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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.

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At least 883 records · Page 49
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

Numerical Investigation of Thermal Stress Convention in Nonisothermal Gases Under Microgravity Conditions

Reported here are our results of our numerical/theoretical investigation into the effects of thermal stress in nonisothermal gases under microgravity conditions. The first part of the report consists of a brief summary of the accomplishments and conclusions of our work. The second part consists of two manuscripts, one being a paper presented at the 1998 MSAD Fluid Physics workshop, and the other to appear in Physics of Fluids.

Mackowski, D. W.↗
NASA NTRS1996

A Comparison of Measurements from ATMOS and Instruments Aboard the ER-2 Aircraft: Halogenated Gases

We compare volume mixing ratio profiles of N2O, CFC-11, CFC-12, CCl4, SF6, and HCl in the mid-latitude lower stratosphere measured by the ATMOS Fourier transform spectrometer on the ATLAS-3 Space Shuttle Mission with in situ measurements acquired from the NASA ER-2 aircraft during Nov. 1994. Good agreement is found between ATMOS and in situ correlations of [CFC-11], [CFC-12], and [SF6] with [N2O]. ATMOS measurements of [CCl4] are 15% high compared to ER-2 data, but agree within the systematic uncertainties. ATMOS observations of [HCl] vs [N2O] are within approximately 10% of ER-2 data for [HCl] > 1 ppbv, but exceed in situ measurements by larger fractional amounts for smaller [HCl]. ATMOS measurements of [ClONO2] agree well with values inferred from in situ observations of [ClO], [NO], and [O3]. The sum of [HCl] and [ClONO2] observed by ATMOS, supplemented by a minor contribution from [ClO] estimated with a photochemical model, is consistent with the levels of inorganic chlorine inferred from in situ measurements of chlorine source gases.

Chang, A. Y.↗
NASA NTRS1999

Climate Change and Greenhouse Gases

The American Geophysical Union (AGU), as a scientific organization devoted to research on the Earth and space sciences, provides current scientific information to the public on issues pertinent to geophysics. The Council of the AGU approved a position statement on Climate Change and Greenhouse Gases in December 1998. The statement, together with a short summary of the procedures that were followed in its preparation, review, and adoption were published in the February 2, 1999 issue of Eos ([AGU, 1999]. The present article reviews scientific understanding of this issue as presented in peer-reviewed publications that serves as the underlying basis of the position statement.

Ledley, Tamara S.↗
NASA NTRS2000

Noble Gases in Iddingsite from the Lafayette Meteorite: Evidence for Liquid Water on Mars in the Last Few Hundred Million Years

We analyzed noble gases from 18 samples of weathering products ("iddingsite") from the Lafayette meteorite. Potassium-argon ages of 12 samples range from near zero to 670 +/- 91 Ma. These ages confirm the martian origin of the iddingsite, but it is not clear whether any or all of the ages represent iddingsite formation as opposed to later alteration or incorporation of martian atmospheric Ar-40. In any case, because iddingsite formation requires liquid water, this data requires the presence of liquid water near the surface of Mars at least as recently as 1300 Ma ago, and probably as recently as 650 Ma ago. Krypton and Xe analysis of a single 34 microg sample indicates the presence of fractionated martian atmosphere within the iddingsite. This also confirms the martian origin of the iddingsite. The mechanism of incorporation could either be through interaction with liquid water during iddingsite formation or a result of shock implantation of adsorbed atmospheric gas.

Swindle, T. D.↗
NASA NTRS2001

Formation of Residual Gases from Source Materials in Closed Crystal Growth Systems

Different, non-constituent cases are present in crystal growth systems and may affect processes like growth rate in PVT or voids formation and detached solidification in melt growth systems. The presence of the gas may be detrimental or advantageous depending on its amount and composition, and on the process in question. The presence of the cases, their amount and composition, can be caused and changed by diffusion through and desorption from the growth container material. We have investigated these phenomena for silica glass ampoules. We also found, that residual cases can be generated by the source materials: even very high purity commercial elements and compounds may contain trace amounts of impurities, particularly oxides. The oxides may have low volatilities themselves but their reaction with other species, particularly carbon and hydrogen, may produce volatile compounds like water or carbon oxides. The amount of the gas and its composition is dependent on the original purity of the material (oxide contaminants) and the heat treatment of the source prior to sealing. In many cases. particularly at temperatures below about 900 C and in well-outgassed ampoules, this mechanism dominates. The problem is of a particular importance in sealed systems where the amount and composition of the gas cannot be directly controlled. Therefore, a reasonable knowledge and understanding of the origin, composition, magnitude, and change with time of gases present in sealed ampoules may be important for a meaningful control and interpretation of crystal growth processes. We have investigated this phenomenon in more details for a number of elements and compounds, primarily for II-VI and IV-VI materials. Different source pre-treatment and annealing procedures were applied, and subsequent consecutive annealings and measurements were done to determine the origin and development of the gas in the systems.

