Particles classification

Fig. 4. Geldart group particle classification diagram for air at ambient conditions (6). Group A consists of fine particles B, coarse particles C, cohesive,...

In sohd—sohd separation, the soHds are separated iato fractions according to size, density, shape, or other particle property (see Size reduction). Sedimentation is also used for size separation, ie, classification of soHds (see Separation, size separation). One of the simplest ways to remove the coarse or dense soHds from a feed suspension is by sedimentation. Successive decantation ia a batch system produces closely controUed size fractions of the product. Generally, however, particle classification by sedimentation does not give sharp separation (see Size MEASUREMENT OF PARTICLES). 

FIG. 14-105 Particle classification and useful collection equipment versus partiele size. 

The product withdrawal pipe is located in the annulus halfway up the draft tube where the vector of the circulation velocity of the suspension and that of the withdrawal velocity of the product point in the same direction. Using this arrangement ensures low particle classification effects. Furthermore, the feed tubes and withdrawal tube can be exactly positioned in the reactor and scaled... 

Brayshaw, M.D., 1990. Numerical model for the inviscid flow of a fluid in a hydrocyclone to demonstrate the effects of changes in the vorticity function of the flow field on particle classification. International Journal of Mineral Processing, 29, 51. 

Silt, in one particle classification. system, consists of rock particles from 0.00.5 to 0.05 mm in size. 

Clay, in one particle classification system, consists of inorganic particles less than 0.005 mm in size. In another system, clay is a fine-grained inorganic. soil that can be made plastic by adjusting the water content. When dried, clay exhibits considerable strength (i.e., clay loses its plasticity when dried and its strength when wetted). Also, it will shrink when dried and expand when moisture is added. 

I. Bondarenko, H. Van Malderen, B. Treiger, P. Van Espen and R. Van Grieken, Hierarchical cluster analysis with stopping rules built on Akaike s information criterion for aerosol particle classification based on electron probe X-ray microanalysis. Chemom. Intell. Lab. Syst., 22 (1994) 87-95. 

Y. Xie, P.K. Hopke and D. Wienke, Airborne particle classification with a combination of chemical composition and shape index utilizing an adaptive resonance artificial neural network. Environ. Sci. Technol., 28 (1994) 1399-1407. 

Most studies of hydrocyclone performance for particle classification have been carried out at particle concentrations of about 1 per cent by volume. The simplest theory for the classification of particles is based on the concept that particles will tend to orbit at the radius at which the centrifugal force is exactly balanced by the fluid friction force on the particles. Thus, the orbits will be of increasing radius as the particle size increases. Unfortunately, there is scant information on how the radial velocity component varies with location. In general, a particle will be conveyed in the secondary vortex to the overflow, if its orbital radius is less than the radius of that vortex. Alternatively, if the orbital radius would have been greater than the diameter of the shell at a particular height, the particle will be deposited on the walls and will be drawn downwards to the bottom outlet. 

Heiskanen K (1993) Particle Classification. Chapman 8t Hall, London... 

Using polished pellets 1 inch in diameter, a microscopic particle classification analysis for lithotypes, developed for this research by the authors (I), was made of the various coals. Only vitrain, durain, and fusain were counted. Results are presented in Table IV. Standard visual parameters were used for particle identification. An analysis of this type, although not necessarily conclusive, is important for a relative comparison. Results of a check between... 

The particle classification scheme is the basis of the particle analysis method for FDR detection and identification. A revised particle classification scheme is presented in a later chapter. 

At the start of 1978 the particle analysis method183 replaced the flameless atomic absorption bulk elemental method184 as the firearm residue detection method in the NIFSL. Since then the particle analysis method has been substantially improved by the use of a sample concentration/cleanup procedure,185 the addition of a backscattered electron detector, and the development of an automated residue detection system.186 187 Despite these improvements the technique remains costly and labor intensive. Certain aspects of the system required further work, in particular, the particle classification scheme discharge particles from mercury fulminate-primed ammunition and discharge particles from new primer types (Sintox). 

The validity of the particle classification scheme was tested by examining items that may produce similar particles, paying particular attention to blank cartridges, the main uses of which that are likely to be encountered in casework are cartridge tools and blank firing replica/imitation firearms. 

The particle classification scheme is based on modern primed ammunition and consequently mercury fulminate-primed ammunition is not included. Mercury-containing particles from the discharge of mercury fulminate-primed ammunition are rarely detected in casework. Discharge residue from such ammunition was tested in an effort to provide an explanation for this. Discharge particles from Sintox-primed ammunition was also examined with a view to anticipating future problems the criminal use of... 

To clarify the list of accompanying elements in the particle classification scheme and the levels at which they are found. 

From casework statistics the unique particles (those containing the combination lead, antimony and barium, and those containing antimony and barium) occur in the ratio 7 3, respectively. Approximate percentages for indicative particles are lead-only 55% lead, antimony 20% lead, barium 8% antimony-only 7% barium, calcium, silicon 5% barium-only 5%. Table 19.3 gives an indication of the levels of the primary elements in each particle type. Table 19.4 gives an indication of the levels of accompanying elements in each particle type and is the basis for note b in Table 19.5, Particle Classification Scheme. 

The original particle classification scheme192 has been revised based on casework experience, research work on blank cartridges, and so forth, and a detailed analysis of 14 years of casework results. The particle classification scheme used in Northern Ireland since 1984 is given in Table 19.5. The indicative particles are in tentative order of decreasing significance. 

The particle classification scheme, developed as described in reference 200, did not include mercury fulminate-primed ammunition, which is frequently encountered in Northern Ireland, and is currently manufactured in some Eastern Bloc countries. 

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