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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 NTRS1995

Testing the DC-electric field model in a solar flare observed by Yohkoh and the Compton Gamma-Ray Observatory

We apply a DC-electric field model to the analysis of soft and hard X-ray observations of a solar flare observed by Yohkoh and the Compton Gamma Ray Observatory (CGRO) on 6 September 1992. The flare was observed simultaneously in the soft X-ray Ca XIX line by the Yohkoh Bragg Crystal Spectrometer (BCS) and in hard X-rays (greater than 50 keV) by the CGRO Burst and Transient Spectrometer Experiment (BATSE). A strong stationary component of Ca XIX emission was present at the start of impulsive hard X-ray emission indicating an extended phase of heating prior to the production of energetic nonthermal electrons. We interpret the preflare Ca XIX emission as a signature of Joule heating by field-aligned currents. We relate the temporal variation of impulsive hard X-ray emission to the rate of runaway electron acceleration by the DC-electric field associated with the current. We find that the initial rise in hard X-ray emission is consistent with electron acceleration by a DC-electric field that increased from a preflare value of less than approximately 10(exp -5) V/cm to approximately (9 +/- 1) x 10(exp -5) V/cm at the time of the first hard X-ray peak and then remained constant during the rest of the impulsive phase. We attribute the increase in electric field strength to the formation of a current sheet at the reconnection point of two loop structures. The decrease in hard X-ray emission after flare maximum is consistent with a reduction in the number of runaway electrons due to an increase in coronal density produced by chromospheric evaporation. The increased density quenches the runaway process by enhancing collisional thermalization of electrons. To avoid the generation of an unrealistically large magnetic field, the flaring region must be highly filamented into greater than approximately 10(exp 6) oppositely directed current channels of approximately 30 cm width with an initial preflare current of approximately 3 x 10(exp 10) A per channel.

Zarro, D. M.↗
NASA NTRS1999

In Situ Monitoring of Crystal Growth Using MEPHISTO, Mission STS 87-Program USMP-4: Experimental Analysis

This report summarizes the results of the In situ Monitoring of Crystal Growth Using MEPHISTO (Material por l'Etude des Phenomenes Interessant de la Solidification sur Terre et en Orbite) experiment on USMP-4. The report includes microstructural and compositional data obtained during the first year of the post flight analysis, as well as numerical simulation of the flight experiment. Additional analyses are being continued and will be reported in the near future. The experiments utilized MEPHISTO hardware to study the solidification and melting behavior of bismuth alloyed with 1 at% tin. The experiments involved repeated melting and solidification of three samples, each approximately 90 cm long and 6mm in diameter. Half of each sample also included a 2 mm. diameter growth capillary, to assist in the formation of single grain inside. One sample provided the Seebeck voltage generated during melting and freezing processes. Another one provided temperature data and Peltier pulsed demarcation of the interface shape for post flight analysis. The third sample provided resistance and velocity measurements, as well as additional thermal data. The third sample was also quenched at the end of the mission to preserve the interface composition for post flight determination. A total of more than 45cm of directionally solidified alloy were directionally solidified at the end of the flight for post mission structural and compositional characterization. Metallurgical analysis of the samples has shown that the interfacial kinetics play a key role in controlling the morphological stability of faceted alloys. Substantial differences were observed in the Seebeck signal between the ground-based experiments and the space-based experiments. The temperature gradient in the liquid for the ground-based experiments was also significantly lower than the temperature gradient in the liquid for the space-based experiments. Both of these observations indicate significant influence of liquid convection for the ground-based experiments.

Abbaschian, Reza↗
NASA NTRS1999

Directional Solidification of Bi-Sn on USMP-4

The experiments used MEPHISTO hardware to study the solidification and melting behavior of bismuth alloyed with 1 at% tin. Three samples, each approximately 900 mm long and 6mm in diameter, were used. A portion of each sample also included a 2 mm diameter growth capillary, to assist in the formation of a single grain. One sample provided the Seebeck voltage generated during melting and freezing processes. Another provided temperature data and Peltier pulsed demarcation of the interface shape for post flight analysis. The third sample provided resistance and growth velocity measurements, as well as additional thermal data. The third sample was also quenched at the end of the mission to preserve the composition of the liquid near the interface for post flight determination. A total of 450mm of directionally solidified samples were preserved for post mission structural and compositional characterization. Substantial differences were observed in the Seebeck signal between the ground-based experiments and the space-based experiments. The temperature gradient in the liquid for the ground-based experiments was significantly lower than the temperature gradient in the liquid for the space-based experiments.

