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All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Combustion Stages of a Single Heavy Oil Droplet in Microgravity

Heavy oil is a common fuel for industrial furnaces, boilers, marines and diesel engines. Previous studies showed that the combustion of heavy oil involves not only the complete burning of volatile matters but also the burn-out of coke residues. Detailed knowledge about heavy oil combustion therefore requires an understanding of the different burning stages of heavy oil droplets in the burner. This in turn, demands knowledge about the single droplet evaporation and combustion characteristics. This study measured the temperature and size histories of heavy oil (C glass) droplets burning in microgravity to elucidate the various stages that occur during combustion. The elimination of the gravity-induced gas convection in microgravity allows the droplet combustion to be studied in greater detail. Noting that the compositions of heavy oil are various, we also tested the fuel blends of a diesel light oil (LO) and a heavy oil residue (HOR).

Ikegami, M.↗
NASA NTRS2001

Gas-Phase Combustion Synthesis of Nonoxide Nanoparticles in Microgravity

Gas-phase combustion synthesis is a promising process for creating nanoparticles for the growing nanostructure materials industry. The challenges that must be addressed are controlling particle size, preventing hard agglomerates, maintaining purity, and, if nonoxides are synthesized, protecting the particles from oxidation and/or hydrolysis during post-processing. Sodium-halide Flame Encapsulation (SFE) is a unique methodology for producing nonoxide nanoparticles that addresses these challenges. This flame synthesis process incorporates sodium and metal-halide chemistry, resulting in nanoparticles that are encapsulated in salt during the early stages of their growth in the flame. Salt encapsulation has been shown to allow control of particle size and morphology, while serving as an effective protective coating for preserving the purity of the core particles. Metals and compounds that have been produced using this technology include Al, W, Ti, TiB2, AlN, and composites of W-Ti and Al-AlN. Oxygen content in SFE synthesized nano- AlN has been measured by neutron activation analysis to be as low as 0.54wt.%, as compared to over 5wt.% for unprotected AlN of comparable size. The overall objective of this work is to study the SFE process and nano-encapsulation so that they can be used to produce novel and superior materials. SFE experiments in microgravity allow the study of flame and particle dynamics without the influence of buoyancy forces. Spherical sodium-halide flames are produced in microgravity by ejecting the halide from a spherical porous burner into a quiescent atmosphere of sodium vapor and argon. Experiments are performed in the 2.2 sec Drop Tower at the NASA-Glenn Research Center. Numerical models of the flame and particle dynamics were developed and are compared with the experimental results.

Axelbaum, R. L.↗
NASA NTRS2000

An Indirect Mixed-Sensitivity Approach to Microgravity Vibration Isolation: The Exploitation of Kinematic Coupling In Frequency-Weighting Design-Filter Selections

Many space science experiments need an active isolation system to provide them with the requisite microgravity environment. The isolation systems planned for use with the International Space Station have been appropriately modeled using relative position, relative velocity, and acceleration states. In theory, frequency design filters can be applied to these state-space models, in order to develop optimal H, or mixed-norm controllers with desired stability- and performance characteristics. In practice. however, the kinematic coupling among the various states can lead, through the associated frequency-weighting-filters, to conflicting demands on the Riccati design "machinery." The results can be numerically ill-conditioned regulator and estimator Riccati equations and/or reduced intuition in the design process. In addition, kinematic coupling can result in a redundancy in the demands imposed by the frequency weights. Failure properly to account for this type of coupling can lead to an unnecessary increase in controller dimensionality and, in turn, controller complexity. This paper suggests a rational approach to the assignment of frequency weighting design filters, in the presence of the kinematic coupling among states that exists in the microgravity vibration isolation problem.

Hampton, R. David↗
NASA NTRS1994

Capillary Movement of Liquid in Granular Beds in Microgravity

A more complete understanding of the dynamics of capillary flow through an g unsaturated porous medium would be useful for a number of space and terrestrial applications. One such application involves the development of an effective water and nutrient delivery system for the growth of plants in space. An experiment was conducted on the Mir Space Station that used an experimental cuvette called "Capillary Test Bed". An objective of this experiment was to compare fluid migration in the "Capillary Test Bed" under terrestrial laboratory simulated microgravity conditions by positioning the cuvette such that the hydrostatic force is negated and on Mir at microgravity conditions. Difference in fluid migration in the cuvette were observed. Based on these observations, improvements in the design of the cuvette are under-way that should allow for collection of more precise data in future flight experiments. The results of the MIR experiment and modifications being made to the cuvette for improved data collection will be discussed.

