Tubular membrane element

Fig. 17. Tubular membrane element with membrane cast in place.

Externally Wound Tubular Membrane Elements in Modular Assemblies Production and Application... 

As noted above, externally wound tubular membrane elements are fabricated primarily of extruded ABS tubing (natural), cellu-loslc or blend membranes and dacron paper. The cartridge assembly designed to house the membrane elements and provide for the uniform dlstrlbutlon/flow of feed stock is fabricated of extruded thin walled polystyrene headers. Pressure vessels were fabricated either by using epoxy coated steel pipe or fiberglass vessels. 

Fabrlcatlon/assembly of externally wound tubular membrane elements is accomplished by specially designed equipment that simultaneously and continuously winds, in helical fashion. Infinite lengths of membrane and backing material strips onto prefabricated tubular support structures. Membrane strip winding overlaps are solvent bonded during the winding process. 

A modular assembly housing externally wound tubular membrane elements may be defined as a pressure vessel within which are assembled a multiplicity of individual elements, means for connecting and sealing said elements to common headers and a feed stock distribution system that provides for adequate feed flow across membrane surfaces. 

In the development and design of modular assemblies housing a multiplicity of externally wound tubular membrane elements, the following factors were considered effectiveness of element packing arrangements and density, feed stock distribution patterns for controlled and uniform feed flow across membrane surfaces, sealing reliability of modular sub-assemblies, overall system reliability, module serviceability and ease of maintenance, system productibil-ity, and economic viability. 

In utilization of externally wound tubular membrane elements in modular assemblies for conventional systems operations, that is, selective separation via the circulation of pressurized feed across membrane surfaces, flow guide tubes were found to be essential for the proper distribution and control of feed flow. This was achieved singularly by the use of individual element shrouds or flow tubes creating an annular gap through which feed stock was circulated across membrane surfaces. 

R.O. systems utilizing externally wound tubular membrane element in modular assemblies have been used in the desalination of brackish and sea waters, the treatment and/or concentration of industrial waste waters, the separation/concentration of fluid food, pharmaceuticals and chemical solutions, and the manufacture of water purifiers for domestic use. Generally, externally wound tubular membrane systems have been found to be highly suitable for ultrafiltration applications in the processing Industry and in water pollution control applications. 

Membrane systems consist of membrane elements or modules. For potable water treatment, NF and RO membrane modules are commonly fabricated in a spiral configuration. An important consideration of spiral elements is the design of the feed spacer, which promotes turbulence to reduce fouling. MF and UF membranes often use a hollow fiber geometry. This geometry does not require extensive pretreatment because the fibers can be periodically backwashed. Flow in these hollow fiber systems can be either from the inner lumen of the membrane fiber to the outside (inside-out flow) or from the outside to the inside of the fibers (outside-in flow). Tubular NF membranes are now just entering the marketplace. 

The first molecule, the Ca2+ channel, is required for coupling at the triad. Skeletal muscle contains higher concentrations of this L-type Ca2+ channel that can be accounted for on the basis of measured voltage-dependent Ca2+ influx because much of the Ca2+ channel protein in the T-tubular membrane does not actively gate calcium ion movement but, rather, acts as a voltage transducer that links depolarization of the T-tubular membrane to Ca2+ release through a receptor protein in the SR membrane. The ryanodine receptor mediates sarcoplasmic reticulum Ca2+ release. The bar-like structures that connect the terminal elements of the SR with the T-tubular membrane in the triad are formed by a large protein that is the principal pathway for Ca2+ release from the SR. This protein, which binds the... 

A few other players in the nuclear membranes activity also developed inorganic membranes for the filtration of liquids. This was the case with Norton-USA who with the know-how of Euroceral developed MF membranes made of an 0-AI2O3 tubular support with an a-Al203 layer. The inner tube diameter was 3 mm and the outer diameter 5 mm. In 1988-1989, Norton also produced the multichannel membrane elements. These membranes produced by Norton are now sold by Millipore under the trademark Ceraflo . 

