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At least 991 records · Page 55

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NASA NTRS1982

Assessing solar energy and water use efficiencies in winter wheat

The water use and solar energy conversion efficiencies of two cultivars of winter wheat (Triticum aestivum L., vars, Centurk and Newton) planted at three densities, were examined during a growing season. Water use, based on soil moisture depletion, was the lowest under the light, and the highest under the heavy planting densities of both cultivars. Water use efficiency of medium and heavy planting densities were greater than the light planting densities in both cultivars. The canopy radiation extinction coefficients of both cultivars increased with increases in planting density. Efficiency of operation interception of photosynthetically active radiation by both cultivars improved from the time of jointing until anthesis, and then decreased during senescence. The efficiency of the conversion of intercepted radiation to dry matter (biochemical efficiency) decreased throughout the growing season both cultivars. The interception, biochemical, and photosynthetic efficiencies improved as planting density increased.

Asrar, G.↗

NASA NTRS1983

Air Force Logistics Command (AFLC) solar thermal plant

The plant proved its capability to deliver the desired energy product in a USAF industrial environment. The collector proved capable of energy conversion at insolation levels up to 25% below design minimum. The plant and the project were negatively affected by severe winter weather, with total insolation during the test period 60 percent less than the expected value. Environmental effects reduced plant availability to 55 percent. Only five, minimally good operating days were experienced during the test period. The subsequent lack of performance data prohibits the drawing of general conclusions regarding system performance. System operability was rated generally high. The only inhibiting factor was the difficulty in procuring replacement parts for rapid repair under USAF stockage and procurement policies. No inherently serious system failures were recorded, although a thermostatic valve malfunction in the freeze protection system ultimately took 30 days to repair.

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NASA NTRS1982

Layered transition metal thiophosphates /MPX3/ as photoelectrodes in photoelectrochemical cells

Layered crystals of the transition metal thiophosphates were synthesized and characterized for use as photoelectrodes in photoelectrochemical cells. Crystals incorporating tin and manganese show n-type response while those with iron and nickel show p-type response. These materials have a measured indirect bandgap of about 2.1 eV. They show ability to photoelectrolyze water in acid solutions with onset potentials which change in a Nernstian way as the PH of the solution changes. The onset potential is near zero volts versus a saturated calomel electrode at pH 2. At n-type crystals, oxygen could be evolved upon irradiation at underpotentials of 850 mV and at p-type crystals, hydrogen could be evolved at underpotentials of 400 mV, indicating a net gain in energy conversion. All crystals were unstable in basic solution. Liquid junction photovoltaic cells in iodide-triiodide acid solution using these layered materials were also constructed and found to have low efficiences.

Byvik, C. E.↗

NASA NTRS1983

Diagnostic analysis and spectral energetics of a blocking event in the GLAS climate model simulation

A synoptic and spectral analysis of a blocking event is presented, with attention given to the temporal evolution, maintenance, and decay of the block. The GLAS numerical climate model was used to generate a blocking event by the introduction of SST anomalies. Wavenumbers 2 and 3 became stationary around their climatological locations, and their constructive interference produced persistent blocking ridges over the west coast of North America and the other over western Europe. Time variations of the kinetic and potential energies and energy conversions during the blocking were performed. Spectrally filtered Hovmoller diagrams were developed for the winter of 1976-77, and showed that long waves were stationary over most of the interval, which featured severe weather conditions.