Abbaschian, Reza↗
NASA NTRS1999

Numerical Analysis of Temperature Gradients and Interface Shape During Directional Solidification of Al and Al-Cu Alloy Under Microgravity Conditions

Numerical modeling was undertaken to analyze the influence of radial thermal gradient on solid/liquid (s/1) interface shape and convection patterns during solidification of pure Al and Al-4 wt% Cu alloy. The objective of the numerical task was to predict the influence of convective velocity on an insoluble particle near a s/l interface. These predictions would then be used to define the minimum gravity level (g) required to investigate the fundamental physics of interaction between a particle and a s/I interface. To satisfy this objective, steady state calculations were performed for different gravity levels and orientations with the gravity vector. ne furnace configuration used in this analysis is the proposed International Space Station Furnace, Quench Module Insert (QMI) 1. Results from a thermal model of the furnace core were used as initial boundary conditions for solidification modeling. General model of binary alloy solidification was based on the finite element code FIDAP. It was found that for the worst case orientation of 90 degrees with the gravity vector and a g level of 10(exp -4)g(sub o) (g(sub o) = 9.8 m/s(exp 2)) the dominant forces acting on the particle would be the fundamental drag and interfacial forces.

Bune, Andris V.↗
NASA NTRS1970

Intumescent Coatings as Fire Retardants

The development of fire-retardant coatings to protect surfaces which may be exposed to fire or extreme heat is a subject of intense interest to many industries. A fire-retardant paint has been developed which represents a new chemical approach for preparing intumescent coatings, and potentially, is very important to fire-prevention authorities. The requirements for a superior coating include ease of application, suitability to a wide variety of surfaces and finishes, and stability over an extended period of time within a broad range of ambient temperature and humidity conditions. These innovative coatings, when activated by the heat of a fire, react to form a thick, low-density, polymeric coating or char layer. Water vapor and sulphur dioxide are released during the intumescent reaction. Two fire-protection mechanisms thus become available: (1) the char layer retards the flow of heat, due to the extremely low thermal conductivity; and (2) water vapor and sulfur dioxide are released, providing fire quenching properties. Still another mechanism functions in cases where the char, by virtue of its high oxidation resistance and low thermal conductivity, reaches a sufficiently high temperature to re-radiate much of the incident heat load. The coatings consist of dispersions of selective salts of a nitro-amino-arornatic compound. Specifically, para-nitroaniline bisulfate and the ammonium salt of para-nitroaniline-ortho sulphuric acid (2-amino-5-nitrobenzenesulphuric acid) are used. Suitable vehicles are cellulose nitrate of lacquer grade, a nitrite-phenolic modified rubber, or epoxy-polysulfide copolymer. Three separate formulations have been developed. A solvent is usually employed, such as methylethyl ketone, butyl acetate, or toluene, which renders the coatings suitably thin and which evaporates after the coatings are applied. Generally, the intumescent material is treated as insoluble in the vehicle, and is ground and dispersed in the vehicle and solvent like an ordinary coating pigment. The char found on intumescence is better in terms of yield and physical properties than chars obtained from many previously known intumescent materials. Prior to intumescence, the coating has a density of 85 pounds per cubic foot. After intumescence, the density is approximately 0.3 pounds per cubic loot. The linear expansion of the coatings ranges from 70 to 200 times the applied coating thickness.

Parker, J. A.↗
NASA NTRS2019

Heat Transfer Enhancement in Cryogenic Quenching Process

This paper reports a heat transfer advancement in the cryogenic quenching process. An experiment was performed to evaluate the enhancement of quenching heat transfer by the use of metal tubes with low thermal conductivity coating layers. Four coating thicknesses with various coolant mass flow rates of liquid nitrogen were investigated. The results indicated that the tube inner surface coating greatly enhanced the quenching efficiency. The quenching efficiency was found to increase with increasing number of coating layers, and the efficiency also increased with decreasing mass flow rates. In general, the efficiencies cover a range between 40.6% and 80%. Comparing to the bare surface case, the percentage increase in the quenching efficiency was the minimum at 4.2% for a single coated layer at the highest flow rate and the maximum of 109.1% for four coated layers at the lowest flow rate. The coated tubes could save up to 53% in the amount of cryogen consumption.

