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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 955 records · Page 53
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

Possible theoretical explanations for occasional days of non-field-aligned diffusion at neutron monitor energies

It has been shown previously (Anath et al., 1973 and Kane, 1974) that 20 to 25% of days, the diffusion component of the cosmic-ray neutron diurnal anisotropy is directed more than 30 degrees away from the ecliptic projection of the interplanetary magnetic field averaged over the same 24 hours. A number of explanations for this deviation are discussed and it is concluded that transverse gradient drifts due to gradients perpendicular to the ecliptic are likely, that diurnal variations in the diffusion component of the neutron anisotropy may affect results from single stations and that the 24 hour mean interplanetary magnetic field may not be the field appropriate to the streaming equation at neutron monitor energies.

Forman, M. A.↗
NASA NTRS1975

Modulation and diffusion theory of cosmic rays

Papers given on the modulation of galactic cosmic rays by the solar wind at the 14th International Cosmic Ray Conference are reviewed. Some of the topics treated in this review are Pioneer and Helios radial gradient measurement, heliolatitude effects in modulation models, diffusion (scattering) theory - including pitch angle diffusion diagrams - solar flare particle transport theory and cosmic ray fluctuations at neutron monitor energies.

Forman, M. A.↗
NASA NTRS1976

Low pressure radon diffusion - A laboratory study and its implications for lunar venting

Results of a study of radon migration through columns of fine particulate materials, at total pressures of 0.02-0.2 torr, are reported. Materials studied were: NBS Glass Spheres (SRM 1003), Emerson & Cuming Eccospheres (IG-101), activated coconut charcoal, Lipaci obsidian, and W-1 Standard Diabase. Rates of diffusion were used to derive heats of adsorption for radon on the materials tested. The most reliable values found clustered around 8-9 kcal/mole. These high heats of adsorption, if typical for most materials, combined with low percentages of radon emanation by lunar soils found by other researchers, imply that random walk diffusion will not be an important mechanism for redistributing the radon and the radon daughters produced in the lunar regolith. In particular, since random walk migration is not a sufficient mechanism to account for localized high concentrations of radon-222 and its daughter polonium-210 observed by the Apollo 15 and 16 command modules, an alternative mechanism is proposed, in which radon would be swept to the surface by other gases during intermittent venting events.

Friesen, L. J.↗
NASA NTRS1976

Viscosity and viscoelasticity of two-phase systems having diffuse interfaces

The equilibrium stability criterion for diffuse interfaces in a two-component solution with a miscibility gap requires that the interdiffusion flux vanish. If the system is continuously deformed, convective fluxes disrupt the equilibrium in the interface regions and induce a counter diffusive flux, which is dissipative and contributes to the apparent viscosity of the mixture. Chemical free energy is recoverably stored, causing viscoelastic phenomena. Both effects are significant.

Hopper, R. W.↗
NASA NTRS1976

The diffusion approximation. An application to radiative transfer in clouds

It is shown how the radiative transfer equation reduces to the diffusion equation. To keep the mathematics as simple as possible, the approximation is applied to a cylindrical cloud of radius R and height h. The diffusion equation separates in cylindrical coordinates and, in a sample calculation, the solution is evaluated for a range of cloud radii with cloud heights of 0.5 km and 1.0 km. The simplicity of the method and the speed with which solutions are obtained give it potential as a tool with which to study the effects of finite-sized clouds on the albedo of the earth-atmosphere system.

Arduini, R. F.↗
NASA NTRS1976

Test particle propagation in magnetostatic turbulence. 1. Failure of the diffusion approximation

The equation which governs the quasi-linear approximation to the ensemble and gyro-phase averaged one-body probability distribution function is constructed from first principles. This derived equation is subjected to a thorough investigation in order to calculate the possible limitations of the quasi-linear approximation. It is shown that the reduction of this equation to a standard diffusion equation in the Markovian limit can be accomplished through the application of the adiabatic approximation. A numerical solution of the standard diffusion equation in the Markovian limit is obtained for the narrow parallel beam injection. Comparison of the diabatic and adiabatic results explicitly demonstrates the failure of the Markovian description of the probability distribution function. Through the use of a linear time-scale extension the failure of the adiabatic approximation, which leads to the Markovian limit, is shown to be due to mixing of the relaxation and interaction time scales in the presence of the strong mean field.

