Particles coarser

Venturi scmbbers can be operated at 2.5 kPa (19 mm Hg) to coUect many particles coarser than 1 p.m efficiently. Smaller particles often require a pressure drop of 7.5—10 kPa (56—75 mm Hg). When most of the particulates are smaller than 0.5 p.m and are hydrophobic, venturis have been operated at pressure drops from 25 to 32.5 kPa (187—244 mm Hg). Water injection rate is typicaUy 0.67—1.4 m of Hquid per 1000 m of gas, although rates as high as 2.7 are used. Increasing water rates improves coUection efficiency. Many venturis contain louvers to vary throat cross section and pressure drop with changes in system gas flow. Venturi scmbbers can be made in various shapes with reasonably similar characteristics. Any device that causes contact of Hquid and gas at high velocity and pressure drop across an accelerating orifice wiU act much like a venturi scmbber. A flooded-disk scmbber in which the annular orifice created by the disc is equivalent to a venturi throat has been described (296). An irrigated packed fiber bed with performance similar to a... 

In particle-size measurement, gravity sedimentation at low soHds concentrations (<0.5% by vol) is used to determine particle-size distributions of equivalent Stokes diameters ia the range from 2 to 80 pm. Particle size is deduced from the height and time of fall usiag Stokes law, whereas the corresponding fractions are measured gravimetrically, by light, or by x-rays. Some commercial instmments measure particles coarser than 80 pm by sedimentation when Stokes law cannot be appHed. 

Units are available in stainless steel or protected mild steel, often prefabricated, up to 12.5 m in diameter, capable of processing >5 m /s depending on the separation efficiency required. When the separator is used for classification of granular soflds, smaller-diameter (<4 m) units are used, separating nearly all particles coarser than - 150 fim. 

ASTM recognizes two types of zinc dust in specification ASTM D 520-51 (reapproved 1976) (143), which includes permissible impurity concentrations. The metallic content of most commercial grades is 95—97%. The zinc oxide content is between 3 and 5% finer dusts contain higher concentrations because of high surface areas. Zinc dusts are manufactured in various size ranges, and a typical commercial dust has an average particle diameter between 4 and 8 p.m. Usually, dusts are screened to be essentially free of particles coarser than 75 p.m (200 mesh). 

Ft Fraction of particles coarser than a given sizes ... 

There are several British Standards that deal with liquid pyknometry applied to specific materials12-13-141516. A pyknometer bottle of up to 50 ml volume is usually sufficient for fine powders but coarse materials may require larger calibrated vessels. BS 1377 1975, for example, requires the use of a 1 litre cylindrical gas jar, closed by a ground plate, to measure the density of soils that contain particles coarser than 2 mm BS test sieve (but not coarser than 37.5 mm). 

Figure 3C shows that a significant amount of Si was initially removed from the zeolite during treatment with either H S0 or HC1 at pH 3. Even filter prolonged treatment an effluent containing 10-20 ppm Si persisted, undoubtedly due to the destruction of the structure at this pH (see Figure 1A). To demonstrate that the high Si content was not due to fine particulates, a sample of one of the early effluents was passed through a Millipore ilter capable of removing particles coarser than /l ym. The Si content decreased only from 140 to 125 ppm, indicating that the relatively high Si content in the effluent was present either in the ionic form or as a fine colloid.

Each adsorption stage consists of a mechanically stirred tank 11 ft (3.3 m) in diameter by 10 ft (3.0 m) deep, from which the mixture of resin and pulp flows to an airlift, which in turn discharges to a set of screens SI. These separate the coarser resin particles from the finer slimes. The resin drops by gravity into the next lower numbered tank, toward the feed end of the cascade, and the slurry flows to the next higher numbered tank, toward the tailings end. This counterflow is made possible by the absence of particles coarser than 325 mesh in the pulp and the absence of particles finer than 50 mesh in the resin. Residence time in each adsorbing stage is 18 to 20 min. 

The total resin inventory is 825 ft the resin circulation rate is 1320 ft /day or 26 liters/min. Despite the continuous flow of resin, attrition rate has been very low, averaging only 0.076 percent per day. Absence of abrasive sand particles coarser than 325 mesh is important in keeping the attrition rate low. 

Boulder The term applied to sediment particles coarser than cobble particles having a... 

This test method is used to determine the in situ density of soils that do not contain significant amounts of particles coarser than 4.75 mm and which can be readily retained in the drive cylinder. 

All of the gravity sedimentation techniques, with the exception of photo-sedimentometers which detect the projected area of the particles (which in turn is proportional to particle surface) measure size distribution by mass. Photosedimentometers can only give useful results for particles coarser than around 5 pm because for finer particles the wavelength of light becomes comparable to the particle size, the laws of geometric optics break down and the so-called light extinction coefficient becomes highly size dependent. 

Sand/gravel particles coarser than approximately 0.5 mm were dispersed due to the shearing action of faster flowing carrier above a bed on a top of the sliding bed. The concentration profile may be estimated as being linear within a shear layer. The thickness of the shear layer is related to the shear stress at the top of the sliding bed. 

If the objective is to obtain a particle-free fluid, then perfect separation means no solid particles in the overflow (equivalent to the heads stream of Section 2.2) and no carrier fluid in the underflow (the tails stream of Section 2.2). If particle classification is the goal, then perfect separation requires all particles above a given size to be in the underflow and all particles smaller than the given size in the overflow. In an imperfect separation, some particles are always present in the overflow (when the goal is to have a particle-free carrier fluid). Similarly, due to imperfections in the separator, some particles coarser than the given size are in the overflow, just as some finer particles are in the underflow from the separator functioning as a classifier. 

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