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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 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

Computation of transonic boattail flow with separation

The relaxation procedure of South and Jameson for the full potential transonic flow equation was coupled to a modified Reshotko-Tucker integral boundary-layer technique with an empirical model for separated flow. The viscous and inviscid flows were solved iteratively until convergence was obtained. This iterative method was then applied to the subsonic and transonic flow over a series of axisymmetric circular-arc boattails with solid jet plume simulators. Comparisons of theoretical and experimental surface pressures and boattail drag are presented over a free-stream Mach numbers below 0.90. The qualitative variation of boattail drag with free-stream Mach number and boattail angle well into the region of transonic drag rise was correctly predicted; however, the absolute drag levels were significantly underpredicted. For separated flows, the empirical discriminating streamline model gives good results up to a free-stream Mach number of about 0.90 and allows reasonable predictions for shock-induced separation if the proper separation location and separation turning angle are known.

Wilmoth, R. G.↗
NASA NTRS1988

Equation of state of ammonia-water liquid - Derivation and planetological applications

The present least-squares fit calculation of the equation of state for ammonia-water liquid has yielded results for the zero-100 wt pct NH3, 170-300 K temperature, and zero-10 kb pressure parameter ranges. In conjunction with solid density and thermodynamic measurements, the present calculated and measured liquid densities are used to yield estimates of density and thermal expansion at 1 bar for the solid phases of ammonia's monohydrate, dihydrate, and hemihydrate between absolute zero and their respective melting points. Attention is given to the implications for icy satellite morphologic and tectonic forms of peritectic ammonia-water liquid that is neutrally buoyant relative to the corresponding solid phases.

Croft, S. K.↗
NASA NTRS1979

Noise from struts and splitters in turbofan exit ducts

An analytical method for calculating noise radiation from isolated airfoils in turbulent flow was combined with a method for calculating transmission of sound through a subsonic exit duct and with an empirical far field directivity shape. This combination provides a method for predicting engine internally generated noise from radial struts and stators and annular splitter rings. Calculated sound power spectra, directivity, and acoustic pressure spectra are compared with data. These data were for noise caused by a fan exit duct splitter ring, large-chord stator blades, and turbine exit struts. However, the lack of turbulence intensity and scale length measurements for these flow ducts prevented an absolute validation of the prediction method.

Fink, M. R.↗
NASA NTRS1980

Temperature dependence of the reaction O/3P/ + OH/2 Pi/ yields O2 + H

Measurements of the absolute rate and temperature dependence of the rate constant for the reaction of ground state atomic oxygen with hydroxyl radicals to yield molecular oxygen and hydrogen atoms over the temperature range 211-499 K are presented. The reaction was monitored in a low-pressure discharge flow resonance fluorescence apparatus under pseudo-first-order conditions in which the oxygen concentration was greater than the hydroxyl concentration. An expression for the temperature dependence of the rate constant is derived from a least-squares fit to the observed bimolecular rate constants, which were found to range from 3.21 to 2.77 x 10 to the -11th cu cm/molecule per sec for temperatures from 211 to 499 K, indicative of a slight negative temperature dependence. Results are compared with those of previous workers, and the significance of the lower value of the rate constant obtained in the present study to models of HO(x) in the upper stratosphere is indicated.

Lewis, R. S.↗
NASA NTRS1986

The reaction H + C4H2 - Absolute rate constant measurement and implication for atmospheric modeling of Titan

The absolute rate constant for the reaction H + C4H2 has been measured over the temperature (T) interval 210-423 K, using the technique of flash photolysis-resonance fluorescence. At each of the five temperatures employed, the results were independent of variations in C4H2 concentration, total pressure of Ar or N2, and flash intensity (i.e., the initial H concentration). The rate constant, k, was found to be equal to 1.39 x 10 to the -10th exp (-1184/T) cu cm/s, with an error of one standard deviation. The Arrhenius parameters at the high pressure limit determined here for the H + C4H2 reaction are consistent with those for the corresponding reactions of H with C2H2 and C3H4. Implications of the kinetic carbon chemistry results, particularly those at low temperature, are considered for models of the atmospheric carbon chemistry of Titan. The rate of this reaction, relative to that of the analogous, but slower, reaction of H + C2H2, appears to make H + C4H2 a very feasible reaction pathway for effective conversion of H atoms to molecular hydrogen in the stratosphere of Titan.

