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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Adhesive evaluation of LARC-TPI and a water-soluble version of LARC-TPI

The results of a study to evaluate two Langley Research Center thermoplastic polimide (TPI) materials, identified as TPI/MTC for the material from Mitsui Toatsu Chemicals Inc. and TPI/H2O for the material from United Technologies Research Center, as high temperature thermoplastic adhesives and primers for bonding titanium (6AL-4V) adherends are discussed. A limited characterization of the materials was performed using a Diffuse Reflectance-Fourier Transform Infrared Spectroscopy (DR-FTIR) technique. Thermomechanical Analysis (TMA) and torsional braid techniques were used to determine glass transition temperature. The adhesive's strength, as determined by simple lap shear tests, was used to evaluate the effects of long term thermal exposure (up to 1000 hrs) at 204 deg C and a 72-hour water-boil.

Progar, D. J.↗
NASA NTRS1994

Van Driest transformation and compressible wall-bounded flows

The transformation validity question utilizing resulting data from direct numerical simulations (DNS) of supersonic, isothermal cold wall channel flow was investigated. The DNS results stood for a wide scope of parameter and were suitable for the purpose of examining the generality of Van Driest transformation. The Van Driest law of the wall can be obtained from the inner-layer similarity arguments. It was demonstrated that the Van Driest transformation cannot be incorporated to collapse the sublayer and log-layer velocity profiles simultaneously. Velocity and temperature predictions according to the preceding composite mixing-length model were presented. Despite satisfactory congruity with the DNS data, the model must be perceived as an engineering guide and not as a rigorous analysis.

TRT-THEORETICAL↗
NASA NTRS2018

Fire Induced Rock Spalls as Long-Term Traps for Ash

Severe fires accelerate rock weathering by spalling and exfoliation, creating abundant peels, flakes or spalls. In the following years, these spalls serve as physical traps which accommodate fine particles of dust, ash, organic matter, etc. We searched for traces of ash trapped under the spalls, after four major fires: 1989, 2005, 2010 and 2015 in Israel. Samples were collected beneath the spalls that formed on the rock outcrops, and in the immediate vicinity above and below them. Three laboratory analyses were performed: pH, EC and color. Five mineral/organic compounds were measured across the Mid-Infrared (MIR) spectral region at diffuse reflectance infrared Fourier transform mode: Hydroxylapatite (HAp), charcoal, organic carbon, montmorillonite and kaolinite. Several statistical analyses were performed: MANOVA, PCA and silhouette analysis on K-means clustering. The results show evidence of ash trapped under the spalls formed during the 2005 and 2010 fires, 6 to 11 years after the fires. Charcoal presence is evident, as well as increased amounts of HAp and organic carbon. In the exposed soil above or below the burned rock outcrop, these values are lower. Negligible amounts of ash were measured 27 years after the fire. In the 2015 burned outcrop, large amounts of charcoal were found above and below the outcrop, but not under the spalls. It seems that on the carbonate slopes of Israel and under Mediterranean climate, the time required for spalls to begin functioning as traps is longer than one rainy season, while ash traces are preserved in these traps for a period of two-three decades.

ash↗
NASA NTRS2020

Polycyclic Aromatic Hydrocarbons and Dust Particle Surface Interactions: Catalytic Hydrogenation of Polycyclic Aromatic Hydrocarbon Molecules under Vacuum Conditions

This work reports experiments on the catalytic interaction occurring between polycyclic aromatic hydrocarbon (PAH) molecules and TiO2 dust grain surfaces under vacuum conditions. The investigation sheds light on the potential catalytic pathways that TiO2 dust surfaces provide in the hydrogenation of PAH molecules and the chemistry that can be driven by PAH-dust interactions under vacuum conditions. Naphthalene, anthracene, and coronene were chosen as the PAH molecules, while titanium dioxide was selected as the dust analog. PAH samples and dust analog mixtures were studied under vacuum for 24 h while monitored via diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The acquired spectra show that PAH molecules are hydrogenated when in contact with TiO2 dust particles without the need for external energy or hydrogen sources. Our results suggest that linear PAHs undergo a similar hydrogenation process where the dominant species are fully hydrogenated PAHs. For larger condensed PAHs, the hydrogenation process yields partially hydrogenated molecules. Fully hydrogenated species can be identified by a band around 2960 per cm, while partially hydrogenated species produce a band around 2825 per cm. In the case of the production of hydrogenated species, our results suggest that the smaller the PAH, the faster the hydrogenation rate.