Klimas, A. J.↗
NASA NTRS1976

Purging of a multilayer insulation with dacron tuft spacer by gas diffusion

The time and purge gas usage required to purge a multilayer insulation (MLI) panel with gaseous helium by means of gas diffusion to obtain a condensable gas (nitrogen) concentration of less than 1 percent within the panel are stipulated. Two different, flat, rectangular MLI panels, one incorporating a butt joint, were constructed of of 11 double-aluminized Mylar (DAM) radiation shields separated by Dacron tuft spacers. The DAM/Dacron tuft concept is known commercially as Superfloc. The nitrogen gas concentration as a function of time within the MLI panel could be adequately predicted by using a simple, one dimensional gas diffusion model in which the boundary conditions at the edge of the MLI panel were time dependent. The time and purge gas usage required to achieve 1 percent nitrogen gas concentration within the MLI panel varied from 208 to 86 minutes and 34.1 to 56.5 MLI panel purge volumes, respectively, for gaseous helium purge rates from 10 to 40 MLI panel volumes per hour.

Sumner, I. E.↗
NASA NTRS1977

Diffusion welding of a directionally solidified gamma/gamma prime - delta eutectic alloy

Hot-press diffusion welding parameters were developed for a directionally solidified, gamma/gamma prime-delta eutectic alloy. Based on metallography, a good diffusion weld was achieved at 1100 C under 34.5 MPa (5 ksi) pressure for 1 hour. In addition, a dissimilar metal weld between gamma/gamma prime-delta and IN-100 was successfully made at 1100 C under 20.7 MPa (3 ksi) pressure for 1 hour.

Moore, T. J.↗
NASA NTRS1977

Computer simulation of the velocity diffusion of cosmic rays

Monte Carlo simulation experiments were performed in order to study the velocity diffusion of charged particles in a static turbulent magnetic field. By following orbits of particles moving in a large ensemble of random magnetic field realizations with suitable chosen statistical properties, a pitch-angle diffusion coefficient is derived. Results are presented for a variety of particle rigidities and rms random field strengths and compared with the predictions of standard quasi-linear theory and the nonlinear partially averaged field theory.

Kaiser, T. B.↗
NASA NTRS1977

Water vapor diffusion membrane development

An application of the water vapor diffusion technique is examined whereby the permeated water vapor is vented to space vacuum to alleviate on-board waste storage and provide supplemental cooling. The work reported herein deals primarily with the vapor diffusion-heat rejection (VD-HR) as it applies to the Space Shuttle. A stack configuration was selected, designed and fabricated. An asymmetric cellulose acetate membrane, used in reverse osmosis application was selected and a special spacer was designed to enhance mixing and promote mass transfer. A skid-mount unit was assembled from components used in the bench unit although no attempt was made to render it flight-suitable. The operating conditions of the VD-HR were examined and defined and a 60-day continuous test was carried out. The membranes performed very well throughout the test; no membrane rupture and no unusual flux decay was observed. In addition, a tentative design for a flight-suitable VD-HR unit was made.

Tan, M. K.↗
NASA NTRS1976

Diffusive isothermal partitioning in a layered medium with geologic applications

The diffusive isothermal partitioning of solute in a layered two-phase material has been analyzed to help elucidate the phenomenon of solute partitioning in multiphase lunar and terrestrial materials and to estimate the cooling history of samples. After reviewing the physical chemistry of partitioning and the case of an infinite one-dimensional diffusion couple, we solve in analytic form the case of a finite one-dimensional couple. The solution can be used to estimate cooling histories or to interpret laboratory experiments on partitioning. A sample calculation is included.