Nava, D. F.↗
NASA NTRS1986

Drag reducing outer-layer devices in rough wall turbulent boundary layers

The ability of outer-layer devices to reduce wall shear stress over a substantial streamwise distance in rough-wall turbulent boundary layers has been studied experimentally. The devices examined are a pair of thin flat ribbons placed in tandem as well as those having symmetric airfoil sections. The wall conditions examined are smooth, d- and k-type transverse-groove and sandgrain roughnesses. The wall drag is found to be reduced from the respective normal levels in all rough walls. All k-type rough walls exhibit a similar level of relative wall drag reduction which is also smaller than that in a smooth-wall. The d-type rough walls exhibit a transitional behaviour - the relative wall drag reduction drops from the smooth wall level to that of the k-type roughness with increasing roughness Reynolds number. However, the absolute reductions in the local wall shear stress are similar in both the rough and smooth walls. On the other hand, the relative reductions are lower in the rough walls because of a higher reference drag which is caused by the unique presence of a pressure component on which the devices are not as effective.

Bandyopadhyay, P. R.↗
DOE OSTI2022

DMC-ICE13 : Ambient and high pressure polymorphs of ice from diffusion Monte Carlo and density functional theory

Ice is one of the most important and interesting molecular crystals, exhibiting a rich and evolving phase diagram. Recent discoveries mean that there are now 20 distinct polymorphs; a structural diversity that arises from a delicate interplay of hydrogen bonding and van der Waals dispersion forces. This wealth of structures provides a stern test of electronic structure theories, with Density Functional Theory (DFT) often not able to accurately characterize the relative energies of the various ice polymorphs. Thanks to recent advances that enable the accurate and efficient treatment of molecular crystals with Diffusion Monte Carlo (DMC), we present here the DMC-ICE13 dataset; a dataset of lattice energies of 13 ice polymorphs. This dataset encompasses the full structural complexity found in the ambient and high-pressure molecular ice polymorphs, and when experimental reference energies are available, our DMC results deliver sub-chemical accuracy. Using this dataset, we then perform an extensive benchmark of a broad range of DFT functionals. Of the functionals considered, revPBE-D3 and RSCAN reproduce reference absolute lattice energies with the smallest error, while optB86b-vdW and SCAN+rVV10 have the best performance on the relative lattice energies. Our results suggest that a single functional achieving reliable performance for all phases is still missing, and that care is needed in the selection of the most appropriate functional for the desired application. The insights obtained here may also be relevant to liquid water and other hydrogen-bonded and dispersion-bonded molecular crystals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Comparative Study for Pressure Gain Combustion-Gas Turbine System Performance in NGCC Configurations

The Department of Energy (DOE) has a goal to increase natural gas combined cycle (NGCC) plant efficiency to greater than 70 percent on a lower heating value (LHV) basis. Improvement in gas turbine (GT) efficiency is key achieving this goal. While many of the traditional improvement methods (higher firing temperature, advanced materials, improved cooling methods, etc.) may increase current GT and NGCC efficiencies incrementally, combining these traditional advancements with breakthrough technologies such as pressure gain combustion (PGC) may provide significant system efficiency gains. PGC is a combustion process that results in a net pressure increase across the combustor (up to pressure ratio of 2.2) rather than the traditional (<5%) pressure drop. There are multiple PGC technologies being developed that create the pressure rise phenomena, including resonant pulse combustors (RPCs), pulse detonation engines (PDEs), wave rotor combustor (WRC) engines and rotating detonation engines (RDEs). In this study, scoping analyses of PGC concepts applied to NGCC power plants were performed by combining simplified analytical models for the RPC, PDE, WRC, and RDE types of pressure gain processes with a GT model to evaluate impacts of using each of the PGC technologies on key GT performance parameters. Sensitivity analyses were also performed. Ultimately, the PGC technologies were found to have the potential to increase simple cycle efficiency by 4–6 percent (absolute) and NGCC efficiency by 2–3 percent (absolute) based on the results of the current study.

03 NATURAL GAS↗
NASA NTRS1983

Absolute intensity measurements of the (11/1/0)II-00/0/0 band of (C-12)(O-16)2 at 5.2 microns

A nonlinear least-squares fitting procedure has been used to derive absolute intensities for lines in the P, R, and Q branches of the (11/1/0)II-00/0/0 band of (C-12)(O-16)2 (band center = 1932/cm) from long-path 0.01/cm resolution laboratory spectra. The spectral data were recorded at room temperature and low pressure (less than 10 torr) with the Fourier transform spectrometer in the McMath solar telescope complex at Kitt Peak National Observatory. The observed line intensities were analyzed to derive the vibrational band intensity and F-factor coefficients. To obtain a good fit to the data, it was necessary to include terms in the expression for the F factor, which account for Coriolis-type and Fermi-type interactions and centrifugal distortion effects.

