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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Solar panel acceptance testing using a pulsed solar simulator

Utilizing specific parameters as area of an individual cell, number in series and parallel, and established coefficient of current and voltage temperature dependence, a solar array irradiated with one solar constant at AMO and at ambient temperature can be characterized by a current-voltage curve for different intensities, temperatures, and even different configurations. Calibration techniques include: uniformity in area, depth and time, absolute and transfer irradiance standards, dynamic and functional check out procedures. Typical data are given for individual cell (2x2 cm) to complete flat solar array (5x5 feet) with 2660 cells and on cylindrical test items with up to 10,000 cells. The time and energy saving of such testing techniques are emphasized.

Hershey, T. L.↗
NASA NTRS1980

Thermal expansion of composites using Moire interferometry

An experimental technique for precise measurement of the thermal response of fiber-reinforced composite materials uses moire interferometry with fringe multiplication which yield a sensitivity of 833 nm (32.8 mu in.) per fringe. Results from the technique are compared with those obtained from electrical resistance strain gages, and also those predicted from classical lamination theory. Temperature dependent coefficients of thermal expansion for composite materials subjected to thermal cycling in the temperature range of 297 K (75 F) to 422 K (300 F) were determined for four laminate configurations (0, 90, 0/ + or - 45/90 sub s and 0/90/ + or - 45 sub s) of T300/5208 graphite epoxy, and ranged from -0.107 mu epsilon K/1 (-0.059 mu epsilon deg F/-) for the 0 laminate to 32.18 mu epsilon K/1 (17.88 mu epsilon F/1) for the 90 laminate. Moisture was found to greatly influence the thermal response of a quasi-isotropic laminate, resulting in hysteresis and residual compressive strain as the moisture content was reduced. Comparisons between moire and strain gage measurements were inconclusive with both techniques giving consistent but systematically different results. Differences of as much as 29% were observed.

Bowles, D. E.↗
NASA NTRS1980

Creep and stress rupture of oxide dispersion strengthened mechanically alloyed Inconel alloy MA 754

The creep and stress rupture behavior of the mechanically alloyed oxide dispersion strengthened nickel-base alloy MA 754 was studied at 760, 982 and 1093 C. Tensile specimens with a fine, highly elongated grain structure, oriented parallel and perpendicular to the longitudinal grain direction were tested at various stresses in air under constant load. It was found that the apparent stress dependence was large, with power law exponents ranging from 19 to 33 over the temperature range studied. The creep activation energy, after correction for the temperature dependence of the elastic modulus, was close to but slightly larger than the activation energy for self diffusion. Rupture was intergranular and the rupture ductility as measured by percentage elongation was generally low, with values ranging from 0.5 to 16 pct. The creep properties are rationalized by describing the creep rates in terms of an effective stress which is the applied stress minus a resisting stress consistent with the alloy microstructure. Values of the resisting stress obtained through a curve fitting procedure are found to be close to the values of the particle by-pass stress for this oxide dispersion strengthened alloy, as calculated from the measured oxide particle distribution.

Howson, T. E.↗
NASA NTRS1981

Thermomechanical response of Gr/Pi composites

The effects of temperature changes upon the stresses and strains in composite laminates having carbon fibers in a polyimide matrix were evaluated. Composites having laminae in which there were nonlinear stress-strain relations for stresses transverse to the fibers and for axial shear stresses were treated. Material properties were considered to be temperature dependent. Separately, the effects of laminae viscoelastic response were also treated. The results suggest that, for this material, nonlinearities due either to stress or time dependent effects do not appear to be of major practical importance for conventional high temperature composite structures.

Rosen, B. W.↗
NASA NTRS1986

Effects of macroscopic inhomogeneities on electron mobility in semi-insulating GaAs

It is shown that defect inhomogeneities of sizes larger than the electron mean free path are responsible for the low values and anomalous temperature dependence of the electron mobility in semi-insulating (SI) GaAs. The room-temperature electron mobility values below about 6000 sq cm/V s cannot be uniquely used for the determination of the concentration of ionized defects, since the contribution from inhomogeneities usually exceeds that from scattering by ionized impurities. The effects of the macroscopically inhomogeneous distribution of residual acceptors and the major deep donor EL2 diminish at elevated temperatures between 600 and 900 K, which offers a means for identification of inhomogeneities, and furthermore explains recently reported steplike mobility versus temperature behavior in SI-GaAs.

