Revisit of the Wall Effect on the Settling of Cylindrical Particles in the Inertial Regime

Abstract

The wall effect on the settling of cylindrical particles in the inertial regime is revisited. This study covers particle Reynolds number from 600-16100 and particle length-to-diameter ratio (l/d) from 4-21. The wall factor (U t /U t,∞ ) is found to decrease initially as the particle-tocolumn diameter ratio (d/D) increases. When wall effect becomes significant, U t /U t,∞ starts to increase with an increase in d/D due to a change of the particle orientation during settling. After U t /U t,∞ reaches a maximum, it decreases to 0 when d/D increases to 1. A semi-empirical model is developed to predict the wall effect of settling of cylindrical particles over the whole range of d/D. The model shows good prediction to the experimental results and matches the wall factor models developed for spherical particles when l/d approaches 1.

Influence of shape and surface charge on the sedimentation of spheroidal, cubic and rectangular cuboid particles

“…that drag increases as shape becomes less spherical, especially for particles with high aspect ratio [23,26,59] and thus expected drag coefficients for ZM and ZMCA would be higher than for the spheroidal CPM, suggesting the Stokes equation may over estimate their respective settling velocities. For ZMCA in particular, drag may be significantly increased, especially if particles orientate towards a flat conformation of maximum drag resistance upon settling [11,27,28].…”

“…The role of particle shape on hindered settling exponents has been a focus of previous studies, where evidence would suggest that values increase as the particles become less spherical [22][23][24][25][26] due to the enhanced drag. For particles with large aspect ratio, orientation may also be an important factor, where research has shown that rod-like particles in particular may naturally orientate towards a flat conformation of maximum resistance upon settling [11,23,27,28].…”

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

“…Alternative approaches include those analysing the transmission-attenuation response of laser light in sample based devices such as the Lumizier (from Lum GmbH) and Turbiscan (Formulation, SA) [9][10][11]; however, these ex situ systems are only suitable for small sample analysis of slowly evolving suspensions. In situ devises include light based transmission/backscatter or fluorescence devices [12][13][14][15][16][17][18], CCD video analysis [19][20][21][22][23], gamma ray [24,25] or x-ray CATSCAN [26], and also tomographic techniques which measure electrical resistance within suspensions [27,28]. However, a number of these techniques suffer from common limitations to their use, such complicated set-ups that encompass specific vessel requirements (and hence are not suitable for deployment industrially) while many are highly intrusive, or complex and expensive in application [29].…”

Comprehensive Characterization of Nano- and Microparticles by In-Situ Visualization of Particle Movement Using Advanced Sedimentation Techniques

“…for CPA) should be 50 particle diameters above the bottom to account for a friction error of less than 0.6 % (Allen, 1999). As shown recently, cylindrical particles may orient with regard to the wall and settle in narrow cylindrical cells even faster (Lau et al, 2010).…”