Rinsland, C. P.↗
NASA NTRS1993

Intensities and broadening coefficients for the Q branch of the 4nu-2 - nu-1 + nu-2 (471.511/cm) band of CO2

Absolute intensities for the Q-branch of the 4nu-2 - nu-1 + nu-1/2 (20,003-11,101) band in CO2 were measured for the first time. Measurements were performed for lines Q10 to Q28, at temperatures ranging from 385 to 426 K, for pressures from 3 to 40 torr, using our long wavelength tunable diode laser spectrometer. The combination of tunable diode lasers, a White cell, and a blocked impurity band detector made it possible to obtain signal to noise ratios greater than 1000 in the 471/cm spectral region, with about 3 x 10 exp -4/cm spectral resolution. The band strength was found to be 8.6(2) x 10 exp -25 cm/molec at 296 K, and the Hermann-Wallis factor was determined. Comparison with the values listed in the HITRAN 92 data base are presented. Self-, N2- and O2-broadening coefficients were also measured.

Sirota, J. M.↗
NASA NTRS2004

Lightweight Stacks of Direct Methanol Fuel Cells

An improved design concept for direct methanol fuel cells makes it possible to construct fuel-cell stacks that can weigh as little as one-third as much as do conventional bipolar fuel-cell stacks of equal power. The structural-support components of the improved cells and stacks can be made of relatively inexpensive plastics. Moreover, in comparison with conventional bipolar fuel-cell stacks, the improved fuel-cell stacks can be assembled, disassembled, and diagnosed for malfunctions more easily. These improvements are expected to bring portable direct methanol fuel cells and stacks closer to commercialization. In a conventional bipolar fuel-cell stack, the cells are interspersed with bipolar plates (also called biplates), which are structural components that serve to interconnect the cells and distribute the reactants (methanol and air). The cells and biplates are sandwiched between metal end plates. Usually, the stack is held together under pressure by tie rods that clamp the end plates. The bipolar stack configuration offers the advantage of very low internal electrical resistance. However, when the power output of a stack is only a few watts, the very low internal resistance of a bipolar stack is not absolutely necessary for keeping the internal power loss acceptably low.

Narayanan, Sekharipuram↗
DOE OSTI2024

Evaluation and development of flow condensation correlations using the data from low GWP refrigerants in an axial micro-fin aluminum tube

To mitigate global warming, the world is transitioning to refrigerants with low global warming potential (GWP). Supporting this shift requires a model that can accurately predict the heat transfer and pressure drop of new refrigerants, crucial for designing efficient heat exchangers. Existing models, however, are largely based on currently deployed refrigerants and primarily developed for unexpanded micro-fin tubes with spiral angles of 6° to 30°. Their applicability to new refrigerants, especially in expanded micro-fin tubes, is uncertain. This study assesses the performance of four well-known condensation models for six emerging refrigerants—R-32, R-454B, R-454C, R-455A, R-1234yf, and R-1234ze(E)—against experimental data. Initially, the Han and Lee (2005) model shows the best prediction accuracy with a mean absolute deviation (MAD) of 22.1 %. To enhance the accuracy of heat transfer models for new refrigerants and geometries with large temperature glides, two approaches are proposed. Here, the first approach applies a simple correction factor, reducing the MAD of the Cavallini et al. (2009) model from 68.2 % to 15.4 %. The second approach uses the variable metric method for minimization, fitting new constants to the data. This optimization results in the Kedzierski and Goncalves (1997) model achieving the highest accuracy, with a MAD of 13.1 %. For pressure drop models, the Cavallini et al. (1997) model is the most accurate with a MAD of 6.4 %, followed by the Haraguchi et al. (1993) model with a MAD of 9.4 %. Due to its simplicity, the Haraguchi et al. (1993) model is a practical option for predicting frictional pressure drop.

Axial micro-fin tubes↗
NASA NTRS1972

Radiative cooling of shock-heated air in an explosively driven shock tube.

Results are presented of an experimental program to measure the effect of radiative cooling on the enthalpy distribution behind incident shock waves traveling in air. The shock velocity was nominally 16 km/sec and the preshock ambient pressure was varied from 0.4 to 1.6 torr. Shock-tube diameters of 4.7 and 9.4 cm were used to investigate the effects of varying optical depths. Radiative cooling rates were determined from spatially resolved measurements of the profile of the H sub alpha line and from absolute measurements of the continuum radiation. The measured enthalpy profiles are in good agreement with the theoretical predictions of Chien and Compton which account for both nongrey and multidimensional aspects of the radiative transport in the shock tube.

Cooper, D. M.↗
NASA NTRS1973

Application of a radiometric method to the measurement of temperature in self-absorbing gases

A radiometric method for the measurement of gas temperature in self-absorbing gases has been applied in the study of shock-tube-generated flows. This method involves making two absolute-intensity measurements at the same wavelength in a specified gas sample, but using two different path lengths. Experimental results are presented for reflected shock waves in air and in xenon at conditions corresponding to shock velocities from 4 to 10 km/sec and an initial driven tube pressure of 1 torr. These results indicate that, with the technique, temperature measurements with an accuracy of 5% can be carried out. The measurements in air suggest certain facility-related problems, and results obtained in the application of this measurement technique to the investigation of these problems and to the study of radiative cooling phenomena in both air and xenon are presented.

