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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 775 records · Page 43
All sourcesNASA NTRSDOE OSTI
NASA NTRS2005

Ball Bearings Equipped for In Situ Lubrication on Demand

In situ systems that provide fresh lubricants to ball/race contacts on demand have been developed to prolong the operational lives of ball bearings. These systems were originally intended to be incorporated into ball bearings in mechanisms that are required to operate in outer space for years, in conditions in which lubricants tend to deteriorate and/or evaporate. These systems may also be useful for similarly prolonging bearing lifetimes on Earth. Reservoirs have been among the means used previously to resupply lubricants. Lubricant- resupply reservoirs are bulky and add complexity to bearing assemblies. In addition, such a reservoir cannot be turned on or off as needed: it supplies lubricant continuously, often leading to an excess of lubricant in the bearing. A lubricator of the present type includes a porous ring cartridge attached to the inner or the outer ring of a ball bearing (see Figure 1). Oil is stored in the porous cartridge and is released by heating the cartridge: Because the thermal expansion of the oil exceeds that of the cartridge, heating causes the ejection of some oil. A metal film can be deposited on a face of the cartridge to serve as an electrical-resistance heater. The heater can be activated in response to a measured increase in torque that signals depletion of oil from the bearing/race contacts. Because the oil has low surface tension and readily wets the bearing-ring material, it spreads over the bearing ring and eventually reaches the ball/race contacts. The Marangoni effect (a surface-tension gradient associated with a temperature gradient) is utilized to enhance the desired transfer of lubricant to the ball/race contacts during heating. For a test, a ball bearing designed for use at low speed was assembled without lubricant and equipped with a porous-ring lubricator, the resistance heater of which consumed a power of less than 1 W when triggered on by a torque-measuring device. In the test, a load of 20 lb (.89 N) was applied and the bearing was turned at a rate of 200 RPM. The lubricator control was turned on at the beginning of the test, turned off for about 800 seconds, then turned on again. As shown in Figure 2, the controlled lubricator stabilized the torque in a low range, starting immediately after initial turn-on and immediately after resumption of the lubricator control.

Marchetti, Mario↗
NASA NTRS2020

Thermodynamic Measurements Using the Knudsen Cell Technique

The Knudsen cell technique has been used for over a century and is a valuable tool for measurement of vapor pressures and thermodynamic properties. It is based on a small enclosure (~1 cm long x 1 cm diameter) in which a condensed phase/vapor equilibria can be established. A small (<1 mm) orifice on the cell allows sampling of the vapor via a variety of techniques including weight loss, torsion effusion, target collection, and mass spectrometry. Many excellent measurements based on these methods have been reported. However in order to obtain reliable measurements, a variety of factors must be considered. They include proper cell material selection, accurate and uniform temperature control and measurement, and proper sampling of the vapor. Each of these factors are discussed in detail in this chapter. Typically these studies are conducted at high temperatures and it is a challenge to select an inert container material. Recommended materials are discussed and in some cases the container may be used as part of the system under study. Temperature control and measurement is perhaps the most important issue. In most systems, the furnace must be compact yet there can be no temperature gradient in the cell. Temperatures are measured with either a thermocouple or pyrometer and the relative advantages of each are discussed. Sampling method considerations depend on the particular technique. It is essential that all of the vapor or a representative portion of the vapor be sampled. The distribution of the effusate from a Knudsen cell is discussed and sampling positions discussed. Mass spectrometry is often used to study the effusing vapor and the relations between ion current and vapor pressure are discussed.

mass spectrometry↗
DOE OSTI2015

Microturbulence studies of pulsed poloidal current drive discharges in the reversed field pinch

Experimental discharges with pulsed poloidal current drive (PPCD) in the Madison Symmetric Torus reversed field pinch are investigated using a semi-analytic equilibrium model in the gyrokinetic turbulence code GENE. PPCD cases, with plasma currents of 500 kA and 200 kA, exhibit a density-gradient-driven trapped electron mode (TEM) and an ion temperature gradient mode, respectively. Relative to expectations of tokamak core plasmas, the critical gradients for the onset of these instabilities are found to be greater by roughly a factor of the aspect ratio. A significant upshift in the nonlinear TEM transport threshold, previously found for tokamaks, is confirmed in nonlinear reversed field pinch simulations and is roughly three times the threshold for linear instability. The simulated heat fluxes can be brought in agreement with measured diffusivities by introducing a small, resonant magnetic perturbation, thus modeling the residual fluctuations from tearing modes. These fluctuations significantly enhance transport.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
NASA NTRS1986

