Mixing mechanical features

Most multicomponent systems undergo phase separation because of their positive mixing enthalpies coupled with low entropy of mixing. Morphological features have been central to the study of multicomponent systems, because domain sizes, shapes, and interfacial bonding characteristics determine the mechanical properties. A proper understanding of these features often allow synergistic behavior to be developed. 

In the following sections the main mechanical features of each type of equipment are described and the range of operating duty is discussed. This is done in a largely qualitative way and it is hoped that this will set the scene for the detailed quantitative treatments of liquid mixing processes which are presented in the subsequent chapters. 

The principal feature of turbulent flows is the presence of eddies which are large compared with the molecular scale and which aid the mixing process (turbulent dispersion). This mixing mechanism in liquids is often rapid compared with the other processes of bulk flow and molecular diffusion. The eddies vary in size, having a maximum scale, L, which is of the order of the scale of the equipment (i.e. impeller or baffles) down to a minimum value, /, which, according to Kolmogoroff, for isotropic turbulence depends only upon the power input per unit mass to the system and the kinematic viscosity of the liquid ... 

Although the model, as well as the analytical techniques, were conceived particularly for the problem of the diffusion flame, it was clear that they would encompass both the case of slow chemistry in a vortex field and the diffusive mixing problem in general. The following work uses the vortex distortion model to study in detail the mixing of two liquids, their rapid chemical reaction and their slow chemical reaction, exhibiting those fluid mechanical features that characterize laminar mixing processes,... 

Each key element of the mechanical characteristics of mixers will be covered in this section. Although not comprehensive with respect to each topic, the equipment and design requirements discussed should cover most of the mixer types and applications. Even with the diversity of mixing equipment, features such as motors and materials of construction are mechanical considerations, common to all types of mixers. 

Based on this low surface tension feature and the commonly observed insolubiUty of defoamers, two related antifoam mechanisms have been introduced (29) (/) The agent dispersed in the form of fine drops enters the Hquid film between bubbles and spreads as a duplex film. The tensions created by this Spreading lead to the mpture of the original Hquid film. (2) A droplet of the agent enters the Hquid film between bubbles, but rather than spreading produces a mixed monolayer on the surface. This monolayer, if of less coherence than the original film-stabilizing monolayer, causes destabilization of the film. 

The procedure which had originally been used by Lehn et al. involved slow addition (over a period of ca. 8 h) of ca. 0.1 M solutions of diamine and diacyl halide in benzene. Dye et al. found that the reactions could be conducted more rapidly as long as stirring was kept efficient. This observation suggested the use of a mixing chamber of the type normally used for stopped-flow kinetic studies. Utilizing this type of set-up, the latter authors were able to obtain a 70% yield for 1, slightly inferior to the yield reported by Lehn, but a similar yield of 3 which is better than that previously ob-tained. Note that the chemical features of this synthetic method are essentially identical to the approach shown in Eq. (8.1) and differ primarily in the mechanics. 

The most critical aspects of the process are those that occur in the transition zone, although it should be recognized that the initial configuration has direct influence on the subsequent processes in the transition zone. In Fig. 6.1, the four critical features are identified as (1) the configuration change (2) mechanical mixing (3) shock activation and (4) heating. 

If we combine mechanics in this way with unobservable receipts, deterministic systems show some cpialitative features that resemble quantum, mixed-state systems. I hus one can always measure the real momentum in event 1 by the location of event 2. But one cannot yet observe the receipt momentum of event 1, because it is not until event 2 that it first combines with any real momeiituni - which cannot be observed until some subsequent event 3 - by which time it is already mixed with another estimate And so on. One can never simultaneously measure both estimate and receipts, though all adds up eventually. And all this involves no probabilities at all, just temporary inaccessibility of information [iuinsky82]... 

---