Showing papers in "Journal of Energy in 1980"

Flow Curvature Effects on Darrieus Turbine Blade Aerodynamics

Abstract: The effects of curvilinear flow on Darrieus turbine blade aerodynamics are described. Analysis shows that these effects can have a sizeable impact on performance for blades of large chord. Experimental data are presented which verify this forecast. Unusually large boundary-layer radial pressure gradients and virtually altered camber and incidence are identified as causal phenomena. Conformaf mapping techniques are used to transform geometric airfoils in curved flow to their virtual equivalents in rectilinear flow. It is argued that flow curvature is an important determinant of Darrieus turbine blade aerodynamic efficiency and that its proper consideration will yield performance improvements, even for blades of small chord. uncovered blade aerodynamic complexities which were beyond initial expectations. Most noteworthy are the peculiar aerodynamic phenomena associated with the orbital motion of the blades. In essence, these blades are subjected to a curvilinear flow and behave very differently than if they were immersed in a rectilinear flow. Furthermore, centrifugal forces alter the boundary layer of the airfoils rotating in this fashion. This situation presents problems in the design and analysis of all cross-flow wind turbines, because virtually all published airfoil data are derived from tests in rectilinear flow. Recent studiesl show that modest improvements in Cp yield desirable reductions in the cost of energy. Since these Cp improvements can be achieved by increasing blade aerodynamic efficiency, there exists ample incentive for considering the aerodynamic idiosyncrasies of rotating blades. In the material which follows, boundary-layer centrifugal effects will be discussed first. Treatment of this subject is brief; its significance has only recently been appreciated and extensive studies of the phenomenon have not been con- ducted. Flow curvature effects are treated next. A simple kinematic analysis demonstrates that the turbine blade relative inflow velocity and angle of attack are unique everywhere on the chord. It is then shown how conformal mapping techniques, which transform airfoils in the curved flow field to their virtual equivalents in rectilinear flow, may be used in the aerodynamic analysis of the turbine blades. The method indicates that flow curvature effects are strongly dependent upon the blade chord to turbine radius C/R. Experimental data are introduced for two sets of blades, both of NACA 0015 airfoil section. The first set of blades had C/R = 0.114 and the second set had C/R = 0.260.

Multiangular Absorption Diagnostics of a Turbulent Argon-Methane Jet

Abstract: Absorption techniques are being applied to three-dimensional combustion diagnostics. Convolution, Fourier transforms, and iterative algorithms have already been proven in x-ray absorption tomography and interferometric applications. They are currently being tested and compared on their ability to determine typical pollutant and radical concentrations as they appear in flames or exhausts. The effect of the number of scans is analyzed for parallel beams. A tradeoff exists between accuracy and the number of viewing angles. A five-angle procedure gives 10% accuracy with a moderately filtered convolution algorithm. An experiment feasibility study shows that the near time-continuous three-dimensional maps of concentration as low as 1 ppm can be obtained at repetition rates up to 20 KHz. The potential of this method was demonstrated in the laboratory. A diluted methane jet was observed at several sections along its axis. Time-averaged two-dimensional profiles were reconstructed from the absorption scans effected from six and twelve angles. The theoretically predicted dependence of the accuracy on the number of observation angles was verified. Real-time experiments are now being prepared.

Evaluation of a locally homogeneous flow model of spray combustion

Abstract: A model of spray combustion which employs a second-order turbulence model was developed. The assumption of locally homogeneous flow is made, implying infinitely fast transport rates between the phase. Measurements to test the model were completed for a gaseous n-propane flame and an air atomized n-pentane spray flame, burning in stagnant air at atmospheric pressure. Profiles of mean velocity and temperature, as well as velocity fluctuations and Reynolds stress, were measured in the flames. The predictions for the gas flame were in excellent agreement with the measurements. The predictions for the spray were qualitatively correct, but effects of finite rate interphase transport were evident, resulting in a overstimation of the rate development of the flow. Predictions of spray penetration length at high pressures, including supercritical combustion conditions, were also completed for comparison with earlier measurements. Test conditions involved a pressure atomized n-pentane spray, burning in stagnant air at pressures of 3, 5, and 9 MPa. The comparison between predictions and measurements was fair. This is not a very sensitive test of the model, however, and further high pressure experimental and theoretical results are needed before a satisfactory assessment of the locally homogeneous flow approximation can be made.

