(331a) The Effect of Surfactants On the Breakup of An Axisymmetric Laminar Jet

The breakup of a laminar axisymmetric jet is a well studied fluid dynamics phenomenon. Despite the extensive literature on the topic, the impact of surface active agents on jet breakup has received limited attention. Many multiphase contactors function by forcing an immiscible fluid through an orifice or nozzle, or by otherwise destabilizing deformed droplets. Many of these processes can be mimicked on a fundamental level by the discharge of an immiscible axisymmetric laminar jet. Once exposed to the surrounding (matrix) phase, waves form on the surface of the jet causing it to destabilize. At a certain distance from the capillary tip (hereafter referred to as the ?breakup length?), the jet disintegrates into a series of discrete droplets. Often, the jet breaks up into large primary drops and smaller satellite droplets, resulting in a multi-modal droplet size distribution.

Several different experimental series' were performed. First, water and aqueous surfactant solutions were injected into otherwise still air. Secondly, Silicone oils of various viscosity grades were injected into clean water and aqueous surfactant solutions. Finally, water and aqueous surfactant solution were also injected into silicone oil. The capillaries used to form the jets have diameters from 200 to 800 microns and are long enough to assure fully developed flow at the capillary tip. Several non-ionic surfactants, all insoluble in silicone oils, were added in turn to the aqueous phase. This creates two distinct experimental conditions - when water is the continuous phase, surfactant must diffuse from within the surrounding continuous phase to the oil jet interface. When water is the jet phase, surfactant must diffuse from within the jet to the jet interface. Therefore, surfactant transport to the interface always occurs within the aqueous phase. Two distinct CCD cameras were used to image droplets. A low frame rate (30 fps), high resolution camera was used to measure breakup length and to quantify droplet population statistics. A high frame rate (up to 20,000 fps), moderate resolution camera was employed to observe detailed breakup phenomena. An automated image processing algorithm was used to acquire droplet geometry and population statistics. To aid in data interpretation, interfacial tension and other relevant interfacial properties were acquired/estimated using both static and dynamic Pendant Drop techniques. CFD simulation of the jet system was also performed, using Fluent with the volume of fluid method. CFD simulation was performed to better understand the effect of the continuous fluid flow patterns on the jet breakup.

Since our last communication, significant new data has been acquired exploring the effect of viscosity ratio and surfactant starting phase (e.g., surfactant soluble in dispersed vs. continuous phase). In addition, new CFD simulation results of the jet system will be presented. We will report the results of this study, and demonstrate the effect of surfactant concentration, jet discharge flow rate, oil phase viscosity and capillary diameter on jet breakup length; and on primary and satellite droplet size distributions and relative population size. The data will be interpreted with respect to the relevant physicochemical phenomena.