NASA - National Aeronautics and Space Administration

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Experiment Overview


Brief Summary

Capillary Flow Experiments - 2 (CFE-2) is a suite of fluid physics experiments that investigates how fluids move up surfaces in microgravity. The results aim to improve current computer models that are used by designers of low gravity fluid systems and may improve fluid transfer systems for water on future spacecraft.

Principal Investigator(s)

Mark Milton Weislogel, Ph.D., Portland State University, Portland, OR, United States

Co-Investigator(s)/Collaborator(s)

Steven H. Collicott, Ph.D., Purdue University, West Lafayette, IN, United States

Yongkang Chen, Ph.D., Portland State University, Portland, OR, United States

Developer(s)

ZIN Technologies Incorporated, Cleveland, OH, United States

Sponsoring Space Agency

National Aeronautics and Space Administration (NASA)

Sponsoring Organization

Human Exploration and Operations Mission Directorate (HEOMD)

Research Benefits

Information Pending

ISS Expedition Duration:

September 2010 - September 2014

Expeditions Assigned

25/26,27/28,29/30,31/32,35/36,37/38,39/40

Previous ISS Missions

The first generation CFE operated during Increments 9, and 11-15.

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Experiment Description

Research Overview

• Wetting describes how well a liquid spreads across a surface. Understanding how wetting happens in microgravity is important for a wide variety of engineering systems being developed for human spaceflight.



• Studies from CFE-2 may serve to demonstrate how liquids can be separated from gas in the absence of gravity. This is a key procedure for water purification systems in microgravity.

Description

The primary objective of Vane Gap experiments is to determine equilibrium interface configurations and critical wetting conditions for interfaces between interior corners separated by a gap. Secondary objectives are to determine critical wetting transient as well as to validate numerical predictions of the large length scale discontinuous or near discontinuous wetting phenomena.

The Vane Gap (VG) experiment identifies a fundamental wetting condition akin to the critical corner wetting condition identified by Concus and Finn (1969), but for interior corners formed by walls that possess a gap at the virtual axis of intersection of the two planar ?walls? (i.e., vanes). Such a ?wall-vane gap? is common in spacecraft systems, but is treated as an ideal corner. The Capillary Flow Experiment (CFE) involves many studies centered around a phenomenon called wetting. Wetting describes the ability for a liquid to spread across a surface. The original CFE tests were highly successful at uncovering the dynamics of wetting in microgravity. Capillary Flow Experiments -2 (CFE-2) determines the critical wetting conditions for screens and perforated plates for perfectly wetting fluids. The impact of such ?porous substrates? has immediate implications to the design of passive geometries to manage highly wetting fuels, cryogens, thermal fluids, and contaminated aqueous solutions for urine processing. The unique vane gap critical wetting phenomena is greatly complicated by the presence of three-dimensional (3-D) porous walls.

The Interior Corner Flow (ICF) experiment determines the rates of 3-D inhibition of wetting fluids in complex containers, the dependence of the dynamical boundary conditions as a function of geometry, and the performance of such devices as passive phase (i.e., bubble) separators. The ICF experiments are designed to benchmark the analytical technique developed to predict such flows. The benchmark theory aids in the design and analysis of capillary devices for positioning liquids passively in containers in microgravity environments by controlling the container geometry. The devices are useful in passive phase separation operations such as in the case of tapered screen galleries for bubble-free collection and positioning of fuels for satellites, to address propellant management aboard spacecraft. Spontaneous capillary flows in containers of increasing complexity such as ICF determine critical transients for low-g propellant management.

The objective of the Capillary Structure (CS) experiment is to add another critical dimension of complexity, interconnectivity, to the ICF experiments. Liquid bearing containers can easily be interconnected by capillary structures. The crew studies the time dependent flows as functions of unit cell dimensions and geometry, unit cell interconnectivity, overall structure dimensions and taper. They also investigate passive phase separation characteristics of such construct. Capillary Structures studies full 3-D wicking at micro-scales. The flows incorporate 3-D capillary driven corner flow networks consisting of a matrix of interconnected pores.

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Applications

Space Applications

Capillary resulting phenomena include critical wetting in discontinuous structures, and capillary flow in complex containers. Specific applications of these results center on particular fluid challenges concerning the storage, transport, and processing of liquids in space. The knowledge assists spacecraft fluid systems designers in increasing system reliability, decreasing system mass, and reducing overall complexity.

Earth Applications

Technologies utilizing capillary flow transfer to Earth for devices with small length scales where capillary forces exceed gravity forces. CFE results are also being considered for improving fluid flow in miniaturized biological devices used for health screening and analysis; this class of devices is often referred to as ?lab-on-a-chip?. In addition, several of the CFE-2 vessels have test chamber geometries that mimic the geometries of ideal pores. The science from these units will provide a more fundamental understanding of capillary effects in porous materials and water uptake in soils.

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Operations

Operational Requirements

Vane Gap - Unimpeded imaging of a fluid interface in right elliptical cylindrical containers following the rotation of a planar vane along the axis of the cylinder is required.

Interior Corner Flow - Unimpeded imaging of a variety of transient capillary driven flows in variously tapered containers and container cross sections is required. The capillary transport of liquid throughout the containers will be compared to theoretical predictions.

