Vacuum dense phase

Dense-phase conveying, also termed "nonsuspension" conveying, is normally used to discharge particulate solids or to move materials over short distances. There are several types of equipment such as plug-phase conveyors, fluidized systems, blow tanks, and, more innovative, long-distance systems. Dilute-phase, or dispersed-phase conveyors, are more versatile in use and can be considered the typical pneumatic conveying systems as described in the literature. The most accepted classification of dilute-phase conveyors comprises pressure, vacuum, combined, and closed-loop systems. 

As seen in Section 17.2.1. the total pressure difference during powder conveying depends on the amount of material in the conveying hne. Basically at vacuum conveying three different types of conditions can be described (Figure 17.5) dilute phase, dense phase and plug flow conveying [4]. 

As two air movers are provided, the most suitable exhauster can be dedicated to the vacuum system and the most appropriate positive pressure system can be used for the onward transfer of material. If the vacuum off-loading section is only a short distance, it is possible that the material could be conveyed in dense phase over the entire conveying distance. 

Pervaporation. Pervaporation differs from the other membrane processes described so far in that the phase-state on one side of the membrane is different from that on the other side. The term pervaporation is a combination of the words permselective and evaporation. The feed to the membrane module is a mixture (e.g. ethanol-water mixture) at a pressure high enough to maintain it in the liquid phase. The liquid mixture is contacted with a dense membrane. The other side of the membrane is maintained at a pressure at or below the dew point of the permeate, thus maintaining it in the vapor phase. The permeate side is often held under vacuum conditions. Pervaporation is potentially useful when separating mixtures that form azeotropes (e.g. ethanol-water mixture). One of the ways to change the vapor-liquid equilibrium to overcome azeotropic behavior is to place a membrane between the vapor and liquid phases. Temperatures are restricted to below 100°C, and as with other liquid membrane processes, feed pretreatment and membrane cleaning are necessary. 

The disperse-phase Knudsen number can also be infinity for dense, elastic systems due to initial conditions. For example, if one releases a dense assembly of particles that are initially at rest in a vacuum, the particles will accelerate due to gravity such that they all have the same velocity. For this case, the granular temperature is null... 

In fact, Equation 5.170 is applicable to the dispersion contribution in the van der Waals interaction. When components 1 and 2 are identical, Ag is positive (see Equation 5.169), therefore, the van der Waals interaction between identical bodies, in any medium, is always attractive. Besides, two dense bodies (even if nonidentical) will attract each other when placed in medium 3 of low density (gas, vacuum). When the phase in the middle (component 3) has intermediate Hamaker constant between those of bodies 1 and 2, Ag can be negative and the van der Waals disjoining pressure can be repulsive (positive). Such is the case of an aqueous film between mercury and gas. ... 

The use of several techniques testing the magnetic response of particles ensembles on different time scales is desirable, especially when their size reaches the limit of resolution in TEM and their diffraction peaks are too broad for permitting the identification of all formed phases. The incorporation of Fe, Ni salts in TH permits to obtain metallic particles by ion irradiation or aimealing at low temperatures, simply in vacuum, while undesired phases are formed in TEOS (often even when heat treated in pure H2 atmosphere [9]). The formation of smaller particles, perfectly encapsulated in dense films of glass, under ion irradiation should permit to increase the areal density of information in magnetic memories. 

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