Particulate character, inertial effects and diffusion effects in concentrated suspensions

In the sedimentation of suspensions, the particles modify their settling ve locity in accordance with the solids concentration, Kynch's theory assumes that in each layer, the settling velocity only depends on the solids concen tration, and neglects the acceleration and deceleration processes when the particles descend with a velocity distinct from that corresponding to the s olids concentration at this layer. The Kynch theory also assumes that there are so many small particles that the solid mass can be considered homogene ously distributed in the suspension, so the particulate character of the su spension is ignored. Kynch's theory also neglects the diffusion effects. An analysis of the particulate character of the suspension, the inertial effe cts and the diffusion effects are discussed in this paper, deducing a criti cal value for considering the particulate character negligible and a critic al size for considering the diffusion effect also negligible. Finally, seve ral data of different flocculated suspensions are satisfactorily analysed i n view of the conclusions obtained previously. (C) 2001 Elsevier Science B. V. All rights reserved.