Yendeler, Boris S.↗
NASA NTRS2001

Absolute And Convective Instability and Splitting of a Liquid Jet at Microgravity

The objective is to establish a definitive role of the capillary, viscous, and inertial forces at a liquid-gas interface in the absence of gravity by using the fluid dynamics problem of the stability of a liquid jet as a vehicle. The objective is achieved by reexamining known theories and new theories that can be verified completely only in microgravity. The experiments performed in the microgravity facility at NASA Glenn Research Center enable the verification of the theory with experimental data. Of particular interest are (1) to capture for the first time the image of absolute instability, (2) to elucidate the fundamental difference in the physical mechanism of the drop and spray formation from a liquid jet, and (3) to find the origin of the newly discovered phenomenon of jet splitting on earth and in space.

Lin, S. P.↗
NASA NTRS2001

Astronaut-Induced Disturbances to the Microgravity Environment of the Mir Space Station

In preparation for the International Space Station, the Enhanced Dynamic Load Sensors Space Flight Experiment measured the forces and moments astronauts exerted on the Mir Space Station during their daily on-orbit activities to quantify the astronaut-induced disturbances to the microgravity environment during a long-duration space mission. An examination of video recordings of the astronauts moving in the modules and using the instrumented crew restraint and mobility load sensors led to the identification of several typical astronaut motions and the quantification or the associated forces and moments exerted on the spacecraft. For 2806 disturbances recorded by the foot restraints and hand-hold sensor, the highest force magnitude was 137 N. For about 96% of the time, the maximum force magnitude was below 60 N, and for about 99% of the time the maximum force magnitude was below 90 N. For 95% of the astronaut motions, the rms force level was below 9.0 N. It can be concluded that expected astronaut-induced loads from usual intravehicular activity are considerably less than previously thought and will not significantly disturb the microgravity environment.

Newman, Dava J.↗
NASA NTRS2001

Microgravity Science Glovebox Investigations SUBSA

Solidification Using a Baffle in Sealed Ampoules (SUBSA) is a Microgravity Science Glovebox Investigation manifested for the UF2 flight, on the U.S. Orbiter 111, to the International Space Station (ISS). SUBSA complements the "parent" flight investigation CG13 (Space-and Groundbased Crystal Growth Using a Baffle). During directional solidification, the disk-shaped baffle acts as a partition, creating a small melt zone at the solid-liquid interface. As a result, the level of buoyancy-driven convection at the interface is significantly reduced. In space, the baffle will reduce convection driven by residual micro acceleration. The baffle reduces the Rayleigh number (Ra) of the melt by a factor of 103. The combined effect of the baffle and microgravity will yield a reduction in Ra by a factor of 107 to 109 approaching effectively the acceleration conditions in "nanogravity". The results of ground based tests and numerical modeling will be presented. The furnace for directional solidification (flight hardware and the ground unit) was developed by Tec-Masters Inc. The flight ampoules were produced jointly at Rensselaer, Tec-Masters Inc. and Crystallod Inc.

Ostrogorsky, A.↗
NASA NTRS2001

Markstein Numbers of Negatively-Stretched Premixed Flames: Microgravity Measurements and Computations

The effect of flame stretch, composed of strain and curvature, plays a major role in the propagation of turbulent premixed flames. Although all forms of stretch (positive and negative) are present in turbulent conditions, little research has been focused on the stretch due to curvature. The present study quantifies the Markstein number (which characterizes the sensitivity of the flame propagation speed to the imposed stretch rate) for an inwardly-propagating flame (IPF). This flame is of interest because it is negatively stretched, and is subjected to curvature effects alone, without the competing effects of strain. In an extension of our previous work, microgravity experiments were run using a vortex-flame interaction to create a pocket of reactants surrounded by an IPF. Computations using the RUN-1DL code of Rogg were also performed in order to explain the measurements. It was found that the Markstein number of an inwardly-propagating flame, for both the microgravity experiment and the computations, is significantly larger than that of an outwardly-propagating flame. Further insight was gained by running the computations for the simplified (hypothetical) cases of one step chemistry, unity Lewis number, and negligible heat release. Results provide additional evidence that the Markstein numbers associated with strain and curvature have different values.

