Dynamic evolution of oil–water interface during displacement in microcavities

Two-phase displacements in cavity-featured configurations are ubiquitous phenomena. However, the morphological evolution of the two-phase interface during displacements in cavities is still unclear. Herein, the dynamic evolution of the oil–water interface morphology in three microcavities and transient flow field characteristics is investigated. The influence of the cavity size, channel width, and inlet flow rate on the interface dynamics and the retention ratio of water is parametrically studied. Furthermore, the slippage distance and slip velocity of the interface on cavity walls are comprehensively characterized. A new interface pining mechanism on a small chamfer is proposed. Flow visualization experiments using micro-particle imaging velocimetry and computational fluid dynamics (CFD) simulations are conducted to further reveal the transient flow field characteristics. The results provide an in-depth understanding of the background physics of two-phase displacements and provide guidance for the design of cavity-based functional surfaces.