A study was made of the behavior of rigid spheres, fluid drops, and flexible fibers subjected to oscillatory and pulsatile flow in suspensions the concentrations of which ranged from 0.5% to 40% and at particle to tube diameter ratios ranging from 0.01 to 0.21. Visual observations of particle radial migration and interaction were combined with measurements of the changes in the displacement profiles and power dissipation in the tube with time. Larger rigid spheres at low concentrations were found to accumulate in groups approximately equally spaced in a central core in which the velocity profiles were blunted. At concentrations >10% and at all particle sizes, a particle-depleted layer developed at the wall. The displacement profiles, although initially blunted, became first more parabolic with time and then again blunted suggesting that a redistribution of spheres also occurred in the center of the tube. This was reflected in the power dissipation, calculated from the measured pressure gradient and phase lag, which exhibited a maximum before falling to a final value lower than the initial. In contrast, the power dissipation in suspensions of fluid drops decreased with time at all particle sizes and concentrations corresponding to an observed inward migration and packing of drops in the core of the tube where the displacement profiles were blunted. In dilute suspensions of pulp fibers, axial migration of particles resulted in a peripheral particle-free zone and mechanical entanglements between the fibers in the center of the tube. Whereas in very dilute suspensions and at low particle sizes, the displacement profiles and power dissipation were in good agreement with theory for Newtonian liquids, the observations made at higher concentrations and particle sizes could only be qualitatively interpreted.
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