polycyclic aromatic hydrocarbons↗
NASA NTRS1997

Diffuse Reflectance Mid-Infrared Spectroscopy as a Tool for the Identification of Surface Contamination on Sandblasted Metals

The SOC 400 Surface Inspection Machine/Infrared (SIMIR) is a small, ruggedized Fourier transform infrared spectrometer having dedicated diffuse reflectance optics. The SOC 400 was designed for the purpose of detecting (qualitatively and quantitatively) oil stains on the inside surface of solid rocket motor casings in the as-sandblasted and cleaned condition at levels approaching 1 mg. sq ft. The performance of this instrument is described using spectral mapping techniques.

G. Louis Powell↗
NASA NTRS1999

Investigation of Diffusion Flame Tip Thermodiffusive and Hydrodynamic Instability under Microgravity Conditions

We employ the opposed flow flame-spread configuration in order to examine flame-front instability of diffusion flames near cold, solid boundaries. The thermo-diffusive and hydrodynamic instabilities can transform an initially planar flame front into an irregularly curved, corrugated, possibly fragmented front. Under ordinary 1-g conditions, the buoyancy-induced flow masks the thermo-diffusive and hydrodynamic instabilities and produces planar flames. Such stable spreading flames have been observed for decades in laboratory experiments. Experiments in zero gravity are necessary to produce unstable flame fronts. The thermo-diffusive/hydrodynamic microgravity instability appears in diffusion flames such as, for example: the candle flame oscillations observed by Dietrich et al.; smolder instabilities on a recent Space Shuttle flight. Drs. T. Kashiwagi and S. Olson have attributed the latter to a lowered oxygen transport rate to the hot, reactive surface. Consider a burning surface near the flame extinction limit. The flow, or stretch, induced by the diffusion flame is weak, hence buoyancy plays a small role, thereby enabling previously secondary mechanisms, such as differential thermo-diffusion, to become the most important mechanisms. The flame leading edge becomes unstable; and diffusion flame breakup, oscillation, and rejoining all occur at a measurable frequency of approximately O(1 Hz). This project has only begun in January of this year, 1999. To date, there have been no flight experiments on flame spread instabilities. However, we have made numerous experiments in the NASA 2.2 and 5 second drop towers on flame spread over very thin cellulosic fuels. We have been very fortunate through a combination of factors, to be explained, to obtain some interesting, perhaps even compelling, results on diffusion flame instability in the presence of heat losses to cold surfaces.

Wichman, I. S.↗
NASA NTRS1990

Mechanism of the gamma-beta phase transformation of Mg2SiO4 at high temperature and pressure

The results of experiments on the phase transformation of Mg2SiO4 olivine at 15 GPa pressure in a multianvil cell are reported. At this pressure and a temperature of 900 C, early formed metastable gamma-spinel transforms partially to the beta-phase. The observed microstructures, which are similar to those in shocked meteorites, show that the gamma-to-beta transformation can occur either by diffusion-controlled growth or by a martensitic mechanism, depending on how far the pressure-temperature conditions deviate from their values at phase equilibrium. The results suggest that the diffusion-controlled mechanism is most likely to operate at the beta/gamma phase boundary in the mantle, but martensitic beta-to-gamma transformation might occur in subduction zones and could reduce the shear strength of the subducting slab.

Rubie, D. C.↗
NASA NTRS1988

Multifrequency imaging radar polarimetry: Depolarisation of radar echoes at three wavelengths

It is shown that high resolution imaging radar polarimeters can describe depolarization effects in great detail by measuring the complete Stokes matrix for small regions on the Earth's surface, permitting to distinguish between coherent polarization transformation by the surface and diffuse interactions that randomize the polarization state of the received wave. Multiwavelength polarimeter observations of a variety of types of terrain, including images of the coherent and diffuse parts of the received signal are presented. The diffuse image, in particular, is highly indicative of small-scale surface roughness, an effect illustrated by analyzing a set of polarimeter images acquired over lava fields of varying roughness.

