Wall effect for the fall of spheres in cylindrical tubes at high Reynolds number

New experimental results on the wall effect for sphere motion in cylindrical tubes are presented and discussed for the conditions d/D less than or equal to 0.9 and Re-m less than or equal to 20000. Extensive comparisons with previous studies have been carried out to evaluate their predictability and to demonstrate the utility of the present results. The wall factor, defined as the ratio of settling velocity in an unbounded medium to that measured in a cylindrical tube, is found to depend on sphere-to-tube diameter ratio and on sphere Reynolds number. However, for small values of the Reynolds number (Re less than or similar to 0.5), as well for large values (Re greater than or similar to 1000), the Reynolds number dependence of the wall factor disappears; in these regions, only the dependence on diameter ratio remains.