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Results for “thermal quench”

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 NTRS1995

A Preliminary Investigation of the Cr3Si-Mo Pseudo-Binary Phase Diagram

An investigation was undertaken to study the phase relations in Cr3Si alloyed with Mo varying from 10 to 83.5 wt. % of the material. Specimens were prepared from arc-melted buttons that were subsequently heat treated at 1673 K for 200 h and air quenched to room temperature to structures. Alloys containing more than 20 wt. % MO were primarily two-phase materials of M3Si and M5Si3, where M is (Cr,Mo). Three alloys contained less than 5% of a third phase, which also had the M5Si3 crystal structure. Differential thermal analysis (DTA) was performed on several specimens at temperatures up to 2073 K in order to determine a solidus curve for the M3Si phase. Since only one DTA peak was observed in each alloy, the M5Si3 phase must melt above 2073 K, the maximum temperature examined. A preliminary pseudo-binary phase diagram for (Cr,Mo)3Si and a portion of the 1673 K isothermal section of the Cr-Mo-Si ternary phase diagram are presented.

Dickerson, R. M.↗
NASA NTRS2002

Microelectric Heterogeneous Hybrid Devices for Space Applications

The existing projects designated as SACA (Sample Ampoule Cartridge/Container Assembly) and QMI (Quench Module Insert) at NASA's MSFC (Marshall Space Flight Center) involve development of high-temperature coating materials. A number of material systems need to be evaluated for this purpose. The requirement of these coating materials included high emissivity (approaching unity), sufficient physical strength, appropriate thermal conductivity to dissipate heat, and above all high temperature (T is equal to or greater than 2000 C) withstanding capability. Potential materials for applications considered were non-oxide based materials such as tungsten carbide, tantalum carbide, compounds of niobium, etc.

Mohammad A. Alim↗
NASA NTRS1986

Surface effects on phase distributions of a fast-quenched miscibility gap type system - Succinonitrile-water

If a binary homogeneous melt is cooled into an immiscible region, the newly formed second phase will generally have a density different from the parent phase, and will separate readily by sedimentation. Observation of solidification processes in microgravity indicates that outside of sedimentation, at least two other important effets can separate the phases: (1) preferential wetting, and (2) thermal migration of second-phase droplets due to interfacial tension gradients. The latter effect would drive the minority phase along the thermal gradient toward the hottest part (assuming the interfacial tension decreases with increasing temperature), which is usually away from the crucible wall. On the other hand, if the minority phase preferentially wets the crucible, a minority phase layer which thickens as initial solution compositions approach critical, will form adjacent to the solid surface and remain in the coldest region of the ingot. This study presents compelling preliminary evidence that these two effects do exist and that they compete with one another. However, the temperature dependence of preferential wetting below T(c) for the current system of study is, as yet, undetermined. These effects are sensitive to the initial concentration of a hypermonotectic solution cooling through a miscibility gap.

Frazier, D. O.↗
NASA NTRS1974

Apollo 17 orange glass - Textural and morphological characteristics of devitrification

Results of a study are presented concerning (1) the significance of nonexcentroradial growth textures in Apollo 17 orange glass and a comparison of these textures with those that develop in lunar and meteoritic chondrules, (2) the development and the nature of the crystalline-glass interface, and (3) the morphology and growth characteristics of olivine and of the opaque mineral oxides that result by devitrification of the orange glass. Observations of the orange glass soil are contrasted with subsequent partial melting of orange glass spherules that were incorporated into mildly metamorphosed breccias, and the quench textures that result in these larger cooling units are compared with the textures produced by supercooling of small particulate spherules. Results show that the expected changes in viscosity due to partial melting and recrystallization do not affect the shape of individual particles, and that neither the thermal gradients that need to be invoked across 20-100 micron spheres nor collision of glass particles during lava fountaining can account for the devitrification textures observed.

Haggerty, S. E.↗
NASA NTRS1979

Coordinated rocket and satellite measurements of an auroral event. II - The rocket observations and analysis

A rocket-borne payload launched into an aurora and a simultaneous overpass of the Atmosphere Explorer C satellite yielded measurements of auroral optical emission rates, thermal ion and electron densities, and low-energy electron fluxes. Model calculations of the thermospheric manifestation of the aurora were performed through use of rocket-determined auroral ionization rates and satellite-determined neutral gas densities. Measured oxygen densities provided a means of assessing the quenching rate of an excited state of N2. Energy transfer from this excited state appears to be the major source of 5577-A emission. Optical emission at 6300 A cannot be explained either by electron impact on atomic oxygen or by dissociative recombination of O2(+).

