Flat sheets

Flat-sheet membranes Flatspotting Flatting agents... 

The original expanded film membranes were sold ia roUs as flat sheets. These membranes had relatively poor tear strength along the original direction of orientation and were not widely used as microfiltration membranes. They did, however, find use as porous inert separating barriers ia batteries and some medical devices. More recentiy, the technology has been developed to produce these membranes as hoUow fibers, which are used as membrane contactors (12,13). 

When a multiplicity of single-hole spinnerettes are assembled across a width, the plexifilaments produced can form a wide web that can be thermally bonded to produce a flat sheet stmcture (49). The web-forming procedure is amehorated by use of a baffle which deflects the stream of plexifilaments after exiting the spinnerette. 

Figure 7 shows the crystal stmctures of graphite, ordinary (cubic) diamond, and hexagonal diamond. The layers of carbon atoms He in flat sheets in graphite, but in diamond the sheets are more wrinkled and He closer together. Taken separately, the sheets are similar, but they may be stacked in various lateral positions and stiU have bonding between them. 

Fan (flat) spray. a. Oval or rectangular orifice (see Fig. l4-87c). Numerous variants on cavity and groove exist. Liquid leaves as a flat sheet or flattened ellipse. Combination of cavity and oriBce produces two streams that impinge within the nozzle. Flat pattern is useful for coating surfaces and for injection into streams. same pattern with different fluids. Small clearances. 

Crossflow units — Flat sheet membranes - Rotating filter elements... 

The second major membrane type is a composite. Starting with a loose asymmetric membrane, usually a UF membrane, a coating is applied which is polymerized in situ to become the salt rejecflng membrane. This process is used for most high-performance flat-sheet RO membranes, as well as for many commercial nanofiltration membranes. The chemistry of the leading RO membranes is known, but... 

Aromatic polyamide (aramid) membranes are a copolymer of 1-3 diaminobenzene with 1-3 and 1-4 benzenedicarboxylic acid chlorides. They are usually made into fine hollow fibers, 93 [Lm outer diameter by 43 [Lm inner diameter. Some flat sheet is made for spirals. These membranes are widely used for seawater desalination and to some extent for other process applications. The hollow fibers are capable of veiy high-pressure operation and have considerably greater hydrolytic resistance than does CA. Their packing density in hoUow-fiber form makes them veiy susceptible to colloidal fouling (a permeator 8 inches in diameter contains 3 M fibers), and they have essentially no resistance to chlorine. 

Ceramics Ceramic microfilters for commercial applications are almost always employed as tube-side feed multitube monoliths. They are also available as flat sheet, single tubes, discs, and other forms primarily suited to lab use. They are used for a few high-temperature applications, in contact with solvents, and particularly at very high pH. 

Cassettes Cassette is a term used to describe two different cross-flow membrane devices. The less-common design is a usually large stack of membrane separated by a spacer, with flow moving in parallel across the membrane sheets. This variant is sometimes referred to as a flat spiral, since there is some similarity in the way feed and permeate are handled. The more common cassette has long been popular in the pharmaceutical and biotechnical field. It too is a stack of flat-sheet membranes, but the membrane is usually connected so that the feed flows across the membrane elements in series to achieve higher conversion per pass. Their popularity stems from easy direct sc e-up from laboratoiy to plant-scale equipment. Their hmitation is that fluid management is inherently veiy hmited and inefficient. Both types of cassette are veiy compact and capable of automated manufacture. 

Spiral membranes are the usual way to form flat sheet into modules. They have the characteristic that the feed and the permeate move at right angles. Since the membrane is always cast on a porous support, point-permeate values are influenced by the substrate. 

The one-time important applications in photographic film, in bicycle parts (pump covers and mudguards) and in toys manufactured by a blowing process from flat sheet are no longer of importance. 

The pieces of cloth are then plied up and moulded at about 170°C for 30-60 minutes. Whilst flat sheets are moulded in a press at about lOOOlbf/in (7 MPa) pressure, complex shapes may be moulded by rubber bag or similar techniques at much lower pressures ( 15 Ibf/in ) (0.1 MPa) if the correct choice of resin is made. A number of curing catalysts have been used, including triethanolamine, zinc octoate and dibutyl tin diacetate. The laminates are then given a further prolonged curing period in order to develop the most desirable properties. 

The finite size effects in the contact between a spherical lens of polyurethane and a soft flat sheet of crosslinked polyfdimethyl siloxane) (PDMS) has been addressed by Falsafi et al. [37]. They showed that for deformations corresponding to contact diameters larger than the sheet thickness, the compliance of the system was affected by the glass substrate supporting the soft sheet. In order to minimize the finite size effects in the adhesion measurement of small elastomeric lenses, Falsafi et al. [38] and Deruelle et al. [39] used relatively thick elastic sheets to support their samples. 

---