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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1998

Final Report

This grant was made to fund two accepted proposals to observe with the ASCA satellite: (1) Debunking the myth of two-temperature coronae of active stars, and (2) Dynamic coronae of dMe stars. We obtained the requested observations and have now completed two papers that will be published in the Astrophysical Journal. The RS CVn binary star UX Ari was observed for 14 hours with all four detectors onboard the ASCA satellite. The X-ray emission was at a constant, quiescent level during the first 12 hours, after which time a powerful flare with a peak luminosity of 1.4 x 10(exp 32) ergs/s started. The flare was observed until shortly after its peak. We present a spectral and temporal analysis of the UX Ari observations and analyze the data with a two-ribbon flare model including estimates for cooling losses. A time-dependent reconstruction of the emission measure (EM) distribution shows that two separate plasma components evolve during the flare (one being identified with the quiescent EM). Most of the flare EM reaches temperatures between 50 MK and 100 MK or more. Magnetic confinement requires the loop arcade to be geometrically large, with length scales on the order of one stellar radius. The electron densities inferred from the model decrease from initial values around 10(exp 12)/cc early in the flare to about 10(exp 11)/cc at the flare peak. The best-fit models require surface magnetic field strengths of a few hundred G, compatible with the maximum photospheric fields expected from equipartition. The flare parameters imply a (conductive and radiative) cooling loss time of less than one hour at flare peak. The elemental abundances increase significantly during the flare rise, with the abundances of the low-FIP elements Fe, Mg, Si, and Ni typically increasing to higher levels than the high-FIP elements such as S or Ne. The Fe abundance increases from (17 +/- 4)% of the solar photospheric value during quiescence up to (89 +/- 18)% at flare peak. A fractionation process that occurs during the chromospheric evaporation phase may selectively enrich low-FIP elements as in the solar corona; alternatively, the chromospheric evaporation may itself bring metal-rich plasma into the metal-poor corona.

Linsky, Jeffrey L.↗
NASA NTRS1974

Shuttle active thermal control system development testing. Volume 5: Integrated radiator/expendable cooling system tests

Tests were conducted to gather data on a space shuttle active control system (ATCS) incorporating both radiators and an expendable cooling device to provide vehicle heat removal. Two systems were tested and design information was provided for both nominal and limit conditions. The tests verified the concept that an integrated radiator/expendable cooling system can adequately maintain desired water quantities while responding to variations in heat loads and environments. In addition, the need for duct heating was demonstrated, while exhaust nozzle heating was also shown to be unnecessary.

Scheps, P. B.↗
NASA NTRS1975

The relationship between hard and soft X-ray bursts observed by OSO 7

The paper reviews the observations of solar X-rays in the range 1-100 keV made by the solar X-ray instrument on board the OSO-7 satellite and explores the relationship between the hard and soft X-ray components in order to glean some information on the physics of solar flares. Some of the results are as follows: The growth of the soft X-ray emission in a burst must be due to the addition of new hot material to the flare plasma. The anticorrelation between cooling time and maximum plasma temperature gives new evidence to support conduction as the principal cooling mechanism of the hot flare plasma. Observations of hard X-ray emission from bursts which occurred behind the limb indicate that hard X-ray emission comes at least in part from considerable heights in the corona.

Datlowe, D. W.↗
NASA NTRS1945

Correlation of the Characteristics of Single-Cylinder and Flight Engines in Tests of High-Performance Fuels in an Air-Cooled Engine I : Cooling Characteristics

Variable charge-air flow, cooling-air pressure drop, and fuel-air ration investigations were conducted to determine the cooling characteristics of a full-scale air-cooled single cylinder on a CUE setup. The data are compared with similar data that were available for the same model multicylinder engine tested in flight in a four-engine airplane. The cylinder-head cooling correlations were the same for both the single-cylinder and the flight engine. The cooling correlations for the barrels differed slightly in that the barrel of the single-cylinder engine runs cooler than the barrel of te flight engine for the same head temperatures and engine conditions.

Wilson, Robert W.↗
NASA NTRS1951

Experimental Investigation of Air-Cooled Turbine Blades in Turbojet Engine. 7: Rotor-Blade Fabrication Procedures

An experimental investigation was conducted to determine the cooling effectiveness of a wide variety of air-cooled turbine-blade configurations. The blades, which were tested in the turbine of a - commercial turbojet engine that was modified for this investigation by replacing two of the original blades with air-cooled blades located diametrically opposite each other, are untwisted, have no aerodynamic taper, and have essentially the same external profile. The cooling-passage configuration is different for each blade, however. The fabrication procedures were varied and often unique. The blades were fabricated using methods most suitable for obtaining a small number of blades for use in the cooling investigations and therefore not all the fabrication procedures would be directly applicable to production processes, although some of the ideas and steps might be useful. Blade shells were obtained by both casting and forming. The cast shells were either welded to the blade base or cast integrally with the base. The formed shells were attached to the base by a brazing and two welding methods. Additional surface area was supplied in the coolant passages by the addition of fins or tubes that were S-brazed. to the shell. A number of blades with special leading- and trailing-edge designs that provided added cooling to these areas were fabricated. The cooling effectiveness and purposes of the various blade configurations are discussed briefly.

