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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 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

Hypervelocity impact tests on Space Shuttle Orbiter RCC thermal protection material

It is noted that the Shuttle Orbiter will be more subject to meteoroid impact than previous spacecraft, due to its greater surface area and longer cumulative time in space. The Orbiter structural material, RCC, a reinforced carbon-carbon laminate with a diffused silicon carbide coating, is evaluated in terms of its resistance to hypervelocity impact. It was found that the specimens (disks with a mass of 34 g and a thickness of 5.0 mm) were cratered only on the front surface when the impact energy was 3 J or less. At 3 J, a trace of the black carbon interior was exposed. The specimens were completely penetrated when the energy was 34 J or greater.

Humes, D. H.↗
NASA NTRS1979

On the rational design of compressible flow ejectors

A fluid mechanics review of chemical laser ejectors is presented. The characteristics of ejectors with single and multiple driver nozzles are discussed. Methods to compute an optimized performance map in which secondary Mach number and performance are computed versus mass ratio, to compute the flow distortion at each optimized condition, and to determine the thrust area for the design point to match diffuser impedence are examined.

Ortwerth, P. J.↗
NASA NTRS1985

Pulsed Excimer Laser Processing for Cost-Effective Solar Cells

Residual lattice damage by 5 keV ion implantation and surface flaws induced by wafer cleaning are proven to affect the V sub oc more adversely for laser annealed cells than conventional thermal diffusion. However, an alternative, molecular implantation of molecular species holds potential. The first experimental results are encouraging. The lack of a commercially available mass analyzed implantation with low energy, high fluence ions is constraining.

Wong, D.↗
NASA NTRS1987

Determination of surface shear stress with the naphthalene sublimation technique

Aeolian entrainment and transport are functions of surface shear stress and particle characteristics. Measuring surface shear stress is difficult, however, where logarithmic wind profiles are not found, such as regions around large roughness elements. An outline of a method whereby shear stress can be mapped on the surface around an object is presented. The technique involves the sublimation of naphthalene (C10H8) which is a function of surface shear stress and surface temperature. This technique is based on the assumption that the transfer of momentum, heat and mass are analogous (Reynolds analogy). If the Reynolds analogy can be shown to be correct for a given situation, then knowledge of the diffusion of one property allows the determination of the others. The analytical framework and data acquisition for the method are described. The technique was tested in the Planetary Geology Wind Tunnel. Results show that the naphthalene sublimation technique is a reasonably accurate method for determining shear stress, particularly around objects where numerous point values are needed.

Lee, J. A.↗
NASA NTRS1988

On the structure and circulation of the polar thermosphere under magnetically quiet conditions

A theoretical study of the thermospheric circulation and composition at polar latitudes is presented. It is suggested that the observed motions and density perturbations in N2, O and He can be understood in terms of electric field momentum coupling, Joule heating, and interactions between these two processes. It is found that the vortex type double cell polar circulation is primarily driven by collisional momentum transfer from electric field induced ion convection. Because of the thermospheric low pass filter, a large time independent component is produced by Joule heating. Due to wind induced diffusion, the N2 is concentrated where the O and He are depleted and vice versa. The electric field driven vortex circulation redistributes the mass and energy in the time independent density and temperature variations, producing primarily diurnal variations in the temperature and composition near the pole and at auroral latitudes.

Mayr, H. G.↗
NASA NTRS1956

Zero-angle-of-attack Performance of Two-dimensional Inlets near Mach Number 3

An extensive program was undertaken to investigate the effect of several geometric variables on the performance of two-dimensional inlets. This investigation included inlets having single-wedge, double-wedge, and isentropic compression ramps with various side-plate configurations and subsonic diffusers. The tests were conducted over a range of Reynolds number based on inlet height from 0.50 to 2.67(sup x)10(sup 6). Generally, the performance levels of the two-dimensional inlets were somewhat below those obtained previously with comparable axisymmetric models. At Mach number 3.05 the optimum total-pressure recovery was obtained with an isentropic inlet which compressed the external flow to a Mach number of 1.88. Rectangular side plates and a long high-exit-Mach-number subsonic diffuser with filleted corners were used with this inlet. A critical total-pressure recovery of 0.71 was realized with a corresponding mass-flow ratio of 0.965. Subcritical stability to a mass-flow ratio of 0.60 was obtained.

