Blending laminar mixing

The scale in chaotic laminar mixing goes down from the machine scale to a scale where the continuum hypothesis breaks down and phenomena are dominated by physical effects, due to intermolecular forces, such as van der Waals. Danescu and Zumbrunnen (21) and Zumbrunnen and Chibber (22) took advantage of this and devised an ingenious device to create controlled three-dimensional chaotic flows, with which they were able to tailor the morphology and properties of blend films and composites. 

There are other data available, e.g. Kenics , but not sufficient to enable the comparison of mixer types that is possible for laminar mixing. The thermal homogenizing of gases is another process where static mixers ate used for blending in the turbulent flow regime . 

The presence of texture in the samples is important in polymer processing, as (1) laminar mixing produces texture (2) the mechanical properties of polymer blends depend on the texture (e.g., skin-core formation, fiber orientation, and distribution of voids along the thickness in structural foams) and (3) the lack or the presence of texture is required in certain products. Samples can exhibit a certain texture, and at the same time they do or do not exhibit concentration gross uniformity. 

Mixing processes involved in the manufacture of disperse systems, whether suspensions or emulsions, are far more problematic than those employed in the blending of low-viscosity miscible liquids due to the multi-phasic character of the systems and deviations from Newtonian flow behavior. It is not uncommon for both laminar and turbulent flow to occur simultaneously in different regions of the system. In some regions, the flow regime may be in transition, i.e., neither laminar nor turbulent but somewhere in between. The implications of these flow regime variations for scale-up are considerable. Nonetheless, it should be noted that the mixing process is only completed when Brownian motion occurs sufficiently to achieve uniformity on a molecular scale. 

Texture is important in polymer processing because (a) laminar and even chaotic distributive mixing inevitably lead to it, (b) many products are visually examined for lack of texture or for a certain desired texture, and (c) mechanical properties of blends depend on the texture of the mixture. 

This study (3) was done to produce an ABS type resin by dry and melt blending SAN and a nitrile rubber in a motionless mixer. In polyblends of two semicompatible polymers, the particle size of the dispersed phase is an important factor concerning final properties, particularly if a rubber is dispersed to improve impact strength. Motionless mixers should give precise control over the final particle size since for laminar flow the number of fluid layers and the striation thickness can be predicted mathematically. The hypothesis that the impact strength should peak out at a precise number of mixing elements was thus investigated. 

The correlation between quality of a laminar mixture and the total shear strain which the material has undergone applies particularly to blends of polymers. When hard or agglomerated components are being mixed, however, it is necessary to subject such materials to a high shear stress gradient, and special equipment and processes have been developed for such purposes. Tlie rubber and coatings industries in particular abound with examples of such techniques. 

In designing blending systems, it is important to establish whether conditions will be turbulent, transitional, or laminar. Turbulent mixing occurs at impeller Reynolds numbers greater than Kf. ... 

Static mixers are widely used in situations where continuous in-line or pipeline mixing is required. Table 9.17 shows that applications span the entire spectrum from laminar to turbulent flow regimes, and they cover a wide variety of mixing processes involving the blending of gas-gas... 

These determine the difficulty of the mixing application, as illustrated in Figure 9.41. The wider the viscosity difference between the component streams, the more difficult is the blending application. The most difficult application is the addition of a small, low-viscosity stream into a large, high-viscosity stream in laminar flow. For example, Tables 9.20(a) and 9.20(b) show effects... 

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