Mechanism of Mixing

Lacey (1954) identified three mechanisms of powder mixing (1) shear mixing  

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. 

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Mass transfer of a solute dissolved in a fluid is not only the fundamental mechanism of mixing processes, it also determines the residence-time distribution in micro fluidic systems. As mentioned in Section 1.4, in many applications it is desir-... 

Counterion Binding. The fractional counterion binding on charged mixed micelles is of fundamental interest because it gives an indication of surface charge density which is related to the mechanism of mixing nonidealities in ionic/nonionic micelles. It is also a necessary... 

Houcine et al. (64) used a non-intrusive laser-induced fluorescence method to study the mechanisms of mixing in a 20 dm CSTR with removable baffles, a conical bottom, a mechanical stirrer, and two incoming liquid jet streams. Under certain conditions, they observed an interaction between the flow induced by the stirrer and the incoming jets, which led to oscillations of the jet stream with a period of several seconds and corresponding switching of the recirculation flow between several metastable macroscopic patterns. These jet feedstream oscillations or intermittencies could strongly influence the kinetics of fast reactions, such as precipitation. The authors used dimensional analysis to demonstrate that the intermittence phenomenon would be less problematic in larger CSTRs. 

To avert the danger arising from the mechanization of mixing appliances, chlorate mixtures are usually prepared either by primitive manual methods or in machines made chiefly of wood. 

Mixing of 56Co into hydrogen-rich envelope may be required to account for the optical light curve and the early emergence of X-rays and 7-rays. Mechanism of mixing needs to be explored. 

Miles and miles across the craton it became apparent that, wherever water or moisture appeared, a thin film of presumably organic nature could be found more or less pronounced. Urschleim No, the osmometer reacted wildly to the slippery material, there must be membranes. The clones and subclones of cells are growing up at various distances that were similar even beyond the reaches of the many mechanisms of mixing. 

The mechanisms of mixing of miscible and immiscible liquids and soft agglomerates are depicted in Fig. 7.5, and that of hard solid agglomerates in Fig. 7.6. In the former, elongational and shear stretching is the dominant mechanism, whereas, the latter is shear stress dominated. 

Deo, N. and Somasundaran, P, Mechanism of mixed liposome solubilization in the presence of sodium dodecyl sulfate. Colloids Surfactants 186 33-41, 2001. 

Chella, R., and Ottino, J. M., Fluid mechanics of mixing in a single-screw extruder. l EC Fundamentals 24, 2,170-180 (1985). 

In order to describe the mechanisms of mixing, it is necessary to understand the local flow behavior. The motion around a point P can be approximated by... 

Thus, despite their large numeric disparity, then-net affects are comparable, and demonstrably important with respect to the global circulation timescale. A detailed discussion of the mechanics of mixing is beyond the scope of this chapter, but it is worthwhile to outline some of their major aspects. The mechanisms of mixing differ fundamentally between the two modes, so the remaining discussion occurs in two parts diapycnal and isopycnal mixing. 

Turbulent mixing includes phenomena on all scales in the turbulence spectra. For reactive mixtures the molecular scale phenomena are also pertinent. In the context of fluid mixing emphasis has been put on the scales assumed relevant to the process and to provide basic understanding of the controlling mechanisms of mixing. A common approach in practical reaction engineering is therefore to describe mixing on macro and micro scales only. 

Oyama and Ayaki s first-order type of rate equation (09) was followed when two substances, identical except for color, were mixed. The major mechanisms of mixing were diffusion and shear, in this case. However, when two different substances were mixed, the equation was... 

The rate studies thus far described have dealt with mixers in which the predominant mechanisms of mixing were diffusion and shear, rather than large scale turbulence. Rate studies in a machine where the latter was predominant would be of interest. 

Although determination of timing and the mechanism of mixing was beyond the scope of this study, the following constraints can be applied ... 

In order to discuss the various levels of complexity and analysis ofthese mixing systems, some of the fluid mechanics of mixing impellers are examined and then examples of how these are used in actual cases are shown. 

Normally, mixing of polymer A and polymer B could result in either synergistic interactions or phase separation, depending on the thermodynamic compatibility of the two components as well as the governing mechanisms of mixing (Aguilera, 1992 Matveev et al., 2000 Tanabe et al., 2002 Cheng et al., 2003). 

Chapter 3 continues the themes developed in the first two chapters and applies to changes made to equipment. This is a topic of special interest to the FDA because in the processing of semisolid products, the equipment plays a pivotal role. The mixing of drags within the base media is highly affected by the process and mechanism of mixing used. Also, because of the nature of product manufactured, often the cleaning and validation of equipment become serious issues. 

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