NASA - National Aeronautics and Space Administration

ISS Science Officer, Mike Fincke in the U.S. Lab during Expedition 9 next to CFE-CL2. (NASA Image: ISS009E23445) What was done on ISS: Controlling the flow of fluids in the absence of gravity is a challenge for designing spacecraft liquid propellant, water and recycling systems. In space, liquids can climb container walls, making it hard to empty containers, measure the contents of storage vessels, and obtain consistent performance in devices where liquids and vapor mix.

The Capillary Flow Experiment (CFE), led by Dr. Mark Weislogel of Portland State University, is a suite of fluid physics experiments whose purpose is to investigate capillary flows and phenomena in low gravity. CFE tests were operated during ISS Expeditions 9 through 16 (August 2004 – December 2007). Each experiment recorded the behavior of fluid in containers with different geometries and under different conditions to test how fluids flow in microgravity. Results of the capillary flow investigations are still being published. Initial results have shown the value of the apparatus as a benchmark for computational fluid dynamics models [1].

View of Capillary Flow Experiment (CFE) in the U.S. Laboratory/Destiny, 2007. (NASA image: ISS015E10587) Significance: The CFE data will be crucial to future space exploration because they provide a foundation for physical models of fluids management in microgravity, including fuel tanks and cryogenic storage systems (e.g., water recycling) and materials processing in the liquid state. Under low-gravity conditions, capillary forces can be exploited to control fluid orientation so that such large mission-critical systems perform predictably. Specific applications of the results center on particular fluids challenges concerning propellant tanks. The knowledge gained will help spacecraft fluid systems designers increase system reliability, decrease system mass, and reduce overall system complexity [2,3,4,5].

The results of the flight experiments are also expected to provide insights into terrestrial interfacial phenomena and ongoing work is expected to develop models predicting fluid flows in porous media (i.e. ground water transport), complex capillary structures (i.e. high performance wicks for heat pipes employed in electronics cooling), and Lab-On-Chip technologies (i.e., microscale biofluids processing). Three patents related to CFE research have been filed so far, including a microgravity condensing heat exchanger, a capillary-based static phase separator for highly variable wetting conditions, and even a low-gravity coffee cup.

[1] Jenson R, Weislogel M, Chen Y, Tavan N, and Bunnell C. 2009. The Capillary Flow Experiments Aboard the International Space Station: Increments 9-15, 8/2004-12/2007. Tech. Rep. NASA/CR-2009-215586, in preparation. [2] Jenson R, Weislogel M, Klatte J, and Dreyer M. 2009. Dynamic Interface and Contact Line Experiments Aboard ISS: a Database for Spacecraft Numerical Benchmarks. AIAA J., in final Preparation. [3] Weislogel, M., Thomas, E., and Graf, J. August 2008a. A Novel Device Addressing Design Challenges for Passive Fluid Phase Separations Aboard Spacecraft. J. Microgravity Sci. Technol. p. 1-12. [4] Weislogel M, Chen Y, Bolleddula D. A Better Non-Dimensionalization Scheme for Slender Flows: The Laplacian Operator Scaling Method. 2008b. Phys. Fluids, 20(9): 1-7. [5] Weislogel M, Jenson R, Chen Y, Collicott S, Klatte J, Dreyer M. 2009; in press. The Capillary Flow Experiments Aboard the International Space Station: Status. Acta Astronautica.

More Information
http://www.nasa.gov/mission_pages/station/science/experiments/CFE.html

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