Control of capillary driven fluid flows for safe operation of spacecraft fluid supply systems using artificial porous media

Abstract

In weightlessness, capillary forces become the main driving forces in the flow of liquids. Fuel supply of engines being started in weightlessness, water supply to life support systems in habitable modules, heat exchange using capillary pumps – all those processes rely heavily on capillary forces. Thus, safety and reliability of Space mission strongly depends on our skills in controlling capillary driven fluid flows. Adequate mathematical models for predicting capillary driven imbibition in artificial porous specimens are needed. The paper discusses the features of the flow of liquids through a porous medium under the action of capillary forces under microgravity conditions. An important feature of such flows is the hysteresis effect: in the case of multiple imbibition of a porous medium, the liquid flows in different ways through the dry medium and through the medium moistened in the process of previous imbibitions. This effect is observed during experiments on repeated imbibition of an artificial porous medium during parabolic flights of an Airbus A300-ZeroG aircraft organized by the European Space Agency. With each subsequent parabola, the liquid rises to a greater height. Modeling such processes requires special mathematical models described in this work. Comparison of the results of numerical modeling and experimental data provides a unique opportunity to choose empirical constants on an experimental basis thus developing a robust tool for predicting fluid behavior in hydraulic loops of Space vehicles.