SEARCH · Engineering Papers

Results for “microgravity”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51

All sources NASA NTRS DOE OSTI

NASA NTRS1997

Ignition, Transition, Flame Spread in Multidimensional Configurations in Microgravity

Ignition of solid fuels by external thermal radiation and subsequent transition to flame spread are processes that not only are of considerable scientific interest but which also have fire safety applications. A material which undergoes a momentary ignition might be tolerable but a material which permits a transition to subsequent flame spread would significantly increase the fire hazard in a spacecraft. Therefore, the limiting condition under which flame cannot spread should be calculated from a model of the transition from ignition instead of by the traditional approach based on limits to a steady flame spread model. However, although the fundamental processes involved in ignition have been suggested there have been no definitive experimental or modeling studies due to the flow motion generated by buoyancy near the heated sample surface. In this study, microgravity experiments which required longer test times such as in air and surface smoldering experiment were conducted in the space shuttle STS-75 flight; shorter experimental tests such as in 35% and 50% oxygen were conducted in the droptower in the Japan Microgravity Center, JAMIC. Their experimental data along with theoretically calculated results from solving numerically the time-dependent Navier-Stokes equations are summarized in this paper.

Kashiwagi, Takashi↗

NASA NTRS1997

Formation and Combustion of Unconfined Drop Clusters in Microgravity

Single-drop and droplet array studies have become common methods to isolate and investigate the effects of any of the complexities that enter into the drop combustion process. Microgravity environments are required to allow larger drops to be studied while minimizing or eliminating the confounding effects of buoyancy. Based on the results from current isolated drop, drop array, and spray studies funded through the Microgravity Science and Applications Division, it has become clear that even with the effects of buoyancy removed, the extrapolation of results from droplet array studies to spray flames is difficult. The problem occurs because even the simplest spray systems introduce complexities of multi-disperse drop sizes and drop-drop interactions, coupled with more complicated fluid dynamics. Not only do these features make the interpretation of experimental data difficult, they also make the problem very difficult to analyze computationally. Group combustion models, in which the interaction between droplets is treated on a statistical manner, have become a popular method to investigate the behavior of large numbers of interacting droplets, particularly through the work of Ryan et al. and Bellan and co-workers. While these models idealize the actual spray systems to a point where they can be treated computationally, the experimental analogy to these models is difficult to achieve because it requires the formation and Combustion of drop clusters without the effects of buoyancy. Therefore, even though these models have provided useful and insightful information, the verification of the results by direct comparison with experimental data is still lacking.

Liu, S.↗

NASA NTRS1997

Heterogeneous Combustion of Porous Graphite Particles in Microgravity

Recent theoretical investigations on graphite particle combustion have employed several levels of heterogeneous reaction models, ranging from global to elementary models, to describe the oxidation of carbon to gaseous products. Unlike the counterpart homogeneous reaction models, these heterogeneous reaction models are not well developed because of the difficulties associated with decoupling the physical characteristics of the solid (e.g. surface area taking part in combustion) from the chemical kinetic data. This is certainly true for porous graphite particle combustion, where heterogeneous and homogeneous reactions occur within the pores and play an important role in the overall oxidation process. As a result, there are considerable uncertainties of physical phenomena predicted using different heterogeneous kinetic models available in the literature. A good example, discussed later in this paper, is the predicted critical particle size below which the mass burning rate becomes exponentially small. The main goal of this study is to understand the basic mechanism controlling such rapid changes in burning rates, by developing a model where physical contributions are decoupled from chemical rate constants in a consistent manner. Another important goal of the proposed study is to develop a truly intrinsic, detailed heterogeneous reaction model for porous graphite combustion at high-temperatures, and to derive a systematically reduced heterogeneous reaction model in terms of the elementary reaction rate constants of the detailed model. The validation of chemical kinetic models describing the heterogeneous and homogeneous combustion in and around a spherically symmetric porous graphite particle can be considerably simplified by experimental measurements obtained under microgravity conditions. A vital component of this study is to conduct such supporting experiments on particle burning rate and surface temperature using NASA microgravity facilities, in close coordination with the theoretical effort. The basic understanding obtained and models developed as part of this project will be useful for optimal design of coal combustion devices. These models can also be extended to investigate the role of heterogeneous chemistry on pollutant formation pathways in combustion devices. The theoretical approach developed here, with pore diffusion effects decoupled from the chemical effects, can also be extended to understand the heterogeneous combustion of other porous fuels, for example, combustion of magnesium in a CO2 environment for propulsion in the Martian atmosphere.

