Drop generation in controlled fluid flows

Recent fabrication methods rely on microfluidics as technology provides great control over fluid flow and mixing of components. In the coflow configuration, a fluid is injected through an injection tube in the presence of an immiscible fluid that flows in parallel. In general, two different regimes can be experimentally observed depending on the operating conditions, namely dripping regime and jetting regime. If only hydrodynamic forces act on the liquid, jetting can be obtained in either the coflow or the flow focusing configurations. Within the jetting regime, the author finds that the jet can either widen or narrow in the downstream direction. Despite these jets break into droplets via either absolute or convective instabilities, respectively, the drop size can be unified by a single scaling law. The flow focusing configuration can be implemented in an axisymmetric device or in a two dimensional device that can be generated by soft-lithography techniques.