Showing papers in "Journal of Energy in 1977"

MHD power generation with fully ionized seed

Abstract: Recovery of power density in the regime of fully ionized seed has been demonstrated experimentally using an MHD disk generator with the effective Hall parameter up to 5.0 when the seed was fully ionized. The experiments were conducted with a shock-heated and potassium-seeded argon plasma under the following conditions: stagnation gas pressure = 0.92 atm, stagnation gas temperature = 2750 K, flow Mach number = 2.5, and seed fraction = 1.4x 10 ~ 5. Measurements of electron-numb er density and spectroscopic observations of both potassium and argon lines confirmed that the recovery of power output was due to the reduction of ionization instability. This fact indicates that the successful operation of a disk generator utilizing nonequlibrium ionization seems to be possible and that the suppression of ionization instability can also provide higher adiabatic efficiency. Furthermore, the lower seed fraction offers technological advantages related to seed problems.

Measurement and Calculation of Furnace-Flow Properties

Abstract: Measurements of the three components of mean velocity, the corresponding normal stresses, mean temperature, and wall heat flux are reported in a model furnace; they were obtained with a coaxial burner with a 20° quarl angle and swirl numbers of 0.3 and 0.5. Particular attention is devoted to the influence of the profiles in the plane of the burner exit; it is shown, for example, that combustion results in large increases in the values of maximum positive and negative velocity in the near-burner region and that the two swirl numbers result in significantly different profiles of all the measured flow properties. The variations in local furnace properties, including the wall heat flux, are quantified for the two swirl numbers and shown to agree, in general terms, with previous calculations; the location of maximum heat flux, for example, is significantly closer to the burner exit for the larger swirl number. Calculations, obtained from the numerical solution of conservation equations in differential form, are presented and compared with the measurements. Particular attention is devoted to the uncertainties associated with density fluctuation correlation and with the specification of a probability density distribution of scalar fluctuations. An attempt is made to quantify the precision with which calculations of furnace flow properties can presently be calculated.

Particle Size and Velocity Measurement by Laser Anemometry

Abstract: The use of a forward scattering Laser Anemometer system for the measurement of particle diameters larger than the fringe spacing is investigated. A systematic calibration experiment demonstrates a direct relationship between signal amplitude and particle diameter for transparent particles between 30 microns and 240 microns in diameter. A light scattering analysis confirms these measurements and indicates how the range of particles which can be measured using the peak (mean) signal depends on the optical arrangement and particle properties. On the basis of this work a real time Laser Anemometer signal processor is modified so that the peak of the mean of each signal can be measured. A method of correcting data for the effect of particles which do not go through the center of the measurement volume is derived. Good agreement is found between particle size distributions measured in sprays by using the Laser Anemometer and size distributions measured by collecting the particles on a slide and using an image analysis computer.

Engineering development status of the Darrieus wind turbine

Abstract: This paper describes the aerodynamic, structural, and system considerations required for the engineering development of the Darrieus turbine. Particular emphasis is given to the necessity for close interaction of these three areas and their effects on energy costs. Currently available experimental data and analytical methods are discussed together with specific results and trends which have been obtained to date. 65 references.

Swirling Flow Combustion

Abstract: Tests in a combustion centrifuge demonstrated that the normal progression from laminar flamespeeds of about 0.3 m/s (in hydrocarbon-air mixtures) to turbulent flamespeeds of up to 6.1 m/s can be advanced to a third stage, where flamespeeds in excess of 19 m/s were measured. A theory explaining how centrifugal-force-enhanced buoyancy produces the increased flamespeeds was developed. This theory was applied to the results of a combustion centrifuge experiment, the design of a 38-cm-dia afterburner research rig, and eventually to the design of a full-scale afterburner, which was tested on a modern turbofan engine. The experimental results confirmed the theory and indicate a potential 2 percent reduction in specific fuel consumption. 16 figures.

Diagnostic Methods in Combustion MHD Flows

Abstract: Methods for the determination of the important properties of combustion MHD channel flows are reviewed, with emphasis on spatially resolved measurements interior to the flow that have actually been applied to combustion MHD systems, or that have reasonable promise of being so applied. The principal parameters whose measurement is discussed include the average velocity and turbulence intensity, the temperature, the electrical conductivity and electron concentration, and, for pulverized fuel, the slag particle concentration and size distribution. Various techniques are illustrated by measurements performed at the High Temperature Gas-dynamics Laboratory, Stanford. The merits of various methods, including both material probes and nonintrusive techniques, are assessed with respect to accuracy, spatial resolution, temporal resolution and relative ease of application. 117 references.

