Directed particles

These derive their name from the method of entrainment. The hood is placed in the path of the particle and uses the momentum of the particle to assist in control. It is important to have a clear understanding of the process, the direction particles take and the movement of air created by the process. Grinding wheels release dust downwards and over the top of the wheels, and considerable air movement... 

Accelerated particle-bubble attachment through coalescence of tiny bubbles frosted on particle surfaces with larger bubbles, instead of the direct particle-bubble contact... 

While the main driving force in [43, 44] was to avoid direct particle transfers, Escobedo and de Pablo [38] designed a pseudo-NPT method to avoid direct volume fluctuations which may be inefficient for polymeric systems, especially on lattices. Escobedo [45] extended the concept for bubble-point and dew-point calculations in a pseudo-Gibbs method and proposed extensions of the Gibbs-Duhem integration techniques for tracing coexistence lines in multicomponent systems [46]. 

Fig. 8. This is a snapshot of a spatial particle distribution. The plane shown is the horizontal cross-section just below the disc of a Rushton turbine in a flat-bottomed stirred tank. The impeller revolves in the counter clockwise direction. Particle size is some 0.468mm Re = 1.5- - x 105 volume fraction amounts to 3.6% number of particles tracked in the simulation just over 6.7 million. Reproduced with permission from Derksen (2003).

Direct particle interception, in depth filtration theory, 11 339 Direct potentiometry, 9 582—585 Direct printing, 9 218 Direct process, silicone synthesis via,... 

Gas evaporation using Ar for the preparation of various sort of metal fine powders was first reported by Kimoto et al. in 1963 (5). The production chamber of this method is basically the same as that of a vacuum sublimation chamber. A target material is heated in this chamber with several torr inert gas atmosphere. The nanometer-sized particles are easily formed in the chamber space. However, by this method, it is difficult to get genuine nanoparticles whose sizes are several nanometers. This is because of the radiation heating in a production chamber, resulting particle coalescence on the chamber wall or particle collector, as well as the direct particle contact in the deposited particle layer (powders). Therefore the size becomes several tens to hundreds of nanometers. Several ultrafme metallic powders are now commercially available, including Cu, Ag, Al, Ni, Co, Fe, and Au, with a size of several tens of nanometers. 

Dust, representing less-volatile materials, is liberated from the comet and propelled outward by the expanding jets of gas. Appreciable quantities of dust are sometimes released for example, the dust production rate from comet Hale-Bopp exceeded its gas production rate by a factor of five. Comet particles range in size from submicron dust to small rocks. Direct particle impacts onto spacecraft suggest that solid particles in the coma can be of at least millimeter size. 

On the basis of the observations in the macroscale, the flow of a fast fluidized bed can be represented by the core-annulus flow structure in the radial direction, and coexistence of a bottom dense region and a top dilute region in the axial direction. Particle clusters are an indication of the heterogeneity in the mesoscale. A complete characterization of the hydrodynamics of a CFB requires the determination of the voidage and velocity profiles. There are a number of mathematical models accounting for the macro- or mesoaspects of the flow pattern in a CFB that are available. In the following, basic features of several types of models are discussed. 

In a horizontal conveying pipeline, motion of the particles is not always straight in the horizontal direction. Particles constantly fall down to the bottom of the pipe by... 

Direct particle counting of an initially monodisperse suspension was used to measure the time dependence of the q-moment M0, as given in the following table. Examine these data for conformity to either transport- or reaction-controlled flocculation kinetics and estimate the characteristic time scale, 2/kn p0, wherekn = kmn for m n 1. (Answer k n= 3.05 x 10 22 m3 s"1 = 2KD/Wmn, corresponding to Wmn = 4.07 X 104 for all m, n.)... 

Fig. 8. Schematic diagrams of concentration profiles and the associated particle currents, (a) Cation interstitials or anion vacancies [(dC/dx)<0] and positively directed particle currents ( 0). (b) Cation vacancies or anion interstitials [(dC/dx) > 0] and negatively directed particle currents (J< 0).

Fig. 19. One of the interior oxide layers labeled i in a sandwich array of multilayered oxides growing by cation interstitial (ci) diffusion illustrated with the relative magnitudes of the positively directed particle currents through layer i and the adjacent layers i — 1 and i + 1.

