A Study into the Pinch-Off Dynamics of Low Viscosity Droplet Drips in a Coaxial Flow

A coaxial droplet consists of two immiscible fluids encapsulated in one another after the point of detachment from a coaxial flow. Scientists are consistently working on newer methods to optimise the existing coaxial flow devices to create smaller, more easily controlled droplets to allow for more precise use in fields like encapsulation for drug delivery and cosmetics. Nevertheless, most droplet pinch-off studies focused on pendant droplet pinching in a still surrounding medium. With the advent of greater computational power, recent novel discoveries showed that for single droplets in a still medium, all three, inertial, viscous, and inertial-viscous, regimes were present within the dynamics of pinch-off, but they varied depending on the initial fluid properties. Unlike single pendant droplets, an extensive study into filament breakup of coaxial filaments has yet to be conducted, despite the research conducted into optimising coaxial flows and, subsequently, coaxial droplets for industrial purposes such as pharmaceutical tablet coatings. Our research effectively studies the pinch-off mechanics of low-viscosity Newtonian coaxial droplets using both experimental and the computational volume of fluid (VOF) method under varying parameters to understand the physics behind these changes further. Our collected data shows a monotonic dependence of the inertial regime scaling perfector on parameters such as the external liquid flow and the nozzle size. These new results open the door for better control over the encapsulation process.