Woollett, Richard R↗
NASA NTRS2005

Review of HxPyOz-Catalyzed H + OH Recombination in Scramjet Nozzle Expansions; and Possible Phosphoric Acid Enhancement of Scramjet Flameholding, from Extinction of H3PO4 + H2 - Air Counterflow Diffusion Flames

Recent detailed articles by Twarowski indicate that small quantities of phosphorus oxides and acids in the fuel-rich combustion products of H2 + phosphine (PH3) + air should significantly catalyze H, OH and O recombination kinetics during high-speed nozzle expansions -- to reform H2O, release heat, and approach equilibrium more rapidly and closely than uncatalyzed kinetics. This paper is an initial feasibility study to determine (a) if addition of phosphoric acid vapor (H3PO4) to a H2 fuel jet -- which is much safer than using PH3 -- will allow combustion in a high-speed scramjet engine test without adverse effects on localized flameholding, and (b) if phosphorus-containing exhaust emissions are environmentally acceptable. A well-characterized axisymmetric straight-tube opposed jet burner (OJB) tool is used to evaluate H3PO4 addition effects on the air velocity extinction limit (flame strength) of a H2 versus air counterflow diffusion flame. Addition of nitric oxide (NO), also believed to promote catalytic H-atom recombination, was evaluated for comparison. Two to five mass percent H3PO4 in the H2 jet increased flame strength 4.2%, whereas airside addition decreased it 1%. Adding 5% NO to the H2 caused a 2% decrease. Products of H-atom attack on H3PO4 produced an intense green chemiluminescence near the stagnation point. The resultant exothermic production of phosphorus oxides and acids, with accelerated H-atom recombination, released sufficient heat near the stagnation point to increase flame strength. In conclusion, the addition of H3PO4 vapor (or more reactive P sources) to hydrogen in scramjet engine tests may positively affect flameholding stability in the combustor and thrust production during supersonic expansion -- a possible dual benefit with system design / performance implications. Finally, a preliminary assessment of possible environmental effects indicates that scramjet exhaust emissions should consist of phosphoric acid aerosol, with gradual conversion to phosphate aerosol. This is compared to various natural abundances and sources.

Pellett, Gerald↗
NASA NTRS2003

Filament Eruption without Coronal Mass Ejection

We report characteristics of quiescent filament eruptions that were not associated with coronal mass ejections (CMEs). We examined 12 quiescent filament eruptions, each of which was located far from disk center (20.7 R(sub sun)) in diffuse remnant magnetic fields of decayed active regions, was well observed in full-disk movies in Ha and Fe XI, and had good coronagraph coverage. Of the 12 events, 9 were associated with CMEs and 3 were not. Even though the two kinds of eruption were indistinguishable in their magnetic setting and in the eruptive motion of the filament in the Ha movies, each of the CME-producing eruptions produced a two-ribbon flare in Ha and a coronal arcade and/or two-ribbon flare in Fe XII, and each of the non-CME-producing eruptions did not. From this result, and the appearance of the eruptive motion in the Fe XII movies, we conclude that the non-CME-associated filament eruptions are confined eruptions like the confined filament eruptions in active regions.

Choudhary, Debi Prasad↗
NASA NTRS2020

Effect of Ram and Zenith Exposure on the Optical Properties of Polymers in Space

The temperature of spacecraft is influenced by the solar absorptance and thermal emittance of the external spacecraft materials in addition to heat generated within the spacecraft. Optical and thermal properties can degrade in the low Earth orbital (LEO) space environment where spacecraft external materials are exposed to various forms of radiation, thermal cycling, and atomic oxygen. One objective of the Polymers and Zenith Polymers Experiments was to determine the effect of LEO space exposure on the optical properties of various spacecraft polymers. These experiments were flown as part of the Materials International Space Station Experiment 7 (MISSE 7) mission on the exterior of the International Space Station (ISS) for 1.5 years. Samples were flown in ram, wake and zenith directions, receiving varying amounts of atomic oxygen and solar radiation. Total and diffuse reflectance, and transmittance, of flight and corresponding control samples were obtained using a Cary 5000 UV-Vis-NIR Spectrophotometer. Integrated air mass zero solar absorptance (as) of the flight and control ram and zenith samples were computed and compared. Optical and atomic oxygen erosion data are compared with similar MISSE 2 polymers exposed to space for four years. Results show that prolonged space exposure increases the solar absorptance of some materials. Knowing which polymers remain stable will benefit future spacecraft design.

Atomic oxygen, erosion, space radiation, optical p↗
DOE OSTI2025

Effects of Temperature Fluctuations on Surface Mobility of Atomic Steps and Oxidation Dynamics in High-Temperature Alloys

In contrast to the traditional perspective that thermal fluctuations are insignificant in surface dynamics, here we report their influence on surface reaction dynamics. Using real-time low-energy electron microscopy imaging of NiAl(100) under both vacuum and O 2 atmospheres, we demonstrate that transient temperature variations substantially alter the direction of atom diffusion between the surface and bulk, leading to markedly different oxidation outcomes. During heating, substantial outward diffusion of atoms from the bulk to the surface results in step growth. Conversely, cooling induces considerable inward diffusion of adatoms, producing a distinct oxide morphology. In both scenarios, initially formed oxide islands impede local atomic step mobility, thereby increasing step length due to mass transfer between the surface and bulk, with atomic steps acting as adatom sinks during heating and sources during cooling. Furthermore, we show that this pinning effect on atomic step mobility can be mitigated by applying persistent temperature fluctuations. As a result, understanding these nuances is vital for accurately predicting and dynamically manipulating the performance of active materials in various chemical processes under transient thermal conditions.

