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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 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Performance Expectations of Closed-Brayton-Cycle Heat Exchangers in 100-kWe Nuclear Space Power Systems

Performance expectations of closed-Brayton-cycle heat exchangers to be used in 100-kWe nuclear space power systems were forecast. Proposed cycle state points for a system supporting a mission to three of Jupiter s moons required effectiveness values for the heat-source exchanger, recuperator and rejection exchanger (gas cooler) of 0.98,0.95 and 0.97, respectively. Performance parameters such as number of thermal units (Nm), equivalent thermal conductance (UA), and entropy generation numbers (Ns) varied from 11 to 19,23 to 39 kWK, and 0.019 to 0.023 for some standard heat exchanger configurations. Pressure-loss contributions to entropy generation were significant; the largest frictional contribution was 114% of the heat-transfer irreversibility. Using conventional recuperator designs, the 0.95 effectiveness proved difficult to achieve without exceeding other performance targets; a metallic, plate-fin counterflow solution called for 15% more mass and 33% higher pressure-loss than the target values. Two types of gas-coolers showed promise. Single-pass counterflow and multipass cross-counterflow arrangements both met the 0.97 effectiveness requirement. Potential reliability-related advantages of the cross-countefflow design were noted. Cycle modifications, enhanced heat transfer techniques and incorporation of advanced materials were suggested options to reduce system development risk. Carbon-carbon sheeting or foam proved an attractive option to improve overall performance.

Barrett, Michael J.↗
NASA NTRS2012

Correction of Excessive Precipitation over Steep Mountains in a General Circulation Model (GCM)

Excessive precipitation over steep and high mountains (EPSM) is a well-known problem in GCMs and regional climate models even at a resolution as high as 19km. The affected regions include the Andes, the Himalayas, Sierra Madre, New Guinea and others. This problem also shows up in some data assimilation products. Among the possible causes investigated in this study, we found that the most important one, by far, is a missing upward transport of heat out of the boundary layer due to the vertical circulations forced by the daytime subgrid-scale upslope winds, which in turn is forced by heated boundary layer on the slopes. These upslope winds are associated with large subgrid-scale topographic variance, which is found over steep mountains. Without such subgrid-scale heat ventilation, the resolvable-scale upslope flow in the boundary layer generated by surface sensible heat flux along the mountain slopes is excessive. Such an excessive resolvable-scale upslope flow in the boundary layer combined with the high moisture content in the boundary layer results in excessive moisture transport toward mountaintops, which in turn gives rise to excessive precipitation over the affected regions. We have parameterized the effects of subgrid-scale heated-slope-induced vertical circulation (SHVC) by removing heat from the boundary layer and depositing it in the layers higher up when topographic variance exceeds a critical value. Test results using NASA/Goddard's GEOS-5 GCM have shown that the EPSM problem is largely solved.

Chao, Winston C.↗
NASA NTRS2012

Correction of Excessive Precipitation Over Steep and High Mountains in a General Circulation Model

Excessive precipitation over steep and high mountains (EPSM) is a well-known problem in GCMs and meso-scale models. This problem impairs simulation and data assimilation products. Among the possible causes investigated in this study, we found that the most important one, by far, is a missing upward transport of heat out of the boundary layer due to the vertical circulations forced by the daytime upslope winds, which are forced by the heated boundary layer on subgrid-scale slopes. These upslope winds are associated with large subgrid-scale topographic variation, which is found over steep and high mountains. Without such subgridscale heat ventilation, the resolvable-scale upslope flow in the boundary layer generated by surface sensible heat flux along the mountain slopes is excessive. Such an excessive resolvablescale upslope flow combined with the high moisture content in the boundary layer results in excessive moisture transport toward mountaintops, which in turn gives rise to EPSM. Other possible causes of EPSM that we have investigated include 1) a poorly-designed horizontal moisture flux in the terrain-following coordinates, 2) the condition for cumulus convection being too easily satisfied at mountaintops, 3) the presence of conditional instability of the computational kind, and 4) the absence of blocked flow drag. These are all minor or inconsequential. We have parameterized the ventilation effects of the subgrid-scale heated-slope-induced vertical circulation (SHVC) by removing heat from the boundary layer and depositing it in layers higher up when the topographic variance exceeds a critical value. Test results using NASA/Goddard's GEOS-S GCM have shown that this largely solved the EPSM problem.

