Assessment of Directions in Microgravity and Physical Sciences Research at NASA (2003) / Chapter Skim
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2. Fluid Physics Research Program
2. Fluid Physics Research Program
Pages 15-27
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From page 15... ...
The motivation for investigating fluid behavior under the unique conditions afforded by NASA's microgravity facilities is the desire to further the understanding of the complex behavior of fluids by taking advantage of near-weightless conditions to make measurements and observations that are not possible in terrestrial laboratories and, thereby, study physical phenomena typically overwhelmed by buoyant convection. Many problems that occur due to the effects of buoyancy, sedimentation, hydrostatic pressure gradients, or limitations due to the small length scales of interracial processes under normal gravity conditions can be avoided in microgravity.
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From page 16... ...
of the program, and their impact is then discussed. FLUID PHYSICS RESEARCH: SELECTED EXAMPLES Thermocapillary Phenomena Thermocapillarity is the variation of a liquid's surface tension (or of the interracial tension between two immiscible liquids)
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From page 17... ...
Colloidal phase diagrams, growth kinetics, and physical properties obtained from flight experiments and supporting ground-based research will yield information that will facilitate the use of colloidal precursors to fabricate novel materials. Flight experiments flown between 1996 and 1998 involved monodisperse hard-sphere colloids, binary colloidal alloys, and colloid-polymer mixtures; they have produced rich and in some cases unexpected results, such as coarsening during crystallization (Cheng et al., 2002~.
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From page 18... ...
Their results agreed with a theoretical model of damped dust acoustic waves, ignoring strong coupling, but not with a strongly coupled dust-lattice wave model. Complex fluid rheology is an emerging research area that promises to take advantage of low-gravity conditions to isolate particular aspects of fluid rheology.
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From page 19... ...
However, results obtained in low-gravity drop facilities and aircraft have been contradictory, with some data showing that pool boiling heat fluxes were insensitive to changes in gravity level, and other data suggesting that heat-transfer rates are enhanced in low-gravity conditions. A significant unknown in the prediction and application of flow boiling heat transfer in microgravity is the upper limit of the heat flux for the onset of dryout (or critical heat flux)
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From page 20... ...
(Marangoni instability of a static fluid state occurs when flow arises due to surface tension gradients caused when an initially flat isothermal surface deforms to a non-planar non-isothermal surface.) Thermocapillary flow research, originally motivated by problems in crystal growth techniques, has been undertaken outside NASA's program and adapted to other technologies.
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From page 21... ...
Furthermore, 4 of the fluid physics program's investigators are members of the National Academy of Sciences, 8 are National Academy of Engineering members, and there were 37 fellows of the American Physical Society, 5 fellows of the American Society of Mechanical Engineers, and 12 fellows of the American Institute of Aeronautics and Astronautics. 1 a, FUTURE DIRECTIONS IN FLUID PHYSICS RESEARCH Fluid physics should continue to serve a dual purpose in NASA's physical sciences research program.
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From page 22... ...
the identification of low-gravity flow regimes, the mechanisms that govern the effects of gravity, and interracial and bulk constitutive laws for specific flow regimes through experiments and the synergistic development of computermodeling capabilities; (2) assessment of the effects of gravity on forced convective boiling, two-phase forced convective heat transfer, and convective condensation heat-transfer; (3)
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From page 23... ...
Complex Fluid Rheology The fluid physics program has already initiated research on the theological behavior of other complex fluids, such as the particle dynamics and segregation flows of dry granular materials, or magnetorheological fluids. Preliminary results are promising, and these studies should be continued.
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and to many related terrestrial applications. Biofluid Dynamics and Related Interdisciplinary Research New synergies gained from using the insight and techniques of fluid physics and transport phenomena in the world of biological sciences hold considerable promise.
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2000. The electrohydrodynamic stability of a liquid bridge: Microgravity experiments on a bridge suspended in a dielectric gas.
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2000. Microgravity experiments and analysis of oscillatory thermocapillary flows in cylindrical containers.
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From page 27... ...
1995. Boiling heat transfer in the quenching of a hot tube under microgravity.
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