Steps toward 8m honeycomb mirrors. VIII - Design and demonstration of a system of thermal control

Directed jets of ambient temperature air are proposed for the maintenance of low internal temperature gradients and conformity with ambient temperatures in honeycomb-structure borosilicate glass telescope mirrors. The use of greater airflow on thicker sections, to match cooling rates, and the cooling or heating of the internal, back, and edge surfaces of the mirror at the same rate established by convection on the front surface, have been tested on a full scale glass thermal model of a single honeycomb cell from an 8-m diameter mirror. The internal thermal gradient (less than 0.1 C) and ambient-temperature-change lag (less than 0.24 C) ensure minimum image degradation.

Cheng, A. Y. S.↗
DOE OSTI2024

Passive Temperature Sensors for Nuclear Applications

Thermocouples are generally used to provide real-time temperature indications in instrumented tests performed at material and test reactors. Passive temperature monitors, such as Silicon Carbide (SiC) and melt wires, may be included in such tests as an independent technique of detecting peak temperatures experienced during irradiation. In less expensive static (drop-in) capsule tests, which have no leads attached for real-time data transmission, melt wires, and SiC temperature monitors (TMs) are essentially the only possibility for peak temperature indication. A melt wire involves placing materials (wires) of a known composition and melting temperature in a test. An inventory is maintained at Material Science Laboratory (MSL) for melt wires ranging in temperatures from 30°C to 1500°C. Unfortunately, melt wires are limited in that it can only detect whether a single temperature is or is not exceeded (melt wire melted or not). SiC TMs, which can also be used to detect peak irradiation temperatures, are advantageous because a single monitor can allow to determine the peak temperature reached within a relatively broad range (100 – 1200°C) resulting in accuracies within ±20°C. Irradiation temperature is determined by measuring a property change after isochronal annealing or during a continuously monitored annealing process using specialized equipment at MSL. Recent research has produced a passive monitor known as sublime temperature monitor. This passive sensor has the capability of recording temperature gradients and pinpointing exactly where a temperature is located along that gradient. Long measurement lengths are achieved with very high accuracy in the location of desired temperature measurements (±2 mm over a 1 m span); however, this sensor has not been deployed in a nuclear reactor. This article will focus only on passive temperature sensors currently being researched and implemented under the Advanced Sensors and Instrumentation (ASI) program at Idaho National Laboratory (INL).

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS1975

Evaluation of thermal X/5-detector Skylab S-192 data for estimating evapotranspiration and thermal properties of soils for irrigation management

An energy budget approach to evaluating the SKYLAB X/5-detector S-192 data for prediction of soil moisture and evapotranspiration rate was pursued. A test site which included both irrigated and dryland agriculture in Southern Texas was selected for the SL-4 SKYLAB mission. Both vegetated and fallow fields were included. Data for a multistage analysis including ground, NC-130B aircraft, RB-57F aircraft, and SKYLAB altitudes were collected. The ground data included such measurements as gravimetric soil moisture, percent of the ground covered by green vegetation, soil texture, net radiation, soil temperature gradients, surface emittance, soil heat flux, air temperature and humidity gradients, and cultural practices. Ground data were used to characterize energy budgets and to evaluate the utility of an energy budget approach for determining soil moisture differences among twelve specific agricultural fields.

