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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Experimental investigation of reactive turbulent recirculating jet mixing in a dump

A ducted, subsonic, hydrogen air turbulent jet mixing flowfield was investigated, both with and without combustion. The geometric configuration was representative of a sudden expansion or dump combustor, with a central air jet surrounded by a low velocity hydrogen stream at an overall equivalence ratio of 0.12. The ratio of the duct to inner nozzle diameter was 2.5. Radial distributions of mean axial and radial velocity, axial and radial turbulent intensity, velocity cross correlation, gas composition, static temperature and total pressure, as well as axial distributions of wall static pressure, were obtained for axial stations from zero to six duct diameters from the combustor entrance. The data indicate that mixing is slower in the chemically reactive flow field than in the nonreactive flow field, and that the presence of combustion has a significant effect on the size and location of the recirculation zone within the mixing duct.

Smith, G. D.↗
NASA NTRS1981

Forebody and base region real gas flow in severe planetary entry by a factored implicit numerical method. II - Equilibrium reactive gas

The factored-implicit, gas-dynamic algorithm has been adapted to the numerical simulation of equilibrium reactive flows. Changes required in the perfect gas version of the algorithm are developed, and the method of coupling gas-dynamic and chemistry variables is discussed. A flow-field solution that approximates a Jovian entry case was obtained by this method and compared with the same solution obtained by HYVIS, a computer program much used for the study of planetary entry. Comparison of surface pressure distribution and stagnation line shock-layer profiles indicates that the two solutions agree well.

Davy, W. C.↗
NASA NTRS1982

Deposition of reactively ion beam sputtered silicon nitride coatings

An ion beam source was used to deposit silicon nitride films by reactively sputtering a silicon target with beams of Ar + N2 mixtures. The nitrogen fraction in the sputtering gas was 0.05 to 0.80 at a total pressure of 6 to 2 millionth torr. The ion beam current was 50 mA at 500 V. The composition of the deposited films was investigated by auger electron spectroscopy and the rate of deposition was determined by interferometry. A relatively low rate of deposition of about 2 nm. one-tenth min. was found. AES spectra of films obtained with nitrogen fractions higher than 0.50 were consistent with a silicon to nitrogen ratio corresponding to Si3N4. However the AES spectra also indicated that the sputtered silicon nitride films were contaminated with oxygen and carbon and contained significant amounts of iron, nickel, and chromium, most probably sputtered from the holder of the substrate and target.

Grill, A.↗
NASA NTRS1982

Chemorheology of reactive systems: Finite element analysis

The equations which govern the nonisothermal flow of reactive fluids are outlined, and the means by which finite element analysis is used to solve these equations for the sort of arbitrary boundary conditions encountered in industrial practice are described. The performance of the computer code is illustrated by several trial problems, selected more for their value in providing insight to polymer processing flows than as practical production problems. Although a good deal remains to be learned as to the performance and proper use of this numerical technique, it is undeniably useful in providing better understanding of today's complicated polymer processing problems.

Douglas, C.↗
NASA NTRS1985

Monitoring of Reactive Atmospheric Species

Reactive atmospheric species produced and detected to provide reference spectra. Compact device insensitive to scattered light and has low power consumption.

Webster, C. R.↗
NASA NTRS1985

Dual-band reactively loaded microstrip antenna

A previously derived theory is applied to a microstrip antenna with a reactive load to produce a dual-band radiator. A model consisting of a rectangular patch radiator loaded with a variable length short-circuited coaxial stub was investigated experimentally. Comparisons of theoretical predictions and experimental data are made for the impedance and resonant frequencies as a function of the position of the load, the length of the stub, and the characteristic impedance of the stub.

Richards, W. F.↗
NASA NTRS1985

Effect of reactive intermediates on the propagation of turbulent premixed flames

The most simple version of the Bray and Libby model of turbulent flame propagation has been extended to include a two-step reaction mechanism in which reactants decompose into reactive intermediates which then form products. A transport equation for the joint pdf of intermediate and product concentrations was derived, the pdf parameterized, and transport equations for the parameters obtained. The one-dimensional concentration equations were then solved for the parameters of the pdf and the turbulent kinetic energy. Flame speed and angle are recovered as eigenvalues of the problem. The results show the essential features observed in experiments. The product pdf is composed of peaks at zero and unity product concentration, with a continuous structure representing partially reacted gas. The intermediates pdf has a peak at zero concentration and a broad bell-shaped distribution at nonzero concentration, representing partially reacted gas. The results also show the effect of partitioning of energy release on the flame thickness and speed.

Azzazy, M.↗
NASA NTRS1985

Automatic Processing of Reactive Polymers

A series of process modeling computer codes were examined. The codes use finite element techniques to determine the time-dependent process parameters operative during nonisothermal reactive flows such as can occur in reaction injection molding or composites fabrication. The use of these analytical codes to perform experimental control functions is examined; since the models can determine the state of all variables everywhere in the system, they can be used in a manner similar to currently available experimental probes. A small but well instrumented reaction vessel in which fiber-reinforced plaques are cured using computer control and data acquisition was used. The finite element codes were also extended to treat this particular process.

Roylance, D.↗
NASA NTRS1985

Dual-band microstrip antennas with monolithic reactive loading

The design and experimental measurement of a dual-band, monolithic microstrip antenna is presented. The structure utilises a short-circuited length of microstrip transmission line to provide reactive loading and, thereby, retains the low-profile characteristic of a normal microstrip patch radiator.

