Search NASA⌕ Search

SEARCH · Search NASA

Results for “Diffusion correlation”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Design of a variable area diffuser for a 15-inch Mach 6 open-jet tunnel

The Langley 15-inch Mach 6 High Temperature Tunnel was recently converted from a Mach 10 Hypersonic Flow Apparatus. This conversion was effected to improve the capability of testing in Mach 6 air at relatively high reservoir temperatures not previously possible at Langley. Elevated temperatures allow the matching of the Mach numbers, Reynolds numbers, and ratio of wall-to-adiabatic-wall temperatures (TW/Taw) between this and the Langley 20-inch Mach 6 CF4 Tunnel. This ratio is also matched for Langley's 31-inch Mach 10 Tunnel and is an important parameter useful in the simulation of slender bodies such as National Aerospace Plane (NASP) configurations currently being studied. Having established the nozzle's operating characteristics, the decision was made to install another test section to provide model injection capability. This test section is an open-jet type, with an injection system capable of injecting a model from retracted position to nozzle centerline between 0.5 and 2 seconds. Preliminary calibrations with the new test section resulted in Tunnel blockage. This blockage phenomenon was eliminated when the conical center body in the diffuser was replaced. The issue then, is to provide a new and more efficient variable area diffuser configuration with the capability to withstand testing of larger models without sending the Tunnel into an unstart condition. Use of the 1-dimensional steady flow equation with due regard to friction and heat transfer was employed to estimate the required area ratios (exit area / throat area) in a variable area diffuser. Correlations between diffuser exit Mach number and area ratios, relative to the stagnation pressure ratios and diffuser inlet Mach number were derived. From these correlations, one can set upper and lower operating pressures and temperatures for a given diffuser throat area. In addition, they will provide appropriate input conditions for the full 3-dimensional computational fluid dynamics (CFD) code for further simulation studies.

Loney, Norman W.↗
NASA NTRS1961

Analysis of Multipoint-Multitime Correlations and Diffusion in Decaying Homogeneous Turbulence

Two-point, two-time correlation equations are obtained by considering the Navier-Stokes equations for two points in a fluid at two time. By neglecting the triple correlations in the equations, a solution is obtained for the final period of decay. The analysis is extended to earlier times by considering three points at three different times. The set of equations is made determinate by neglecting the quadruple correlations in comparison with the triple correlations. The diffusion of particles from a source in a decaying turbulent field is calculated approximately by assuming that the velocity fluctuations are small.

Deissler, Robert G.↗
NASA NTRS1984

Ultraviolet extinction and diffuse band strength correlations

Correlations between UV extinction parameters and diffuse band strengths are south, using a data base of 50 stars with recently measured extinction curves. A novel aspect of this study is that the basic dependence of most interstellar parameters on E(B-V) (or, nearly equivalently, on the total hydrogen column density) has been largely canceled out. After this cancellation, a weak correlation is found between the 4430 A diffuse band and the 2175 A extinction feature. No other correlations are found. These results support a molecular origin for the 5780 A and 6284 A bands. It is speculated that the correlation pattern found for the 4430 A band can be explained if this band originates in reactions on disordered grain surfaces.

Seab, C. G.↗
NASA NTRS1976

Handbook of liquid metals

Metals are described by physical appearance followed by atomic weight, atomic number, and valence. Data includes laboratory handling and safety procedures, heat transfer correlations, diffusion coefficients in liquid gallium/indium solution, melting and boiling points, thermal conductivity, heat capacity, and electrical resistivity.

Ukanwa, A. O.↗
NASA NTRS1986

Numerical simulation of diffusion-controlled droplet growth Dynamical correlation effects

Diffusion-controlled coarsening (Ostwald ripening) of precipitated solutions is studied by numerical simulation. An algorithm is devised which exploits the screening of solute concentration fields, thereby removing the restriction to small systems of previous work. Simulation of the coarsening of 5000 droplets at 10-percent volume fraction reveals long-ranged dynamical correlations which broaden the droplet size-distribution function and increase the coarsening-rate coefficient.

