A Computational Study of Drop Formation in an Axisymmetric Flow-Focusing Device

We investigate the formation and dynamics of drops computationally in an axisymetric geometry using a Front-Tracking/Finite-Difference (FT/FD) method. The effects of viscosity ratio between inner and outer liquids on the drop creation process and drop size distribution are examined. It is found that the viscosity ratio critically influences the drop formation process and the final drop distribution. We found that, for small viscosity ratios, i.e., 0.1 < λ < 0.5 drop size is about the size of the orifice and drop distribution is highly monodisperse. When viscosity ratio is increased, i.e., 0.5 < λ < 1 a smaller drop is created just after the main drop. For even higher viscosity ratios, the drop distribution is usually monodisperse but a satellite drop is created in some cases. The effect of the flow rates in the inner jet and the co flowing annulus are also studied. It is found that the drop size gets smaller as Q_in / Q_out is reduced while keeping the outer flow rate constant.