Flow behavior of a droplet in viscous fluids through asymmetric bifurcating microchannels

Understanding the droplet dynamics in asymmetric bifurcating microchannels is crucial to the precise sorting and size control of the droplets in microchannels. This work presents an experimental investigation of droplet behaviors in viscous fluids through asymmetric bifurcating microchannels. Three viscosity ratios of the continuous phase to the dispersed phase are examined, i.e., λ = 33.7, 56.2, and 112.4. Three asymmetric junction angles are explored, including θ = 30°, 45°, and 60°. Two flow regimes are identified, i.e., droplet breakup and non-breakup. The droplet evolutions for both regimes are discussed in detail, and the dynamics of the droplet parameters are examined, including the droplet length in subchannels, neck thickness, and tunnel distance between the droplet head and the wall. The regime diagrams of the droplet behaviors in asymmetric bifurcating microchannels are explored. It is found that the boundary between the droplet breakup and non-breakup follows the power-law equation l0/w = χCacrβ, where l0/w is the dimensionless initial length of the droplet and Cacr is the critical capillary number. The factors χ and β depend on the viscosity ratio and the junction angle.