High-throughput controlled droplets generation through a flow-focusing microchannel in shear-thinning fluids

Abstract: This study presents a three-dimensional transient computational fluid dynamics simulation of droplet generation in a flow-focusing microfluidic device using the Coupled Level Set and Volume of Fluid method for interface capturing. We systematically investigated the effects of shear-thinning non-Newtonian fluids, specifically carboxymethyl cellulose solutions, on the generation of mineral oil droplets. The rheological properties of carboxymethyl cellulose were analyzed at concentrations of 0.1%, 0.25%, 0.5%, and 1.0%, with the parameters K and n specified in terms of viscosity. The study examines the influence of rheological properties, continuous and dispersed phase flow rates, and interfacial tension forces on the generation and dynamics of controlled high-throughput droplets. The numerical results provide insights into droplet characteristics, including droplet length, velocity, formation frequency, liquid film thickness, pressure distribution, and flow regimes. The findings revealed that increasing the carboxymethyl cellulose concentration (0.1% to 1.0%) and continuous phase flow rate (10 {\mu}L/min to 30 {\mu}L/min) reduces droplet length by 53% and 45%, respectively. while increasing the dispersed phase flow rate (2 {\mu}L/min to 18 {\mu}L/min) and interfacial tension results in increased droplet length by 62% and 42%. At lower concentrations of carboxymethyl cellulose, plug-shaped droplets fully occupy the channel width in the squeezing regime. As concentration increases, a transition to the dripping and jetting regimes is observed. The study further explores non-dimensional parameters, expressing the Weber and modified Capillary numbers as functions of flow rate and interfacial tension. These insights impact drug delivery, material synthesis, and microfluidic technologies requiring precise droplet control.