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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Lunar Lava Tube Sensing

Large (greater than 300 m diameter) lava tube caverns appear to exist on the Moon and could provide substantial safety and cost benefits for lunar bases. Over 40 m of basalt and regolith constitute the lava tube roof and would protect both construction and operations. Constant temperatures of -20 C reduce thermal stress on structures and machines. Base designs need not incorporate heavy shielding, so lightweight materials can be used and construction can be expedited. Identification and characterization of lava tube caverns can be incorporated into current precursor lunar mission plans. Some searches can even be done from Earth. Specific recommendations for lunar lava tube search and exploration are (1) an Earth-based radar interferometer, (2) an Earth-penetrating radar (EPR) orbiter, (3) kinetic penetrators for lunar lava tube confirmation, (4) a 'Moon Bat' hovering rocket vehicle, and (5) the use of other proposed landers and orbiters to help find lunar lava tubes.

York, Cheryl Lynn↗
NASA NTRS1992

A search for intact lava tubes on the Moon: Possible lunar base habitats

We have surveyed lunar sinuous rilles and other volcanic features in an effort to locate intact lava tubes that could be used to house an advanced lunar base. Criteria were established for identifying intact tube segments. Sixty-seven tube candidates within 20 rilles were identified on the lunar nearside. The rilles, located in four mare regions, varied in size and sinuosity. We identified four rilles that exhibited particularly strong evidence for the existence of intact lava tube segments. These are located in the following areas: (1) south of Gruithuisen K, (2) in the Marius Hills region, (3) in the southeastern Mare Serenitatis, and (4) in the eastern Mare Serenitatis. We rated each of the 67 probable tube segments for lunar base suitability based on its dimensions, stability, location, and access to lunar resources. Nine tube segments associated with three separate rilles are considered prime candidates for use as part of an advanced lunar base.

Coombs, Cassandra R.↗
NASA NTRS1992

The effects of crushing surface roughness on the crushing characteristics of composite tubes

The effects of crushing-surface roughness on the energy-absorption capability of graphite and glass-epoxy composite tubes were investigated. Fifty different combinations of fiber, matrix, and specimen ply orientation were evaluated. Two different crushing surface roughnesses were used in this investigation. Crushing surface significantly influences the energy-absorption capability only of tubes that crush in the lamina bending crushing mode; tubes that crush in other modes are not influenced because their lamina bundles do not slide against the crushing surface. Those tubes that crush in the lamina bending mode can achieve higher, lower, or no change in energy-absorption capability as crushing surface roughness increases. If the fiber failure strain of tubes that crush in the lamina bending crushing mode exceeds the matrix failure strain then the energy-absorption capability increases as crushing surface roughness increases. However, if the matrix failure strain exceeds the fiber failure strain then the energy-absorption capability increases as crushing surface roughness decreases. Energy-absorption capability is uninfluenced by crushing surface roughness for tubes that have equal fiber and matrix failure strains.

Farley, Gary L.↗
NASA NTRS1993

Siphon flows in isolated magnetic flux tubes. V - Radiative flows with variable ionization

Steady siphon flows in arched isolated magnetic flux tubes in the solar atmosphere are calculated here including radiative transfer between the flux tube and its surrounding and variable ionization of the flowing gas. It is shown that the behavior of a siphon flow is strongly determined by the degree of radiative coupling between the flux tube and its surroundings in the superadiabatic layer just below the solar surface. Critical siphon flows with adiabatic tube shocks in the downstream leg are calculated, illustrating the radiative relaxation of the temperature jump downstream of the shock. For flows in arched flux tubes reaching up to the temperature minimum, where the opacity is low, the gas inside the flux tube is much cooler than the surrounding atmosphere at the top of the arch. It is suggested that gas cooled by siphon flows contribute to the cool component of the solar atmosphere at the height of the temperature minimum implied by observations of the infrared CO bands at 4.6 and 2.3 microns.

