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渣浆泵的性能曲线怎么绘制
添加时间:2019.11.18

渣浆泵的性能曲线怎么

泵的性能曲线或称特性曲线是指:在额定的转速下,泵的流量Q与扬程H;流量Q与功率P;流量Q与效率η之间的关系曲线,称泵的性能曲线。我们常以流量Q为横坐标,以扬程H、功率P、效率η为纵坐标,按一定比例绘制而成的关系曲线图。如图2 - 39所示。有时还将泵的流量Q与必需汽蚀余量(NPSH)a 绘制在性能曲线图上。

的性能曲钱迄今为止还不能以算方法确确定,而是通过试验的方法来求得的。

在性能曲线图上、对于一个任意的流量点,都可以找出组其对应的扬程、功率和效率及汽蚀余量值。通常,把这组相对应的参数称为工况点。相应于泵最高效率点的工况,称为最佳工况点。最佳工况点一应与设计工况点重合。
    泵的性能曲线图在实际使用中是很有用的,通过泵的性能曲线图可以确定这台泵的各个性能参数及泵的水平,在设计中是相似设计的依据。选用时,可以确定各个工况点的性能及这台泵的使用范围,尤其是在非设计工况时,只能通过性能曲线图才能确定该工况的性能参数。运行时,可以用来确定泵运行的工作点。所以,泵的性能曲线对于泵的设计、选用、使用都是很重要的。
一、流量-扬程曲线(Q-H)

1. 流量-扬程曲线的推导

根据式(2-15)及出口速度三角形,设o=0,可以得出:
    对于给定的泵,在一定的转速下的u2F2都是常数,所以理论扬程Ht是随流量Q变化的一个直线方程式。

在离心泵中,叶片出口安放角B:通常是小于90°的,canB,是正值。则°H是一条向下倾斜的直线,在这条直线上
    实际中,叶片数是有限的,液体在叶轮里并不完全沿叶片流动,此时叶轮所产生的理论扬程H.5H的关系见式(2-18), --0)0条直线

理论机理论拓程 H与实际扬程H之差就是水力损失。水力损失包过流件的沿程摩擦损失和冲击损失,沿程损失与流量平方成正比,即条抛物线。冲击损失,在设计工时,由于流方向与叶片方向致,所以冲击损失较小,接近为零。在流量大于或小于设计流量时,由于液流方向与设计工况的液流方向偏离,冲击损失增大,如图2- 40(b)所示。从Q' - H.线上减去相应的水力损失,就得到理论流量Q和实际扬程H的关系曲线Q'-H
    考虑到容积损失对泵性能曲线的影响,由式(2 -23)知容积损失的泄漏量与扬程H是平方根关系,在图2-40 (a)上作出容 积损失与扬程的关系曲线q-H。从流量-扬程曲线Q' -H的横坐标中减去相应的泄漏量q后,最后得到了泵的实际流量和实际扬程的曲线Q-H0
2.影响泵Q -H曲线形状的因素
    (1)叶片出口安放角B:上面推导时,假设出口安放角B <90°,即称后弯叶片,Ctanp, 是正值。此时Q-H是一条问下倾斜的直线,即随流量Q增加, 扬程H是下降的。本股泵的叶片都采用后弯的叶片。但就是在B <0情况下因采用的安放角大小不同,对性能

曲线的形状也有不同的影响。当出口安放角B,取较大值时,Q - H曲线就会变得平坦些并且弯曲得比较厉害,容易产生驼峰。当出口安放角β2取小值时,Q - H曲线就会变得陡降些,见图2 -41
    β2 >90°时,即称前弯叶片,此时clanB2是负值,Q-H是一条上翘的直线,即随流量Q的增加扬程是增加的,如图2 -42所示。这种情况,叶轮中的水力损失较大,并且轴功率也随着流量的增加急速增加,易使原动机过载,所以很少采用,只有在特殊情况下采用。三种叶型的Q-P性能曲线如图2-44所示。
    B2 =90°时,即称径向叶片,ctanB2 等于零,故理论上Q-H是一条水平直线。实际中是一条极平坦的下弯曲线。在部分流泵中经常采用的是这样的径向叶片。
    (2)叶片出口宽度bz:如果增大叶片出口宽度b2,也会使Q-H曲线变得平坦些。
    (3)压水室断面面积Fr:如果增加压水室断面面积Fm,会减小关死点的扬程,并使Q-H曲线变得平坦。渣浆泵厂家

What is the performance curve of slurry pump




The performance curve or characteristic curve of pump refers to the relationship curve between flow Q and head h, flow Q and power P, flow Q and efficiency η at rated speed, which is called the performance curve of pump. We often take flow Q as abscissa, lift h, power P, efficiency η as ordinate, and draw the relation curve in a certain proportion. As shown in Figure 2 - 39. Sometimes, the flow Q and NPSH a of the pump are plotted on the performance curve.





