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渣漿泵抽送固液混合物的特性曲線
第一節(jié) 泵的功率特性曲線
一、泵抽送固液混合物時特性曲線繪制的基本資料
在泵的樣本和手冊中，列出的特性曲線，通常是針對泵抽送清水的工作條件，而與泵用于什么樣液體和固液混合物無關(guān)。為了確定泵抽送其他液體和固液混合物時的參數(shù)，一般求出與泵抽送清水時參數(shù)相比的相對變化量。因此在泵制造業(yè)中，為了獲得泵抽送不同液體和固液混合物時的特性曲線，采用各種修正和一些系數(shù)，這些修正和系數(shù)考慮到所抽送介質(zhì)的物理機械性質(zhì)和流動狀態(tài)。系抽送固液混合物時和抽送清水時揚程下降與葉輪中附加水力損失(在個別情況下隨著理論揚程成小)有關(guān)，根據(jù)式(3-5-8)來確定這種水力損失。為了簡化計算，將式(3-5-8) 變形。下列兩項
在數(shù)值上小于項[(p e)/=](u2一a3)12如果不考慮這些項，那么確定oh,的誤差將不超過泵揚程的2%，于是式(3-5- 8)將有下式形式
為了繪制泵抽送固液混合物時特性曲線，應(yīng)具備下列資料：
（1）泵抽送清水時特性曲線。
(2)固體顆粒的級配和密度。
(3)固液混合物的體積濃度P.
(4)載體介質(zhì)特性(密度，黏性)。
（5)葉輪讓口和出口直徑D1和D2(用于確定圓同速度u1和u2)
二、泵抽送混合物時的揚程計算
計算泵抽送固液混合物時所產(chǎn)生的揚程順序如下:
(1)確定固體本顆粒臨界尺寸(m).
對于最常用的轉(zhuǎn)數(shù)和=1X10-*m/s, d,值見表3 6-1
(2)根據(jù)級配圖，確定混合物中顆粒百分比含量，這些顆粒尺寸小于dr,為此在級配圖上(參閱圖2-1-1)由對應(yīng)于顆粒臨界尺寸dr點畫水平軸的垂直線并延長與級配曲線相交。如果所有顆粒數(shù)量取為100%，而小顆粒占總數(shù)的百分?jǐn)?shù)為工,那么小顆粒的體積濃度P1=xP/100，由于大顆粒的存在并產(chǎn)生附加水力損失，所以大顆粒的濃度為
這時體積濃度用十進小數(shù)而不用百分?jǐn)?shù)表示。
(3)求項[(ρτ-pr)/pr](u2-u3)/2g 之值，為此要計算圓周速度u2和u1(如果不知道直徑D1,那么就近似地采用它等于直徑Do).
(4)計算泵抽送清水時葉輪內(nèi)的水力損失
同時按照本篇第四章第一節(jié)的資料確定抽送清水時葉輪效率n，在整個流量范用內(nèi)采用值hno為常效，張的水力效率根據(jù)公式T一mgo求出，其中壓水室效率7on,按照式(3-4-4) 近似計算。
(5)根據(jù)式(3-6-1)確定Shk.
(6)根據(jù)公式H=H-Ohx求出泵抽送固液混合物時不同流量對應(yīng)的揚程H值，采用簡化公式(3-6-1),假定忽略流量變化對Oix的影響，即對于給定的泵，可以認(rèn)為Ohx為常數(shù)。根據(jù)所求出的H值，繪制泵抽送固液混合物時的揚程特性曲線(圖3-6-1).
三、附加損失的影響因素
下面分析各種因素對修正值Ohx的影響。
當(dāng)泵的轉(zhuǎn)速變化時，顆粒臨界尺寸dr、大顆粒和小顆粒的百分?jǐn)?shù)含量都變化，因此揚程修正量也變化，當(dāng)泵轉(zhuǎn)速增大時，尺寸dr減小，大顆粒含量和Ohk增大，即與抽送清水時揚程相比，泵抽送固液混合物時的揚程下降。如果固液混合物中所有固體顆粒尺寸相同，那么可能有兩種情況:
(1)顆粒尺寸大于臨界顆粒尺寸，因此，P1=0。于是，根據(jù)式(3-6-1)，在給定的濃度下，附加損失為最大，與顆粒絕對尺寸無關(guān)。
這種情況已由E. H柯熱夫尼柯娃采用固體顆粒尺寸為0.5~0.7mm的固液混合物進
行實驗研究結(jié)果所證實。因為用轉(zhuǎn)速n=1450r/min的泵進行試驗，所以臨界尺寸為0.26mm，即小干固液混合物中固體顆粒尺寸(固體顆粒為大顆粒)。所得到的揚程特性曲線與顆粒絕對尺寸無關(guān)。
(2) 顆粒尺寸小于臨界顆粒尺寸。于是，P1=P,根據(jù)式(3-6-1)，附加損失sh,等于零，也就是說，抽送清水和固液混合物時的揚程近化似相同。
利用式(3-6-1)，可以研究載體介質(zhì)密度對泵抽送固液混合物時特性曲線變化的影響。當(dāng)載體介質(zhì)密度增大(體積濃度P為恒定)時，附加水力損失下降，即泵抽送清水和固液混合物時特性曲線接近。
采用上述方法管理泵抽送各種固液混合物時的試驗結(jié)果，這時不但實型試驗數(shù)據(jù)，面且實驗室研究數(shù)據(jù)都可以利用，轉(zhuǎn)速變化范圍為500 ~ 300i葉輪直徑為180~1250mm周液混合物中固相級配在很寬粒度范圍內(nèi)變化:從小顆粒的砂到礫石砂土。
由試驗得出，通過試驗和計算方法得到的附加水力損失Ah..和Ah.,之差不超過0.5m，即Sh..- Ah.p<0.5m.
應(yīng)當(dāng)注意，在著名的揚程特性曲線計算方法中，采用顆粒粒徑平均值和相應(yīng)的迎面阻力值作為固相粒度對揚程修正量影響的參數(shù)。這種計算方法，應(yīng)該認(rèn)為原則上是不正確的，因為第一點，根據(jù)顆粒絕對尺寸，不能判斷它們屬于大顆粒還是屬于小顆粒;第二點，不能確定大顆粒和小顆粒濃度之間的關(guān)系。
因為泵抽送均質(zhì)液體和二組分(二相)流體時理論揚程實際上是相同的，所以水力功率變化與抽送固液混合物的密度成正比，即NmP = Nnmp-rXpr/p.渣漿泵廠家
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.
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