Above the threshold, deformation occurs as a consequence of direct particle interaction. Several mechanisms of interaction have been suggested solution-precipitation flow of fluid between particles and cavity formation at the particle matrix interface. These theories of creep suggest several rules to improve creep behavior (1) increase the viscosity of the matrix phase in multiphase materials (2) decrease the volume fraction of the intergranular phase (3) increase the grain size (4) use fiber or whisker reinforcement when possible. As the creep rupture life is inversely proportional to creep rate, lifetime can be improved by improving creep resistance. 

Equation 4 was foimd to explain particle size data fairly well, with reasonable kinetic and coverage parameter values (k s and Sent), in the dispersion polymerization of styrene in ethanol with PVP dispersant [24]. Many other dispersion polymerization systems with homopolymer dispersants appear to be explained by Eq. 4, except for the frequently observed direct particle size dependence on initiator concentration [27]. 

The main advantage of the Eulerian-Lagrangian approach (i.e., compared to the alternative Euler-Euler model described in the next subsection) is its flexibility with respect to the incorporation of the microscopic transport phenomena. Particle dynamics can in principle be described in detail, a particle size distribution can easily be incorporated, direct particle-particle interactions can be accounted for as well as the hydrodynamic interaction between neighboring particles. 

The second method for obtaining the rate constant of flocculation is by direct particle counting as a function of time. For this purpose, optical microscopy or image analysis may be used, provided that the particle size is within the resolution hmit of the microscope. Alternatively, the particle number may be determined using electronic devices such as the Coulter counter or flow ultramicroscopy. 

DLVO theory explained major principles of coagulation of hydrosols by electrolytes and brought to common grounds all previous observations (primarily of qualitative nature) that related to individual cases and often seemed to be contradictory. In years that followed further extensions of DLVO theory that took into account the possibility of reversible particle aggregation were developed. At very small distances between particles in addition to the usual long-range interaction, molecular attraction and electrostatic repulsion, one must account for other factors that play role at a direct particle contact. The formation of peculiarly structured hydration layers in the vicinity of solid surface, the appearance of elastic forces that are responsible for the Born repulsion between surface atoms at the point of contact, the repulsion between the adsorbed surfactant molecules in contact zone between two particles, all represent the so-called non-DLVO stability factors . This means that more or less deep primary minimum remains finite. 

Structure formation that takes place in disperse systems is the result of spontaneous thermodynamically favorable processes of particle aggregation that lead to a decrease in free energy of the system. These processes include coagulation of dispersed phase or condensation of substance in the zones of direct particle contact. The development of spacial networks (disperse structures) of different kinds defines the ability of disperse system to be converted into a material with particular mechanical properties. Such system becomes qualitatively different from its initial, unstructured state. 

The Newtonian viscosity of a liquid is modified, and may become non-Newtonian, if it contains colloidal particles. This results from the complex interplay of interactions including hydrodynamic interactions between the liquid and solid particles, attractive or repulsive forces between the particles, and, in concentrated systems, direct particle-particle contact. 

Other phenomena may also be observed in concentrated dispersions. Thus, as the concentration increases, direct particle—particle contacts increase in importance, and as the limiting packing fraction is approached (j) = 0.625 for the random close-packing of spheres) the suspension ceases to flow and the viscosity becomes infinite. Shortly before this limit is reached the suspension (especially if the particles are monodisperse spheres) often exhibits dilatency. When the particles are nearly close-packed, flow can occur only by the particles rolling past one another (Figure 8.8), and this results in an increase in volume the shear thickening is accompanied by dilatence of the system. If the amount of liquid present is insufficient to fill the extra void volume produced, the surface may become dry. This is the familiar phenomenon observed when one steps on wet sand. 

Williams, R. C., and R. C. Backus Macromolecular Weights Determined by Direct Particle Counting. I. The Weight of the Bushy Stunt Virus Particle. J. Amer. chem. Soc. 71, 4052—4057 (1949). 

Sonication increased particle aggregation, rather than disaggregating them, suggesting that titanium dioxide may have a strong tendency to aggregate. This caused Churg and coworkers to speculatively raise the question of direct particle effects (18). This proved prophetic with regard to later work with carbonaceous particles. 

Surprisingly a number of epidemiology studies in the early nineties showed associations between ambient particulate matter and increases in cardiac-related deaths and/or morbidity indicators and that the risk of PM-related cardiac effects may be so great or greater than those attributed to respiratory causes. These effects appear to be induced via direct particle uptake into the blood and/or via mediation by the nervous system. Such effects may be especially deleterious to individuals... 

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