JPS59165895A - Impeller of centrifugal pump - Google Patents

Abstract

PURPOSE:To prevent lowering of efficiency, by a method wherein, provided height of a vane is (h) and a distance between two vanes is (a), a ratio h/a of the length to the width of a plane, which is present between the entry end of a vane and the back of an adjoining vane and extends at right angles to the virtual curve of fluid flowing between adjoining vanes, is set to a specified value. CONSTITUTION:In an impeller 3, a plane, which extends at right angles to the virtual curve l of fluid flowing between an optional vane 4a and a vane 4b located adjacent to the vane 4a and has length, being (h) that is the height of the vanes 4a and 4b, and the breadth being (a) that is a distance between the two vanes 4a and 4b, is imagined to be present between the vane 4a and the back of the vane 4b, and a ratio h/a of the length to the breadth of the plane is set to a value less than 2, for exmple, a value being nearly 1. Even if a suction specific speed is approximately 2000, this permits maintenance of sufficient cavitation performance, and besides, enables prevention of lowering of the pump efficiency, and allows to prevent the occurrence of low frequency pulsation and the like, with which reverse flow is attended, at a partial flow rate range.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an impeller for a centrifugal centrifugal pump with high cavitation performance.

Conventionally, when trying to improve the cavitation performance of a centrifugal centrifugal pump, the specific measures are as follows: TI) Increase the inlet diameter of the impeller.

(2) Increase the entrance angle of the blade.

(3) Make the inlet tip of the blade thinner.

(4) Reduce the number of blades.

(5) Smooth the path from the suction casing to the impeller.

Such measures have been taken.

Of these, (1) increasing the impeller inlet diameter is widely recognized as an effective means of improving suction performance, but recently, pumps have become larger and faster. As technology continues to progress and higher cavitation performance is required, simply increasing the impeller inlet diameter to meet these demands will lead to a decrease in efficiency. There is a risk of causing undesirable effects on pump operation, such as the occurrence of low frequency pulsation due to backflow in the partial flow range. It is being

S: n X Q3A/ N P S, Hr 4S:
Suction specific speed n: Pump rotation speed (rpm) Q: Pump discharge amount (door/TIdn) NPSHrq
: Required suction head (c) According to the above equation, if the pump becomes larger, the discharge amount Q of the pump will increase, and if the speed increases, the number of revolutions n of the pump will increase.

Now, if the required suction head NPSHrq is kept constant, the suction specific speed S increases as the pump becomes larger and faster.

Conventionally, a suction specific speed S of around 1000 has been regarded as a normal level, but recently, a suction specific speed S of around 2000 is often required.

Therefore, in order to obtain a pump with a suction specific speed S of 200 o'U after which the cavitation performance is sufficiently satisfied, various experiments were repeated through trial and error, and the following was discovered. did.

That is, as shown in Figure 2, consider the area of A (hereinafter referred to as AW) that is orthogonal to the vector of relative flow velocity at the blade inlet, and take Aw as a parameter (Awl > Aw
2) Aw3>A'w4), suction specific speed S and aspect ratio h
/a, the results shown in FIG. 4 were obtained. Note that h and a are as shown in Figure 3, and A
h=h'+h2, a=a'--2" f h
tte, htri, feather 4 a.

2 2 4b, and a is the average distance between the inner blades 4a and 4b.

Therefore, as can be understood from FIG. 4, even if Aw remains the same, the suction specific speed S increases as the aspect ratio h/a decreases.

On the other hand, if we try to obtain the same suction specific speed S, the aspect ratio h
/ Regardless of a, the larger of the applicable Aw,
For example, it can be seen that there are two methods: to select A w 4, or to select the smaller value of Aw, for example A Wl, in order to make this as small as possible considering the relationship of the aspect ratio h/a.

By the way, if the suction specific speed S is after 1500ffrJ, the purpose could be achieved with the former method, but if the suction specific speed S is after 2'0OOD, such a method will cause a decrease in efficiency and a problem in the partial flow area. This causes problems such as low-frequency pulsation due to backflow.

The reason why the efficiency decreases is that if Ay is increased,
If the impeller inlet diameter Do is large, the gap Sc between the impeller and the liner ring must be increased accordingly for machining accuracy. The amount of leakage QJ from the liner ring is expressed as QJ DrS, c, 81 - (ΔH differential pressure before and after the liner ring) (Dr: outer diameter of the impeller inlet), so the impeller inlet diameter Do With a large impeller, this leakage amount QA' is large, and the pump efficiency is reduced accordingly.

