固體顆粒粒度對固體顆粒在液流斷面上分布不均勾度有顯著影響

Movement of Fine Particles in Curved Channels

The centrifugal force is produced when the liquid is turning in the curved channel. Under this force, the solid particles are squeezed to the outer wall of the channel (their density is greater than that of the carrier medium). It should be considered that only liquid flocculation usually occurs in the flow passage of the pump, so when the solid particles turn, the fluctuating velocity can be obtained, and the results should be uniformly distributed on the flow section. The influence of fluctuating velocity and centrifugal force on the distribution of solid particles in liquid flow is estimated. It is assumed that under the action of centrifugal force, the settling velocity increases when the particles turn, because the settling velocity is related to the particle head-on resistance. In the semimeridian direction, in the quasi-fixed state of particle motion, the equation is actually

D - The diameter of frontal grains studied in this study:

The circumferential velocity of particles in u-turn;

R-radius of curvature of particle trajectory moving with liquid during steering;

W. - settling velocity of particles. So the settling velocity of solid particles is

The cylindrical surface is introduced in the fluid flow, which is equidistant from some surfaces of the curved channel (Fig. 2-22 (o). The volume concentration of solid particles on one side of this surface is equal to P, and the volume of solid particles passing through the unit surface in unit time is equal to P in flocculation mixing.

Because of the centrifugal force in the same direction, the solid particle volume PW. Move from low concentration area to high concentration area. In the process of stabilization, the concentration distribution of solid particles should be so that the total movement of particles through the studied surface AB is equal to zero. Thereupon

It can be seen from the equation that the larger the fluctuating velocity and the smaller the settling velocity of particles, the smaller the ratio of P/P, that is, the more uniform the distribution of solid particles in liquid flow. It can be considered that the pulsating speed is proportional to the turning speed.

V'=ku

K-proportional coefficient in formula.

When turning, the concentration distribution of solid particles in liquid flow is determined by the following ratio.

In order to find out the conditions under which solid particles distribute uniformly in liquid flow due to fluctuating velocity, the individual case of AP/P=0.1 is studied.

The C1 value was estimated by the following equation: the head-on drag coefficient C=0.5 and the solid particle density 2650 kg/m3 were used.

The ratio of particle diameter to streamline turning radius is equal to 0.1 as the fluctuating velocity changes to 0.1 during turning.

If the turning radius is 300 mm, for example, the particle size is about 0.006 mm, so the effect of flocculation on the distribution of solid particles will be obvious only when there are very fine particles.

2. Motion of Large Particles in Curved Channels

Next, we study the flow of solid-liquid mixture with large enough particles along a plane curved channel [Fig. 2-2 (b)]. At the same time, the equilibrium effect of flocculation can be neglected compared with the effect of particle settling velocity when turning.

The motion of solid particles is quasi-fixed, i.e. the centrifugal force is balanced with the head-on resistance at every point of its trajectory. It can be considered that the radial acceleration of particles moving along the radius of curvature of the trajectory is very small when compared with the centripetal acceleration. In addition, it is assumed that solid particles move along streamlines with liquid circumferential velocity equal to u.

The dynamic equilibrium condition of particles in the radial direction is the same as that of fine particles.

U-the circumferential velocity of particle motion in steering;

W - The settling velocity of particles is characterized by the velocity of particles along the radius direction at point a (rotation is 0 angle).

Particle velocity along radius

The const value of the formula is related to the initial position of solid particles on the entrance section of the channel.

When the solid particles suspended in the liquid flow turn, they are on the outer wall of the radial extrusion channel. Next, we study how the particles are distributed in the cross section when the flow is diverted. At the liquid flow angle, the particles at the entrance between radius concentrate on the wall, and increase at the intersection point between the track CB and the wall of the runner. The same number of particles passing through the entrance section pass through the angle section at unit time. Assuming that the particles are evenly distributed at the entrance of the channel, the ratio of the number of particles falling on the wall at point B to the number of solid particles on the entrance section of the channel can be estimated.

Formula (2-2-7) includes two unknown variables R1 and r2. For the schematic diagram, the wall radius of the runner is drawn from the common center, so the width of the runner will change when one radius changes and the second radius is fixed. It can be seen from equation (2-2-7) that the radius of the runner varies proportionally, that is to say, keeping geometric similarity will not cause the concentration distribution of solid particles along the cross section of the runner to be similar and the geometric size of the runner to be changed. When the concentration of solid particles changes a times and the size of the runner increases, the non-uniform distribution of solid particles on its cross-section decreases.

The particle size of solid particles has a significant influence on the uneven distribution of solid particles on the liquid flow section. In fact, the finer the solid particles in the mixture, the smaller the concentration of the solid particles on the channel profile when turning. Qualitative analysis of the mixture flow during steering shows the cause of uneven wear at the blade inlet. In fact, the process of fluid flow before the blade inlet is more complex. However, it can be concluded that the redistribution pattern of solid particles in the runner, as well as the effect of particle size and liquid steering angle on the redistribution are the same in terms of quality.

Under the actual conditions, when the AF foam pump is turning to the liquid flow, the liquid flow and the internal (front) wall defLOW often occur, that is, the working section of the flow path shrinks. However, in this case, with the increase of concentration, the concentration distribution is not uniform on the inner wall. A considerable amount of particles even extrude the outer wall on the flow section behind the stripping zone.