Impact of Carreau-Yasuda fluid properties on droplet dynamics in bifurcation microchannels

This study investigates the three-dimensional dynamics of droplet splitting in bifurcation microchannels using a two-phase flow simulation with the Level Set method implemented in COMSOL Multiphysics, capturing the behavior of a Carreau-Yasuda non-Newtonian fluid. The influence of fluid properties, droplet size, flow velocity, and channel geometry on the splitting process are systematically analyzed. The results reveal three distinct regimes: cutting with gap, cutting without gap, and no-cutting, determined by the droplet length and fluid conditions. Higher sodium carboxymethyl cellulose concentrations (0.80%) increase viscosity, promoting splitting even at shorter droplet lengths (ε ≈ 1.0), while lower concentrations require longer droplets (ε ≈ 2.0) for efficient splitting. Increased flow velocity enhances splitting by inducing pronounced viscosity variations, while lower velocities hinder complete separation. Channel geometry also plays a significant role, with a 60° bifurcation angle generating higher shear stresses and promoting more efficient splitting than a 120° angle. These findings provide valuable insights for optimizing microfluidic systems, offering practical strategies for applications requiring precise droplet control, such as drug delivery and biochemical analysis. This work contributes to advancing next-generation microfluidic device design by fine-tuning fluid viscosity, flow velocity, and channel geometry to achieve efficient droplet manipulation.