Nerem, R. M.↗
NASA NTRS2011

Multi-Segment Radius Measurement Using an Absolute Distance Meter Through a Null Assembly

This system was one of the test methods considered for measuring the radius of curvature of one or more of the 18 segmented mirrors that form the 6.5 m diameter primary mirror (PM) of the James Webb Space Telescope (JWST). The assembled telescope will be tested at cryogenic temperatures in a 17-m diameter by 27-m high vacuum chamber at the Johnson Space Center. This system uses a Leica Absolute Distance Meter (ADM), at a wavelength of 780 nm, combined with beam-steering and beam-shaping optics to make a differential distance measurement between a ring mirror on the reflective null assembly and individual PM segments. The ADM is located inside the same Pressure-Tight Enclosure (PTE) that houses the test interferometer. The PTE maintains the ADM and interferometer at ambient temperature and pressure so that they are not directly exposed to the telescope s harsh cryogenic and vacuum environment. This system takes advantage of the existing achromatic objective and reflective null assembly used by the test interferometer to direct four ADM beamlets to four PM segments through an optical path that is coincident with the interferometer beam. A mask, positioned on a linear slide, contains an array of 1.25 mm diameter circular subapertures that map to each of the 18 PM segments as well as six positions around the ring mirror. A down-collimated 4 mm ADM beam simultaneously covers 4 adjacent PM segment beamlets and one ring mirror beamlet. The radius, or spacing, of all 18 segments can be measured with the addition of two orthogonally-oriented scanning pentaprisms used to steer the ADM beam to any one of six different sub-aperture configurations at the plane of the ring mirror. The interferometer beam, at a wavelength of 687 nm, and the ADM beamlets, at a wavelength of 780 nm, pass through the objective and null so that the rays are normally incident on the parabolic PM surface. After reflecting off the PM, both the ADM and interferometer beams return to their respective instruments on nearly the same path. A fifth beamlet, acting as a differential reference, reflects off a ring mirror attached to the objective and null and returns to the ADM. The spacings between the ring mirror, objective, and null are known through manufacturing tolerances as well as through an in situ null wavefront alignment of the interferometer test beam with a reflective hologram located near the caustic of the null. Since total path length between the ring mirror and PM segments is highly deterministic, any ADM-measured departures from the predicted path length can be attributed to either spacing error or radius error in the PM. It is estimated that the path length measurement between the ring mirror and a PM segment is accurate to better than 100 m. The unique features of this invention include the differential distance measuring capability and its integration into an existing cryogenic and vacuum compatible interferometric optical test.

Merle, Cormic↗
NASA NTRS1979

A Copernicus survey of Mg II emission in late-type stars

The behavior of Mg II emission in late-type stars is examined using scan data obtained with the Copernicus satellite. The luminosity in the Mg II k emission line was found to be closely related to stellar absolute magnitude, leading to the suggestion that such correlation may be very useful for future UV observations. The stellar surface flux in the k line was observed to be roughly constant or to decrease slowly with later spectral type, a finding which is then used to show that the pressure at the top of the chromosphere decreases with later spectral type, in agreement with the conclusions by McClintock et al. (1975). An asymmetry in the Mg II k line was noticed to be present in the available data for the stars later than K2-K5.

Weiler, E. J.↗
NASA NTRS1982

Rate constant for the reaction NH2 + NO from 216 to 480 K

The absolute rate constant was measured by the technique of flash photolysis-laser induced fluorescence (FP-LIF). NH2 radicals were produced by the flash photolysis of ammonia and the fluorescent NH2 photons were measured by multiscaling techniques. At each temperature, the results were independent of variations in total pressure, and flash intensity. The results are compared with previous determinations using the techniques of mass spectrometry, absorption spectroscopy, laser absorption spectroscopy, and laser induced fluorescence. The implications of the results are discussed with regard to combustion, post combustion, and atmospheric chemistry. The results are also discussed theoretically.

Stief, L. J.↗
NASA NTRS1997

NLTE analysis of SUMER filament observations on SOHO

The observations of hydrogen Lyman delta, epsilon, six and seven lines are described. These data were acquired by the solar ultraviolet measurement of emitted radiation (SUMER) spectrograph onboard the Solar and Heliospheric Observatory (SOHO). All the spectral lines were calibrated to absolute intensities. The multilevel NLTE code was used to evaluate the theoretical line profiles of the four Lyman lines studied. The line cores of all these lines are good indicators of the temperature structure of the filament. The study showed that the line wings are sensitive to the gas pressure. A steep temperature increase in the prominence-corona transition region seems to be consistent with the observed intensities in the line cores of the Lyman lines.

Heinzel, P.↗