Characteristic Time Emissions Correlations and Sample Optimization: GT-309 Gas Turbine Combustor

Abstract: A characteristic time model for pollutant formation (combustion inefficiency and NO/sub x/), previously quantified for axisymmetric turbulent diffusion flame combustion of a liquid fuel spray, is extended to a conventional gas turbine combustor. The model predicts the effect of changes in both combustor inlet conditions and combustor geometry on exhaust emissions and is used to demonstrate the design of a low-NO/sub x/ burner of the GT-309 class; other important design criteria such as flame stabilization are not included, however. 8 figures, 3 tables.

Characteristic time emissions correlations: the T-63 helicopter gas turbine combustor

Abstract: Gaseous pollutant emissions from conventional diffusion flame T-63 combustors are correlated as functions of combustor geometry and inlet conditions in terms of a characteristic time model. New aspects of the present study show partial inclusion of effects of alternate fuel properties, suggest a generalization of the Lipfert NO/sub x/ correlation, compare advanced film injected and prevaporizing/premixing with conventional combustors, and demonstrate a quantitative relation between emissions of unburned hydrocarbons and CO. 9 figures, 4 tables.

Improved theory of the silicon p-n junction solar cell

Abstract: The theory of the silicon p-n junction solar cell in its present state is inadequate to explain the observed fall-off in power output and open-circuit voltage with increasing substrate doping. The present work removes this deficiency by incorporating into the theory the generation-recombination dark current in the junction appropriately corrected for the thermal counterpart of the Franz-Keldysh effect. The light generated short-circuit current is calculated from the known solar spectrum and band gap and from estimates of reflection, absorption, obstruction, transmission, and recombination losses. The improved theory permits a detailed quantitative explanation of the experimentally measured current-voltage characteristics of conventional, violet, and nonreflective silicon solar cells for beginning-of-life and end-of-life performance in a space environment and as a function of thickness. It also explains the temperature coefficient of the short-circuit current, of the open-circuit voltage, and of the power output of these three types of cell. Finally, the theory explains the observed fall-off in power output and open-circuit voltage with increasing substrate doping and predicts the maximum efficiency to be expected in state-of-the-art material for optimized cell thickness and doping for both beginning-of-life and end-of-life situations. 34 references.

Entry region heat transfer in rotating radial tubes.

Abstract: An experimental study of the effect of rotation on the entrance region heat transfer inside straight radially aligned circular tubes is presented. Average coolant passage Nusselt numbers were determined for passage length-to-diameter ratios of 6, 12, and 24 over ranges of radially outward air flows and rotational speeds. Results are presented in terms of the ratio of rotating-to-s tationary heat transfer. Comparisons are made with the rotational heat-transfer enhancement expected for fully developed flow conditions with rotation. The present results, conducted in the absence of entry swirl, show that only a small rotational effect on heat transfer can be expected for relatively short cooling passages.

Heat pipe reactors for space power applications

Abstract: A family of heat pipe reactors design concepts has been developed to provide heat to a variety of electrical conversion systems. Three power plants are described that span the power range 1-500 kWe and operate in the temperature range 1200-1700 K. The reactors are fast, compact, heat-pipe cooled, high-temperature nuclear reactors fueled with fully enriched refractory fuels, UC-ZrC or UO2. Each fuel element is cooled by an axially located molybdenum heat pipe containing either sodium or lithium vapor. Virtues of the reactor designs are the avoidance of single-point failure mechanisms, the relatively high operating temperature, and the expected long lifetimes of the fuel element components.

Survey of selective absorber coatings for solar energy technology

Abstract: Solar photothermal electric powerplants are being conceptualized that will produce turbine-generated electricity from fluids heated to high temperatures by concentrated sunlight. A key research objective is to design coatings for the receiver optics that are highly absorbing in the visible out to about two microns but are highly reflecting (therefore have low emittance) beyond two microns. This dual requirement has generated a research program in composite materials coatings. Past accomplishments and promising new materials are described.

Perspectives on Satellite Solar Power

Abstract: The potential for solar energy conversion is reviewed and the rationale for solar energy conversion in geosynchronous orbit is outlined The evolution of the concept of the Satellite Solar Power Station (SSPS) is presented and the technology options for converting solar energy in space, transmitting microwave power and converting it on earth are summarized The development of the design concept of the SSPS based on photovoltaic and solar thermal conversion is examined and salient characteristics are provided The details of microwave power generation, beam transmission, and conversion to DC at the receiving antenna on earth are discussed The requirements for a space transportation system, orbital construction and assembly, maintenance and operations are reviewed The environmental impacts of SSPS operations, such as stratospheric pollution by space vehicle exhaust products and of the microwave beam, including atmospheric attenuation and scattering, ionospheric propagation, and microwave biological effects, are highlighted Economic and social issues are considered Development programs for the SSPS are outlined; critical technology areas are listed and the potential contributions of the SSPS to meet future energy demands and the industrialization of space are projected