Ibarreta, Alfonso F.↗
NASA NTRS2001

Characterization and In-Situ Monitoring of ZnSe Crystal Growth by Seeded PVT for Microgravity Applications

Crystal growth from the vapor phase continues to play a significant role in the production of II-VI semiconductor compounds (ZnO, ZnTe, CdTe, etc.) and SiC. As compared to melt growth methods (where available) the advantages are: (1) lower growth temperature(s); (2) reduction in defect concentration; (3) additional purification; and (4) enhanced crystal perfection. A powerful tool in determining the mechanism of PVT is microgravity. Under normal gravity conditions the transport mechanism is a superposition of diffusive and convective fluxes. Microgravity offers the possibility of studying the transport properties without the influence of convective effects. Research on the crystal growth of ZnSe by PVT (P.I.: Su of NASA/MSFC) will help to clarify the effects of convection on crystal growth. A crystal growth furnace with in-situ and real time optical monitoring capabilities was constructed and used to monitor the vapor composition and growing crystal surface morphology during the PVT growth of ZnSe. Using photoluminescence and SIMS, ex-situ, the incorporation of point defects (Zn vacancy) and impurities was found to be correlated to the gravity vector due to the influence of the convective flow. A summary of the results to date will be presented.

Feth, Shari T.↗
NASA NTRS2001

Sooting Limits Of Microgravity Spherical Diffusion Flames

Limiting conditions for soot-particle inception were studied in microgravity spherical diffusion flames burning ethylene at atmospheric pressure. Nitrogen was supplied in the fuel and/or oxidizer to obtain the broadest range of stoichiometric mixture fraction. Both normal flames (oxygen in ambience) and inverted flames (fuel in ambience) were considered. Microgravity was obtained in the NASA Glenn 2.2-second drop tower. The flames were observed with a color video camera and sooting conditions were defined as conditions for which yellow emission was present throughout the duration of the drop. Sooting limit results were successfully correlated in terms of adiabatic flame temperature and stoichiometric mixture fraction. Soot free conditions were favored by increased stoichiometric mixture fractions. No statistically significant effect of convection direction on sooting limits was observed. The relationship between adiabatic flame temperature and stoichiometric mixture fraction at the sooting limits was found to be in qualitative agreement with a simple theory based on the assumption that soot inception can occur only where temperature and local C/O ratio exceed threshold values (circa 1250 K and 1, respectively).

Sunderland, P. B.↗
NASA NTRS2001

Radiation-Driven Flame Spread Over Thermally-Thick Fuels in Quiescent Microgravity Environments

Microgravity experiments on flame spread over thermally thick fuels were conducted using foam fuels to obtain low density and thermal conductivity, and thus large spread rate (Sf) compared to dense fuels such as PMMA. This scheme enabled meaningful results to lie obtained even in 2.2 second drop tower experiments. It was found that, in contrast conventional understanding; steady spread can occur over thick fuels in quiescent microgravity environments, especially when a radiatively active diluent gas such as CO2 is employed. This is proposed to be due to radiative transfer from the flame to the fuel surface. Additionally, the transition from thermally thick to thermally thin behavior with decreasing bed thickness is demonstrated.

Honda, Linton K.↗
NASA NTRS2000

The Burning of Large N-Heptane Droplets in Microgravity

Experimental results are presented on the burning and sooting behavior of large n-heptane droplets in air at atmospheric pressure under microgravity conditions. The experiments were performed at the Japanese Microgravity Center (JAMIC) 10 sec dropshaft in Hokkaido, Japan. Soot volume fraction, burning rate, flame standoff and luminosity were measured for droplets of 2.6 mm and 2.9 mm in initial diameter. These are the largest droplets for which soot volume fraction measurements have ever been performed. Previous measurements of soot volume fractions for n-heptane droplets, confined to smaller droplet sizes of less than 1.8 mm, indicated that maximum soot volume fraction increased monotonically with initial droplet size. The new results demonstrate for the first time that sooting tendency is reduced for large droplets as it has been speculated previously but never confirmed experimentally. The lower soot volume fractions for the larger droplets were also accompanied by higher burning rates. The observed phenomenon is believed to be caused by the dimensional influence on radiative heat losses from the flame. Numerical calculations confirm that soot radiation affects the droplet burning behavior.

