Coalescence dynamics of two droplets in T-junction microchannel with a lantern-shaped expansion chamber

Abstract

BackgroundTo improve the coalescence efficiency of droplets in microchannel, a lantern-shaped expansion chamber is proposed to facilitate droplets coalescence. MethodsA high-speed digital camera was used to study the coalescence process and the mechanism of droplet coalescence was analyzed based on the liquid film draining model. FindingsThe existence of shrinkage mouth could prolong the contact time of droplets and accordingly promote droplet coalescence. The drainage time of continuous phase liquid film decreases with the increase of superficial flow velocity and droplet size, but increases with increasing dispersed phase viscosity. The film drainage time for contact coalescence, squeeze coalescence and tail coalescence increases successively. There exists a minimum critical capillary number Camin and a maximum critical capillary number Camax, and coalescence can occur only when Camin < Ca < Camax. The correlations for predicting the minimum critical capillary number and the maximum critical capillary number are proposed.