Selected wind tunnel test results for the Darrieus wind turbine

Abstract: Five blade configurations of a 2-m-diam Darrieus wind turbine have been tested in the Vought Corporation 46-x61-m (15-x20-ft) Low-Speed Wind Tunnel Rotor solidity, Reynolds number, and freestream velocities tested were in the following ranges: solidity, 13-30%; Reynolds number, 1-3 x l O 5 ; freestream velocity, 7-11 m/s The airfoil selection for all configurations was NACA 0012 The parameters measured were rotor torque, rotor rotational speed, and tunnel conditions Data are presented in the form of power coefficient as a function of tip-speed ratio along with comparative results from an analytical model

Electron concentration measurements in combustion MHD flows by submillimeter laser interferometry

Abstract: Methods for the determination of electron concentration are discussed as an alternative to, or a check on, measure of electrical conductivity and temperature for characterizing plasma properties in combustion MHD flows. In particular, the interferometric method of determining the free electron concentration is analyzed, and its potential assessed. A submillimeter laser Michelson interferometer is described and preliminary measures of electron concentration in the free jet of the Stanford M-8 combustor are reported. It appears that accurate measurements of the path integral of electron concentration can be made which give good agreement with values calculated from Saha equilibrium at temperatures measured by the line reversal technique. A measure of the electron mobility also may be obtained, and hence the electrical conductivity may be derived by a single nonintrusive measurement technique which is applicable to ash-laden flows.

Two-Dimensional Analysis of a Flat-Plate Solar Collector

Abstract: The main objective of this study was to develop a two-dimensional theoretical model of a flat-plate solar collector which later could be used for optimizing the configuration parameters based on least cost per unit of energy absorbed. A rational and systematic two-dimensional analysis of a flat-plate solar collector is presented. By means of this model, for any given set of operating conditions, the instantaneous collector performance can be evaluated without having to assume average plate temperature. The results of this model vary significantly from those of the traditional lumped models, which as one should expect, give higher efficiencies in certain flow regimes. This may prove important in choosing physical dimensions of the collector for many applications.

Isotope Enrichment by Aerodynamic Means: A Review and Some Theoretical Considerations

Abstract: Aerodynamic separation processes are characterized as those involving diffusion of disparate masses driven either by a pressure gradient or by inertia effects. Seven aerodynamic schemes are identified for the separation of isotopes and their salient features discussed briefly. Numerical methods are developed for analyzing the flowfields associated with those devices. The methods consist of a finite-difference solution of the ternary gas mixture equations and two Monte Carlo numerical simulation techniques. A test case is employed to compare the three techniques. The tracer-field Monte Carlo method is then used to evaluate the separation characteristics of two of the seven aerodynamic devices. 12 figures, 4 tables.

Reduced truck fuel consumption through aerodynamic design

Abstract: Full-scale fuel consumption and drag tests were performed on a conventional cab-over-engine tractor-trailer combination and a version of the same vehicle with significant forebody modifications. The modified configuration had greatly increased radii on all front corners and edges of the tractor and a smooth fairing of the modified tractor top and sides extending to the trailer. Concurrent highway testing of the two configurations showed that the modified design used 20% to 24% less fuel than the baseline configuration at 88.5 km/hr (55 mph) with near-calm wind conditions. Coastdown test results showed that the modified configuration reduced the drag coefficient by 0.43 from the baseline value of 1.17 at 88.5 km/hr (55 mph) in calm wind conditions.

Evaluating Characteristic Time Emissions Predictions for Three Vehicular Gas Turbine Combustors

Abstract: The standard GT-309 combustor and two modified versions were tested in a flow-rig over the range of steady-state conditions simulating combustor operation in a GT-309 regenerative gas turbine engine. Based on measured emissions of the standard combustor, a characteristic time model developed by Mellor was used to predict the carbon monoxide, total oxides of nitrogen, and total hydrocarbons emissions for the two modified combustors. The total oxides of nitrogen emissions were predicted to within one standard deviation for all conditions. The carbon monoxide emissions were not usually predicted within one standard deviation, and the predicted and experimental trends were conflicting. The predicted total hydrocarbons emissions suffered the same inaccuracy. However, the modified combustors did exhibit reduced emissions. The strong dependence of carbon monoxide emissions from the standard combustor on atomizing-air pressure drop at low engine-power conditions was successfully correlated by the model as a shift in quenching location. The oxides of nitrogen emissions for the standard combustor at high power conditions were not accurately correlated by the model because the quenching of nitric oxide formation was not completed within the combustor. 16 figures.

