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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
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NASA NTRS1981

Effect of zone size on the convergence of exact solutions for diffusion in single phase systems with planar, cylindrical or spherical geometry

Exact solutions for diffusion in single phase binary alloy systems with constant diffusion coefficient and zero-flux boundary condition have been evaluated to establish the optimum zone size of applicability. Planar, cylindrical and spherical interface geometry, and finite, singly infinite, and doubly infinite systems are treated. Two solutions are presented for each geometry, one well suited to short diffusion times, and one to long times. The effect of zone-size on the convergence of these solutions is discussed. A generalized form of the diffusion solution for doubly infinite systems is proposed.

Unnam, J.↗
NASA NTRS1981

Parametric analysis of diffuser requirements for high expansion ratio space engine

A supersonic diffuser ejector design computer program was developed. Using empirically modified one dimensional flow methods the diffuser ejector geometry is specified by the code. The design code results for calculations up to the end of the diffuser second throat were verified. Diffuser requirements for sea level testing of high expansion ratio space engines were defined. The feasibility of an ejector system using two commonly available turbojet engines feeding two variable area ratio ejectors was demonstrated.

Wojciechowski, C. J.↗
NASA NTRS1981

Diffuse radiation

A diffuse celestial radiation which is isotropic at least on a course scale were measured from the soft X-ray region to about 150 MeV, at which energy the intensity falls below that of the galactic emission for most galactic latitudes. The spectral shape, the intensity, and the established degree of isotropy of this diffuse radiation already place severe constraints on the possible explanations for this radiation. Among the extragalactic theories, the more promising explanations of the isotropic diffuse emission appear to be radiation from exceptional galaxies from matter antimatter annihilation at the boundaries of superclusters of galaxies of matter and antimatter in baryon symmetric big bang models. Other possible sources for extragalactic diffuse gamma radiation are discussed and include normal galaxies, clusters of galaxies, primordial cosmic rays interacting with intergalactic matter, primordial black holes, and cosmic ray leakage from galaxies.

Source record↗
NASA NTRS1981

Effects of free-stream turbulence on diffuser performance

An experimental evaluation of the effects of free-stream turbulence on the performance of a subsonic two-dimensional diffuser has been made. Increases of the diffuser's static pressure recovery coefficient of 11.3 and 23.9 percent at total included divergence angles of 12 and 20 degrees respectively were obtained when the value of the inlet integral free-stream scale of turbulence in the flow direction was at least 7.2 times larger than the inlet boundary layer displacement thickness, when the inlet total free-stream turbulence intensity was at least 3.5 percent, and when the axes of upstream rods used to generate turbulence were perpendicular to the flow and parallel to the diverging walls of the diffuser. It is hypothesized that a larger scale of turbulence with the specified eddy axis orientation transmits the free-stream energy to the walls more effectively and, when coupled with large turbulence intensities, are mechanisms which act to decrease the distortion and delay separation within the diffuser.

Hoffmann, J. A.↗
NASA NTRS1981

Factors governing the ratio of inward to outward diffusing flux of satellite ions

The sensitivity of the flux ratio to the uncertainties in the boundary conditions and diffusion coefficient is analyzed. The principal result is that if the diffusion is driven externally, for example, by winds in Jupiter's ionosphere, the inward flux exceeds or is of the same order of magnitude as the outward flux. On the other hand, if the diffusion is driven locally by the centrifugal interchange instability, as suggested by one interpretation of Voyager plasma data, the outward flux can be one or two orders of magnitude greater than the inward flux. Fits to the Voyager in situ plasma torus data obtained through solutions to the transport equations appropriate to wind driven and centrifugally driven diffusion are compared.

Richardson, J. D.↗
NASA NTRS1982

Surface diffusion activation energy determination using ion beam microtexturing

The activation energy for impurity atom (adatom) surface diffusion can be determined from the temperature dependence of the spacing of sputter cones. These cones are formed on the surface during sputtering while simultaneously adding impurities. The impurities form clusters by means of surface diffusion, and these clusters in turn initiate cone formation. Values are given for the surface diffusion activation energies for various materials on polycrystalline Cu, Al, Pb, Au, and Ni. The values for different impurity species on each of these substrates are approximately independent of impurity species within the experimental uncertainty, suggesting the absence of strong chemical bonding effects on the diffusion.

Rossnagel, S. M.↗
NASA NTRS1983

Dynamic Distortion in a Short S-Shaped Subsonic Diffuser with Flow Separation

An experimental investigation of the time varying distortion at the diffuser exit of a subscale HiMAT forebody and inlet was conducted at Mach 0.9 in the Lewis 8 by 6 foot Supersonic Wind Tunnel. A transitory separation was detected within the subsonic diffuser. Vortex generators were installed to eliminate the flow separation. Results from a study of the instantaneous pressure variations at the diffuser exit are presented. The time unsteady total pressures at the diffuser exit are computer interpolated and presented in the form of a movie showing the transitory separation. Limited data showing the instantaneous distortion levels is also presented.