Walukiewicz, W.↗
NASA NTRS1989

Conjugate (solid/fluid) computational fluid dynamics analysis of the space shuttle solid rocket motor nozzle/case and case field joints

Three-dimensional, conjugate (solid/fluid) heat transfer analyses of new designs of the Solid Rocket Motor (SRM) nozzle/case and case field joints are described. The main focus was to predict the consequences of multiple rips (or debonds) in the ambient cure adhesive packed between the nozzle/case joint surfaces and the bond line between the mating field joint surfaces. The models calculate the transient temperature responses of the various materials neighboring postulated flow/leakpaths into, past, and out from the nozzle/case primary O-ring cavity and case field capture O-ring cavity. These results were used to assess if the design was failsafe (i.e., no potential O-ring erosion) and reusable (i.e., no excessive steel temperatures). The models are adaptions and extensions of the general purpose PHOENICS fluid dynamics code. A non-orthogonal coordinate system was employed and 11,592 control cells for the nozzle/case and 20,088 for the case field joints are used with non-uniform distribution. Physical properties of both fluid and solids are temperature dependent. A number of parametric studies were run for both joints with results showing temperature limits for reuse for the steel case on the nozzle joint being exceeded while the steel case temperatures for the field joint were not. O-ring temperatures for the nozzle joint predicted erosion while for the field joint they did not.

Doran, D.↗
NASA NTRS1994

Tectonic plates, D (double prime) thermal structure, and the nature of mantle plumes

It is proposed that subducting tectonic plates can affect the nature of thermal mantle plumes by determining the temperature drop across a plume source layer. The temperature drop affects source layer stability and the morphology of plumes emitted from it. Numerical models are presented to demonstrate how introduction of platelike behavior in a convecting temperature dependent medium, driven by a combination of internal and basal heating, can increase the temperature drop across the lower boundary layer. The temperature drop increases dramatically following introduction of platelike behavior due to formation of a cold temperature inversion above the lower boundary layer. This thermal inversion, induced by deposition of upper boundary layer material to the system base, decays in time, but the temperature drop across the lower boundary layer always remains considerably higher than in models lacking platelike behavior. On the basis of model-inferred boundary layer temperature drops and previous studies of plume dynamics, we argue that generally accepted notions as to the nature of mantle plumes on Earth may hinge on the presence of plates. The implication for Mars and Venus, planets apparently lacking plate tectonics, is that mantle plumes of these planets may differ morphologically from those of Earth. A corollary model-based argument is that as a result of slab-induced thermal inversions above the core mantle boundary the lower most mantle may be subadiabatic, on average (in space and time), if major plate reorganization timescales are less than those acquired to diffuse newly deposited slab material.

Lenardic, A.↗
NASA NTRS1998

Mechanistic Models of Friction Stir Welding

Friction stir welding is a welding process developed at The Welding Institute (TWI) in England. The method uses very large strain plastic deformation of the material to join two pieces of metal together. The material is deformed using a tool which is forced between the two pieces which rotates causing a bond. Beyond this, very little is actually known although many people working in the field are willing to speculate on the detailed mechanisms involved. Some measurements made using sacrificial thermocouples at the weld joint indicate that the maximum temperature during the weld process is on the order of 370C - well below the melting temperature of the material. However, at this temperature, the material properties are highly temperature dependent, and the yield stress is approximately an order of magnitude less at this temperature than it is at room temperature. As expected, there are many interpretations of the physical mechanisms occurring during the weld process. Although there is very little published concerned with FSW, some of the anecdotal theories will be described. One describes the primary mechanism as frictional heating at the front of the tool caused by slip between the tool and the material. At elevated temperatures, the weld material becomes soft and deforms around the tool but not essentially altered by the tool rotation, similar to an extrusion. As the material meets again at the rear of the tool, the temperatures and pressures are sufficient to cause the material to bond. All other structures seen are secondary and unimportant. Another theory examined last summer at NASA's Marshall Space Flight Center (MSFC) was that there was no slip between the tool and the material resulting in a rotating mass of plastic weld material traveling at a variety of angular velocities - the greatest at the tool surface diminishing to zero at the outer edge of the plastic mass surrounding the tool. This conceptual model was followed by simplified calculations which showed that the balance of moments through the weld plug was not possible under steady state conditions and realistic temperature profiles. This led to some consideration of a quasi-steady oscillating process. Later when force measurements became available some models were modified and new ones were proposed.