Montesinos, Benjamin↗
NASA NTRS1952

Internal-liquid-film-cooling Experiments with Air-stream Temperatures to 2000 Degrees F. in 2- and 4-inch-diameter Horizontal Tubes

Report presents the results of an investigation conducted to determine the effectiveness of liquid-cooling films on the inner surfaces of tubes containing flowing hot air. Experiments were made in 2- and 4-inch-diameter straight metal tubes with air flows at temperatures from 600 degrees to 2000 degrees F. and diameter Reynolds numbers from 2.2 to 14 x 10(5). The film coolant, water, was injected around the circumference at a single axial position on the tubes at flow rates from 0.02 to .24 pound per second per foot of tube circumference (0.8 to 12 percent of the air flow). Liquid-coolant films were established and maintained around and along the tube wall in concurrent flow with the hot air. The results indicated that, in order to film cool a given surface area with as little coolant flow as possible, it may be necessary to limit the flow of coolant introduced at a single axial position and to introduce it at several axial positions. The flow rate of inert coolant required to maintain liquid-film cooling over a given area of tube surface can be estimated when the gas-flow conditions are known by means of a generalized plot of the film-cooling data.

Kinney, George R↗
NASA NTRS1999

Radially Focused Eddy Current Sensor for Detection of Longitudinal Flaws in Metallic Tubes

A radially focused eddy current sensor detects longitudinal flaws in a metal tube. A drive coil induces eddy currents within the wall of the metal tube. A pick-up cod is spaced apart from the drive coil along the length of the metal tube. The pick@up coil is positioned with one end thereof lying adjacent the wall of the metal tube such that the pick-up coil's longitudinal axis is perpendicular to the wall of the metal tube. To isolate the pick-up coil from the magnetic flux of the drive coil and the flux from the induced eddy currents. except the eddy currents diverted by a longitudinal flaw. an electrically conducting material high in magnetic permeability surrounds all of the pick-up coil except its one end that is adjacent the walls of the metal tube. The electrically conducting material can extend into and through the drive coil in a coaxial relationship therewith.

Wincheski, Russell A.↗
NASA NTRS2001

Flight Investigation of the Effects of Pressure-Belt Tubing Size on Measured Pressure Distributions

The pressure-belt technique is commonly used to measure pressure distributions on lifting and nonlifting surfaces where flush, through-the-surface measurements are not possible. The belts, made from strips of small-bore, flexible plastic tubing, are surface-mounted by a simple, nondestructive method. Additionally, the belts require minimal installation time, thus making them much less costly to install than flush-mounted pressure ports. Although pressure belts have been used in flight research since the early 1950s, only recently have manufacturers begun to produce thinner, more flexible tubing, and thin, strong adhesive tapes that minimize the installation-induced errors on the measurement of surface pressures. The objective of this investigation was to determine the effects of pressure-belt tubing size on the measurement of pressure distributions. For that purpose, two pressure belts were mounted on the right wing of a single-engine, propeller-driven research airplane. The outboard pressure belt served as a baseline for the measurement and the comparison of effects. Each tube had an outer diameter (OD) of 0.0625 in. The inboard belt was used to evaluate three different tube sizes: 0.0625-, 0.1250-, and 0.1875-in. OD. A computational investigation of tube size on pressure distribution also was conducted using the two-dimensional Multielement Streamtube Euler Solver (MSES) code.

Rivers, Natale A.↗
NASA NTRS2001

Electronic Transport Through Carbon Nanotubes: Effects of Structural Deformation and the Tube Chirality

Atomistic simulations using a combination of classical force field and Density-Functional-Theory (DFT) show that carbon atoms remain essentially sp2 coordinated in either bent tubes or tubes pushed by an atomically sharp AFM tip. Subsequent Green's-function-based transport calculations reveal that for armchair tubes there is no significant drop in conductance, while for zigzag tubes the conductance can drop by several orders of magnitude in AFM-pushed tubes. The effect can be attributed to simple stretching of the tube under tip deformation, which opens up an energy gap at the Fermi surface.