Moore, D. G.↗
DOE OSTI2015

PRD3000: A novel Personnel Radiation Detector with Radiation Exposure Monitoring

PRD3000{sup TM} is a novel Personal Radiation Detector (PRD) with personnel radiation dose exposure monitoring. It is intended for First Responders, Law Enforcement, Customs Inspectors protecting critical infrastructures for detecting unexpected radioactive sources, who also need real time Hp(10) dose equivalent information. Traditional PRD devices use scintillator materials instrumented through either a photomultiplier tube or a photodiode photodetector. While the former is bulky and sensitive to magnetic fields, the latter has to compromise radiation sensitivity and energy threshold given its current noise per unit of photo-detection surface. Recently, solid state photodetectors (SiPM), based on arrays of Geiger operated diodes, have emerged as a scalable digital photodetector for photon counting. Their strong breakdown voltage temperature dependence (on the order of tens of milli-volts per K) has however limited their use for portable instruments where strong temperature gradients can be experienced, and limited power is available to temperature stabilize. The PRD3000 is based on the industry standard DMC3000 active dosimeter that complies with IEC 61526 Ed. 3 and ANSI 42.20 for direct reading personal dose equivalent meters and active personnel radiation monitors. An extension module is based on a CsI(Tl) scintillator readout by a temperature compensated SiPM. Preliminary nuclear tests combined with a measured continuous operation in excess of 240 hours from a single AAA battery cell indicate that the PRD3000 complies with the IEC 62401 Ed.2 and ANSI 42.32 without sacrificing battery life time. We present a summary of the device test results, starting with performance stability over a temperature range of - 20 deg. C to 50 deg. C, false alarm rates and dynamic response time. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2012

Evolution of block-copolymer order through a moving thermal zone

We investigate block-copolymer (BCP) thin film ordering kinetics during annealing across a moving in-plane temperature gradient. We operate in the so-called cold zone annealing (CZA) regime, where ordering temperatures are above the glass-transition, but well below the order-disorder transition. By measuring the order through the in-plane gradient, using atomic force microscopy and grazing-incidence small-angle X-ray scattering (GISAXS), we confirm that CZA greatly enhances ordering kinetics, as compared to uniform oven annealing. The maximal ordering occurs over a narrow range of the heating-up phase, and not during the subsequent cooling phase. The large grain sizes obtained using CZA are due to enhanced kinetics, and not the preferential formation of certain grain orientations. Kinetic enhancement is apparent even below the bulk glass-transition temperature. We suggest that the in-plane temperature gradient drives enhanced kinetics.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Electro-diffusion in a plasma with two ion species

Electric field is a thermodynamic force that can drive collisional inter-ion-species transport in a multicomponent plasma. In an inertial confinement fusion capsule, such transport causes fuel ion separation even with a target initially prepared to have equal number densities for the two fuel ion species. Unlike the baro-diffusion driven by ion pressure gradient and the thermo-diffusion driven by ion and electron temperature gradients, electro-diffusion has a critical dependence on the charge-to-mass ratio of the ion species. Specifically, it is shown here that electro-diffusion vanishes if the ion species have the same charge-to-mass ratio. An explicit expression for the electro-diffusion ratio is obtained and used to investigate the relative importance of electro- and baro-diffusion mechanisms. In particular, it is found that electro-diffusion reinforces baro-diffusion in the deuterium and tritium mix, but tends to cancel it in the deuterium and helium-3 mix.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Stabilization of electron-scale turbulence by electron density gradient in national spherical torus experiment

Theory and experiments have shown that electron temperature gradient (ETG) turbulence on the electron gyro-scale, k{sub ⊥}ρ{sub e} ≲ 1, can be responsible for anomalous electron thermal transport in NSTX. Electron scale (high-k) turbulence is diagnosed in NSTX with a high-k microwave scattering system [D. R. Smith et al., Rev. Sci. Instrum. 79, 123501 (2008)]. Here we report on stabilization effects of the electron density gradient on electron-scale density fluctuations in a set of neutral beam injection heated H-mode plasmas. We found that the absence of high-k density fluctuations from measurements is correlated with large equilibrium density gradient, which is shown to be consistent with linear stabilization of ETG modes due to the density gradient using the analytical ETG linear threshold in F. Jenko et al. [Phys. Plasmas 8, 4096 (2001)] and linear gyrokinetic simulations with GS2 [M. Kotschenreuther et al., Comput. Phys. Commun. 88, 128 (1995)]. We also found that the observed power of electron-scale turbulence (when it exists) is anti-correlated with the equilibrium density gradient, suggesting density gradient as a nonlinear stabilizing mechanism. Higher density gradients give rise to lower values of the plasma frame frequency, calculated based on the Doppler shift of the measured density fluctuations. Linear gyrokinetic simulations show that higher values of the electron density gradient reduce the value of the real frequency, in agreement with experimental observation. Nonlinear electron-scale gyrokinetic simulations show that high electron density gradient reduces electron heat flux and stiffness, and increases the ETG nonlinear threshold, consistent with experimental observations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Volatility Studies of Lanthanide Hexafluoroacetylacetone Chelates

