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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Experiments at high temperature and pressure - Laser heating through the diamond cell

CW laser heating through a diamond anvil cell by means of a focused Nd:YAG laser has resulted in the achievement of temperatures in the 1500-5000 K range for pressures of 10-100 GPa. Temperatures are determined radiometrically, with an accuracy of about 200 K, and temperature variation across the laser-heated spot is derived by means of spatial filtering with a slit that can be scanned. Melting temperatures are thus determined either on the basis of observed temperature at the liquid-solid interface or on that of the peak temperature at which glass is first produced with increasing laser power.

Jeanloz, R.↗
NASA NTRS1985

Mechanical properties of Inconel 718 and Nickel 201 alloys after thermal histories simulating brazing and high temperature service

An experimental investigation was made to evaluate two nickel base alloys (Nickel-201 and Inconel-718) in three heat treated conditions. These conditions were: (1) annealed; (2) after thermal exposure simulating a braze cycle; and (3) after a thermal exposure simulating a braze cycle plus one operational lifetime of high temperature service. For the Nickel-201, two different braze cycle temperatures were evaluated. A braze cycle utilizing a lower braze temperature resulted in less grain growth for Nickel-201 than the standard braze cycle used for joining Nickel-201 to Inconel-718. It was determined, however, that Nickel-201, was marginal for temperatures investigated due to large grain growth. After the thermal exposures described above, the mechanical properties of Nickel-201 were degraded, whereas similar exposure on Inconel-718 actually strengthened the material compared with the annealed condition. The investigation included tensile tests at both room temperature and elevated temperatures, stress-rupture tests, and metallographic examination.

James, W. F.↗
NASA NTRS1985

Auroral thermosphere temperatures from observations of 6300 A emissions

Doppler temperatures determined from observations of the atomic oxygen OI 6300 A line during March 1984 at the University of Alaska/Fairbanks are presented. Temperatures are obtained from Fabry-Perot Interferometer pressure scans using a Fourier transform smoothing and fitting technique; this technique is presented in detail. The temperatures and the spread in the temperatures are consistent from day to day. On the clear nights of March 10 to 13, the temperatures were 800, 750, 750 and 800 K, respectively, with a spread of + or - 100 K. These temperatures are compared to the MSIS (84) model atmosphere for similar geomagnetic conditions and found to be in general agreement; they are also consistent with results obtained by other investigators.

Bird, J. C.↗
NASA NTRS1986

Dynamic measurement of total temperature, pressure and velocity in the Langley 0.3-meter transonic cryogenic tunnel

There is theoretical and experimental evidence which indicates that a sudden or step change in the rate at which the liquid nitrogen is injected into the circuit of a cryogenic wind tunnel can cause a temperature front in the flow for several tunnel circuit times. A temperature front, which occurs at intervals equal to the circuit time, is a sudden increase or decrease in the temperature of the flow followed by a nearly constant temperature. Since these fronts can have an effect on the control of the tunnel as well as the time required to establish steady flow conditions in the test section of cryogenic wind tunnel, tests were conducted in the settling chamber in the Langley 0.3-meter Transonic Cryogenic Tunnel (0.3-m TCT) in which high response instrumentation was used to measure the possible existence of these temperature fronts. Three different techniques were used to suddenly change the rate of liquid nitrogen being injected into the tunnel and the results from these three types of tests showed that temperature fronts do not appear to be present in the 0.3-m TCT. Also included are the velocity and pressure fluctuations measured in the settling chamber downstream of the screens and the associated power spectra.

Johnson, C. B.↗
NASA NTRS1985

Profiles of temperature and density based on extremes at 5, 10, 20, 30 and 40 km

Information on the vertical distribution of expected extremes of temperature and density are required for the design and operation of systems traversing the atmosphere. Such data are particularly important at altitudes from the surface to approximately 80 km for developing all types of airborne vehicles ranging from helicopters and airplanes to sophisticated aerospace systems. Vertical profiles of temperature and density have been developed based on 1- and 10-percent hot and cold temperatures and 1- and 10- percent high and low densities occurring during the most severe month at the worst locations for which reliable upper-air data are available. The model profiles, from the surface to 80 km, are based on extremes that occur at 5, 10, 20, 30, and 40 km. There are 20 profiles for extreme temperatures (5 levels by 4 percentiles) that include associated densities, and 20 analogous profiles for extreme densities including associated temperatures. Consequently, a set of realistic profiles (rather than envelopes) of temperature and density, associated with extremes at each of 5 specified levels in the troposphere and stratosphere, are now available for altitudes up to 80 km.