Maiti, Amitesh↗
NASA NTRS2002

Effects of Fuel Distribution on Detonation Tube Performance

A pulse detonation engine (PDE) uses a series of high frequency intermittent detonation tubes to generate thrust. The process of filling the detonation tube with fuel and air for each cycle may yield non-uniform mixtures. Lack of mixture uniformity is commonly ignored when calculating detonation tube thrust performance. In this study, detonation cycles featuring idealized non-uniform H2/air mixtures were analyzed using the SPARK two-dimensional Navier-Stokes CFD code with 7-step H2/air reaction mechanism. Mixture non-uniformities examined included axial equivalence ratio gradients, transverse equivalence ratio gradients, and partially fueled tubes. Three different average test section equivalence ratios (phi), stoichiometric (phi = 1.00), fuel lean (phi = 0.90), and fuel rich (phi = 1.10), were studied. All mixtures were detonable throughout the detonation tube. It was found that various mixtures representing the same test section equivalence ratio had specific impulses within 1 percent of each other, indicating that good fuel/air mixing is not a prerequisite for optimal detonation tube performance.

Perkins, Hugh Douglas↗
NASA NTRS1947

Gas-Dynamic Investigations of the Pulse-Jet Tube

Based upon a simplified representation of the mode of operation of the pulse-jet tube, the effect of the influences mentioned in the title were investigated and it will be shown that, for a jet tube with a fccmndesigned to be aerodynamically favorable, the ability to operate is at least questionable. By taking into account the course of the development of pressure by combustion, a new insight has been obtained into the processes of motion within the jet tube, an insight that explains a number of empirical observations, namely: certain particulars of the sequence of pressure variations; the existence of an optimum valve-opening ratio; the occurrence of an intrusion of air; and the existence of a flight speed above lrhichthe jet tube ceases to operate. At too great an opening ratio or at too great a flight s-peed, the continuous flow through the tube is too predominant over the oscilla~ory process to perinitthe occurrence of an explosion powerful enough to maintain continuous operation. Certain possible means of making the operation of the jet tube more independent of the flight speed and of reducing the flow losses were proposed and discussed.

Shultz-Grunow, F.↗
NASA NTRS2003

Effects of Non-Uniform Fuel Distribution on Detonation Tube Performance

A pulse detonation engine uses a series of high frequency intermittent detonation tubes to generate thrust. The process of filling the detonation tube with fuel and air for each cycle may yield non-uniform mixtures. Uniform mixing is commonly assumed when calculating detonation tube thrust performance. In this study, detonation cycles featuring idealized non-uniform H2/air mixtures were analyzed using a two-dimensional Navier-Stokes computational fluid dynamics code with detailed chemistry. Mixture non-uniformities examined included axial equivalence ratio gradients, transverse equivalence ratio gradients, and partially fueled tubes. Three different average test section equivalence ratios were studied; one stoichiometric, one fuel lean, and one fuel rich. All mixtures were detonable throughout the detonation tube. Various mixtures representing the same average test section equivalence ratio were shown to have specific impulses within 1% of each other, indicating that good fuel/air mixing is not a prerequisite for optimal detonation tube performance under the conditions investigated.

Perkins, H. Douglas↗
NASA NTRS2003

Effects of Fuel Distribution on Detonation Tube Performance

A pulse detonation engine uses a series of high frequency intermittent detonation tubes to generate thrust. The process of filling the detonation tube with fuel and air for each cycle may yield non-uniform mixtures. Uniform mixing is commonly assumed when calculating detonation tube thrust performance. In this study, detonation cycles featuring idealized non-uniform Hz/air mixtures were analyzed using a two-dimensional Navier-Stokes computational fluid dynamics code with detailed chemistry. Mixture non-uniformities examined included axial equivalence ratio gradients, transverse equivalence ratio gradients, and partially fueled tubes. Three different average test section equivalence ratios were studied; one stoichiometric, one fuel lean, and one fuel rich. All mixtures were detonable throughout the detonation tube. Various mixtures representing the same average test section equivalence ratio were shown to have specific impulses within 1% of each other, indicating that good fuel/air mixing is not a prerequisite for optimal detonation tube performance under conditions investigated.

