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At least 1,045 records · Page 58
All sourcesNASA NTRSDOE OSTI
NASA NTRS2013

Shear Stress Sensing using Elastomer Micropillar Arrays

The measurement of shear stress developed as a fluid moves around a solid body is difficult to measure. Stresses at the fluid-solid interface are very small and the nature of the fluid flow is easily disturbed by introducing sensor components to the interface. To address these challenges, an array of direct and indirect techniques have been investigated with various advantages and challenges. Hot wire sensors and other indirect sensors all protrude significantly into the fluid flow. Microelectromechanical systems (MEMS) devices, although facilitating very accurate measurements, are not durable, are prone to contamination, and are difficult to implement into existing model geometries. One promising approach is the use of engineered surfaces that interact with fluid flow in a detectable manner. To this end, standard lithographic techniques have been utilized to generate elastomeric micropillar arrays of various lengths and diameters. Micropillars of controlled length and width were generated in polydimethylsiloxane (PDMS) elastomer using a soft-lithography technique. The 3D mold for micropillar replication was fabricated using laser ablative micromachining and contact lithography. Micropillar dimensions and mechanical properties were characterized and compared to shear sensing requirements. The results of this characterization as well as shear stress detection techniques will be discussed.

Wohl, Christopher J.↗
NASA NTRS2017

The Chemistry of Pluto and its Satellites

Pluto's bulk composition and the composition of the surface layers hold clues to the origin and evolution of a number of other Solar System bodies of comparable size in the region beyond Neptune. The July 14, 2015 flyby of the Pluto system with the New Horizons spacecraft afforded the opportunity to corroborate and greatly improve discoveries about the planet and its satellites derived Earth-based studies. It also revealed extraordinary details of the surface and atmosphere of Pluto, as well as the geology and composition of Charon and two smaller satellites. With a mean density of 1.86 g/sq cm, the bulk composition of Pluto is about two-thirds anhydrous solar composition rocky material and one-third volatiles (primarily H2O in liquid and solid states) by mass, the surface is a veneer of ices dominated by N2, with smaller amounts of CH4 and CO, as well as limited exposures of H2O ice (considered to be "bedrock"). N2, CH4, and CO occur as solid solutions at temperature-dependent mutual concentrations, each component being soluble in the others. Frozen C2H6 as a minor component has also been identified. Sublimation and recondensation of N2, CH4, and CO over seasonal (248 y) and Milankovich-type megaseasons (approx. 3 My) result in the redistribution of these ices over time and with latitude control. Solid N2 is found in glaciers originating in higher elevations and flowing at the present time into a basin structure larger than the State of Texas, forming a convecting lens of N2 that overturns on a timescale of order 10 My. The varied colors of Pluto's landscape arise from the energetic processing of the surface ices in processes that break the simple molecules and reassemble complex organic structures consisting of groups of aromatic rings connected by aliphatic chains. When synthesized in the laboratory by UV or electron irradiation of a Pluto mix of ice, this material, called tholin, has colors closely similar to Pluto. The Pluto ice tholin analog contains carboxylic acids, urea, ketones, aldehydes, amines, and some nitriles. The largest satellite, Charon has density 1.70 g/sq cm and it is about 3/5 anhydrous solar composition rock, with the remainder in H2O ice. The surface H2O ice is infused in some way with NH3, probably as a hydrate, distributed nonuniformly, but to some degree related to geological structures. Pluto's atmosphere is N2, CH4, with CO, C2-hydrocarbons, HCN, and other molecules in trace but detectable amounts. The atmosphere supports a complex haze structure with about 20 discrete layers, and suspected clouds. The haze is presumed to be made of aggregates of complex hydrocarbons (tholins) produced by photolysis of the atmospheric gases, and with similar composition to the ice tholins made on the planet's surface. Urea and a suite of carboxylic acids are of interest for prebiotic and biological chemistries.

SOLAR SYSTEMS↗
NASA NTRSDate not supplied

Atmospheric Escape and Planetary Atmosphere Evolution. the Complex Role of Magnetization

Exoplanetary research is currently steered by investigations into the characteristics and evolution of their atmospheres. The fundamental inquiries encompass whether a given exoplanet possesses an atmosphere and, if so, how its attributes have evolved over time. The atmospheric composition reflects a delicate equilibrium between the inbound and outbound flows of volatiles, whether between space, surface, or between liquid and solid phases. Understanding atmospheric escape is, therefore, a critical facet of such studies. Especially, exoplanets that are relatively light and situated near their host stars are prone to substantial atmospheric loss, potentially resulting in barren celestial bodies. Thus, it becomes vital to comprehend the atmospheric responses to the host stars' activities, alongside other factors influencing atmospheric evolution. In that context, there persists a common narrative in the scientific community that frames a planetary magnetic field as a 'shield' against atmospheric escape. However, this study challenges the oversimplification of this premise, taking a closer look at the nuanced role magnetization plays in planetary atmospheric defense mechanisms. We will review the escape processes in the light of the different mechanisms and of the recent observations to highlight which processes have to carefully be taken into account.

