Droplet coalescence in a sudden expansion microchannel

The coalescence dynamics of two droplets flowing through the sudden expansion microchannel is studied numerically, in this work. The integral equation of the Brinkman's differential equation is solved numerically by applying the boundary element method. The effect of the droplet-droplet distance, capillary number, droplet size, viscosity ratio of droplet phase to continuous phase, and ratio of outlet channel width to inlet channel width on the coalescence dynamics is studied. The occurrence of different coalescence regimes is summarized in phase diagrams relating the droplet-droplet distance, capillary number, droplet area, and viscosity ratio. The critical initial droplet-droplet distance is presented where the coalescence of the droplets is inhibited.