DROP FORMATION AND DETACHMENT FROM ROTATING CAPILLARIES

The mechanisms governing drop formation and detachment from liquid-filled capillaries in a centrifugal field have been studied. Two different systems, the "reservoir-connected" capillary and the "free" capillary, have been modeled and compared. In the former, the capillary is connected to an infinite reservoir of the liquid. In the latter, the capillary is open to the ambient atmosphere on its two ends and is initially full of liquid. Critical rotation speeds for drop detachment have been calculated for various capillary lengths and ratios of the outer to inner radius. Experiments were performed to test some of the theoretical predictions. The results show that for the reservoir-connected system, the drop detaches when it becomes approximately hemispherical, with a radius which is equal to the outer radius of the capillary. The behavior of the free capillary system is more complex and strongly depends on the radii ratio. In general, the free capillary system sustains a pendent drop at equilibrium at higher rotation speeds than the reservoir-connected system. © 1990.