Kantor, A. J.↗
NASA NTRS1986

Temperature sensitive oscillator

An oscillator circuit for sensing and indicating temperature by changing oscillator frequency with temperature comprises a programmable operational amplifier which is operated on the roll-off portion of its gain versus frequency curve and has its output directly connected to the inverting input to place the amplifier in a follower configuration. Its output is also connected to the non-inverting input by a capacitor with a crystal or other tuned circuit also being connected to the non-inverting input. A resistor is connected to the program input of the amplifier to produce a given set current at a given temperature, the set current varying with temperature. As the set current changes, the gain-bandwidth of the amplifier changes and, in turn, the reflected capacitance across the crystal changes, thereby providing the desired change in oscillator frequency by pulling the crystal. There is no requirement that a crystal employed with this circuit display either a linear frequency change with temperature or a substantial frequency change with temperature.

Kleinberg, L. L.↗
NASA NTRS1986

Temperature and velocity profiles in sooting free boundary layer flames

Temperature and velocity profiles are presented for cyclohexane, n-heptane, and iso-octane free, laminar, boundary layer, sooting, diffusion flames. Temperatures are measured with 3 mil Pt/Pt-13 percent Rh thermocouples. Corrected gas temperatures are derived by performing an energy balance of convection to and radiation from the thermocouple bead incorporating the variation of air conductivity and platinum emissivity with temperature. Velocities are measured using laser doppler velocimetry techniques. Profiles are compared with previously reported analytic temperature and velocity fields. Comparison of theoretical and experimental temperature profiles suggests improvement in the analytical treatment is needed, which accounts more accurately for the local soot radiation. The velocity profiles are in good agreement, with the departure of the theory from observation partially due to the small fluctuations inherent in these free flows.

Ang, J. A.↗
NASA NTRS1986

Assessment of two-temperature kinetic model for dissociating and weakly-ionizing nitrogen

The validity of the author's two-temperature, chemical/kinetic model which the author has recently improved is assessed by comparing the calculated results with the existing experimental data for nitrogen in the dissociating and weakly ionizing regime produced behind a normal shock wave. The computer program Shock Tube Radiation Program (STRAP) based on the two-temperature model is used in calculating the flow properties behind the shock wave and the Nonequilibrium Air Radiation (NEQAIR) program, in determining the radiative characteristics of the flow. Both programs were developed earlier. Comparison is made between the calculated and the existing shock tube data on (1) spectra in the equilibrium region, (2) rotational temperature of the N2(+) B state, (3) vibrational temperature of the N2(+) B state, (4) electronic excitation temperature of the N2 B state, (5) the shape of time-variation of radiation intensities, (6) the times to reach the peak in radiation intensity and equilibrium, and (7) the ratio of nonequilibrium to equilibrium radiative heat fluxes. Good agreement is seen between the experimental data and the present calculation except for the vibrational temperature. A possible reason for the discrepancy is given.

Park, C.↗
NASA NTRS1986

The structure of high-temperature flare plasma. II Comparison with observations

In Emslie, (1985) scaling law's which relate peak loop temperature to injected nonthermal electron flux in electron-heated models of the flare corona are derived. These predicted relationships are compared with recent coordinated observations in hard X-rays and soft X-rays. Satisfactory agreement is found for large events, while for smaller events the plasma electron temperature determined by soft X-ray spectral fitting is too high. A possible resolution of this apparent discrepancy through careful examination of the method used to determine the temperature of the soft X-ray emitting plasma is discussed. It is concluded that temperatures determined by spectral fitting over a series of lines are not necessarily representative of the true temperature of the plasma, since the fitting technique is plagued by the same difficulties as a more straightforward technique involving a single spectral line or portion of continuum (Craig and Brown, 1976). The differences between actual and derived temperatures are sufficiently large to remove the above discrepancy between observations and modeling of electron-heated coronae.

