Orientation and flow

The mold temperature, on the other hand, affects the thickness of skin layers [82,83,87]. In general, the effect of temperature on the mechanical properties is relatively small compared to the injection speed. Mathematical modeling and computer simulations based on Doi s molecular theory for the motion of rigid rods were recently used in an attempt to predict the orientation and flow behavior of TLCPs in the mold as a function of processing conditions. A reasonably good agreement between the simulation and the experiment was reported [88]. 

Ultrasonic devices can also be used very effectively as powerful tools for inline monitoring of the composition of polymer blends, residence time distribution, injection-molding processes, temperature, polymer orientation, and flow instabilities. Franca et al. [59] demonstrated the sensitivity of ultrasonic waves... 

To obtain the relations between rii 2,3 and the Leslie coefficients oti 2,one could evaluate the stress tensor and the shear rate 0 13 for various director orientations and flow and velocity gradient directions. From these considerations, the following relationships are obtained ... 

The Driving Module houses power supply, circuits for determination of travel distance (odometer wheels) and circumferential orientation, and a computer and a storage facility for all data recorded. The Driving Module has cups extending to the pipe wall, thus providing the movement of the tool after its launching into the continuous oil flow. 

Flow processes iaside the spinneret are governed by shear viscosity and shear rate. PET is a non-Newtonian elastic fluid. Spinning filament tension and molecular orientation depend on polymer temperature and viscosity, spinneret capillary diameter and length, spin speed, rate of filament cooling, inertia, and air drag (69,70). These variables combine to attenuate the fiber and orient and sometimes crystallize the molecular chains (71). 

Traditionally, the electron and proton transport pathways of photosynthetic membranes (33) have been represented as a "Z" rotated 90° to the left with noncycHc electron flow from left to right and PSII on the left-most and PSI on the right-most vertical in that orientation (25,34). Other orientations and more complex graphical representations have been used to depict electron transport (29) or the sequence and redox midpoint potentials of the electron carriers. As elucidation of photosynthetic membrane architecture and electron pathways has progressed, PSI has come to be placed on the left as the "Z" convention is being abandoned. Figure 1 describes the orientation in the thylakoid membrane of the components of PSI and PSII with noncycHc electron flow from right to left. 

Liquid crystals represent a state of matter with physical properties normally associated with both soHds and Hquids. Liquid crystals are fluid in that the molecules are free to diffuse about, endowing the substance with the flow properties of a fluid. As the molecules diffuse, however, a small degree of long-range orientational and sometimes positional order is maintained, causing the substance to be anisotropic as is typical of soflds. Therefore, Hquid crystals are anisotropic fluids and thus a fourth phase of matter. There are many Hquid crystal phases, each exhibiting different forms of orientational and positional order, but in most cases these phases are thermodynamically stable for temperature ranges between the soHd and isotropic Hquid phases. Liquid crystallinity is also referred to as mesomorphism. 

An example of research in the micromechanics of shock compression of solids is the study of rate-dependent plasticity and its relationship to crystal structure, crystal orientation, and the fundamental unit of plasticity, the dislocation. The majority of data on high-rate plastic flow in shock-compressed solids is in the form of ... 

The melt-spinning process used to convert mesophase pitch into fiber form is similar to that employed for many thermoplastic polymers. Normally, an extruder melts the pitch and pumps it into the spin pack. Typically, the molten pitch is filtered before being extruded through a multi-holed spinnerette. The pitch is subjected to high extensional and shear stresses as it approaches and flows through the spinnerette capillaries. The associated torques tend to orient the liquid crystalline pitch in a regular transverse pattern. Upon emerging from the... 

The fuel for the Peach Bottom reactor consisted of a uranium-thorium dicarbide kernel, overcoated with pyrolytic carbon and silicon carbide which were dispersed in carbon compacts (see Section 5), and encased in graphite sleeves [37]. There were 804 fuel elements oriented vertically in the reactor core. Helium coolant flowed upward through the tricusp-shaped coolant channels between the fuel elements. A small helium purge stream was diverted through the top of each element and flowed downward through the element to purge any fission products leaking from the fuel compacts to the helium purification system. The Peach... 