The sawtooth coverslide - A new means of coupling light into solar cells

Abstract: In recent years major improvements have been made in silicon solar cell output by increasing the percent of incident light that actually penetrates into the active volume of the cell through the use of shallow junctions, p/sup +/ back contacts, new antireflection coatings, and etched front surfaces. A new coverslide design described herein reduces the reflection from coverslide surfaces and redirects the light to fall only between the grids, thus increasing the effective area of the cell. With all of these improvements combined, the light collection capability of a solar cell assembly is close to the maximum value possible without using external light concentrators.

Preliminary study of smoke formed in the combustion of various jet fuels

Abstract: A simplified, disk-stabilized combustor has been used to study participate sampling methodology and fuel effects on combustion zone particulate concentration. These samples were extracted via filtration with subsequent gravimetric analysis at six axial positions ranging from 3.8 to 29.2 cm from the fuel injector. Sampling techniques, including the effects of sample temperature, particle deposition, sample drying, and sampling rate, have been evaluated. Measurement guidelines are proposed. Five fuels—petroleum-based Jet A, low-aromatic Jet A, Jet A blended with 15% rubelene, petroleum based JP-4, and JP-5 refined from an oil shale derived syncrude—were investigated. Axial concentration profiles suggest a particulate emission dependence on fuel hydrogen (or aromatic) content as well as volatility. Measured primary zone particulate concentrations were two orders of magnitude greater than exhaust values. I. Introduction W ITHIN the last two years the necessity for future utilization of U.S. coal and oil shale reserves to supplement and eventually replace disappearing crude oil reserves has become increasingly apparent. Although oil shale syncrudes are quite similar to petroleum crudes in analysis,l they are generally somewhat more viscous, less volatile, and higher in aromatic content. Efficient utilization of these syncrudes will therefore require either that fuel processing and resultant expenses increase to meet present fuel specifications or that specifications be changed to minimize processing costs at the expense of engine emissions and performance in existing combustors. To create a reasonable balance between these alternatives, it will be necessary to better understand the effects of fuel properties on combustion processes. This paper presents the initial results from a study of the influence of fuel properties on smoke formation in gas turbine engines. Smoke formed in gas turbine combustors is composed of small, almost pure carbon particles.2 These particles have been reported to appear as agglomerates having diameters of about 0.5 /mi which are composed of solid particles an order of magnitude smaller.3 Problems arising from these smoke particles include engine damage due to increased radiative heat transfer to the combustor walls, deposition on and erosion of turbine blades, visible pollution in the engine exhaust plume, and health hazards resulting from particle inhalation. To date, these problems have been fairly well controlled in engines burning present specification petroleum based fuels; however, in recent tests with coal and oil shale derived fuels,1'4 smoke emissions (by SAE smoke no.) have been shown to be up to 70% higher than with similar petroleum fuels. This increase has generally been attributed to increased fuel aromatic content, but the mechanism by which aromatic content increases smoke emission is not well understood, and effects due to other fuel properties have not been fully investigated.

Leading-Edge Injection for Film Cooling of Turbine Vanes

Abstract: An experimental film-cooling study was conducted on a 3 X -size model turbine vane. Injection at the leading edge was from a single row of holes angled in a spanwise direction for two configurations of holes at 18° or 35° to the surface. Results indicate that optimum cooling occurs near a coolant-to-mainstream velocity ratio of 0.5. Shallow injection angles appear to be most beneficial when injecting into a highly accelerated mainstream.

Subsonic MHD-diffuser performance with high blockage

Abstract: Diffuser performance with high blockages is analyzed by a two-dimensional turbulent-flow model. This model is used to analyze the performance of simple two-dimensional, plane-walled diffusers and also of threedimensional diffusers up to and beyond the blockage limits for which previous analytical or experimental data are available. The effects of important design parameters on diffuser performance are investigated. The parameters considered are the blockage, divergence angle, Mach number, aspect ratio, and wall-to-freest ream temperature ratio. The first two parameters affect the diffuser performance significantly; the other parameters influence the performance only slightly. Results obtained from the subject model agree reasonably well with the available experimental data. The diffuser design of the U-25 facility is analyzed and the analysis predicts a pressure recovery of 0.49, which agrees very well with the measured experimental value of approximately 0.48, obtained from a small-scale model. Nomenclature = geometric cross-sectional area of diffuser, A = H> W = effective flow cross-sectional area of diffuser, Aeft=(H-2dH*)(W-2dw*) = aspect ratio , ^ = HI W - diffuser blockage parameter, B s- J — (Acff/A) = static pressure recovery coefficient, Cp - (Pexit ~ Anlet V(Po ~ P ) inlet >

