Fiber diameter selectivity

A selection of fiber property data is given ia Table 2 as an illustration of the range of fiber properties available commercially for use ia manufacturiag nonwoven fabrics. In general, fiber diameters range from 5 to >40 p.m for natural fibers, and from less than 10 p.m (microdenier) to as high as needed for manufactured fibers. 

In the fixed catalyst method, the residence time in the reactor may be easily controlled to generate fibers of selected length and diameter, both dimensions which can vary over several orders of magnitude. Most of the physical properties which have been measured for VGCF have been made on this type of fiber. 

In this last section some recent developments are mentioned in relation to gas separations with inorganic membranes. In porous membranes, the trend is towards smaller pores in order to obtain better selectivities. Lee and Khang (1987) made microporous, hollow silicon-based fibers. The selectivity for Hj over Nj was 5 at room temperature and low pressures, with permeability being 2.6 x 10 Barrer. Hammel et al. 1987 also produced silica-rich fibers with mean pore diameter 0.5-3.0nm (see Chapter 2). The selectivity for helium over methane was excellent (500-1000), but permeabilities were low (of the order of 1-10 Barrer). 

In this chapter, we reviewed the structure-controlled syntheses of CNFs in an attempt to offer better catalyst supports for fuel cell applications. Also, selected carbon nanofibers are used as supports for anode metal catalysts in DMFCs. The catalytic activity and the efficiency of transferring protons to ion-exchange membranes have been examined in half cells and single cells. The effects of the fiber diameter, graphene alignment and porosity on the activity of the CNF-supported catalysts have been examined in detail. 

Hollow fine fiber membranes are extremely fine polymeric tubes 50-200 micrometers in diameter. The selective layer is on the outside surface of the fibers, facing the high-pressure gas. A hollow-fiber membrane module will normally contain tens of thousands of parallel fibers potted at both ends in epoxy tube sheets. Depending on the module design, both tube sheets can be open, or as shown in Figure 8.1, one fiber end can be blocked and one open. The high-pressure feed gas flows past the membrane surface. A portion of the feed gas permeates the membrane and enters the bore of the fiber and is removed from the open end of the tube sheet. Fiber diameters are small because the fibers must support very large pressure differences feed-to-permeate (shell-to-bore). 

A polyester resin P-43 (Rohm and Haas) was selected as a matrix material. The glass fiber reinforcement was in the form of a chopped strand mat (M 700) weighing 1 Vz oz/sq ft bonded together with a high solubility polyester resin. The chopped fibers were about 2 in. long and the fiber diameter was about 0.0004 in. 

Although they are specifically treated in Chapter 17, activated carbon fibers (ACFs) and derived cloths and felts deserve special mention here due to their uniform pore size distribution (PSD) and small and uniform fiber diameter, which confer on them, respectively, both size selectivity and rapid... 

The essential method to obtain sterile air, whether packed-bed or cartridge filters are used, is to reduce the humidity of the air after compression so that the filter material always remains dry. The unsterilized compressed air must never reach 100% relative humidity. Larger plants install instrumentation with alarms set at about 85% relative humidity. Careful selection of the cartridge design or the design of packed-bed filters will result in units that can operate in excess of three years without replacement of filter media. If a fiber material is used in a packed-bed type filter, the finer the fiber diameter the shallower the bed depth needs to be for efficient filtration. Other filter media are less common and tend to have special problems and/or shorter life. The bed depth of filters is only 10 to 18 inches for fibers of less than 10 microns. These filters run clean for 2 weeks or longer before being resterilized. 

At this point in the analysis, it was possible to define a tolerance for bondline thickness, whereby all points within a prescribed tolerance would be considered adhesive failure, and all points outside this tolerance would be considered wood failure. Furthemtore, a second tolerance could be specified to distinguish shallow" wood failure fi-om deep" wood failure (Fig. 10). For the specimens evaluated in this study, two tolerances ( 40 pm and 60 pm) were selected for both the bondline thickness and the depth of shallow wood failure. A typical bondline thickness for block-shear specimens is about 80 pm, and the thickness of a small fiber bundle is 40-60 pm (or 2-5 fiber diameters). Table 1 summarizes the results from this analysis as well as the visual grading values obtained from the trained observers. 

Glass mats or co-knits of wire plus fiberglas usual design velocity 5.6-12.5 L/s m. Fibrous bed select fiber diameter that is about the diameter of droplets, fibers about 10 to 40 pm typical exit drop diameter 2 to 4 times the inlet diameter flood velocities 1 cm/s usually design for 0.5 cm/s or 5 L/s m with velocity decreasing as surface tension decreases. Try for surface tension > 20 mN/m. 

The radial CTE of selected carbon fibers has been measured up to 800"C by a hot stage TEM technique using surface defects of the fibers as markers, and between 800 to 1600 C by laser diffraction [60]. The data are considerably scattered because of the small fiber diameter and the inhomogeneity of the transverse microtexture. Nevertheless, the transverse thermal expansion of those carbon fibers which have been studied is large and positive (Table IV). 

One of these processes can be selected, or several processes can be combined to achieve a desired quality [13,56], Each added step will increase the cellulose content while decreasing variability and fiber diameter [8], Storing the agro-residue for a certain period such as one year before fiber extraction may also lead to a more efficient fiber seperation than new harvested fiber source [38]. 

Eiber lengths between 5 and 10 mm are conveniently selected for the microindentation test (111). Eor a carbon fiber/epoxy system, as the fiber volume fraction increases from 10 to 50 vol%, the indentation displacement distance decreases from 44 to 36 pm but the interfacial shear strength increases from 33 to 46 MPa. When the interphase-to-matrix modulus ratio increases from 1.0 to 7.5, the interfacial shear stress increases by only 10%. Likewise, the interphase thickness and fiber diameter have marginal effects on the interfacial shear stress. Three types of thermoplastic polymers (polyester, polyamide, and polypropylene) were tested for their interfacial shear strength to the glass fiber by Desaeger and... 

The small gain in the selective mechanical properties sometimes cannot make up the higher cost of finer diameter of fiber glass. More important to the molders is the increased melt viscosity associated with smaller fiber diameter (Fig. 9.14). At 20 wt% of glass content, the melt flow decreases from 1.9 to 1.35 g/10 min. 

The morphology of the gold-sputtered electrospun fibers were observed by scanning electron microscope (SEM, Philips XL-30). The average fiber diameter and distribution was determined from selected SEM image by measuring at least 50 random... 

Types of optical fiber probes are presented in Table 5, and some examples of probes are shown in Fig. 16. In the case of the reflection-type optical flber probe, the volume from which the probe can detect the in form a -tion depends on flber conflguration. The intensity distribution of reflected light as a function of the distance between a fiber tip and a flat surface is shown in Fig. 17. The size of the core of the optical fiber should be selected depending on the maximum diameter of particles being investigated. If individual particle passages are to be detected, the fiber core diameter should be less than or equal to the particle diameter. On the other hand, if only the passage of solids or the solids concentration is to be detected, the fiber diameter of a... 

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