Chao, Winston C.↗
NASA NTRS1980

Outer atmospheres of cool stars. VI - Models for Epsilon Eridani based on IUE spectra of C II, Mg II, Si II, and Si III

Observations of the ultraviolet line spectrum of the active chromosphere star, Epsilon Eridani, obtained with the IUE satellite have been analyzed. The coupled statistical equilibrium and radiative transfer equations for the prominent transitions of C II, Mg II, Si II, and Si III. A satisfactory fit to all of the line strengths can be achieved with a model similar to that recently proposed to explain bright points on the quiet sun. A surface pressure at the base of the transition region of 0.5 dynes/sq cm is derived, which is a factor of 3 higher than the quiet sun value, but a factor of 3 smaller than predicted by scaling laws, assuming a conductively heated stellar transition region. It is found that the surface fluxes of the C II 1334, 1335 and Si III 1892 emission lines are good diagnostics of pressure at the base of the transition region, but line ratio techniques using the 1892 line for estimating electron densities may be valid.

Simon, T.↗
NASA NTRS2006

CFD-Predicted Tile Heating Bump Factors Due to Tile Overlay Repairs

A Computational Fluid Dynamics investigation of the Orbiter's Tile Overlay Repair (TOR) is performed to assess the aeroheating Damage Assessment Team's (DAT) existing heating correlation method for protuberance interference heating on the surrounding thermal protection system. Aerothermodynamic heating analyses are performed for TORs at the design reference damage locations body points 1800 and 1075 for a Mach 17.9 and a=39deg STS-107 flight trajectory point with laminar flow. Six different cases are considered. The computed peak heating bump factor on the surrounding tiles are below the DAT's heating bump factor values for smooth tile cases. However, for the uneven tiles cases the peak interference heating is shown to be considerably higher than the existing correlation prediction.

Lessard, Victor R.↗
NASA NTRS1980

Saturn's atmospheric temperature structure and heat budget

The effective temperature of Saturn from 30 deg S to 10 deg N is 96.5 + or - 2.5 K. This value is 1.9 K higher than a preliminary estimate (Ingersoll et al., 1980). The atmospheric mole fraction of H2 + He is 90 + or - 3%. This value is derived by comparing infrared and radio occultation data (Kliore et al., 1980) for the same latitude. The high value of the effective temperature suggests that Saturn has an additional energy source besides cooling and contraction. The high mole fraction of H2 suggests that separation of heavier He toward the core may be supplying the additional energy. Atmospheric temperatures in the 60- to 600-mbar range are 2.5 K lower within 7 deg of the equator than at higher latitudes. An almost isothermal layer exists between 60 and 160 mbar at all latitudes.

Orton, G. S.↗
NASA NTRS1979

SRB TPS closeout materials characterization

The recession characteristics of the materials used to closeout the Thermal Protection System (TPS) on the Space Shuttle Solid Rocket Booster (SRB) were assessed. Two candidate closeout materials namely, K5NA and MTA2 is the Marshall Trowelable Ablator. Test panels of each of these two materials were subjected to aerodynamic heat and shear in the NASA Hot Gas Facility. Pretest and Post-test measurements were taken and the rate of recession (R) thus determined was correlated with the heating rate. A least squares curve fit of the data together with another least squares 95% confidence level fit, was performed. The characteristics of the two materials when compared showed that both materials performed equally well at the higher heating rates (10 q 30 Btu/sq ft/sec) but MTA2 was slightly better, not receding as fast, at the lower q values. The comparison of the R versus q curves for K5NA and MTA2 with that of primary TPS P-50 cork on the SRB Aft Skirt was good.

