Predicting sizes of droplets made by microfluidic flow-induced dripping

We present a model to predict the size of droplets dripping into an immiscible flowing fluid in glass capillary microfluidic devices. Despite the complex flow behavior in the confined geometry of microfluidic devices, we find that the size of dripping droplets can be accurately predicted by a simple analytic expression based on the ratio of shear and interfacial forces acting on the droplet surface, also known as the Capillary number. We show that data obtained for a wide range of fluid properties and flow conditions including single and multiple dripping events and other experimental data previously reported in the literature can be quantitatively described using one single universal value for the critical Capillary number leading to droplet rupture.