Results for “DEPOSITION” — Page 18

NASA NTRS2013

Historical and Future Black Carbon Deposition on the Three Ice Caps: Ice Core Measurements and Model Simulations from 1850 to 2100

Ice core measurements in conjunction with climate model simulations are of tremendous value when examining anthropogenic and natural aerosol loads and their role in past and future climates. Refractory black carbon (BC) records from the Arctic, the Antarctic, and the Himalayas are analyzed using three transient climate simulations performed with the Goddard Institute for Space Studies ModelE. Simulations differ in aerosol schemes (bulk aerosols vs. aerosol microphysics) and ocean couplings (fully coupled vs. prescribed ocean). Regional analyses for past (1850-2005) and future (2005-2100) carbonaceous aerosol simulations focus on the Antarctic, Greenland, and the Himalayas. Measurements from locations in the Antarctic show clean conditions with no detectable trend over the past 150 years. Historical atmospheric deposition of BC and sulfur in Greenland shows strong trends and is primarily influenced by emissions from early twentieth century agricultural and domestic practices. Models fail to reproduce observations of a sharp eightfold BC increase in Greenland at the beginning of the twentieth century that could be due to the only threefold increase in the North American emission inventory. BC deposition in Greenland is about 10 times greater than in Antarctica and 10 times less than in Tibet. The Himalayas show the most complicated transport patterns, due to the complex terrain and dynamical regimes of this region. Projections of future climate based on the four CMIP5 Representative Concentration Pathways indicate further dramatic advances of pollution to the Tibetan Plateau along with decreasing BC deposition fluxes in Greenland and the Antarctic.

Antarctic Regions↗

NASA NTRS2018

Atmospheric Energy Deposition Modeling and Inference for Varied Meteoroid Structures

Asteroids populations are highly diverse, ranging from coherent monoliths to loosely-bound rubble piles with a broad range of material and compositional properties. These different structures and properties could significantly affect how an asteroid breaks up and deposits energy in the atmosphere, and how much ground damage may occur from resulting blast waves. We have previously developed a fragment-cloud model (FCM) for assessing the atmospheric breakup and energy deposition of asteroids striking Earth. The approach represents ranges of breakup characteristics by combining progressive fragmentation with releases of variable fractions of debris and larger discrete fragments. In this work, we have extended the FCM to also represent asteroids with varied initial structures, such as rubble piles or fractured bodies. We have used the extended FCM to model the Chelyabinsk, Benesov, Kosice, and Tagish Lake meteors, and have obtained excellent matches to energy deposition profiles derived from their light curves. These matches provide validation for the FCM approach, help guide further model refinements, and enable inferences about pre-entry structure and breakup behavior. Results highlight differences in the amount of small debris vs. discrete fragments in matching the various flare characteristics of each meteor. The Chelyabinsk flares were best represented using relatively high debris fractions, while Kosice and Benesov cases were more notably driven by their discrete fragmentation characteristics, perhaps indicating more cohesive initial structures. Tagish Lake exhibited a combination of these characteristics, with lower-debris fragmentation at high altitudes followed by sudden disintegration into small debris in the lower flares. Results from all cases also suggest that lower ablation coefficients and debris spread rates may be more appropriate for the way in which debris clouds are represented in FCM, offering an avenue for future model refinement.

Deposition↗

NASA NTRS2021

Electrolytic Co-deposition Neutron Production Evaluation

Co-deposition electrochemical cells are a simple means to examine novel nuclear reactions. In this study, palladium and deuterium atoms were co-deposited on a cathode at stoichiometric densities, forming dendritic morphologies. Bubble detector neutron dosimeters were used to measure equivalent dose levels during electrolytic deposition. Standard configuration cells expected to produce excess neutrons were denoted as experimental cells and contained an electrolyte consisting of palladium(II) chloride, lithium chloride, and heavy water. The control cells used copper(II) chloride, lithium chloride, and heavy water electrolyte. Experimental and control cells were supplied current, increasing from 0.1 to 100.0 mA over a period of 20 days. For test days 9 through 20, the standard configuration experimental cells exhibited significantly higher average neutron radiation than the controls at a 99% confidence level. Alternative configurations involving more increasing current over a shortened time scale, substitutions of water in place of heavy water or potassium chloride for lithium chloride, as well as inclusion of depleted uranium near the cell cathodes all resulted in inconclusive evidence for promoting neutron production.

neutron↗

NASA NTRSDate not supplied

Integral Channel Nozzles and Heat Exchangers using Additive Manufacturing Directed Energy Deposition NASA HR-1 Alloy

