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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 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Theory of Ostwald ripening in a two-component system

When a two-component system is cooled below the minimum temperature for its stability, it separates into two or more immiscible phases. The initial nucleation produces grains (if solid) or droplets (if liquid) of one of the phases dispersed in the other. The dynamics by which these nuclei proceed toward equilibrium is called Ostwald ripening. The dynamics of growth of the droplets depends upon the following factors: (1) The solubility of the droplet depends upon its radius and the interfacial energy between it and the surrounding (continuous) phase. There is a critical radius determined by the supersaturation in the continuous phase. Droplets with radii smaller than critical dissolve, while droplets with radii larger grow. (2) The droplets concentrate one component and reject the other. The rate at which this occurs is assumed to be determined by the interdiffusion of the two components in the continuous phase. (3) The Ostwald ripening is constrained by conservation of mass; e.g., the amount of materials in the droplet phase plus the remaining supersaturation in the continuous phase must equal the supersaturation available at the start. (4) There is a distribution of droplet sizes associated with a mean droplet radius, which grows continuously with time. This distribution function satisfies a continuity equation, which is solved asymptotically by a similarity transformation method.

Baird, J. K.↗
NASA NTRS1989

Coronal activity in F-, G-, and K-type stars. III - The coronal differential emission measure distribution of Capella, Sigma-squared CrB, and Procyon

EXOSAT soft X-ray spectra of three binary systems of cool stars are analyzed: Capella (G6 III + F9 III), Sigma-squared CrB (F8 V + G1 V), and Procyon (F5 IV-V + DF). The EXOSAT transmission grating spectrometer permits the study of individual spectral lines and line complexes between 10 and 200 A with approximately 3 A resolution. First it is demonstrated that the spectra can be described reasonably well by a two-temperature model corona. Then the assumption that only two temperatures exist in the stellar coronas is relaxed and differential emission measure distributions are derived from the three spectra. The results from the multithermal modeling are consistent with those of the two-temperature models: emission from the coronas of each of the three stars is dominated by plasma in two relative narrow temperature intervals. These intervals are centered on 5 MK and 25 MK in the cases of Capella and Sigma-squared CrB, and 0.6 MK and 3 MK in the case of Procyon. The implications of the results for the structure of stellar coronas are briefly discussed.

Lemen, J. R.↗
NASA NTRS1990

Parametric studies to determine the effect of compliant layers on metal matrix composite systems

Computational simulation studies are conducted to identify compliant layers to reduce matrix stresses which result from the coefficient of thermal expansion mismatch and the large temperature range over which the current metal matrix composites will be used. The present study includes variations of compliant layers and their properties to determine their influence on unidirectional composite and constituent response. Two simulation methods are used for these studies. The first approach is based on a three-dimensional linear finite element analysis of a 9 fiber unidirectional composite system. The second approach is a micromechanics based nonlinear computer code developed to determine the behavior of metal matrix composite system for thermal and mechanical loads. The results show that an effective compliant layer for the SCS 6 (SiC)/Ti-24Al-11Nb (Ti3Al + Nb) and SCS 6 (SiC)/Ti-15V-3Cr-3Sn-3Al (Ti-15-3) composite systems should have modulus 15 percent that of the matrix and a coefficient of thermal expansion of the compliant layer roughly equal to that of the composite system without the CL. The matrix stress in the longitudinal and the transverse tangent (loop) direction are tensile for the Ti3Al + Nb and Ti-15-3 composite systems upon cool down from fabrication. The fiber longitudinal stress is compressive from fabrication cool down. Addition of a recommended compliant layer will result in a reduction in the composite modulus.

Caruso, J. J.↗
NASA NTRS1990

Parametric studies to determine the effect of compliant layers on metal matrix composite systems

Computational simulation studies are conducted to identify compliant layers to reduce matrix stresses which result from the coefficient of thermal expansion mismatch and the large temperature range over which the current metal matrix composites will be used. The present study includes variations of compliant layers and their properties to determine their influence on unidirectional composite and constituent response. Two simulation methods are used for these studies. The first approach is based on a three-dimensional linear finite element analysis of a 9 fiber unidirectional composite system. The second approach is a micromechanics based nonlinear computer code developed to determine the behavior of metal matrix composite system for thermal and mechanical loads. The results show that an effective compliant layer for the SCS 6 (SiC)/Ti-24Al-11Nb (Ti3Al + Nb) and SCS 6 (SiC)/Ti-15V-3Cr-3Sn-3Al (Ti-15-3) composite systems should have modulus 15 percent that of the matrix and a coefficient of thermal expansion of the compliant layer roughly equal to that of the composite system without the CL. The matrix stress in the longitudinal and the transverse tangent (loop) direction are tensile for the Ti3Al + Nb and Ti-15-3 composite systems upon cool down from fabrication. The fiber longitudinal stress is compressive from fabrication cool down. Addition of a recommended compliant layer will result in a reduction in the composite modulus.

