Sedimentation of multisized particles in concentrated suspensions

Abstract

A model is developed for predicting the sedimentation velocity in suspensions of multisized nonflocculating solids, in which the retarding effect of the smaller particles on the setting velocities of the larger ones is taken into account. Tests of the model, and comparisons with other models, demonstrate that it provides improved prediction of data on suspensions comprising both discrete particle size mixtures and continuous size distributions, and that it is applicable to continuous countercurrent solid-liquid operations. CONCLUSIONS AND SIGNIFICANCEOperations involving relative motion between a fluid and suspended particles arise often and include sedimentation, fluidization and co-or countercurrent solid-liquid operations.The hydrodynamics of slow vertically flowing liquid-particle mixtures, involving noncolloidal particles of uniform size and density, are understood in the dilute limit and can now be reliably treated empirically in the intermediate and concentrated limits. The presence of particles of mixed sizes enhances in-Correspondence concerning this paper should be addressed to M S. Selim.

In situ characterisation of a concentrated colloidal titanium dioxide settling suspension and associated bed development: Application of an acoustic backscatter system

“…This suggests a gradual reduction in suspension homogeneity, likely due to particle segregation in the suspension system which comprises a broad size distribution. This observation is consistent with the batch settling of polydisperse suspensions with a wide distribution, where particles of different sizes segregate and the larger aggregated particles settle out expeditiously [67,[72][73][74]. Markedly here we have identified the potentially complex settling behaviour of this suspension system from brief observation of the evolving backscatter profiles.…”

“…Also, sedimentation is hindered markedly with increasing particulate concentration which enhances fluid drag [62][63][64][65][66]. Additionally, titanium dioxide slurry is known to have strong inter-particle interactions, which could increase hindered settling effects (from changes expected for discrete spheres) [51] and the presence of a wide size range is expected to enhance these interactions [67].…”

Particle mixing and separation in a binary solids floating fluidized bed

“…Law et al [25] showed that the models of Masliyah [21] and Patwardhan and Tien [24] predict the settling velocities better than the models of Lockett and A1-Habbooby [9] and Mirza and Richardson [22]. On comparing experimental results with predictions by a variety of models, AI-Naafa and Selim [26] concluded that slip velocities are best described by the so-called Selim model reported in 1983 [27,28]. Essentially, their model accounts for particle-particle interactions by applying the terminal falling velocity of the fastest falling particle, which is based on the suspension density [Eq.…”

Solid–Liquid Separation Properties in Centrifugal Sedimentation of Bidisperse Colloidal Suspension

“…A number of studies have been reported over the years on the analysis of the gravity sedimentation of bidisperse suspension (Smith, 1965;Dorrell and Hogg, 2010) or polydisperse suspension (Selim et al, 1983;Ha and Liu, 2002), which was able to be easily extended to the analysis of centrifugal sedimentation of bidisperse suspensions. Although a variety of models (Smith, 1997;Kondrat' ev and Naumova, 2006;Krishnamoorthy, 2010) have been proposed, Al-Habbooby (1973, 1974) initially applied the Richardson and Zaki (1954) correlation for monodisperse suspension to bidisperse suspensions, and their model played an important role contributing to the subsequent studies.…”