the vanes in a portion near the side wall at the core plate end is made larger. Hence, a rise in pressure due to the deceleration of the main stream flowing in the vicinity of the side wall of the side plate of the diffuser decreases so as to control the boundary layer which develops along the side wall at the core plate end, and the loss attributable to a secondary flow of the boundary layer is decreased and the separation of the flow on the side wall at the side plate end which takes place in the low flow rate zone is prevented.
In the diffusers having the two-dimensional or three-dimensional vanes, no consideration has been given to the flow of a fluid in the diffuser in the low flow rate zone or to the flow of a fluid which comes out of a multi-stage diffuser and passes through a bent passage. Regarding a flow on

REFERENCES:
patent: 4938661 (1990-07-01), Kobayashi et al.
patent: 5178516 (1993-01-01), Nakagawa et al.
patent: 5595473 (1997-01-01), Nagaoka et al.
Japanese Patent Unexamined Publication No. 61-258998, Nov. 17, 1986.
Japanese Patent Unexamined Publication No. 4-334798, Nov. 20, 1992.

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