On the other hand, the mechanism behind the occurrence of low frequency pulsation is not clear, but the inlet diameter of the pump
It is said that in an impeller with a large o, the flow pattern inside the impeller changes in the partial flow region, causing a backflow.

When this pulsation occurs, it causes severe vibrations and noise, and sometimes even makes it impossible to operate. In particular, this phenomenon is often observed in impellers with good cavitation performance.

The present invention was made against this background, and its purpose is to reduce the suction specific speed to 2000#r.
A centrifugal centrifugal pump impeller that can ensure sufficient cavitation performance even after J, and is free from the risk of reduced pump efficiency and low-frequency pulsations due to backflow in the partial flow range. It's about providing cars.

In order to achieve this object, the present invention is characterized by the following configuration. In other words, a plane is assumed between the blade and the back surface of the adjacent blade, which is perpendicular to the imaginary streamline of the fluid flowing between the blades, the height of the blade is h, and the distance between the blades is a. This is an impeller for a centrifugal centrifugal pump characterized in that the aspect ratio h/a of this plane is set to a value smaller than 2.0.

In other words, by paying attention to the aspect ratio h/'a of the plane and setting this value to a value smaller than 2.0, the pump's suction specific speed S can be raised to 2000 or more without deteriorating the cavitation performance. Furthermore, since the inlet area of the vanes is not expanded, the above-mentioned reduction in pump efficiency and low-frequency pulsation due to backflow in the partial flow rate region do not occur.

Hereinafter, one embodiment of the present invention will be specifically described with reference to the drawings.

FIG. 1 shows a centrifugal centrifugal pump as viewed from the suction port side, where 1 represents the casing, 2 represents the suction port, and 3 represents the impeller.

Incidentally, this figure shows a state in which the impeller nut, which is attached to the center of the impeller 3, has been removed.

By the way, in the impeller-3, between any blade 4a and the back surface of the blade 4b adjacent to this blade 4a, as shown in FIG. Assuming a plane A that is perpendicular to the line l, the height of the blades 4a and 4b is h, and the distance between the inner blades 4a' and 4b is a, and the aspect ratio of this plane A is h/
Third, set a to a value smaller than 2.0, for example, a value close to 1, as shown in J(,).

Note that the height h of the blades 4a and 4b and the distance a between the inner blades 4a and 4b are once h+1.
The average value is taken if I, a=a'-.

Here, in evaluating the effects of the present invention, FIG.
) and an impeller based on the present invention shown in FIG. 3(b), for example.
As shown in Figure 3(b), we fabricated an impeller with a larger blade inlet area and tried the experiment from various angles.
As mentioned above, in the pump shown in Figure 3(a), a decrease in pump efficiency and the occurrence of low frequency pulsations in the partial flow range were observed. As can be seen, the suction specific speed S increased to 2000 or more, and the cavitation performance did not deteriorate. Of course, no decrease in pump efficiency or occurrence of low frequency pulsations in the partial flow range was observed.

In the present invention, the blade inlet area is set to 9.9 mm as long as the required suction specific speed can be obtained. Needless to say, it is necessary to set it small.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing one embodiment of the present invention, FIG. 2 is an explanatory diagram showing the relationship between adjacent blades in the same embodiment,
Fig. 3 (,) (b) is an explanatory diagram showing the blade inlet area according to the present invention and the conventional blade inlet area, respectively, and Fig. 4 shows the aspect ratio h/a when Aw is taken as a parameter.
It is a graph which shows the relationship between and suction specific speed S. 1...Casing, 2...Suction port, 3...Impeller,
4a, 4b...Blade, A...Plane, l...Virtual streamline Patent applicant Kubota Iron Works Co., Ltd. Agent Patent attorney Takashi Suzue - Continued from page 1 0 Inventor Teruaki Fukamachi Nakamiya Oike, Hirakata City 1-1-1 Kubota Iron Works Co., Ltd. Hirakata Machinery Works 0 Inventors Juno Tsukamoto 1-1-1 Nakamiya Oike Hirakata City Hirakata Machinery Works Kubota Iron Works Co., Ltd.

Claims (1)

[Claims] Between the inlet end of the blade and the back surface of the blade adjacent to this blade, there is a line that is perpendicular to the imaginary streamline of the fluid flowing between the blades, the height of the blade is h, and the distance between the blades is a. An impeller for a centrifugal centrifugal pump characterized in that the aspect ratio h/a of this plane is set to a value smaller than 2.0.