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At least 289 records · Page 16

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NASA NTRS1971

A thermal conductivity cell for small powdered samples.

A thermal conductivity cell is described for making measurements of the thermal conductivity and thermal diffusivity of small samples of powdered dielectric materials. The principle used is that of the line heat source. A novel way is described for applying this method so that much smaller samples than normal may be tested. This size requirement is necessary for investigations involving limited samples as does the Lunar Science Program. The method is checked by measuring the conductivity of standard samples and comparing the results with those found in the literature.

Cremers, C. J.↗

NASA NTRS1972

Collision integrals for isotopic hydrogen molecules.

The study was undertaken to determine the effects of reduced mass and differences in asymmetry on the collision integrals and thermal diffusion factors of isotopic hydrogen systems. Each system selected for study consisted of two diatoms, one in the j = 0 rotation state and the other in the j = 1 state. The molecules interacted with a Lennard-Jones type potential modified to include angular terms. A set of cross sections and collision integrals were obtained for each system.

Brown, N. J.↗

NASA NTRS1972

Dispersive waves in a seeded MHD generator.

The equations giving the response of a slightly ionized plasma with monatomic components to sinusoidal perturbations have been formulated. Included in the model equations were the electron Hall effect, electron thermal diffusion, radiation, and electron-atom rate processes. Plasma conditions were limited to those where viscous effects, the induced magnetic field, ion slip, and atom-atom inelastic processes can be neglected. Presented are results of numerical calculations for MHD generators with a working fluid of potassium seeded argon.

Harstad, K. G.↗

NASA NTRS1972

Thermal characteristics of the lunar surface layer.

The thermophysical properties of the fines from the Apollo 12 landing site have been determined as a function of their relevant parameters. These properties include the thermal conductivity, thermal diffusivity, directional reflectance and emittance. The density used was the same as that observed from the returned core-tube samples and so should be close to the true density of the surface layer at the Apollo 12 site. The measured properties are used to calculate the diurnal temperature variation of the moon's surface as well as for several depths below the surface. The maximum surface of 389 K is obtained at lunar noon while the minimum temperature of 86.1 K is obtained at sunrise. It is shown that the most significant effects on temperature, as compared with previous calculations, are caused by using the directional reflectance which controls the amount of solar energy absorption during the day in place of a constant hemispherical reflectance. The results are compared with previous analyses and remote measurements.

Cremers, C. J.↗

NASA NTRS1972

Fission xenon from extinct Pu-244 in 14,301.

Xenon extracted in step-wise heating of lunar breccia 14,301 contains a fission-like component in excess of that attributable to uranium decay during the age of the solar system. There seems to be no adequate source for this component other than Pu-244. Verification that this component is in fact due to the spontaneous fission of extinct Pu-244 comes from the derived spectrum which is similar to that observed from artificially produced Pu-244. It thus appears that Pu-244 was extant at the time lunar crustal material cooled sufficiently to arrest the thermal diffusion of xenon. Subsequent history has apparently maintained the isotopic integrity of plutonium fission xenon. Of major importance are details of the storage itself. Either the fission component is the result of in situ fission of Pu-244 and subsequent storage in 14,301 material, or the fission xenon was stored in an intermediate reservoir before incorporation into 14,301.

Drozd, R.↗

NASA NTRS1973

Two-phase charge-coupled device

A charge-transfer efficiency of 99.99% per stage was achieved in the fat-zero mode of operation of 64- and 128-stage two-phase charge-coupled shift registers at 1.0-MHz clock frequency. The experimental two-phase charge-coupled shift registers were constructed in the form of polysilicon gates overlapped by aluminum gates. The unidirectional signal flow was accomplished by using n-type substrates with 0.5 to 1.0 ohm-cm resistivity in conjunction with a channel oxide thickness of 1000 A for the polysilicon gates and 3000 A for the aluminum gates. The operation of the tested shift registers with fat zero is in good agreement with the free-charge transfer characteristics expected for the tested structures. The charge-transfer losses observed when operating the experimental shift registers without the fat zero are attributed to fast interface state trapping. The analytical part of the report contains a review backed up by an extensive appendix of the free-charge transfer characteristics of CCD's in terms of thermal diffusion, self-induced drift, and fringing field drift. Also, a model was developed for the charge-transfer losses resulting from charge trapping by fast interface states. The proposed model was verified by the operation of the experimental two-phase charge-coupled shift registers.