Sharp, W. E.↗
NASA NTRS1998

Numerical Examination of Silicon Avalanche Photodiodes Operated in Charge Storage Mode

The behavior of silicon-based avalanche photodiodes (APD's) operated in the charge storage mode is examined. In the charge storage mode, the diodes are periodically biased to a sub-breakdown voltage and then open-circuited. During this integration period, photo-excited and thermally generated carriers are accumulated within the structure. The dynamics of this accumulation and its effects upon the avalanching of the diode warrants a detailed, fully numerical analysis. The salient features of this investigation include device sensitivity to the input photo-current including the self-quenching effect of the diode and its limitations in sensing low light levels, the dependence of the response on the bulk lifetime and hence on the generation current within the device, the initial gain, transient response, dependence of the device uniformity upon performance, and the quantity of storable charge within the device. To achieve these tasks our device simulator, STEBS-2D, was utilized. A modified current-controlled boundary condition is employed which allows for the simulation of the isolated diode after the initial reset bias has been applied. With this boundary condition, it is possible to establish a steady-state voltage on the ohmic contact and then effectively remove the device from the external circuit while still including effects from surface recombination, trapped surface charge, and leakage current from the read-out electronics.

Parks, Joseph W., Jr.↗
NASA NTRS2002

Thin-film Organic-based Solar Cells for Space Power

Recent advances in dye-sensitized and organic polymer solar cells have lead NASA to investigate the potential of these devices for space power generation. Dye-sensitized solar cells were exposed to simulated low-earth orbit conditions and their performance evaluated. All cells were characterized under simulated air mass zero (AM0) illumination. Complete cells were exposed to pressures less than 1 x 10(exp -7) torr for over a month, with no sign of sealant failure or electrolyte leakage. Cells from Solaronix SA were rapid thermal cycled under simulated low-earth orbit conditions. The cells were cycled 100 times from -80 C to 80 C, which is equivalent to 6 days in orbit. The best cell had a 4.6 percent loss in efficiency as a result of the thermal cycling. In a separate project, novel -Bridge-Donor-Bridge- Acceptor- (-BDBA-) type conjugated block copolymer systems have been synthesized and characterized by photoluminescence (PL). In comparison to pristine donor or acceptor, the PL emissions of final -B-D-B-A- block copolymer films were quenched over 99 percent. Effective and efficient photo induced electron transfer and charge separation occurs due to the interfaces of micro phase separated donor and acceptor blocks. The system is very promising for a variety high efficiency light harvesting applications. Under an SBIR contract, fullerene-doped polymer-based photovoltaic devices were fabricated and characterized. The best devices showed overall power efficiencies of approx. 0.14 percent under white light. Devices fabricated from 2 percent solids content solutions in chlorobenzene gave the best results. Presently, device lifetimes are too short to be practical for space applications.

Bailey, Sheila G.↗
NASA NTRS2001

Thin-Film Organic-Based Solar Cells for Space Power

Recent advances in dye-sensitized and organic polymer solar cells have lead NASA to investigate the potential of these devices for space power generation. Dye-sensitaized solar cells were exposed to simulated low-earth orbit conditions and their performance evaluated. All cells were characterized under simulated air mass zero (AM0) illumination. Complete cells were exposed to pressures less than 1 x 10 (exp -7)torr for over a month, with no sign of sealant failure or electrolyte leakage. Cells from Solaronix SA were rapid thermal cycled under simulated low-earth orbit conditions. The cells were cycled 100 times from -80 C to 80 C, which is equivalent to 6 days in orbit. The best cell had a 4.6% loss in efficiency as a result of the thermal cycling. In a separate project, novel -Bridge-Donor-Bridge-Acceptor- (-BDBA-) type conjugated block copolymer systems have been synthesized and characterized by photoluminescence (PL). In comparison to pristine donor or acceptor, the PL emissions of final -B-D-B-A- block copolymer films were quenched over 99%. Effective and efficient photo induced electron transfer and charge separation occurs due to the interfaces of micro phase separated donor and acceptor blocks. The system is very promising for a variety high efficiency light harvesting applications. Under an SBIR contract, fullerene-doped polymer-based photovoltaic devices were fabricated and characterized. The best devices showed overall power efficiencies of approximately 0.14% under white light. Devices fabricated from 2% solids content solutions in chlorobenzene gave the best results. Presently, device lifetimes are too short to be practical for space applications.

Bailey, Sheila G.↗
NASA NTRS1974

Development of improved amorphous materials for laser systems

Crystallization calculations were performed in order to determine the possibility of forming a particular type of laser glass with the avoidance of devitrification in an outer space laboratory. It was demonstrated that under the homogenuous nucleating conditions obtainable in a zero gravity laboratory this laser glass may be easily quenched to a virtually crystal-free product. Experimental evidence is provided that use of this material as a host in a neodymium glass laser would result in more than a 10 percent increase in efficiency when compared to laser glass rods of a similar composition currently commercially available. Differential thermal analysis, thermal gradient oven, X-ray diffraction, and liquidus determination experiments were carried out to determine the basics of the crystallization behavior of the glass, and small-angle X-ray scattering and splat-cooling experiments were performed in order to provide additional evidence for the feasibility of producing this laser glass material, crystal free, in an outer space environment.