Heat exchangers for use in propulsion applications are very critical components because they must be efficient, compact and light and often operate with working fluids at extreme temperatures or pressures or both. Various components and systems use heat exchangers such as combustion chambers of gas turbines and internal combustion engines, fuel cells (air supply and thermal management), electric batteries (thermal management), evaporators and recuperators of waste-heat-to-power systems, and rocket engines. Even if the results are more generally applicable, the heat exchangers applications to which this study is more closely related are regeneratively cooled rocket nozzles and chambers, and repressurization systems for the launch vehicles. These components are often thin-walled and contain pressurized fluids, like propellants at cryogenic or elevated temperatures. Given that the environments that these propulsion components must endure are challenging, the manufacturing to meet these specifications often require long lead times due to specialty processes and unique tooling associated with the combined thin-wall integral channel and large-scale structures. Additive manufacturing (AM) offers programmatic advantages for reduction in processing time and cost in addition to various technical advantages, including the possibility to achieve enhanced hardware complexity targeted to superior performance, part consolidation, and the capability of processing of novel alloys. While AM is already being utilized for heat exchanger components in propulsion applications, almost all these AM components are made by means of Laser Powder Bed Fusion (L-PBF). L-PBF allows for fine features but is rather limited with respect to the overall size of the components that can be manufactured. Recent developments are maturing the Laser Powder Directed Energy Deposition (LP-DED) process which may be used, for example, to make integral channel thin-wall regeneratively-cooled rocket nozzles with diameters greater than 1 m. This paper highlights some integral channel heat exchanger demonstrator hardware applications of LP-DED, as well as the characterization of this process in combination with the use of the NASA HR-1 alloy. To properly utilize LP-DED for heat exchanger manufacturing, various aspects are being characterized such as geometry limitations, measurement of surface texture and geometric angled surfaces, surface enhancements for internal channels, and material evaluation. NASA HR-1 (FeNi-Cr) is a high strength hydrogen resistant superalloy developed for use in aerospace applications, such as heat exchangers. Some aspects and considerations about the design of heat exchangers are summarized together with data relevant to LP-DED manufacturing in combination with the NASA HR-1 alloy. Microchannels were successful deposited down to 2.54 mm and 1 mm wall thickness, wall angles of 30°, both with high reproducibility. It was also found that the areal surface roughness is highly dependent on the size of the powder feedstock used for deposition. The characterization of these LP-DED features is critical for fluid flow and heat transfer predictions as it can be exploited to enhance heat transfer at the cost of increased pressure drop.

Additive Manufacturing↗

NASA NTRSDate not supplied

Integral Channel Nozzles and Heat Exchangers using Additive Manufacturing Directed Energy Deposition NASA HR-1 Alloy

Heat exchangers for use in propulsion applications are very critical components because they must be efficient, compact and light and often operate with working fluids at extreme temperatures or pressures or both. Various components and systems use heat exchangers such as combustion chambers of gas turbines and internal combustion engines, fuel cells (air supply and thermal management), electric batteries (thermal management), evaporators and recuperators of waste-heat-to-power systems, and rocket engines. Even if the results are more generally applicable, the heat exchangers applications to which this study is more closely related are regeneratively cooled rocket nozzles and chambers, and repressurization systems for the launch vehicles. These components are often thin-walled and contain pressurized fluids, like propellants at cryogenic or elevated temperatures. Given that the environments that these propulsion components must endure are challenging, the manufacturing to meet these specifications often require long lead times due to specialty processes and unique tooling associated with the combined thin-wall integral channel and large-scale structures. Additive manufacturing (AM) offers programmatic advantages for reduction in processing time and cost in addition to various technical advantages, including the possibility to achieve enhanced hardware complexity targeted to superior performance, part consolidation, and the capability of processing of novel alloys. While AM is already being utilized for heat exchanger components in propulsion applications, almost all these AM components are made by means of Laser Powder Bed Fusion (L-PBF). L-PBF allows for fine features but is rather limited with respect to the overall size of the components that can be manufactured. Recent developments are maturing the Laser Powder Directed Energy Deposition (LP-DED) process which may be used, for example, to make integral channel thin-wall regeneratively-cooled rocket nozzles with diameters greater than 1 m. This paper highlights some integral channel heat exchanger demonstrator hardware applications of LP-DED, as well as the characterization of this process in combination with the use of the NASA HR-1 alloy. To properly utilize LP-DED for heat exchanger manufacturing, various aspects are being characterized such as geometry limitations, measurement of surface texture and geometric angled surfaces, surface enhancements for internal channels, and material evaluation. NASA HR-1 (FeNi-Cr) is a high strength hydrogen resistant superalloy developed for use in aerospace applications, such as heat exchangers. Some aspects and considerations about the design of heat exchangers are summarized together with data relevant to LP-DED manufacturing in combination with the NASA HR-1 alloy. Microchannels were successful deposited down to 2.54 mm and 1 mm wall thickness, wall angles of 30°, both with high reproducibility. It was also found that the areal surface roughness is highly dependent on the size of the powder feedstock used for deposition. The characterization of these LP-DED features is critical for fluid flow and heat transfer predictions as it can be exploited to enhance heat transfer at the cost of increased pressure drop.

