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固液混合物液流參數(shù)對磨損的影響
下面分析混合物液流各個參數(shù)對零件磨損的影響。首先，研究固體顆粒濃度的影響。固體顆粒與表面接觸的數(shù)量越多，零件表面磨損就越快，即零件磨損與固體顆粒濃度成正比。但是，在顆粒與被磨損表面接觸時，固體顆粒反射回去并形成遮蓋層，妨礙部分固體到達(dá)磨損的表面。
根據(jù)下列理由來估價遮蓋層對磨損過程的影響。
研究其底面積為F而高度等于混合物液流速度w的棱柱，被包括在棱柱體積內(nèi)的固體顆粒數(shù)量為
另一方面，假定固體顆粒之間平均距離為b.得到同核柱體積內(nèi)顆粒數(shù)最為
在混合物液流中固體顆粒之間平均重高6= T.而顆粒在單位液流斷面積上的分布密度為
例如，如果研究面積為F葉片表面的混合物液流繞流，那么在表面上可以布置固體顆粒的數(shù)量，由此，可得到
在磨損開始瞬時，所有A固體顆粒都可能落在面積F的表面上；同時其中一部分顆粒從這個表面上反射回去并與混合物液流一起運動顆粒相撞，即產(chǎn)生被磨損表面的掩蓋層。在第一次反射后，一部分到達(dá)磨損表面的新顆粒將不等于A，而是A（1-n）
式中，n為反射顆粒與眼混合物液流運動的下一部分顆粒相撞的概率。在第三部分顆粒加入時，它們與數(shù)量為A(1-0)口的反射顆粒相遇，并且則有A-A(1- 0)Q-A(1-0+n4)的顆粒到達(dá)磨損表面。
在i部分顆粒接近所研究表面時，到達(dá)表面的顆粒數(shù)量n=A(1-n+n*-n*+0+..-).
當(dāng)i趨于無限大時，數(shù)列將趨于n=A/(1+a>，這時顆粒在混合物中的數(shù)量和落到磨損表面上顆粒數(shù)量之間的關(guān)系為=1/(1+0)。
下面確定從磨損表面反射的固體顆粒與運動液流中所含顆粒相撞的概率。
計算指出，如果所有反射顆粒(采用球形)最大截面的總面積等于所研究面積的0.48倍，那么遮蓋層相當(dāng)大，使混合物液流中所含的顆粒不能落在磨損表面上。于是，混合物運動液流中的顆粒和從表面上反射的顆粒之間相撞概率為
因此，零件線性磨損與0.4P/(0.4+P2n)成正比，這一點已由B.N.卡爾林、A.n.斯切尼金和E. I.札爾尼茨基用安放在流體中的柱體試祥和葉輪葉片的試驗所證實。
由式(3-7-1)可以看出，混合物對泵零件的磨損慢于固體顆粒濃度的增加，下面研究濃度增加對泥沙的數(shù)量有何影響，在泵零件磨損相同時，泵可以輸送的泥沙數(shù)量。令易磨損件如葉輪的線性磨損量等于A.So，于是aSo值與比值0. 4/(0. 4+ p/a)和磨損時間to成正比，即
因為以足夠的精度可以用P2/3代替比值0.4P/(0.4+P2/3),所以O(shè)S,≈kP2/2no，由泵輸送泥沙的體積為
假定在固液混合物中固體顆粒濃度P1=0.1,通過泵泥沙的數(shù)量Vn,于是在輸送濃度P的固液混合物時，通過泵泥沙數(shù)量增加為Vr/Vπ= VP/0. I,即在濃度增大時，在零件磨損相同的情況下可以輸送較大量的泥沙。在濃度從0.1增大到0.25時，所輸送泥沙量可以增加36%。
但是，應(yīng)該注意，實際上固體顆粒濃度的提高，通常與泵的流量減少有關(guān)，即輸送固體物料實際數(shù)量較少。
下面研究所輸送固體顆粒度即顆粒直徑對零件磨損的影響。
葉輪葉片前緣(入口邊)扭曲和繞流，可以認(rèn)為與圓柱繞流相似，所以對于估價泥沙粒度對磨損的影響，可以采用用本篇第二章第四節(jié)的資料。在其他條件相同的情況下，固體顆粒落在磨損表面上的數(shù)量越多，零件磨損就越快。在式(3-7-1)中，顆粒相對數(shù)量用系數(shù)確定，其數(shù)值與顆粒相對尺寸有關(guān)，即與顆粒直徑和葉片厚度的比值有關(guān)，參閱本篇第二章第四節(jié)。
根據(jù)式(3-7-1),表面線性磨損與混合物液流速度三次方有關(guān)。這與顆粒動能有關(guān)，在其作用下產(chǎn)生磨損。動能與混合物液流速度二次方成正比，而參與磨損的顆粒數(shù)量與泵的流量或者速度一次方成正比。因此，在泵的流量(或者在任意流道中的流量)變化時，例如在流道斷面變化時，磨損與液流速度二次方成正此。這些情況已被很多試驗所證實。渣漿泵廠家
Effect of Liquid Flow Parameters of Solid-liquid Mixture on Wear
Next, the influence of various parameters of liquid flow of mixture on the wear of parts is analyzed. Firstly, the influence of solid particle concentration is studied. The more solid particles contact with the surface, the faster the surface wear of parts, that is, the wear of parts is proportional to the concentration of solid particles. However, when the particles contact the worn surface, the solid particles reflect back and form a covering layer, which prevents some solids from reaching the worn surface.
