Capillary fibers

The second type of hoUow-fiber module is the bore-side feed type illustrated in Figure 23b. The fibers in this type of unit are open at both ends, and the feed fluid is usually circulated through the bore of the fibers. To minimize pressure drops inside the fibers, the fibers often have larger diameters than the very fine fibers used in the shell-side feed system and are generally made by solution spinning. These so-called capillary fibers are used in ultrafiltration, pervaporation, and in some low to medium pressure gas appHcations. Feed pressures are usually limited to less than 1 MPa (150 psig) in this type of module. 

Knight, J. C. Driver, H. S. T. Hutcheon, R. J. Robertson, G. N., Core resonance capillary fiber whispering gallery mode laser, Opt. Lett. 1992, 17, 1280 1282... 

Crossflow technology is increasing, as it proves practical. Micioliltration membranes are of an isotropic and homogeneous morphology, i.e., the pore structure is consistent throughout. There is some movement, however, toward ihe use of "skinned" anisotropic membranes. Microliltration membranes are available in a wide variety ol polymers, including some that arc quite chemically inert. They also tire available as tubular, hollow fiber, or capillary fiber elements. 

The types of hollow fiber membranes in production are illustrated in Figure 3.32. Fibers of 50- to 200-p.m diameter are usually called hollow fine fibers. Such fibers can withstand very high hydrostatic pressures applied from the outside, so they are used in reverse osmosis or high-pressure gas separation applications in which the applied pressure can be 1000 psig or more. The feed fluid is applied to the outside (shell side) of the fibers, and the permeate is removed down the fiber bore. When the fiber diameter is greater than 200-500 xm, the feed fluid is commonly applied to the inside bore of the fiber, and the permeate is removed from the outer shell. This technique is used for low-pressure gas separations and for applications such as hemodialysis or ultrafiltration. Fibers with a diameter greater than 500 xm are called capillary fibers. 

Another factor is the ease with which various membrane materials can be fabricated into a particular module design. Almost all membranes can be formed into plate-and-frame, spiral-wound and tubular modules, but many membrane materials cannot be fabricated into hollow fine fibers or capillary fibers. Finally, the suitability of the module design for high-pressure operation and the relative... 

Figure 6.14 Backflushing of membrane modules by closing the permeate port. This technique is particularly apphcable to capillary fiber modules...

Nitrogen from air Permea Polysulfone/capillary fiber 150... 

Water from air Medal Polyimide/capillary fiber ... 

Benoit V, Yappert MC (1996) Effect of capillary properties on sensitivity enhancement in capillary - fiber optical sensors. Anal Chem 68 183-188... 

A solution for these drawbacks was found in using commercially available New Objective Picospray emitters with distal coating, mounted onto the chip with Upchurch Nanoport connectors. To facilitate mounting of the needles and to connect the chip with capillary fibers to the mass spectrometer, a holder was designed as shown in Figure 9.4. The electrical connection to the liquid was realized by using a metal-coated needle, electrically contacted via a gold-plated... 

K. Uezu, K. Saito, T. Hori, S. Furusaki, T. Sugo and J. Okamoto, Performance of Fixed-Bed Charged with Chelating Resin of Capillary Fiber Form for Recovery of Uranium from Seawater, J. Atom. Energy Soc. Jpn., 30 (1988) 359. 

M.H. Rahimy, G.A. Peyman, S.Y. Chin, R. Golshani, C. Aras, H. Borhani, H. Thompson, Polysulfone capillary fiber for intraocular drug delivery in vitro and in vivo evaluations, J. Drug Target. 2 (4) (1994) 2455-2480. 

The second advance that made industrial membrane-separation processes possible was the development of methods to incorporate large membrane areas into economical membrane packets or modules. Even with the best anisotropic membranes, most industrial processes require several hundred, sometimes several thousand, square meters of membrane to perform the separation. The three most important configurations, shown schematically in Fig. 7.1, are hollow-fme-fiber, capillary-fiber and spiral-wound modules. Tubular and plate-and-frame... 

Fig. 3.9 Raman spectroscopy of liquid samples in a thin capillary fiber (a) production of the fiber (b) incoupling of an argon laser beam with a microscope objective into the fiber and imaging of the outcoupled radiation into a spectrometer (c) fiber with liquid [320]...

Solid-phase microextraction (SPME) SPME consists in the adsorption of the target compounds on a thin polymeric film deposed on the surface of a capillary fiber. The mass transfer can be achieved from liquid media in direct contact with the extracting coated fiber as well as from gaseous environments. Volatile or semivolatile herbicides existing in solid samples can be easily transferred in the gas phase on heating in closed vials, followed by trapping of the resulting vapors in the coated fiber (procedure is known as Headspace HD/SPME). 

Mass transport in the plasma fluid flowing inside the capillary fiber. 

Hollow-fine fibers Capillary fibers Spiral-woimd Plate-and-frame Tubular... 

A number of module designs are possible and all are based on two types of membrane geometry (i) flat sheet membranes and (ii) capillary fibers. Typical dimensions are shown in Figure 5.2. 

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