Vertical hollow fiber

Figure 10.42 [92] depicts the likely mechanisms of depolarization and flux enhancement with vertical hollow fibers. For bubble flow outside hollow fibers, the vertical flow channels are less distinct and comprise the outer edge of fibers rather randomly positioned. Surface shear on the hollow fiber... 

Module Design Where the packing density needs to be sufficiently low for high solids feeds. Modules most prone to blocking could be vertical hollow fibers, rather than horizontal fibers or vertical flat-plate cassettes. One design that overcomes this uses vertical hollow fibers attached (to suction) only at the base and closed at the top end, which is free to move (see Section 10.3.1). 

Koch Hollow-fiber membrane of 0.1-pm pore size. They were arranged in a vertical position with intermittent air scouring and back-flushing. 

The most important process in the fabrication of silicon hollow fibers is deep reactive ion etching (DRIE). This process is very similar to the standard reactive ion etching (RIE) [ 122] process but permits us to achieve perfect vertical structures with low roughness. The results shown in Figs. 12 and 13 clearly confirm the required verticality of the walls to assure good confinement can be achieved. 

Figure 11.26 Performance of a 37 m2 hollow fiber silver-nitrate-impregnated facilitated transport membrane for the separation of propylene/propane mixtures. The feed pressure was 5-13 atm the permeate was a hexane liquid sweep stream. The vertical dotted lines show when the membrane was regenerated with fresh silver nitrate solution [27]. Reprinted with permission from R.D. Hughes, J.A. Mahoney and E.F. Steigelmann, Olefin Separation by Facilitated Transport Membranes, in Recent Developments in Separation Science, N.N. Li and J.M. Calo (eds) (1986). Copyright CRC Press, Boca Raton, FL...

Commercial modules are usually mounted vertically to avoid difficulties from sagging of the hollow fibers. Typically, commercial modules are 4-8 in. in diameter and 10 ft long [13]. 

FIGURE 10.36 Schematics of different vibration strategies for submerged hollow fiber membranes, (a) Vertical vibration, (b) transverse vibration, and (c) liquid oscillation. 

A number of studies have been carried out to evaluate the effect of injection of air into the lumen of tubular and hollow fiber membranes on the performance of membrane filtration. Figure 10.38 shows the filtration results obtained by Cui et al. [85] using a vertically installed tubular membrane module (12.7 mm i.d., PVDF, MWCO, 100 kDa) with dextran solution... 

B. Bechmann, Vertical Cylindrical Skien of Hollow Fiber Membranes and Method of Maintaining Clean Fiber Surfaces , US Patent 5783083 (July 1998). 

Figure 18.8 shows the flow chart of the hollow fiber membrane system for oxygen production with the vacuum operating mode. The membrane module is placed under a vertically positioned tubular furnace with the sealing points kept out of the bottom inlet of the furnace tube. An oil-free vacuum pump is connected to the lumen of the fibers to yield a negative pressure and to collect the oxygen product. 

The application of MF and UF technology in water treatment is still relatively new, as many full-scale plants are less than 10 years old. Consequently, the design of MF and UF systems varies from plant to plant as no single design has proved itself to be the best (see Table 6.2). For example, MF/UF systems may be positioned horizontally or vertically, operate in deadend or cross-filtration mode, the membranes may be immersed/submerged in a feed tank where permeate is sucked (via vacuum) into the inside of the hollow fiber (outside-in filtration) or the membranes may be housed in modules where pressurized feed water is forced through the fiber and permeate is collect on the outside (inside-out filtration). 

The early references to submerged membranes came from Japan. Ohkubo et al. (1988) obtained a patent describing hollow fibers in a vertical bundle in a vessel with air scour to vibrate the fibers to remove the cake. The first reported use of submerged hollow fibers in a wastewater membrane bioreactor (MBR) was by Yamamoto et al. (1989), who used fibers in a bundle and air bubbles for aeration, mixing, and induced liquid flow. Permeate was removed by suction. At that time the concept was more of a curiosity, but within a decade the submerged membrane has become the dominant approach for low-pressure membrane processing in the water and wastewater industry. 

Submerged membranes are operated with the feed in a vessel at atmospheric pressure. To obtain a TMP, the permeate side has to be below atmospheric pressure, and this is achieved by suction provided by permeate pumping. The pressure on the permeate side will be determined by the TMP defined by Eq. (10.3) as well as a presstrre drop due to permeatc-side (lumen) flow, which may be significant for hollow fibers. This situation has been analyzed for vertical submerged hollow fibers closed at the bottom and with suction at the top. The situation is depicted in Figure 10.18a for a clean water feed, and the axial flux distribution can be estimated from (Chang et al., 2000)... 

The diaphragm cell consists of multiple electrolytic cells having the anode plates and cathodes mounted vertically and parallel to each other. The cathodes, often flat hollow perforated steel structures that are covered with asbestos fibers, serve as the diaphragm that prevents the mixing of hydrogen and chlorine and back diffusion of hydroxide (OH) ions from the cathode to the anode. Brine fed into the cell is decomposed to approximately half of its original concentration to produce chlorine gas at the anode and hydrogen and sodium hydroxide at the cathode. 

Figure 8.8 Photograph of a Permea hydrogen recovery unit installed at an ammonia plant. The hollow fine fiber modules are mounted vertically [6].

The predominant cell type in softwoods is the vertically oriented (along the stem axis) longitudinal tracheid. More commonly known as fibers, these tracheids are hollow, square to rectangular in cross section, have closed and tapering ends, and are arranged so that their... 

Industrial diaphragm cells consist of a box in which the anode plates are mounted vertically parallel to one another. The cathodes are flat hollow steel mesh structures covered with asbestos fibers, optionally impregnated with fluoro-organic resins, and fit between the anodes (see Fig. 1.7-8, 1.7-9 and 1.7-10). 

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