Emslie, A. G.↗
NASA NTRS1986

Temperature diagnostic line ratios of Fe XVII

Based on extensive calculations of the excitation rates of Fe XVII, four temperature-sensitive line ratios are investigated, paying special attention to the contribution of resonances to the excitation rates and to the contributions of dielectronic recombination satellites to the observed line intensities. The predictions are compared to FPCS observations of Puppis A and to Solar Maximum Mission (SMM) and SOLEX observations of the sun. Temperature-sensitive line ratios are also computed for emitting gas covering a broad temperature range. It is found that each ratio yields a differently weighted average for the temperature and that this accounts for some apparent discrepancies between the theoretical ratios and solar observations. The effects of this weighting on the Fe XVII temperature diagnostics and on the analogous Fe XXIV/Fe XXV satellite line temperature diagnostics are discussed.

Raymond, J. C.↗
NASA NTRS1984

Response of a small-turboshaft-engine compression system to inlet temperature distortion

An experimental investigation was conducted into the response of a small-turboshaft-engine compression system to steady-state and transient inlet temperature distortions. Transient temperature ramps range from less than 100 K/sec to above 610 K/sec and generated instantaneous temperatures to 420 K above ambient. Steady-state temperature distortion levels were limited by the engine hardware temperature list. Simple analysis of the steady-state distortion data indicated that a particle separator at the engine inlet permitted higher levels of temperature distortion before onset of compressor surge than would be expected without the separator.

Biesiadny, T. J.↗
NASA NTRS1986

On the location of the maximum homogeneous crystal nucleation temperature

Detailed considerations are given to the location of the temperature of maximum homogeneous nucleation as predicted by classical nucleation theory. It is shown quite generally that this maximum temperature, T-asterisk, must occur above the Kauzmann temperature and that the T-asterisk is such that T-asterisk is greater than T(m)/3, where T(m) is the melting temperature. Also, it is demonstrated tha T-asterisk may be considered to be approximately dependent upon two parameters: gamma, the ratio of the difference in specific heat between the crystal and liquid divided by the entropy of fusion, and E, a reduced activation energy for viscous flow. The variation of T-asterisk with these parameters is described. The relationship of the relative location of T-asterisk to the glass transition temperature, is discussed too. This discussion is couched within the framework of the strong and fragile liquid notion introduced by Angell (1981) and coworkers. Finally, the question of the ultimate limits to the undercooling of liquid metals is considered and its relationhsip to computations of the maximum nucleation temperature in such systems.

Weinberg, Michael C.↗
NASA NTRS1986

Theoretical study of the electron temperature in the high-latitude ionosphere for solar maximum and winter conditions

The T(e) variation in the high-latitude ionosphere at altitudes between 120 and 800 km has been modeled for solar maximum, winter solstice, and strong magnetic activity conditions. The calculated electron temperatures are consistent with the plasma densities and ion temperatures computed from a time-dependent ionospheric model. Heating rates for both solar EUV and auroral precipitation were included. In general, the predicted UT variation of the electron temperature that results from the displacement between the magnetic and geographic poles is only a few hundred degrees. However, in sunlit trough regions, T(e) hot spots develop, and these hot spots show a marked UT variation, by as much as 2500 K. The dominant parameter controlling the T(e) variation above 200 km is the magnetospheric heat flux into the ionosphere, which is essentially unknown. For realistic values of the magnetospheric heat flux, the maximum electron temperature ranges from 5000 to 10,000 K at 800 km. A magnetospheric heat flux is particularly effective in enhancing trough electron temperatures. In general, the electron heat flux at high altitudes is uniquely related to the electron temperature and gradient, except on auroral field lines where thermoelectric heat flow is important.

