Numerical and experimental study of oil-in-water (O/W) droplet formation in a co-flowing capillary device

摘要

Graphical abstractDisplay OmittedHighlights?The simulation of droplet formation agrees well with the experimental results.?Effects of flow condition and physical properties on the droplet size were studied.?Effects of the wall size and wetting property on the droplet size were studied.?Transition condition from dripping to jetting regime in O/W system was presented.?A correlation for dimensionless droplet size in dripping regime was developed.AbstractOil-in-water (O/W) emulsion droplet formation in a co-flowing capillary device was observed through experiments and simulated by using the volume-of-fluid/continuum-surface-force (VOF/CSF) method. Two flow regimes in droplet formation, namely dripping and jetting, were observed in the experiment and perfectly simulated by the numerical method. Further the effects of two phase flow rates, viscosities, interfacial tension, and wall effect as well as the wetting property of capillary surface on the droplet forming process were extensively investigated by numerical simulation. It is found that the droplet diameter mainly depends on the flow rate and viscosity of the continuous phase and the interfacial tension. With increasing the flow rate and viscosity of the continuous phase or decreasing the interfacial tension, the droplet diameter decreases. Based on the experimental and simulated results, a correlation of dimensionless droplet diameter with the Capillary number, Reynolds number and a wall effect factor was presented for the dripping regime in different-sized devices. Finally the transition from dripping to jetting flow regime was studied. The results indicate that the Capillary number of the dispersed phase (Cad) plays a significant role in this transition. When Cadexceeds about 0.3, the transition from dripping to jetting regime occurs. These study results can provide a useful guide for the preparation of monodisperse droplet with controllable size by using the co-flowing microfluidic device.]]>