Rolling particles

Aluminum particle rolling directly into continuous strip. Molten metal is sprayed into particles about the size of rice in a controlled environment, then brought to a desired rolling temperature and continuously rolled into instant coiled sheet This process can handle alloys which normally cannot be cast in ingot form. 

The incipient gas velocity for a particle rolling along the wall can be determined by the torques exerted on the particle. Assuming that the drag force, gravitational force, and lift force are exerted through the central point of the sphere, the balance of the torques about the uppermost point of the particle-wall contact plane (see Fig. 11.8) can be given by... 

There is evidence (129) that large seed particles rolled to form flakes of a definite thickness can be extracted more rapidly than small particles, presumably because they undergo greater internal dismption in the rolling process. Laboratory and pilot plant work on soybeans by Othmer and Agarwal (137) has led them to conclude that for hexane extraction of soybeans ... 

If the powder has been charged on the conveyor, fines concentrate at the center of the belt while coarse particles roll to the outer edges such as the segregation seen when sampling from a heap. 

Impinging motion Stream of abrasive particles Rolling contact (normal component) Striker against plate... 

Other phenomena may also be observed in concentrated dispersions. Thus, as the concentration increases, direct particle—particle contacts increase in importance, and as the limiting packing fraction is approached (j) = 0.625 for the random close-packing of spheres) the suspension ceases to flow and the viscosity becomes infinite. Shortly before this limit is reached the suspension (especially if the particles are monodisperse spheres) often exhibits dilatency. When the particles are nearly close-packed, flow can occur only by the particles rolling past one another (Figure 8.8), and this results in an increase in volume the shear thickening is accompanied by dilatence of the system. If the amount of liquid present is insufficient to fill the extra void volume produced, the surface may become dry. This is the familiar phenomenon observed when one steps on wet sand. 

Mixing due to diffusion occurs when particles roll over a sloping powder surface. The random movement of particles on the free surface results in a redistribution of the particles. As was discussed in section 1.2.2.I, the movement of particles on a free surface can also give rise to segregation due to the percolation of fine particles if particles of different size are present in the mixture. Only when the particles within the mixture have identical properties can diffusional mixing be a truly randomizing process. 

If the kinetic term F(p) belongs to Case A, the potential has a minimum at the point p = 0 and a maximum at p = 1. The second term, -vp, in (4.2) represents a damping force, where v represents the viscosity. Then (4.2) describes the motion of a particle rolling down from the top of the potential at p = 1 to the bottom of the potential well, p = 0, in the presence of a viscous force. If v is small, i.e., the viscosity is small, the particle oscillates near the bottom of the well before it settles down at the minimum p = 0. If u increases, there exists a threshold value at which the oscillations cease. In other words, the particle rolls down monotonically from p = 1 to p = 0 in mechanics this is known as critical damping. If v increases even further, the particle continues to roll down monotonically and has less and less velocity at every point of its trajectory. Consequently, there exists a critical value of V, which we denote by v, such that for v > v, there will be monotonically decreasing solutions to (4.2). The front is said to be propagating into the... 

On the basis of Eq. (XII.28) Zvonkov [349] calculated the critical velocities characterizing the main stages of erosion Pc-i > the first critical velocity, at which = F1, when the particles roll or slide but are not removed from the original ground surface Pc-2 > the second critical velocity, at which Fiif =... 

Slope failure in coarse soils is a surface phenomenon that is caused by the particles rolling over each other down the slope. As far as sands are concerned, their packing density is important. For example, densely packed sands that are very slightly cemented may have excavated faces with high angles that are stable. The water content is of paramount importance in loosely packed sands, for if these are saturated they are likely to flow on excavation. 

Diffusive mixing the particles roll on top of each other under the infiuence of the gravity... 

Even when the particles are completely destabilized, with no repulsion energy barrier, there is evidence" that orthokinetic collisions will be reduced by particles rolling around one another without aggregating. This will multiply the orthokinetic rate (equation 4.42) by a factor of less than one, which will make the sizes of particles undergoing equal effective rates of perikinetic and orthokinetic flocculation smaller than those hsted above (which assumed that all collisions were permanent and effective). 

In shear mixing, shear stresses give rise to slip zones and mixing takes place by interchange of particles between layers within the zone. Diffusive mixing occurs when particles roll down a sloping surface. Convective mixing is by deliberate bulk movement of packets of powder around the powder mass. 

Tumbling Mixers. As the name suggests, these mixers tumble the powder mass. Mixing is achieved predominantly by random motion when particles roll down a sloping surface. As the whole shell tumbles either on its... 

Another very good indication in that case is the sedimentation volume, which is small in the case of a stable suspension (the particles roll over one another until the densest packing is obtained), but larger for a flocculated one (the particles remain in the position, in which they were when they touched for the first time) ... 

Table 2 also shows that the number of ideal mixers is so large that solids mixing in axial direction can be neglected. It appears that the number of mixers is of the same order of magnitude as the average number of times a particle rolls down the surface of the solids bed. 

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