Shear-thinning effects on double emulsion formation in microfluidic systems

This numerical study investigates the formation dynamics of double emulsion droplets in a coaxial microfluidic device, focusing on shear-thinning effects in the outer continuous phase modeled via the Carreau–Yasuda equation. The inner and middle phases are Newtonian. Using the volume of fluid method, we simulate three-phase immiscible flows and validate our model against experimental data. A parametric analysis examines the influence of power-law index (n), inner capillary number (Cain), middle capillary number (Camid), Carreau number (Cr), and flow rate ratio (Q*) on droplet size, generation frequency, and flow regime transitions. Results identify three distinct regimes—dripping, jetting, and tubular—whose emergence depends on rheological properties and hydrodynamic conditions. Lower n and Camid values promote dripping, while increasing either parameter triggers transitions to jetting or tubular regimes. Droplet size and frequency exhibit sharp changes at critical thresholds, correlating with regime shifts. Higher Q* values intensify outer shear forces, reducing droplet size and enhancing generation frequency, particularly at elevated n. These findings provide fundamental insights into controlling double emulsion generation in microfluidic systems and offering design guidelines for emulsification and encapsulation processes involving complex fluid behaviors.