Caruso, J. J.↗
NASA NTRS1992

Electrochemical System Would Supply O2, H2O, N2, And H2

Electrochemical system includes fuel cells that convert high-energy-density chemical propellants to atmospheric gases. System provides cooling, water, and electrical energy. Applicable to terrestrial enclosed environments, laboratories, chemical processing plants, or portable medical facilities.

Walter, Richard T.↗
NASA NTRS1992

The Astromag superconducting magnet facility configured for a free-flying satellite

The magnet parameters of a free-flying version of Astromag and the parameters of the space cryogenic system for the magnet are presented. Consideration is given to the free-flyer version of the Astromag magnet. The diameter of the magnet, its cryostat, the satellite and the two instruments is limited by the 4.27-m shroud diameter of the Atlas IIa. The magnet coil must use a stable reliable superconductor which can carry the full magnet current at 4.2 K at a peak induction in the coil of 7.5 T. The magnet must operate in the persistent mode. The changes in the overall design and operating requirements for the free-flying-design Astromag suggest that the coils, the cryogenic system, and the charging system can be simplified without a loss of required magnet function. Attention is given to switches, trim coils, and plumbing in the low field region between the coils; the magnet charging system and the quench protection system; and cooled helium supply to the magnet gas-cooled electrical leads.

Green, M. A.↗
NASA NTRS1993

Launches and the environment - Lessons learned

An evaluation is presented of the consequences of NASA's study of the ways in which the launch of a Space Shuttle generates a plume of HCl and Al2O3; in combination with water from the Shuttle's sound-suppressor cooling water system, these substances can create a corrosive and hard-to-remove Al2O3 coating on nearby surfaces. Attention is given to the site-specific character of such environmental complications, the need to involve environmental-risk specialists in hardware-development teams, and the nonlinearity of many environmental impacts.

Vaughan, William W.↗
NASA NTRS1952

Investigations of Air-cooled Turbine Rotors for Turbojet Engines II : Mechanical Design, Stress Analysis, and Burst Test of Modified J33 Split-disk Rotor / Richard H. Kemp and Merland L. Moseson

A full-scale J33 air-cooled split turbine rotor was designed and spin-pit tested to destruction. Stress analysis and spin-pit results indicated that the rotor in a J33 turbojet engine, however, showed that the rear disk of the rotor operated at temperatures substantially higher than the forward disk. An extension of the stress analysis to include the temperature difference between the two disks indicated that engine modifications are required to permit operation of the two disks at more nearly the same temperature level.

TURBINES - WHEELS, DISK - STRENGTH↗
NASA NTRS1994

Compliant Metal Enhanced Convection Cooled Reverse-Flow Annular Combustor

A joint Army/NASA program was conducted to design, fabricate, and test an advanced, reverse-flow, small gas turbine combustor using a compliant metal enhanced (CME) convection wall cooling concept. The objectives of this effort were to develop a design method (basic design data base and analysis) for the CME cooling technique and tben demonstrate its application to an advanced cycle, small, reverse-flow combustor with 3000 F (1922 K) burner outlet temperature (BOT). The CME concept offers significant improvements in wall cooling effectiveness resulting in a large reduction in cooling air requirements. Therefore, more air is available for control of burner outlet temperature pattern in addition to the benefit of improved efficiency, reduced emissions, and smoke levels. Rig test results demonstrated the benefits and viability of the CME concept meeting or exceeding the aerothermal performance and liner wall temperature characteristics of similar lower temperature-rise combustors, achieving 0.15 pattern factor at 3000 F (1922 K) BOT, while utilizing approximately 80 percent less cooling air than conventional, film-cooled combustion systems.

