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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Surface effects in high voltage silicon solar cells

The surface of low-resistivity silicon solar cells appears to be a major source of dark diffusion current. This region, consisting of the interface and the adjacent heavily doped layer, therefore, prevents attainment of the high open-circuit voltages expected from these cells. This paper describes the experimental effort carried out to reduce the various contributions of dark current from the surface. Analysis of results from this effort points to means of improving cell voltages by changing processing and structures.

Meulenberg, A.↗
NASA NTRS1984

Catalytic surface effect on ceramic coatings for an aeroassisted orbital transfer vehicle

Surface catalytic efficiencies of glassy coatings were determined from a reaction boundary layer computation and arc-jet data. The catalytic efficiencies of the various coatings examined are discussed in terms of their reaction-rate constants. These constants are a function of the wall temperature (1290 K to 2000 K). In addition, the advantage of a thermal protection system for a bent biconic, aeroassisted orbital transfer vehicle with a low surface catalytic efficiency is discussed.

Steward, D. A.↗
NASA NTRS1988

Heating requirements and nonadiabatic surface effects for a model in the NTF cryogenic wind tunnel

A theoretical study has been made of the severity of nonadiabatic surface conditions arising from internal heat sources within a model in a cryogenic wind tunnel. Local surface heating is recognized as having an effect on the development of the boundary layer, which can introduce changes in the flow about the model and affect the wind tunnel data. The geometry was based on the NTF Pathfinder I wind tunnel model. A finite element heat transfer computer code was developed and used to compute the steady state temperature distribution within the body of the model, from which the surface temperature distribution was extracted. Particular three dimensional characteristics of the model were represented with various axisymmetric approximations of the geometry. This analysis identified regions on the surface of the model susceptible to surface heating and the magnitude of the respective surface temperatures. It was found that severe surface heating may occur in particular instances, but could be alleviated with adequate insulating material. The heat flux through the surface of the model was integrated to determine the net heat required to maintain the instrumentation cavity at the prescribed temperature. The influence of the nonadiabatic condition on boundary layer properties and on the validity of the wind tunnel simulation was also investigated.

Macha, J. M.↗
NASA NTRS1981

Catalytic surface effects experiment on the Space Shuttle

A Space Shuttle experiment planned to measure the surface catalytic efficiency of the baseline high-temperature reusable surface insulation (HRSI) during earth entry is described. A spray-on overcoat, with high catalytic efficiency, will be used as a comparative basis for determining the HRSI surface catalytic efficiency through surface temperature measurement. Catalytic efficiency, as well as aerothermal response of the overcoat, was evaluated, using various models made of HRSI material in arc-plasma flow environments. Agreement is obtained between the measured and computed heating rise of the coated surfaces. Computed predictions for the flight case are presented.

Stewart, D. A.↗
NASA NTRSDate not supplied

Evaluation of CFD for Simulation of High-Supersonic Control Surface Effectiveness

This is the set of slides describing the CFD and wind-tunnel test studying the control surfaces of the CobraMRV concept for entry, descent, and landing on Mars. Difference between the CFD and wind-tunnel results are highlighted with the intent of showing whether CFD can replace wind-tunnel testing in the high supersonic flight regime.

wind tunnel↗
NASA NTRS1980

Surface effects on the microwave backscatter and emission of snow

Measurements were performed with active and passive microwave sensors for both dry and wet snow conditions. A layer of Rayleigh scatterers with irregular surface boundaries is found to be a reasonable model for interpreting passive and active measurements in X- and Ku-bands. It was found that roughness had a significant effect on both backscatter and emission from wet snow; however, only a small effect was noted for dry snow.

Fung, A. K.↗
NASA NTRS1984

Real Surface Effects in Elastohydrodynamic Lubrication

Following a general discussion of real effects in EHL, consideration is given in detail to the role played by stochastic roughness superimposed on the nominal solid boundaries. Particular attention is given to the full-film EHL regime where incipient asperity contact bears a negligible fraction of the load. Flow, from which an averaged Reynolds equation can be formed, is nonetheless modified by the amplitude and texture of the roughness patterns. In describing these effects by means of certain well-defined flow factors, it is found that only two extra parameters are needed - the rms surface height and the ratio of the correlation lengths in the two principal roughness directions. In a lowest order perturbation expansion of these flow factors in powers of the ratio of rms roughness to nominal film thickness, no other properties of the roughness appear. In most cases of practical interest, the factors describing Poiseuille flow are separable into the sum of two single-surface flow factors which means that a combination of a single equivalent rough surface versus an ideal smooth surface can always be found. For flow entrained by slip velocity the factors separate instead into a difference of single-surface factors and it becomes significant which of the two surfaces carries the equivalent roughness. Results are discussed of some applications of the averaged Reynolds equation based on the flow factor method to the EHL line contact problem. Finally, the partial EHL regime is considered where comparable load fractions are carried by the hydrodynamic film and by incipient mechanical contact. An extension of the method into this regime by combining it with asperity contact models appears most encouraging.

John H Tripp↗
NASA NTRS1986

Surface effects on phase distributions of a fast-quenched miscibility gap type system - Succinonitrile-water

If a binary homogeneous melt is cooled into an immiscible region, the newly formed second phase will generally have a density different from the parent phase, and will separate readily by sedimentation. Observation of solidification processes in microgravity indicates that outside of sedimentation, at least two other important effets can separate the phases: (1) preferential wetting, and (2) thermal migration of second-phase droplets due to interfacial tension gradients. The latter effect would drive the minority phase along the thermal gradient toward the hottest part (assuming the interfacial tension decreases with increasing temperature), which is usually away from the crucible wall. On the other hand, if the minority phase preferentially wets the crucible, a minority phase layer which thickens as initial solution compositions approach critical, will form adjacent to the solid surface and remain in the coldest region of the ingot. This study presents compelling preliminary evidence that these two effects do exist and that they compete with one another. However, the temperature dependence of preferential wetting below T(c) for the current system of study is, as yet, undetermined. These effects are sensitive to the initial concentration of a hypermonotectic solution cooling through a miscibility gap.

Frazier, D. O.↗