Guillaume Gronoff↗
DOE OSTI2021

Novel Membrane-Based Corrosion Sensors For Operating In Natural Gas Pipelines

Membrane-based electrochemical sensors (MBES) provide an attractive option for real-time continuous humidity and corrosion rate measurements inside of natural gas pipelines. The MBES, can use electrochemical techniques such as linear polarization resistance and electrochemical impedance spectroscopy even when a conductive aqueous phase is intermittent or unavailable. We now present field-test performance data of our MBES operated inside a multiphase water and natural gas flow facility. The MBES measured internal corrosion and conductivity at the top, bottom, and side of the pipe spool. Tests were carried out with flow rates of 4.6, 9.1, and 18.3 m/s, temperatures of 21, 29, and 35 °C, and a pressure of 1000 psia. All sensors followed similar trends in open circuit potential, corrosion rate, and conductivity over time. Neither flow rate, temperature, nor build-up of metal-based solids on the sensor surfaces impacted the quality of the electrochemical measurements. The field-test results confirm that the membrane-based electrochemical sensors are suitable for monitoring internal corrosion of operational natural-gas pipelines.

Duffy, Timothy↗
DOE OSTI2023

Electrochemical Characterization of Molten Salt Chemistry During Atmospheric Ingressions

This report describes the salt chemistry and sedimentation studies that were completed in FY23 as part of the Pyrochemical Fuel Cycles – ANL project. The primary objective of these activities was to employ electrochemical methods in order to quantify and gain insights into the reaction mechanisms associated with the interaction of O2 and moisture impurities with the molten chloride salts used for the pyrochemical processing of nuclear materials. If not monitored and controlled, the ingression of these atmospheric impurities can lead to changes in the salt redox conditions and initiate the formation of oxide particles, potentially resulting in operational and safeguards challenges. By elucidating the mechanisms underlying the formation of oxide particles, we can effectively monitor the conditions of the salt and design systems to mitigate the influence of atmospheric O2 and H2O. To achieve these goals, we designed a test system that allowed for precisely controlled gas ingressions into the molten salt vessel. This system included on-line monitoring provided by electrochemical probes that enable near real-time measurements of the salt conditions throughout the course of the experiment. Using this system, we systematically varied experimental conditions, including O2/Ar flow rates and O2 concentrations, to comprehensively understand their impact on solid particle formation. We also used a particle size and shape analyzer to characterize the particles that were generated. Tests in FY23 concentrated on the formation of CeO2 particles, but we also prepared a separate apparatus targeting UO2 particles for use in FY24. We additionally conducted extensive modeling activities in support of this work. This included multiphysics simulations of the gas ingressions along with the development of a machine learning workflow to enable accelerated molecular dynamics modeling of the molten salt chemistry of LiCl-KCl-UCl3. The combination of experimental and modeling tools has allowed us to begin to get a more complete understanding of the reactions that occur when atmospheric ingressions occur in pyroprocessing systems.

Guo, Jicheng↗
NASA NTRS1969

Fundamental considerations for future solid lubricants

Properties important to the performance of solid lubricants are discussed. Those properties include shear characteristics, coherence between particles, resistance to cold flow, adherence to the substrate, applicable chemical thermodynamics and kinetics of materials and environments, polymorphism, and rheology. The following generalizations are made: (1) chemical thermodynamics and kinetics are powerful tools for use in determining the useful environments and methods of application for solid film lubricants; (2) the primary requirement for a solid lubricant is low shear strength; (3) the rheology of solid film constituents and formulations is likely to be of vital importance to performance and life; and (4) adherence and mobility of surface films is another primary requirement for long lived solid lubricants.

Johnson, R. L.↗
NASA NTRS1980

Combustion behavior of solid fuel ramjets

Nonreacting flowfield characteristics and fundamental fuel properties are considered with respect to their use in estimating the obtainable combustion efficiency for fuels and/or combustor geometries. It is shown that near wall turbulence intensity in nonreacting flow appears to correlate reasonably well with the fuel regression pattern in identical geometries. The HTPB based fuels exhibit solid phase exothermic reactions in contrast to purely endothermic reactions for plexiglas. It is further shown that combustion pressure oscillations appear to be related to physically induced disturbances to the fluctuating shear layers at the fuel grain and aft mixing chamber inlets.