Karu, Z. S.↗
NASA NTRS1961

Supersonic Free-Flight Measurements of Heat Transfer and Transition on a 10 degree Cone having a Low Temperature Ratio

Heat-transfer coefficients in the form of Stanton number and boundary-layer transition data were obtained from a free-flight test of a 100-inch-long 10 deg. total-angle cone with a 1/16-inch tip radius which penetrated deep into the region of infinite stability of laminar boundary layer over a range of wall-to-local-stream temperature radius and for local Mach numbers from 1.8 to 3.5. Experimental heat-transfer coefficients, obtained at Reynolds numbers up to 160 x 10(exp 6), were in general somewhat higher than theoretical values. A maximum Reynolds number of transition of only 33 x 10(exp 6) was obtained. Contrary to theoretical and some other experimental investigations, the transition Reynolds number initially increased while the wall temperature ratio increased at relatively constant Mach number. Further increases in wall temperature ratio were accompanied by a decrease in transition Reynolds number. Increasing transition Reynolds number with increasing Mach number was also indicated at a relatively constant wall temperature ratio.

Merlet, Charles F.↗
NASA NTRS2011

Inferring Absorbing Organic Carbon Content from AERONET Data

Black carbon, light-absorbing organic carbon (often called brown carbon) and mineral dust are the major light-absorbing aerosols. Currently the sources and formation of brown carbon aerosol in particular are not well understood. In this study we estimated globally the amount of light absorbing organic carbon and black carbon from AERONET measurements. We find that the columnar absorbing organic carbon (brown carbon) levels in biomass burning regions of South-America and Africa are relatively high (about 15-20 magnesium per square meters during biomass burning season), while the concentrations are significantly lower in urban areas in US and Europe. However, we estimated significant absorbing organic carbon amounts from the data of megacities of newly industrialized countries, particularly in India and China, showing also clear seasonality with peak values up to 30-35 magnesium per square meters during the coldest season, likely caused by the coal and biofuel burning used for heating. We also compared our retrievals with the modeled organic carbon by global Oslo CTM for several sites. Model values are higher in biomass burning regions than AERONET-based retrievals, while opposite is true in urban areas in India and China.

Arola, A.↗
NASA NTRS2016

Laser-Induced Fluorescence Measurements of Energetic Ions in a 100-A LaB6 Hollow Cathode

Increasingly long-duration space missions require a better understanding of the failure mechanisms of hollow cathodes to enable prediction of lifetime. Energetic ions have been measured in the plume of hollow cathodes but the energies are higher than can be explained classically. One of the mechanisms that appears to be contributing to the ion heating is ion acoustic turbulence (IAT), which has been investigated with plasma probes recently at JPL. In this work the ion velocity distribution has been measured using laser-induced fluorescence (LIF) at several high-current operating conditions on the centerline of a 100 A class hollow cathode at JPL. A retarding potential analyzer was (RPA) was used to measure the ion energy profile in the far plume and a Langmuir probe was used to measure electron temperature and plasma potential fluctuations. RPA energies are shown to correlate with the values measured by LIF. The ion temperature is shown to increase with distance downstream of the cathode. A parametric study of the ion heating as a function of discharge current and cathode flow rate was performed. It was found that for increasing current the ion temperature evolution did not vary even though the wave IAT wave energy increased. The effect of flow rate was more pronounced, with higher values reducing both ion temperature and wave energy linearly. These results indicate that IAT is at least partially responsible for energetic ion production in the hollow cathode plume.

Dodson, Christopher A.↗
NASA NTRS1995

Measurements of the H2(13)CO ortho/para ratio in cold dark molecular clouds

H2(13)CO has been detected for the first time toward cold dark molecular clouds using the NRAO 12 m telescope. The H2(13)CO ortho/para abundance ratio R for B335, which we report as R approximately 1.7, suggests equilibrium at the local kinetic temperature and appears to be distinctly different from that for both TMC-1 and L134N, where R is close to or higher than the statistical value 3. Since only B335 among the observed positions includes an imbedded IR source, this difference may result from heating of the grain surfaces, providing the energy necessary for desorption of formaldehyde formed on the grains.