In order for membranes to be used in a commercial separation system they must be packaged in a manner that supports the membrane and facilitates handling of the two product gas streams. These packages are generally referred to as elements or bundles. The most common types of membrane elements in use today include the spiral-wound, hollow fiber, tubular, and plate and frame configurations. The systems currently being marketed for gas separation are of the spiral-wound type, such as the SEPAREX and Delsep processes, and the hollow-fiber type such as the Prism separator and the Cynara Company process. 

Figure 5.1 Photograph of alumina membrane elements in tubular and monolithic honeycomb shapes [Courtesy of U.S. Filters]...

The porosity at both ends of a tubular or monolithic honeycomb membrane element can be a potential source of leakage. These extremities need to be made impervious to both permeates and retentates so that the two streams do not remix. Typically the end surfaces and the outer surfaces near the ends of a commercial membrane element are coated with some impervious enamel or ceramic materials. 

Two types of connection (and therefore sealing) are involved in assembling membrane modules. The first type connects tubular or monolithic membrane elements in bundles using header plates at the ends and, in some cases, in the middle of the module length. The second type provides sealing between the plates and the module housing. 

FIGURE 6.27 General working principle of a pervaporation or vapor permeation module equipped with tubular ceramic membrane elements. 

The term membrane element refers to the basic form in which a membrane is prepared. There are three types of membrane elements flat sheets, hollow hbers, and tubular membranes. The device within which the membrane element is housed is referred to as the membrane module. The design of the membrane module largely depends on the type of membrane element, as well as on additional requirements such as the need for cleaning and disassembling, the required transmembrane pressure (TMP), and the required hydrodynamic conditions. Some of the different modules types are (see Figures 18.3 through 18.7) ... 

Of the various types of ultrafiltration membranes, tubular membranes have so far found the widest acceptance in engineering practice. This is becasusd the membrane module has a simple structure, the tube elements are easy to renew, and the membranes display quite a good reastance to the influence of pollutants. The only disadvantage of tubular membranes is a low packing density [1, 2 ]. 

Serviceability and maintenance. Being on the outer surface of tubular elements, the membranes are readily accessible to Inspection and cleaning. Assembly and disassembly of modules can be accomplished easily and quickly in the fluid. Good mechanical reliability of the system. The membrane elements are subjected to compressive stresses only, therefore, non-corrosive materials of lower tensile strength may be used. 

Membrane materials are available in various shapes, such as flat sheets, tubular, hollow fiber, and monolithic. Flat sheets have typical dimensions of 1 m by 1 m by 200 pm thickness. Tubular membranes are typically 0.5 to 5.0 cm in diameter and up to 6 m in length. The thin, dense layer is on either the inside or the outside of the tube. Very small-diameter hollow fibers are typically 42 pm i.d. by 85 pm o.d. by 1.2 m long. They provide a very large surface area per unit volume. Honeycomb, monolithic elements of inorganic oxide membranes are available in hexagonal or circular cross section. The circular flow channels are typically 0.3 to 0.6 cm in diameter (Seader and Henley, 2006). 

Tubular membranes Flat sheet membranes Rotating filter elements By gravity... 

The sarcoplasmic reticulum membranes are the main constituents of muscle s intracellular membranes, consisting of the transverse tubular membrane system and the longitudinally oriented sarcoplasmic reticulum proper [7,8], The transverse tubules are narrow invaginations of the plasma membrane along which the electrical excitation spreads inwards [9j. They must be considered as differentiated plasma-lemma [10-12], In contrast, the sarcoplasmic reticulum membranes constitute a closed intracellular membrane system not connected with the external fluid [13,14]. It consists of different structural elements, (1) the large cistemae which are opposed to the transverse tubules or the plasmalemma, and (2) the so-called free sarcoplasmic... 

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