Particulate Phases

Filtration is the separation of two phases, particulate form, ie, soHd particles or Hquid droplets, and continuous, ie, Hquid or gas, from a mixture by passing the mixture through a porous medium. This article discusses the more predominant separation of soHds from Hquids. Filtration of soHd particles or Hquid droplets from gases is dealt with elsewhere (see Airpollution controlmethods). The oldest recorded appHcations of filtration are the purifications of wine and water practiced by the ancient Greeks and Romans. Cake filters, such as the rotary vacuum filter and the filter press, were developed much later from the necessity to filter sewage. 

The last point is worth considering in more detail. Most hydrocarbon diffusion flames are luminous, and this luminosity is due to carbon particulates that radiate strongly at the high combustion gas temperatures. As discussed in Chapter 6, most flames appear yellow when there is particulate formation. The solid-phase particulate cloud has a very high emissivity compared to a pure gaseous system thus, soot-laden flames appreciably increase the radiant heat transfer. In fact, some systems can approach black-body conditions. Thus, when the rate of heat transfer from the combustion gases to some surface, such as a melt, is important—as is the case in certain industrial furnaces—it is beneficial to operate the system in a particular diffusion flame mode to ensure formation of carbon particles. Such particles can later be burned off with additional air to meet emission standards. But some flames are not as luminous as others. Under certain conditions the very small particles that form are oxidized in the flame front and do not create a particulate cloud. 

There are three definitions needed to accurately describe this process. (1) Compaction is the compression and consolidation of a two-phase (particulate solid/gas) system by the application of an external force (2) compression causes an increase in the apparent density (or a reduction in volume) by the displacement of air and (3) consolidation is defined as an increase in mechanical strength due to particle-particle interaction [1,2]. 

FILTRATION. Filtration is the separation of two phases, particulate form. i.e.. sulid particles or liquid droplets, and continuous, i.c.. liquid or gas, from a mixture by passing the mixture through a porous medium. This article discusses Ihe more predominant separation of solids from liquids. 

As already mentioned, electron microscopy (both transmission and scanning) has been used to characterize the precipitated particles. The information obtained in this way includes (i) the nature of the precipitated phase (particulate or non-particulate), (ii) the average particle size, if particulate, (iii) the distribution of particle sizes, (iv) the degree to which the particles are well defined, and (v) the degree of agglomeration of the particles.18... 

The research on persistent pesticides in the atmosphere has focused on the gas phase, particulate phase, rainfall, and pine needles. In China, there are only a limited number of studies on POP pesticides in the atmosphere, and these focus mainly on airborne particles. The spatial difference in concentration of persistent pesticides in air is small due to diffusion and transport. Since the agricultural ban on use in 1983, the concentration of POP pesticides in the atmosphere has decreased dramatically in China. In some regions, however, the concentrations of pesticide POPs in the atmosphere are unusually high, particularly for DDTs, which indicates that there might be new sources of POPs in these regions, such as Dicofol. In China, no environmental quality standards about pesticide POPs in the atmosphere have been established. 

Studies on the rheology of two-phase particulate systems suggest the existence of a deformation threshold that depends on the concentration of particles in the composite. Below this threshold (—68 vol.% for spherical particles), deformation occurs primarily by the flow of the composite matrix. Particles increase the effective viscosity of the matrix by absorbing energy and by forming clusters. 

The weight of the total MSS (vapor phase + particulate phase) from an 85-mm filtered cigarette smoked under FTC conditions approximates 0.5 g. 

Cigarette smoke can be divided into two phases, particulate- and vapor-phase smoke, by the use of a Cambridge filter... 

Regression analysis of Cd concentration in soil solntion (CdJ with pH and solid-phase particulate-bonnd Cd fractions (from Krishnamnrti and Naidn, 2003)... 

This difference in efficiency can be attributed to several complicating factors which contributed to the Duluth outcome, the most significant of which is the unanticipated but overwhelming influence of solid-phase particulate coal tar on both sampling and analytics. These factors and additional analytical results are discussed and presented in greater detail in the remainder of this chapter, as are lessons learned and related recommendations and observations. 

Fig. 32. Viscosity at the cloud point vs average diameter of dispersed phases particules for particular rubber (ETBN) modified epoxies (based on DGEBA) cured at different temperatures a) and b) differ in the nature of the rubber while c) corresponds to a different diamine (Reprinted from Journal of Applied Polymer Science, 42, D. Verchere, J.P. Pascault, H. Sautereau, S.M. Moschiar, C.C. Riccardi, R.J.J. Williams, Rubber-modified epoxies. If. Influence of the cure schedule and rubber concentration on the generated morphology, 701-716, Copyright (1991), with kind permission from John Wiley Sons, Inc., New York, USA)...

Essentially, the methods of epoxy resin modification are based on attaining a dispersion of second-phase particulates in the epoxy matrix the second phase may be either rubbery or rigid in nature, or both. Substantial enhancement of fracture toughness has been achieved in the hybrid systems. 

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