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渣漿泵的性能曲線怎么
泵的性能曲線或稱特性曲線是指:在額定的轉(zhuǎn)速下，泵的流量Q與揚(yáng)程H;流量Q與功率P;流量Q與效率η之間的關(guān)系曲線，稱泵的性能曲線。我們常以流量Q為橫坐標(biāo)，以揚(yáng)程H、功率P、效率η為縱坐標(biāo)，按一定比例繪制而成的關(guān)系曲線圖。如圖2 - 39所示。有時還將泵的流量Q與必需汽蝕余量(NPSH)a 繪制在性能曲線圖上。
泵的性能曲錢迄今為止還不能以計算方法精確確定，而是通過試驗(yàn)的方法來求得的。
在性能曲線圖上、對于一個任意的流量點(diǎn)，都可以找出一組其相對應(yīng)的揚(yáng)程、功率和效率及汽蝕余量值。通常，把這一組相對應(yīng)的參數(shù)稱為工況點(diǎn)。相應(yīng)于泵最高效率點(diǎn)的工況，稱為最佳工況點(diǎn)。最佳工況點(diǎn)一般應(yīng)與設(shè)計工況點(diǎn)重合。
泵的性能曲線圖在實(shí)際使用中是很有用的，通過泵的性能曲線圖可以確定這臺泵的各個性能參數(shù)及泵的水平，在設(shè)計中是相似設(shè)計的依據(jù)。選用時，可以確定各個工況點(diǎn)的性能及這臺泵的使用范圍，尤其是在非設(shè)計工況時，只能通過性能曲線圖才能確定該工況的性能參數(shù)。運(yùn)行時，可以用來確定泵運(yùn)行的工作點(diǎn)。所以，泵的性能曲線對于泵的設(shè)計、選用、使用都是很重要的。
一、流量-揚(yáng)程曲線(Q-H)
1. 流量-揚(yáng)程曲線的推導(dǎo)
根據(jù)式(2-15)及出口速度三角形，設(shè)o。=0，可以得出:
對于給定的泵，在一定的轉(zhuǎn)速下的u2、F2都是常數(shù)，所以理論揚(yáng)程Ht是隨流量Q變化的一個直線方程式。
在離心泵中，葉片出口安放角B:通常是小于90°的，canB,是正值。則°一H是一條向下傾斜的直線，在這條直線上
實(shí)際中，葉片數(shù)是有限的，液體在葉輪里并不完全沿葉片流動，此時葉輪所產(chǎn)生的理論揚(yáng)程H.5H的關(guān)系見式(2-18), --0)0一條直線。
理論機(jī)理論拓程 H與實(shí)際揚(yáng)程H之差就是水力損失。水力損失包括過流部件的沿程摩擦損失和沖擊損失，沿程損失與流量平方成正比，即一條拋物線。沖擊損失，在設(shè)計工況時，由于液流方向與葉片方向一致，所以沖擊損失較小，接近為零。在流量大于或小于設(shè)計流量時，由于液流方向與設(shè)計工況的液流方向偏離，沖擊損失增大，如圖2- 40(b)所示。從Q' - H.線上減去相應(yīng)的水力損失，就得到理論流量Q和實(shí)際揚(yáng)程H的關(guān)系曲線Q'-H。
考慮到容積損失對泵性能曲線的影響，由式(2 -23)知容積損失的泄漏量與揚(yáng)程H是平方根關(guān)系，在圖2-40 (a)上作出容 積損失與揚(yáng)程的關(guān)系曲線q-H。從流量-揚(yáng)程曲線Q' -H的橫坐標(biāo)中減去相應(yīng)的泄漏量q后，最后得到了泵的實(shí)際流量和實(shí)際揚(yáng)程的曲線Q-H。0
2.影響泵Q -H曲線形狀的因素
(1)葉片出口安放角B:上面推導(dǎo)時，假設(shè)出口安放角B <90°，即稱后彎葉片，Ctanp, 是正值。此時Q-H是一條問下傾斜的直線，即隨流量Q增加， 揚(yáng)程H是下降的。本股泵的葉片都采用后彎的葉片。但就是在B <0情況下因采用的安放角大小不同，對性能
曲線的形狀也有不同的影響。當(dāng)出口安放角B,取較大值時，Q - H曲線就會變得平坦些并且彎曲得比較厲害，容易產(chǎn)生駝峰。當(dāng)出口安放角β2取小值時，Q - H曲線就會變得陡降些，見圖2 -41。
當(dāng)β2 >90°時，即稱前彎葉片，此時clanB2是負(fù)值，Q-H是一條上翹的直線，即隨流量Q的增加揚(yáng)程是增加的，如圖2 -42所示。這種情況，葉輪中的水力損失較大，并且軸功率也隨著流量的增加急速增加，易使原動機(jī)過載，所以很少采用，只有在特殊情況下采用。三種葉型的Q-P性能曲線如圖2-44所示。
當(dāng)B2 =90°時，即稱徑向葉片，ctanB2 等于零，故理論上Q-H是一條水平直線。實(shí)際中是一條極平坦的下彎曲線。在部分流泵中經(jīng)常采用的是這樣的徑向葉片。
(2)葉片出口寬度bz:如果增大葉片出口寬度b2,也會使Q-H曲線變得平坦些。
(3)壓水室斷面面積Fr:如果增加壓水室斷面面積Fm，會減小關(guān)死點(diǎn)的揚(yáng)程，并使Q-H曲線變得平坦。渣漿泵廠家
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
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