Settling velocities in batch sedimentation

The sedimentation of mixtures containing one and two sizes of spherical particles (44 and 62 μm in diameter) was studied. Radioactive tracing with 57Co was used to measure the settling velocities. The ratio of the settling velocity U of uniformly sized particles to the velocity predicted to Stokes' law U0 was correlated to an expression of the form U/U0 = epsilon/sup α/, where epsilon is the liquid volume fraction and α is an empirical constant, determined experimentally to be 4.85. No effect of viscosity on the ratio U/U0 was observed as the viscosity of the liquid medium was varied from 1x10-3 to 5x10-3 Pa.s. The settling velocities of particles in a bimodal mixture were fit by the same correlation; the ratio U/U0 was independent of the concentrations of different-sized particles