Sizing of particles

For smaller particles, the theory indicates that efficiency decreases according to the dotted line of Figure 7. Experimental data (134) (sofld line of Eig. 7) for a cyclone of Eig. 9 dimensions show that equation 15 tends to overstate collection efficiency for moderately coarse particles and understate efficiency for the finer fraction. The concept of particle cut-size, defined as the size of particle collected with 50% mass efficiency, determined by equation 16 has been proposed (134). 

The size of particles removed by such filters is less than the size of the passages. The mechanism of removal includes adsorption (qv) of the impurities at the interface between the media and the water either by specific chemical or van der Waals attractions or by electrostatic interaction when the medium particles have surface charges opposite to those on the impurities to be removed. 

Precipitated Calcium Carbonate. Precipitated calcium carbonate can be produced by several methods but only the carbonation process is commercially used in the United States. Limestone is calcined in a kiln to obtain carbon dioxide and quicklime. The quicklime is mixed with water to produce a milk-of-lime. Dry hydrated lime can also be used as a feedstock. Carbon dioxide gas is bubbled through the milk-of-lime in a reactor known as a carbonator. Gassing continues until the calcium hydroxide has been converted to the carbonate. The end point can be monitored chemically or by pH measurements. Reaction conditions determine the type of crystal, the size of particles, and the size distribution produced. 

In drying solutions or slurries of solutions, the location of the feed-injection nozzle (spray nozzle) has a great effecl on the size of particle formed in the bed. Also of importance are the operating temperature, relative humidity of the off gas, and gas velocity. Particle growth can occur as agglomeration or as an onion sldnuing. ... 

The energy laws of Bond, Kick, and Rittinger relate to grinding from some average feed size to some product size but do not take into account the behavior of different sizes of particles in the mill. Computer simulation, based on population-balance models [Bass, Z. Angew. Math. Phys., 5(4), 283 (1954)], traces the breakage of each size of particle as a function of grinding time. Furthermore, the simu-... 

In the investigations mentioned earlier the breakage function was assumed to be normahzable i.e., the shape was independent of Xq. Austin and Luclde [Powder Technol., 5(5X 267 (1972)] allowed the coefficient A to vary with the size of particle breaking when grinding soft feeds. 

The powders of zeolites of various trademarks are used to produce petroleum-refining catalysts. In this connection, it is very important to have complete information concerning not only chemical composition and distribution of impurity elements, but also shape, surface, stmcture and sizes of particles. It allows a more detailed analysis of the physical-chemical characteristics of catalysts, affecting their activity at different stages of technological process. One prospective for solving these tasks is X-ray microanalysis with an electron probe (EPMA). 

The detailed study of chemical composition, stmcture, surface, shape and sizes of particles of fine-dispersed zeolite powder by EPMA will provide useful recommendations to improve the technology of producing alkanes and alkyl benzenes catalysts. 

Suspended particles are the most important factor in visibility reduction. In most instances, the visual quality of air is controlled by partide scattering and is characterized by the extinction coeffident The size of particles plays a crucial role in their interaction with light. Other factors are the refractive index and shape of the particles, although their effect is harder to measure and is less well understood. If we could establish these properties, we could calculate the amount of light scattering and absorption. Alternatively, the extinction coeffident associated with an aerosol can be measured directly. 

Permeability is a volume-averaged property for a finite but small volume of a medium. Anisotropy in natural or manmade packed media may result from particle (or grain) orientation, bedding of different sizes of particles or layering of media of different permeability. A dilemma arises when considering whether to treat a directional effect as anisotropy or as an oriented heterogeneity. 

The settling capacity for a given size of particles is a function of R, C and u, which itself is proportional to R. In general, for the sedimentation of heavy particles in a suspension it is sufficient that the radial component of Uf be less than at a radius greater than Rj. 

Design methodology consists of determining capacity, approximate sizes of particles settled and horsepower requirements for pumping. The flowrate of a... 

Using SI units, and from some literature reported values for hydroclones with D between 125 and 600 ram, and a cone angle of 38°, a value for coefficient K is 2.8 X 10. The maximum size of particles in the cleared liquid can be estimated from ... 

FIGURE 5.35 Regions of pulmonary pathways and size of particles that can reach different regions of the lungs. 

The size of particles is often indicated in pm (microns). 1 p,m = l(H m. Particles in the atmosphere vary, from particles less than 0.01 pm up to leaves, ind insects. 

The collection efficiency curve is usually employed to demonstrate the performance of a cyclone. Figure 13.3 shows a typical collection efficiency curve for a cyclone at a particular airflow rate. The size of particles that have a collection efficiency of 50% is usually employed as a simple indication of the separation efficiency of the cyclone, and is known as the cut-off particle size... 

FIGURE 13.2 A schematic diagram of the trajectories for two different sizes of particles in a typical cyclone. 

As a simple and efficient particle separation device, cyclone collectors can be used for anything from dust removal in a fluid stream to material collection in the fluid conveying system. However, the cyclone is not suitable or economical for the separation of extremely small particles (say, less than 1 /xm), which frequently occur in industrial processes. It is recommended that the size of particles to be separated in an industrial ventilation cyclone be in the region of around 10 to 100 p.m. However, for the purpose of aerosol sampling, the size of particles to be separated may be much less than 10 jxm. 

For a specific size of particle to be separated by the cyclone, a first rough estimate of the cyclone size may be obtained by estimating the particle drift vekx -ity in the cyclone. A large cyclone may be used if the particle drift velocity is large. If n is the number of the revolutions that the particle travels with the fluid in the cylindrical part of the cyclone, then the smallest particle of diameter d that can be separated by the cyclone may be approximated by (see Baturin )... 

In the previous section we determined the equivalent particle diameter of a set of particles of different sizes, with the aid of which we can treat the mixture as composed of one size of particles, namely The mean free-falling velocity of the mixture is the same. 

In the stirred tank, the final mean size of particles was reduced by the increase of stirring rate, being consistent with increased fluid shear induced particle disruption relative to aggregation. Use of three different gas velocities in the bubble column, however, results in no significant difference in agglomerate size but since the size is relatively small, it may simply reflect an asymptotic value. 

The construction of calibration curves is recommended in nephelometric and turbidimetric determinations, since the relationship between the optical properties of the suspension and the concentration of the disperse phase is, at best, semi-empirical. If the cloudiness or turbidity is to be reproducible, the utmost care must be taken in its preparation. The precipitate must be very fine, so as not to settle rapidly. The intensity of the scattered light depends upon the number and the size of the particles in suspension, and provided that the average size of particles is fairly reproducible, analytical applications are possible. 

Tables. Effect of size of particles CaC03 and treatment of the filler by stearinic acid on the value of the yield strength zy of the molten polycarbonate [162]...

Mean size of particles, mm Specific surface area, m2/g Value zy for composition with the filler ... 

How does yield stress depend on the size of particles We have mentioned above that increasing the specific surface, i.e. decreasing an average size of particles of one type, causes an increase in yield stress. This fact was observed in many works (for example [14-16]). Clear model experiments the purpose of which was to reveal the role of a particle s size were carried out in work [8], By an example of suspensions of spherical particles in polystyrene melt it was shown that yield stress of equiconcentrated dispersions may change by a hundred of times according to the diameter d of non-... 

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