An experimental characterization of capillary driven flows in microgravity

This work investigates the capillary rise dynamics of highly wetting liquids in a divergent U-tube in the microgravity conditions provided by 78th European Space Agency (ESA) parabolic flight. This configuration produces a capillary-driven channel flow. We use image recording in backlight illumination to characterize the interface dynamics and dynamic contact angle of HFE7200 and Di-Propylene Glycol (DPG). For the case of HF7200, we complement the interface measurements with Particle Tracking Velocimetry (PTV) to characterize the velocity fields underneath the moving meniscus. In the experiments with DPG, the liquid column reaches different heights within various experiments, and the measurements show a sharp reduction of the meniscus curvature when the contact line moves from a pre-wet to a dry substrate. In experiments with HFE7200, the interface always moves on a pre-wet surface. Yet a curvature reduction is observed due to the inertial forces on the underlying accelerating flow. The PTV measurements show that the distance from the interface within which the velocity profile adapts to the meniscus velocity shortens as the interface acceleration increases.