additive manufacturing↗

NASA NTRS2021

Evaluation of SO2, SO4(2−) and an Updated SO2 Dry Deposition Parameterization in the United Kingdom Earth System Model

In this study we evaluate simulated surface SO2 and sulphate (SO4(2-)) concentrations from the United Kingdom Earth System Model (UKESM1) against observations from ground based measurement networks in the USA and Europe for the period 1987 to 2014. We find that UKESM1 captures the historical trend for decreasing concentrations of atmospheric SO2 and SO4(2-) in both Europe and the USA over the period 1987 to 2014. However, in the polluted regions of the eastern USA and Europe, UKESM1 over-predicts surface SO2 concentrations by a factor of 3, while under-predicting surface SO4(2-) concentrations by 25-35%. In the cleaner western USA, the model over-predicts both surface SO2 and SO4(2-) concentrations by a factor of 12 and 1.5 respectively. We find that UKESM1’s bias in surface SO2 and SO4(2-) concentrations is variable according to region and season. We also evaluate UKESM1 against total column SO2 from the Ozone Monitoring Instrument (OMI) using an updated data product. This comparison provides information about the model’s global performance, finding that UKESM1 over predicts total column SO2 over much of the globe, including the large source regions of India, China, the USA and Europe as well as over outflow regions. Finally, we assess the impact of a more realistic treatment of the model’s SO2 dry deposition parameterization. This change increases SO2 dry deposition to the land and ocean surfaces, thus reducing the atmospheric loading of SO2 and SO(sup 2-)(sub 4). In comparison with the ground-based and satellite observations, we find that the modified parameterization reduces the models over prediction of surface SO2 concentrations and total column SO2. Relative to the ground-based observations the simulated surface SO4(2-) concentrations are also reduced, while the simulated SO2 dry deposition fluxes increase.

SO2↗

NASA NTRS1968

Improved process for epitaxial deposition of silicon on prediffused substrates

Process for fabricating integrated circuits uniformly deposits silicon epitaxially on prediffused substrates without affecting the sublayer diffusion pattern. Two silicon deposits from different sources, and deposited at different temperatures, protect the sublayer pattern from the silicon tetrachloride reaction.

Clarke, M. G.↗

NASA NTRS1971

Alloy vapor deposition using ion plating and flash evaporation

Method extends scope of ion plating technique to include deposition of alloy films without changing composition of plating alloy. Coatings flow with specimen material without chipping or peeling. Technique is most effective vacuum deposition method for depositing alloys for strong and lasting adherence.

Spalvins, T.↗

NASA NTRS1972

Sputtering - A vacuum deposition method for coating material.

The sputtering method is discussed in terms of the unique features which sputter offers in depositing coatings. These features include versatility, momentum transfer, configuration of target, precise controls, and a relatively slow deposition rate. Sputtered films are evaluated in terms of adherence, coherence, and the internal stresses. The observed strong adherence is attributed to the high kinetic energies of the sputtered material, sputter etched surface, and the submicroscopic particle size. Film thickness can be controlled to a millionth of a centimeter. Very adherent films of sputtered PTFE (teflon) can be deposited in a single operation on any type of material and on any geometrical configuration.

Spalvins, T.↗

NASA NTRS1974

Vapor-deposited platinum as a fuel-cell catalyst

Electrodes are prepared by vacuum deposition of platinum on nickel substrate with conventional vapor-deposition apparatus. Amount of platinum loaded on substrate can be veried by changing exposure time during deposition. These electrodes are significantly more effective than conventional oxygen electrodes.

Asher, W. J.↗

NASA NTRS1973

Development of chemically vapor deposited rhenium emitters of (0001) preferred crystal orientation

Rhenium thermionic emitters were prepared by the pyrolysis of rhenium chlorides formed by the chlorination of rhenium pellets. The impurity contents, microstructures, degrees of (0001) preferred crystal orientation, and vacuum electron work functions of these emitters were determined as a function of deposition parameters, such as substrate temperature, rhenium pellet temperature and chlorine flow rate. A correlation between vacuum electron work function and degree of (0001) preferred crystal orientation was established. Conditions for depositing porosity-free rhenium emitters of high vacuum electron work functions were defined. Finally, three cylindrical rhenium emitters were prepared under the optimum deposition conditions.

Yang, L.↗

NASA NTRS1973

Production of carbon monoxide by charged particle deposition.

