Stochastic agglomeration

Agglomeration of particles by stochastic movement on the soot particles... 

An alternative to stochastic reconstruction of multiphase media is the reconstruction based on the direct simulation of processes by which the medium is physically formed, e.g., phase separation or agglomeration and sintering of particles to form a porous matrix. An advantage of this approach is that apart from generating a medium for the purpose of further computational experiments, the reconstruction procedure also yields information about the sequence of transformation steps and the processing conditions required in order to form the medium physically. It is thereby ensured that only physically realizable structures are generated, which is not necessarily the case when a stochastic reconstruction method such as simulated annealing is employed. 

The first edition of this book, published in 1977, included an extended discussion of aerosol dynamics, the study of the factors that determine the distribution of aerosol properties with respect to particle size. The distributions change with position and time in both natural and industrial processes. The ability to predict and measure changes in the distribution function are of central importance in many appl ications from air pollution to the commercial synthesis of powdered materials. The aerosol dynamics approach makes it possible to integrate abroad set of topics in aerosol science usually treated in an unconnected manner. These include stochastic processes, aerosol transport, coagulation, formation of agglomerates, classical nucleaiion theory, and the synthesis of ulirafine solid particles,... 

Terrazas-Velarde, K., Peglow, M. Tsotsas, E. 2009 Stochastic simulation of agglomerate formation in fluidized bed spray drying a micro-scale approach. Chemical Engineering Science 64, 2631-2643. 

Low Shear Mixers The most simple low shear mixers use horizontally oriented cylindrical drums that rotate about their axis. Many of these mixers are operating in a batch mode and feature differently shaped lifters or internal baffles or the vessels are shaped such that the otherwise regular flow of material is modified to a stochastic movement. Continuously operating cylindrical drum blenders resemble the previously described drum agglomerators (see Section 7.4.1). 

As a result of the mechanical action of mixing tools in high intensity mixers (see Section 7.4.2) an aerated, turbulent particulate matter system with stochastic particle movement develops. Similar conditions exist if the particles are suspended in a fluidized bed. The main difference between the two methods is that in the mixers particle movement is caused by mechanical forces while in fluidized beds drag forces, that are induced by a flow of gas, are the main reason for the movement of the particulate matter. Therefore, fluidized beds are not only used as excellent environments in which gas efficiently and intimately contacts particles but also for dry mixing of particulate solids and coalescence of particles which, in the presence of binding mechanisms, causes agglomeration. 

Agglomeration in low density fluidized beds is different in that at least part of the drying takes already place during growth and in the equipment itself The stochastic movements of gases, droplets, and particles, the occurrence of coalescence and bonding and the mechanisms of drying can be modeled and mass, particle size, heat and moisture balances can be established [B.49, B.72, B.93]. Nevertheless, it is an art, performed by experienced personnel of specialized vendors, to successfully scale-up from the performance of test units to commercial equipment and systems. Capacity increases are often obtained by installation of multiple feed points (gas and powder inlets, liquid spray nozzles), which are housed in suitably sized and shaped containments (e.g., towers). 

Since industrial plants process large amounts of solids, the forces required to transport these masses and to cause the turbulent, stochastic movement of individual particles, nuclei, and agglomerates are much bigger than those experienced in the smaller developmental systems. Therefore, it is not unusual that additional and/or more effective binder(s) is (are) required or the feed size must be adjusted to feature a smaller surface equivalent diameter of the fresh input, possibly combined with modified recycle properties, such as smaller size obtained by a suitable mill to be installed in the return loop. 

Hong and Selman [48, 49] Stochastic structure model A, C No Used to identify structure parameters for agglomerate models... 

The stochastic approach treats the size enlargement process as an increase in the number of primary particles per agglomerate. In order to be able to compare the model results with a real process, this number is correlated with the agglomerate diameter by assuming a constant agglomerate porosity of 60%. The structure of the primary particles within the agglomerate is based on a concept of fractional... 

Investigation of the kinetics of fluidized bed spray agglomeration based on stochastic methods. AIChE J., doi 10.1002/ aic. 12506... 

It is important to point out that the nano-metric scale ( inside an agglomerate scale) was not experimentally studied. Nevertheless, the CL internal micro-structure was characterized at 5000 x resolution. In this scale we can define stochastic micro-pores but it is not possible to define CL primary components (Pt, C and ionomer). On the other hand, because the DECAL technique (used for the fabrication of CLs) generates very thin CLs (10-20 p.m), the 500 x resolution characterizes a macro-superficial and isotropic structure. 

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