Interfacial Dynamics of Immiscible Liquid-Liquid Displacement in Capillary Tubes

The interfacial liquid film dynamics of two immiscible fluids in a micropipe is of interest in microfluidics and two-phase flows. Liquid film displacement is essential for fluid dynamics, heat and mass transfer. Understanding interfacial dynamics and liquid film thickness in two immiscible fluids is important in two-phase flow research because the interfacial area of fluid film and its thickness have a significant impact on the heat and mass transfer processes. However, the processes of liquid film formation, development and breakup are complex which involve the interfacial tension between fluid-fluid and fluid-solid, the beating process of fluid dynamics, the thermal effect and the capillary induced instability of thin liquid film breakup. As a consequence of the small length scale, the capillary forces play a fundamental role in the physics of the phenomena. For the high surface area and volume ratio will affects the evaporation of the film fluid. In this paper, annual type thin water film displacement, velocity field and breakup in a two immiscible fluid system in a capillary tube are presented. A novel method for measuring the interfacial liquid film thickness between immiscible liquids of annual oil liquid and an oil slug/droplet (oil-water-oil) in a capillary tube is proposed. A water plug/droplet was introduced into kerosene oil and pushed forwarded under a constant pressure. Water droplet adhesion to the glass capillary wall was observed and the dynamic changes of interfacial liquid film thickness were visualized and measured against different capillary numbers by using light absorption techniques utilizing high speed CCD camera and Beer-Lambert law. The mean film propagation velocity was measured by micro resolution particle image velocimetry (μPIV). The experimental results show the film thickness against the capillary number at certain cross-section obeys a power law. The measured velocity can also be used to demonstrate the liquid film break up processes. Furthermore, a ripple pattern film thickness was presented when a long annual water film was formed.