Stewart, Michael B.↗
NASA NTRS1997

Accurate Heats of Formation for SiF(n) and SiF(n+), for N=1-4

Accurate heats of formation are computed for SiFn and SiFn+, for n=1-4. The vibrational frequencies are determined at the B3LYP level of theory. The energetics are determined at the CCSD(T) level of theory. Basis set limit values are obtained by extrapolation. In those cases where the CCSD(T) calculations become prohibitively large, the basis set extrapolation is performed at the MP2 level. The temperature dependence of the heat of formation, heat capacity, and entropy are computed for the temperature range 300 to 4000 K and fit to a polynomial. The CCSD(T) bond energies are compared with those obtained at the B3LYP, MP2, G2, and G2MP2 levels of theory.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1998

Accurate Heats of Formation for SFn, SFn+, and SFn- for n=1-6

Accurate heats of formation are computed for SFn, SFn+, and SFn-, for n=1-6. The geometries and vibrational frequencies are determined at the B3LY-P level of theory. The energetics are determined at the CCSD(T) level of theory. Extrapolation to the basis set limit is discussed. The temperature dependence of the heat of formation, heat capacity, and entropy are computed for the temperature range 300 to 4000 approx. K and fit to a polynomial.

Bauschlicher, Charles W., Jr.↗
NASA NTRS1997

Accurate Heats of Formation for PHn, PHn+, and PHn-

Accurate heats of formation are computed for PHn and PHn+, for n=1-3, and for PHn-, for n= 1-2. The geometries and vibrational frequencies are determined at the B3LYP level of theory. The energetics are determined at the CCSD(T) level of theory. Basis set limit values are obtained by extrapolation. Spin-orbit effects are taken from experiment. The temperature dependence of the heat of formation, heat capacity, and entropy are computed for the temperature range 300 to 4000 K and fit to a polynomial.

Ricca, Alessandra↗
NASA NTRS1998

Heats of Formation for CF(sub n) (n = 1 - 4), CF(sup +, sub n) (n = 1 - 4), and CF(sup -, sub n) (n = 1 - 3)

Accurate heats of formation are computed for CF(sub n) (n = 1 - 4), CF(sup +, sub n) (n = 1 - 4), and CF(sup -, sub n) (n = 1 - 3). The geometries and vibrational frequencies are determined at the B3LYP level of theory. The energetics are determined at the CCSD(T) level of theory. Basis set limit values are obtained by extrapolation. In those cases where the CCSD(T) calculations become prohibitively large, the basis set extrapolation is performed at the MP2 level. The temperature dependence of the heat of formation, heat capacity, and entropy are computed for the temperature range 300 to 4000 K and fit to a polynomial.

Ricca, Alessandra↗
NASA NTRS1998

Heats of NF(sub n) (n= 1-3) and NF(sub n)(+)(n = 1-3)

Accurate heats of formation are computed for NF(sub n) and NF(sub n)(+), for n = 1-3. The geometries and the vibrational frequencies are determined at the B3LYP level of theory. The energetics are determined at the CCSD(T) level of theory. Basis set limit values are obtained by extrapolation. In those cases where the CCSD(T) calculations become prohibitively large, the basis set extrapolation is performed at the MP2 level. The temperature dependence of the heat of formation, heat capacity, and entropy are computed for the temperature range 300 to 4000 K and fit to a polynomial.