Stumpf, R.↗
NASA NTRS1983

Radial diffusion in Saturn's radiation belts - A modeling analysis assuming satellite and ring E absorption

A modeling analysis is carried out of six experimental phase space density profiles for nearly equatorially mirroring protons using methods based on the approach of Thomsen et al. (1977). The form of the time-averaged radial diffusion coefficient D(L) that gives an optimal fit to the experimental profiles is determined under the assumption that simple satellite plus Ring E absorption of inwardly diffusing particles and steady-state radial diffusion are the dominant physical processes affecting the proton data in the L range that is modeled. An extension of the single-satellite model employed by Thomsen et al. to a model that includes multisatellite and ring absorption is described, and the procedures adopted for estimating characteristic satellite and ring absorption times are defined. The results obtained in applying three representative solid-body absorption models to evaluate D(L) in the range where L is between 4 and 16 are reported, and a study is made of the sensitivity of the preferred amplitude and L dependence for D(L) to the assumed model parameters. The inferred form of D(L) is then compared with that which would be predicted if various proposed physical mechanisms for driving magnetospheric radial diffusion are operative at Saturn.

Hood, L. L.↗
NASA NTRS1983

Status and future of high energy diffuse gamma-ray astronomy

There are two distinctly different high energy diffuse gamma-ray components, one well correlated with broad galactic features and the other apparently isotropic and presumably extragalactic. The observed diffuse galactic high energy gamma radiation is generally thought to be produced in interactions between the cosmic rays and the interstellar matter and photons. It should then ultimately be possible to obtain from the diffuse galactic emission a detailed picture of the galactic cosmic-ray distribution, a high contrast view of the general structure of the galaxy, and further insight into molecular clouds. Two of the candidates for the explanation of the extragalactic diffuse radiation are the sum of emission from active galaxies and matter-antimatter annihilation. A major advancement in the study of the properties of both galactic and extragalactic gamma radiation should occur over the next decade.

Fichtel, C. E.↗
NASA NTRS1983

Dynamic distortion in a short s-shaped subsonic diffuser with flow separation

An experimental investigation of the time varying distortion at the diffuser exit of a subsonic HiMAT forebody and inlet was conducted at Mach 0.9 in the Lewis 8 by 6 foot Supersonic Wind Tunnel. A transitory separation was detected within the subsonic diffuser. Vortex generators were installed to eliminate the flow separation. Results from a study of the instantaneous pressure variations at the diffuser exit are presented. The time unsteady total pressures at the diffuser exit are computer interpolated and presented in the form of a movie showing the transitory separation. Limited data showing the instantaneous distortion levels are also presented. Previously announced in STAR as N83-26838

Stumpf, R.↗
NASA NTRS1982

Electrostatic waves and the strong diffusion of magnetospheric electrons

A comprehensive review of electron pitch angle scattering in the magnetosphere and the plasma waves responsible for it is presented, emphasizing the strong diffusion of diffuse auroral electrons by electrostatic electron cyclotron harmonic waves. The weak diffusion of energetic radiation belt electrons within the plasmasphere is reviewed briefly. Several new suggestions concerning the quasilinear diffusion from and saturation of electrostatic waves are included.

Kennel, C. F.↗
NASA NTRS1983

Diffusion barriers

The choice of the metallic film for the contact to a semiconductor device is discussed. One way to try to stabilize a contact is by interposing a thin film of a material that has low diffusivity for the atoms in question. This thin film application is known as a diffusion barrier. Three types of barriers can be distinguished. The stuffed barrier derives its low atomic diffusivity to impurities that concentrate along the extended defects of a polycrystalline layer. Sacrificial barriers exploit the fact that some (elemental) thin films react in a laterally uniform and reproducible fashion. Sacrificial barriers have the advantage that the point of their failure is predictable. Passive barriers are those most closely approximating an ideal barrier. The most-studied case is that of sputtered TiN films. Stuffed barriers may be viewed as passive barriers whose low diffusivity material extends along the defects of the polycrystalline host.

Nicolet, M. A.↗
NASA NTRS1984

Oxygen diffusion in alpha-Al2O3

Oxygen self diffusion coefficients were determined in single crystal alpha-Al2O3 using the gas exchange technique. The samples were semi-infinite slabs cut from five different boules with varying background impurities. The diffusion direction was parallel to the c-axis. The tracer profiles were determined by two techniques, single spectrum proton activation and secondary ion mass spectrometry. The SIMS proved to be a more useful tool. The determined diffusion coefficients, which were insensitive to impurity levels and oxygen partial pressure, could be described by D = .00151 exp (-572kJ/RT) sq m/s. The insensitivities are discussed in terms of point defect clustering. Two independent models are consistent with the findings, the first considers the clusters as immobile point defect traps which buffer changes in the defect chemistry. The second considers clusters to be mobile and oxygen diffusion to be intrinsic behavior, the mechanism for oxygen transport involving neutral clusters of Schottky quintuplets.

