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渣漿泵流量系數(shù)對(duì)計(jì)算速度的影響
下面研究系數(shù)a對(duì)只有隔舌斷面高度hg變化時(shí)，即泵流量和揚(yáng)程恒定情況下面積Fs變化時(shí)壓水室斷面上速度的影響。這種分析在抽送細(xì)固體顆粒固液混合物泵壓水室設(shè)計(jì)時(shí)具有重要意義。在這種情況下，hg 尺寸的選擇，不是根據(jù)固體顆粒粒徑，而是根據(jù)壓水室內(nèi)的水力損失和決定其磨損的速度值。
壓水室計(jì)算斷面上 A值，因而面積F...隨著系數(shù)。值的增大面增大。因?yàn)橄鄬?duì)比值A(chǔ)/a為恒定值，其參數(shù)A與a成正比增大，計(jì)算斷面上的流量與a也成正比增大。為了簡(jiǎn)化分析，采用壓水室為矩形，于是得到
從這些表達(dá)式中看出，參數(shù)A與相對(duì)比值R3/R2的對(duì)數(shù)值成正比增大，而計(jì)算斷面面積與(R3/R2-1)值成正比增加，即隨著相對(duì)流量系數(shù)。增大，計(jì)算斷面上的液流速度減小，而且在環(huán)形壓水室內(nèi)其平均值最小。
壓力短管喉部斷面面積也隨著a的增大而增大，因而速度u減小。在環(huán)形壓水室時(shí)，壓力短管喉部液體流速將有最小值。在其他條件相同時(shí)，在環(huán)形壓水室內(nèi)特征速度u最小。
知道泵的參數(shù)和主要尺寸，就可確定在下列情況下其隔舌斷面高度h不同的壓水室計(jì)算斷面上的系數(shù)a和速度u：
(1)擴(kuò)散管喉品固積F與計(jì)算斷面面積F,.之比，在各種a值情況下是恒定的(在個(gè)別情況下，為簡(jiǎn)化分析，可以采用F-F..).。
(2) 盡管水力效率有一定變化，當(dāng)R,=常數(shù)時(shí)，水泵揚(yáng)程H=常數(shù)。
(3)在估算普通螺旋形壓水室內(nèi)流速時(shí)，水力效率可以采用清水泵統(tǒng)計(jì)資料(在n,相似情況下)。
如來(lái)不考慮壓水室斷面尺才變化時(shí)泵的水力效率(m) 變化，那么根據(jù)表達(dá)式(3-3 -5)可以寫(xiě)為
式中K,一當(dāng)泵的參數(shù)恒定時(shí)為常數(shù)， 根據(jù)式(3-3-4) 計(jì)算，K =0.010DxO/B
根據(jù)對(duì)不同參數(shù)和尺寸泵的對(duì)應(yīng)于最高水力效率狀態(tài)的關(guān)系式U.c= f(a)和ur=f(a)的數(shù)值分析結(jié)果，得到所研究參數(shù)的相似變化(圖3-3-5)。 值a從1增大到1.85，將導(dǎo)致計(jì)算斷面上液流平均速度和擴(kuò)散管入口速度下降(后種速度下降特別大)。如果考慮在最高水力效率狀態(tài)時(shí)工作，速度Uy和Ur相等，那么對(duì)Ug=f(a)來(lái)說(shuō)關(guān)系式Ur=f(a)是正確的。這樣，在螺旋形壓水室過(guò)渡到環(huán)形壓水室時(shí)，在壓水室各斷面上速度都將下降。
眾所周知，泵在最佳和大流量狀態(tài)工作時(shí)，在計(jì)算斷面區(qū)最大半徑R3 (圖3-3-1上點(diǎn)A)上，觀(guān)察到渣漿泵壓水室內(nèi)磨損穿透。在大多數(shù)情況下，決定整個(gè)壓水室壽命的這種磨損，與計(jì)算斷面上平均速度大小無(wú)關(guān)，而與半徑R,斷面壁面上速度大小有關(guān)。因此，感興趣的是相對(duì)流量系數(shù)(即壓水室形狀)對(duì)泵參數(shù)恒定時(shí)速度u的影響的分析。
為了簡(jiǎn)化起見(jiàn)，在個(gè)別情況下，采用E-F... 于是根據(jù)式(3-3-5),擴(kuò)散管喉部速度為
在簡(jiǎn)比分析所采用矩形壓水室斯面壁面上的液流速度，根據(jù)在對(duì)應(yīng)最高水力效率狀態(tài)下工作時(shí)這個(gè)斷面上的速度矩為常數(shù)，則為
在推導(dǎo)速度u3的表達(dá)式時(shí)，采用了R3=R2+h..=RreM
從圖3-3-5上可知，在壓水室計(jì)算斷面外壁上速度也隨著相對(duì)流量系數(shù)a的增大而減小。
如果采用在各種個(gè)斷面上速度相等時(shí)，其磨損將近似相同，那么擴(kuò)散管喉部斷面和計(jì)算斷面耐磨性相等的 。條件是速度Ur和..相等，可以寫(xiě)成下列形式
上述分析指出，甚至在不要求增大隔舌斷面高度的情況下，根據(jù)大固體顆粒通過(guò)的可能性，為了降低壓水室斷面上的速度，放棄螺旋式壓水室是合理的，同時(shí)如下指出那樣，水力損失增加，即降低整臺(tái)泵的水力效率。應(yīng)該注意，因?yàn)槟p與液體速度二次方成正比(如下面指出那樣)，降低承受最強(qiáng)烈磨損的壓水室斷面上的速度，是提高渣漿泵體壽命的重要方向之一。渣漿泵廠(chǎng)家
Effect of Flow Coefficient of Slurry Pump on Calculating Speed
Next, the influence of coefficient a on the velocity of the pressure chamber section is studied when only the height of the tongue section changes with hg, that is, the area Fs changes with constant pump flow and head. This analysis is of great significance in the design of pump chamber for pumping fine solid-liquid mixture. In this case, the selection of the size of Hg is not based on the size of solid particles, but on the hydraulic loss in the water chamber and the speed of wear.
