Capillary channel flow experiments aboard the International Space Station

Abstract

The forced flow of liquid through an open capillary channel consisting of two parallel plates is studied in the microgravity environment aboard the International Space Station. The two free surfaces of the open conduit deform only slightly in what is termed the subcritical flow regime. However, as flow rates are increased a critical condition is observed above which the free surface collapses ingesting gas into the channel following an imbalance of local hydrodynamic and capillary pressures. The focus of the present article is the steady subcritical flow regime where the free surface resists the inward suction caused by the accelerating liquid. The experimental data collected is compared to predictions based on a one-dimensional model that accounts for the hydrodynamic and capillary pressures as well as local momentum losses. Favorable agreement is obtained between experiment and theory adding increased design capabilities for the prediction of important rate limiting flow conditions.