Chelliah, Harsha K.↗

NASA NTRS1996

Bubble and Slug Flow at Microgravity Conditions: State of Knowledge and Open Questions

Based on the experiments carried out over the past decade at microgravity conditions, an overview of our current knowledge of bubbly and slug flows is presented. The transition from bubble to slug flow, the void fraction and the pressure drop are discussed from the data collected in the literature. The transition from bubble to slug flow may be predicted by introducing a critical void fraction that depends on the fluid properties and the pipe diameter; however, the role of coalescence which controls this transition is not clearly understood. The void fraction may be accurately calculated using a drift-flux model. It is shown from local measurements that the drift of the gas with respect to the mixture is due to non-uniform radial distribution of void fraction. The pressure drop happens to be controlled by the liquid flow for bubbly flow whereas for slug flow the experimental results show that pressure drops is larger than expected. From this study, the guidelines for future research in microgravity are given.

Colin, C.↗

NASA NTRS1997

Laser-Induced Incandescence in Microgravity

Microgravity offers unique opportunities for studying both soot growth and the effect of soot radiation upon flame structure and spread. LII has been characterized and developed at NASA-Lewis for soot volume fraction determination in a wide range of 1-g combustion applications. Reported here are the first demonstrations of LII performed in a microgravity environment. Examples are shown for laminar and turbulent gas-jet diffusion flames in 0-g.

VanderWal, Randall L.↗

NASA NTRS1996

Measurements and Modeling of Soot Formation and Radiation in Microgravity Jet Diffusion Flames

This is a computational and experimental study for soot formation and radiative heat transfer in jet diffusion flames under normal gravity (1-g) and microgravity (0-g) conditions. Instantaneous soot volume fraction maps are measured using a full-field imaging absorption technique developed by the authors. A compact, self-contained drop rig is used for microgravity experiments in the 2.2-second drop tower facility at NASA Lewis Research Center. On modeling, we have coupled flame structure and soot formation models with detailed radiation transfer calculations. Favre-averaged boundary layer equations with a k-e-g turbulence model are used to predict the flow field, and a conserved scalar approach with an assumed Beta-pdf are used to predict gaseous species mole fraction. Scalar transport equations are used to describe soot volume fraction and number density distributions, with formation and oxidation terms modeled by one-step rate equations and thermophoretic effects included. An energy equation is included to couple flame structure and radiation analyses through iterations, neglecting turbulence-radiation interactions. The YIX solution for a finite cylindrical enclosure is used for radiative heat transfer calculations. The spectral absorption coefficient for soot aggregates is calculated from the Rayleigh solution using complex refractive index data from a Drude- Lorentz model. The exponential-wide-band model is used to calculate the spectral absorption coefficient for H20 and C02. It is shown that when compared to results from true spectral integration, the Rosseland mean absorption coefficient can provide reasonably accurate predictions for the type of flames studied. The soot formation model proposed by Moss, Syed, and Stewart seems to produce better fits to experimental data and more physically sound than the simpler model by Khan et al. Predicted soot volume fraction and temperature results agree well with published data for a normal gravity co-flow laminar flames and turbulent jet flames. Predicted soot volume fraction results also agree with our data for 1-g and 0-g laminar jet names as well as 1-g turbulent jet flames.

Ku, Jerry C.↗

NASA NTRS1996

NASA's Microgravity Science Research Program

The ongoing challenge faced by NASA's Microgravity Science Research Program is to work with the scientific and engineering communities to secure the maximum return from our Nation's investments by: assuring that the best possible science emerges from the science community for microgravity investigations; ensuring the maximum scientific return from each investigation in the most timely and cost-effective manner; and enhancing the distribution of data and applications of results acquired through completed investigations to maximize their benefits.

