如果叶轮宽度变化与入口直径成正比，那么所得到的关系式是正确的。但是，在设计输送固液混合物泵时，除了流量和扬程之外，过流断面最小允许尺寸也是给定的，即在转速变化时，断面尺寸，其中包括叶轮宽度，都应该保持恒定。因此，在评价转速对磨损影响时，具有实际意义的是下列情况，即此时除Q=const和H= const外，叶轮宽度b是常数。这时，轴面速度之比与D,b积成反比cna2/c1o =(n2/m)/0.
因此，入口速度三角形不相似。因为圆周速度与转速的2/3次方成反比，所以相对速度之比(unin/un.n)<n/m)0.完全可以确信，在转速降低时，液流角B.增大，即hinl./ing..>1n [根据式(3-7- 4)]，这将导致磨损有所增加。因而，叶片人口线性磨损量之比为转速的函数，即有
根据全加速度在圆周切线方向上投影响的分析[式(3- 7 -3)]，可以确定固体颗粒在叶片迎面上浓度与转速之间的关系，而颗粒在叶片之间流道内浓度重新分布强度与切线加速度有关。加速度ar的三个组成部分中的最大值，通常是式(3-7-3) 右边第一项，一般它决定了aT值。在转速降低时，第二项和第三项有所减小，并且第二项是由于叶轮流道长度增加所致，第三项是由于叶轮尺寸其中包括叶片曲率半径Ru增大所致，但是第三项的值远小于前两项之值。
Effect of Slurry Pump Speed on Impeller Wear
1. The effect of pump speed on impeller wear and outlet side wear.
In the similar state, the liquid flow velocity is proportional to the ratio of rotational speed, while the wear rate is proportional to the ratio of rotational speed cubic. Therefore, the working parts of the pump include the unit volume wear of impeller when conveying solid-liquid mixture, which is proportional to the second square ratio of rotational speed. The average particle size of gravel solid-liquid mixture is pumped by FrY160/31.5 test pump. At rotational speed, the wear rate of impeller is proportional to the second square ratio of rotational speed.
The relationship was confirmed when 1000r/mnin changed to 1450 r/min.
When choosing the speed of the redesigned pump, under the given conditions of flow Q and head H, it is necessary to evaluate the wear of pump parts at different speeds (when Q and H are unchanged). At this time, the most significant is to bear the most severe wear impeller.
Because the hydraulic abrasive wear process at the inlet and outlet sides of impeller blades is different, the effect of rotation speed on them is evaluated respectively.
Now the wear strength of the blade inlet is studied. According to the formula (3-7-2), the wear rate at the inlet depends on the ratio between the three power and the liquid liquid angle and the sine angle of the blade placement angle. The ratio of impeller to population diameter is equal to the ratio of unit diameter (when the same inlet diameter coefficient is KO), and the value is
If the width of impeller is directly proportional to the inlet diameter, the relationship is correct. However, in the design of solid-liquid mixture pump, in addition to the flow rate and head, the minimum allowable size of the cross-section is also given, that is, when the speed changes, the cross-section size, including the impeller width, should be kept constant. Therefore, when evaluating the effect of rotational speed on wear, it is of practical significance that the width of impeller B is constant except for Q = const and H = const. At this time, the ratio of axle velocity to D, B product is inversely proportional to cna2/c1o=(n2/m)/0.
Therefore, the entrance velocity triangle is not similar. Because the circumferential velocity is inversely proportional to the second-third power of the rotational speed, the ratio of relative velocity (unin/un.n) < n/m) is 0. It is absolutely certain that when the rotational speed decreases, the liquid flow angle B. increases, i.e. hinl. / ing. > 1n [according to formula (3-7-4)], which will lead to an increase in wear. Thus, the ratio of linear wear of blade population to rotational speed is a function of the rotational speed.
According to the analysis of relative velocity value, the wear on the blade face and the wear on the blade outlet can not be evaluated.
For the solid particle concentration on the blade front is not constant and not equal to the average concentration, the wear is not only related to the velocity, but also to the particle concentration. Therefore, to determine the influence of impeller speed on blade surface wear, not only the relative velocity but also the concentration change of solid-liquid mixture near the worn surface should be considered.
In order to calculate the relative velocity of liquid flow at the exit edge of blade under the most severe wear, the change of velocity triangle is analyzed when the speed decreases, that is, when the specific speed decreases. In this case, the circumferential velocity U2 and radial partial velocity Cn at the impeller outlet decrease (due to the increase of diameter D at Q= onst), but C. increases and the relative velocity W at the impeller outlet decreases, which will lead to lower wear.
Since the above calculation results of velocity and wear can be obtained, they can be used to a certain degree of approximation.
According to the analysis of the projection of the total acceleration in the tangential direction of the circumference [Formula (3-7-3)], the relationship between the concentration of solid particles on the blade face and the rotational speed can be determined, and the redistribution intensity of the concentration of particles in the flow passage between the blades is related to the tangential acceleration. The maximum of the three components of acceleration AR is usually the first item on the right side of equation (3-7-3), which generally determines the aT value. When the speed decreases, the second and third terms decrease, and the second is due to the increase of the length of the impeller passage. The third is due to the increase of the impeller size including the radius of curvature Ru of the blade, but the value of the third term is much smaller than that of the first two terms.
II. THE EFFECT OF SOLID PARTICLE CONCENTRATION
In further analysis, the second and third terms of equation (3-7-3) are not considered, and the concentration of solid particles in the flow passage between blades is proportional to ar. Therefore, at different rotational speeds, the ratio of the concentration of particles on the blade front is equal to the ratio of their settling velocity in the corresponding acceleration field.
According to formula (3-7-2) and formula (3-7-5), considering the change of relative velocity and solid particle concentration, the linear wear ratio is obtained when the rotational speed changes.
Determine the change of linear wear when the speed decreases, for example, when the speed decreases by 1/3 (from n=1500r/min to n=1000r/min), that is, the linear wear at the blade outlet decreases roughly.
It's about a second lower.
Formula 3-7-7 and calculation results can be obtained by analyzing the phenomena occurring in the flow passage between blades and considering some assumptions. The complexity of these phenomena does not allow all factors affecting blade wear during cavitation at rotating speed to be taken into account. Therefore, in fact, when rotating speed decreases, the wear rate decreases. There may be some other reasons, which are the above reasons. For example, according to the analysis carried out, all the particles in the solid-liquid mixture are small. If the mixture contains large solid particles without affecting the wear of the blade working face (or face to face), the reduction of wear due to the decrease of rotational speed will be quite small. Here, the decrease of rotational speed will lead to the increase of critical dimension D (according to formula d, -1.26.6N yuan), i.e. the increase of the small particles in the solid-liquid mixture which participate in the wear of the blade working face: at this time, the increase of wear, i.e. the decrease of wear obtained according to formula 3-7-7, will be smaller.
No special tests have been carried out to check the relationship between impeller wear and speed (when all other parameters remain equal)