Droplet Fall and Head-On Coalescence in a Liquid–Liquid System: An Experimental and Numerical Approach

The behavior of chlorobenzene and aniline droplets as they fall into water is investigated combining experimental observations with numerical simulations. In the experimental stage, key parameters such as the time-dependent velocity u(t), the terminal velocity UT, and the equivalent diameter deq of each droplet were accurately measured. For the numerical approach, computational fluid dynamics (CFD) methods were applied, employing the finite volume technique to solve the Navier–Stokes equations, along with the volume of fluid (VOF) model to capture the liquid–liquid interface. The experimental velocity–time data served as a basis for validating the simulations through curve fitting and regression analysis, revealing a strong correlation between the experimental and numerical outcomes. Additionally, the study explored the coalescence dynamics of two identical droplets positioned side by side in water. Results showed that a smaller initial distance between the droplets notably hastens the coalescence process, especially during direct, head on collisions.