Experimental investigation of the creeping motion of a drop in a vertical tube

New experimental data regarding the motion of a drop along the axis of a vertical tube, filled with another highly viscous liquid, are obtained. The experiments are realized with sufficiently large drops for an internal circulation to develop and also for different pairs of fluids; the preponderant role of the gravity on the drop shape and consequently on its terminal velocity is pointed out. Moreover, by means of a visualization technique, details on the flow both inside and outside the drop are given. (Author)