Particle flow patterns

Flow patterns of hydrodynamic systems like the compendial dissolution apparatus may be qualitatively characterized by means of dilute dye injection (e.g., methylene blue) or by techniques using particulate materials such as aluminum powders or polystyrene particles. Flow patterns may be also visualized by taking advantage of density or pH differences within the fluid stream. The Schlieren method, for instance, is based on refraction index measurement. Hot wire anemo-metry is an appropriate method to quantitatively characterize flow rates. The flow rate is proportional to the cooling rate of a thin hot wire presented to the stream. Using laser Doppler... 

Equation (6.16) indicates that the maximum brittle wear occurs at ct = 90°, i.e., normal collision. The variation of the ratio of Eb to Bm (= B( m, b)) with a as a function of Kb is plotted on the basis of Eq. (6.16) as given in Fig. 6.7. The figure reflects that for a given Kb, the degree of abrasive damage due to brittle erosion may be estimated from the given particle flow pattern. 

Several observations about particle flow patterns can be made from this plot. First, although particles can enter the impactor with any y velocity at any location, their subsequent paths are quite well determined depending on initial velocity and location. Particles with an absolute value of initial y velocity greater than pxy or p have the potential for crossing the impactor centerline. Particles inside this range may reverse their direction but will never cross the impactor centerline. 

Fluid-particle flow patterns are often clarified by application of phase diagrams. Kwauk (1963) and Matsen (1983) proposed such phase diagrams for moving beds. 

Fig. 52. (a) Gas and particle flow pattern near a bubble, a == 2.5 and (b) a photograph showing cloud size and bubble size rt, by using NOi-containing-bubble technique, a = 2.5, 230 /itm ballotini (after Rl7). 

The spouted bed technique has become established as an alternative to fluidization for handling particulate solids that are too coarse and uniform in size for good fluidization. Although the areas of application of spouted beds overlap with those of fluidized beds, the flow mechanisms in the two processes are very different. Agitation of particles in a spouted bed is caused by a steady axial jet and, as compared with the more random and complex bubble-induced particle flow patterns in most fluidized beds, is regular as well as cyclic. 

Malhotra, K., A. S. Mujumdar and M. Okazaki, Particle flow patterns in a mechanically stirred two-dimensional cylindrical vessel . Powder Technol. 60, 179-189 (1990). 

FIGURE 7.30 (See color insert.) DEM simulation of particle flow pattern (left) and force network (right) in a horizontal section of a bladed mixer. (Reprinted from Chem. Eng. ScL, 59, Zhou, Y.C., Yu, A.B., Stewart, R.L., and Bridgwater, J., Microdynamic analysis of the particle flow in a cylindrical bladed mixer, 1343-1364, Copyright 2004, with permission from Elsevier.)... 

Figure 21 Particle flow patterns under various liquid contents in a fluidized bed reactor, (a) Dry particle fluidization, (b) particle agglomeration, (c) agglomerate segregation, (d) bottom channeling, (e) whole bed channeling, (1) paste or slurry bed.

Figure 6 Particle flow patterns observed for vertical flow with electrostatic charging.

Figure4 shows the experimental relationship between and y/a at r=0.055 second for two different where is x/a when /2. From this figure it is seen that the particle flow pattern in the vessel is classified into two regions at y/fl=0.8. The region of >/n>0.8, x/a.) and are almost constant and independent oiy/a and e. Then, it is possible for velocity distribu-...

On the analogy of hydraulic jump in open channel flow, the granular jump can occur in a horizontal pneumatic conveying, provided that for a given U the particle flow pattern belongs to the suspension flow accompanied with the settled layer and that the particles are introduced into the pipe with velocity hi er than the equilibrium particle velocity for U. Since the deceleration of particle is not observed in the upstream side of the jump, it is infared that the particle is discontinuously decelerated at the jump. 

Separation in the turbulent particle flow pattern can only be achieved with appropriate separation sharpness if the separator has a comparably high number of separation stages and if a sufficiently high ratio between the lightweight and heavy material volume flow rates Vl / can be maintained. This is commensurate with practical experience gained with classification experiments, Kaiser [4],... 

It is not easy to study the particle flow pattern experimentally. In order to give an impression of the flow of a particle through a cyclone, we can resort to CFD simulations. Figure 3.1.4 shows a series of particle trajectories. The particles are injected at different radial positions along the inlet in a precalculated gas flow field. The swirling motion is not shown. 

Derksen (2003) studied the gas and particle flow pattern and the separation efficiency in a Stairmand HE cyclone (see Fig. 15.1.1 and Table 15.1.1). Important simplifying assumptions in the simulations were ... 

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