Manzello, Samuel L.↗
NASA NTRS2001

Microgravity Acceleration Environment of the International Space Station (panel)

This paper examines the microgravity environment provided to the early science experiments by the International Space Station vehicle which is under construction. The microgravity environment will be compared with predicted levels for this stage of assembly. Included are initial analyses of the environment and preliminary identification of some sources of accelerations. Features of the operations of the accelerometer instruments, the data processing system, and data dissemination to users are also described.

DeLombard, Richard↗
NASA NTRS1996

Capillary Movement in Granular Beds in Microgravity

Understanding the dynamics of capillary flow through unsaturated porous media is very important for the development of an effective water and nutrient delivery system for growing plants in microgravity and chemical engineering applications. Experiments were conducted on the Space Shuttle during the STS-63 mission using three experimental cuvettes called "Capillary Testbed-M." These experiments studied the effect of bead diameter on capillary flow by comparing the capillary flow in three different granular beds. It was observed that the speed of water propagation in the granular bed consisting of 1.5 mm diameter particles was less than that in the bed consisting of 1.0 mm. diameter particles. Such results contradict the existing theory of capillary water propagation in granular beds. It was found also that in microgravity water propagates independently in adjacent layers of a layered granular bed .

Yendler, Boris S.↗
NASA NTRS1999

Development of Optical Diagnostic Techniques for Microgravity Materials Processing

Materials processing including crystal growth, either under a gravity environment on ground or a microgravity environment in space, involves complicated phenomena of fluid motions in gas or liquid phases as well as interaction of various species. To obtain important physical insight, it is very necessary to provide gross-field optical diagnostics for monitoring various physical properties. Materials processing inhibits easy access by ordinary instruments and thus characterizing gross-field physical properties is very challenging. Typical properties of importance can be fluid velocity, temperature, and species concentration for fluids, and surface topology and defects for solids. Observing surface grow rate during crystal growth is also important. Material microstructures, i.e., integrity of crystal structures, is strongly influenced by the existence of thermally-induced flow as well as local nucleation of particles during solidification, which may act in many detrimental ways. In both ground-based and microgravity experiments, the nature of product property changes resulting from three-dimensional fluid or particle motions need be characterized. Gross-field diagnostics is thus required to identify their effects on product defects and process deficiencies. The quantitative visualization techniques can also be used for validation of numerical modeling. For optical nonintrusive gross-field diagnostic techniques, two approaches were developed as summer projects. One optical approach allows us to provide information of species concentration and temperature for monitoring in real time. The other approach, that is, the concept which is formulated for detection of surface topography measurement can provide unprecedented spatial resolution during crystal growth.

Cha, Soyoung Stephen↗
NASA NTRS2002

Small Particle Response to Fluid Motion using Tethered Particles to Simulate Microgravity

This paper reports on ground based work conducted to support the Spaceflight Definition project SHIVA (Spaceflight Holography Investigation in a Virtual Apparatus). SHIVA will advance our understanding of the movement of a particle in a fluid. Gravity usually dominates the equations of motion, but in microgravity as well as on earth other terms can become important. Before two members of our team found an analytical solution of the equations, numerical methods and/or neglecting terms were required. The general solution predicts that the usually neglected history term becomes important when the characteristic viscous time is in the same order as the vibration period and peaks when the two times are equal. In this case three force terms, the Stokes drag, the added mass, and the history drag must all be included in predicting particle movement. We also developed diagnostic recording methods using holography to save all of the particle field data, allowing the experiment to essentially be transferred from space back to earth in what we call the "virtual apparatus". Using state-of-the-art methods in holography we will quantify the three-dimensional motion of sets of particles, allowing us to test and apply the new analytical solutions. The motion of particles up to 4 mm in diameter in a fluid that oscillates at frequencies up to 100 Hz with amplitudes up to 200 microns is being examined. Ground studies to support the flight development program have employed various schemes to simulate microgravity. One of the most reliable and meaningful methods uses spheres tethered to a fine hair suspended in the fluid. We have also investigated particles with nearly neutral buoyancy. Recordings are made at the peak amplitudes of vibration of the cell providing a measure of the ratio of fluid to particle amplitude. The experiment requires precise location of the particle at the time of recording. The hologram of the particle provides microscopic images of the particle that are used for finding the position with an accuracy of a few microns. To make the experiment more versatile, the spaceflight system will record holograms both on film and electronically. The electronic holograms can be downlinked providing real time data. Results of the ground experiments, the flight experiment design, and data analysis procedures are reported.