Perkins, H. Douglas↗
NASA NTRS2001

Boiler Tube Corrosion Characterization with a Scanning Thermal Line

Wall thinning due to corrosion in utility boiler water wall tubing is a significant operational concern for boiler operators. Historically, conventional ultrasonics has been used for inspection of these tubes. Unfortunately, ultrasonic inspection is very manpower intense and slow. Therefore, thickness measurements are typically taken over a relatively small percentage of the total boiler wall and statistical analysis is used to determine the overall condition of the boiler tubing. Other inspection techniques, such as electromagnetic acoustic transducer (EMAT), have recently been evaluated, however they provide only a qualitative evaluation - identifying areas or spots where corrosion has significantly reduced the wall thickness. NASA Langley Research Center, in cooperation with ThermTech Services, has developed a thermal NDE technique designed to quantitatively measure the wall thickness and thus determine the amount of material thinning present in steel boiler tubing. The technique involves the movement of a thermal line source across the outer surface of the tubing followed by an infrared imager at a fixed distance behind the line source. Quantitative images of the material loss due to corrosion are reconstructed from measurements of the induced surface temperature variations. This paper will present a discussion of the development of the thermal imaging system as well as the techniques used to reconstruct images of flaws. The application of the thermal line source coupled with the analysis technique represents a significant improvement in the inspection speed and accuracy for large structures such as boiler water walls. A theoretical basis for the technique will be presented to establish the quantitative nature of the technique. Further, a dynamic calibration system will be presented for the technique that allows the extraction of thickness information from the temperature data. Additionally, the results of the application of this technology to actual water wall tubing samples and in-situ inspections will be presented.

Cramer, K. Elliott↗
NASA NTRS2000

Multisorbent tubes for collecting volatile organic compounds in spacecraft air

The sampling capability of Tenax-TA tubes, used in the National Aeronautics and Space Administration's solid sorbent air sampler to trap and concentrate contaminants from air aboard spacecraft, was improved by incorporating two sorbents within the tubes. Existing tubes containing only Tenax-TA allowed highly volatile compounds to "break through" during collection of a 1.5 L air sample. First the carbon molecular sieve-type sorbents Carboxen 569 and Carbosieve S-III were tested for their ability to quantitatively trap the highly volatile compounds. Breakthrough volumes were determined with the direct method, whereby low ppm levels of methanol or Freon 12 in nitrogen were flowed through the sorbent tubes at 30 mL/min, and breakthrough was detected by gas chromatography. Breakthrough volumes for methanol were about 9 L/g on Carboxen 569 and 11 L/g on Carbosieve S-III; breakthrough volumes for Freon 12 were about 7 L/g on Carboxen 569 and > 26 L/g on Carbosieve S-III. Next, dual-bed tubes containing either Tenax-TA/Carbosieve S-III, Tenax-TA/Carboxen 569, or Carbotrap/Carboxen 569 to a 10-component gas mixture were exposed, in dry and in humidified air (50% relative humidity), and percentage recoveries of each compound were determined. The Tenax-TA/Carboxen 569 combination gave the best overall recoveries (75-114% for the 10 compounds). Acetaldehyde had the lowest recovery (75%) of the 10 compounds, but this value was still an improvement over either the other two sorbent combinations or the original single-sorbent tubes.

