A microgravity experiment of the on-orbit fluid transfer technique using swirl flow.

The cryogenic fluid transfer technique will prove useful for flexible and low-cost space activities by prolonging the life cycle of satellites, orbital transfer vehicles, and orbital telescopes that employ cryogenic fluids, such as reactants, coolants, and propellants. Although NASA has conducted extensive research on this technique to date, a complicated mechanism is required to control the pressure in the receiver tank and avoid a large liquid loss by vaporization. We have proposed a novel fluid transfer method by using swirl flow combined with vapor condensation facilitated by spray cooling. This technique enables gas-liquid separation in microgravity and effectively facilitates vapor condensation without any special device like a mixer. In addition, since the incoming liquid flows along the tank wall, the tank wall would be cooled effectively, thereby minimizing the liquid loss due to vaporization. In this paper, the influence of the number of inlet points, fluid velocity at the inlet, fluid type, and boiling condition on swirl flow under microgravity conditions is investigated experimentally. The results indicated that the new fluid transfer technique using the swirl flow proposed by us is effective for cryogenic fluids that generally exhibit low surface tension and good wettability. In addition, it is possible to apply this technique to the real system because the swirl flow conditions are determined by the Froude number, which is dimensionless. Thus, the fundamental technique of fluid transfer by using the swirl flow under microgravity conditions was established.