The effect of the covering layer on the wear process is evaluated for the following reasons.
A prism with a base area of F and a height equal to the liquid velocity W of the mixture is studied. The number of solid particles included in the volume of the prism is as follows.
On the other hand, it is assumed that the average distance between solid particles is B. The maximum number of particles in the volume of the same core column is obtained.
The average weight of solid particles in liquid flow of mixture is 6= T, while the distribution density of particles in the cross section of liquid flow is 6= T.
For example, if the flow of liquid mixture over the surface of F blade is studied, the number of solid particles can be arranged on the surface, from which the number of solid particles can be obtained.
At the beginning of wear, all A solid particles may fall on the surface of area F. At the same time, some of them reflect back from the surface and collide with particles moving along with the liquid flow of the mixture, that is to say, a covering layer on the worn surface is formed. After the first reflection, a portion of the new particles reaching the worn surface will not be equal to A, but A(1-n)
In the formula, n is the probability of collision between the reflecting particles and the next part of the fluid flow of the eye mixture. In the third part, when the particles are added, they meet with the reflective particles whose number is A (1-0), and the particles of A-A (1-0) Q-A (1-0+n4) reach the wear surface.
The number of particles reaching the surface n=A (1-n+n*-n*+0+. -) when part I particles approach the studied surface.
When I tends to be infinite, the sequence tends to n=A/(1+a>), and the relationship between the number of particles in the mixture and the number of particles falling on the worn surface is equal to 1/(1+0).
Next, the probability of collision between the solid particles reflected from the worn surface and the particles contained in the moving fluid flow is determined.
It is pointed out that if the total area of the maximum cross section of all reflecting particles (spherical) is equal to 0.48 times of the studied area, the covering layer is quite large, so that the particles contained in the liquid flow of the mixture can not fall on the worn surface. Thus, the probability of collision between particles in the moving liquid flow of a mixture and particles reflecting from the surface is zero.
Therefore, the linear wear of parts is proportional to 0.4P/(0.4+P2n), which has been confirmed by the tests of B.N. Karlin, A.n. Schenickin and E.I. Zarnitzky on cylinders and impeller blades mounted in fluids.
Formula (3-7-1) shows that the wear rate of the mixture on the pump parts is slower than that of the solid particle concentration. Next, the influence of the increase of the concentration on the amount of sediment is studied. When the wear of the pump parts is the same, the amount of sediment that can be transported by the pump. The linear wear of wearable parts such as impellers is equal to A. So the aSo value is proportional to the ratio of 0.4/(0.4+p/a) and the wear time to.
Because the ratio of 0.4P/(0.4+P2/3) can be replaced by P2/3 with sufficient accuracy, the volume of sediment transported by pumps is 0.4P/(0.4+P2/3), so OS, kP2/2no.
Assuming the solid particle concentration P1 = 0.1 in the solid-liquid mixture and the amount of sediment through the pump Vn, the amount of sediment through the pump increases to Vr/Vpi= VP/0.I in the solid-liquid mixture with the concentration P, i.e. when the concentration increases, a large amount of sediment can be transported under the same wear condition of parts. When the concentration increases from 0.1 to 0.25, the sediment transported can increase by 36%.
However, it should be noted that, in fact, the increase of solid particle concentration is usually related to the decrease of pump flow, that is, the actual quantity of solid material conveyed is less.
The influence of solid particle size conveyed, i. e. particle diameter, on the wear of parts is studied below.
The distortion and flow around the leading edge (entrance) of impeller blade can be considered to be similar to that around a cylinder. Therefore, the data in Section IV of Chapter II of this chapter can be used to evaluate the effect of sediment particle size on wear. Under the same other conditions, the more solid particles fall on the worn surface, the faster the parts wear. In formula (3-7-1), the relative number of particles is determined by the coefficient. Its value is related to the relative size of particles, i.e. the ratio of particle diameter to blade thickness. See Section 4 of Chapter 2 of this chapter.
According to formula (3-7-1), the linear wear of the surface is related to the cubic velocity of liquid flow in the mixture. This is related to the kinetic energy of particles, which causes wear and tear under the action of particles. Kinetic energy is proportional to the quadratic square of the liquid flow velocity of the mixture, and the number of particles involved in wear is proportional to the flow rate or the first square of the velocity of the pump. Therefore, when the flow rate of the pump (or the flow rate in any channel) changes, such as when the cross-section of the channel changes, the wear and liquid flow velocity quadratic square here. These conditions have been confirmed by many experiments.
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