The translation of two identical, coaxial, nonhomogeneously structured flocs in a Newtonian fluid normal to a plate is analyzed theoretically for the case where the Reynolds number ranges from 0.1 to 40. The geometry considered is capable of simulating the behavior of a floc near a boundary when other flocs may present. The description of the structure of a floc is based on a two-layer model where the permeability of its inner layer can be different from that of its outer layer. We show that the influence of the plate on the flow field near the near floc is more significant than that near the far floc, but the behavior of the corrected drag coefficient of the far floc is more complicated than that of the near floc. In general, the presence of the plate has the effect of raising the drag on a floc. The more nonhomogeneous the floc structure is, the more appreciable the deviation of the corrected drag coefficient–Reynolds number curve from the corresponding Stokes’ law-like relation. An empirical relation, which correlates the corrected drag coefficient with the Reynolds number, the separation distance between two flocs, the floc–floc distance, and the ratio permeability of outer layer to permeability of inner layer, is proposed.
Colloid and Polymer Science 286(14-15), pp.1593-1604