Weirs

When used to separate solid-solid mixtures, the material is ground to a particle size small enough to liberate particles of the chemical species to be recovered. The mixture of solid particles is then dispersed in the flotation medium, which is usually water. Gas bubbles become attached to the solid particles, thereby allowing them to float to the surface of the liquid. The solid partices are collected from the surface by an overflow weir or mechanical scraper. The separation of the solid particles depends on the different species having different surface properties such that one species is preferentially attached to the bubbles. A number of chemicals are added to the flotation medium to meet the various requirements of the flotation process ... 

All static studies at pressures beyond 25 GPa are done with diamond-anvil cells conceived independently by Jamieson [32] and by Weir etal [33]. In these variants of Bridgman s design, the anvils are single-crystal gem-quality diamonds, the hardest known material, truncated with small flat faces (culets) usually less than 0.5 nun in diameter. Diamond anvils with 50 pm diameter or smaller culets can generate pressures to about 500 GPa, the highest static laboratory pressures equivalent to the pressure at the centre of the Earth. 

Blades, M. W. Weir, D. G. Fundamental Studies of the Inductively Goupled Plasma, Spectroscopy 1994,... 

The two procedures primarily used for continuous nitration are the semicontinuous method developed by Bofors-Nobel Chematur of Sweden and the continuous method of Hercules Powder Co. in the United States. The latter process, which uses a multiple cascade system for nitration and a continuous wringing operation, increases safety, reduces the personnel involved, provides a substantial reduction in pollutants, and increases the uniformity of the product. The cellulose is automatically and continuously fed into the first of a series of pots at a controlled rate. It falls into the slurry of acid and nitrocellulose and is submerged immediately by a turbine-type agitator. The acid is deflvered to the pots from tanks at a rate controlled by appropriate instmmentation based on the desired acid to cellulose ratio. The slurry flows successively by gravity from the first to the last of the nitration vessels through under- and overflow weirs to ensure adequate retention time during nitration. The overflow from the last pot is fully nitrated cellulose. 

Flow meters have traditionally been classified as either electrical or mechanical depending on the nature of the output signal, power requirements, or both. However, improvement in electrical transducer technology has blurred the distinction between these categories. Many flow meters previously classified as mechanical are now used with electrical transducers. Some common examples are the electrical shaft encoders on positive displacement meters, the electrical (strain) sensing of differential pressure, and the ultrasonic sensing of weir or flume levels. 

Fig. 10. Stream flow over (a) a broad-crested, rectangular weir (b) a cross-current view of the rectangular and CipoUetti weirs (c) a trape2oidal-notch or CipoUetti weir (d) a sharp-crested, triangular, or V-notch weir (e) a cross-current view of the V-notch and hyperboHc-notch weirs and ( a...

Eiquid Flow Measurement in Open Channels Using Thin Plate Weirs and Venturi Flumes, ISO 1438-1975(E), International Organization for Standardization, Geneva, Switzerland, 1975. 

P. Ackers and co-workers, Weirs andFlumes, oVnNrA. y Sons, Inc., New York, 1978. 

Fig. 22. Common flow meteis (a) orifice, (b) venturi, (c) target, (d) rotameter, and (e) weir. See text.

Measurement by Liquid Level. The flow rate of Hquids flowing in open channels is often measured by the use of weirs (see Liquid-LEVEL measurement). The most common type is the rectangular weir shown in Figure 22e. The flow rate across such a weir varies approximately with the quantity. Other shapes of weirs are also employed. Standard civil engineering handbooks describe the precautions necessary for constmcting and interpreting data from weirs. 

A. J. Weir and co-workers, "Methanol Dual-Fuel Combustion," paper presented at 1987Joint Symposium on Stationay Combustion MO Control, New Odeans, La., Mar. 23—26, 1987. 

The length of time the particles stay in the pool determines the distance the particles settle in the pool. Thus, the feed entrance must be located so that the velocity of the pulp toward the weir, together with the distance, allows sufficient time for the fine particles to be carried out over the weir as the... 

Analysis of this type of classifier (15) suggests that the sharpness iadex is between 0.5 and 0.6, consistent with calculated results, because the degree of turbulence can be high ia these devices (16). A DSF Dorr classifier (1.8 m x 7 m), operating at 19 strokes per minute and having a weir depth of 100 cm and a slope of 19.4 cm/m, produced a cut size equal to 240 p.m, a sharpness iadex of 0.5, and an apparent bypass of approximately 26% when the water spht was 26% (15). 

Several plants employ cooled-belt flakers. These consist of flexible steel belts, ca 1-m wide and up to 50-m long, that have short mbber skirting at the edges. Molten pitch flows from a thermostatically controlled tank over a weir to give a flat thin sheet on the belt, which is cooled from below by water sprays. At the end of the belt, the solid pitch is broken up by rotating tines. The pitch flakes are drained and transported to a covered storage silo by belt conveyor, during which time the surface moisture evaporates. 

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