Dispersive mixers

Cas/Liquid Micro Flow Dispersive Mixers Generating Slug and Annular Patterns... 

However, in contrast to the dispersive mixers forming slug and aimular flow patterns, here the flow-fhrough channel is much larger than the typical dimensions of the dispersed phase (compare with Section 5.1.2). As a result, bubbly flows and foams are the common flow patterns. 

The need for analytical (flow-pattern) characterization in advance of the experiment is less than for the dispersive mixers forming slug and annular flow patterns, because the dispersion typically is formed in an attached tube. This tube is commonly made of glass and mostly of larger inner diameter. Hence visual inspection by the operator is routinely possible. 

Dispersive mixers are aiso used to reduce the size of soiid components in a moiten poiymer matrix. Soiid components inciude pigments, flame-retardant additives, and fiiiers. Many of these feedstock materiais are in the form of iooseiy bounded aggiomerates of smaiier primary particies. As the aggiomerate enters the shear stress fieid in the mixer, the aggiomerate wiii be decreased in size if the appiied shear stress is higher than the cohesive forces bonding the primary particies together. 

Although the full history of this screw is unknown, the mixing pins appeared to have been added to the screw after the screw failed to mix and homogenize the extrudate. Pin mixers have been retrofitted to screws for many years as a way to improve the distributive mixing for an extruder. Here the pin mixers would distribute the solid polymer fragments evenly in the extrudate, hut the mixers lacked the ability to trap and disperse them. Pin mixers were clearly the wrong type of mixer to use for this application. Instead, a dispersive mixer such as a Maddock-style mixer would be preferred see Section 8.5.1. 

There are no standard engineering classification methods for mixing equipment, and often, quite different types of mixers can fulfill the same mixing task. Nevertheless, we can subdivide mixers used in processing into three broad categories particulate solids mixers, laminar distributive mixers, and laminar dispersive mixers. This classification, on the basis of application, is supported by the nature of the primary mixing mechanism taking place in them. 

After the molecular weight and composition of the block polymer were fixed at appropriate levels, mechanical blending was scaled-up to both larger and continuous dispersion mixers. An acceptable and reproducible product was made at all levels up to the highest output tried, e.g., 1000 lbs/hr. 

Plant food dispersions such as tomato concentrates and concentrated orange juice are important items of commerce. The viscosity function and the yield stress are two important rheological properties that have received considerable attention. Corrections for slip, due to the formation of a thin layer of fluid next to solid surfaces, in a concentric cylinder viscometer depended on the magnitudes of applied torque and on the shear-thinning characteristics of the dispersion. Mixer viscometers were used for obtaining shear rate-shear stress and yield stress data, but the latter were higher in magnitude than those obtained by extrapolation of flow data. 

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