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 cylin drical tubes are presented and discussed for the conditions d/D less t han or equal to 0.9 and Re-m less than or equal to 20000. Extensive co mparisons with previous studies have been carried out to evaluate thei r predictability and to demonstrate the utility of the present results . The wall factor, defined as the ratio of settling velocity in an unb ounded medium to that measured in a cylindrical tube, is found to depe nd on sphere-to-tube diameter ratio and on sphere Reynolds number. How ever, 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 th ese regions, only the dependence on diameter ratio remains.