From: Microgravity Research Program Office
Posted: Thursday, July 18, 2002
Physical Sciences Division
Weekly Highlights for Week Ending 7/18/2002
*** Indicates item is appropriate for the HQ senior staff and may appear on the OBPR Web site: http://spaceresearch.nasa.gov
EDUCATION and OUTREACH
Berkeley University and the Chicago School District are collaborating with the SETI Institute (providing physics and math high school students) to conduct GAS can experiments on Shuttle for Electrostatics of Granular Materials (EGM) experiment. Fluid Physics PI Dr. John Marshall (SETI Institute) has been assisting the students design shuttle experiments. The experiments will try to address the major issue of control experimentation by looking at the pure dipole case using magnets. The experiment will use tiny magnetic spheres in a dilute suspension --similar to EGM concepts, and also large magnetic spheres suspended in a viscous liquid in microgravity. The large spheres will have their north and south pole hemispheres painted black and white so that motion can be easily tracked. The students have conducted ground experiments with spherical magnets and found that they produce chains (like electrostatic dipoles), but also rings (closure of the chain ends). The latter has not been observed in USML filamentary structures, suggesting that either the two-dimensionality of the experiments, or the "purity" of the dipoles (unmasked from monopole effects) is the reason for this finding.
POROUS GRAPHITE COMBUSTION EXPERIMENT: The objective to this research, led by Prof. H. Chelliah of University of Virginia, is to experimentally determine the oxidation rates, flame stand-off distances, and surface temperatures of a variety of porous, carbonaceous particles as they burn in microgravity to help further develop a detailed numerical model. This research is significant in understanding the details of the coal burning process which occurs by a two-stage combustion of small, porous particles, namely, rapid pyrolysis followed by slow char oxidation. The goal of achieving self-sustained particle combustion is now accomplished by three factors; (a) laser drilled particles (1mm glassy carbon spheres with roughly 75 micron drilled holes), (b) suspension of the particles using alumina (Al2O3) fibers, and (c) use of air enriched with oxygen, up to about 60%. Silicon carbide (SiC) fibers, which were used until recently, did not survive the hot, enriched oxygen conditions. Alumina fibers, with a lower reported melting point than SiC, were able to hold the particle in place up to about 15 s. Two KC-135 campaigns were recently completed at NASA Glenn employing for the first time enriched oxygen in microgravity tests. Particle oxidation rates for 60, 65, and 70% oxygen were obtained. Below 60% the particles extinguished. Temperatures were successfully measured with the spectrometer, and showed oxidation temperatures of around 2100 K for self-sustained combustion (the laser was used only for ignition and then turned off). A significant difference between 1g and µg oxidation rates was found, with the microgravity case burning more slowly. These data are now ready to be compared to the numerical model.
DETECTING ONSET OF FIRE IN AIRCRAFT BY EMPLOYING CORRELATION SPECTROSCOPY: This effort is a Small Business Innovation Research (SBIR) Phase II project led by Dr. Kisholoy Goswami of Intelligent Optical Systems, Inc. The objective is the development of fiber-optic based sensors employing correlation spectroscopy for the sensitive detection of marker species indicative of cabin fires. The technique uses Fiber Bragg Gratings (FBGs) to simulate the spectra of marker species and provide the reference for correlation with observed spectra in the probe region. Though submitted to the Aviation Safety subtopic this project is of value to spacecraft fire safety as well. The Principal Investigator recently constructed an FBG modulator which allows tuning the grating to within 5 nm, and also constructed an Erbium-doped fiber laser suitable for detection of CO spectral lines. Four laser lines were selected for CO detection. A multipass cell was constructed for testing the optical system, and using this cell, CO was detected originally at 250 ppm without using modulation or lock-in detection. More recently, the PI used this fiber laser with several different FBGs of varying reflection/transmission ratios and bandwidths. An optimal combination of properties was determined, which now allowed CO detection in a multi-pass cell at about 100 ppm. The findings of this correlation spectroscopy work for fire sensors is published in the July 2002 issue of NASA Tech Briefs. (
FLUID PHYSICS RESEARCH MAY HELP HARNESS FUSION ENERGY: The research work of Fluid Physics PI Prof. Jeffrey Jacobs was recently featured in the periodical Arizona Engineer 225 (1), 8 (Spring 2002). For the past six years, Prof. Jacobs and Dr. Charles Niederhaus, now a NASA GRC employee, have been studying the phenomenon known as the Richtmyer-Meshkov instability, which is closely related to the more well known Rayleigh-Taylor instability. These instabilities have long thwarted scientists attempts to harness the phenomenon of nuclear fusion in a manner that could be used to produce useful energy. For the past several years, Jacobs and Niederhaus have used a small drop tower to study the instabilities in moderate scale fluids experiments. In the near future, they will extend these experiments to the GRC 2.2-Second Drop Tower and the KC-135. These relatively large scale experiments serve as analogs to the microscale fusion phenomenon. Results from this work will help the nuclear scientists validate computer codes that model fusion. "They can take our data and compare it to their computer simulations to see if they get the same results that we get experimentally," Jacobs says. "It's important for them to determine whether their simulations accurately model these turbulent flows."
FINITE-WEBER-NUMBER MOTION OF BUBBLES THROUGH A NEARLY INVISCID LIQUID: Fluid Physics PI Prof. Sangani (Syracuse) and his colleagues describe a numerical method for simulating the motion of finite-Weber-number potential flow induced by the motion of bubbles. The method uses ellipsoidal harmonics to represent the shape of the bubbles and the velocity induced by the bubbles together with an O(N) algorithm for computing flows induced by a distant group of bubbles. The method is applied to study several problems involving one, two, or many bubbles. The results obtained would be useful in establishing an analytical framework for developing equations of motion of finite-Weber-number bubbly liquids. [Volodymyr I. Kushch , Ashok S. Sangani ,Peter D. M. Spelt and Donald L. Koch, "Finite-Weber-number motion of bubbles through a nearly inviscid liquid," J. Fluid Mech. (2002), vol. 460, pp. 241-280.
EFFECT OF INTERFACIAL PHENOMENA ON A CONDENSING SESSILE DROPLET:
Fluid Physics PI Prof. Wayner (RPI) and his colleagues presented an overview of complementary experimental and theoretical procedures to determine the effect of interfacial phenomena on phase change heat transfer at The Third International Conference on Transport Phenomena in a Multiphase System, Kielce, Poland, June 24 - 27, 2002. Interfacial effects on the processes of evaporation or condensation have been researched using a Kelvin-Clapeyron (KC) model based on the Gibbs-Duhem equation. The pressure field in the liquid film is obtained from the optically measurable thickness profile using the extended Young-Laplace equation, whereas the temperature field is related to the phase change flux and the pressure field using the KC model. Additional models based on both the polar and apolar components of the excess free energy have been developed to relate the measurable changes in the contact angle and profile to the interfacial pressure jump (capillary and disjoining pressures), the spreading coefficient, and the adsorbed thin film thickness. [Wayner, P. C., Jr., "Effect of Interfacial Phenomena on a Condensing Sessile Droplet", The Third International Conference on Transport Phenomena in a Multiphase System, Kielce, Poland, June 24 - 27, 2002.]
Additional meetings and symposia can be found at: http://microgravity.grc.nasa.gov/ugml/ugmltext.htm
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