On the genesis of droplet stream microspeed dispersions

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Abstract
Mechanisms that govern uniform droplet generation have been investigated. Droplet formation of viscous low vapor pressure fluids has been achieved by imposing sinusoidal pressure disturbances on a capillary stream. The capillary stream breakup and subsequent droplet propagation took place in a vacuum so that there were no significant interactions with the surrounding atmosphere. Microfluctuations of the droplet speeds have been examined after the droplets have traveled approximately 30 000 droplet diameters, and can vary from 1×10−6 to 1×10−4 times the average droplet speed depending on forcing conditions. Growth rate measurements were made of the streams radial disturbance prior to breakup, and were found to be intrinsically related to the measurements of the droplet stream’s speed microfluctuations. From this relation, it is suggested that studies of the characteristics of the droplet stream gives information about the capillary wave instabilities, which lead to droplet formation. A model that describes the microfluctuations is developed and is in excellent agreement with the experimentally obtained values. The model suggests that the source of droplet stream microspeed dispersions is the growth of a noise disturbance that modulates the otherwise controlled periodic pressure perturbation, which initiates droplet breakup.

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