An Investigation into Microgravity Capillary Two-Phase Flows Regarding Passive Bubble Dynamics

Spacecraft fluid systems require unique considerations to function effectively in microgravity. An open wedge channel can passively separate bubbles from two-phase flows, mimicking the role of buoyancy on Earth. For large bubbles, or those that merge within the channel, capillary forces drive them upwards and outwards, allowing them to coalesce and escape through the free surface. In low-gravity environments, smaller bubbles tend to follow paths along their inscribed elevations rather than leaving the liquid. These 'unseparated' bubbles can lead to downstream pump failure, cavitation, flow instabilities, and other adverse effects in spacecraft fluid systems. Understanding these mechanisms is crucial for reliable passive capillary fluid management in space applications, such as liquid fuel and propellant transport, thermal fluid circulation, water recycling, and plant watering systems.

The DLR and NASA Capillary Channel Flow (CCF) experiment on the International Space Station has provided a valuable database on these phenomena. Utilizing this resource, we aim to benchmark our numerical study of zero-gravity bubbly two-phase flow in open wedge channels, focusing on the interplay of Saffman lift and the Magnus effect on bubble motion. Our findings are expected to guide the development of more robust passive phase separation methods for spacecraft plumbing systems.