The pressure chamber calculates the A value on the section, so the area F... With the coefficient. The increasing face of the value increases. Because the relative ratio A/a is constant, its parameter A increases in direct proportion to a, and the calculated cross-section flow also increases in direct proportion to a. In order to simplify the analysis, the pressure chamber is used as a rectangle, and the result is obtained.
From these expressions, it can be seen that the value of parameter A increases in direct proportion to the relative ratio R3/R2, while the calculated cross-section area increases in direct proportion to the value of (R3/R2-1), that is, with the relative flow coefficient. With the increase of pressure, the velocity of liquid flow on the calculated section decreases, and the average value is the smallest in the annular pressure chamber.
The throat section area of pressure short pipe increases with the increase of a, so the velocity u decreases. In the annular pressure chamber, the liquid velocity in the throat of the pressure short pipe will have the minimum value. When other conditions are the same, the characteristic velocity u is the smallest in the annular pressurized water chamber.
Knowing the parameters and main dimensions of the pump, the coefficient a and velocity U of the calculated section of the pressure chamber with different tongue section height h can be determined under the following conditions:
(1) The ratio of the throat volume F of the diffuser to the calculated cross-section area F is constant under various A-values (in some cases, F-F.) can be used to simplify the analysis).
(2) Despite some changes in hydraulic efficiency, when R, = constant, pump head H = constant.
(3) When estimating the flow velocity in a common spiral pressure chamber, the hydraulic efficiency can be calculated by using the statistical data of clean water pumps (in n, similar cases).
If the hydraulic efficiency (m) of the pump is not considered when the section size of the pressure chamber changes, the expression (3-3-5) can be written as follows.
In formula K, when the pump parameters are constant, it is constant. According to formula (3-3-4), K = 0.010DxO/B.
According to the numerical analysis results of the relations U.c= f(a) and ur=f(a) corresponding to the highest hydraulic efficiency state of pumps with different parameters and sizes, the similar changes of the studied parameters are obtained (Fig. 3-3-5). When the value a increases from 1 to 1.85, the average velocity of liquid flow and the inlet velocity of diffuser will decrease (especially the latter). If the velocity U and Ur are equal when working at the highest hydraulic efficiency state, then the relation Ur = f (a) is correct for Ug = f (a). In this way, when the spiral pressure chamber transits to the annular pressure chamber, the velocity will decrease on all sections of the pressure chamber.
It is well known that wear and tear penetration in the pressure chamber of slurry pump is observed on the maximum radius R3 (point A of Figure 3-3-1) of the calculated section when the pump works in the optimum and large flow state. In most cases, the wear that determines the life of the whole chamber has nothing to do with the average velocity on the calculated section, but with the radius R and the velocity on the wall of the section. Therefore, it is interesting to analyze the influence of the relative flow coefficient (i.e. the shape of the pressure chamber) on the velocity u when the pump parameters are constant.
In order to simplify the process, in some cases, E-F is used. According to formula (3-3-5), the throat velocity of the diffuser is 0.
In the simplified comparison analysis, the velocity of liquid flow on the wall of the rectangular pressure chamber is constant according to the velocity moment on the section working at the corresponding maximum hydraulic efficiency.
In deriving the expression of velocity u3, R3 = R2 + h.. = RreM is used.
From Figure 3-3-5, it can be seen that the velocity decreases with the increase of the relative discharge coefficient a on the outer wall of the calculated section of the pressurized water chamber.
If the velocity is equal on all sections, the wear resistance of the throat section and the calculated section of the diffuser will be approximately the same. The condition is that the velocity Ur and... are equal and can be written in the following form
The above analysis points out that it is reasonable to abandon the spiral chamber in order to reduce the speed of the chamber section, even without increasing the height of the tongue section, according to the possibility of passing large solid particles. At the same time, it is pointed out as follows that the hydraulic loss increases, that is to say, the hydraulic efficiency of the whole pump is reduced. It should be noted that because the wear is proportional to the quadratic of the liquid velocity (as indicated below), reducing the speed on the section of the pressure chamber withstanding the strongest wear is one of the important directions to improve the life of the slurry pump body. Slurry Pump Manufacturer
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