Source record↗

NASA NTRS1997

Development of a Device to Deploy Fluid Droplets in Microgravity

A free-floating droplet in microgravity is ideal for scientific observation since it is free of confounding factors such as wetting and nonsymmetrical heat transfer introduced by contact with surfaces. However, the technology to reliably deploy in microgravity has not yet been developed. In some recent fluid deployment experiments, droplets are either shaken off the dispenser or the dispenser is quickly retracted from the droplet. These solutions impart random residual motion to deployed droplet, which can be undesirable for certain investigations. In the present study, two new types of droplet injectors were built and tested. Testing of the droplet injectors consisted of neutral buoyancy tank tests, 5-sec drop tower tests at the NASA Lewis Zero Gravity Facility, and DC-9 tests. One type, the concentric injector, worked well in the neutral buoyancy tank but did not do well in low-gravity. However, it appeared that it makes a fine apparatus for constructing bubbles in low-gravity conditions. The other type, the T-injector, showed the most promise for future development. In both neutral buoyancy and DC-9 tests, water droplets were formed and deployed with some control and repeatability, although in low-gravity the residual velocities were higher than desirable. Based on our observations, further refinements are suggested for future development work.

Robinson, David W.↗

NASA NTRS1997

Second International Microgravity Laboratory (IML-2)

This report highlights the scientific and engineering accomplishments achieved during the 14-day Second International Microgravity Laboratory (IML-2) mission. The mission, managed by the National Aeronautics and Space Administration's Marshall Space Flight Center in Huntsville, Alabama, laid the groundwork for broader international partnerships and scientific alliances. Five other space agencies joined NASA on the mission: the Canadian Space Agency (CSA), the European Space Agency (ESA), the French Space Agency (CNES), the German Space Agency (DARA), and the National Space Development Agency of Japan (NASDA). For the mission, microgravity and life sciences investigations were completed inside Spacelab by a crew working around the clock. The report foreword and introduction describe the mission and the facilities used for IML-2. By the end of the mission, hundreds of primary and secondary experiments were completed. With the help of the principal investigators, most of the primary investigations and some of the co-investigations are described in this document. The lead report authors are cited at the beginning of each experiment description The remainder of the description includes the experiment objectives, flight activities postflight analysis, conclusions, illustrations, and references for further research. The major scientific accomplishments of each investigation are highlighted.

Snyder, Robert S.↗

NASA NTRS1996

NASA's Microgravity Technology Report, 1996: Summary of Activities

This report covers technology development and technology transfer activities within the Microgravity Science Research Programs during FY 1996. It also describes the recent major tasks under the Advanced Technology Development (ATD) Program and identifies current technology requirements. This document is consistent with NASA,s Enteprise for the Human Exploration and development of Space (HEDS) Strategic Plan. This annual update reflects changes in the Microgravity Science Research Program's new technology activities and requirements. Appendix A. FY 1996 Advanced Technology Development. Program and Project Descriptions. Appendix B. Technology Development.

Kierk, Isabella↗

NASA NTRS1992

Effects of Microgravity or Simulated Launch on Testicular Function in Rats

Testes from flight rats on COSMOS 2044 and simulated-launch, vivarium, or caudal-elevation control rats (5/group) were analyzed by subjective and quantitative methods. On the basis of observations of fixed tissue, it was evident that some rats had testicular abnormalities unassociated with treatment and probably existing when they were assigned randomly to the four treatment groups. Considering rats without preexisting abnormalities, diameter of seminiferous tubules and numbers of germ cells per tubule cross section were lower (P less than 0.05) in flight than in simulated-launch or vivarium rats. However, ratios of germ cells to each other or to Sertoli cells and number of homogenization-resistant spermatids did not differ from values for simulated-launch or vivarium controls. Expression of testis-specific gene products was not greatly altered by flight. Furthermore, there was no evidence for production of stress-inducible transcripts of the hsp7O or hsp9O genes. Concentration of receptors for rat luteinizing hormone in testicular tissue and surface density of smooth endoplasmic reticulum in Leydig cells were similar in flight and simulated-launch rats. However, concentrations of testosterone in testicular tissue or peripheral blood plasma were reduced (P less than 0.05) in flight rats to less than 20% of values for simulated-launch or vivarium controls. Thus spermatogenesis was essentially normal in flight rats, but production of testosterone was severely depressed. Exposure to microgravity for more than 2 wk might result in additional changes. Sequelae of reduced androgen production associated with microgravity on turnover of muscle and bone should be considered.

