Flows local structures

Once the explosion occurs it creates a blast wave that has a very steep pressure rise at the wave front and a blast wind that is a transient flow behind the blast wave. The impact of the blast wave on structures near the explosion is known as blast loading. The two important aspects of the blast loading concern is the prediction of the magnitude of the blast and of the pressure loading onto the local structures. Pressure loading predications as a result of a blast, resemble a pulse of trapezoidal or triangular shape. They normally have a duration of between approximately 40 msec and 400 msec. The time to maximum pressure is typically 20 msec. 

While in the case of noninteracting dispersions one needed to consider only the effect of the particle concentration, in interacting dispersions one needs to consider the time over which the flow behavior is observed and its magnitude relative to the time scales over which either shear or colloidal forces alter the local structure of the dispersions. What the flow behavior is, which interaction effects dominate the behavior, and how they do depend on the competing influences of the applied shear and interaction effects. In this section, we outline some of the important parameters one can formulate to judge the relative effects of various colloidal interactions and the physical significance of those parameters. 

Hartge, E.-U., Li, Y. and Werther, J. (1986). Analysis of the Local Structure of the Two Phase Flow in a Fast Fluidized Bed. In Circulating Fluidized Bed Technology. Ed. P. Basu. Toronto Pergamon Press. 

Figure 4 A schematic representation of the experimentai approach for time-resoived XAS measurements. XAS provides local structural and electronic information about the nearest coordination environment surrounding the catalytic metal ion within the active site of a metalloprotein in solution. Spectral analysis of the various spectral regions yields complementary electronic and structural information, which allows the determination of the oxidation state of the X-ray absorbing metal atom and precise determination of distances between the absorbing metal atom and the protein atoms that surround it. Time-dependent XAS provides insight into the lifetimes and local atomic structures of metal-protein complexes during enzymatic reactions on millisecond to minute time scales, (a) The drawing describes a conventional stopped-flow machine that is used to rapidly mix the reaction components (e.g., enzyme and substrate) and derive kinetic traces as shown in (b). (b) The enzymatic reaction is studied by pre-steady-state kinetic analysis to dissect out the time frame of individual kinetic phases, (c) The stopped-flow apparatus is equipped with a freeze-quench device. Sample aliquots are collected after mixing and rapidly froze into X-ray sample holders by the freeze-quench device, (d) Frozen samples are subjected to X-ray data collection and analysis.

Guo Q, Werther J (2004) Flow Behaviours in a Circulating Fluidized Bed with Various Bubble Cap Distributors. Ind Eng Chem Res 43 1756-1764 Hartge E-U, Li Y, Werther J (1986) Analysis of the local structure of the two phase flow in a fast fluidized bed. In CFB Technology, Pergamon press, pp 153-160... 

Note that here the formation of nanoporous structure in crystalline matrix of the anodized semiconductor is considered as a primary event, which results from the specific physical processes caused by current flow localization. However, the contribution of chemical processes cannot be excluded either. In particular, coexistence of two competing mechanisms (porous structure formation and SiC dissolution) resulting in formation of non-SPSC, was proposed above. 

A dilute polymer solution is a system where polymer molecules are dispersed among solvent molecules. An assumption common to any existing theory for flow properties of polymer solutions is that the structure of solvent molecules is neglected and the solvent is assumed to be replaced by a continuous medium of a Newtonian nature. Thus, macroscopic hydrodynamics may be used to describe the motion of the solvent. Recently, some ordering or local structure of solvent molecules around a polymer chain has been postulated as an explanation of the stress-optical coefficient of swollen polymer networks (31,32) so that the assumption of a solvent continuum may not apply. The high frequency behavior shown in Chapter 4 could possibly due to such a microscopic structure of the solvent molecules. Anyway, the assumption of the continuum is employed in every current theory capable of explicit predictions of viscoelastic properties. In the theories of Kirkwood or... 

For the better understanding of blend morphologies, the fundamental mechanisms of morphology development are discussed, viz. the liquid-solid phase transition (crystallization), the liquid-liquid phase separation e.g., spinodal decomposition under non-isoquench depth), as well as the complex mechanism of the morphology generation that results from the competition between these two transitions. The effects of chemical reactions and flow fields on morphology development have also been discussed. Finally, several evidences of a local structure in single-phase polymer-polymer mixtures are presented. 

While the images shown in Plate 4 are very time consuming to acquire, they are of great value when trying to understand the relationship between local structure and local Significant heterogeneity in the flow is... 

In experiments with cholesteric liquid crystals (geometry III), extraordinary high viscosity rim is observed, few orders of magnitude higher than the viscosity of the isotropic phase or a non-twisted nematic. It seems surprising because the local structure of nematics and cholesterics is the same. In addition such a flow is strongly non-Newtonian with increasing shear rate (s) rim decreases, as schematically shown in Fig. 9.9. In the case of the Poiseuille flow, the viscosity depends also on the radius of a capillary. 

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