Netzer, D. W.↗
DOE OSTI2025

A real-time distributed solid oxide electrolysis cell (SOEC) model for cyber-physical simulation

System integration and dynamic operability between SOEC and balance-of-plant (BoP) components are major technical challenges before realizing rapid load following of SOEC systems. Cyber-physical simulation (CPS) is a leading-edge digital engineering approach and is regarded as the next step beyond Digital Twins. CPS approach can be used to research SOEC system integration and develop dynamic controls prior to actual pilot testing without using a real SOEC. To seamlessly couple with BoP hardware and access non-observable operational parameters (e.g., local temperature gradient) during transients, a distributed one-dimensional (1D) real-time SOEC model was developed. Its real-time execution was demonstrated for 20 to 640 nodes at the fixed time step of 5 ms. A higher excess air ratio enabled smaller local temperature gradients on SOEC solid materials and faster transients upon current density step change from 0.15 to 0.55 A cm -2 . During the transients, the magnitude of the peak temperature gradient nearly doubled in 10 s from -3.5 to -5.9 °C cm -1 . This represents a significant operating risk that can impact the dynamic operability of SOEC systems. In addition, the local temperature gradient was found to change directions on all nodes in SOEC solid materials, with the greatest impact on the upstream nodes. The SOEC model was also tested at the thermal neutral voltage using actual process air flow parameters as variable model inputs. Variable process air temperatures were found to induce alternating local temperature gradients on SOEC solid materials. These are new operational mechanisms for SOEC degradation relevant for load following operational modes yet distinct from previous reports. To mitigate these unfavorable features, the SOEC can be operated at voltages that are slightly (±20 mV) deviated from the thermal neutral voltage. Here, the corresponding net thermal energy change was less than 1.6% of the electric power consumption. This 1D real-time SOEC model established the basis of cyber-physical simulation of SOEC hybrid systems.

24 POWER TRANSMISSION AND DISTRIBUTION↗
NASA NTRS1990

Keyhole and weld shapes for plasma arc welding under normal and zero gravity

A first order study of the interfacial (keyhole) shape between a penetrating argon plasma arc jet and a stationary liquid metal weld pool is presented. The interface is determined using the Young-Laplace equation by assuming that the plasma jet behaves as a one-dimensional ideal gas flow and by neglecting flow within the weld pool. The solution for the keyhole shape allows an approximate determination of the liquid-solid metal phase boundary location based on the assumption that the liquid melt is a stagnant thermal boundary layer. Parametric studies examine the effect of plasma mass flow rate, initial plasma enthalpy, liquid metal surface tension, and jet shear on weldment shape under both normal and zero gravity. Among the more important findings of this study is that keyhole and weld geometries are minimally affected by gravity, suggesting that data gathered under gravity can be used in planning in-space welding.

Keanini, R. G.↗
DOE OSTI2025

Operando Neutron Imaging of Reaction Extent and Particle Swelling Informs Limiting Factors for Salt Hydrate Thermochemical Energy Storage

Salt hydrates are a promising thermochemical energy storage medium that stores heat through the reversible uptake (hydration) and release (dehydration) of water vapor. Our study deploys operando neutron imaging to investigate salt hydrate performance with high spatial resolution (42 μm pixels). For flow over a packed bed with diffusion-driven transport, measurements reveal the formation of a solid diffusion layer due to particle swelling for the pure SrBr2 salt. In contrast, the SrBr2–vermiculite composite exhibits significantly less swelling and more than a 2-fold increase in the apparent water vapor diffusivity. For axial flow through a packed bed, neutron imaging confirms theoretically predicted transitions from a moving reaction front to a homogeneous profile with an increase in humid air flow rate. Our study establishes neutron imaging as a powerful technique to advance fundamental understanding of thermochemical systems and help guide composite material design.

Kinzer, Bryan [ORNL] (ORCID:0000000337804910)↗
NASA NTRS1994

Compton scattering in jets: A mechanism for approximately 0.4 and less than or approximately 0.2 MeV line production

We show that gamma-ray line emission at approximately 0.4 and less than or approximately 0.2 MeV can be produced by Compton scattering of beamed radiation in the jets of Galactic black hole candidates. This mechanism has the novel feature of not invoking the presence of e(exp +)-e(exp -) pairs. To produce the two lines, we employ a symmetric double-sided jet with bulk flow velocity of about 0.5c and incident beam radiation with a hard energy spectrum. We show that the two lines can be seen at viewing-angle cosines relative to the jet ranging from 0.2 to 0.6. This comprises 40% of the total solid angle. In addition, the line radiation is approximately 10% polarized. Depending on the bulk flow and viewing angle, the model can produce lines at other energies as well. In particular, a broad feature near 1 MeV can be seen by viewing the jet close to its axis. Our model can also accommodate single-line spectra if the beamed gamma-ray emission or the jets themselves are asymmetric.