Beenakker, C. W. J.↗
NASA NTRS1977

Correlation of total, diffuse, and direct solar radiation

Present requirements for realistic solar energy system evaluations necessitate a comprehensive body of solar-radition data. The data should include both diffuse and direct solar radiation as well as their total on an hourly (or shorter) basis. In general, however, only the total solar radiation values were recorded. This report presents a correlation that relates the diffuse component of an hourly total solar radiation value to the total radiation ratio of the maximum value attainable. The data used were taken at the Blue Hill Observatory in Milton, Massachusetts, for the period 1952. The relation - in the form of the data plots - can be used in situations in which only the hourly total radiation data are available but the diffuse component is desired.

Buyco, E. H.↗
NASA NTRS1973

Correlation and prediction of gaseous diffusion coefficients.

A new correlation method for binary gaseous diffusion coefficients from very low temperatures to 10,000 K is proposed based on an extended principle of corresponding states, and having greater range and accuracy than previous correlations. There are two correlation parameters that are related to other physical quantities and that are predictable in the absence of diffusion measurements. Quantum effects and composition dependence are included, but high-pressure effects are not. The results are directly applicable to multicomponent mixtures.

Marrero, T. R.↗
NASA NTRS1972

Effect of slow rotational diffusion on angular correlations.

The theory for perturbed angular correlations of gamma radiation has been extended to include the possibility of adiabatic variation in the interaction Hamiltonian, K, for the intermediate state. The calculation begins from a polycrystalline model. It is shown that adiabatic variation in K introduces a time dependence into the angles which express the orientation of the molecular frame. The relevance of the adiabatic limit to the use of perturbed angular correlations of gamma radiation for study of the motion of radioactive species in viscous media is discussed.

Marshall, A. G.↗
NASA NTRS1994

Long-term modulation of galactic cosmic radiation and its model for space exploration

As the human exploration of space has received new attention in the United States, studies find that exposure to space radiation could adversely impact the mission design. Galactic Cosmic Radiation (GCR), with its very wide range of charges and energies, is particularly important for a mission to Mars, because it imposes a stiff mass penalty for spacecraft shielding. Dose equivalent versus shielding thickness calculations, show a rapid initial drop on exposure with thickness, but an asymptotic behavior at a higher shielding thickness. Uncertainties in the radiobiology are largely unknown. For a fixed radiation risk, this leads to large uncertainties in shielding thickness for small uncertainties in estimated dose. In this paper we investigate the application of steady-state, spherically-symmetric diffusion-convection theory of solar modulation to individual measurements of differential energy spectra from 1954 to 1989 in order to estimate the diffusion coefficient, kappa(r,t), as a function of time. We have correlated the diffusion coefficient to the Climax neutron monitor rates and show that, if the diffusion coefficient can be separated into independent functions of space and time: kappa(r,t)=K(t) k(sub 0) beta Pk(sub 1) (r), where beta is the particle velocity and P the rigidity, then (i) The time dependent quantity 1/K(t), which is proportional to the deceleration potential, phi(r,t), is linearly related to the Climax neutron monitor counting rate. (ii) The coefficients obtained from hydrogen or helium intensity measurements are the same. (iii) There are different correlation functions for odd and even solar cycles. (iv) The correlation function for the Climax neutron monitor counting rate for given time, t, can be used to estimate mean deceleration parameter phi(t) to within +/- 15% with 90% confidence. We have shown that k(r,t) determined from hydrogen and/or helium data, can be used to fit the oxygen and iron differential energy spectra with a root mean square error of about +/- 10%, and essentially independent of the particle charge or energy. We have also examined the ion chamber and C-14 measurements which allow the analysis to be extended from the year 1906 to 1990. Using this model we have defined reference GCR spectra at solar minimum and solar maximum. These can be used for space exploration studies and provide a quantitative estimate of the error in dose due to changes in GCR intensities.

Badhwan, G. D.↗
NASA NTRS1980

The effect of minority carrier mobility variations on the performance of high voltage silicon solar cells

A multistep diffusion processing schedule is described which allows the attainment of high open circuit voltages in 0.1 ohm/cm silicon cells. The schedule consists of a deep primary diffusion, followed by an acid etch of emmitter surface which is then followed by a shallow secondary diffusion. A correlation is made between the observed voltage increases and the time of primary diffusion. Results indicate that as the primary diffusion time increases, the voltage rises monotonically.