Palosz, W.↗
NASA NTRS1967

A Study to Analyze the Permeation of High Density Gases and Propellant Vapors Through Single Layer Teflon or Teflon Structure Materials and Laminations

This report contains the results of a fifteen month analytical and experimental study of the leakage rate of the pressurant gases (N2, He) and the propellant vapors (N2O4,N2H4) through bladder structures consisting of two layers of Teflon separated by a metallic foil diffusion barrier containing microscopic or larger holes. Results were obtained for the steady state leakage rate through circular holes and long rectangular openings in the barrier for arbitrary thicknesses of the two Teflon layers. The effect of hole shape and relative hole position on the leakage rate were studied. The transient problem was analyzed and it was shown that steady state calculations are adequate for estimating the leakage rate. A computer program entitled "Diffusion Analyzer Program" was developed to calculate the leakage rate, both transient and steady state. Finally, the analytical results were compared to experimentally determined values of the leakage rate through a model laminated bladder structure. The results of the analysis are in good agreement with experiment. The experimental effort (Part II of the Bladder Permeation Program) measured the solubility, diffusion coefficient and permeability of helium, nitrogen and nitrogen tetroxide vapor through Teflon TFE and FEP membranes. Data were obtained in the temperature range of 25 to 100 C at pressures ranging from near vacuum to about 20 atmospheres. Results of the experimental effort were compared with the limited data previously reported. As a verification to the applicability of results to actual bladder systems, counter diffusion tests were performed with a laminated sample containing aluminum foil with a selected group of holes.

Johnson, R. L.↗
NASA NTRS2001

Membrane Separation of Gases From The Martian Atmosphere

A test bed has been constructed to test membrane modules for separation of gases under temperature and pressure conditions normally encountered on the surface of Mars. The test bed allows independent control of (1) feed flow rates, (2) feed composition, (3) feed pressure, (4) permeate pressure, and (5) operating temperature. Preliminary data obtained at a nominal feed pressure of 760 torr and permeate pressure of 10 torr has demonstrated the ability of one membrane module to operate at temperatures as low as -70 C. At temperatures below -40 C, however, significant loss of carbon dioxide and argon was observed, probably indicating condensation at the relatively high pressure used. As expected, permeation flow rates decreased with decreasing temperature, the flow at -30 C approximately 37% of the value at +23 C. Values of permeability for individual gas components showed similar decreases with decreasing temperature, but permeability ratios changed significantly. For example, the ratio of the permeabilities of carbon dioxide and nitrogen increased from 2.6 at 23 C to 5.6 at -30 C. Additional data at lower operating pressures and temperatures must be obtained in order to optimize design of a usable separation system.

Jennings, Paul A.↗
NASA NTRS2002

Measurements of Long-Lived Trace Gases from Commercial Aircraft Platforms: Development of Instrumentation

The upper troposphere (6-12 km altitude) is a poorly understood and highly vulnerable region of the atmosphere. It is important because many trace species, including ozone, have their greatest impact as greenhouse (infrared-absorbing) gases in this region. The addition of relatively small amounts of anthropogenic chemicals, such as nitrogen oxides, can have a dramatic effect on the abundance of ozone. Some of these pollutants are deposited directly, e.g., by aircraft, while others are transported in. The primary goal of this project was to measure several chemical compounds in the upper troposphere that will help us to understand how air is to transported to that part of the atmosphere; that is, does it come down from the stratosphere, does it rise from the surface via convection, and so on. To obtain adequate sampling to accomplish this goal, we proposed to make measurements from revenue aircraft during normal flight operations.