Amann, R. P.↗

NASA NTRS1997

Cardiovascular regulation in microgravity

The human cardiovascular adaptation to microgravity was investigated in the framework of the German Spacelab D2 mission. Preflight and postflight studies were performed to examine the relationship between disuse atrophy and the function of cardiac and skeletal muscles. Special attention was given to fluid load responses and postflight orthostatic hypotension. The preflight measurements were obtained, in supine and sitting positions. These measurements, carried out in the four D2 crew members, were performed six and nine months before flight and on mission day number five. The results obtained on the male crew showed that the stroke volume data from microgravity are virtually identical to preflight measurements in the sitting position.

C. G. Blomqvist↗

NASA NTRS1996

Expression of Contractile Protein Isoforms in Microgravity

The general objective of this experiment is to determine the effect of space flight parameters, including microgravity, on ontogenesis and embryogenesis of Japanese quail. Nine U.S. and two Russian investigators are cooperating in this study. Specific objectives of the participating scientists include assessing the gross and microscopic morphological and histological development of the embryo, as well as the temporal and spacial development of specific cells, tissues, and organs. Temporally regulated production of specific proteins is also being investigated. Our objective is to determine the effects of microgravity on developmentally programmed expression of Troponin T and I isoforms known to regulate cardiac and skeletal muscle contraction.

Anderson, Page A. W.↗

NASA NTRS1997

Baroreflex Function in Rats after Simulated Microgravity

Prolonged exposure of humans to decreased gravitational forces during spaceflight results in a number of adverse cardiovascular consequences, often referred to as cardiovascular deconditioning. Prominent among these negative cardiovascular effects are orthostatic intolerance and decreased exercise capacity. Rat hindlimb unweighting is an animal model which simulates weightlessness, and results in similar cardiovascular consequences. Cardiovascular reflexes, including arterial and cardiopulmonary baroreflexes, are required for normal adjustment to both orthostatic challenges and exercise. Therefore, the orthostatic intolerance and decreased exercise capacity associated with exposure to microgravity may be due to cardiovascular reflex dysfunction. The proposed studies will test the general hypothesis that hindlimb unweighting in rats results in impaired autonomic reflex control of the sympathetic nervous system. Specifically, we hypothesize that the ability to reflexly increase sympathetic nerve activity in response to decreases in arterial pressure or blood volume will be blunted due to hindlimb unweighting. There are 3 specific aims: (1) To evaluate arterial and cardiopulmonary baroreflex control of renal and lumbar sympathetic nerve activity in conscious rats subjected to 14 days of hindlimb unweighting; (2) To examine the interaction between arterial and cardiopulmonary baroreflex control of sympathetic nerve activity in conscious hindlimb unweighted rats; (3) to evaluate changes in afferent and/or central nervous system mechanisms in baroreflex regulation of the sympathetic nervous system. These experiments will provide information related to potential mechanisms for orthostatic and exercise intolerance due to microgravity.