NASA Discipline Exobiology↗
NASA NTRS2011

High Heat Flow from Enceladus' South Polar Region Measured using 10-600/cm(exp -1) Cassini/CIRS Data

Analysis of 2008 Cassini Composite Infrared Spectrometer (CIRS) 10 to 600/cm thermal emission spectra of Enceladus shows that for reasonable assumptions about the spatial distribution of the emission and the thermophysical properties of the solar-heated background surface, which are supported by CIRS observations of background temperatures at the edge of the active region, the endogenic power of Enceladus' south polar terrain is 15.8 +/- 3.1 GW. This is significantly higher than the previous estimate of 5.8 +/- 1.9 GW. The new value represents an improvement over the previous one, which was derived from higher wave number data (600 to 1100/cm-I) and was thus only sensitive to high-temperature emission. The mechanism capable of producing such a high endogenic power remains a mystery and challenges the current models of proposed heat production.

Howett, C. J. A.↗
NASA NTRS1983

The evolution of Enceladus

Evidence is adduced for several episodes of geologic resurfacing and extensional tectonism spreading over much of the history of the small, icy Saturn moon Enceladus. Resurfacing was the product of fresh material eruptions that may have contained ammonia, which may also have made melting in the interior more likely. Tidal dissipation seems to be the only heating mechanism capable of melting Enceladus. For the thermal properties of pure H2O, the orbital eccentricity would have to be higher than the present value of 0.0044 by a factor of 5-7 in order to maintain a molten interior, and may have to be greater by a factor of 20 in order to cause melting in an initially frozen body. Removal of eccentricity forcing would result in rapid eccentricity damping, freezing, and the cessation of tectonic activity.

Squyres, S. W.↗
NASA NTRS1991

Viscoplastic response of structures for intense local heating

A thermoviscoplastic finite element method employing the Bodner-Partom constitutive model is used to investigate the response of simplified thermal-structural models to intense local heating. With rapid rises of temperature, the nickel alloy structures display initially higher yield stresses due to strain rate effects. As temperatures approach elevated values, yield stress and stiffness degrade rapidly and pronounced plastic deformation occurs.

Thornton, Earl A.↗
NASA NTRS1992

An extensive ab initio study of the structures, vibrational spectra, quadratic force fields, and relative energetics of three isomers of Cl2O2

Quantum mechanical computational methods are employed for an ab initio investigation of: (1) the molecular properties of the lowest isomers of the ClO dimer; and (2) predicted molecular and thermochemical properties. Techniques employed include electron correlation and particularly singles and doubles coupled-cluster (CCSD) theory with or without perturbational estimates of the effects of connected triple excitations. The isomers ClOClO and ClClO2 are found to have higher energies than the ClOOCl isomer, and the theoretical vibrational frequencies of the isomers are well correlated with experimental data. Experimental values of the heat of formation for the isomers are also compared with calculations based on an isodesmic reaction with Cl2O, H2O, and HOOH.

Lee, Timothy J.↗
NASA NTRS1983

Advanced LOX/H sub 2 engine technologies for future OTVs

The optimization methods and trade studies which were used to define a 1980 state-of-the-art design of orbital transfer vehicles are summarized. The advanced thrust chamber, turbomachinery, and engine power cycle technologies recommended for development and verification during the 1980's are discussed. The state-of-the-art design serves as one of the reference points for evaluation of the advanced technology concepts. A second reference point is provided by the 1960 state-of-the-art RL-10 engine. Advanced heat energy extraction concepts in the combustor and injector are presented that will permit the high chamber pressures expected of the advanced expander cycle engine concept. Advanced turbomachinery concepts are selected that will help utilize efficiently the heat energy extracted in the thrust chamber and aid in uprating chamber pressures to values five times those realized with 1960 to 1980 technologies. The higher chamber pressure benefits are maximized with nozzle concepts that will package within a short retracted length and extend to the very high expansion area ratios required for specific impulse values significantly higher than those now realized by operational systems. Control system component concepts studied will allow utilization of the high turbine drive energy levels in a reliable repeatable manner that will reduce program risk and enhance overall space transportation system mission life cycle cost.