Chen, T.-C.↗

NASA NTRS1983

Comparison of broadband noise mechanisms, analyses, and experiments on helicopters, propellers, and wind turbines

Experimental data on broadband noise from airfoils are compared, together with analytical methods, in order to identify the mechanisms of noise emission. Rotor noise is categorized into discrete frequency, impulsive, and broadband components, the last having a continuous spectrum originating from a random source. The results of computer simulations of different rotor blade types which produce broadband noise were compared with experimental data and among themselves in terms of predictions of the spectra obtained. Consideration was given to the overall sound pressure level, unsteady turbulence forces, rotational forces, inflow turbulence, self-generated turbulence, and turbulence in the flow. Data are presented for a helicopter rotor and light aircraft propeller. The most significant source was found to be inflow turbulence induced lift fluctuations in helicopter rotors and boundary layer trailing edge noise on large wind energy conversion systems

George, A. R.↗

NASA NTRS1982

Gain-enhanced free-electron laser with an electromagnetic pump field

The feasibility of enhancing the gain for the free electron laser (FEL) with an electromagnetic (EM) pump field has been considered. The enhancement is provided by reacceleration of the electrons in the interaction region by means of a static, axial electric field. A FEL utilizing a low energy electron beam and a wiggler magnet with a periodicity on the order of 1 cm would produce far infared (FIR) radiation with wavelengths on the order of a few hundred microns. The use of the FIR radiation as the pump field in a two-stage FEL is envisioned to obtain visible radiation with a low energy electron beam. A summary is provided regarding the theory and equations of motion for the EM-pumped FEL. The derived relations are applied to the second stage of such a two-stage FEL. The obtained equations have been incorporated into a computer code which has been used to calculate laser gain and energy conversion efficiency.

Hiddleston, H. R.↗

NASA NTRS1983

Long-range surface plasmons in electrode structures

Surface polaritons guided by symmetric double metal film structures are analyzed, with particular attention given to the attenuation of the two long-range modes that occur. It is found that long-range surface plasmon polariton modes do exist for double electrode structures over a limited range of material parameters. Guided by thin metal electrodes, surface plasmon polaritons can achieve millimeter plus propagation distances in the near infrared. It is pointed out that if the slab is electrooptic, then very low voltages will be needed to manipulate the waves. The fact that long-range modes exist simultaneously with junction tunnel plasmons may be of use in providing directional radiation from light-emitting junctions or the inverse process of light to electrical energy conversion.

Stegeman, G. I.↗

NASA NTRS1983

Plasma-enhanced CVD silicon nitride antireflection coatings for solar cells

Multilayer plasma-enhanced chemical vapor deposition (PECVD) silicon nitride antireflection coatings were deposited on space quality silicon solar cells. Preliminary experiments indicated that multilayer coatings decreased the total reflectance of polished silicon from 35 percent to less than 3 percent over the spectral range 0.4-1.0 micron. The solar cell energy conversion efficiency was increased from an average of 8.84 percent to an average of 12.63 percent.

Johnson, C. C.↗

NASA NTRS1982

Picosecond kinetics of excited state decay processes in internally hydrogen-bonded polymer photostabilizers

A construction of economically practical solar energy conversion devices could be based on the employment of inexpensive, visible-radiation transparent, durable, light-fast materials. Difficulties arise in connection with the availability of such materials. Plastics which are not particularly susceptible to solar ultraviolet degradation are, in general, expensive, while less expensive optically transparent films are susceptible to deterioration when exposed to solar radiation. However, techniques are known for protecting polymers from photochemical degradation. According to these techniques, the composition or structure of polymeric material is modified by incorporation of photostabilizers. Two classes of ultraviolet absorbers are used as commercial photostabilizers. These classes include 2-hydroxybenzophenone (HB) and 2-(2-prime -hydroxyphenyl)benzotriazole (HPB). The present investigation is concerned with the results of spectroscopic and kinetics measurements related to the study of the mechanism of excited-state relaxation of polymer photostabilizers in the class HB and HPB.

Huston, A. L.↗

NASA NTRS1981

JPL highlights, 1981

Deep space exploration, energy and energy conversion technology, Earth orbital applications, information systems and space technology development, and technology applications are discussed.

