Screw, helical

Power generates bigb settling forces. Slurry centrifuged against rotating bowl, and removed by slower rotating helical screw conveyor within bowl. 

The unit consists essentially of tvv o rotating elements, the outer being a solid-shell conical-shaped bowl and the inner comprising a helical-screw conveyor revolving at a speed slightly lovv er than that of the bowl. Raw feed sliiri v is delivered through a stationai"v feed pipe... 

Figure 4-8. The two rotor profiles of helical screw compressors.

Figure 7-3. Flow pattern in a baffled helical screw system. (Source Holland F. A. and Bragg, R. Fluid Flow for Chemical Engineers, 2nd ed., Edward Arnold, 1995.)...

The spiral-lobe and helical-screw compressors are rotary positive-displacement machines and quite adaptable to a wide assortment of process and refrigeration gases. This class of equipment is usually built to comply with the American Petroleum Institute Standard 619. These units oper-... 

The screw configuration is normally either a ribbon-type helical screw or a series of paddles mounted on a common shaft. Materials of construction are selected based on the specific application and materials to be mixed. Typically, the screws are either steel or stainless steel, but other materials are available. 

Figure 7,20. Commonly used impellers (a) Three-bladed propeller ( >) Six-bladed disc turbine (Rushton turbine) (c) Simple paddle (d) Anchor impeller (e) Helical ribbon (/) Helical screw with draft tubs...

Anchors, helical ribbons and screws, are generally used for high viscosity liquids. The anchor and ribbon are arranged with a close clearance at the vessel wall, whereas the helical screw has a smaller diameter and is often used inside a draft tube to promote fluid motion throughout the vessel. Helical ribbons or interrupted ribbons are often used in horizontally mounted cylindrical vessels. 

In this type of machine the solids deposited on the wall of the bowl are removed by a scroll (a helical screw conveyer) which revolves at a slightly different speed from the... 

Screw conveyors, also called worm conveyors, are used for materials that are free flowing. The basic principle of the screw conveyor has been known since the time of Archimedes. The modem conveyor consists of a helical screw rotating in a U-shaped trough. They can be used horizontally or, with some loss of capacity, at an incline to lift materials. Screw conveyors are less efficient than belt conveyors, due to the friction between the solids and the flights of the screw and the trough, but are cheaper and easier to maintain. They are used to convey solids over short distances, and when some elevation (lift) is required. They can also be used for delivering a metered flow of solids. 

Another significant cooperativity effect in preferential helical screw sense optically active copolymers is the majority rule phenomenon.18bl8q In this case, the screw sense of a helical main chain with unequal proportions of opposite chirality enantiopure chiral side groups is controlled by the enantiomeric excess only. Since this phenomenon was first reported from poly-a-olefins made of vinyl co-monomers bearing nonenantiopure chiral moieties by Green et al.8b and Pino et al.,16b this majority rule has been established in... 

Figure 7.4 Simplified macroscopic model for cholesteric (a) lateral and (b) top view of left-handed superhehx (photographs display a half-pitch length) composed of left-handed helical screws with pitch-to-diameter ratio much smaller than Jt. (Reprinted with permission of John Wiley Sons from Circular Dichroism—Principles and Applications, 2nd ed., N. Berova, K. Nakanishi, R. W. Woody, Eds., Copyright 2000.)...

Agitators with a large blade area which rotate at low speeds. These include anchors, paddles and helical screws. 

Helical screws normally function by pumping liquid from the bottom of a tank to the liquid surface. The liquid then returns to the bottom of the tank to fill the void created when fresh liquid is pumped to the surface. A rotating helical screw positioned vertically in the centre of an unbaffied cylindrical tank produces a mild swirling motion in the liquid. Since the liquid velocity decreases towards the tank wall, the liquid at the wall of an... 

Flow pattern in a baffled helical screw system... 

Incorporation of the (.S )-2-mcthyloctoxy group afforded optically active polymers with preferential helical screw sense (see Section 3.11.6.1). The observed helicity was corroborated by force field calculations, which indicated similar helical conformations for both dialkoxy- and dialkyl-substituted polymers. Based on their similar conformational properties, it was suggested that the origin of the spectral red shift was electronic, due to a a-n mixing interaction, as for polymers 76 above, rather than conformational. 

Preferential helical screw sense polysilanes with main-chain chirality are essentially of two types those in which PSS chirality is induced by an internal chiral field, for example, incorporation of enantiopure chiral (unichiral) side chains or end groups, and those which are inherently achiral, in which PSS chirality is induced by an external chiral field, such as a unichiral additive or solvent. 

Moller and co-workers co-polymerized dichlorodi- -pentylsilane with either dichloro-bis-(d )-2-methylbutylsilane or dichloro-(d )-2-methylbutyl- -pentylsilane in various ratios and found a linear dependence of optical activity on mole fraction of chiral co-monomer.313 On the other hand, studies by Fujiki on co-polymers 109 formed by the copolymerization of achiral (racemic) dichlorohexyl-2-methylbutylsilane and chiral dichlorohexyl-(d )-2-methylbutylsi-lane or dichlorohexyl-(l )-2-methylbutylsilane have shown that a preferential helical screw sense can be induced by even as little as 0.6 mol% of chiral co-monomer, and that at 5 mol%, the helicity, as gauged by the gabs value, is essentially the same as that of the chiral homopolymer, as shown in Figure 40. This indicates a positive non-... 

The (—) and racemo forms were also prepared. The CD spectrum of the (+) and (—) polymers in ethanol showed negative and positive bisigned profiles respectively, indicating main-chain helical screw sense chirality. The origin of... 

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