Weizer, V. G.↗
NASA NTRS1977

The velocity correlation function in cosmic-ray diffusion theory

It is shown that Earl's (1973) eigenvalue sum for the cosmic-ray spatial diffusion coefficient parallel to the mean magnetic field is precisely equivalent to the time integral of the particle-velocity correlation function parallel to the mean field. A derivation due to Kubo (1957) is applied to cosmic-ray pitch-angle scattering, and it is proven that all nine components of the cosmic-ray diffusion tensor can be expressed as integrals over the velocity correlation function. A pitch-angle correlation function is derived, and the effect of long-wavelength turbulence on the velocity correlation function and spatial diffusion coefficients is examined. Application of the velocity-correlation method to a realistic case involving both pitch-angle scattering and appreciable fluctuation in the direction of the local field indicates that long-wavelength turbulence in the local field reduces the parallel diffusion coefficient and places an upper limit on the ratio of the perpendicular to parallel diffusion coefficients.

Forman, M. A.↗
NASA NTRS1998

A Search for Hot, Diffuse Gas in Superclusters

The HEA01 A2 full sky, 2-10 keV X-ray map was searched for diffuse emission correlated with the plane of the local supercluster of galaxies and a positive correlation was found at the 99% confidence level. The most obvious interpretation is that the local supercluster contains a substantial amount of hot (10(exp 8) OK), diffuse gas, i.e. ionized hydrogen, with a density on the order of 2 - 3 x 10(exp -6) ions per cubic centimeter. This density is about an order of magnitude larger than the average baryon density of the universe and is consistent with a supercluster collapse factor of 10. The implied total mass is of the order of 10(exp 16) times the mass of the sun and would constitute a large fraction of the baryonic matter in the local universe. This result supports current thinking that most of the ordinary matter in the universe is in the form of ionized hydrogen; however, the high temperature implied by the X-ray emission is at the top of the range predicted by most theories. The presence of a large amount of hot gas would leave its imprint on the Cosmic Microwave Background (CMB) via the Sunyaev-Zel'dovich (SZ) effect. A marginal decrement (-17 muK) was found in the COBE 4-year 53 GHz CMB map coincident with the plane of the local supercluster. Although the detection is only 1beta, the level is consistent with the SZ effect predicted from the hot gas. If these results are confirmed by future observations they will have important implications for the formation of large-scale structure in the universe. Three other projects related directly to the HEAO 1 map or the X-ray background in general benefited from this NASA grant. They are: (1) "Correlations between the Cosmic X-ray and Microwave Backgrounds: Constraints on a Cosmological Constant"; (2) "Cross-correlation of the X-ray Background with Radio Sources: Constraining the Large-Scale Structure of the X-ray Background"; and (3) "Radio and X-ray Emission Mechanisms in Advection Dominated Accretion Flow".

Boughn, Stephen P.↗
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 NTRS1994

Far-Infrared sources and diffuse emission in M31

A study on the far-infrared (FIR) emission of M31 has been carried out with the High Resolution (HiRes) maps (approx. 1 min) derived from IRAS data. Sixty-eight FIR sources are detected in M31, which in general coincide with optical HII regions, and contribute 15, 23, 29, and 23 percent to the fluxes in 12, 25, 60, and 100 micron bands, respectively. The remaining diffuse emission, which dominates the FIR emission of M31, is studied using a dust heating model which utilizes the UV and optical photometry maps and the HI maps available in the literature. It is found that the global dust-to-gas ratio in M31 disk is 6.5 10(exp -3), very close to the dust-to-gas ratio in the solar neighborhood. There is a significant galactocentric gradient of the dust-to-HI-gas ratio, with an e-folding scale length of 9 kpc. The diffuse dust correlates tightly with the HI gas. The model indicates that the non-ionizing UV (913-4000A) radiation from massive and intermediate massive stars contributes only about 30 percent of the heating of the diffuse dust, while the optical-NIR (4000-9000A) radiation from the old stellar population is responsible for the most of the heating.

Xu, Cong↗
NASA NTRS1979

Effect of rotor meridional velocity ratio on response to inlet radial and circumferential distortion

Three single transonic fan stages, each having a different meridional velocity ratio across its rotor, were tested with two magnitudes of tip radial distortion and with a 90 deg circumferential distortion imposed on the inlet flow. The rotor with the lowest meridional velocity ratio (less than 0.9 at the tip) demonstrated the least degradation of performance due to these distortions. Loss and deviation angle data (as needed for performance prediction with radial distortion) calculated along actual streamlines for radially distorted flow and correlated against diffusion factor, showed consistent agreement with data calculated along design streamlines for undistorted flow.

Sanger, N. L.↗