在数值上小于项[(p e)/=](u2一a3)12如果不考虑这些项，那么确定oh,的误差将不超过泵扬程的2%，于是式(3-5- 8)将有下式形式
对于最常用的转数和=1X10-*m/s, d,值见表3 6-1
采用上述方法管理泵抽送各种固液混合物时的试验结果，这时不但实型试验数据，面且实验室研究数据都可以利用，转速变化范围为500 ~ 300i叶轮直径为180~1250mm周液混合物中固相级配在很宽粒度范围内变化:从小颗粒的砂到砾石砂土。
因为泵抽送均质液体和二组分(二相)流体时理论扬程实际上是相同的，所以水力功率变化与抽送固液混合物的密度成正比，即NmP = Nnmp-rXpr/p.渣浆泵厂家
Characteristic curve of solid-liquid mixture pumped by slurry pump
Section I Power Characteristic Curve of Pump
I. Basic Data for Drawing Characteristic Curves of Solid-liquid Mixtures by Pumping
In pump samples and manuals, the characteristic curves listed are usually for the working conditions of pumping clean water, regardless of what kind of liquid and solid-liquid mixture the pump is used for. In order to determine the parameters of pumping other liquids and solid-liquid mixtures, the relative variation of parameters compared with those of pumping clean water is generally calculated. Therefore, in the pump manufacturing industry, in order to obtain the characteristic curve of pumping different liquid and solid-liquid mixtures, various amendments and some coefficients are adopted, which take into account the physical and mechanical properties and flow state of the pumped medium. When pumping solid-liquid mixture and clear water, the head drop is related to the additional hydraulic loss in impeller (in some cases, with the theoretical head becoming smaller), which is determined by formula (3-5-8). In order to simplify the calculation, the formula (3-5-8) is deformed. The following two items
If these terms are not considered, the error of determining Oh will not exceed 2% of the pump head. Thus, the formula (3-5-8) will have the following form.
In order to draw the characteristic curve of pumping solid-liquid mixture, the following information should be provided:
(1) Characteristic curve of pumping clear water.
(2) Gradation and density of solid particles.
(3) Volume concentration of solid-liquid mixture P.
(4) Characteristic of carrier medium (density, viscosity).
(5) Diameters D1 and D2 of impeller concessions and outlets (used to determine the circular velocity U1 and u2)
2. Calculating the Head of Mixture Pumping
The order of lift generated by pumping solid-liquid mixture is as follows:
(1) Determine the critical size (m) of solid particles.
For the most commonly used revolutions and = 1X10-*m/s, d, the values are shown in Table 36-1.
(2) According to the gradation diagram, the percentage content of particles in the mixture is determined, and the size of these particles is less than Dr. For this reason, the vertical line corresponding to the critical size of particles DR is plotted on the gradation diagram (see Figure 2-1-1) and extended to intersect with the gradation curve. If the number of all particles is 100%, and the percentage of small particles in the total is work, then the volume concentration of small particles P1 = xP/100. Because of the existence of large particles and additional hydraulic loss, the concentration of large particles is as follows:
At this point, the volume concentration is expressed in decimal numbers rather than percentages.
(3) To find the value of [(p_-pr)/pr] (u2-u3)/2g, we need to calculate the circumferential velocities U2 and U1 (if we do not know the diameter D1, then approximately adopt it equal to the diameter Do).
(4) Calculating hydraulic loss in impeller when pumping clean water
At the same time, according to the data in the first section of Chapter IV of this chapter, the impeller efficiency n is determined when pumping clean water. The value HNO is used as the constant efficiency in the whole flow norm. The hydraulic efficiency of Zhang is calculated according to formula T-mgo, in which the pressure chamber efficiency 7on is approximately calculated according to formula (3-4-4).
(5) Shk is determined by formula (3-6-1).
(6) According to the formula H=H-Ohx, the head H value corresponding to different flow rates in pumping solid-liquid mixtures can be calculated. The simplified formula (3-6-1) is adopted. It is assumed that the influence of flow rate change on Oix is neglected, that is to say, Ohx can be considered as a constant for a given pump. According to the calculated H value, the head characteristic curve of pumping solid-liquid mixture is drawn (Fig. 3-6-1).
3. Influencing factors of additional losses
The influence of various factors on the revised value Ohx is analyzed below.
When the pump speed changes, the critical particle size dr, the percentage content of large particles and small particles all change, so the head correction also changes. When the pump speed increases, the size Dr decreases, the content of large particles and Ohk increase. That is to say, the head of pumping solid-liquid mixture decreases compared with that of pumping clean water. If all solid particles in a solid-liquid mixture have the same size, there may be two cases:
(1) The particle size is larger than the critical particle size, so P1 = 0. Thus, according to formula (3-6-1), at a given concentration, the additional loss is the largest, independent of the absolute size of particles.
This situation has been introduced by E. H. Korzevnikova using solid-liquid mixtures with solid particle sizes of 0.5-0.7 mm.
The experimental results confirm that. The critical size is 0.26 mm, i.e. the size of solid particles in small dry solid-liquid mixtures (the size of solid particles is large), because the pump with rotational speed n=1450 r/min is used to carry out the test. The head characteristic curve obtained is independent of the absolute size of particles.
(2) The particle size is smaller than the critical particle size. Thus, P1 = P, according to formula (3-6-1), the additional loss sh equals zero, that is to say, the head approximation for pumping clean water and solid-liquid mixtures is similar.
Formula 3-6-1 can be used to study the influence of carrier medium density on the variation of characteristic curve of solid-liquid mixture pumped by pump. When the density of carrier medium increases (the volume concentration P is constant), the additional hydraulic loss decreases, i.e. the characteristic curve of pump pumping clean water and solid-liquid mixture is close.
Using the above method to manage the experimental results of pumping various solid-liquid mixtures, not only the real test data, but also the laboratory research data can be used. The rotational speed range is 500-300i impeller diameter is 180-1250mm. The solid phase gradation in liquid mixtures varies in a wide range of particle size: from small particles of sand to gravel. Sandy soil.
It is concluded from the test that the difference between the additional hydraulic loss Ah. and Ah. obtained by the test and calculation method is not more than 0.5 m, i.e. Sh. - Ah. P < 0.5 m.
It should be noted that in the well-known calculation method of head characteristic curve, the average particle size and the corresponding head resistance value are used as the parameters of the influence of solid particle size on head correction. This calculation method should be considered incorrect in principle, because the first point is that according to the absolute size of particles, it can not be judged.