Hasser, Eileen M.↗

NASA NTRS1996

Evidence for Increased Beta-Adrenoreceptor Responsiveness Induced by 14 Days of Simulated Microgravity in Humans

We studied hemodynamic responses to alpha and beta receptor agonists in 8 healthy men ( 38+- 2 yrs) before and after 14 days of 6 degree head-down tilt (HDT) to test the hypothesis that increased adrenergic responsiveness is induced by prolonged exposure to microgravity. Immediately following a 30-min baseline period, a steady-state infusion of isoproterenol (ISO) was used to assess beta 1- and beta 2-adrenergic responsiveness. ISO was infused at three graded constant rates of 0.005, 0.01 and 0.02 ug/kg/min. After heart rate and blood pressure had been allowed to return to baseline levels following ISO infusion graded infusion of phenylephrine (PE) was used to assess responsiveness of alpha I-vascular receptors. PE was infused at three graded constant rates of 0.25, 0.50 and 1.00 ug/kg/min. Each infusion interval for both drugs was 9 min. During the infusions, constant monitoring of beat-to-beat blood pressure and heart rate was performed and leg blood flow was measured with occlusion plethysmography at each infusion level. The slopes calculated from linear regressions between ISO and PE doses and changes in heart rate, blood pressure, and leg vascular resistance for each subject were used to represent alpha- and beta- adrenoreceptor responsiveness. Fourteen days HDT increased the slopes of heart rate (1056 +- 107 to 1553 +- 83 beats/ug/kg/min; P= 0.014) and vasodilation (-469ft +- 111 to -l446 +- 309 PRU/ug/kg/min; P =0.0224) to ISO infusion. There was no alteration in blood pressure or vascular resistance responses to PE infusion after HDT. Our results provide evidence that microgravity causes selective increases in beta 1- and beta 2-adrenergic responsiveness without affecting alpha 1-vascular responses.

CARDIOVASCULAR SYSTEM↗

NASA NTRS1998

Damping Mechanisms for Microgravity Vibration Isolation (MSFC Center Director's Discretionary Fund Final Report, Project No. 94-07)

As a research facility for microgravity science, the International Space Station (ISS) will be used for numerous investigations such as protein crystal growth, combustion, and fluid mechanics experiments which require a quiescent acceleration environment across a broad spectrum of frequencies. These experiments are most sensitive to low-frequency accelerations and can tolerate much higher accelerations at higher frequency. However, the anticipated acceleration environment on ISS significantly exceeds the required acceleration level. The ubiquity and difficulty in characterization of the disturbance sources precludes source isolation, requiring vibration isolation to attenuate the anticipated disturbances to an acceptable level. This memorandum reports the results of research in active control methods for microgravity vibration isolation.

Whorton, M. S.↗

NASA NTRS1995

Electromagnetic Levitation: A Useful Tool in Microgravity Research

Electromagnetic levitation is one area of the electromagnetic processing of materials that has uses for both fundamental research and practical applications. This technique was successfully used on the Space Shuttle Columbia during the Spacelab IML-2 mission in July 1994 as a platform for accurately measuring the surface tensions of liquid metals and alloys. In this article, we discuss the key transport phenomena associated with electromagnetic levitation, the fundamental relationships associated with thermophysical property measurement that can be made using this technique, reasons for working in microgravity, and some of the results obtained from the microgravity experiments.

Szekely, Julian↗

NASA NTRS1997

Mechanisms of Orthostatic Intolerance During Real and Simulated Microgravity

Session MP1 includes short reports on: (1) Orthostatic Tests after 42 Days of Simulated Weightlessness; (2) Effects of 12 Days Exposure to Simulated Microgravity on Central Circulatory Hemodynamics in the Rhesus Monkey; (3) Increased Sensitivity and Resetting of Baroflex Control of Exercise Heart Rate After Prolonged Bed-Rest; (4) Complex Cardiovascular Dynamics and Deconditioning During Head-down Bed Rest; (5) The Cardiovascular Effects of 6 Hours of Head-down Tilt Upon Athletes and Non-athletes; (6) Individual Susceptibility to Post-spaceflight Orthostatic Intolerance: Contributions of Gender-related and Microgravity-related Factors; (7) Cassiopee Mission 1996: Comparison of Cardiovascular Alteration after Short and Long-term Spaceflights; (8) Cerebral and Femoral Flow Response to LBNP during 6 Month MIR Spaceflights (93-95); and (9) Cerebrovascular Changes due to Spaceflight and Postflight Presyncope.

Source record↗