Cawley, J. D.↗
NASA NTRS1984

A new concept for exhaust diffusers of altitude test cells

A new exhaust diffuser concept for jet engine altitude test cells which greatly reduces operating power and cost requirements for exhausters is discussed. The concept utilizes the capture duct as an efficient diffuser only, while evacuating the secondary air via a separate path using an auxiliary suction system. Implementation of the concept would reduce the peak exhauster power requirement during a TF-30 altitude test by 48 percent and the overall exhaust power cost of the test program by 41 percent. The design accommodates various engine sizes and can achieve optimum pressure recovery performance during both A/B and IRP modes of engine operation. The pressure recovery performance of the proposed exhaust diffusers does not deteriorate with increasing cooling air fraction. The disadvantages of the proposed scheme are: increased mechanical complexity of the extended variable geometry diffuser duct and the need for an auxiliary suction system for evacuating cell-cooling air.

Parikh, P. G.↗
NASA NTRS1984

Flow and heat transfer measurements along a cooled supersonic diffuser

An experimental investigtion was conducted to ascertain the mean flowfield, including shock wave structure, separated flow regions, turbulent boundary-layer growth, static pressure variations, wall heat transfer, and shear stresses in a second-throat, axisymmetric, supersonic diffuser with wall cooling. The diffuser inlet Mach number of the heated air flow was 3.76, the stagnation pressure was 6.8 atm, the ratio of wall to total gas temperature was 0.44, and the diffuser discharged to the atmosphere. The complex flowfield involved deceleration and acceleration regions, supersonic and embedded subsonic regions, and strong viscous regions with relatively large radial and axial variations. The heat transfer and wall static pressure distributions were remarkably similar, and heat transfer rates were high locally at oblique shock/turbulent boundary-layer interactions, in the pseudoshock region, and in the separation region in the diffuser outlet section.

Back, L. H.↗
NASA NTRS1984

Low temperature diffusion coefficients in the Fe-Ni and FeNiP systems: Application to meteorite cooling rates

The interdiffusion coefficient of FeNi in fcc taenite (gamma) of Fe-Ni and Fe-Ni-0.2 P alloys was measured as a function of temperature between 600 and 900 C. This temperature range is directly applicable to the nucleation and growth of the Widmanstatten pattern in iron meteorites and metal regions of stony and stony-iron meteorites. Diffusion couples were made from FeNi or FeNiP alloys which ensured that the couples were in the taenite phase at the diffusion temperature. The presence or absence of grain boundary diffusion was determined by measuring the Ni profile normal to the existing grain boundaries with the AEM. Ignoring any variation of interdiffusion coefficient with composition, the measured data was plotted versus the reciprocal of the diffusion temperature. The FeNi data generally follow the extrapolated Goldstein, et al. (1965) data from high temperatures. The FeNiP data indicates that small additions of P (0.2 wt%) cause a 3 to 10 fold increase in the FeNi interdifussion coefficient increasing with decreasing temperature. This increase is about the same as that predicted by Narayan and Goldstein (1983) at the Widmanstatten growth temperature.

Dean, D. C.↗
NASA NTRS1983

Study of controlled diffusion stator blading

Tests were conducted on a high tip speed, highly loaded front compressor stage having low aspect ratio rotor and stator airfoils. The stator airfoils were designed by the controlled diffusion procedure recently developed by P&WA for designing transonic cascade airfoils. The rotor blades consisted of multiple-circular-arc airfoil sections. The stage had a tip speed of 442 m/sec (1450 ft/sec), a hub/tip ratio of 0.597, a rotor aspect ratio of 1.3, and a stator aspect ratio of 1.45. At design speed the rotor-stator stage achieved an adiabatic efficiency of 89.1% at design flow and pressure ratio. Surge margin was 14%. The stage efficiency exceeded the design goal by 0.6 percentage points. The rotor efficiency was 92.4%, exceeding design by 0.3 percentage points. The controlled diffusion stator demonstrated a lower minimum loss over the multiple-circular-arc stator from the root to 70 percent span. A surge diffusion factor of 0.72 was reached at both the rotor tip and the stator root. The NAS3-22008 program demonstrated its intent: high efficiency and loading levels with low aspect ratio blades and the controlled diffusion stator in the unfavorable front stage environment.

Behlke, R. F.↗
NASA NTRS1985

Current understanding of point defects and diffusion processes in silicon

The effects of oxidation of Si which established that vacancies (V) and Si self interstitials (I) coexist in Si at high temperatures under thermal equilibrium and oxidizing conditions are discussed. Some essential points associated with Au diffusion in Si are then discussed. Analysis of Au diffusion results allowed a determination of the I component and an estimate of the V component of the Si self diffusion coefficient. A discussion of theories on high concentration P diffusion into Si is then presented. Although presently there still is no theory that is completely satisfactory, significant progresses are recently made in treating some essential aspects of this subject.

Tan, T. Y.↗