Stratification of particles

Figure 12.7. Rotating dish granulator applications and performance (Sherrington and Oliver, 1981). (a) Edge and face view of a dish granulator, diameters to 25 ft, Froudc no. n2D/gc = 0.5-0.8. (b) Stratification of particle sizes during rotation, (c) Typical applications of dish granulation (Dravo Corp.). (d) Capacity and power (Dravo Corp.). (e) Performance on cement kiln feed.

Inconsistency of the published estimates of the haze-particle effective radius are discussed in [24, 29, 51]. The cause of the differences is discussed in [53]. Using the assumption that the haze (for heights greater than 66 km) is a continuation of the underlying cloud layer [30], it was shown that stratification of particles should take place due to turbulent intermixing. 

Data analyses of circular polarization also yielded an ambiguous solution rir= 1.44 and reff = 1.4 micrometers, and r= 1-60 and 2 < r ff < 5 micrometers, the effective variance being Veff = 0.07 for both solutions [25]. Recalculation of the size distribution for the first solution using a log normal distribution gives an average geometrical particle radius of about 1.2 micrometers. Therefore, nearly the same results were obtained independently of the Stokes parameters used in the analyses. This means that the vertical stratification of particle sizes in the Saturn atmosphere is weak. 

As the feed suspension enters the drum from the bottom (in the most common bottom feed version), fast settling slurries are not suitable for most rotary drum filters. Nor are very fine slurries because of the inevitable penetration problems. Note the unfavourable stratification of particle size within the cake discussed in section 13.10.2 and shown in Figure 13.15. In units designed to use a pre-coat filter aid (rotary drum pre-coat filters), the drum can be evacuated over the full 360 degrees and fitted with an advancing knife system that continuously shaves off the deposited solids together with a thin layer of the pre-coat. The pre-coat has to be renewed periodically. 

Stratification of the particles making up the bed, caused by the fluidization (fines on top), is not desirable. The soflds holding capacity of the bed is best utilized if the filtration flow encounters progressively finer sand particles. This is achieved in upflow filters where the fluidization due to backwash produces the correct stratification in the bed. Unfortunately, the filtration flow and the backwash take place in the same direction the disadvantage is that the washwater goes to the clean side of the filter. 

A variation to the top-feed dmm filter is the dual dmm filter which uses two dmms of the same size in contact with each other and rotating in opposite directions. The feed enters into the V-shaped space formed on top of the two dmms and the cake that starts forming initially contains coarser particles due to the settling which takes place in the feed zone. This is beneficial to the clarity of the filtrate because the coarser particles act as a precoat. Erom the point of view, however, of the final moisture content of the cake the stratification of the soHds in the cake may lead to somewhat wetter cakes. Utilization of the area of the dmms is poor since there are dead spaces under the two dmms. The primary appHcation of the dual dmm filters is in dewatering coarse mineral or coal suspensions at feed concentrations greater than 200 kg/m. ... 

More recently, Wells and Goldberg (1991) report that very small marine colloids (d < 120 nm) are, by at least three order of magnitudes, more abundant. A vertical stratification of these particles was found (very high concentrations in the thermodine and season-dependent in the bottom-waters). This stratification indicates that these very small colloidal particles are reactive. The apparent close association of metals with these colloids suggests that they may play an important part in the transport and fate of trace elements in seawater (Wells and Goldberg,... 

Jigs machines that produce stratification of the particles in a bed or particles of differing densities by repeated differential agitation of the bed, the heaviest particles migrating to the lowest layer. The jigging action may be carried out in air or with the bed immersed in water or other liquids. 

In more complicated cases, different combinations of phase transitions of stratification and ordering are possible. For example, a system may pass over to the disordered and ordered phases or to two different ordered phases. The type of the phase transitions and the regions of their realization are determined by the concentrations of the components, the temperature, and the potentials of particle interaction. Similar transitions also occur in multicomponent solutions. An increase in the number of components increases the number of different combinations of the phase transitions [29]. 

The negative values of the diffusivities in processes of particle aggregation and a change in the rates of processes under conditions of stratification of the adsorption system. 

The potentiality of hierarchical stratification of complex reactive systems, according to the characteristic times of the involved processes, makes it difficult to use direcdy thermodynamic tools as well as to apply the con cept of stability to very compHcated (in particular, biological) systems. The statistical approach to describe the behavior of a system that contains a large number of particles takes into account the instabihty of mechanical trajectories of individual particles. Indeed, any infinitesimally small distur bances in the particles motion can make it impossible to determine from the starting conditions the trajectory of even one particle s motion. As a result, a global instabihty of mechanical states of individual particles is observed, the system becomes statistical as a whole, and the trajectories of individual particles are no longer predictable. At the same time, the states that correspond to stable solutions of any dynamic (kinetic) problem can only be observed in real systems. In terms of a statistical approach, the dynamic solution of a particular initial state of an ensemble of particles is a fluctuation, while the evolution of instabihty upon destruction of this solution is a relaxation of this fluctuation. 

The correlation of olefin production and dilution shown in Figure 2 for the 6-m coil is better than that shown in Figure 3 for the 2-m coil. This is probably because the 2-m reactor data are more extensive and, therefore, differences in the feedstock composition and particle size due to stratification of the heterogeneous MSW in the barrel would become more important. 

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