In Situ Optical Particle Sizing Technique

Abstract: This paper discusses the application of an in situ optical counter to the measurement of liquid fuel droplets and solid coal particles under combustion conditions. Mie theory computations are used to determine an optimal near-forward light-scattering geometry for sizing both spherical transparent particles and irregularly shaped light-absorbing particles in the 5-80 /im range. Results are presented for a burning methanol spray and for reacting coal particles. I. Introduction T HERE is considerable interest in the measurement of particle size distributions in two-phase flows. Specific examples of energy-conversion devices in which such measurements are desirable include liquid spray and pulverized fuel combustors, and particulate cleanup devices such as electrostatic precipitators. While the particulate characteristics such as mean diameter, size distribution, mass loading, and material properties may vary in such systems, the sizes of interest generally fall in the submicron to 100 jim range, with number concentrations up to 107 cm~ 3 for submicron-sized particulates. The available measurement techniques1'2 also vary widely in type and capability. Several, including microscopy, cascade impactors, Coulter counters, mobility analyzers, and commercial optical counters, require a sample to be extracted from the flow. This poses problems related to obtaining a representative sample, especially for the larger-sized and volatile materials in hot, high-velocity flows. Also, many sampling methods are cumbersome and slow in operation. For these reasons, optical techniques are of special interest since they are capable of making in situ measurements with continuous and rapid readout. Moreover, by using lasers, they are adaptable to high-temperat ure systems having high thermal radiation background. Optical techniques all depend on Mie scattering3'4 and can be broadly divided into imaging and nonimaging types. The former, including flash photography5 and holography,6'7 are limited in practice to sizes 19 the theory and initial measurements of a new in situ counter technique utilizing the last approach have been described. The present paper briefly reviews the basis of the measurement technique described in Refs. 18 and 19, and then discusses the instrument requirements necessary for measurements of relatively large (5-80 /ion) particles with variable light-absorbing properties. Light-scattering computations using the Mie theory are presented for several nearforward light-collection geometries, and optimal conditions are defined. Based on these results and previous corn

Siting of Wind Turbine Generators in Complex Terrain

Abstract: Accurate determination of wind distributions in the atmospheric surface layer is a prerequisite for the successful siting and design of wind turbine generators. A general methodology which combines a climatological approach and a diagnostic wind model is proposed for selecting optimum wind power sites in complex terrain. The development of the diagnostic wind model, which is based upon the numerical solution of the threedimensional mass continuity equation with the appropriate physical processes parameterized, is delineated. To demonstrate its utility, the proposed methodology is applied to the island of Maui in Hawaii. The predicted wind field appears to retrieve quantitatively the essential features of the measured wind flows; additionally, the areas identified as potential wind power application sites correspond to those determined earlier via field studies.

CARS Diagnostics of Combustion

Abstract: CARS is being developed for practical temperature and concentration measurement in flames. Current research effort includes the testing of a high-performance conventional CARS spectrometer and the study of electronic resonance enhancement for improved detection sensitivities. The conventional CARS spectrometer is described. It allows BOXCARS measurements with background cancellation to be made. The spectral resolution is adjusted at 0.7 or 0.07 cm ~* in the narrow-band mode, and 0.7 cm ~ in the broadband mode with an OMA for single-shot spectroscopy. Typical results obtained with this instrument on a simulated turbomachine combustor are presented. The detectivity is 100-1000 ppm in general. With resonance-enhanced CARS, one expects gains on the order of 100-1000, as demonstrated recently in I2 vapor.

Aerodynamic performance of a 5-m diameter Darrieus turbine

Abstract: A 5-m-diam vertical-axis wind turbine has undergone continued testing since 1976 at the Sandia National Laboratories Wind Turbine Site. The latest tests of this machine have been with extruded aluminum blades of NACA-0015 airfoil cross section. The results of these tests at several turbine rotational speeds are presented and compared with earlier test results. A performance comparison is made with a vortex/lifting line computational code. The performance of the turbine with the extruded blades met all expectations.

Performance of Pressure-Gain Combustors Without Moving Parts

Abstract: An outline is presented of the main findings of recent work aimed at establishing the performance potential of pulsed, pressure-gain combustors. Recent advances in methods of performance analysis are described briefly and test results are presented showing that a significant increase of stagnation pressure can be generated. The importance of Reynolds number effects is discussed and the results of tests which quantify these are included. It is shown that the testing of small scale pulsed, pressure-gain combustors generally tends to produce pessimistic results. For example, a stagnation pressure gain of 6% has been achieved at a combustor stagnation temperature ratio of 2.5/1, under laboratory conditions using a small prototype. Predictions indicate that pressure gains of up to twice this value should be attainable with a combustor of four times the diameter of the laboratory prototype. The incorporation of pulsed, pressure-gain combustors in gas turbines as substitutes for conventional combustors is also discussed. Predictions based upon test results show that these devices can have very beneficial effects on the overall performances of gas turbines to which they are fitted.