Neilson, G. F.↗
NASA NTRS1991

Crystallization and properties of Sr-Ba aluminosilicate glass-ceramic matrices

Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glasss transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder x ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structure transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.

Bansal, Narottam P.↗
NASA NTRS1991

Crystallization and properties of Sr-Ba aluminosilicate glass-ceramic matrices

Powders of roller quenched (Sr,Ba)O-Al2O3-2SiO2 glasses of various compositions were uniaxially pressed into bars and hot isostatically pressed at 1350 C for 4 hours or cold isostatically pressed and sintered at different temperatures between 800 to 1500 C for 10 or 20 hours. Densities, flexural strengths, and linear thermal expansion were measured for three compositions. The glass transition and crystallization temperatures were determined by Differential Scanning Calorimetry (DSC). The liquidus and crystallization temperature from the melt were measured using high temperature Differential Thermal Analysis (DTA). Crystalline phases formed on heat treatment of the glasses were identified by powder X ray diffraction. In Sr containing glasses, the monoclinic celsian phase always crystallized at temperatures above 1000 C. At lower temperatures, the hexagonal analog formed. The temperature for orthorhombic to hexagonal structural transformation increased monotonically with SrO content, from 327 C for BaO-Al2O3-2SiO2 to 758 C for SrO-Al2O3-2SiO2. These glass powders can be sintered to almost full densities and monoclinic celsian phase at a relatively low temperature of 1100 C.

Bansal, Narottam P.↗
NASA NTRS2021

Compact Augmented Spark Igniters for Liquid Rocket Engines

The objective of this dissertation is to characterize augmented spark impinging (torch) igniters. Torch igniters inject propellants into a small prechamber where a spark igniter imparts the activation energy to initiate combustion. The flame stabilizes within the prechamber and exits into the main combustion chamber where it ignites the main flow directly or by mixing with a coaxial flow to create a secondary flame. The underlying phenomena that promote reliable ignition are multifaceted and required a broad scope of investigations. Initial efforts focused on spark discharges across an annular geometry. Gaseous propellent projects the electrical arc toward the prechamber, where the arc and the thermal energy is imparted to the surrounding fluid then meets with a combustible mixture. Discharges are parametrically examined against pressure, spark-gap size, and exciter types to emulate transient engine startup. The energy imparted to the flow, approximate velocity, and distance traveled by the exhaust plume are determined. Spark quenching (no energy deposition) and its effects on perceived versus actual measurements are shown. Results outline the prechamber target zone where a combustible mixture is necessary for ignition. Next, three-dimensional, time-accurate, and nonreacting computational fluid dynamics simulations assess effects of geometric and mass flow differences on the size, location, and composition of a combustible mixture. Fluid dynamic phenomena are elucidated. Correlations between nondimensional variables are found. Results are coupled with a conservation-law analysis to produce novel objective functions. Lastly, a full-scale, modular torch igniter is tested. Injector sizes, mixture ratios, and injector momentum ratios are systematically varied to map ignition probability and ignition delay. Results show the importance of local mixture ratios, provide injector momentum ratios guidelines, and demonstrate reliable ignition of core mixture ratios typically outside flammability limits. The deliverable of this project is not a torch igniter or derivative thereof. Instead, this dissertation produces novel objective-functions for igniter design. These equations are functions of variables that may be constrained by engine-level requirements, physics, and experimental results from this work. They provide a foundation for future igniter design and will minimize iterative processes from the design cycle for next-generation ignition hardware.

Torch Igniter↗
NASA NTRSDate not supplied

Parametric Analysis of the Charge-Hold-Vent Method for Cryogenic Propellant Tank Chill Down

In the absence of external heat exchangers, the on-orbit transfer of cryogenic propellants requires the receiver tank to first be quenched to a sufficiently low energy state to allow for a continuous no-vent fill to avoid unnecessary venting of liquid. One proposed method for tank chilldown that minimizes the potential for venting liquid is the charge hold vent (CHV) method. CHV follows a cyclic process that gradually removes thermal energy from the receiver tank by injecting liquid with the vent valve closed and allowing the fluid and wall to reach near-thermal equilibrium before venting the superheated vapor. However, the CHV method must be optimized to minimize complexity, mass, and time. This paper presents a modular CHV analytical model used to quantify the number of cycles and propellant mass consumed based on first principles. The model is used to examine the effect of eight parameters: receiver tank material, volume, mass, maximum expected operating pressure, and initial pressure, liquid injection pressure and temperature, and the target temperature. The model is validated against the only two available CHV datasets. Based on results, the tank mass-to-volume ratio is the most important factor in determining the number of CHV cycles and thus degree of difficulty in tank chilldown. The model can easily be used for early-stage design, sizing, and analysis of cryogenic propellant transfer systems.

