On the role of stress-induced migration on time-dependent terminal velocities of falling spheres

Abstract

Abstract." There is experimental evidence to suggest that even under steady-state conditions the velocity of solid spheres or bubbles moving through viscoelastic fluids can become time dependent. One of the possible explanations offered for interpreting this phenomenon has been the generation of a polymer depleted layer in the line of passage Of the particles, which disappears due to the counterbalancing effect of molecular diffusion in the long range. We have done some careful experiments and measured these concentrations to show that no such depletion layers are formed. Alternative explanations of the phenomenon have been examined and the importance of the possible effects of microstructures generated through temporary associations has been emphasised.

Motion of viscous drops in tubes filled with yield stress fluid

“…The axisymmetric interaction results in a substantial acceleration of the trailing particle as was earlier observed for the solid spheres interacting in Carbopol solutions (Gheissary and van den Brule, 1996;Hariharaputhiran et al, 1998) as well as in other non-Newtonian fluids (Ambeskar and Mashelkar, 1990). As a result, two equal-size drops tend to approach each other and coalesce.…”

“…This is in contrast to a wide range of non-Newtonian fluids without yield stress, where wake effects are relaxed at much shorter relaxation time (see, e.g. Ambeskar and Mashelkar, 1990, for a comprehensive review). Hariharaputhiran et al (1998) reported on the variation in the steady settling velocity of spheres with a time interval between experiments in a 0.3 wt% aqueous Carbopol-941 dispersion.…”

Interaction between Taylor bubbles rising in stagnant non-Newtonian fluids

“…nomenon was also observed in the sedimentation of spheres through viscoelastic fluids (Ambeskar and Mashelkar, 1990). In these experiments, long-lasting effects (from minutes to several hours) were observed for fluids with relaxation times on the order of several seconds.…”

In Situ Rheo-NMR Investigations of Shear-Dependent 1H Spin Relaxation in Polymer Solutions

“…Bissgaard, Cho et al ., and Ambeskar and Mashelkar conducted experiments wherein they dropped spheres in aqueous PAM solutions. They measured the terminal settling velocities of these spheres and showed that the settling velocities of identical spheres, dropped consecutively along the same path in a PAM solution, kept increasing until a saturation velocity was reached.…”