Numerical and experimental analysis of droplet dynamics in constricted milli and microchannels

Abstract

This study investigates the dynamics of droplets flowing through constricted channels at milli and microscales using a combination of experimental and numerical approaches. Experiments were conducted in a 3D-printed millichannel with three immiscible fluid pairs, spanning a wide range of viscosity ratios between dispersed and continuous phases (10^–2<X<10²) and Capillary numbers of the continuous phase (10^-4<Ca_c<10^-1). Numerical simulations, employing the Volume of Fluid (VOF) methodology and performed with Ansys FLUENT® 2021 R2, complemented the experiments by exploring two geometrical scales: milli (aspect ratio: 5:3 at the inlet channel; 1:3 in the constricted region) and micro (aspect ratio: 5:1.5 before the contraction; 1:1.5 after contraction). For milliscale simulations, X ranged from 10^–1 to 10² and Ca_c from 10^–3 to 10^–1, while in microscale simulations, 10^–2<X<10² and 10^–4<Ca_c<10⁰. A comprehensive analysis of velocity profiles, film thickness, and droplet deformation was conducted numerically. Strong agreement between experimental and numerical results for average droplet velocity and length within the constricted region validated the computational model’s robustness. This work elucidates the influence of Ca_c and X on droplet deformation, velocity, and film thickness, providing valuable insights into the optimization of multiphase microfluidic systems.