Size methods elutriation

Sizing by elutriation is the reverse of the technique used for sedimentation. While any fluid may be used for elutriating particles, air has been found most satisfactory thus far. The basis of elutriation methods is... 

Sedimentation methods are also useful in determining particle size distribution. Webb (28) describes the techniques employed in liquid sedimentation and gives data comparing the results with those obtained in mechanical screening. Sedimentation methods are particularly useful in measuring sub-sieve sizes. Air-elutriation methods (Roller, 29) are also useful, especially when used in connection with microscopic examination (Wiley, Deloney, and Denton, 30 Matheson, 31). 

Countercurrent Separation and Elutriation. The process known as elutriation in cell separation is a refined method for separation of cells having close mass densities. Cells can be separated by making use of differences in the critical velocity of cells. If the mass densities of two cells are identical, but the sizes are different, then the larger particle has a higher critical velocity than the smaller one. 

Beckman Elutriation Method. The Beckman elutriation method uses a chamber designed so that the centrifugal effect of the radial inward fluid flow is constant (Fig. 3). The separation chambers are made of transparent epoxy resin which faciUtates observation of the movements of the cell boundary in strobe light illumination. This enables detection of the radius at which the cells are separating. When a mixture of cells, eg, mononuclear white cells, enters the chamber, separation can be achieved by fine tuning centrifuge speed and inward fluid flow to the specific cell group. This is a laboratory method suitable for relatively small numbers of cells. Chambers are available in sizes to handle 2-3 x 10 , 1 2 x 10 , and 1 x 10 ° cells. The Beckman chambers can be appHed to collect mononuclear cells from bone marrow aspirates. 

The terminal velocity in the case of fine particles is approached so quickly that in practical engineering calculations the settling is taken as a constant velocity motion and the acceleration period is neglected. Equation 7 can also be appHed to nonspherical particles if the particle size x is the equivalent Stokes diameter as deterrnined by sedimentation or elutriation methods of particle-size measurement. 

One method for improving the size distribution still further is to employ fines destruction (Jones etal., 1984 Jones and Chianese, 1988). In this technique, a classified stream of suspension, i.e. containing only fine not coarse crystals, is removed from the crystallizer in an elutriation leg (Figure 7.6(a)). 

Elutriation differs from sedimentation in that fluid moves vertically upwards and thereby carries with it all particles whose settling velocity by gravity is less than the fluid velocity. In practice, complications are introduced by such factors as the non-uniformity of the fluid velocity across a section of an elutriating tube, the influence of the walls of the tube, and the effect of eddies in the flow. In consequence, any assumption that the separated particle size corresponds to the mean velocity of fluid flow is only approximately true it also requires an infinite time to effect complete separation. This method is predicated on the assumption that Stokes law relating the free-falling velocity of a spherical particle to its density and diameter, and to the density and viscosity of the medium is valid... 

The dynamic methods involve the placement of particles to be measured in an environment which is subsequently disturbed. The members belonging to the particle set react differently to these imposed environmental impulses. These different reactions are observed and therefrom deductions are made as regards the size characteristics. As examples of dynamic methods mention may be made of sieving, streaming, elutriation, and sedimentation. 

The elutriation method is really a reverse sedimentation process in which the particles are dispersed in an upward flowing stream of fluid. All particles with terminal falling velocities less than the upward velocity of the fluid will be carried away. A complete size analysis can be obtained by using successively higher fluid velocities. Figure 1.4 shows the standard elutriator (BS 893)(6i for particles with settling velocities between 7 and 70 mm/s. 

Of the various mechanical properties of a formed catalyst containing zeolite, attrition resistance is probably the most critical. This is particularly the case for FCC catalysts because of the impact on the addihon rate of fresh catalyst, particulate emissions of fines and overall catalyst flow in the reactor and regenerator. Most attrition methods are a relative determination by means of air jet attrition with samples in the 10 to 180 xm size range. For example the ASTM D5757 method attrites a humidified sample of powder with three high velocity jets of humidified air. The fines are continuously removed from the attrition zone by elucidation into a fines collection assembly. The relative attrition index is calculated from the elutriated fines removed at a specific time interval. 

Often a range of particle sizes is used as feed to a mixed flow reactor. For such a feed and a single-exit stream (no elutriation of the fines) the methods leading to Eqs. 2 and 6, when combined, should yield the required conversion. 

Flutriation methods can be used successfully with sub-sieve sizes and for particles which arc. not much below 1 n in diameter. The effectiveness of elutriation is determined by the type of filter used to capture the dust. Smaller particles could undoubtedly be obtained if an electrical precipitator, instead of cloth filters, were used for the dust passing the elutriation cylinder. 

