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Journal of Non-Newtonian Fluid Mechanics, Volume 192, February 2013, Pages 29-36.
Abbas H. Sulaymon, Catherine A.M.E. Wilson, Abeer I. Alwared
Environmental Engineering Department, College of Engineering, Baghdad University, Baghdad, Iraq
Hydro-environmental Research Centre, Environmental Hydraulics, Cardiff School of Engineering, Cardiff, United Kingdom
Abstract
Experiments were conducted to examine the settling motion of two stainless steel spheres at two sphere arrangements in a power law fluid (carboxymethylcellulose solution) with different concentrations (0.7%, 0.9% and 1.1% weight to volume). Both ‘in line’ and ‘side by side’ sphere arrangements were investigated. The impact of the initial separation distance between spheres; defined as a ratio of the distance between the spheres centers to their diameter, on their behavior was examined. The velocity ratio, defined by the velocity of the two interacting spheres compared to the velocity of a single isolated sphere, was determined. When the spheres are touching in their initial position, the velocity ratio was equal to 2.14, however as the separation distance increased, the velocity ratio decreased until a value of 1.14 at a separation distance of 5.41 indicating that the spheres behaved as isolated spheres for this condition. The behavior for both the in line and side by side sphere arrangements in the power law fluid was found to be very similar to that observed in a Newtonian fluid, with the exception of the case of the two spheres side by side. The behavior of the side by side spheres diverged from that observed for a Newtonian fluid at a separation distance of between two and five, implying that at some stage within this range a stable equilibrium distance may be reached. While when the initial separation distance was less than two, the two spheres repelled each other that are similar to the behavior in a Newtonian fluid, when the separation distance increased to five, the two spheres kept the same distance between them for a while before coming together.