Hopper, R. W.↗
NASA NTRS1976

Diffusion in mixed solvents. III - The heat of mixing parameter and the Soret coefficient

New evidence is presented that for aqueous glycerol solutions, the Soret coefficient of glycerol, sigma sub 1 = D sub 1 T/D sub 1 (where D sub 1 T and D sub 1 are the thermal and self-diffusion coefficients, respectively, of glycerol in aqueous solutions), is an integral part of the heat of mixing parameter. Expressions are presented indicating the importance of the Soret coefficients to correlations for diffusion processes in glycerol water solvents.

Carapellucci, P. A.↗
NASA NTRS1976

Catalogue of diffuse interstellar band measurements

Diffuse-band data have been collected from the literature and reduced statistically to a common measurement system, enabling correlation analyses to be made with a larger quantity of data than previously possible. A full listing of the catalogued data is presented, along with some discussion of the correlations. One important application of such studies is the identification of cases of peculiar diffuse-band behavior, and a table is given showing all cases of band strengths deviating by more than twice the mean dispersion from the best-fit correlations. This table may be useful in planning further observations.

Snow, T. P., Jr.↗
NASA NTRS1976

Thermal diffusivity of four Apollo 17 rock samples

The modified Angstrom technique was used to measure the thermal diffusivity of four Apollo 17 rock samples in air at pressures of 1 atm and one-millionth torr in the temperature range 80-460 K, and in CO2 at different pressures for various temperature ranges and at different temperatures for the range of interstitial CO2 gas pressure 1 atm to 0.0001 torr. The experiments with CO2 were intended to simulate Martian conditions, and it was found that the thermal diffusivity of lunar crystalline basalt and breccia varies very little with temperature in a simulated Martian environment, which indicates that the thermal processes in the Martian regolith could be more straightforward than in the lunar regolith.

Horai, K.-I.↗
NASA NTRS1977

Turbulent diffusion from a quasi-kinematical point of view

An estimate for the coefficient of self-diffusion can be derived whenever the Eulerian velocity spectrum is known. The result is more general than those previously obtained. A comparison is made with computed test-particle diffusion in an inviscid two-dimensional Navier-Stokes fluid.

Salu, Y.↗
NASA NTRS1979

Cosine-corrected optical diffuser

In solar energy utilization studies, correct measurements of flux arriving at other angles to optical axis must be given. Developed device (Cosine diffuser) significantly reduces measurement errors. In combination of radiation transmitter and diffuser co-operating with collimated optical instrument, relative aperture of instrument is filled.

Estey, R. S.↗
NASA NTRS1977

Surface recombination velocity and diffusion length of minority carriers in heavily doped silicon layers

Quantitative analysis of the electron beam-induced current and the dependence of the effective diffusion length of the minority carriers on the penetration depth of the electron beam were employed for the analysis of the carrier recombination characteristics in heavily doped silicon layers. The analysis is based on the concept of the effective excitation strength of the carriers which takes into consideration all possible recombination sources. Two dimensional mapping of the surface recombination velocity of P-diffused Si layers will be presented together with a three dimensional mapping of minority carrier lifetime in ion implanted Si. Layers heavily doped with As exhibit improved recombination characteristics as compared to those of the layers doped with P.

Gatos, H. C.↗
NASA NTRS1978

Numerical analyses for treating diffusion in single-, two- and three-phase binary alloy systems

Numerical solutions were applicable for planar, cylindrical, or spherical geometries with any diffusion-zone size and any continuous variation of the diffusion coefficient with concentration. Special techniques were included in the analyses to account for differences in molal volumes, initiation and growth of an intermediate phase, disappearance of a phase, and the presence of an initial composition profile in the specimen. A major improvement in solution accuracy was achieved in the two phase analysis by employing a mass conservation criterion to establish the location of the interface rather than the conventional interface-flux-balance criterion. In the three phase analysis, computation time was minimized without sacrificing solution accuracy by treating the three phase problem as a two phase problem when the thickness of the intermediate phase was less than a preset small value. Three computer codes were developed to perform these analyses.

Tenney, D. R.↗