式中R2——葉輪出口半徑;
u——壓水室內(nèi)液體速度

水室計(jì)算斷面流量的影響并不大。

實(shí)際上如中. A.鮑格尼茨卡婭在全蘇水力機(jī)械科學(xué)研究所和B. n.格爾諾夫斯基在非金屬建筑材料研究所進(jìn)行開(kāi)進(jìn)行的試驗(yàn)研究指出那樣

根據(jù)公式(3-3-3)和式(3-3-4)可以確定泵比轉(zhuǎn)速與壓水室計(jì)算斷面特征尺寸AF泡沫泵之間的關(guān)系。

Section I Flow Spectrum of Pressure Chamber with Wide Section Channel

1. Flow of liquid in pressurized water chamber

According to the passing conditions of large particles, the pressure chamber of slurry pump is made into a semi-helical or slightly helical annular pressure chamber (constant section). The minimum section of the pressure chamber, that is, the section between the tongue and the impeller, should have such a large size that the large particles passing through the impeller can pass through the pressure chamber without hindrance. Experiments conducted by the Institute of Non-metallic Building Materials show that the distance between the tongue and impeller decreases (smaller than the size of solid particles pumped), which will cause solid particles to be trapped between the impeller and the water chamber, resulting in impact load and increasing wall wear of the water chamber on the tongue section.

The typical slurry pump pressure chamber sketch is shown in Figure 3-3-1. The section II-II of the pressure chamber along the axis of the vertical diffuser (pressure short tube) is generally called the calculation section. The section III-III of the diffuser inlet is called the throat section, and the section I-I (the narrowest liquid flow in the pressure chamber) is called the tongue-separated section. The liquid flowing in the pressurized water chamber flows partly to the throat of the diffuser and partly to the cross section of the tongue. The two streams formed in the pressurized chamber can be divided by the surface, starting at the entrance of the pressurized chamber (for example, the surface is projected at point a above figure 3-3-2), and ending at the tongue separator (point b).

The sum of the flow through the throat section and the tongue section is the flow through the calculated section. The liquid flowing into the tongue-separated section flows in the pressurized water chamber, returns to the calculated section and flows from the pressurized water chamber through the throat of the pressure short pipe. According to the continuous condition of liquid flow, the relationship between the calculated liquid flow rate at the cross-section and the flow rate at the tongue and throat cross-section can be obtained.

In the formula Q,.C. Qa, Qr - calculate the flow of cross section, tongue section and throat section.

4O - The angle between the vertical axis and section I-I (see Figure 3-3-1).

The [(90 degree qo)/360"] Q value is the flow rate from impeller to pressurized water chamber between the studied sections.

According to Figure 3-3-2, the influence of pump flow Q on flow Qp.c can be studied in detail. For the optimum working condition, point a will be the separation point of the two streams (see Figure 3-3-2). When the flow rate decreases, it moves to the A1 position, and when the flow rate decreases greatly, it moves to the A2 position. In these states, the flow rate of the calculated section will exceed the flow rate of the pump.

Under the condition of large flow rate (see Fig. 3-3-2), the liquid flowing through the calculated section is less than that flowing through the throat section of the diffuser. The reverse liquid flow appears in the tongue section of the water chamber [Q has negative sign value in formula (3-3-1)], i.e. surface a, B.

According to the experimental results of B.I. Gervanovsky's pump specific speed varies in a wide range of impellers and water chambers with different structures, it is found that under the condition of maximum hydraulic efficiency, the average velocity T of the liquid flow in the throat of the diffuser is equal to the velocity mouth of the tongue section (Figure 3-3-3). At the same time, Qr/Qx = Fr/Fx (in the form, Fr and Fa are throats). The area of cross-section and tongue-separated cross-section. If Q = Q (pump flow rate) is taken into account, then formula (3-3-1) can be written in the following form

2. The influence of pump flow rate on the calculated cross-section flow rate of pressure chamber

The influence of pump flow Q on the calculated cross-section flow rate of the pressurized water chamber can be approximately determined according to the following conditions. Assuming that in the optimal state, the velocity of liquid in the calculated section is distributed according to the law of constant velocity moment, which is the same as that of a pump with a screw pressure chamber. So get

Type R2 - impeller outlet radius;

U - The liquid velocity in the pressurized water chamber.

The integral faRIR is a linear parameter of the pressurized water chamber, which is expressed by symbol A. So Qp. = c2R2A.

The change of pump flow Q leads to the change of tangential velocity C. at the impeller outlet because of the change of pump flow Q.

According to C suitable for slurry pump. The theoretical analysis results of the above relationship show that when the pump flow varies, for example, when the pump flow varies by two times, the tangential velocity Ca of the fluid flow at the outlet of the impeller, so the calculated cross-section flow varies by about 30%, that is, the pump flow counterpressure.

The influence of calculated cross-section flow rate of water chamber is not great.

In fact, as pointed out in the experimental study conducted by China a. bognitskaya in the Institute of hydromechanical science of the whole Soviet Union and B. n. gernofsky in the Institute of nonmetal building materials, the specific speed of the pump is in a wide range (n, = 70-150) and the flow of the liquid in the calculated section is actually a fixed value.

According to the formula (3-3-3) and formula (3-3-4), the relationship between the pump specific speed and the characteristic dimension A of the calculated section of the pressure chamber can be determined.