Surface coating↗
NASA NTRS1996

Thermal analysis of HGFQ using FIDAP(trademark): Solidification front motion

The High Gradient Furnace with Quench (HGFQ) is being designed by NASA/MSFC for flight on the International Space Station. The furnace is being designed specifically for solidification experiments in metal and metallic alloy systems. The HGFQ Product development Team (PDT) has been active since January 1994 and their effort is now in early Phase B. Thermal models have been developed both by NASA and Sverdrup (support contractor) to assist in the HGFQ design effort. Both these models use SINDA as a solution engine, but the NASA model was developed using PATRAN and includes more detail than the Sverdrup model. These models have been used to guide design decisions and have been validated through experimentation on a prototypical 'Breadboard' furnace at MSFC. One facet of the furnace operation of interest to the designers is the sensitivity of the solidification interface location to changes in the furnace setpoint. Specifically of interest is the motion (position and velocity) of the solidification front due to a small perturbation in the furnace temperature. FIDAP(TM) is a commercially available finite element program for analysis of heat transfer and fluid flow processes. Its strength is in solution of the Navier-Stokes equations for incompressible flow, but among its capabilities is the analysis of transient processes involving radiation and solidification. The models presently available from NASA and Sverdrup are steady-state models and are incapable of computing the motion of the solidification front. The objective of this investigation is to use FIDAP(TM) to compute the motion of the solidification interface due to a perturbation in the furnace setpoint.

Woodbury, Keith A.↗
NASA NTRS1980

Effects of temperature, thermal exposure, and fatigue on an alumina/aluminum composite

An experimental investigation of the mechanical properties and microstructure of an aluminum matrix/polycrystalline alumina fiber composite material is discussed. The effects of fabrication, isothermal exposure (up to 10,000 hours at 590 K), thermal cycling (6000 cycles between 200 K and 590 K), fatigue (1,000,000 tension-tension cycles) were determined by mechanical testing and metallurgical analysis. The fabrication process severely degraded the fiber strength by reducing the alumina to a nonstoichiometric form and quenching in the resultant vacancies and stress fields. However, isothermal exposure, thermal cycling, and fatigue cycling all restored the fiber strength by enhancing vacancy annihilation. Comparison of the as-fabricated material with other aerospace materials shows that it is an attractive candidate for select applications. Long duration isothermal exposure weakened the matrix by overaging and through the diffusional loss of lithium to a surface reaction forming lithium carbonate. Thermal cycling initiated cracks in the matrix and fibers. Tension-tension fatigue cycling caused no apparent damage to the as-fabricated material but in fact, strengthened it to the rule-of-mixtures value. Fatigue cycling after thermal exposure did have a cumulative damage effect.

Olsen, G. C.↗
NASA NTRS1993

Polymer morphologh

All polymeric materials in their final application are aggregates of many molecules. For linear macromolecules, these aggregates are highly entangled and their macroscopic properties are affected in a little-known way by the interpenetration and entanglements of the molecules. Over the years, we have done occasional investigations of single molecule single crystals and found that there are many unsolved questions about their nucleation, growth, kinetically determined shape, and ultimate path to equilibrium morphology on annealing. This initial work could be extended by a study of the applicability of microgravity methods for the production and study of the formation of single molecule particles. The production of separated molecules of sufficient size to produce phase-like behavior would involve perhaps a spray of solutions containing single molecules, followed by evaporation of the volatiles, or precipitation out of dispersion droplets. Other methods may involve Langmuir films etc., as shown in our prior work. The microgravity environment should enhance the efficiency of any of these methods by avoiding the joining of growing particles by reduction of convection and settling due to density differences. Once produced, the single molecule droplets are to be quenched into the glassy state and analyzed morphologically and thermally. Their shape alone can be used for molecular mass determination (an old problem that suffered from the need to estimate the shape of collapsed (flat) droplets on a surface). Next would be the study of changes of properties as a function of time, temperature, and molecular mass (and distribution) on fusion to macroscopic single phases.