Kosonocky, W. F.↗

NASA NTRS1971

Extrapolation of thermophysical properties data for oxygen to high pressures (5000 to 10,000 psia) at low temperatures (100-600 R)

Thermophysical properties data for oxygen at pressures below 5000 psia have been extrapolated to higher pressures (5,000-10,000 psia) in the temperature range 100-600 R. The tables include density, entropy, enthalpy, internal energy, speed of sound, specific heat, thermal conductivity, viscosity, thermal diffusivity, Prandtl number, and dielectric constant.

Weber, L. A.↗

NASA NTRS1973

Characterization of the mechanical and physical properties of TD-NiCr (Ni-20Cr-2ThO2) alloy sheet

Sheets of TD-NiCr processed using techniques developed to produce uniform material were tested to supply mechanical and physical property data. Two heats each of 0.025 and 0.051 cm thick sheet were tested. Mechanical properties evaluated included tensile, modulus of elasticity, Poisson's Ratio, compression, creep-rupture, creep strength, bearing strength, shear strength, sharp notch and fatigue strength. Test temperatures covered the range from ambient to 1589K. Physical properties were also studied as a function of temperature. The physical properties measured were thermal conductivity, linear thermal expansion, specific heat, total hemispherical emittance, thermal diffusivity, and electrical conductivity.

Fritz, L. J.↗

NASA NTRS1972

Fast differential thermal analysis.

A study is conducted of the limits of time-dependent differential thermal analysis (DTA). Applications of DTA to the hysteresis phenomena of glasses are also reported. The computation of DTA sample temperatures is discussed, giving attention to feasible heating rates, transient effects to be measured, and the simulation of DTA responses to changes in thermal diffusivity similar to hysteresis phenomena in glasses. The reproducibility of temperature recording is checked with zone-refined organic chemicals.

Wunderlich, B.↗

NASA NTRS1974

Use of visible, near-infrared, and thermal infrared remote sensing to study soil moisture

Two methods are described which are used to estimate soil moisture remotely using the 0.4- to 14.0 micron wavelength region: (1) measurement of spectral reflectance, and (2) measurement of soil temperature. The reflectance method is based on observations which show that directional reflectance decreases as soil moisture increases for a given material. The soil temperature method is based on observations which show that differences between daytime and nighttime soil temperatures decrease as moisture content increases for a given material. In some circumstances, separate reflectance or temperature measurements yield ambiguous data, in which case these two methods may be combined to obtain a valid soil moisture determination. In this combined approach, reflectance is used to estimate low moisture levels; and thermal inertia (or thermal diffusivity) is used to estimate higher levels. The reflectance method appears promising for surface estimates of soil moisture, whereas the temperature method appears promising for estimates of near-subsurface (0 to 10 cm).

Blanchard, M. B.↗

NASA NTRS1974

Concentration changes during eutectic solidification

Thermotransport (or thermal diffusion, Soret effect) is shown to cause significant amount of segregation during the directional solidification of aluminum-copper eutectic. The concentration changes are predicted quantitatively and they are a function of temperature gradient, rate of melting and solidification and the time of soaking. There is a fair agreement between the experiments and calculations. A process is suggested where these concentration changes may be minimized.

Bhat, B. N.↗

NASA NTRS1974

Thermophysical properties of Apollo 14 fines

The vacuum thermal conductivity of lunar fines sample 14163 was measured for the approximate temperature range of 100 to 400 K. Sample densities of 1500 kg/cu m and 1800 kg/cu m were used. The temperature dependence of the conductivity was found to be well represented by the relation k = A + BT-cubed, which is predicted by elementary theory. The coefficients A and B were obtained by least-squares analysis of the data. The thermal diffusivity was calculated for the various densities using specific heat data from the literature along with the measured conductivities. The results are compared with those obtained for Apollo 11, Apollo 12, and terrestrial basalt samples.