Glass, J.↗
NASA NTRS2008

Experimental Measurement of RCS Jet Interaction Effects on a Capsule Entry Vehicle

An investigation was made in NASA Langley Research Center s 31-Inch Mach 10 Tunnel to determine the effects of reaction-control system (RCS) jet interactions on the aft-body of a capsule entry vehicle. The test focused on demonstrating and improving advanced measurement techniques that would aid in the rapid measurement and visualization of jet interaction effects for the Orion Crew Exploration Vehicle while providing data useful for developing engineering models or validation of computational tools used to assess actual flight environments. Measurements included global surface imaging with pressure and temperature sensitive paints and three-dimensional flow visualization with a scanning planar laser induced fluorescence technique. The wind tunnel model was fabricated with interchangeable parts for two different aft-body configurations. The first, an Apollo-like configuration, was used to focus primarily on the forward facing roll and yaw jet interactions which are known to have significant aft-body heating augmentation. The second, an early Orion Crew Module configuration (4-cluster jets), was tested blowing only out of the most windward yaw jet, which was expected to have the maximum heating augmentation for that configuration. Jet chamber pressures and tunnel flow conditions were chosen to approximate early Apollo wind tunnel test conditions. Maximum heating augmentation values measured for the Apollo-like configuration (>10 for forward facing roll jet and 4 for yaw jet) using temperature sensitive paint were shown to be similar to earlier experimental results (Jones and Hunt, 1965) using a phase change paint technique, but were acquired with much higher surface resolution. Heating results for the windward yaw jet on the Orion configuration had similar augmentation levels, but affected much less surface area. Numerical modeling for the Apollo-like yaw jet configuration with laminar flow and uniform jet outflow conditions showed similar heating patterns, qualitatively, but also showed significant variation with jet exit divergence angle, with as much as 25 percent variation in heat flux intensity for a 10 degree divergence angle versus parallel outflow. These results along with the fabrication methods and advanced measurement techniques developed will be used in the next phase of testing and evaluation for the updated Orion RCS configuration.

Buck, Gregory M.↗
NASA NTRS1995

Ames Research Center Mars/Pathfinder Heat Shield Design Verification ARC-JET Test

Design verification tests were performed on samples representing the aerobrake of the Mars/Pathfinder vehicle. The test specimens consisted of the SLA-561V ablator bonded to the honeycomb structure. The primary objective was to evaluate the ablation materials performance and to measure temperatures within the ablator, at the structural bondline and at the back sheet of the honeycomb structure. Other objectives were to evaluate the effect of ablative repair plug material treatment and voids in the heat shield. A total of 29 models were provided for testing in the Ames 60MW arc-jet facility. Of these, 23 models were flat-faced and six remaining models were curved edge ones, intended to simulate the conditions on the curved rim of the forebody where the maximum shear occurred. Eight sets of test conditions were used. The stagnation point heating rates varied from 47 to 240 W/cm2 and the stagnation pressures from 0.15 to 0.27 atm. (The maximum flight values are 132 W/cm2 and 0.25 atm) The majority of these runs were made at a nominal stagnation pressure of 0.25 atm. Two higher pressure runs were made to check the current (denser) ablation material for spallation, or other forms of thermal stress failure. Over 60% of the flatfaced models yielded good thermocouple data and all produced useful surface recession information. Of the five curved-edge models that were tested, only one gave good data; the remaining ones experienced model-holder failure. The test results can be summarized by noting that no failure of the ablative material was observed on any model. Also, the bondline temperature design limit of 250 C was never reached within an equivalent flight time despite a stagnation point heat load that exceeded the maximum flight value by up to 130%. At heating rates of over 200W/cm2 and stagnation pressures of 0.25 atm, or greater, the average surface recessions exceeded 0.5 cm on some models. The surface roughness increased dramatically at pressures above 0.25 atm and was four times greater at 0.27 atm than at 0.25 atm. Procured repair plug material performed much better than room-temperature cured plugs, as observed in the previous tests. Voids in the ablator did not increase local temperatures and gaps did not grow during testing.

Tran, Huy K.↗