Wunderlich, Bernhard↗
NASA NTRS1972

Study of beryllium and beryllium-lithium complexes in single-crystal silicon.

When beryllium is thermally diffused into silicon, it gives rise to acceptor levels 191 and 145 meV above the valence band. Quenching and annealing studies indicate that the 145-meV level is due to a more complex beryllium configuration than the 191-meV level. When lithium is thermally diffused into a beryllium-doped silicon sample, it produces two new acceptor levels at 106 and 81 meV. Quenching and annealing studies indicate that these new levels are due to lithium forming a complex with the defects responsible for the 191- and 145-meV beryllium levels, respectively. Electrical measurements imply that the lithium impurity ions are physically close to the beryllium impurity atoms. The ground state of the 106-meV beryllium-lithium level is split into two levels, presumably by internal strains. Tentative models are proposed to explain these results.

Crouch, R. K.↗
NASA NTRS1972

A study of beryllium and beryllium-lithium complexes in single crystal silicon

When beryllium is thermally diffused into silicon, it gives rise to acceptor levels 191 MeV and 145 meV above the valence band. Quenching and annealing studies indicate that the 145-MeV level is due to a more complex beryllium configuration than the 191-MeV level. When lithium is thermally diffused into a beryllium-doped silicon sample, it produces two acceptor levels at 106 MeV and 81 MeV. Quenching and annealing studies indicate that these levels are due to lithium forming a complex with the defects responsible for the 191-MeV and 145-MeV beryllium levels, respectively. Electrical measurements imply that the lithium impurity ions are physically close to the beryllium impurity atoms. The ground state of the 106-MeV beryllium level is split into two levels, presumably by internal strains. Tentative models are proposed.

Crouch, R. K.↗
NASA NTRS2001

An Overview of the Thermal Challenges of Designing Microgravity Furnaces

Marshall Space Flight Center is involved in a wide variety of microgravity projects that require furnaces, with hot zone temperatures ranging from 300 C to 2300 C, requirements for gradient processing and rapid quench, and both semi-conductor and metal materials. On these types of projects, the thermal engineer is a key player in the design process. Microgravity furnaces present unique challenges to the thermal designer. One challenge is designing a sample containment assembly that achieves dual containment, yet allows a high radial heat flux. Another challenge is providing a high axial gradient but a very low radial gradient. These furnaces also present unique challenges to the thermal analyst. First, there are several orders of magnitude difference in the size of the thermal 'conductors' between various parts of the model. A second challenge is providing high fidelity in the sample model, and connecting the sample with the rest of the furnace model, yet maintaining some sanity in the number of total nodes in the model. The purpose of this paper is to present an overview of the challenges involved in designing and analyzing microgravity furnaces and how some of these challenges have been overcome. The thermal analysis tools presently used to analyze microgravity furnaces and will be listed. Challenges for the future and a description of future analysis tools will be given.

Westra, Douglas G.↗
NASA NTRS1989

Nonlinear evolution of high frequency R-mode waves excited by water group ions near comets - Computer experiments

An ion beam resonates with R-mode waves at a high-frequency RH mode and a low-frequency RL mode. The nonlinear evolution of ion beam-generated RH waves is studied here by one-dimensional hybrid computer experiments. Both wave-particle and subsequent wave-wave interactions are examined. The competing process among coexisting RH and RL mode beam instabilities and repeated decay instabilities triggered by the beam-excited RH mode waves is clarified. It is found that the quenching of the RH instability is not caused by a thermal spreading of the ion beam, but by the nonlinear wave-wave coupling process. The growing RH waves become unstable against the decay instability. This instability involves a backward-traveling RH electromagnetic wave and a forward-traveling longitudinal sound wave. The inverse cascading process is found to occur faster than the growth of the RL mode. Wave spectra decaying from the RH waves weaken as time elapses and the RL mode waves become dominant at the end of the computer experiment.