NASA Center JSC↗
NASA NTRS2006

Flight Data Update on Long-Term Compound Stability in Dual Sorbent Tubes

Dual Sorbent Tubes (DSTs) are currently the primary method for collecting volatile organic compounds in the cabin air of the International Space Station (ISS). Data from groundbased analysis of these archival air samplers provide a major component of the assessment of ISS air quality by the NASA toxicologist. At the 2005 ICES conference data from the positive control DSTs, returned on Soyuz 7S and 8S, were presented. Positive control tubes are dosed, preflight, with known concentrations of representative contaminant compounds and they are launched to ISS in the DST kit as trip controls. Upon return of the DST kit to the ground, results from analysis of the trip (positive) and laboratory control tubes are used to determine the recoveries: concentration of dosed compounds retained in the tube. Results from positive controls, returned on 7S and 8S showed substantial losses of some compounds dosed into the tubes 156 to 240 days prior to the analysis. Low recoveries are expected for spacecraft air contaminants with similar properties to the poorly recovered dosed compounds. It was shown that compound losses in the control tubes were consistent, which led to the generation of acceptable correction factors for spacecraft air contaminants. Correction factors decrease the accuracy of derived compound concentrations and substantial error could arise under some conditions. An investigation into the mechanism for compound loss is necessary before design modifications can be implemented to improve the DST performance. This paper will update results from the DSTs returned on Soyuz 9S and 10S missions during the latter part of 2005. The data acquired from these returned DSTs will be compared to the 7S and 8S data presented last year. Discussion will focus on the reliability of correction factors and identify any trends in the data. This paper will describe the experimental design and plans to identify the compound loss mechanism.

James, John T.↗
NASA NTRS2007

On Flow Stagnation in a Tube Radiator

An analysis of the physical process for occurrence of flow stagnation in a space tube-radiator is performed and the mechanism and mathematic description for the flow stagnation are presented. Two causes for pressure drop unbalance between tubes of the radiator are identified: non-uniform cooling environment and different local flow resistances between the tubes. This analysis provides a theoretical basis for experimental simulations of the flow stagnation in a ground-based lab as well as two suggested methods to experimentally simulate flow stagnation. Criteria for the flow stagnation, depending on the viscosity data regressive polynomial, are derived from the extreme condition of the pressure drop in colder tubes. A preliminary numerical calculation is conducted for a space tube-radiator model which confirms the physical and mathematical analyses. The prediction by the criteria for flow stagnation in the tube-radiator model coincides with the numerical calculation result.

Motil, Brian↗
NASA NTRS2009

Ultimate Temperature of Pulse Tube Cryocoolers

An ideal pulse tube cryocooler using an ideal gas can operate at any temperature. This is not true for real gases. The enthalpy flow resulting from the real gas effects of He-3, He-4, and their mixtures in ideal pulse tube cryocoolers puts limits on the operating temperature of pulse tube cryocoolers. The discussion of these effects follows a previous description of the real gas effects in ideal pulse tube cryocoolers and makes use of models of the thermophysical properties of He-3 and He-4. Published data is used to extend the analysis to mixtures of He-3 and He-4. The analysis was done for pressures below 2 MPa and temperatures below 2.5 K. Both gases and their mixtures show low temperature limits for pulse tube cryocoolers. These limits are in the 0.5-2.2 K range and depend on pressure and mixture. In some circumstances, even lower temperatures may be possible. Pulse tube cryocoolers using the two-fluid properties of dilute 3He in superfluid He-4 appear to have no limit.

Kittel, Peter↗
NASA NTRS2009

Ultimate Temperature of Pulse Tube Cryocoolers

An ideal pulse tube cryocooler using an ideal gas can operate at any temperature. This is not true for real gases. The enthalpy flow resulting from the real gas effects of 3He, 4He, and their mixtures in ideal pulse tube cryocoolers puts limits on the operating temperature of pulse tube cryocoolers. The discussion of these effects follows a previous description of the real gas effects in ideal pulse tube cryocoolers and makes use of models of the thermophysical properties of 3He and 4He. Published data is used to extend the analysis to mixtures of 3He and 4He. The analysis was done for pressures below 2 MPa and temperatures below 2.5 K. Both gases and their mixtures show low temperature limits for pulse tube cryocoolers. These limits are in the 0.5-2.2 K range and depend on pressure and mixture. In some circumstances, even lower temperatures may be possible. Pulse tube cryocoolers using the ha-fluid properties of dilute 3He in superfluid 4He appear to have no limit.

Kittel, Peter↗