Photovoltaic, gravitationally-stabilized solid-state, satellite solar power station /GSS4PS/

Abstract: The salient feature of a gravitationally-stabilized satellite solar power system (SSPS) for a photovoltaic system is that the large solar array is separated into smaller segments or subunits, joined together in a linear array oriented along the local vertical. Applicability of gravitational stabilization to the design of photovoltaic SSPS is demonstrated. Both actively controlled systems using multiple solar panels oriented to the sun and passively controlled systems requiring no sun orientation are considered and determined to be feasible. Expressions for gravity-gradient induced tension and restoring torques about the local vertical are assessed. Particular attention is directed to the applicability of solid-state approaches to the design of SSPS. It is shown that an all solid-state SSPS utilizing the LITOMIC (light-to-microwave conversion) concept is feasible but that a hybrid system employing a combination of both solid-state and cryogenic cooled low-voltage techniques to the design of the power management and distribution subsystem may also provide a solution.

Conversion of laser energy to gas kinetic energy

Abstract: Techniques for the gas-phase absorption of laser energy with ultimate conversion to heat or directed kinetic energy are reviewed. It is shown that the efficiency of resonance absorption by the vibration/rotation bands of the working gas can be enhanced by operating at sufficiently high pressures so that the linewidths of the absorbing transition exceed the line spacing. Within this limit, the gas can absorb continuously over the full spectral region of the band, and bleaching can be minimized since the manifold of molecular vibrational levels can simultaneously absorb the laser radiation.

Application of optimization techniques to solar heating and cooling

Abstract: Lockheed is designing a solar heating and cooling system for the city of Santa Clara's new community center. Water heated by solar collectors is used to heat the building in winter and cool the building in summer (using absorption cycle water chillers). This paper shows how optimization techniques can be applied to the operation of a solar driven heating and cooling system such as the Santa Clara facility and outlines practical problems encountered in the design. In the optimization problem the loss function includes not only the cost of heating and cooling but also the equivalent cost of discomfort involved when the temperature is not held at its desired value. The discomfort is assumed to be a quadratic function of temperature. An interesting feature of the resulting optimization problem is a region of singular control because the Hamiltonian is linear in the heating and cooling variable. An optimal control strategy is derived, and numerical examples are presented to show desired building temperatures throughout the day which minimize the sum of energy consumption and the discomfort factor. Additional analysis derives the necessary conditions for the optimal operation of the separate components involved in a solar driven heating and cooling system.

Calculations of Three-Dimensional Transonic Compressor Flowfields by a Relaxation Method

Abstract: A finite-difference technique for describing transonic flow through an axial compressor blade row is described. The method is an adaptation, to turbomachinery flows, of relaxation techniques previously developed for external-aerodynamics studies of flows over wings and bodies. In the work presented here, the flow is treated in the nonlinear small-disturbance approximation, which applies to the case of thin, lightly loaded blades. The modifications of the external-flow techniques necessitated by the blade-row geometry and periodicity conditions are described. This problem formulation is cast in finite-difference form, and details of the relaxation method used to solve the difference equations are given. Results of sample calculations are presented which show interesting features of the three-dimensional interactions that occur between subsonic and supersonic flows at neighboring spanwise stations. Also presented in these results are the locations of shock waves, which decrease in strength and eventually vanish in the subsonic regions near the hub. These shock waves are generated by the artificial viscosity implicit in the finite-difference equations. A method for limiting their thickness to three or four grid points, even in a skew coordinate system, is presented. In addition, a shock-fitting method capable of representing the shock by a discontinuity is described, and results of a two-dimensional application of this method are shown. Recommendations are made for a number of improvements, including the incorporation of higher-order effects not present in the nonlinear small-disturbance approximation.

Gaseous-fuel reactor systems for aerospace applications

Abstract: Research on the gaseous fuel nuclear rocket concept continues under the programs of the U.S. National Aeronautics and Space Administration (NASA) Office for Aeronautics and Space Technology and now includes work related to power applications in space and on earth. In a cavity reactor test series, initial experiments confirmed the low critical mass determined from reactor physics calculations. Recent work with flowing UF6 fuel indicates stable operation at increased power levels. Preliminary design and experimental verification of test hardware for high-temperature experiments have been accomplished. Research on energy extraction from fissioning gases has resulted in lasers energized by fission fragments. Combined experimental results and studies indicate that gaseous-fuel reactor systems have significant potential for providing nuclear fission power in space and on earth.