The manipulation of capillary stream breakup using amplitude-modulated disturbances: A pictorial and quantitative representation

Abstract

Droplet formation from capillary streams of viscous low vapor pressure fluids in a vacuum has been studied. A new form of capillary stream breakup, which entails the use of an amplitude-modulated sinusoidal disturbance, has been employed extensively in this work. The genesis of droplets formed due to an amplitude-modulated disturbance on a stream is reviewed in some detail and illustrated pictorially. Because capillary stream breakup and subsequent droplet propagation took place in a vacuum there were no significant interactions with the surrounding atmosphere. Sensitive measurements of the relative speeds of each drop have been made by allowing them to travel 6 m in a vertical vacuum chamber, and measuring the time between drops using an optical method. Speed differences as low as 3.5×10−7 times the average stream speed have been measured. New information about capillary stream breakup is inferred by comparing the speed variations for droplet streams generated with both amplitude-modulated disturbances and single-frequency disturbances. An autoregressive model is developed and found to represent the deviations in time between droplets with consistency and reproducibility.