Analysis of co-flowing immiscible liquid streams and their interfaces in a high-throughput solvent extraction chip

Liquid–liquid flow profiles are central to the operation of microfluidic devices in a range of applications. We recently demonstrated a multi-stream solvent extraction (SX) chip that combines high-surface-to-volume ratios and volumetric throughput. Here, we study these flow profiles in detail using numerical simulations, with consideration of different boundary conditions. The two liquids differ in viscosity, modelled on platinum (aqueous) and extractant (organic) phases, and the position of the liquid–liquid interfaces (and therefore surface/volume and phase ratios) can be controlled by adjustment of flow rates. The prediction of the position of the interface requires the solution of the governing equations of fluid mechanics. The volume of fluid (VOF) method was used to simulate the dynamics of the organic and aqueous phases to reveal stable flow profiles. This experimentally validated computational model with the root-mean-square deviation of about 11 µm will be useful for simulation of microfluidic SX design and operation, particularly where process intensification is sought through scale-out. Graphic abstract