Nuclear forensics has become very important to the field of nuclear security, where there is considerable interest in developing rapid separations of radionuclides and isotopes. Although prevention and detection form the foundation of nuclear security science, in the unfortunate event of detonation of a nuclear device, the fallout debris can be analyzed for signature isotopes that may provide evidence on the origin and type of nuclear materials. This is of considerable political importance to many governing bodies and this information is desired in a timely manner. One method of analysis is the rapid gas phase separation of rare earth metals from other components of the debris via isothermal thermochromatography. Lanthanides cover a portion of the fission product curve with varying yields dependent on a number of variables (e.g. neutron energy, fissile parent, etc), motivating the chromatographic separation of these elements. In previous work, 1,1,1,5,5,5 - hexafluoroacetylacetone (hfac) has been shown to produce volatile complexes with lanthanides. Thermochromatography is a gas phase separation method that utilizes temperature gradients on a column to vary adsorption location or constant column temperatures to vary retention time. The adsorption time of a compound on a column, i.e. retention time, is dependent on the thermodynamics, most notably the adsorption enthalpy. Studies of heavy metals have generated empirical correlations between adsorption enthalpy on a quartz column and sublimation enthalpy of the solid material. Thermogravimetric analysis (TGA) is useful in the characterization of the thermodynamics of materials, especially the sublimation enthalpy. Many methods analyze weight loss curves as a function of a constant heating rate. Another method introduced by Ashcroft analyzes weight loss curves over isothermal heating regions. Work presented here focuses on the determination of the sublimation enthalpies of thirteen lanthanide hfac complexes via the latter method. Additionally, there is investigation into the degradation of the compound via constant heating TGA up to higher temperatures. This provides information on the onset and end-set temperatures of degradation stages, as well as the peak temperature at which total sublimation occurs. (authors)

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Scrape-off layer tokamak plasma turbulence

Two-dimensional (2D) interchange turbulence in the scrape-off layer of tokamak plasmas and their subsequent contribution to anomalous plasma transport has been studied in recent years using electron continuity, current balance, and electron energy equations. In this paper, numerically it is demonstrated that the inclusion of ion energy equation in the simulation changes the nature of plasma turbulence. Finite ion temperature reduces floating potential by about 15% compared with the cold ion temperature approximation and also reduces the radial electric field. Rotation of plasma blobs at an angular velocity about 1.5 Multiplication-Sign 10{sup 5} rad/s has been observed. It is found that blob rotation keeps plasma blob charge separation at an angular position with respect to the vertical direction that gives a generation of radial electric field. Plasma blobs with high electron temperature gradients can align the charge separation almost in the radial direction. Influence of high ion temperature and its gradient has been presented.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2012

Spatially resolving variations in giant magnetoresistance, undetectable with four-point probe measurements, using infrared microspectroscopy

Magnetorefractive infrared (IR) microspectroscopy is demonstrated to resolve spatial variations in giant magnetoresistance (GMR) and, by modelling, provide an insight into the origin of the variations. Spatial variations are shown to be masked in conventional four-point probe electrical or IR spectral measurements. IR microspectroscopy was performed at the SMIS beamline at the SOLEIL synchrotron, modified to enable measurements in magnetic fields. A GMR gradient was induced in a CoFe/Cu multilayer sample by annealing in a temperature gradient. Modelling revealed that variations in GMR at 900 Oe could be attributed to local variations in interlayer coupling locally changing the switching field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1982

Einstein Observatory solid state spectrometer observations of M87 and the Virgo cluster

X-ray observations of the galaxy M87 and of a region in the Virgo cluster displaced 7 arcmin from the center of M87 are reported. X-ray spectra were obtained at these two locations with the Solid State Spectrometer onboard the Einstein Observatory. Emission lines were observed in both locations, indicating the presence of heavy elements at abundances near solar. There is no strong abundance gradient, within the errors. A temperature gradient has been detected: T increases from about 1.4 keV at the position of M87 to about 3.35 keV 7 arcmin away. There is lower temperature thermal emission at the center of M87 with T about 0.6 keV, consistent with models for cooling flows in this cluster. A mass infall rate of nearly 20 solar masses/yr has been obtained. In addition to the thermal emission, a power-law component has been detected in the spectrum of M87, consistent with that observed by HEAO 1, indicating that this component probably originates in the galaxy itself. Comparison of the results with those of other observers and with theoretical models for this source indicates the presence of intracluster gas having density near 1/1000 per cu cm and temperature of about 30,000,000 K.

