Fiber Geometry

Solid PET polymer is relatively hard and brittle. It must be formed into very fine fibers in order to exhibit a bending stiffness that is low enough for textile materials. Most commercial PET fibers are produced in a diameter range of about 10-50 pm, considerably smaller than a human hair. Within this range lie large differences in the softness, drape and feel of fabrics formed from the fibers, since the bending stiffness of a cylindrical fiber depends on the 4th power of its diameter. 

One key requirement in the commercial production of fibers is to control fiber diameters within narrow ranges of the target. Another is to control the internal structure of the fiber, particularly the orientation of the polymer molecules. It is this orientation along the fiber axis that controls the morphology, and hence the fiber properties, such as dye uptake, shrinkage and tensile strength. 

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Membrane systems consist of membrane elements or modules. For potable water treatment, NF and RO membrane modules are commonly fabricated in a spiral configuration. An important consideration of spiral elements is the design of the feed spacer, which promotes turbulence to reduce fouling. MF and UF membranes often use a hollow fiber geometry. This geometry does not require extensive pretreatment because the fibers can be periodically backwashed. Flow in these hollow fiber systems can be either from the inner lumen of the membrane fiber to the outside (inside-out flow) or from the outside to the inside of the fibers (outside-in flow). Tubular NF membranes are now just entering the marketplace. 

Cross-Sectional View of Soil/Fiber Geometry,... 

Since the linker DNA is assumed straight and the nucleosome non-deformable, the fiber geometry of the two-angle model is completely determined by the entry-exit angle of the linker DNA at each nucleosome and by the rotational angle... 

The second factor that affects performance in discontinuously reinforced FMCs is fiber length. This has an effect primarily on the ease with which the composite can be manufactured. Very long fibers can create difficulties with methods used to create discontinuously reinforced FMCs and can result in nonuniform mechanical properties. The third factor is also related to fiber geometry, namely, the fiber shape. Recall that the... 

A.2.4 Discontinuous-Fiber-Reinforced Polymer-Matrix Composites Sheet Molding Compound. Of the parameters influencing the mechanical properties in short-fiber-reinforced polymer-matrix composites, fiber composition, matrix composition, fiber geometry, and manufacturing method will be elaborated upon here. 

We can, however, write a list of parameters for cure optimization. To limit the possible combinations, we assume that the composite composition is known (i.e., resin, fibers, geometry, etc., are given, and the mold design and mold material is known). This reduces the number of buttons for control of cure to the following ... 

The diffusion coefficient D is 10 10 to 10 12 cm2/s and can be increased only by an increase in temperature. The diffusion path h is predetermined by fiber geometry the concentration gradient CL-CF, by CL. 

If we take the schematic of a differential fiber element presented in Fig. 6.19, we can define the fiber geometry by the function R(x) and the unit normal vector n. The continuity equation tells us that the volumetric flow rate through any cross-section along the rr-direction must be Q... 

Fig. 2 Waveguide mode-surface plasmon coupling in fiber geometry with an area of removed cladding and a gold deposition therein, a) Experimental scheme for a single wavelength transmission experiment under controlled coupling angle a into the fiber, b) Experimental scheme for a spectral transmission experiment...

Wickramasinghe S.R., Semmens J., and Cussler E.L., Mass transfer in various hollow fiber geometries, J. Membr. Sci. 69, 235, 1992. 

Figure 8 shows four wide-angle X-ray diagrams with fiber geometry for material C. The extrusion temperature was varied firom 180 to 65 °C from (a) to (d). In all four cases the... 

L-liquid, G-gas, S-solid, Ll-Liquid phase 1, L2-Liquid phase 2 Geometry (2) packings, plates, films, spray, uniform, specific structures, fiber Geometry (3) even, rough, porous, chemically/physically inert/active surface... 

The hollow-fiber geometry is preferred for CCRO because it is more convenient to provide circulation on both sides of fibers than it is for flat-sheet membranes. A number of hollow-fiber NS-lOO membrane modules were tested at 250 psi. The fibers were stable for several days at this operating pressure at feed concentrations up to 25 volZ ethanol. However, higher operating pressure and/or feed concentration caused these membranes to fail rapidly due to plasticization weakening of the polysulfone support. The CTA... 

The low ethanol rejection and the instability of the hollow-fiber NS-100 membranes preclude the use of this membrane for practical ethanol enrichment. Nevertheless, for the purpose of demonstrating the concept of CCRO using hollow-fiber membranes, CCRO experiments were conducted at the reduced ethanol concentration of 10 vol%. The permeate fluxes of NS-100 modules were measured at 250 psi in the absence and presence of recirculation with a 10-volX ethanol solution. The results were varied recirculation brought about flux increases ranging from 5% to about 20%. The limited flux increase may again be explained in terms of the formation of a polyamine gel during NS-100 membrane fabrication. Nevertheless, the flux increase shows that the hollow-fiber geometry is a viable one for CCRO operation. 

Based on this analysis and from (20) and (21), it is clear that for sensors application, any change in the core or cladding indices as well as the fiber geometry will result in modal power redistribution, which can be exploited for chemical and biosensing applications. 

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