Size selectivity, classifiers

Specific advancements ia the chemical synthesis of coUoidal materials are noteworthy. Many types of genera ting devices have been used to produce coUoidal Hquid aerosols (qv) and emulsions (qv) (39—43) among them are atomizers and nebulizers of various designs (30,44—50). A unique feature of produciag Hquid or soHd coUoids via aerosol processes (Table 3) is that material with a relatively narrow size distribution can be routinely prepared. These monosized coUoids are often produced by relying on an electrostatic classifier to select desired particle sizes ia the final stage of aerosol production. 

Size selectivity is the most thorough method of expressing classifier performance under a given set of operating conditions. Cut size and sharpness can be calcinated from size-selectivity data. Size selectivity is defined by... 

The detector converts a change in the column effluent into an electrical signal that is recorded by the data system. Detectors are classified as selective or universal depending on the property measured. Selective (solute property) detectors, such as fluorescence detectors, measure a physical or chemical property that is characteristic of the solute(s) in the mixture only those components which possess that characteristic will be detected. Universal (bulk property) detectors measure a physical property of the eluent. Thus, with refractive index (RI) detectors, for example, all the solutes which possess a refractive index different from that of the eluent will be detected. Selective detectors tend to be more sensitive than universal detectors, and they are much more widely used. Universal detectors are more commonly used in preparative chromatography, where a universal response is desired and sample size is large. 

Selectivity of a typical classifier is plotted as a function of size in Figure 4.15. Selectivity monotonically increases from 0 to 1 as size increases (Curve 6-6 ). Even thou size selectivity is a complete measure of classifier performance, the user is often required to take a shortcut method of expressing performance on a specific feed material. A practical measurement of overall classification performance for a given application can be obtained by calculating recovery and 3rield. Recovery is the relative amount of material in the feed that is finer than size d that is recovered in the product. Recovery, R(d expressed... 

The effects of bypass on size selectivity are shown in Figure 4.15. Bypass reporting to the fine stream changes curve b to curve c. Bj ass reporting to the coarse stream moves from curve b to curve c. Comminution of the particles in a classifier will give rise to a size selectivity curve such as d. 

FIGURE 4SO Size selectivity function for sieves and classifiers. 

In order to validate this approach, we first tested it on simulated classifiers meant to simulate chemist selections by selecting desirable compounds based on only a few predefined parameters (e.g., size) and value preferences (e.g., all compounds with >10 atoms are desirable). A given amount of noise was also included in each classifier, to mimic human error. SNBM were then built to try to reproduce each simulated classifier s selections, and to extract what parameters were actually used by the classifier. Importantly, this strategy was able to extract all the parameters that were actually used by the simulated classifiers in an automated fashion, and did not identify any parameters that were not used as important (Figure. 7.3b). 

Principal Adsorbent Types. Commercially useful adsorbents can be classified by the nature of their stmcture (amorphous or crystalline), by the sizes of their pores (micropores, mesopores, and macropores), by the nature of their surfaces (polar, nonpolar, or intermediate), or by their chemical composition. AH of these characteristics are important in the selection of the best adsorbent for any particular appHcation. 

Classified removal of course material also can be used, as shown in Figure 16. In a crystallizer equipped with idealized classified-product removal, crystals above some size ate removed at a rate Z times the removal rate expected for a perfecdy mixed crystallizer, and crystals smaller than are not removed at all. Larger crystals can be removed selectively through the use of an elutriation leg, hydrocyclones, or screens. Using the analysis of classified-fines removal systems as a guide, it can be shown that the crystal population density within the crystallizer magma is given by the equations... 

Although many commercial crystallizers operate with some form of selective crystal removal, such devices can be difficult to operate because of fouling of heat exchanger surfaces or blinding of screens. In addition, several investigations identify interactions between classified fines and course product removal as causes of cycling of a crystal size distribution (7). Often such behavior can be rninirnized or even eliminated by increasing the fines removal rate (63,64). 

In the forced-circulation-type crystallizer (Fig. 19-43) primaiy control over particle size is exercised by the designer in selecting the circulating system and volume of the body. From the operating standpoint there is little that can be done to an existing unit other than supply external seed, classify the discharge ciystals, or control the shiny... 

AN Incremental number of particles in size- classifier-selectivity value ... 

Pai+icle size enlargement equipment can be classified into several groups, with advantages, disadvantages, and applications summarized in Table 20-36. Comparisons of bed-agitation intensity, compaction pressures, and product bulk density for selected agglomeration processes are highlighted above in Fig. 20-71. 

The fields of application of each type, classified by the size range of the solid particles separated, are given in Figure 10.16. A similar selection chart is given by Schroeder (1998). 

Apart from the classification based on the mode of generation of cavities, cavitation can also be classified as transient cavitation and stable cavitation [3]. The classification is based on the maximum radius reached (resonant size), life time of cavity (which decides the extent of collapse) in the bulk of liquid and the pattern of cavity collapse. Generation of transient or stable cavitation usually depends on the set of operating parameters and constitution of the liquid medium. Depending on the specific application under question, it is very important to select particular set of operating conditions such that maximum effects are obtained with minimum possible energy consumption. 

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