Kojima, H.↗
NASA NTRS1996

Magnetothermal Convection in Nonconducting Diamagnetic and Paramagnetic Fluids

Nonuniform magnetic fields exert a magnetic body force on electrically nonconducting classical fluids. These include paramagnetic fluids such as gaseous and liquid oxygen and diamagnetic fluids such as helium. Recent experiments show that this force can overwhelm the force of gravity even at the surface of the earth; it can levitate liquids and gases, quench candle flames, block gas flows, and suppress heat transport. Thermal gradients render the magnetic force nonuniform through the temperature-dependent magnetic susceptibility. These thermal gradients can therefore drive magnetic convection analogous to buoyancy-driven convection. This magnetothermal convection can overwhelm convection driven by gravitational buoyancy in terrestrial experiments. The objectives of the proposed ground-based theoretical study are (a) to supply the magnetothermohydrodynamic theory necessary to understand these recent experiments and (b) to explore the consequences of nonuniform magnetic fields in microgravity. Even the linear theory for the onset of magnetothermal convection is lacking in the literature. We intend to supply the linear and nonlinear theory based on the thermohydrodynamic equations supplemented by the magnetic body force. We intend to investigate the effect of magnetic fields on gas blockage and heat transport in microgravity. Since magnetic fields provide a means of creating arbitrary, controllable body force distributions, we intend to investigate the possibility of using magnetic fields to position and control fluids in microgravity. We also intend to investigate the possibility of creating stationary terrestrial microgravity environments by using the magnetic force to effectively cancel gravity. These investigations may aid in the design of space-based heat-transfer, combustion, and human-life-support equipment.

Edwards, Boyd F.↗
NASA NTRS1988

Thermal effects on the mechanical properties of SiC fiber reinforced reaction bonded silicon nitride matrix (SiC/RBSN) composites

The elevated temperature four-point flexural strength and the room temperature tensile and flexural strength properties after thermal shock were measured for ceramic composites consisting of 30 vol pct uniaxially aligned 142 micron diameter SiC fibers in a reaction bonded Si3N4 matrix. The elevated temperature strengths were measured after 15 min of exposure in air at temperatures to 1400 C. Thermal shock treatment was accomplished by heating the composite in air for 15 min at temperatures to 1200 C and then quenching in water at 25 C. The results indicate no significant loss in strength properties either at temperature or after thermal shock when compared with the strength data for composites in the as-fabricated condition.

Bhatt, R. T.↗
NASA NTRS1990

Thermal effects on the mechanical properties of SiC fibre reinforced reaction-bonded silicon nitride matrix composites

The elevated temperature four-point flexural strength and the room temperature tensile and flexural strength properties after thermal shock were measured for ceramic composites consisting of 30 vol pct uniaxially aligned 142 micron diameter SiC fibers in a reaction bonded Si3N4 matrix. The elevated temperature strengths were measured after 15 min of exposure in air at temperatures to 1400 C. Thermal shock treatment was accomplished by heating the composite in air for 15 min at temperatures to 1200 C and then quenching in water at 25 C. The results indicate no significant loss in strength properties either at temperature or after thermal shock when compared with the strength data for composites in the as-fabricated condition.

Bhatt, R. T.↗
NASA NTRS1988

Microsegregation in directionally solidified Pb-8.4 at. pct Au alloy

The dependence of microsegregation behavior on growth rate and thermal gradient has been examined in a Pb-8.4 at. pct Au alloy material partially directionally solidified and quenched. The composition of the quenched 'liquid' at the dendrite tip (Ct), that of the eutectic-like solid phase freezing from the interdendritic liquid at the base of dendrite (Cse), the volume fraction of this eutectic-like region (fe), and solute profiles in the interdendritic quenched liquid and ahead of the dendrite have been measured. Two dendritic growth models for solidification of a binary alloy melt in a positive thermal gradient at the liquid-solid interface, one for dendrites with 'minimum undercooled dendrite tip' and the other for an Ivantsov type of dendrite with 'marginally stable tip', have been examined for a quantitative comparison with measured values of Ct, Cse, and fe. Convection in the melt, possibly due to horizontal density gradients, is found to be a serious limitation for theoretical understanding of the observed experimental behavior and meaningful comparison of theories.

Tewari, S. N.↗