Zebker, H. A.↗
NASA NTRS1989

Infrared spectroscopy (2.3-20 microns) for the geological interpretation of remotely-sensed multispectral thermal infrared data

The spectral radiance and spectral reflectance of natural weathered surfaces of common sedimentary and igneous rocks is determined from in situ and in the laboratory measurements. In situ spectral radiance measurements (5-14 microns) were made with a portable spectral radiometer and were used to derive the spectral emissivity of the rocks. The spectral reflectance measurements (2.3-20 microns) were made in a laboratory with a Fourier transform IR spectrometer with a diffuse reflectance accessory. Good agreement is found between the two techniques. The field portable spectrometer has a larger field of view and the in situ data provide more accurate measurements of the intensity of spectral features related to temperature and atmospheric effects.

Bartholomew, Mary Jane↗
NASA NTRS1986

The evolution and growth of Al2O3 scales on beta-NiAl

The formation and growth of Al2O3 scales on (beta)-NiAl were studied using electron microscopy and other analytical techniques to gain an understanding of the oxidation properties of (beta)-NiAl and of alumina-forming alloys, in general. The transient and mature stages of oxidation were studied as well as the transformation stage during which the oxide scale transforms from metastable Al2O3 phases to the thermodynamically stable alpha-Al2O3 phase. The transient oxidation stages were studied at 800 deg C and for short times at 1100C. At 800C, the scales consist predominantly of delta-Al2O3 which forms by cation vacancy ordering in the defective spinel lattice of gamma-Al2O3. At 1100C, a fast-growth morphology of theta-Al2O3 forms as a surface layer over delta-Al2O3. For both oxidation temperatures, the scales are often epitaxially oriented with respect to the metal. The transient scales grow by outward cation diffusion as evidenced by surface growth morphologies. The transformation to alpha-Al2O3 occurs within 1 hour at 1100C by a nucleation and radial growth process. The large volume decrease associated with the transformation results in a highly strained alpha-Al2O3 microstructure. A change in scale growth mechanism from outward cation to inward anion diffusion allows transient surface morphologies to be smoothed by surface diffusion. The mature stage of oxidation involves the growth of an alpha-Al2O3 scale having the lacey morphology formed as a result of the gamma yields alpha transformation. Growth of the scale occurs by counterdiffusion along grain boundaries resulting in ridges formed by impingement of alpha-Al2O3 nuclei during the transformation stage. Also scale growth occurs by inward oxygen diffusion through healed cracks; the cracks result from transformation stresses. The measured growth rates of scales having the lacey morphology are an order of magnitude less than fine-grained alpha-Al2O3 scales. Metal orientations were found to have a large effect on oxide morpholoies during all stages of oxidation.

Doychak, J. K.↗
NASA NTRS2010

Phase Transformation and Creep Behavior in Ti50Pd30Ni20 High Temperature Shape Memory Alloy in Compression

The creep behavior and the phase transformation of Ti50Pd30Ni20 High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

Kumar, Parikshith K.↗
NASA NTRS1983

Resin characterization in cured graphite fiber reinforced composites using diffuse reflectance-FTIR

The feasibility of using diffuse reflectance in combination with Fourier transform infrared spectroscopy to obtain information on cured graphite fiber reinforced polymeric matrix resin composites was investigated. Several graphite/epoxy, polysulfone, and polyimide composites exposed to thermal or radiation environments were examined. An experimental polyimide-sulfone adhesive tape was also studied during processing. In each case, significant changes in resin molecular structure was observed due to environmental exposure. These changes in molecular structure were correlated with previously observed changes in material properties providing new insights into material behavior.

