Angular Liquid Bridge Experiment (ALB) - MGBX

ALB Wedge Vessel ALB Wedge Vessel

Objectives

The objective of this experiment is to explore the behavior of liquid-vapor interfaces in a low-gravity environment, by comparing experimental with mathematical results that predict major shifts of liquid with small changes in container configuration or in contact angle. The particular configurations investigated were those of a liquid between parallel and tilted plates.

Shuttle-Mir Missions
NASA-4

Approach
Two test vessels were flown: The Movable Wedge Vessel and the Angular Liquid Bridge Vessel. Both vessels were constructed largely of acrylic plastic with aluminum fittings. Liquid drops were deployed on the plate surfaces by the crewmember, in some cases after a fluoropolymer coating to achieve the desired wetting properties had been applied. Intersection angles between the plates were varied, and the liquid behavior was recorded on videotape, along with verbal comments by the crewmember.

Results
The on-board procedures for applying coating to the plates worked successfully to achieve desired contact angles. Essentially all drops were deployed in a controlled fashion and exhibited a high degree of symmetry, despite drop sizes with diameters as large as 20 mm. Nevertheless, sufficient time to overcome hysteresis was not always allowed and additionally vessel tapping was not always introduced to initiate drop reorientation, so that the information obtained on drop transitions between the various configurations was incomplete.

More than the 12 planned drops were deployed for liquid bridge formation and study. Bridge extension and rupture were studied as a function of plate tilt angle and initial condition. Multiple tests could be performed, as ruptured bridges could be readily reformed. Stable bridge, edge blob, and corner flow configurations were observed, as anticipated from the underlying mathematical theory. Critical angles at points where the fluid changed configurations were quantified by means of video recordings of a protractor scale.

Contact angle measurements for the various drops studied reveal that equilibrium contact angles did not change over the course of the approximately 4 month stowage time and the 6 hours of inflight testing. Contact angles for the distilled water fluid on the freshly fluoropolymer coated surfaces were measured between 105 and 116 degrees. The spread of values is attributable to contact angle hysteresis; measurements from the video footage on tests performed prior to the angular liquid bridge formation and following the bridge rupture experiments revealed no significant changes in these values. Such a change would have signaled the presence of contamination of either the test fluid, or test surfaces, or both. The drops were deployed in a controlled fashion and exhibited a high degree of symmetry despite the large drop sizes. Data from orthogonal views are currently being collected for the quantitative behavior of the angular liquid bridges as a function of plate spacing, test procedure, and test fluid. A detailed report of the results from ALB awaits complete analysis of the data.

The procedure employed for on-board coating of the plates is effective and can be a useful tool for other space experiments. The experiment suffered, however, from lack of availability from Mir for communication between the ground-based investigators and the crewmember during the course of the experiment.

Earth Benefits
Liquids behave differently in microgravity than they do on the ground. The problem is that the position and shape of liquids in container is not as predictable as on the ground. This makes it difficult to design liquid fuel systems for space vehicles. By understanding how liquids take shape between solid surfaces, scientists and engineers can build better fluid systems. Better knowledge of liquid surface forces can be applied to situations where surface forces predominate over gravitational forces such as in pore spaces of granular materials like rocks.

Publications
P. Concus and R. Finn, Discontinuous behavior of liquids between parallel and tilted plates, Phys. Fluids, 10 (1998), pp. 39-43.

P. Concus, R. Finn, and J. McCuan, A discontinuous dependence of liquid bridge configurations, Preprint PAM727, Center for Pure and Applied Mathematics, Univ. California, Berkeley, 1998, submitted Zeit. Anal. Anwend.

R. Finn, J-T. Chen, and E. Miersemann, Capillary surfaces in wedge domains: behavior at the vertex, continuity and discontinuity, asymptotic expansions, Univ. Leipzig preprint, 1998, submitted to J. Math. Pures Appl.

R. Finn and J. McCuan, Vertex theorems for capillary drops on support planes, MSRI preprint 1997-077, to appear in Mathematische Nachrichten.

Principal Investigators
Paul Concus
University of California at Berkeley

Co-Investigators
Robert Finn
Mark Weislogel

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