Transient Capillary Channel Flow Stability - Experiments on the International Space Station

Abstract

Capillary techniques with free surfaces provide very reliable means for liquid management in space. However, capillary channel flow is subject to limitations due to surface instability. Steady flow rate limitation is well understood and provides the basis for a new generic model for critical flow acceleration. The transient stability model is defined by liquid and geometrical properties and is therefore very easy to use. Due to the aggregate of steady and transient flow, the critical flow rate and the critical acceleration are inversely proportional. In 2011, experiments were performed in cooperation with NASA on the International Space Station (ISS) to confirm the model for steady flow and validate the new transient model. A new phenomenon is discussed, the flexibility effect, based on internal liquid relocation. It provides significant additional transient stability for channels of sufficient length. Effects caused by liquid re-circulation in the experimental setup are considered by a model for the feedback ratio.