Ricca, Alessandra↗
NASA NTRS2013

Cryogenic Refractive Index and Coefficient of Thermal Expansion for the S-TIH1 Glass

Using the CHARMS facility at NASA GSFC, we have measured the cryogenic refractive index of the Ohara S-TIH1 glass from 0.40 to 2.53 micrometers and from 120 to 300 K. We have also examined the spectral dispersion and thermo-optic coefficients (dn/dT). We also derived temperature-dependent Sellmeier models from which refractive index may be calculated for any wavelength and temperature within the stated ranges of each model. The S-TIH1 glass we tested exhibited unusual behavior in the thermo-optic coefficient. We found that for delta < 0.5 micrometers, the index of refraction decrease with a decrease in temperature (positive dn/dT). However, the situation was reversed for delta larger than 0.63 micrometers, where the index will increase with a decrease in temperature (negative dn/dT). We also measured the coefficient of thermal expansion (CTE) for the similar batch of S-TIH1 glass in order to understand its thermal properties. The CTE showed a monotonic change with a decrease in temperature.

Quijada, Manuel A.↗
NASA NTRS2019

Measuring the D/H Ratios of Exoplanets and Brown Dwarfs

The relative abundance of deuterium and hydrogen is a potent tracer of planet formation and evolution. Jupiter and Saturn have protosolar atmospheric D/H ratios, a relic of substantial gas accretion from the nebula, while the atmospheres of Neptune and Uranus are enhanced in D by accretion of ices into their envelopes. For terrestrial planets, D/H ratios are used to determine the mechanisms of volatile delivery and subsequent atmosphere loss over the lifetime of the planet. Planets and brown dwarfs more massive than ~13 M(J) quickly fuse their initial D reservoir. Here, we simulate spectra for giant exoplanets and brown dwarfs (2 M(Neptune) to ~10 M(Jupiter)) from T(eff) = 200–1800 K including both CH3D and HDO to determine the observability of these dominant deuterium isotopologues in mid-infrared thermal emission spectra. Colder objects have stronger molecular features in their spectra, due to the temperature dependence of molecular cross sections. CH3D is easier to observe than HDO at all temperatures considered, due to the strength of its absorption bands and locations of features at wavelengths with few other strong absorption features. We predict that for nearby cool brown dwarfs, the CH3D abundance can be measured at high signal to noise with the James Webb Space Telescope (JWST); for objects from 200 to 800 K closer than 10 pc, a protosolar D/H ratio would be readily observable in 2.5 hr. Moderately young Jupiter-mass planets (100–300 Myr) and young Neptunes (10 Myr) may be discovered with JWST and provide the best targets for detecting deuterium on an exoplanet in the coming decade. Future telescope designs should consider the importance of isotopes for understanding the formation and evolution of planetary atmospheres.

Caroline V. Morley↗
NASA NTRS1972

The turbulent boundary layer on a porous plate - Experimental heat transfer with uniform blowing and suction, with moderately strong acceleration.

Experimental data are presented for heat transfer to the turbulent boundary layer subjected to transpiration and acceleration at constant values of the acceleration parameter K of approximately .00000145. This is a moderately strong acceleration, but not so strong as to result in laminarization of the boundary layer. The results for transpiration fractions F of -0.002, 0.0, and +0.0058 are presented in detail in tabular form, and in graphs of Stanton number versus enthalpy thickness Reynolds number. In addition, temperature profiles at several stations are presented. Stanton number results for F = -0.004, +0.002, and +0.004 are also presented, but in graphical form only. The data were obtained using air as both the free-stream and the transpired fluid, at relatively low velocities, and with temperature differences sufficiently low so that the influence of temperature-dependent fluid properties is minimal. All data were obtained with the surface maintained at a temperature invariant in the direction of flow.

Thielbahr, W. H.↗
NASA NTRS1978

The vibrational overtone spectrum of liquid methane in the visible and near infrared - Applications to planetary studies

The strengths of 10 bands in the absorption spectrum of liquid methane between 19,400 and 6190 A have been measured. After a small correction for the polarizability of the liquid is applied for the purpose of comparison with similar gas-phase measurements, it is found that there is no temperature dependence of the band strengths between 95 and 295 K. Changes of band shape with temperature cause the 95 K laboratory spectra to resemble Saturn more than room-temperature observations do. Gas-phase absorption clearly dominates the liquid in planetary spectra, so liquid methane cannot be detected in the outer solar system by earth-based observations.

Ramaprasad, K. R.↗