Cremers, C. J.↗

NASA NTRS1974

Thermal preparation of foods in space-vehicle environments

Convection is the primary heat transfer mechanism for most foods heated in an earth-based environment. In contrast, in the low-gravity environment of space flight, the primary heat transfer mechanism is conduction (or radiation in the absence of a conducting medium). Conduction heating is significantly slower and less efficient than convection heating. This fact poses a problem for food heating during space flight. A numerical model has been developed to evaluate this problem. This model simulates the food-heating process for Skylab. The model includes the effect of a thermally controlled on/off heat flux. Parametric studies using this model establish how the required heating time is affected by: the thermal diffusivity of the nutrient materials, the power level of the heater, the initial food temperatures, and the food container dimensions.

Bannerot, R. B.↗

NASA NTRS1974

Thermal characteristics of Apollo 16 lunar fines

The vacuum thermal conductivity of the Apollo 16 fines is presented as a function of temperature for the approximate range of diurnal temperatures on the moon. The density used is 1500 kg/cu m, which is approximately the density of the core tube samples returned from the landing site. The thermal diffusivity was calculated from the conductivity, density and specific heat and is also presented. These properties along with the reflectance and emittance are used in a calculation of temperature in the lunar surface layer.

Cremers, C. J.↗

NASA NTRS1974

Use of visible, near-infrared, and thermal infrared remote sensing to study soil moisture

Two methods are used to estimate soil moisture remotely using the 0.4- to 14.0-micron wavelength region: (1) measurement of spectral reflectance, and (2) measurement of soil temperature. The reflectance method is based on observations which show that directional reflectance decreases as soil moisture increases for a given material. The soil temperature method is based on observations which show that differences between daytime and nighttime soil temperatures decrease as moisture content increases for a given material. In some circumstances, separate reflectance or temperature measurements yield ambiguous data, in which case these two methods may be combined to obtain a valid soil moisture determination. In this combined approach, reflectance is used to estimate low moisture levels; and thermal inertia (or thermal diffusivity) is used to estimate higher levels. The reflectance method appears promising for surface estimates of soil moisture, whereas the temperature method appears promising for estimates of near-subsurface (0 to 10 cm).

Blanchard, M. B.↗

NASA NTRS1974

Thermal conductivity of Apollo 16 lunar fines

The vacuum thermal conductivity of the Apollo 16 fines is presented as a function of temperature for the approximate range of diurnal temperatures on the moon. The density used is 1500 kg/cu m, which is approximately the density of the core-tube samples returned from the landing site. The thermal diffusivity was calculated from the conductivity, density, and specific heat and is also presented.

Cremers, C. J.↗

NASA NTRS1975

Thermophysical properties of Apollo 14 fines

The vacuum thermal conductivity of lunar fines sample 14163 was measured for the approximate temperature range 100 to 400 deg K. Several sample densities from 1100 to 1800 kg/cu m were used. The temperature dependence of the conductivity was found to be well represented by the relation k = A + BT cubed, which is predicted by elementary theory. The coefficients A and B were obtained by least squares analysis of the data. The thermal diffusivity was calculated for the various densities by using specific heat data from the literature along with the measured conductivities. The results are compared with those obtained for Apollo 11, Apollo 12, and terrestrial basalt samples.

Cremers, C. J.↗

NASA NTRS1977

Radio and EUV observations of a coronal hole

Current ideas and modeling assumptions concerning the structure of the transition region and corona are summarized. Observations of a specific coronal hole are reported which were made with the EUV spectroheliometer aboard Skylab and with high-resolution radio telescopes in Australia and West Germany. Theoretical EUV line intensities and radio brightness temperatures are calculated, and an attempt is made to analyze the observations on the basis of standard one-dimensional plane-parallel hydrostatic-equilibrium models for the transition region and corona. It is found that any given standard model predicts either higher radio brightnesses or lower EUV line intensities than are observed. Several potential problem areas are examined in order to resolve this conflict. It is concluded that a model involving departures from hydrostatic equilibrium, varying conductive flux, mass outflow, as well as effects of thermal diffusion and nonequilibrium ionization should be investigated in more detail.

Dulk, G. A.↗