Paskin, Marc D.↗
NASA NTRS1994

NASA Lewis Propulsion Systems Laboratory Customer Guide Manual

This manual describes the Propulsion Systems Laboratory (PSL) at NASA Lewis Research Center. The PSL complex supports two large engine test cells (PSL-3 and PSL-4) that are capable of providing flight simulation to altitudes of 70,000 ft. Facility variables at the engine or test-article inlet, such as pressure, temperature, and Mach number (up to 3.0 for PSL-3 and up to 6.0 planned for PSL-4), are discussed. Support systems such as the heated and cooled combustion air systems; the altitude exhaust system; the hydraulic system; the nitrogen, oxygen, and hydrogen systems; hydrogen burners; rotating screen assemblies; the engine exhaust gas-sampling system; the infrared imaging system; and single- and multiple-axis thrust stands are addressed. Facility safety procedures are also stated.

Soeder, Ronald H.↗
NASA NTRS1994

HNO3 profiles obtained during the EASOE campaign

A small cryogenically cooled spectrometer system designed to obtain atmospheric emission spectra in the 7.5 micrometer to 13.0 micrometer region was flown piggyback on 9 balloon flights from ESRANGE (67.9 deg N, 21.2 deg E) during the European Arctic Stratospheric Ozone Experiment (EASOE) campaign. Initial analysis of the spectra obtained has been concentrated on obtaining HNO3 profiles for the various flights. HNO3 profiles for 17 December 1991, 9 January 1992, 22 January 1992, 5 February 1992 and 14 March 1992 are presented.

Murcray, F. J.↗
NASA NTRS2002

Detection of Intergranular Corrosion in Cold Plate Face Sheets

Cold plates are critical for cooling electronic systems in the shuttle. As a result of the environmental conditions in which they operate, water can condense between them and a support shelf. In some cases, this water results in intergranular corrosion in the face sheet. If the intergranular corrosion sufficiently penetrates the face sheet, a coolant leak could occur and jeopardize cold plate operation. This paper examines techniques for detecting and characterizing the intergranular corrosion, to enable recertification of cold plates that have been in operation for 15 plus years. Intergranular corrosion was artificially induced in the face sheets of a series of cold plate specimens using an electrochemical process. Some of the cold plate specimens were separated for destructive characterization of the extent of corrosion produced by the electrochemical process and to insure the induced corrosion was intergranular. The rest of the specimens were characterized nondestructively using several techniques. X-ray tomography and ultrasonic techniques provided the best indication of corrosion in these specimens and will be the focus of this paper. An x-ray tomography technique was shown to be the most effective technique for characterizing depth of the intergranular corrosion. From these measurements, corrosion profile maps were developed that were consistent with subsequent destructive evaluations of the specimens. This enabled the assessment of NDE (ondestructive evaluation) standards to evaluate the viability of other NDE techniques. Due to system constraints, a different technique must be used to inspect an entire cold plate. An ultrasonic technique was shown to be very reliable for detection of corrosion in the unbacked regions of the face sheet. The ultrasonic technique was performed in an alcohol bath to avoid additional corrosion during the NDE evaluation. A pulse echo technique that focuses on the RMS value of the signal is shown to be very sensitive to the presence of intergranular corrosion.

Winfree, William P.↗
NASA NTRS2004

Cloud Detection from Satellite Imagery: A Comparison of Expert-Generated and Automatically-Generated Decision Trees

Automated cloud detection and tracking is an important step in assessing global climate change via remote sensing. Cloud masks, which indicate whether individual pixels depict clouds, are included in many of the data products that are based on data acquired on- board earth satellites. Many cloud-mask algorithms have the form of decision trees, which employ sequential tests that scientists designed based on empirical astrophysics studies and astrophysics simulations. Limitations of existing cloud masks restrict our ability to accurately track changes in cloud patterns over time. In this study we explored the potential benefits of automatically-learned decision trees for detecting clouds from images acquired using the Advanced Very High Resolution Radiometer (AVHRR) instrument on board the NOAA-14 weather satellite of the National Oceanic and Atmospheric Administration. We constructed three decision trees for a sample of 8km-daily AVHRR data from 2000 using a decision-tree learning procedure provided within MATLAB(R), and compared the accuracy of the decision trees to the accuracy of the cloud mask. We used ground observations collected by the National Aeronautics and Space Administration Clouds and the Earth s Radiant Energy Systems S COOL project as the gold standard. For the sample data, the accuracy of automatically learned decision trees was greater than the accuracy of the cloud masks included in the AVHRR data product.

Shiffman, Smadar↗