Young, P. R.↗
NASA NTRS1984

Matrix Resin Characterization in Cured Graphite Composites Using Diffuse Reflectance-Ftir

The chemical characterization of cured graphite fiber reinforced polymer matrix composites is complicated by the fact that the resins are insoluble and the composites are apaque. Standard analyses which depend either on the ability to dissolve the sample or to detect transmitted radiation are impossible. As a result, data reported on environmentally exposed composites primarily concern macroscopic information such as weight loss or changes in selected mechanical properties. Diffuse reflectance in combination with fourier transform infrared spectroscopy was developed to gain a basic chemical understanding of composite and adhesive behavior. Several composite and adhesive materials were characterized before and after environmental exposure. In each case significant changes in resin molecular structure were observed and correlated with changes in mechanical properties, providing new insights into material performance.

Young, P. R.↗
NASA NTRS1986

Migration of the separation point on a deforming cylinder

An iterative scheme of solving the Navier-Stokes equations for unsteady two-dimensional flow about a deforming and translating cylinder is given. In the kth iteration, the convected vorticity appears as the source term in an equation of transient diffusion of vorticity. A novel integral transform is used to reduce this transient vorticity equation to a k-dimensional heat equation. The bounded solution of this equation is obtained with a general method of superposition for problems involving a moving boundary. An equation describing the migration of the separation point on a deforming cylinder in unsteady cross flows is derived from the analytically obtained velocity field. The radial expansion of the cylinder surface is shown to hasten the separation time and to increase the separation angle. The results imply that in the steady flow past a body that is moving forward and sinking at constant rates, the locus of points at which the azimuthal component of skin friction changes sign originates on the leeward ray at a point downstream of the front tip.

Lin, S. P.↗
NASA NTRS1988

Dendritic growth in the presence of convection

The motion of the freezing front between a dendritic crystal and a supercooled liquid is studied using an interface evolution equation derived from a boundary integral transformation of the transient convective-diffusion equation. A new steady-state theory is introduced that incorporates the effects of convection in dendritic growth. It is shown that in the absence of capillary effects the shape of the crystal-melt interface is a paraboloid of revolution, similar to that found in situations where diffusion is the sole heat transfer mechanism. A relation between the supercooling, the product of the tip velocity and tip radius, and the strength of the flow is derived which reduces to the well-known Ivantsov theory in the absence of convection. A non-linear interface-tracking algorithm is developed and used to study the temporal and spatial evolution of the dendritic interface. The important role of capillarity and convection on the interface dynamics is established and the response of the interface to finite amplitude disturbances is examined for the first time. Tip splitting is identified as the dominant destabilization mechanism in the limit of zero surface tension. Finite surface tension leads to interface stabilization, irrespective of the magnitude and structure of the external perturbations. Finally, convection significantly decreases the magnitude of the freezing velocity.

Beaghton, Pantelis John↗
NASA NTRS1992

Airborne Lidar Observations of the Stratosphere After the Pinatubo Eruption

The eruption of Mt. Pinatubo in June 1991 injected the largest mass of gases and ash into the stratosphere observed since lidar and satellite monitoring of the stratosphere became possible in the middle 1960's. Because of early indications of the significance of the eruption, NASA mounted an airborne mission to survey the stratospheric plume soon after the eruption. The NASA Wallops Electra aircraft was outfitted with a depolarization lidar, a correlation spectrometer (for SO2 measurements), a total-direct-diffuse spectral radiometer, and a Fourier transform spectrometer. Six flights were made during the period July 7-14.

Winker, David M.↗
NASA NTRS1993

Clouding tracing: Visualization of the mixing of fluid elements in convection-diffusion systems

This paper describes a highly interactive method for computer visualization of the basic physical process of dispersion and mixing of fluid elements in convection-diffusion systems. It is based on transforming the vector field from a traditionally Eulerian reference frame into a Lagrangian reference frame. Fluid elements are traced through the vector field for the mean path as well as the statistical dispersion of the fluid elements about the mean position by using added scalar information about the root mean square value of the vector field and its Lagrangian time scale. In this way, clouds of fluid elements are traced and are not just mean paths. We have used this method to visualize the simulation of an industrial incinerator to help identify mechanisms for poor mixing.

Ma, Kwan-Liu↗