Capillary Structures ? Unimpeded imaging of a variety of transient capillary driven flows in a 3-D macro-porous capillary structure is required.

Operational Protocols

The CFE-2 test vessels use similar fluid injection hardware, have simple and similarly sized reservoir chambers, and rely on video for highly quantitative data. The 1-2kg test vessels require no power and are mounted to the maintenance work area where video imaging records the experimental tests.

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Results/More Information

The primary objective of Vane Gap experiments is to determine equilibrium interface configurations and critical wetting conditions for interfaces between interior corners separated by a gap. Secondary objectives are to determine critical wetting transient as well as to validate numerical predictions of the large length scale discontinuous or near discontinuous wetting phenomena.

The Vane Gap (VG) experiment identifies a fundamental wetting condition akin to the critical corner wetting condition identified by Concus and Finn (1969), but for interior corners formed by walls that possess a gap at the virtual axis of intersection of the two planar walls(i.e., vanes). Such a "wall-vane gap" is common in spacecraft systems, but is treated as an ideal corner. The Capillary Flow Experiment (CFE) involves many studies centered around a phenomenon called wetting. Wetting describes the ability for a liquid to spread across a surface. The original CFE tests were highly successful at uncovering the dynamics of wetting in microgravity. Capillary Flow Experiments -2 (CFE-2) determines the critical wetting conditions for screens and perforated plates for perfectly wetting fluids. The impact of such porous substrateshas immediate implications to the design of passive geometries to manage highly wetting fuels, cryogens, thermal fluids, and contaminated aqueous solutions for urine processing. The unique vane gap critical wetting phenomena is greatly complicated by the presence of three-dimensional (3-D) porous walls.

The Interior Corner Flow (ICF) experiment determines the rates of 3-D inhibition of wetting fluids in complex containers, the dependence of the dynamical boundary conditions as a function of geometry, and the performance of such devices as passive phase (i.e., bubble) separators. The ICF experiments are designed to benchmark the analytical technique developed to predict such flows. The benchmark theory aids in the design and analysis of capillary devices for positioning liquids passively in containers in microgravity environments by controlling the container geometry. The devices are useful in passive phase separation operations such as in the case of tapered screen galleries for bubble-free collection and positioning of fuels for satellites, to address propellant management aboard spacecraft. Spontaneous capillary flows in containers of increasing complexity such as ICF determine critical transients for low-g propellant management.

The objective of the Capillary Structure (CS) experiment is to add another critical dimension of complexity, interconnectivity, to the ICF experiments. Liquid bearing containers can easily be interconnected by capillary structures. The crew studies the time dependent flows as functions of unit cell dimensions and geometry, unit cell interconnectivity, overall structure dimensions and taper. They also investigate passive phase separation characteristics of such construct. Capillary Structures studies full 3-D wicking at micro-scales. The flows incorporate 3-D capillary driven corner flow networks consisting of a matrix of interconnected pores.

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Results Publications

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Ground Based Results Publications

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ISS Patents

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Related Publications

Dreyer M, Weislogel MM, C.  Parametric Regimes for low-g Fluids Transport, Habitation. Habitation: International Journal for Human Support Research. 2006; 10(3-4): 233.

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Related Websites

ISS Research Project-CFE-2

ME Faculty

PSU soars with zero gravity research

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Imagery

NASA Image ISS0026E01793 A close-up view of the Capillary Flow Experiments-2 Vane Gap-1 (CFE-2 VG1) vessel mounted on the Maintenance Work Area (or MWA). Perforated vane is in a 180 deg position and the test fluid (silicone oil with red dye) can be seen in the test chamber on left. Digital "egg" timer is used to time stamp the video science data. Picture courtesy of NASA John H. Glenn Research Center.
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NASA Image ISS026E017298 NASA astronaut Scott Kelly, Expedition 26 commander, and the Capillary Flow Experiments-2 Vane Gap-1 (CFE-2 VG1) after Scott has completed setup on the Maintenance Work Area (MWA). A High Definition (HD) camera, seen on right in foreground, is used to record video image data, the primary science data for this experiment. Picture courtesy of NASA John H. Glenn Research Center.
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NASA Image: ISS026E018760 - NASA astronaut Catherine (Cady) Coleman, Expedition 26 flight engineer, performs a Capillary Flow Experiment (CFE) Interior Corner Flow 2 (ICF-2) test. The CFE is positioned on a Maintenance Work Area in the Destiny laboratory of the International Space Station. CFE observes the flow of fluid, in particular capillary phenomena, in microgravity.
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The primary science goal for the Vane Gap (VG) experiments is to find the critical wetting angles at which fluid wicks up the edges of a perforated vane. An unexpected phenomenon (seen above) occurs when the perforations are filled prior to the running of the experiment. A bulk shift of the fluid is easily identified when the perforations are filled, and stands out distinctly when compared to the relative symmetry of a test run with un-filled perforations. Image courtesy of Mark Weislogel .
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NASA Image: ISS029E015122 - Expedition 29 Commander Mike Fossum is conducting the first operation on CFE (Capillary Flow Experiments) with the VG2 (Vane Gap 2) vessel,monitored from the ground on live video via MPC (Multi Protocol Converter) and Ku-band. The VG2 is on the work station in front of him. In this photo Fossum is performing the Dry Surface Test.
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