Mixing sampling considerations

A fundamental study of solids mixing is given, with experimental data for a rotating horizontal cylinder containing salt and sand. Theoretical random equilibrium mixture, chi-square test, and sampling considerations are discussed. Also rate equations and segregating effects are covered. 

In 70/30 PP/epoxy blends containing 6 parts of carbon black, the volume resistivity of simultaneously melt-mixed sample and epoxy/CB/PP composites were similar at 10 and 100 V. The value at 100 V was considerably lower than that at lOV. In PP/epoxy/CB 40/60/4 samples, epoxy/CB/PP, and simultaneously melt-mixed samples exhibited similar volume resistivity, whereas the volume resistivity of PP/CB/epoxy system was much low. The variation in the volume resistivity was due to the difference in the carbon black distribution and morphology change. The scanning electron micrographs of epoxy/CB/PP (30/6/70) and PP/CB/epoxy (70/6/30) systems are shown in Fig. 21.27. 

The thickness consideration can shed some light on the enhanced catalytic effect of the mixed samples with 1.5 and 1.0 pg/cm of Ru over the sample with pure 2 pg/cm of Ru. Mattos et al. ascribed the enhanced activity of the mixed Ru + Ir samples to a combination of catalytic and roughness effect. In the case of our samples, the catalyst is so thin that we cannot speak of any kind of layer and consequently we can disregard the roughness factor as a contributor to the enhanced activity. This leaves the enhanced inherent activity as the predominant reason for the increased activity. 

Microtubing systems allow 50% flow rates for the pump tubes. Mixing is considerably reduced and thus sample times of less than 1 min may be achieved (about 800 fd sample volume). 

As established in [214], in roller-mixed PVC-based composites one observes a much better uniformity of filler distribution over the matrix volume the relative viscosity is thereby considerably reduced. That is, for a fixed filler content, the viscosity of a system with agglomerates is always higher than that of the well-dispersed sample. 

Typically it took about 160 to 200 seconds to inject a pulse of about 455 kg coarse tracer particles into the bed pneumatically from the coaxial solid feed tube. It can be clearly seen from Figs. 38 to 42 that the tracer particle concentration increases from essentially zero to a final equilibrium value, depending on the location of the sampling port. The steady state was usually reached within about 5 minutes. There is considerable scatter in the data in some cases. This is to be expected because the tracer concentration to be detected is small, on the order of 4%, and absolute uniformity of mixing inside a heterogeneous fluidized bed is difficult to obtain. 

In the adsorption with Tenax alone satisfactory results were obtained, while in the presence of mineral oil a considerable proportion of the organophos-phorus pesticides (particularly Malathion and Parathion-methyl) was not adsorbed and was recovered in the filtered water. This drawback can be overcome by adding a layer of Celite 545 which, in order to prevent blocking of the column, is mixed with silanised glass wool plugs. A number of analyses of surface and estuarine sea waters were carried out by this modified Tenax column and simultaneously by the liquid-liquid extraction technique. To some of the samples taken, standard mixtures of pesticides were also added, each at the level of 1 xg/l (i.e., in concentration from 13 to 500 times higher than that usually found in the waters analysed). One recovery trial also specifically concerned polychlorobiphenyls. The results obtained in these tests show that the two extraction methods, when applied to surface waters that were not filtered before extraction, yielded very similar results for many insecticides, with the exception of compounds of the DDT series, for which discordant results were frequently obtained. 

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