Sedimentation of bidisperse suspensions

Robert Dorrell, Andrew J. Hogg*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

23 Citations (Scopus)


The average settling velocity of a suspension of identical particles through otherwise quiescent fluid is smaller than the settling velocity of a single particle in an unbounded fluid. When a suspension settles out to form a deposit, this hindered settling effect may lead to complicated sedimentation behaviour, even if the initial suspension is uniformly distributed. This study analyses the bulk sedimentation of bidisperse suspensions and calculates the evolution of the volume fraction of each species from an initially vertically uniform state through to the final steady state where both species have fully settled out of suspension and have formed a deposit. These calculations are analytical and employ the method of characteristics to reveal how both particle species evolve. The profiles often include 'shocks', across which discontinuous changes in volume fraction occur. Rarefaction fans may also be found across which the gradients of volume fraction are discontinuous. These new analytical solutions reveal the evolving composition of the suspension and the deposit and may be compared to experimental observations. They also provide test cases that can be used to verify recent numerical techniques for computing the bulk sedimentation behaviour of polydisperse suspensions.

Original languageEnglish
Pages (from-to)481-490
Number of pages10
JournalInternational Journal of Multiphase Flow
Issue number6
Publication statusPublished - 1 Jun 2010


  • Bidisperse
  • Deposition
  • Mass conservation
  • Method of characteristics
  • Sedimentation


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