Skibo, J. G.↗
NASA NTRS1971

The combustion of pure and composite propellants - The expansion and application of laminar flame theory to heterogeneous solid propellants.

Development of a combustion theory based on the laminarized solutions to the energy and flow conservation equations, which is more realistic in recognizing the nature of the heating-rate problem and in obtaining a practical solution to estimating its magnitude. A new experimental approach is used for studying the combustion behavior of pure monopropellants and composite propellants which uses a laser beam to supply additional heat feedback to a burning surface. New experimental data are presented for the laser-induced combustion rate and ignition delay of pure ammonium perchlorate. The pure monopropellant theory is generalized to include such nonadiabatic effects, and the new experimental data are in good agreement with the nonadiabatic theory.-

Hertzberg, M.↗
NASA NTRS1973

Experimental and theoretical investigations in two-dimensional transonic flow.

Experimental and theoretical results are presented from a study of the flow over a family of transonically scaled circular-arc bodies mounted in a solid-wall wind tunnel. Data are presented for Reynolds numbers between 30,000 and 3,600,000, based on chord. The high Reynolds number results are compared with computations based on inviscid theory, and are used to investigate transonic similarity and the behavior of the flow near choking. The results at low Reynolds number are used to demonstrate the effect of viscosity on the overall flowfield, and comparisons are made with existing laminar viscous/inviscid interaction theory.

Collins, D. J.↗
NASA NTRS1999

Multiphysics Simulation of Active Hypersonic Lip Cooling

This article describes the application of the Multidisciplinary Analysis (MDA) solver, Spectrum, in analyzing a hydrogen-cooled hypersonic cowl leading-edge structure. Spectrum, a multiphysics simulation code based on the finite element method, addresses compressible and incompressible fluid flow, structural, and thermal modeling, as well as the interactions between these disciplines. Fluid-solid-thermal interactions in a hydrogen impingement-cooled leading edge are predicted using Spectrum. Two- and semi-three-dimensional models are considered for a leading edge impingement coolant, concept under either specified external heat flux or aerothermodynamic heating from a Mach 5 external flow interaction. The solution accuracy is demonstrated from mesh refinement analysis. With active cooling, the leading edge surface temperature is drastically reduced from 1807 K of the adiabatic condition to 418 K. The internal coolant temperature profile exhibits a sharp gradient near channel/solid interface. Results from two different cooling channel configurations are also presented to illustrate the different behavior of alternative active cooling schemes.