Trolinger, J. D.↗
NASA NTRS2002

Small Particle Response to Fluid Motion using Tethered Particles to Simulate Microgravity

This paper reports on ground based work conducted to support the Spaceflight Definition project SHIVA (Spaceflight Holography Investigation in a Virtual Apparatus). SHIVA will advance our understanding of the movement of a particle in a fluid. Gravity usually dominates the equations of motion, but in microgravity as well as on earth other terms can become important. Before two members of our team found an analytical solution of the equations, numerical methods and/or neglecting terms were required. The general solution predicts that the usually neglected history term becomes important when the characteristic viscous time is in the same order as the vibration period and peaks when the two times are equal. In this case three force terms, the Stokes drag, the added mass, and the history drag must all be included in predicting particle movement. We also developed diagnostic recording methods using holography to save all of the particle field data, allowing the experiment to essentially be transferred from space back to earth in what we call the "virtual apparatus". Using state-of-the-art methods in holography we will quantify the three-dimensional motion of sets of particles, allowing us to test and apply the new analytical solutions. The motion of particles up to 4 mm in diameter in a fluid that oscillates at frequencies up to 100 Hz with amplitudes up to 200 microns is being examined. Ground studies to support the flight development program have employed various schemes to simulate microgravity. One of the most reliable and meaningful methods uses spheres tethered to a fine hair suspended in the fluid. We have also investigated particles with nearly neutral buoyancy. Recordings are made at the peak amplitudes of vibration of the cell providing a measure of the ratio of fluid to particle amplitude. The experiment requires precise location of the particle at the time of recording. The hologram of the particle provides microscopic images of the particle that are used for finding the position with an accuracy of a few microns. To make the experiment more versatile, the spaceflight system will record holograms both on film and electronically. The electronic holograms can be downlinked providing real time data. Results of the ground experiments, the flight experiment design, and data analysis procedures are reported.

Trolinger, J. D.↗
NASA NTRS2002

Effects of Microgravity On Oxidative and Antioxidant Enzymes In Mouse Hindlimb Muscle

Gastrocnemius muscle of mice were analyzed in order to examine the effects of 12 days of microgravity on the oxidative enzyme climate synthase (CS) and the antioxidant enzyme superoxide dismutase (SOD). The female C57BL/6J mice utilized for this study were part of the Commercial Biomedical Testing Module (CBTM) payload that flew aboard STS-108. Mice were housed in Animal Enclosure Modules (AEMs) provided by NASA Ames. The flight (FLT) group and the ground control (CON) group each had 12 mice per group. The AEMs that held the CON group operated on a 48-hour delay from the FLT group and were located inside the Orbital Environmental Simulator (OES) at Kennedy Space Center. The temperature, CO2 and relative humidity inside the OES was regulated based on downlinked information from the shuttle middeck. Student T tests were used to compare groups and a p < 0.05 was used to determine statistical significance. Results indicated that CS levels for the FLT group were significantly lower than the CON group while the SOD levels were significantly higher. The CS FLT mean was 19% lower and the SOD FLT mean was 17% higher than the respective CON group means. Although these findings are among the first muscle enzyme values reported for mice from a shuttle mission, these results are similar to some results previously reported for rats exposed to microgravity or hindlimb suspension. The changes seen during the CBTM payload are reflective of the deconditioning that takes place with disuse of the hindlimbs and indicate that muscle enzyme changes induced by disuse deconditioning are similar in both rodent species.

Girten, B.↗