Davidson, S. E.↗
NASA NTRS1985

Evaluation of a catalytic reduction technique for the measurement of total reactive odd-nitrogen NOy in the atmosphere

The suitability of a technique for the measurement of total reactive odd-nitrogen NOy-containing species in the atmosphere has been examined. In the technique, an NOy component species, which may include NO, NO2, NO3, HNO3, peroxyacetyl nitrate, and particulate nitrate, are catalytically reduced by CO to form NO molecules on the surface of a metal converter tube, and the NO product is detected by chemiluminescence produced in reaction with O3. Among the catalysts tested in the temperature range of 25-500 C, Au was the preferred catalyst. The results of laboratory tests investigating the effects of pressure, O3, and H2O on NOy conversion, and the possible sources of interference, have shown that the technique is suitable for atmospheric analyses. The results of a test in ambient air at a remote ground-based field site are included.

Fahey, D. W.↗
NASA NTRS1986

Low-temperature deposition of low resistivity ZnSe films by reactive sputtering

The use of reactive dc magnetron cosputtering of Zn and the dopant In in an H2Se/Ar gaseous mixture is described. It is observed that initial deposition using pure Zn targets produced yellowish transparent ZnSe films on glass with a film resistivity of 10 to the 8th ohms cm and deposition using a Zn target doped with a fixed 1 percent of In produced ZnSe films with resistivities of about 10,000 ohms cm. The improvement of film conductivity by optimizing the In content in the ZnSe films is discussed; the ZnSe resistivity dependence on In flux is studied. Optical absorption/transmission measurements reveal a photon energy band gap of 2.65 eV at room temperature and X-ray diffraction show highly oriented polycrystalline films on glass with the c axis parallel to the plane of the film. Compositional analysis was performed and the Zn/Se ratio is measure as 48.8/49.0 with an In concentration of 1.16 percent. ZnSe films deposited on glass and conducting SnO2-coated glass substrates with a resistance of 20 ohms cm and a substrate temperature of 120 C have been fabricated.

Stirn, R. J.↗
NASA NTRS1986

Highly conducting ZnSe films by reactive magnetron sputtering

This paper presents the results of an effort to deposit high-conductivity ZnSe on glass and conducting SnO2-coated glass substrates by reactive magnetron sputter deposition, using pure metal sputter targets of Zn and dopants such as In, Ga, and Al. Clear yellow ZnSe films were successfully obtained. By using substrate temperatures as low as 150 C, cosputtered dopants, and sputter parameters and H2Se injection rates which maximize the Zn-to-Se ratio in the films, ZnSe bulk resistivities have been lowered by up to seven orders of magnitude, reaching values as low as 20 ohm cm. The most effective dopant to data has been In, cosputtered with Zn in amounts leading to In atomic concentrations as high as 1.4 percent. Atomic-absorption measurements show an average 49.9/48.9 ratio of Zn to Se.

Nouhi, A.↗
NASA NTRS1987

Microwave surface resistance of reactively sputtered NbN thin films

The surface resistance of niobium nitride (NBN) thin films was measured at 7.78 and 10.14 GHz in the temperature range of 1.5 to 4.2 K. The films were reactively sputtered on sapphire substrates to a thickness of approximately 1 micron. The surface resistance was determined by measuring the quality factor (Q) of the TE sub 011 mode of a lead-plated copper cavity where the NbN served as one end-cap of the cavity.

Bautista, J. J.↗
NASA NTRS1986

Synthesis of diamino terminated poly(arylene ether sulfone) oligomers as reactive intermediates in copolymer systems

Reactive diamino terminated oligomers of pre-determined molecular weights can be prepared by either of two synthetic routes depending upon the compound used to introduce the amine functionality. After characterization by spectroscopic and thermal methods, these oligomers can be used in several post-reactions to yield novel block and segmented copolymer systems. A potential application for these poly(arylene ether sulfone) oligomers exists in the curing or co-curing of epoxy resins for improving toughness. They can also be used to prepare toughened bismaleimide systems as well as producing copolymers with improved solvent resistance, especially with respect to chlorinated solvents.

Jurek, M. J.↗
NASA NTRS1987

Preliminary results on CuInSe2/ZnSe solar cells using reactively sputter-deposited ZnSe

In this paper preliminary results on CuInSe2/ZnSe thin film heterojunction photovoltaic devices are presented. High-conductivity ZnSe films were reactively sutter-deposited onto CuInSe2 films and overcoated with ZnO to reduce the sheet resistance. The highest short-circuit current density, as determined from a spectral response weighted for air mass 1.5 global insolation, was 37.4 mA/sq cm. The highest pen-circuit voltage observed was 430 mV.

Nouhi, A.↗
NASA NTRS1986

Reactivity of seventeen- and nineteen-valence electron complexes in organometallic chemistry

A guideline to the reactivity of 17- and 19-valence electron species in organometallic chemistry is proposed which the authors believe will supersede all others. The thesis holds that the reactions of 17-electron metal radicals are associatively activated with reactions proceeding through a 19-valence electron species. The disparate reaction chemistry of the 17-electron metal radicals are unified in terms of this associative reaction pathway, and the intermediacy of 19-valence electron complexes in producing the observed products is discussed. It is suggested that related associatively activated pathways need to be considered in some reactions that are thought to occur by more conventional routes involving 16- and 18-electron intermediates. The basic reaction chemistry and electronic structures of these species are briefly discussed.

Stiegman, Albert E.↗
NASA NTRS1988

Dual-Band Microstrip Antenna With Reactive Loading

Effective but bulky coaxial stub replaced. Short-circuited microstrip transmission line serves as reactive loading element for microstrip antenna. Constructed integrally with stripline radiating element, shorted line preserves low microstrip profile and enables tuning of antenna for two-band operation.

Davidson, Shayla E.↗