Long, Roger A.↗
NASA NTRS1972

Removal of metabolic heat from man working in a protective suit

A water cooled garment was constructed and used to study the characteristics of independent regional cooling of the body in contrast to the current practice of uniform cooling. The cooling pads in the garment were grouped to provide independent control of water inlet temperatures and flow rates to six regions: head, upper torso, lower torso, arms, thighs, and lower legs. Experiments with and without the cooling suit were conducted with five test subjects standing and walking on a treadmill on selected schedules. Steady state and, to a lesser extent, transient characteristics were obtained.

Shitzer, A.↗
NASA NTRS1973

The theory of charged particle temperatures in the upper atmosphere.

The thermal structure of the earth's upper atmosphere is examined in detail, with emphasis on the physical processes that govern the behavior of charged-particle temperatures. The characteristic features of and competition between the heating, cooling, and thermal conduction processes that govern electron and ion temperatures in the mid-latitude and auroral ionospheric regions are theoretically analyzed, and appropriate comparisons are made with experimental data. The proposed elaborate theory is considered qualitatively successful in accounting for the thermal structure of the ionosphere, and points requiring quantitative verification are delineated.

Schunk, R. W.↗
NASA NTRS1976

Hot interstellar tunnels. 1: Simulation of interacting supernova remnants

The theory required to build a numerical simulation of interacting supernova remnants is developed. The hot cavities within a population of remnants will become connected, with varying ease and speed, for a variety of assumed conditions in the outer shells of old remnants. Apparently neither radiative cooling nor thermal conduction in a large-scale galactic magnetic field can destroy hot cavity regions, if they grow, faster than they are reheated by supernova shock waves, but interstellar mass motions disrupt the contiguity of extensive cavities necessary for the dispersal of these shocks over a wide volume. Monte Carlo simulations show that a quasi-equilibrium is reached in the test space within 10 million yrs of the first supernova and is characterized by an average cavity filling fraction of the interstellar volume. Aspects of this equilibrium are discussed for a range of supernova rates. Two predictions are not confirmed within this range: critical growth of hot regions to encompass the entire medium, and the efficient quenching of a remnant's expansion by interaction with other cavities.

Smith, B. W.↗
NASA NTRS1977

Flare heating by energetic nonthermal electrons

A model has been developed which includes, in a self-consistent fashion, the energy degradation and attendant bremsstrahlung emission of a high-energy electron beam, heating of a flare plasma by the beam, and subsequent cooling by thermal conduction and radiation. To assist in the interpretation of experimental diagnostics, the model also characterizes the radiative behavior of iron ions present in the flare plasma. Electron deposition is described by the Fokker-Planck equation for an initial power-law particle distribution. Results are presented for the bremsstrahlung radiation emitted by the incident beam as it impinges on the disturbed atmosphere. A comparison is made between direct beam heating and thermal-conduction heating of the flare plasma. The radiation emitted by several selected spectral lines of Fe ions is determined as a function of time during and after deposition

Davis, J.↗
NASA NTRS1980

Dynamic spectral characteristics of thermal models for solar hard X-ray bursts

It is proposed that the source for solar hard X-ray bursts may consist of a distribution of many small impulsively-heated kernels, each cooled by anomalous conduction, with lifetimes shorter than current burst data temporal resolution. The dynamic spectra of bursts are governed by the dynamic evolution of the kernel production process, such as magnetic-field dissipation in the tearing mode. An integral equation is formulated, the solution of which yields information on this kernel production process from dynamic burst spectra, for any kernel model.

Brown, J. C.↗
NASA NTRS1981

Two-phase models of quasar emission line regions

It is demonstrated that the emitting gas in clouds of quasar emission line regions must be confined by a hot intercloud medium, provided only that the heating mechanisms are strong enough to drive the low-density intercloud gas above a few tens of millions degrees K. The study of the thermal properties of the gas presented includes heating by photoionization, Compton scattering, suprathermal particles, absorption of radio frequency radiation, cloud friction, thermal conduction, and shocks. Cooling curves for photoionized gases are presented, and phase diagrams analogous to the pressure-temperature diagrams used in studying the interstellar medium are constructed for various conditions. It is shown that two-phase equilibria occur over a wide range of mean density, but over a much narrower range of pressure. The implications of these results for the emission line region are discussed, and it is shown that the emission clouds may be short-lived.