Tank Chilldown↗
NASA NTRSDate not supplied

Parametric Analysis of the Charge-Hold-Vent Method for Cryogenic Propellant Tank Chill Down

Abstract. In the absence of external heat exchangers, the on-orbit transfer of cryogenic propellants requires the receiver tank to first be quenched to a sufficiently low energy state to allow for a continuous no-vent fill to avoid unnecessary venting of liquid. One proposed method for tank chilldown that minimizes the potential for venting liquid is the charge hold vent (CHV) method. CHV follows a cyclic process that gradually removes thermal energy from the receiver tank by injecting liquid with the vent valve closed and allowing the fluid and wall to reach near-thermal equilibrium before venting the superheated vapor. However, the CHV method must be optimized to minimize complexity, mass, and time. This paper presents a modular CHV analytical model used to quantify the number of cycles and propellant mass consumed based on first principles. The model is used to examine the effect of eight parameters: receiver tank material, volume, mass, maximum expected operating pressure, and initial pressure, liquid injection pressure and temperature, and the target temperature. The model is validated against the only two available CHV datasets. Based on results, the tank mass-to-volume ratio is the most important factor in determining the number of CHV cycles and thus degree of difficulty in tank chilldown. The model can easily be used for early-stage design, sizing, and analysis of cryogenic propellant transfer systems. Keywords: tank chilldown, charge-hold-vent, no-vent fill

Tank Chilldown↗
NASA NTRS1986

Physical aging in epoxy matrices and composites

Postcured specimens of Thornell 300 carbon-fiber/Fiberite 934 epoxy as well as Fiberite 934 epoxy resin were quenched from above the glass transition temperature and annealed at 140, 110, or 80 C for times up to 100,000 min. No weight gain or loss was observed during annealing at these temperatures, but significant time-dependent variations were observed in density, modulus, hardness, damping, moisture absorption ability, and thermal expansion characteristics. The relations between the excess thermodynamic properties of epoxy glasses and their time-dependent behavior are discussed. The discussion is illustrated by results obtained by differential scanning calorimetry, dynamic mechanical analysis, tensile testing, solid state nuclear magnetic resonance spectroscopy, and small-angle X-ray scattering.

Kong, Eric Siu-Wai↗
NASA NTRS1992

Fluorescence of thermal control coatings on S0069 and A0114

Many of the thermal control surfaces exposed to the space environment during the 5.8 year LDEF mission experienced changes in fluorescence. All of the thermal control coatings flown on LDEF experiments S0069 and A0114 were characterized for fluorescence under ambient conditions. Some of the black coatings, having protective overcoats, appear bright yellow under ultraviolet exposure. Urethane based coatings exhibited emission spectra shifts toward longer wavelengths in the visible range. Zinc oxide pigment based coatings experienced a quenching of fluorescence, while zinc orthotitanate pigment based and other ceramic type coatings had no measurable fluorescence.

Zwiener, James M.↗
NASA NTRS1974

Preparation, testing and analysis of zinc diffusion samples, NASA Skylab experiment M-558

Transport mechanisms of zinc atoms in molten zinc were investigated by radiotracer techniques in unit and in near-zero gravity environments. Each melt in the Skylab flight experiments was maintained in a thermal gradient of 420 C to 790 C. Similar tests were performed in a unit gravity environment for comparison. After melting in the gradient furnace followed by a thermal soak period (the latter was used for flight samples only), the samples were cooled and analyzed for Zn-65 distribution. All samples melted in a unit gravity environment were found to have uniform Zn-65 distribution - no concentration gradient was observed even when the sample was brought rapidly to melting and then quenched. Space-melted samples, however, showed textbook distributions, obviously the result of diffusion. It was evident that convection phenomena were the dominant factors influencing zinc transport in unit gravity experiments, while diffusion was the dominant factor in near-zero gravity experiments.

Braski, D. N.↗
NASA NTRS1994

On the Influence of a Fuel Side Heat-Loss (Soot) Layer on a Planar Diffusion Flame

A model of the response of a diffusion flame (DF) to an adjacent heat loss or 'soot' layer on the fuel side is investigated. The thermal influence of the 'soot' or heat-loss layer on the DF occurs through the enthalpy sink it creates. A sink distribution in mixture-fraction space is employed to examine possible DF extinction. It is found that (1) the enthalpy sink (or soot layer) must touch the DF for radiation-induced quenching to occur; and (2) for fuel-rich conditions extinction is possible only for a progressively narrower range of values ot the characteristic heat-loss parameter, N(sub R)(Delta Z(sub R)) Various interpretations ot the model are discussed. An attempt is made to place this work into the context created by previous experimental and computational studies.

Wichman, Indrek S.↗