Size classification effect

The number of inputs which are available for controlling crystallisation processes is limited. Possible Inputs for a continuous evaporative crystallisation process are, crystalliser temperature, residence time and rate of evaporation. These Inputs affect the crystal size distribution (CSD) through overall changes in the nucleatlon rate, the number of new crystals per unit time, and the growth rate, the increase in linear size per unit time, and therefore do not discriminate directly with respect to size. Moreover, it has been observed that, for a 970 litre continuous crystalliser, the effect of the residence time and the production rate is limited. Size classification, on the other hand, does allow direct manipulation of the CSD. 

Narrow product size distribution, in part due to a classification effect at the top of the annulus which allows the outlet pipe to be located so as to remove primarily the largest granules. 

FIGURE 6 5 (a) Classification function as described in equation (6.101). (b) Particle size distribution effects with classified product removal (ie., equation (6.102). Both redrawn with permission ftom Dirksen and Ring [4a]. Reprinted from [4a], cop3rri t 1991, with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB, UK... 

Usually, the width of the distribution is expressed by dp,xt/dpW, which should be lower than 2.5 for the chromatographic application dp,xt (dpV t) equals the value at 90% (10%) of the cumulative size distribution. Figure 3.24a and b visualize the effect of size classification and effident removal of fine particles. 

A classification effect at the top of the bed allows selective removal of the largest particles through the outlet pipe, yielding a relatively narrow product particle size distribution. 

Rulkens WH and Bruning H (1995) Clean-up possibilities of contaminated soil by extraction and wet classification effect of particle size, pollutant properties and physical state of pollutants. In Van den Brink WJ, Bosman R, Arendt E, eds. Contaminated Soil 95, pp. 761-773. Kluwer Academic Publ, Dordrecht. 

Zeolites can be classified in many ways. Two convenient methods are on the basis of pore size and chemical composition, that is, the Si/Al ratio. The pore diameter is determined by the size of the free apertures in the structure, which is dependent on the number of T atoms (T = Si or Al) that form the aperture. Table 10.1 summarizes some examples of zeolites based on pore size classification. It should be noted that the values typically reported in the literature are determined by crystallographic studies. While these numbers are good guides, it is important to note that the actual pore size depends on many factors, including temperature, firamework composition, and the type of extra-framework cations present in the zeolite. These factors can lead to subtle changes in effective pore sizes and subsequently large changes in material properties (adsorption/reactivity). 

Data on grain size distribution of the various strata is important to the overall site characterization and provides information related to other properties and behavior, such as permeability and water flow. Two main concerns are testing procedures and texture (grain size) classification systems. At present, there is no universally accepted classification system and testing methods can be quite different. The presence of significant biogenous materials, effects of flocculation due to salts, and the fact that some deep-sea clays are extremely fine-grained, requires that special procedures be considered. 

To dry a wet product with different particle sizes, the dryer has to act as a classifier. In a conventional air-flow dryer the classification effect is not sufficient during the residence time in the first drying stage coarse... 

USP and EP suture size classification, 334 effect of sterilisation of new, experimental monofilament sutures, 165 future trends, 304-16... 

The basis of the classification is that each of the size ranges corresponds to characteristic adsorption effects as manifested in the isotherm. In micropores, the interaction potential is significantly higher than in wider pores owing to the proximity of the walls, and the amount adsorbed (at a given relative pressure) is correspondingly enhanced. In mesopores, capillary condensation, with its characteristic hysteresis loop, takes place. In the macropore range the pores are so wide that it is virtually impossible to map out the isotherm in detail because the relative pressures are so close to unity. 

Classification of size enlargement methods reveals two distinct categories (8,39). The first is forming-type processes in which the shape, dimensions, composition, and density of the individual larger pieces formed from finely divided materials are of importance. The second is those processes in which creation of a coarse granular material from fines is the objective, and the characteristics of the individual agglomerates are important only in their effect on the properties of the bulk granular product. 

A useful classification of lands of reaclors is in terms of their concentration distributions. The concentration profiles of certain limiting cases are illustrated in Fig. 7-3 namely, of batch reactors, continuously stirred tanks, and tubular flow reactors. Basic types of flow reactors are illustrated in Fig. 7-4. Many others, employing granular catalysts and for multiphase reactions, are illustratea throughout Sec. 23. The present material deals with the sizes, performances and heat effects of these ideal types. They afford standards of comparison. 

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