Melis, Matthew E.↗
NASA NTRS2012

Real-Time X-ray Radiography Diagnostics of Components in Solid Rocket Motors

Solid rocket motors (SRMs) typically use nozzle materials which are required to maintain their shape as well as insulate the underlying support structure during the motor operation. In addition, SRMs need internal insulation materials to protect the motor case from the harsh environment resulting from the combustion of solid propellant. In the nozzle, typical materials consist of high density graphite, carbon-carbon composites and carbon phenolic composites. Internal insulation of the motor cases is typically a composite material with carbon, asbestos, Kevlar, or silica fibers in an ablative matrix such as EPDM or NBR. For both nozzle and internal insulation materials, the charring process occurs when the hot combustion products heat the material intensely. The pyrolysis of the matrix material takes away a portion of the thermal energy near the wall surface and leaves behind a char layer. The fiber reinforcement retains the porous char layer which provides continued thermal protection from the hot combustion products. It is of great interest to characterize both the total erosion rates of the material and the char layer thickness. By better understanding of the erosion process for a particular ablative material in a specific flow environment, the required insulation material thickness can be properly selected. The recession rates of internal insulation and nozzle materials of SRMs are typically determined by testing in some sort of simulated environment; either arc-jet testing, flame torch testing, or subscale SRMs of different size. Material recession rates are deduced by comparison of pre- and post-test measurements and then averaging over the duration of the test. However, these averaging techniques cannot be used to determine the instantaneous recession rates of the material. Knowledge of the variation in recession rates in response to the instantaneous flow conditions during the motor operation is of great importance. For example, in many SRM configurations the recession of the solid propellant grain can drastically alter the flow-field and effect the recession of internal insulation and nozzle materials. Simultaneous measurement of the overall erosion rate, the development of the char layer, and the recession of the char-virgin interface during the motor operation can be rather difficult. While invasive techniques have been used with limited success, they have serious drawbacks. Break wires or make wire sensors can be installed into a sufficient number of locations in the charring material from which a time history of the charring surface can be deduced. These sensors fundamentally alter the local structure of the material in which they are imbedded. Also, the location of these sensors within the material is not known precisely without the use of an X-ray. To determine instantaneous recession rates, real-time X-ray radiography (X-ray RTR) has been utilized in several SRM experiments at PSU. The X-ray RTR system discussed in this paper consists of an X-ray source, X-ray image intensifier, and CCD camera connected to a capture computer. The system has been used to examine the ablation process of internal insulation as well as nozzle material erosion in a subscale SRM. The X-ray source is rated to 320 kV at 10 mA and has both a large (5.5 mm) and small (3.0 mm) focal spot. The lead-lined cesium iodide X-ray image intensifier produces an image which is captured by a CCD camera with a 1,000 x 1,000 pixel resolution. To produce accurate imagery of the object of interest, the alignment of the X-ray source to the X-ray image intensifier is crucial. The image sequences captured during the operation of an SRM are then processed to enhance the quality of the images. This procedure allows for computer software to extract data on the total erosion rate and the char layer thickness. Figure 1 Error! Reference source not found.shows a sequence of images captured during the operation the subscale SRM with the X-ray RTR system. The X-rayTR system, alignment procedure, uncertainty determination, and image analysis process will be discussed in detail in the full manuscript.

Cortopassi, A. C.↗
NASA NTRS1994

Crystallization history of the 1984 Mauna Loa lava flow

During a 3-week eruption in 1984, Mauna Loa produced vent lavas that increased in crystallinity from less than 1 to 30%, and 27-km-long flows that increased in crystallinity as they moved downstream. We examined the crystallization history of these lavas using crystal size distribution (CSD) analysis to study the rates of crystallization, viscosity increase, and latent heating. Typical average growth and nucleation rates were 5 x 10(exp -9) cm/s and 5/cu cm/s for microphenocrysts (20- to 500-micron size crystals nucleated in the rift zone) and 5 x 10(exp -8) cm/s and 5 x 10(exp 4)/cu cm/s for microlites (1- to 20-micron size crystals nucleated in the channel). These crystallization rates are high compared with those found in other CSD studies of igneous rocks, probably due to highly nonequilibrium conditions brought on by rapid degassing in the rift zone and cooling in the lava channel. Growth and nucleation rates decreased with time at the vent and with distance downstream. The maximum downstream total crystallinity measured is 39% (25% microlites, 14% microphenocrysts) in a quenched sample 14 km from the vent. Growth and nucleation rates cannot be calculated for postemplacement samples, but they place upper limits of 53-58% on the amount of crystallization in the channel 9-20 km from the vent. Crystallization could have been mostly responsible for the 10(exp 5)-fold downstream increase in apparent viscosity, although degassing and increasing incorporation of solid lava fragments also contributed. Another effect of crystallization on the lava flow was the sizeable latent heating (0.01 J/g/s over the first half of the flow length, if the crystallinity of downstream quench samples is representative of the hot fluid core), which may have been counteracted by entrainment of cooler material. Measurements of crystallization are shown to be crucial in the study of lava flow emplacement dynamics.

Crisp, Joe↗
NASA NTRS1977

Analytical study of viscous effects on transonic flow over boattail nozzles

An analytical study has been made of the effects of viscous/inviscid interactions on the transonic flow over boattail nozzles. The theoretical method couples a relaxation solution of the full potential transonic flow equations with a conventional boundary-layer solution to account for displacement-thickness effects. Surface pressures calculated on circular-arc boattails with solid jet-plume simulators show good agreement with experiment for free-stream Mach numbers less than 0.90. For separated flows, an empirical discriminating streamline model of the separation bubble gives good results until the onset of shock-induced separation, which occurs typically at a Mach number of about 0.90.

Wilmoth, R. G.↗
NASA NTRS1989

Constitutive Relationships and Models in Continuum Theories of Multiphase Flows

In April, 1989, a workshop on constitutive relationships and models in continuum theories of multiphase flows was held at NASA's Marshall Space Flight Center. Topics of constitutive relationships for the partial or per phase stresses, including the concept of solid phase pressure are discussed. Models used for the exchange of mass, momentum, and energy between the phases in a multiphase flow are also discussed. The program, abstracts, and texts of the presentations from the workshop are included.

Decker, Rand↗