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NASA NTRS1983

Thermal conductivity behavior of boron carbides

Knowledge of the thermal conductivity of boron carbides is necessary to evaluate its potential for high temperature thermoelectric energy conversion applications. The thermal diffusivity of hot pressed boron carbide B/sub 1-x/C/sub x/ samples as a function of composition, temperature and temperature cycling was measured. These data in concert with density and specific heat data yield the thermal conductivities of these materials. The results in terms of a structural model to explain the electrical transport data and novel mechanisms for thermal conduction are discussed.

Wood, C.↗

NASA NTRS1984

Photovoltaic energy systems: Program summary fiscal year 1983

An overview of government funded activities in photovoltaic energy conversion research is given. Introductory information, a list of directing organizations, a list of acronyms and abbreviations, and an index of current contractors are given.

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NASA NTRS1984

The Base Engine for Solar Stirling Power

A new concept in Stirling engine technology is embodied in the base engine now being developed at Stirling Thermal Motors, Inc. This is a versatile energy conversion unit suitable for many different applications and heat sources. The base engine, rated 40 kW at 2800 RPM, is a four-cylinder, double-acting variable displacement Stirling engine with pressurized crankcase and rotating shaft seal. Remote-heating technology is incorporated with a stacked-heat-exchanger configuration and a liquid metal heat pipe connected to a distinctly separate combustor or other heat source. High efficiency over a wide range of operating conditions, long life, low manufacturing cost and low material cost are specifically emphasized. The base engine, its design philosophy and approach, its projected performance, and some of its more attractive applications are described.

Meijer, R. J.↗

NASA NTRS1984

Theoretcial studies of solar-pumped lasers

A method of pumping a COhZ laser by a hot cavity was demonstrated. The cavity, heated by solar radiation, should increase the efficiency of solar pumped lasers used for energy conversion. Kinetic modeling is used to examine the behavior of such a COhZ laser. The kinetic equations are solved numerically vs. time and, in addition, steady state solutions are obtained analytically. The effect of gas heating filling the lower laser level is included. The output power and laser efficiency are obtained as functions of black body temperature and gas ratios (COhZ-He-Ar) and pressures. The values are compared with experimental results.

Harries, W. L.↗

NASA NTRS1984

18-percent efficient terrestrial silicon solar cells

Silicon solar cells are described which operate at energy conversion efficiencies in excess of 18 percent under standard terrestrial test conditions (AM1.5, 100 mW/sq cm, 28 C). These are believed to be the most efficient silicon cells reported to date. The high efficiency is a result of the combination of high open-circuit voltage due to the careful attention paid to passivation of the top surface of the cell; high fill factors due to the high open-circuit voltage and low parasitic resistance losses; and high short-circuit current due to the use of shallow diffusions, a low grid coverage, and an optimized double-layer antireflection coating.

Blakers, A. W.↗

NASA NTRS1985

Spectrophotovoltaic Power Generation

Optical Components of spectrophotovoltaic system concentrate light from Sun and redirect short-wavelength portion of spectrum to solar cell having large gap in energy band (gallium arsenide cell). Longer-wavelength portion of spectrum passes through beam splitter to cell with smaller gap in energy band (silicon band). Available energy in Sunlight thus exploited more fully and, improvements in energy-conversion efficiency possible.

Knowles, G.↗

NASA NTRS1984

Advanced and Nontraditional Concepts Working Group Report

Advanced and nontraditional concepts relating to future space power requirements were examined with special emphasis on the requirements for the space station. Key findings in the following ares are outlined: dynamic radiation concepts, space nuclear reactors, energy conversion cycles, beam power transmission, electrodynamic tethers and advanced photovoltaics.

Hertzberg, A.↗

NASA NTRS1984

Resident research associateships. Postdoctoral and senior research awards: Opportunities for research at the Jet Propulsion Laboratory

Opportunities for research as part of NASA-sponsored programs at the JPL cover: Earth and space sciences; systems; telecommunications science and engineering; control and energy conversion; applied mechanics; information systems; and observational systems. General information on applying for an award for tenure as a guest investigator, conditions, of the award, and details of the application procedure are provided.

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