Spiral wound tubes, fabrication

The spirally wound tubes were fabricated into manholes by Plastic Constructions Ltd of Birmingham. The base and access platform were made from 25.4 mm thick extruded HOPE sheet. They were attached by extrusion welding. See Figs 24.8 and 24.9. The manholes were tested for water tightness to a head of 1 m. In service they will only fill to the... 

The third main class of separation methods, the use of micro-porous and non-porous membranes as semi-permeable barriers (see Figure 2c) is rapidly gaining popularity in industrial separation processes for application to difficult and highly selective separations. Membranes are usually fabricated from natural fibres, synthetic polymers, ceramics or metals, but they may also consist of liquid films. Solid membranes are fabricated into flat sheets, tubes, hollow fibres or spiral-wound sheets. For the micro-porous membranes, separation is effected by differing rates of diffusion through the pores, while for non-porous membranes, separation occurs because of differences in both the solubility in the membrane and the rate of diffusion through the membrane. Table 2 is a compilation of the more common industrial separation operations based on the use of a barrier. A more comprehensive table is given by Seader and Henley.1... 

Polymeric membrane elements and modules which consist of elements come in different sh4>es. The shape strongly determines the packing density of the element or module which is indicative of the available membrane filtration area per unit volume of the element or module the packing density, in turn, can affect the capital and operating costs of the membranes. The packing density is often balanced by other factors such as ease and cost of maintenance and replacement, energy requirements, etc. Most of the polymeric membranes are fabricated into the following forms tube, tubes-in-shell, plate-and-frame, hollow-fiber, and spiral-wound. 

The key to the successful use of the RO/UF membrane is in the packaging of the membrane. Until economical, easily fabricated and stable packages were developed, membranes were of little commercial value. We use the spiral wound type of membrane element for all of our equipment. Other packages such as the tube, the hollow fiber with bore flow and the hollow fiber with outside flow are all valuable and useful packages. However, the spiral package is by far the most universal in its ability to... 

Spiral Wound. This device, pictured in Fig. 18.2-1, consists of a membrane envelope containing a peimeate-conducting channel, usually a woven fabric. Between membrane envelopes, a feed spacer conducts the feed across the membrane face. There are several variants, but the usual device has the permeate channel connected to an axial product tube. The spiral has been veiy successful commercially, as an inexpensive device for commercializing flat sheet membranes. Spirals are made commonly in 100 and 200 mm diameters, but new desalination plants are using elements 300 mm in diameter by 1.5 m long. 

The spiral-wound fabrication shown in Figure 1.3 is analogous to a single tube-in-tube or double-pipe heat exchanger. The hollow-fiber concept lends itself to the shell-and-tube type of heat exchanger. The hollow fibers are mounted as a tube bundle inside a shell, as indicated in Figure 1.4. A few applications are indicated in Figure 1.5. 

Composite membranes of 12 in x 9 ft were submitted to Osmonics, MN, for fabrication into spiral wound modules of approximately 14 in width and a diameter of 2 in. The membrane with polyester backing was wrapped around the PVC center tube and sealed with epoxy around the edges. Polypropylene turbulence promoters acted as spacers between two membranes. Two types of tubular modules, one with 20 tubes and the other with 14 tubes, were constructed. The length of the tube was 14 in. 

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