Source record↗
NASA NTRS2002

Inerting Aircraft Fuel Systems Using Exhaust Gases

Our purpose in this proposal was to determine the feasibility of using carbon dioxide, possibly obtained from aircraft exhaust gases as a substance to inert the fuel contained in fuel tanks aboard aircraft. To do this, we decided to look at the effects carbon dioxide has upon commercial Jet-A aircraft fuel. In particular, we looked at the solubility of CO2 in Jet-A fuel, the pumpability of CO2-saturated Jet-A fuel, the flashpoint of Jet-A fuel under various mixtures of air and CO2, the static outgassing of CO2-Saturated Jet-A fuel and the dynamic outgassing of Jet-A fuel during pumping of Jet-A fuel.

Hehemann, David G.↗
NASA NTRS2002

Using Compressed Gases and Novel Liquids for Lubrication on the Martian Surface

This presentation discusses the use of compressed gases and novel liquids for lubricating the drives of roving vehicles which may be employed for exploring the surface of Mars. Topics cover include: Mars atmospheric and temperature conditions, the Sojourner Rover, the Martian surface, liquids of interest for lubrication studies and CO2 gellation.

Morales, Wilfredo↗
NASA NTRS2002

Membrane Separation of Gases from the Martian Atmosphere

A test bed has been constructed to test membrane modules for separation of gases under temperature and pressure conditions normally encountered on the surface of Mars. The test bed allows independent control of: (1) feed flow rates, (2) feed composition, (3) feed pressure, (4) permeate pressure, and (5) operating temperature. Preliminary data obtained at a nominal feed pressure of 760 torr and permeate pressure of 10 torr has demonstrated the ability of one membrane module to operate at temperatures as low as -70 C. At temperatures below -40 C, however, significant loss of carbon dioxide and argon was observed, probably indicating condensation at the relatively high pressure used. As expected, permeation flow rates decreased with decreasing temperature, the flow at -30 C approximately 37% of the value at +23 C. Values of permeability for individual gas components showed similar decreases with decreasing temperature, but permeability ratios changed significantly. For example, the ratio of the permeabilities of carbon dioxide and nitrogen increased from 2.6 at 23 C to 5.6 at -30 C. Additional data at lower operating pressures and temperatures must be obtained in order to optimize design of a usable separation system.

Jennings, Paul A.↗
NASA NTRS2003

Residual Gas in Closed Systems: Formation of Gases from the Source Materials - 2

The amount and composition of residual gases formed in sealed ampoules loaded with different elements or binary II-VI or IV-VI compounds were investigated. The source materials underwent different thermal processings, annealing and/or resublimation conducted under different conditions. The results of these experiments are discussed in terms of the procedural, thermochemical, and kinetic limitations to the process.

Palosz, W.↗
NASA NTRS2003

Elastic Properties of Films of Water and Noble Gases Condensed at Low Temperatures

We have shown that there are extensive similarities between the quench-condensed noble gas films and those of amorphous water ice. In particular, both can be quite soft upon deposition and can stiffen considerably when annealed. Furthermore, this stiffening follows a logarithmic time dependence for all substances. The temperature dependence of these behaviors scales with the triple point. The results shown here show a strong thickness dependence, which has implications for any study of mechanical properties of films on substrates. The temperature dependence of the stiffening and the stiffening rate have now been characterized for the noble gases, and these observations provide a roadmap for new experiments on amorphous water ice.

Pohl, Robert O.↗
NASA NTRS2003

Residual Gas in Closed Systems: Formation of Gases from the Source Materials - 2

The amount and composition of residual gases formed in sealed ampoules loaded with different elements or binary II-VI or IV-VI compounds and subjected to various thermal processings, annealing and/or resublimation conducted under different conditions were investigated. The results of these experiments are discussed in terms of the procedural, thermochemical, and kinetic limitations to the process.

Palosz, W.↗
NASA NTRS2003

Production Rates of Noble Gases in the Near-Surface Layers of Europa by Energetic Charged Particles and the Potential for Determining Exposure Ages

The surface of Europa is expected to be extremely active, undergoing tectonic and/or tidal geological activity and sputtering/ deposition, as well as impact cratering. Determination of the actual age of the surface at one or more places would greatly simplify trying to sort out what processes are occurring, and at what rate. If there is K present, as the spectral and compositional modeling discussed predict, it should be possible, in principle, to determine K-Ar crystallization ages. Whether or not there is K present, a consideration of the environment suggests we can determine an energetic particle exposure age if we can make in situ measurements of the abundances of major elements and of noble gas isotopes. This requires instrumentation that is within reach of current technology. In this paper, we calculate production rates for noble-gas isotopes in a simplified Europan surface, to quantify the amount of light noble gases produced by exposure to energetic particles.

Swindle, T. D.↗