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第一節(jié) 寬斷面流道壓水室內(nèi)流譜
一、液體在壓水室內(nèi)的流動
根據(jù)大顆粒通過條件，渣漿泵壓水室制造成半螺旋形或者略呈螺旋形的環(huán)狀壓水室(恒定斷面)。壓水室最小斷面，即隔舌和葉輪之間的斷面，應(yīng)該具有這樣大的尺寸，即能使通過葉輪的大顆粒無阻礙地通過壓水室。由非金屬建筑材料研究所進行的試驗得到隔舌和葉輪之間距離減小(小于抽送的固體顆粒尺寸)，將導(dǎo)致固體顆?？ㄔ谌~輪和壓水室之間，產(chǎn)生沖擊負荷，使隔舌斷面壓水室壁面磨損增加。
典型渣漿泵壓水室示意圖見圖3-3-1.垂直擴散管(壓力短管)軸線的壓水室斷面II一II,一般稱為計算斷面，在擴散管入口斷面III-III稱為喉部斷面，斷面I一I (壓水室最窄液流)稱為隔舌斷面。在壓水室內(nèi)流動的液體，一部分流向擴散管喉部，一部分流向隔舌斷面。在壓水室內(nèi)形成的這兩股液流，可以用表面來劃分，在壓水室入口(例如，這個表面投影在圖3-3-2上點a,)開始，這個表面在隔舌處結(jié)束(點b).
流過喉部斷面和隔舌斷面的流量之和為通過計算斷面的流量。流入隔舌斷面的液體在壓水室內(nèi)流動，返回計算斷面并從壓水室流經(jīng)壓力短管的喉部。根據(jù)液流連續(xù)條件，可以得到計算斷面液流流量與隔舌和喉部斷面流量之間的關(guān)系
式中Q,.c.Qa,Qr-計算斷面，隔舌斷面和喉部斷面的流量;
4o——垂直的軸線與斷面I一 I之間的夾角(參閱圖3-3-1).
[(90° qo)/360“]Q值是所研究斷面之間從葉輪流入壓水室的流量.
根據(jù)圖3-3-2可以詳細研究泵流量Q對流量Qp.c的影響。對于最佳工作狀態(tài)，點a,將是兩股液流的分開點(參閱圖3-3-2），在流量減少時，它移到a1位置，在流量下降很大時，移到a2位置，在這些狀態(tài)，計算斷面的流量將超過泵的流量。
在大流量工作狀態(tài)下(參閱圖3-3-2），流過計算斷面液體比擴散管喉部斷面少，在壓水室隔舌斷面出現(xiàn)反向液流[在式(3-3-1)中Q具有負號值】，即表面a,b
根據(jù)B.I.格爾瓦諾夫斯基在不同結(jié)構(gòu)葉輪和壓水室的試驗泵比轉(zhuǎn)速在很寬范圍內(nèi)變化的試驗研究結(jié)果得到，在最高水力效率狀態(tài)下，在擴散管喉部液流平均速度T和隔舌斷面的流速口相等(圖3-3-3).同時Qr/Qx=Fr/Fx (式中，F(xiàn)r、Fa為喉部斷面和隔舌斷面的面積)。如果考慮Q=Q (泵的流量),那么式(3-3- 1)可經(jīng)寫成下列形式
二、泵流量對壓水室計算斷面流量的影響
泵流量Q對壓水室計算斷面流量的影響，可以根據(jù)下列條件近似地確定。假定在最佳狀態(tài)，計算斷面液體速度按照速度矩恒定規(guī)律分布，與具有螺旋式壓水室的泵一樣。于是得到
式中R2——葉輪出口半徑;
u——壓水室內(nèi)液體速度。
推廣在壓水室計算斷面整個面積上，積分faRIR是壓水室線性參數(shù)，用符號A表示。于是Qp.=c2R2A.
泵流量Q變化導(dǎo)致葉輪出口切向分速度C.變化，因為
根據(jù)適合于渣漿泵的C。上述關(guān)系的理論分析結(jié)果得到，在泵流量變化時，例如變化2倍時，液流在葉輪出口切向分速度Ca，因而計算斷面流量大約變化分30%，即泵流量對壓
水室計算斷面流量的影響并不大。
實際上如中. A.鮑格尼茨卡婭在全蘇水力機械科學(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行開進行的試驗研究指出那樣，泵的比轉(zhuǎn)速在很寬范圍內(nèi)(n,=70~150）液體在計算斷面的流量實際上為定值。
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.
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