Krolik, J. H.↗
NASA NTRS1986

The flare kernel in the impulsive phase

The impulsive phase of a flare is characterized by impulsive bursts of X-ray and microwave radiation, related to impulsive footpoint heating up to 50 or 60 MK, by upward gas velocities (150 to 400 km/sec) and by a gradual increase of the flare's thermal energy content. These phenomena, as well as non-thermal effects, are all related to the impulsive energy injection into the flare. The available observations are also quantitatively consistent with a model in which energy is injected into the flare by beams of energetic electrons, causing ablation of chromospheric gas, followed by convective rise of gas. Thus, a hole is burned into the chromosphere; at the end of impulsive phase of an average flare the lower part of that hole is situated about 1800 km above the photosphere. H alpha and other optical and UV line emission is radiated by a thin layer (approx. 20 km) at the bottom of the flare kernel. The upward rising and outward streaming gas cools down by conduction in about 45 s. The non-thermal effects in the initial phase are due to curtailing of the energy distribution function by escape of energetic electrons. The single flux tube model of a flare does not fit with these observations; instead we propose the spaghetti-bundle model. Microwave and gamma-ray observations suggest the occurrence of dense flare knots of approx. 800 km diameter, and of high temperature. Future observations should concentrate on locating the microwave/gamma-ray sources, and on determining the kernel's fine structure and the related multi-loop structure of the flaring area.

Dejager, C.↗
NASA NTRS1986

A shock condensation mechanism for loop prominences

Self-consistent, numerical solutions of the resistive MHD equations in two dimensions show that a quasi-stationary, fast-mode shock is a characteristic feature of the reconnection dynamics of the Kopp-Pneuman model of two-ribbon flares. A preliminary analysis of the effects of radiative cooling and thermal conduction suggests that the fast shock can help trigger a thermal condensation (i.e., a loop prominence)if the reconnecting magnetic fields are sufficiently strong.

Forbes, T. G.↗
NASA NTRS1986

The energetics of the gradual phase

Reseachers compare results with those in the chapter by Moore et al. (1980), who reached five main conclusions about the gradual phase: (1) the typical density of the soft X-ray emitting plasma is between 10 to the 11th power and 10 to the 12th power cm-3 for compact flares and between 10 to the 10th power and 10 to the 11th power cm-3 for a large-area flare; (2) cooling is by conduction and radiation in roughly equal proportions; (3) continual heating is needed in the decay phase of two-ribbon flares; (4) continual heating is probably not needed in compact events; (5) most of the soft-X-ray-emitting plasma results from chromospheric evaporation. The goal was to reexamine these problems with the data from the Solar Maximum Mission (SMM) and other supporting instruments as well as to take advantage of recent theoretical advances. SMM is capable of measuring coronal temperatures more accurately and with a better cadence than has been possible before. The SMM data set is also unique in that the complete transit of an active region was observed, with soft X-ray and UV images being taken every few minutes. Researcher's were therefore able to establish the pre-flare conditions of the region and see whether anything has changed as a result of the flare. The assumptions made in attempting to determine the required plasma parameters are described. The derived parameters for the five prime flares are presented, and the role of numerical simulations is discussed.

Strong, K. T.↗
NASA NTRS1986

Thermal stability analysis of the fine structure of solar prominences

The linear thermal stability of a 2D periodic structure (alternatively hot and cold) in a uniform magnetic field is analyzed. The energy equation includes wave heating (assumed proportional to density), radiative cooling and both conduction parallel and orthogonal to magnetic lines. The equilibrium is perturbed at constant gas pressure. With parallel conduction only, it is found to be unstable when the length scale 1// is greater than 45 Mn. In that case, orthogonal conduction becomes important and stabilizes the structure when the length scale is smaller than 5 km. On the other hand, when the length scale is greater than 5 km, the thermal equilibrium is unstable, and the corresponding time scale is about 10,000 s: this result may be compared to observations showing that the lifetime of the fine structure of solar prominences is about one hour; consequently, our computations suggest that the size of the unresolved threads could be of the order of 10 km only.

Demoulin, Pascal↗
NASA NTRS1986

Evaluation of on-orbit cryogenic propellant depot options for the orbital transfer vehicle

An orbital cryogenic propellant storage facility will be required for a space-based Orbital Transfer Vehicle. The facility tanks will have features to permit fluid acquisition and transfer in low gravity and to limit cryogen boiloff caused by environmental heating. Boiloff management features will include thick multilayer insulation, vapor-cooled shields, low conductance structural supports and penetrations, and possibly refrigeration systems.

Schuster, J. R.↗