Recent studies of electron energy deposition in CO2 and CO based upon a large set of electron impact cross sections are utilized to estimate the telluric CO directly produced by various charged-particle deposition mechanisms. The mechanisms considered are (1) lightning, (2) cloud coronal discharges, (3) background radioactivity, (4) natural electrostatic discharges, (5) photoelectrons in the ionosphere, (6) auroral electrons, (7) auroral protons, (8) cosmic rays, and (9) solar wind. 'Ball park' estimates of the global CO production by each of these mechanisms are given. Apart from mechanisms 1, 2, and 5, all CO production mechanisms are estimated to be small compared to artificial sources. If, as appears to be the case, the hot oxygen atoms and ions and other atomic species immediately produced by these three charged-particle deposition mechanisms react rapidly with CO2 to produce CO, these mechanisms can readily lead to CO production levels in the multimegaton-per-year range.

Green, A. E. S.↗

NASA NTRS1973

Anode power deposition in quasi-steady MPD arcs

The power deposited in the anode of a quasi-steady MPD accelerator has been measured directly by thermocouples attached to the inside surface of a shell anode which provide a local measurement of anode heat flux. The results over a range of arc currents from 5.5 to 44 kiloamperes and argon mass flows from 1 g/sec to 48 g/sec show that the fraction of the total input power deposited in the anode decreases drastically from 50% at an arc power of 200 kW to 10% at 20 MW, and that anode power is not uniformly deposited in the anode. A theoretical model of the anode heat transfer, including effects of anode work function, electron thermal energy, and anode sheath, can be brought into reasonable agreement with the measurements, provided the effective range of the conduction electrons from within the discharge plasma to the anode surface is properly acknowledged.

Saber, A. J.↗

NASA NTRS1974

Monte Carlo approach to the spatial deposition of energy by electrons in molecular hydrogen

The Monte Carlo (MC) and continuous slowdown approximation (CSDA) approaches to the spatial deposition of energy by electrons are compared using the same detailed atomic cross section (DACS). It is found that the CSDA method overestimates the amount of energy that is deposited near the end of the path for electrons above a few hundred electron volts. The MC results are in approximate agreement with experimental data in such a way as to be relatively independent of the actual gas used. Our MC results are extended to obtain the three-dimensional deposition of energy by sub-keV electrons in molecular hydrogen.

Heaps, M. G.↗

NASA NTRS1974

System for depositing thin films

A system for depositing a thin film of one material on another is described. A mass filter is interposed between the source of material being deposited and the object upon which deposition is being made.

Tashbar, P. W.↗

NASA NTRS1975

NO sub x deposited in the stratosphere by the space shuttle, phase 1

The results of calculations to determine the amount of NOx deposited in the stratosphere by space shuttle solid rocket motors (SRM) are presented. Flow properties and chemical composition in the exhaust nozzle and plume were analyzed. The nozzle calculations show that about 4.5 lbm/sec of NOx leaves the two SRMs. The total amount of NOx deposited in the stratosphere is related to the amount leaving the nozzle via an overall plume enhancement factor (OPEF), which depends upon the influence of afterburning and shocks in enhancing the exit plane NOx mole fraction. Calculations show that the OPEF is approximately 2, indicating the mass flow of NOx in the plume to be approximately l0 lbm/sec at 30 km altitude with a possible error factor of 4. For a vehicle velocity of 3750 ft/sec, therefore, the NOx deposition rate in the stratosphere is about 2.7 x 10(-3) lbm/ft.

Pergament, H. S.↗

NASA NTRS1974

Io - A surface evaporite deposit

A model is suggested for Io's surface composition involving evaporite salt deposits, rich in sodium and sulfur. According to this model, these deposits were produced as a result of the migration of salt-saturated aqueous solutions to Io's surface from a warm or hot interior followed by loss of the water to space. This model satisfies cosmochemical constraints based on Io's initial composition, current density, and thermal history. Salt-rich assemblages are easily derivable from the leaching of carbonaceous chondritic material. The chemical and optical properties of such deposits, after modification by irradiation, can be used to explain Io's overall albedo and spectral reflectance, its dark reddish poles, and the observed sodium emission as well as or better than other currently suggested materials.

Fanale, F. P.↗

NASA NTRS1975

Monte Carlo simulation of energy deposition by low-energy electrons in molecular hydrogen

A set of detailed atomic cross sections has been used to obtain the spatial deposition of energy by 1-20-eV electrons in molecular hydrogen by a Monte Carlo simulation of the actual trajectories. The energy deposition curve (energy per distance traversed) is quite peaked in the forward direction about the entry point for electrons with energies above the threshold of the electronic states, but the peak decreases and broadens noticeably as the electron energy decreases below 10 eV (threshold for the lowest excitable electronic state of H2). The curve also assumes a very symmetrical shape for energies below 10 eV, indicating the increasing importance of elastic collisions in determining the shape of the curve, although not the mode of energy deposition.

Heaps, M. G.↗