Extension of the Richardson–Zaki equation to suspensions of multisized irregular particles

The settling velocities of aqueous slurries of praseodymium oxalate are well represented by the Maude–Whitmore equation in both the fairly dilute and very concentrated cases. Extensive channeling occurs in some slurries with intermediate concentrations, but not in other slurries at the same concentration. Thus, there is a duplicity of values rather than a transition. Aqueous slurries of calcium carbonate also follow the Maude–Whitmore equation at low and high concentrations. Extensive channeling occurs at intermediate values, but there is a region of instability rather than a duplicity of values.

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► We studied the settling velocities of aqueous slurries of praseodymium oxalate.
► A log–log plot of settling velocity vs. void fraction has two linear regions.
► These slurries obey the Maude–Whitmore equation in the linear regions.
► One linear region overlaps the nonlinear, yielding two disparate sets of velocities.
► The second and third results also apply to aqueous slurries of calcium carbonate.