Particle Assemblages

Clair, B. L. and Hamielec, A. Viscous flow through particle assemblages at intermediate Reynolds numbers. leEC Fundam. 7, 308-315, 1968. 

Tal, R. and Sirignano, W. Cylindrical cell model for hydrodynamics of particles assemblages at intermediate Reynolds numbers. AIChE J. 28(2), 233-237, 1982. 

Heat transfer in the bed of a rotary kiln is similar to heat transfer in packed beds except that in addition to the heat flow in the particle assemblage of the static structure (Figure 8.3), there is an additional contribution of energy transfer as a result of advection of the bed material itself. The effective thermal conductivity of packed beds can be modeled in terms of thermal resistances or conductance within the particle ensemble. As shown in Figure 8.3 almost all the modes of heat transfer occurs within the ensemble, that is, particle-to-particle conduction and radiation heat transfer as well as convection through the interstitial gas depending upon the size distribution of the material and process temperature. Several models are available in the literature for estimating the effective thermal conductivity of packed beds. 

Agglomeratef Assemblage of particles rigidly held together. 

Aggregatef Assemblage of particles which is loosely coherent. 

Solid Density. SoHds can be characterized by three densities bulk, skeletal, and particle. Bulk density is a measure of the weight of an assemblage of particles divided by the volume the particles occupy. This measurement includes the voids between the particles and the voids within porous particles. The skeletal, or tme soHd density, is the density of the soHd material if it had zero porosity. Fluid-bed calculations generally use the particle... 

We shall use the term "Log Normal" for reasons which will clear later. It should be now apparent that we use terms borrowed from statistics and a statistical approach to describe a distribution of particles. The two disciplines are well suited to each other since statistics is easily capable Of handling large assemblages, and the soUd state process with which we deal are random growth processes which produce large numbers of pcirticles. 

All the examples gathered here demonstrate the possibility to control the growth of metallic and oxide nanoparticles using biological templates. A wide variety of chemical composition, particle size and assemblage can be obtained via these approaches. Moreover, due to the biological nature of the template, applications in fields related to biotechnology and medicinal science can be envisioned. 

An assemblage of even lightly charged particles can result in very high electrostatic field intensities at the surface of the assemblage. It is readily shown that for a volume of unipolar and uniformly distributed charged particles bounded by a surface equidistant from a center of symmetry, the... 

Rowe and Henwood(26) made similar studies by supporting a spherical particle 12.7 mm diameter, in water, at the end of a 100 mm length of fine nichrome wire. The force exerted by the water when flowing in a 150 mm square duct was calculated from the measured deflection of the wire. The experiments were carried out at low Reynolds numbers with respect to the duct (< 1200), corresponding to between 32 and 96 relative to the particle. The experimental values of the drag force were about 10 per cent higher than those calculated from the Schiller and Naumann equation. The work was then extended to cover the measurement of the force on a particle surrounded by an assemblage of particles, as described in Chapter 5. 

Richardson, J. F. and Meikle, R. A. Trans. Inst. Chem. Eng. 39 (1961) 357. Sedimentation and fluidisation. Part IV. Drag force on individual particles in an assemblage. 

A study of mass transfer between a liquid and a particle forming part of an assemblage of particles was made by Mulun and Treleaven1116, who subjected a sphere of benzoic acid to the action of a stream of water. For a fixed sphere, or a sphere free to circulate in the liquid, the mass transfer coefficient was given, for 50 < Re c < 700, by ... 

At the beginning of the nineteenth century, John Dalton (see plate 15 (sic should be 16 ) put forward his Atomic Theory in explanation of these facts. This theory assumes (1) that all matter is made up of small indivisible and indestructible particles, called "atoms" (2) that all atoms are not alike, there being as many different sorts of atoms as there are elements (3) that the atoms constituting any one element are exactly alike and are of definite weight and (4) that compounds are produced by the combination of different atoms. Now, it is at once evident that if matter be so constituted, the stoichiometric laws must necessarily follow. For the smallest particle of any definite compound (now called a "molecule") must consist of a definite assemblage of different atoms, and these... 

Conventional studies generally involve the collection of an assemblage of airborne particles followed by determinations of the average or bulk concentrations of pollutant species present (12). However, the results often lack the analytical specificity required to identify particle sources, to determine particle speciation and reactivity, or to assess particle toxicity. 

One of the remarkable features of Coulomb s law when applied to nuclei and electrons is its additivity. The potential energy of an assemblage of particles is just the sum of all the pairwise interaetions in the form given in Eq. (1.1). Thus, consider a system with K nuclei, a =, 2,..., K having atomic numbers Z . We also consider the molecule to have N eleetrons. If the molecule is uncharged as a whole, then = N. We will use lower ease Latin letters, /, j,k,..to label electrons and lower case Greek letters, a, f, y,..., to label nuclei. The full potential energy may then be written... 

The mechanisms operating in the formation of textures seen in polycrystalline aggregates of the same species have been discussed in Sections 8.1-8.4. This may correspond to the analysis of a mechanism controlling the so-called selforganization or self-assemblage. Other mechanisms are possible for example, tiny spherical particles are assembled and a close-packed structure is formed due to surface tension. The formation of opal consisting of a close-packed structure of minute amorphous silica spheres maybe such a case. 

There are several other types of minerals commonly found in clay particle size mineral assemblages (i.e.,< 2 microns diameter, Krumbein and Pettijhon, 1938). Aside from quartz and amorphous materials, the two most important mineral groups are sepiolite-palygorskite and zeolites. These two groups are similar in that they both contain free 1 0 molecules in their structure. However the Si-0 linkage is quite different in each case. 

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