Particulate Binary Mixtures:  Dependence of Packing Porosity on Particle Size Ratio

Abstract

Binary mixtures with significant size ratios are scarcely studied. Yet, contaminants of chromatographic columns or ion-exchange resins have size ratios of δ < 0.1. Binary mixtures of glass beads with δ ) 0.1-0.0375 were used experimentally to measure packing porosity. Simultaneously, a significant number of published data was analyzed. A linear mixing model was adopted to predict the porosity of each particle fraction in the binary mixture. Deviations from the model may be caused by wedging of small particles between the large ones. Large particles may disturb the porous medium properties by inducing a wall effect over the small particles. Wedging analysis led to the conclusion that, for δ < 0.01, its effect is insignificant. The wall effect yields an additional void around the large particles as long as δ > 0.0035. For δ < 0.0035, the small particles form a monosized dense packing and both wedging and wall effects become negligible.

Characterising porosity of multi-component mixtures in rotary mills

“…The porosity of multi-component mixtures has been studied by many authors (Ouchiyama andTanaka 1986, Standish andStandish 1987, 1991;Dias, et al 2004). …”

“…The studies above have shown that the packing of monosized particles is different from that of multi-component mixtures. This is due to the fact that in particle mixtures, smaller particles tend to fill the interstices that may occur among larger particles (Dias et al 2004). However, such mathematical models are difficult to apply to aggressive systems like rotating drums, since they were developed for simpler systems.…”

“…However, such mathematical models are difficult to apply to aggressive systems like rotating drums, since they were developed for simpler systems. In fact, for dynamic systems, appropriate corrector functions are necessary in order to arrive at accurate porosity estimates (Dias et al, 2004).…”

“…For the cataracting-centrifuging regime, the particle bed is spread out along the mill shell, with a more uniform but lower packing. For more than two components, the porosity distribution is expected to be even more different, and more difficult to predict (Dias et al, 2004). The porosity of multi-components is, therefore, worth investigating.…”

“…The packing of mixtures has been studied widely (Ouchiyama and Tanaka, 1986;Standish 1987, 1991;Dias et al, 2004;Arntz et al, 2008). From such studies, key concepts can be understood that help in studying multi-component mixtures.…”