Up to now, the performance curve of the pump can not be accurately determined by the calculation method, but by the test method.




On the performance curve, for any flow point, a set of corresponding head, power, efficiency and NPSH values can be found. Generally, this group of corresponding parameters is called operating point. The working condition corresponding to the highest efficiency point of the pump is called the best working condition point. The optimum operating point shall generally coincide with the design operating point.


The performance curve of the pump is very useful in practical use. The performance parameters and the level of the pump can be determined by the performance curve of the pump, which is the basis of similar design in the design. During selection, the performance of each operating point and the range of use of this pump can be determined, especially in non design conditions, the performance parameters of this operating condition can only be determined through the performance curve. During operation, it can be used to determine the working point of the pump. Therefore, the performance curve of the pump is very important for the design, selection and use of the pump.


I. flow head curve (Q-H)




1. Derivation of flow head curve




According to formula (2-15) and outlet velocity triangle, set o. =0, we can get:


For a given pump, U2 and F2 are constant at a certain speed, so the theoretical head HT is a linear equation varying with flow Q.




In centrifugal pump, the blade outlet angle B: usually less than 90 °, can b, is positive. Then ° h is a straight line inclined downward, on which


In fact, the number of blades is limited, and the liquid does not flow completely along the blades in the impeller. At this time, the theoretical head h.5h generated by the impeller is shown in formula (2-18), -- 0) 0 as a straight line.




The difference between the theoretical head h and the actual head h of the theoretical machine is the hydraulic loss. The hydraulic loss includes friction loss and impact loss along the flow passage. The loss along the passage is directly proportional to the square of flow, that is, a parabola. Impact loss, in the design condition, because the direction of liquid flow is consistent with the direction of blade, the impact loss is small, close to zero. When the flow is greater than or less than the design flow, the impact loss increases due to the deviation of the flow direction from the design flow direction, as shown in Figure 2-40 (b). By subtracting the corresponding hydraulic loss from the Q '- H. line, the relation curve Q' - H between the theoretical discharge Q and the actual lift h is obtained.


Considering the influence of volume loss on the performance curve of the pump, it is known from equation (2-23) that the leakage of volume loss and lift h are the square root relationship, and the relationship curve Q-H between volume loss and lift is made in Figure 2-40 (a). After subtracting the corresponding leakage Q from the abscissa of the flow head curve Q '- H, the curve Q-H of the actual flow and the actual head of the pump is obtained. Zero


2. Factors affecting the shape of pump Q-H curve


(1) blade outlet setting angle B: in the above derivation, it is assumed that the outlet setting angle B is less than 90 °, that is, the backward curved blade, ctanp, is a positive value. At this time, Q-H is a straight line inclined downward, that is to say, with the increase of flow Q, head h decreases. The blades of the unit pump are backward curved. However, in the case of B < 0, due to the different placement angle, the




The shape of the curve also has different effects. When the exit angle B is larger, the Q - H curve will become flat and bent more severely, which is easy to produce humps. When the exit angle β 2 is small, the Q-H curve will become steeper, as shown in figure 2-41.


When β 2 > 90 °, it is called forward curved blade. At this time, clamb2 is negative, and Q-H is a straight line of upwarping, that is, the head increases with the increase of flow Q, as shown in figure 2-42. In this case, the hydraulic loss in the impeller is large, and the shaft power increases rapidly with the increase of flow, which is easy to overload the prime mover, so it is rarely used, only in special cases. The Q-P performance curves of the three blade types are shown in figure 2-44.


When B2 = 90 °, it is called radial blade, ctanb2 is equal to zero, so theoretically Q-H is a horizontal straight line. In fact, it is a very flat downward curve. In partial flow pumps, such radial blades are often used.


(2) blade outlet width BZ: if the blade outlet width B2 is increased, the Q-H curve will also become flat.


(3) section area fr of the water pressure chamber: if the section area FM of the water pressure chamber is increased, the head of the dead point will be reduced and the Q-H curve will become flat. Slurry pump manufacturer