Experimental Results—Gottschalk and Wartman (loc cit) investigated the properties of a number of magnetite powders. Magnetites from four sources were purified and sized, each size-fraction then being analyzed for FesC>4. Only size-fractions below 100-U. S. mesh were studied. Sizes below 350-mesh were air elutriated by the Roller method. 

Related Calculations. This method can be used for determining separation effectiveness for classifying screens, elutriators, cyclones, or hydroclones in which a known feed of a known crystal size distribution is segregated into a fine and a coarse fraction. If a cut size cannot be predetermined, assume one at a time and complete the described effectiveness analysis. The assumed cut size that gives the largest effectiveness is the cut size that best describes the separation device. 

BS 3406, (1963) reconfirmed (1983), British Standard Methods for Determining Particle Size Distribution, Part 3 Air Elutriation Methods, 266 Stein, F. and Com, M. (1976), Powder TechnoL, 13, 133-141,266 Crandall, W.A. (1964), Development of standards for determining the properties of fine particulate material. Winter Annual Meeting ASME,... 

In elutriation methods, particles are classified in a column by a rising fluid stream. A series of cyclones are used to separate particles into different size ranges. Gas adsorption of a gas on a powder is another method for determining surface area. Measurements are usually interpreted by using the Braunauer, Emmett, and Teller (BET) theory. 

There is a wide variety of methods for particle size measurement which measure different types of particle size. When selecting a method, it is best to take one that measures the type of size which is most relevant to the property or the process which is under study. Thus, for example, in powder elutriation, pneumatic conveying or gas cleaning, it is most relevant to use one of the sedimentation methods which measure the Stokes diameter, i.e. the diameter of a sphere of the same density as the particle itself, which would fall in the gas at the same velocity as the real particle (assuming Stokes law). In flow through packed or fluidized beds, on the other hand, it is the surface-volume diameter (or diameter... 

There are numerous options for combining phospholipids with an aqueous phase, but two major methods are used to make liposomal systems for drug delivery. The first is simple hydration (swelling) of the phospholipid. This is followed by high-intensity agitation using sonication or a high-shear impeller. Liposomes are then sized by filtration, extrusion or elutriation. The second method is an emulsion... 

All these samples, except No. 7, were powders of 5-7 /n grain size, which had been elutriated in toluene. Sample 7 was prepared by simple grinding in an agate mortar (this sample was used simply to check the presence of a second phase in a method for growing stoichiometric crystals from a melt which was enriched with mercury in order to establish an equilibrium vapor pressure durii growth). 

In large-scale industrial crystallization processes, the most commonly used classification device is a hydrocyclone. The advantages of the hydrocyclone are its high capacity within a small equipment volume and an easily adjustable cutting size by the control of the feed-flow rate and the ratio of the up-flow to the down-flow. The fluid bed or elutriation leg is another method often used for classification in crystallization processes. With the elutriation leg, the feed or clear solution is fed from the bottom of the elutriation leg. The up-flow velocity is set based on the settling velocity of the cutting size... 

Several methods are available for the measurement of the size of particles, e.g. toicroscopic inspection, sieving, elutriation, sedimentation. Generally, the results obtained will depend on the method of measurement since different fimdamental dimensions are involved in the different methods. For irregularly ped particles it is usual to use a particle size technique which duplicates the process of interest, e.g. to use projected diameter (microscopic) or area in paint or pigment studies diameters based on surface area determinations would have relevance in chemical reactions involving solids, such as catalysis and adsorption. 

Lights Removal Air classification methods are used to remove light contaminants such as dust, film and foam fi agments, and paper glass powder in a recycling operation in the absence of water [1, 10]. Two common types of air classifier systems, cyclone separators and multiaspirators, are shown in Figures 14.16 and 14.17. Other types of air classifiers are air knives, elutriators, zig-zag classifiers, and air tables. Air classifiers are rather simple equipment where control is often more art than science, and the equipment must be tuned for each stream of material. Separations of materials are based on differences in terminal velocities in an airstream and are highly dependent on particle size and shape. 

Various sedimentation and elutriation methods are available but these are of value only after standardization for a given type of powder or gel with constant aggregate density. The same applies to measurement of permeability to a stream of air or liquid. The external surface area of porous aggregates, which is an indirect measure of aggregate, size, can be measured by ambient pressure permeametric measurements. Gas is forced through a bed of powder and the flow rate and pressure drop are measured. The apparatus that is used for the flow method of measuring surface area by nitrogen adsorption (Quantasorb from Quantochrome Corporation) can be adapted to this measurement. 

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