Layer of Particles

Denudation of Erosion. In the detachment of an adherent layer of dust by an air stream, the following processes may take place removal of upper particles, i.e., overcoming the forces of autohesion detachment of the dust layer, i.e., overcoming the forces of adhesion of the layer and detachment of the individual particles remaining after removal of the layer. The removal of the upper layers is possible when Fad Faut- In this case, the dust is raised only a relatively short distance above the original surface. The autohesion process of dust-layer removal is termed erosion [279]. 

When the forces of autohesion are large, greater than the forces of adhesion, the detachment will take place at the boundary between the surface and the dust layer. In this case, it is the forces of adhesion that must be overcome [280]. This process is termed denudation. In denudation, particle detachment begins at the leading edge of the dust deposit, and a cloud rapidly fills the entire passage. 

There is a certain class of particles for which Fad - aut- In such systems, no denudation is manifested. In this class of systems we would include room dust, shale, certain types of gypsum, carbonate, and other materials. 

An adherent layer of particles with a regular shape (with flat faces) is detached more rapidly than a layer of irregular particles. With an air velocity of 30 m/sec, within 0.25 sec from the moment at which the air stream starts to act, approximately 60% of an adherent layer of regularly shaped particles is detached, but only 20% are detached if the particles are irregularly shaped. The denudation rate can be calculated  

8 for dust deposits with irregularly shaped particles,Ki = 16.6 and K2 = 26.6. 

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Electrodecantation or electroconvec tion is one of several operations in which one mobile component (or several) is to be separated out from less mobile or immobile ones. The mixture is introduced between two vertical semipermeable membranes for separating cations, anion membranes are used, and vice versa. When an electric field is apphed, the charged component migrates to one or another of the membranes but since it cannot penetrate the membrane, it accumulates at the surface to form a dense concentrated layer of particles which will sink toward the bottom of the apparatus. Near the top of the apparatus immobile components will be relatively pure. Murphy [J. Electrochem. Soc., 97(11), 405 (1950)] has used silver-silver chloride electrodes in place of membranes. Frilette [J. Phys. Chem., 61, 168 (1957)], using anion membranes, partially separated and Na, ... 

In the case of multiparticle blockage, as the suspension flows through the medium, the capillary walls of the pores are gradually covered by a uniform layer of particles. This particle layer continues to build up due to mechanical impaction, particle interception and physical adsorption of particles. As the process continues, the available flow area of the pores decreases. Denoting as the ratio of accumulated cake on the inside pore walls to the volume of filtrate recovered, and applying the Hagen-Poiseuille equation, the rate of filtration (per unit area of filter medium) at the start of the process is ... 

FIG. 16 SEM pictures of self-assembled layers of particles Ic after different dipping times t (concentration 3 mg/mL T = 23.5°C pH = 5.8). (From Ref. 98, with permission from Elsevier, Amsterdam.)... 

FIG. 17 Plot of normalized surface coverage C of self-assembled layer of particles Ic vs. dipping time of substrate for different concentrations of the latex dispersion (T = 23.5°C, pH = 5.8). 

These results could be explained as an increase in the dipole-dipole interactions along the z-axis, which could favor the electron tunneling from the tip to the substrate via several layers of particles arranged in a FCC structure. Furthermore, the Fermi level of nanocrystals subjected to a given bias is perturbed. 

Porous-layer- open tubular (PLOT) and support-coated open tubular (SCOT) columns are prepared by extending the inner surface area of the capillary tube. A layer of particles can be deposited on the surface or the column wall can be chemically treated to create a porous adsorbent layer. Obviously some of the wall-modified open tubular columns discussed in section 2.3.3 could be... 

Dispersion of polymeric viscosifiers is often difficult because the initial contact of the untreated polymer with water results in very rapid hydration of the outer layer of particles which creates a sticky, rubbery exterior layer that prevents the interior particles from contacting water. The net effect is formation of what are referred to as nfish eyes" or "gel balls." These hamper efficiency by lowering the viscosity achieved per pound of gelling agent and by creating insoluble particles that can restrict flow both into the formation and back out of it. The normal remedy for this behavior... 

Ideally, the axial velocity through the cross-flow unit should be greater than about 4-6 m/s to minimize the boundary layer of particles near the membrane surface. The wax permeate flow from the filter is limited by a control valve actuated by a reactor-level controller. Hence, a constant inventory of slurry is maintained within the SBCR system as long as the superficial gas velocity remains constant. Changes in the gas holdup due to a variable gas velocity are calculated... 

A layer of particles may be deposited on a peripheral surface, for example, a steam pipe or the outer wall of a vessel. The particles are then exposed on the surface area and by the gas phase to temperatures that are generally high. 

The angle of repose may also be measured using a plane sheet to which is stuck a layer of particles from the powder. Loose powder is then poured on to the sheet which is then tilted until the powder slides. The angle of slide is known as the static angle of repose or the drained angle. 

An angle which is similar to the static angle of repose is the angle of slide which is measured in the same manner as the drained angle except that the surface is smooth and is not coated with a layer of particles. 

In the diffuse reflectance technique (Fig. 14.2d), light scattered by a thick layer of particles is directed by the integrating sphere to a detector. Absorption... 

We can estimate the magnitude of the shift attributable to interaction between particles by appealing to the Maxwell Garnett theory (Section 8.5). This theory is strictly applicable only to a medium consisting of small particles distributed throughout a volume, whereas the slides consist of a single layer of particles on a surface. Nevertheless, for our limited purposes here the Maxwell Garnett theory is adequate. 

The SEM pictures of samples are shown in Fig.5. They provide a direct evidence for the corrosion on the outer surface of crystallites. For the parent sample, the average size of the crystal particles is 200 nm (Fig.5a). After the boronation, the average particle size decreases since the corrosion and dissolution of the outer layer of particles occurs. In the case of [B]-Naft-2 with a more severe dissolution, the average particle size is only about half as large as that of the parent sample (see Fig.5b). 

When the takes-off are more numerous, the layers of particles are blown off faster. Consequently, the decrease of emitted mass flux is greater. 

To understand the mechanisms of solids slug flows, a two-dimensional coupled DEM/CFD numerical model was built to simulate the motion of a pre-formed slug (ca. 0.3 m long) in a 1 m long horizontal 50 mm bore pipe as shown in Fig. 1. The pipe was initially filled with a layer of particles, approximately 15 mm thick at the bottom. (The thickness of this stationary layer was determined based on experience from previous experiments and computer test runs). 

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