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渣漿泵懸浮液的流動(dòng)特點(diǎn)
一、懸浮液流動(dòng)特點(diǎn)
下面研究懸浮液的流動(dòng)，其流變特性遵守公式(2-1-1)所描述的規(guī)律。懸浮液在壓降引起的摩擦應(yīng)力t (或者管壁面切應(yīng)力)未達(dá)到確定值0之前是固定的。當(dāng)r≥0時(shí)，在壁面上開(kāi)始形成一定厚度的液體活動(dòng)層。
圓管中切應(yīng)力r按線性規(guī)律分布，即tR=z,R/r [式中，TR和r.分別為管壁面(半徑為R)和有效半徑r上的應(yīng)力]，隨者中心到管聯(lián)面的半徑增大而增大(與流動(dòng)特性無(wú)關(guān))。因此，在半徑r值得小時(shí)，r<0， 懸浮液是不動(dòng)的，而半徑很大時(shí)，r≥0，懸浮液開(kāi)始流動(dòng)。在懸浮液開(kāi)始流動(dòng)后，當(dāng)半徑很大時(shí)，在壓降作用下，整個(gè)懸浮液都運(yùn)動(dòng)。同時(shí)在管壁面上產(chǎn)生切應(yīng)力tR，在確定半徑(用ro表示)上產(chǎn)生應(yīng)力日。如果用L0表示半徑為ro的圓柱體表面上流動(dòng)速度，那么可以說(shuō)位于離中心距離小于To處的所有其余液體層，將以同樣速度mo運(yùn)動(dòng)。這樣在管中心就形成運(yùn)動(dòng)懸浮液所包用的具有不破環(huán)結(jié)構(gòu)的半徑為n的四柱體(稱(chēng)為流動(dòng)核》 對(duì)于這種情況。切應(yīng)力-0Fphl/dr (圖2-2 43. 在流動(dòng)核和管使面之間層內(nèi)，應(yīng)力大于技內(nèi)應(yīng)力，巡度小于核內(nèi)速度。因此，核的速度同時(shí)是流體最大度，山uu/dr在選用的坐標(biāo)系中為負(fù)值。因?yàn)榘霃?nbsp;,減小dr,液體層運(yùn)動(dòng)速度增大du,比值d根據(jù)式(2-1-1)，懸浮液在所謂液體層中流動(dòng)速度變化
由此可以認(rèn)為，在管壁面上流動(dòng)速度等于零，
二、白金漢方程
可塑液流核應(yīng)力增大時(shí)，在其表面開(kāi)始破壞和黏性為的液體層將增大。以速度u運(yùn)動(dòng)的液流核開(kāi)始變厚。在極限情況下，壓降相當(dāng)大，因而懸浮液流動(dòng)速度相當(dāng)大，液流核完全被破壞，從層流轉(zhuǎn)變?yōu)樾趿鳡顟B(tài)。在塑性核表面上應(yīng)力減少時(shí)，其部分結(jié)構(gòu)恢復(fù)，在核和管整之間液體層減薄。這樣，可塑層半徑為
當(dāng)壓降變?yōu)榱銜r(shí)，等式第一項(xiàng)變?yōu)榱?，懸浮液流?dòng)將停止。等式右邊等三項(xiàng)隨著壓降增大而迅速減小。
如果結(jié)構(gòu)完成破壞的懸浮液對(duì)不動(dòng)固體繞流或者被擋住，那么液流變慢。同時(shí)，在繞流物體附近，由于速度局部變慢，可能形成結(jié)構(gòu)不破壞的液體層。與牛頓體液流對(duì)物體繞流條件相比，其物體繞流條件有明顯變化。具有流動(dòng)結(jié)構(gòu)狀態(tài)的懸浮液層(連續(xù)有破壞結(jié)構(gòu))，也稱(chēng)為賓漢體，只有接近繞流物體，不論在其前面或者在其表面上，渣漿泵液體其余部分將具有完全破壞的結(jié)構(gòu)。
Flow characteristics of slurry pump suspension
I. Flow characteristics of suspension
Next, the flow of suspension is studied. The rheological properties of suspension follow the rules described in formula (2-1-1). The suspension is fixed before the frictional stress t (or the wall shear stress) caused by the pressure drop does not reach the determined value of 0. When R is greater than or equal to 0, a liquid active layer with a certain thickness begins to form on the wall.
The distribution of shear stress r in a circular pipe is linear, i.e. tR=z, R/r [in the formula, TR and R. are stresses on the wall (radius R) and effective radius r, respectively], which increase with the increase of the radius from the center to the joint (independent of the flow characteristics). Therefore, when the radius R is small, r < 0, the suspension is immobile, and when the radius is large, r < 0, the suspension begins to flow. After the suspension begins to flow, when the radius is large, the whole suspension moves under the action of pressure drop. At the same time, the shear stress tR is generated on the wall of the pipe, and the stress day is generated on the determined radius (expressed by ro). If L0 is used to represent the velocity of flow on the surface of a cylinder with radius ro, it can be said that all the remaining liquid layers located at a distance less than to the center will move at the same velocity mo. In this way, a four-cylinder with a radius of n (called a flow core) enclosed in a moving suspension is formed at the center of the tube. Shear stress-0Fphl/dr (Fig. 2-243). In the layer between the flow core and the tube, the stress is greater than the technical stress and the patrol is less than the velocity in the core. Therefore, the velocity of the core is the maximum of the fluid at the same time, and Shanuu/dr is negative in the selected coordinate system. Because the radius decreases and the Dr increases, the velocity of liquid layer increases du. The ratio D varies according to formula (2-1-1), and the velocity of suspension in the so-called liquid layer varies.
It can be concluded that the velocity of flow on the wall of the pipe is equal to zero.
2. Buckingham equation
When the core stress of plastic fluid flow increases, the liquid layer which begins to destroy on its surface and has viscous properties will increase. The liquid core moving at velocity u begins to thicken. In the extreme case, the pressure drop is quite large, so the suspension flow velocity is quite large, and the core of the liquid flow is completely destroyed, which changes from laminar flow to flocculation state. When the stress on the plastic core surface decreases, part of its structure restores and the liquid layer between the core and the tube becomes thinner. In this way, the radius of the plastic layer is
When the pressure drop becomes zero, the first term of the equation becomes zero and the suspension flow stops. The three terms on the right side of the equation decrease rapidly with the increase of pressure drop.
If the suspension is blocked or flowed around the immobile solid after the structure is destroyed, the fluid flow is slow. At the same time, near the flow object, due to the local slowdown of velocity, a liquid layer with structural damage may be formed. Compared with Newton's fluid flow, the fluid flow around an object has obvious changes. The suspension layer with flowing structure (continuous destructive structure), also known as Bingham body, is only close to the object around it. No matter in front of it or on its surface, the rest of the liquid will have completely destructive structure.