Lea, S. M.↗
NASA NTRS1999

Double Diffusive Convection in Materials Processing

A great number of crystals grown in space are plagued by convective motions which contribute to structural flaws. The character of these instabilities is not well understood but is associated with density variations in the presence of residual gravity (g-jitter). As a specific example, past HgCdTe crystal growth space experiments by Lehoczky and co-workers indicate radial compositional asymmetry in the grown crystals. In the case of HgCdTe the rejected component into the melt upon solidification is HgTe which is denser than the melt. The space grown crystals indicate the presence of three dimensional flow with the heavier HgTe-rich material clearly aligned with the residual gravity (0.55-1.55 micro g) vector. This flow stems from double-diffusive convection, namely, thermal and solutal buoyancy driven flow in the melt. The study of double-diffusive convection is multi-faceted and rather vast. In our investigation, we seek to focus on one specific aspect of this discipline that is of direct relevance to materials processing especially crystal growth, namely, the side ways heating regime. This problem has been widely studied, both experimentally and numerically, in the context of solar ponds wherein the system is characterized by a linear salt (solutal) gradient with an imposed lateral temperature gradient. The induced flow instabilities arise from the wide disparity between the fluid thermal diffusivity and the solute diffusivity. The extension of the analysis to practical crystal growth applications has however not been rigorously made and understood. One subtle but important difference in crystal growth systems is the fact that die system solute gradient is non-linear (typically exponential). Besides, the crystal growth problem has the added complexities of solidification, both lateral and longitudinal thermal gradients and segregation phenomena in systems where binary and ternary compounds are being grown. This paper treats the side ways heating problem alone in a model fluid system. Results from detailed numerical calculations, mainly two dimensional are provided. The interactions between a non-linear solute gradient and an imposed transverse thermal gradient are investigated. The buoyancy effects are treated in the traditional Boussinesq approximation and also in a more complete density formulation to address recent concerns of the first approach especially in simulations of the system response in a reduced gravity environment. Detailed flow, temperature and solute field plots along with heat and mass transfer results are presented in the paper. Implications to practical crystal growth systems as discerned from the modeling results are also explored and reported.

Ramachandra, Narayanan↗
DOE OSTI2014

Magneto-Seebeck effect in spin-valve with in-plane thermal gradient

We present measurements of magneto-Seebeck effect on a spin valve with in-plane thermal gradient. We measured open circuit voltage and short circuit current by applying a temperature gradient across a spin valve stack, where one of the ferromagnetic layers is pinned. We found a clear hysteresis in these two quantities as a function of magnetic field. From these measurements, the magneto-Seebeck effect was found to be same as magneto-resistance effect.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Atmospheric Turbulent Intermittency Over the Arctic Sea‐Ice Surface During the MOSAiC Expedition

Turbulent motions in the Arctic stable boundary layer are characterized by intermittency, but they are rarely investigated due to limited observations, in particular over the sea‐ice surface. In the present study, we explore the characteristics of turbulent intermittency over the Arctic sea‐ice surface using data collected during the Multidisciplinary drifting Observation for the Study of Arctic Climate expedition from October 2019 to September 2020. We first develop a new algorithm, which performs well in identifying the spectral gap over the Arctic sea‐ice surface. Then the characteristics of intermittency are investigated. It is found that the strength of intermittency increases under the conditions of light surface wind speed, small surface wind speed gradient, and strong surface air temperature gradient. The momentum flux, sensible heat flux, and latent heat flux calculated by raw eddy‐covariance fluctuations are overestimated by 3%, 10%, and 24%, respectively, because submesoscale motions are included. Furthermore, the characteristics of the atmospheric boundary layer structure under various intermittency conditions reveal that strong low‐level jets are favorable to surface turbulent motions that result in weak intermittency, while strong temperature inversions above the surface layer suppress surface turbulent motions and lead to strong intermittency.

54 ENVIRONMENTAL SCIENCES↗