渣浆泵抽送固液混合物的特性曲线

第一节  泵的功率特性曲线
一、泵抽送固液混合物时特性曲线绘制的基本资料
    在泵的样本和手册中，列出的特性曲线，通常是针对泵抽送清水的工作条件，而与泵用于什么样液体和固液混合物无关。为了确定泵抽送其他液体和固液混合物时的参数，一般求出与泵抽送清水时参数相比的相对变化量。因此在泵制造业中，为了获得泵抽送不同液体和固液混合物时的特性曲线，采用各种修正和一些系数，这些修正和系数考虑到所抽送介质的物理机械性质和流动状态。系抽送固液混合物时和抽送清水时扬程下降与叶轮中附加水力损失(在个别情况下随着理论扬程成小)有关，根据式(3-5-8)来确定这种水力损失。为了简化计算，将式(3-5-8) 变形。下列两项
    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
    为了绘制泵抽送固液混合物时特性曲线，应具备下列资料：

（1）泵抽送清水时特性曲线。

(2)固体颗粒的级配和密度。

(3)固液混合物的体积浓度P.

(4)载体介质特性(密度，黏性)。

（5)叶轮让口和出口直径D1和D2(用于确定圆同速度u1和u2)

二、泵抽送混合物时的扬程计算

计算泵抽送固液混合物时所产生的扬程顺序如下:

(1)确定固体本颗粒临界尺寸(m).

对于最常用的转数和=1X10-*m/s, d,值见表3 6-1

(2)根据级配图，确定混合物中颗粒百分比含量，这些颗粒尺寸小于dr,为此在级配图上(参阅图2-1-1)由对应于颗粒临界尺寸dr点画水平轴的垂直线并延长与级配曲线相交。如果所有颗粒数量取为100%，而小颗粒占总数的百分数为工,那么小颗粒的体积浓度P1=xP/100，由于大颗粒的存在并产生附加水力损失，所以大颗粒的浓度为
这时体积浓度用十进小数而不用百分数表示。
    (3)求项[(ρτ-pr)/pr](u2-u3)/2g 之值，为此要计算圆周速度u2和u1(如果不知道直径D1,那么就近似地采用它等于直径Do).
    (4)计算泵抽送清水时叶轮内的水力损失
    同时按照本篇第四章第一节的资料确定抽送清水时叶轮效率n，在整个流量范用内采用值hno为常效，张的水力效率根据公式T一mgo求出，其中压水室效率7on,按照式(3-4-4) 近似计算。
    (5)根据式(3-6-1)确定Shk.
    (6)根据公式H=H-Ohx求出泵抽送固液混合物时不同流量对应的扬程H值，采用简化公式(3-6-1),假定忽略流量变化对Oix的影响，即对于给定的泵，可以认为Ohx为常数。根据所求出的H值，绘制泵抽送固液混合物时的扬程特性曲线(图3-6-1).
三、附加损失的影响因素
    下面分析各种因素对修正值Ohx的影响。
    当泵的转速变化时，颗粒临界尺寸dr、大颗粒和小颗粒的百分数含量都变化，因此扬程修正量也变化，当泵转速增大时，尺寸dr减小，大颗粒含量和Ohk增大，即与抽送清水时扬程相比，泵抽送固液混合物时的扬程下降。如果固液混合物中所有固体颗粒尺寸相同，那么可能有两种情况:
    (1)颗粒尺寸大于临界颗粒尺寸，因此，P1=0。于是，根据式(3-6-1)，在给定的浓度下，附加损失为最大，与颗粒绝对尺寸无关。
    这种情况已由E. H柯热夫尼柯娃采用固体颗粒尺寸为0.5~0.7mm的固液混合物进

行实验研究结果所证实。因为用转速n=1450r/min的泵进行试验，所以临界尺寸为0.26mm，即小干固液混合物中固体颗粒尺寸(固体颗粒为大颗粒)。所得到的扬程特性曲线与颗粒绝对尺寸无关。

(2) 颗粒尺寸小于临界颗粒尺寸。于是，P1=P,根据式(3-6-1)，附加损失sh,等于零，也就是说，抽送清水和固液混合物时的扬程近化似相同。

利用式(3-6-1)，可以研究载体介质密度对泵抽送固液混合物时特性曲线变化的影响。当载体介质密度增大(体积浓度P为恒定)时，附加水力损失下降，即泵抽送清水和固液混合物时特性曲线接近。
  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。
  由试验得出，通过试验和计算方法得到的附加水力损失Ah..和Ah.,之差不超过0.5m，即Sh..- Ah.p<0.5m.
  应当注意，在著名的扬程特性曲线计算方法中，采用颗粒粒径平均值和相应的迎面阻力值作为固相粒度对扬程修正量影响的参数。这种计算方法，应该认为原则上是不正确的，因为第一点，根据颗粒绝对尺寸，不能判断它们属于大颗粒还是属于小颗粒;第二点，不能确定大颗粒和小颗粒浓度之间的关系。
  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.