Suspension of spheres by a bounded fluid

Abstract

The suspension of solid spheres in fully developed vertical pipe flow has been investigated between particle Reynolds numbers of 2 and 10000 and between pipe Reynolds numbers of 25 and 37000 for sphere to conduit diameter ratios ranging from 0.046 to 0.274. It was found that the drag coefficient obtained in the present study was higher than that reported for spheres suspended or traveling in bounded or unbounded quiescent fluids. The drag coefficient was found to depend upon the particle Reynolds number and the sphere to conduit diameter ratio. The radial position adopted by the spheres was found to be near the conduit axis at particle Reynolds numbers below 80 but near the conduit wall at particle Reynolds numbers greater than 200. A secondary sphere to conduit diameter ratio effect upon radial position was observed when spheres were suspended near the conduit wall. The spheres underwent four distinct modes of motion; the particular mode adopted was primarily dependent upon the particle Reynolds number with a secondary dependency upon the sphere to conduit diameter ratio. Transitions between modes occurred at particle Reynolds numbers which were approximately the same as values reported for changes in the wake structure behind spheres.