Keller, A. and Kolnaar, H.W.H. (1997) Flow-induced orientation and structure formation, in Processing of Polymers, ed. Meijer, H.E.H. Materials Science and Technology, A Comprehensive Treatment, eds. Cahn, R.W., Haasen, P. and Kramer, E.J. (VCH, Weinheim) p. 189. 

Axial flow, in which the liquid enters the impeller and discharges along a parallel path to the axis, is shown in Figure 9. The radial and longitudinal components are primarily responsible for the derived mixing action. The tangential component is important when the shaft has a vertical orientation and is positioned near the center of the tank. 

A microscopic description characterizes the structure of the pores. The objective of a pore-structure analysis is to provide a description that relates to the macroscopic or bulk flow properties. The major bulk properties that need to be correlated with pore description or characterization are the four basic parameters porosity, permeability, tortuosity and connectivity. In studying different samples of the same medium, it becomes apparent that the number of pore sizes, shapes, orientations and interconnections are enormous. Due to this complexity, pore-structure description is most often a statistical distribution of apparent pore sizes. This distribution is apparent because to convert measurements to pore sizes one must resort to models that provide average or model pore sizes. A common approach to defining a characteristic pore size distribution is to model the porous medium as a bundle of straight cylindrical or rectangular capillaries (refer to Figure 2). The diameters of the model capillaries are defined on the basis of a convenient distribution function. 

Specifically, within the aerospace industry, for aircraft, the airframe manufacture itself is one of the major cost drivers, using the factors already addressed. Let s look at the character of how we would build an aerospace vehicle. There is typically a lot of manpower dependence. The industry itself is cyclic because the demands ebb and flow. There is typically little automation simply because of relatively low production rates, and there are very few customers. But, despite all those characteristics, there is typically also a large capacity that is founded on many highly skilled personnel, and the orientation is much more high tech than that of most other industries. Without product excellence as a driving factor, the whole industry would be an unworkable mess. 

The formation of a fibrillar structure in TLCP blends makes the mechanical properties of this kind of composites similar to those of conventional fiber reinforced thermoplastics [11,26]. However, because the molecular orientation and fibrillation of TLCPs are generally flow-induced, the formation, distribution, and alignment of these droplets and fibers are considerably more processing-dependent. We do not know ... 

In all cases of the processing conditions, TLCP domains were well dispersed and deformed to droplets in the core layer, but there was only a narrow distribution of their aspect ratio (about Hd 6) and less orientation. In both transition and skin layers, the domains were also well dispersed, but more oriented and fibrillated in the flow direction. From this reason, we give the distribution of aspect ratio Ud) and fiber number (N) versus fiber length class in Fig. 22, only for skin and transition layers, respectively. 

For scaly fillers the increase of relative viscosity with filler concentration is not as pronounced as in case of fibrous fillers [177,178]. Owing to filler orientation, the flow curves for systems with different concentrations of a fibrous and a scaly filler may merge together at high shear rates [181]. In composites with a dispersed filler the decrease of the effective viscosity of the melt with increasing strain rate is much weaker. 

There is not too much orientation that is permanently added to material as it passes through the gate since the continued flow in the cavity basically tends to produce turbulence that destroys the orientation. The last material to pass through, however, does retain its orientation and the gate area in a molded product is usually highly oriented and could be weak. In the case of jetting, the result is a patch of highly oriented material somewhere on the molded product near where the first material entered the mold. 

In the very first model of molecular orientation in flow, Kuhn and Kuhn [2] depicted the polymer as having one chain end anchored in space (Fig. 39). In... 

Figure 2.45 Design of a multilamination mixer with hydrodynamic focusing (upper left) and flow pattern in such a mixer for a total volume flow of 10 ml h of water (lower left), taken from [141. The right side of the figure shows the orientation of liquid lamellae over a cross-section of the constriction for different Reynolds numbers [142].

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