Schunk, R. W.↗
NASA NTRS1986

Derivation of photochemical information near 1 mbar from ozone and temperature data

An analysis procedure has been developed for derivation of information about the photochemical behavior of ozone near 1 mbar by explicitly accounting for the dynamical transport terms in the continuity equation for perturbations from the zonal mean. The procedure is shown to be valid using data from a numerical transport model and is then applied to LIMS ozone and temperature data, using geostrophic winds to estimate the transport terms. The data study is restricted to March at 2, 1, and 0.7 mbar. Because the temperature deviations are dynamically produced, large temperature deviations are associated with significant ozone transport terms. The anticorrelation between the deviations of ozone and temperature disappears when the transport terms are small. The derived photochemical information is compared to photochemical theory. Although there is overall agreement in the magnitude as well as the latitude, altitude, and time dependencies, discrepancies are suggested which may be related to the long-standing failure of photochemical models to calculate ozone accurately near 1 mbar. The theory suggests that the addition of Cl(x) to the stratosphere will affect the relationship of ozone and temperature at 2 and 1 mbar. Comparison of the photochemical information derived from future ozone and temperature measurements with the results of the present analysis should provide a critical test of the photochemical scheme thought to describe the behavior of odd chlorine in the stratosphere.

Douglass, Anne R.↗
NASA NTRS1986

Masking of the circadian rhythms of heart rate and core temperature by the rest-activity cycle in man

Experiments were conducted to estimate the magnitude of the masking effect produced in humans by alternate periods of physical activity and rest or sleep on the circadian rhythms of heart rate and core temperature. The heart rate, rectal temperature, and nondominant wrist activity were monitored in 12 male subjects during 6 days of normal routine at home and during 6 days of controlled bed-rest regimen. The comparisons of averaged waveforms for the activity, heart rate, and temperature indicated that about 45 percent of the range of the circadian heart rate rhythm during normal routine and about 14 percent of the range of the circadian temperature rhythm were attributable to the effects of activity. The smaller effect of activity on the temperature rhythm may be partially attributable to the fact that core temperature is being more rigorously conserved than heart rate, at least during moderate exercise.

Gander, Philippa H.↗
NASA NTRS1987

Surface temperature and albedo relationships in Senegal derived from NOAA-7 satellite data

The interaction between surface albedo and local climate in Senegal, Africa, is examined using NOAA AVHRR data collected from September 1981-October 1982. The temporal variations of albedo and surface temperature are calculated and examined. It is observed that the albedo and ground temperature are largest in the winter and spring (dry season) and smallest in the late summer and fall (wet season). From the wet to the dry seasons the albedo varied by about 3 percentage points and the ground temperature by about 13 K. A positive correlation between albedo and ground temperatures is detected; this indicates that the albedo does not control the ground temperature. Other factors that can influence ground temperatures are atmospheric turbulence, soil moisture, thermal inertia, and ground emissivity, which are all affected by the presence or absence of vegetation.

Vukovich, Fred M.↗
NASA NTRS1986

Exhaust-Gas Pressure and Temperature Survey of F404-GE-400 Turbofan Engine

An exhaust-gas pressure and temperature survey of the General Electric F404-GE-400 turbofan engine was conducted in the altitude test facility of the NASA Lewis Propulsion System Laboratory. Traversals by a survey rake were made across the exhaust-nozzle exit to measure the pitot pressure and total temperature. Tests were performed at Mach 0.87 and a 24,000-ft altitude and at Mach 0.30 and a 30,000-ft altitude with various power settings from intermediate to maximum afterburning. Data yielded smooth pressure and temperature profiles with maximum jet temperatures approximately 1.4 in. inside the nozzle edge and maximum jet temperatures from 1 to 3 in. inside the edge. A low-pressure region located exactly at engine center was noted. The maximum temperature encountered was 3800 R.

Walton, James T.↗
NASA NTRS1988

Noncontact true temperature measurement, 2

A laser pyrometer was developed for acquiring the true temperature of a levitated sample. The reflectivity is measured by first expanding the laser beam to cover the entire cross-sectional surface of the diffuse target. The reflectivity calibration of this system is determined from the surface emissivity of a target with a blackbody cavity. The emissivity of the real target can then be calculated. The overall system constant is obtained by passively measuring the radiance of the blackbody cavity (emissivity = 1.0) at a known, arbitrary temperature. Since the photosensor used is highly linear over the entire operating temperature range, the true temperature of the target can then be computed. The latest results available from this on-going research indicate that true temperatures thus obtained are in very good quantitative agreement with thermocouple measured temperatures.

Lee, Mark C.↗