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The lack of a simple method for generating drops whose radii (Rd) are much smaller than those (R) of nozzles which produce them has heretofore been a major limitation of the drop-on-demand technique. Therefore, the only reliable way to reduce Rd to date has been to reduce R. A new method is reported which allows an order of magnitude reduction in drop volume while using the same nozzle. It is shown that the key to forming drops with RdR is to judiciously control the capillary, viscous, and inertial time scales that govern the flow within the nozzle and the forming drop. The time scales are controlled in experiments by appropriately driving a piezoelectric sleeve surrounding a microcapillary tube, and the interplay between them is elucidated through computation.
Chen et al. (Tue,) studied this question.