36 MATERIALS SCIENCE↗
NASA NTRS1997

Application of Shear Plate Interferometry to Jet Diffusion Flame Temperature Measurements

The recent ban on the production of bromotrifluoromethane (CF3Br) because of its high stratospheric ozone depletion potential has led to interest in finding alternative agents for fire extinguishing applications. Some of the promising alternatives are fluorinated hydrocarbons. A clear understanding of the effects of CF3Br and alternative chemical suppressants on diffusion flames is therefore necessary in the selection of alternative suppressants for use in normal and microgravity. The flame inhibition effects of halogen compounds have been studied extensively in premixed systems. The effect of addition of halocarbons (carbon-halogen compounds) to diffusion flames has been studied experimentally in coflow configurations and in counterflow gaseous and liquid-pool flames. Halogenated compounds are believed to inhibit combustion by scavenging hydrogen radicals to form the relatively unreactive compound HF, or through a catalytic recombination cycle involving HBr to form H2. Comparisons between halogens show that bromine inhibition is significantly more effective than chlorine or fluorine. Although fluorinated compounds are only slightly more effective inhibitors on a mass basis than nitrogen, they are more effective on a volume basis and are easily stored in liquid form. The objectives of this study are (a) to determine the stability limits of laminar jet diffusion flames with respect to inhibitor concentration in both normal and microgravity, and (b) to investigate the structure of halocarbon-inhibited flames. In the initial phase of this project, visual diagnostics were used to observe the structure and behavior of normal and microgravity flames. The initial observations showed significant changes in the structure of the flames with the addition of halocarbons to the surrounding environment, as discussed below. Furthermore, the study established that the flames are more stable relative to the addition of halocarbons in microgravity than in normal gravity. Visual diagnostics of flames are, however, necessarily limited to detection of radiative emission in the visible range, and offer only qualitative information about the nature of the processes in the flame. In particular, the study sought to understand the structure of the inhibitor-perturbed flames with regard to temperature and species concentration in the outer region of the flame. Whereas thermocouple measurements can be used in ground based studies, their implementation in drop-tower rigs is limited. A possible approach to determine the temperature field around the flame is to use interferometric techniques. The implementation and testing of a shear-plate interferometry technique is described below.

VanDerWege, Brad A.↗
NASA NTRS1973

Quasi-steady plasma acceleration.

A coaxial plasma accelerator driven by protracted pulses of current in the range of 10,000 to 100,000 A and synchronized mass flows from 1.0 to 36 g/sec argon attains, after some tens of microseconds, a stable magnetoplasmadynamic acceleration mode. This 'quasi-steady' discharge form is characterized by constant terminal voltage and current, a diffuse, fixed current distribution within the discharge, and a steady plasma efflux at velocities of approximately 20 km/sec. Measured potential distributions reveal that the bulk of the arc voltage gradient, exclusive of the electrode falls, occurs within two diameters of the cathode, and is normal to it. The anode fall voltage varies inversely with local current density, implying substantially lower anode losses at higher power arc operation. Spectroscopic, potential, and velocity measurements indicate the existence of a characteristic mass flow rate for a given current, below which arc operation becomes erratic.

Jahn, R. G.↗
DOE OSTI2021

Mass transport in nanoarray monolithic catalysts: An experimental-theory study

Reducing the mass transfer resistance globally of a catalyst is a key to enhancing the catalytic reaction kinetics and fully utilizing the catalyst activity. Despite the success in tailoring the external mass transfer in the widely studied washcoat monoliths, the internal mass transfer resistance is difficult to be reduced due to the requirement of increasing macroporosity while maintaining high specific surface area and mechanical stability. Therefore, nanostructured array-based monolithic catalysts (nanoarray catalysts) have been developed in the past decade as a promising class of structured catalysts that may complement or substitute washcoat catalysts. This work fundamentally elucidates the enhanced mass transport properties of the nanoarray monolithic catalysts by a combination of experimental measurements and theoretical modeling. Using a low-dimensional model, the relative contributions of resistances were quantified in terms of chemical kinetics, internal and external mass transfers based on a probe model of C2H4 oxidation over the TiO2 supported Pt-based monolithic catalysts. The nanoarray catalysts displayed a lower internal mass transfer resistance than the washcoat counterparts as a result of the high macroporosity and small thickness of nanoarray layers. Finally, the nanoarray configuration provides a new pathway towards designing high-performance monolithic reactors and catalysts with low internal diffusion limitations for various gas phase reactions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Merging of transport theory with the time-dependent Hartree-Fock approach: Multinucleon transfer in U + U collisions

