Water Movement in Various Shapes of Tube Under Microgravity.

Water movement under microgravity plays an important role in various scenes of space missions, such as developing life support systems growing crops. Capillary force may be a major driving force for water movement in porous media under microgravity. Previous study reports that the difficulty of water movement on the concave of particle surfaces under microgravity. Our objective of this study was revealing the concave and convex effects on water movement driven by capillary force under microgravity. Water movement in five different shapes (straight, bumpy, curved, narrow-wide, and wide-narrow) of tubes was observed under microgravity made by a free-fall tower. The straight, bumpy, and curved tubes were also compared with different diameters (0.8, 1.2, and 5.5 mm in diameter) of the tubes. Water in all the shapes of tubes moved upward to the end of the tubes under microgravity, except in the narrow-wide shape of tube. In the narrow-wide shape tubes, water moved up to a joint where tube diameters changed. Water did not go beyond the sharp concave surface observed in the narrow-wide shape tubes, but moved on the blunt concave surface or on any convex surfaces observed in the bumpy, curved and wide-narrow tubes. We also observed that water moved faster in the narrow part than in the wide part in the bumpy shape tubes.