Shrouds

Kuhni contacters (Eig. 15e) have gained considerable commercial application. The principal features are the use of a shrouded impeller to promote radial discharge within the compartments, and a variable hole arrangement to allow flexibility of design for different process applications. Columns up to 5 m in diameter have been constmcted (176). Description and design criteria for Kuhni extraction columns have been reported (177,178). 

Dating of textiles is possible by means of radiocarbon dating. Developments in this technique have greatly improved its utihty for that purpose, as exemplified by its appHcation in the dating of the Turin Shroud (121). 

Particle Attrition. Distributor jets are a potential source of particle attrition. Particles are swept into the jet, accelerated to a high velocity, and smash into other particles as they leave. To reduce attrition at distributors, a shroud or larger-diameter pipe is often added concentric to the jet hole, as shown in Figure 15. The required length of the concentric shroud is given by the relation... 

This shroud length allows the jet issuiag from the orifice to expand and fill the shroud. The gas velocity leaving the shroud should not exceed 70 m/s, to minimize attrition. 

Fig. 15. Schematic of a distributor grid shroud used to allow jets to expand and enter the fluid bed at lower velocity.

Fig. 24. Elements of a bubbleless turbulent fluid-bed reactor design where the internals create four stages. A represents the shrouded grid B, the first feed ...

Fypass Flow Effects. There are several bypass flows, particularly on the sheUside of a heat exchanger, and these include a bypass flow between the tube bundle and the shell, bypass flow between the baffle plate and the shell, and bypass flow between the shell and the bundle outer shroud. Some high temperature nuclear heat exchangers have shrouds inside the shell to protect the shell from thermal transient effects. The effect of bypass flow is the degradation of the exchanger thermal performance. Therefore additional heat-transfer surface area must be provided to compensate for this performance degradation. 

Upon the United States entry into World War 1 in 1917, helium became a war material of first priority. Helium was sought to replace hydrogen as the lifting gas in lighter-than-air craft for military use. As a war material, helium became a government monopoly, was given a code name, and was shrouded in secrecy. By the war s end, quantities of helium had been produced, but none had reached combat. 

Fast reactor fuel assembhes are shrouded with a relatively heavy metal envelope. This envelope is removed before shearing by either laser cutting (14) or stress cracking (15). 

Most rotating equipment includes electric motors or steam dryers that generate noise at a constant frequency. Air cooler fans are a source of noise that can be reduced by lowering the fan speed and increasing the number of blades. Pump motor noise can be reduced by including a shroud or fan cover that is accurately lined. Centrifugal compressor noise reduction can be achieved by blade design and the use of compressor pulsation noise reduction, silencers, and vibration isolation. 

Fig. 16. Gaps A (between impeller shrouds and diffusor wall) and B (between impeller and diffusor vane tips) corrective option where D = diameter and is diameter reduction (a) overall diameter reduction (b) vane diameter reduction (c) angle-cut, single-suction impeller and (d) angle-cut,...

The most common supported tubes are those with membranes cast in place (Fig. 17). These porous tubes are made of resin-impregnated fiber glass, sintered polyolefins, and similar materials. Typical inside diameters are ca 25 mm. The tubes are most often shrouded to aid in permeate collection and reduce airborne contamination. 

Externally cast membranes are first formed on the iaside of paper, polyester, or polyolefin tubes. These ate then iaserted iato reusable porous stainless-steel support tubes inside diameters ate ca 12 mm. The tubes ate generally shrouded in bundles to aid in permeate collection. 

A large number of fibers ate cut to length, and potted in epoxy resin at each end (see Embedding). The fiber bundle is shrouded in a cylinder which aids in permeate collection, reduces airborne contarnination, and allows back pressing of the membrane. HoUow-fiber membranes (qv) have also found use in ultrafilttation. 

Alumina—graphite refractories, almost all continuous casting ware, have come into much greater use as continuous casting has spread in steelmaking. These refractories are used in shrouds that conduct the molten metal from the ladle to the tundish, in the subentry tubes that take the metal from the tundish to the mold, in isostatically pressed stopper rods, and in shroud tubes for slab and bloom casters. The alumina—graphite compositions are used in these products because of the thermal-shock resistance and corrosion resistance they impart to the product. 

The hand-apphed shroud of shrinkable PE usually consists of a premade bag large enough to envelop the load. Equipment to shrink the wrap ranges from small propane-fired hand-held units, which take... 

Interna] Insulation The practice of insulating within the vessel (as opposed to applying insulating materials on the equipment exterior) is accomplished by the use of fiber blankets and hghtweight aggregates in ceramic cements. Such construction frequently incorporates a thin, high-alloy shroud (with slip joints to allow for thermal expansion) to protect the ceramic from erosion. In many cases this design is more economical than externally insulated equipment because it allows use of less expensive lower-alloy structural materials. 

Carbon steel, low-alloy steels Transfer lines, beat exchanger shells, baffles, pump components, heat exchanger tubing, fan blades and shrouds, valves, screens, fasteners... 

Galvanized steel Cooling tower components, fan blades and shrouds, transfer pipes, plumbing fixtures... 

Control bus and wire way chamber (shrouded Irom main bus)... 

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