Multinucleon transfer mechanism in the collision of 238 U + 238 U system is investigated at E c.m. = 833 MeV in the framework of the quantal diffusion description based on the stochastic mean-field approach. Double cross sections σ (N, Z ) as a function of the neutron and proton numbers, the cross sections σ (Z ) and σ (A) as a function of the atomic numbers and the mass numbers are calculated for production of the primary fragments. The calculation indicates the 238 U + 238 U system may be located at an unstable equilibrium state at the potential energy surface with a slightly negative curvature along the β stability line on the (N, Z ) plane. Here, this behavior may lead to rather large diffusion along the β stability direction.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2019

Adjoint-Based Mesh Adaptation and Shape Optimization for Simulations with Propulsion

We demonstrate a well-posed formulation of permeable boundary conditions and mass- flow-rate functionals for adjoint-based mesh refinement and shape optimization governed by the steady Euler equations. The boundary conditions are used to model propulsion- system effects of inlets and nozzles. A two-shock diffuser with an analytic solution is used to verify the implementation. Numerical examples show that the adjoint solution is smooth at the boundary, indicating that the discretization is adjoint consistent when exit pressure is specified at subsonic outflow, and stagnation temperature and pressure at subsonic inflow. The results focus on improving simulation techniques for low-boom aircraft analysis and design. By including mass-flow-rate outputs, we obtain reliable estimates of engine flow rates concurrently with nearfield pressure signatures without increasing simulation cost. We also demonstrate the importance of mass-flow-rate constraints in shape optimization by examining trade-offs between maximizing performance of a shrouded supersonic nozzle and minimizing shocks in its nearfield.

Nemec, Marian↗
NASA NTRS1974

A new model of atmospheric gamma rays and its implications for measurement of diffuse cosmic gamma rays from within the atmosphere

A semi-empirical model is discussed which describes atmospheric gamma rays in the range 0.3 less then or equal to E less than or equal to 10 MeV based on the production per unit mass of air. The model is based on the concept of a source strength (photon/g sec MeV) which is energy- and depth-dependent, and derived from measured fluxes. Quantities such as directional fluxes, angular distributions, and growth curves are calculated directly from this model. The source function is described by four energy-dependent parameters determined empirically from fluxes measured with a 7.5 cm x 7.5 cm Nal counter over the atmospheric depth range from 3.5 to 500 g/sq cm. From S(E,x), obtained for both continuum and discrete gamma rays at lambda = 40 deg, the depth and angle dependence of directional fluxes were calculated. Growth-curve predictions needed to separate atmospheric from diffuse cosmic fluxes were determined.

Matteson, J. L.↗
NASA NTRS1985

The importance of Soret transport in the production of high purity silicon for solar cells

Temperature-gradient-driven diffusion, or Soret transport, of silicon vapor and liquid droplets is analyzed under conditions typical of current production reactors for obtaining high purity silicon for solar cells. Contrary to the common belief that Soret transport is negligible, it is concluded that some 15-20 percent of the silicon vapor mass flux to the reactor walls is caused by the high temperature gradients that prevail inside such reactors. Moreover, since collection of silicon is also achieved via deposition of silicon droplets onto the walls, the Soret transport mechanism becomes even more crucial due to size differences between diffusing species. It is shown that for droplets in the 0.01 to 1 micron diameter range, collection by Soret transport dominates both Brownian and turbulent mechanisms.

Srivastava, R.↗
DOE OSTI2021

Taylor dispersion in osmotically driven laminar flows in phloem

Sucrose is among the main products of photosynthesis that are deemed necessary for plant growth and survival. It is produced in the mesophyll cells of leaves and translocated to different parts of the plant through the phloem. Progress in understanding this transport process remains fraught with experimental difficulties, thereby prompting interest in theoretical approaches and laboratory studies. The Münch pressure and mass flow model is one of the accepted hypotheses describing the physics of sucrose transport in the phloem. It is based on osmosis creating an energy potential difference between the source and the sink. The flow responding to this energy potential is assumed laminar and described by the Hagen–Poiseuille equation. This study revisits such osmotically driven flows in tubes with membrane walls by including the effects of Taylor dispersion on mass transport. This effect has been overlooked in phloem flow studies. Taylor dispersion can increase the effective transport of solutes by increasing the apparent diffusion coefficient. It is shown that, in addition to the conventional diffusive correction derived for impermeable tube walls, a new adjustment to the mean advective terms arises because of osmotic effects. Because the molecular Schmidt number is very large for sucrose in water, the sucrose front speed and travel times have a direct dependence on the Péclet number for different ranges of the Münch number. Fially, this study establishes upper limits on expected Taylor dispersion enhancement of sucrose transport.

42 ENGINEERING↗