Application of CARS to Simulated Practical Combustion Systems

Abstract: Results are presented of coherent anti-Stokes Raman spectroscopy (CARS) experiments performed in a combustor which produces a bluff-body-stabilized flame having recirculating flow characteristics similar to those in many practical combustion systems. These results were obtained from the following CARS measurements with gaseous propane used as the fuel: determination of temperature profiles in the flame based upon analysis of the scanned N2 spectra (time-averaged spectra), and the mapping of the concentration of N2 and O2 based upon the broadband integration of all Q-branch lines using a single laser pulse. Presented also are: 1) comparison of CARS temperature data and those from a thermocouple taken at the same locations in the combustor, 2) comparison of CARS concentration data for O2 and those obtained with a gas-sampling probe, and 3) comparison of temperature data obtained by single-pulse CARS and by the sodium line-reversal method. In addition, preliminary results obtained in experiments using the liquid fuels JP-4 and shale-oil-derived JP-8 are also reported. The results obtained to date indicate that with the CARS technique spatially and temporally resolved measurements of species concentration and temperature can be made in the reacting zone of large-scale combustors using gaseous or liquid fuel.

Magnetic Refrigeration in Space—Practical Considerations

Abstract: Various schemes of using adiabatic demagnetization to provide refrigeration in the 10-1000 mK range are discussed with particular reference to the requirements for use in space. The methods considered are complete demagnetization, isothermal demagnetization, moving magnet demagnetization, and continuous refrigeration. The requirements that are important for use in space are low mass, low power dissipation, high mechanical rigidity, modular design, and ease of use.

Convective heat transfer in MHD channels and its influence on channel performance

Abstract: The limitations of the integral boundary-layer methods and the potential of the differential boundary-layer method in analyzing MHD channel flows are assessed. By showing the sensitivity of results from the integral method to the choice of parameters, the importance of prescribing accurate boundary-layer profiles and wall heat flux in the integral method is emphasized. A mixing-length-type turbulence model for flow on rough walls is developed and validated by comparison with experimental data. The turbulence model is used in a quasi-threedimensional boundary-layer model to evaluate the influence of wall roughness and pressure gradients on the flow characteristics and performance of MHD channels. The behaviors of skin friction and Stanton number calculated from the analytical model are found to differ considerably from the empirical correlations valid for non-MHD flows without pressure gradients. Nomenclature A, B = parameters in mixing length model B = magnetic field Cf = skin friction E = electric field H = total enthalpy IL = current load

Survey of Advanced Gasdynamic Laser Concepts

Abstract: Introduction E is transported between the thermal heat source and the optical cavity of a gasdynamic laser (GDL) in the vibrational modes of the nitrogen molecule. Pure nitrogen exhibits relatively long vibrational relaxation times, making it well suited to the formation of an inversion during a rapid gasdynamic expansion. The carbon dioxide and catalyst that are necessary to allow efficient extraction of this stored energy in an optical cavity act as deactivants during the gasdynamic expansion, causing significant loss of stored vibrational energy. Management of this energy loss has required the use of very rapid expansions in nozzles with very small throats. The overall efficiency of GDLs is the product of the fraction of the invested thermal energy stored in the nitrogen vibrational modes, the freezing efficiency of the nozzle, and the extraction efficiency of the optical cavity. The stored energy fraction increases with stagnation temperature; however, the freezing efficiency falls with increased stagnation temperature. Consequently, an optimum stagnation temperature occurs near 2000 K for the conventional premixed GDL. The specific energy that can be stored in the vibrational levels of nitrogen as the temperature is raised is shown in Fig. 1. The conventional premixed GDL falls far short of attaining the full potential of the gasdynamic laser concept. Nozzle freezing efficiency increases as the carbon dioxide and catalyst concentrations are lowered. However, a certain concentration of both is required to allow good extraction efficiency. A small throat size provides a rapid rate of expansion which increases the freezing efficiency. However, the viscous losses increase with the lower Reynolds numbers associated with smaller nozzles, limiting the extraction efficiency in the cavity. The development of the conventional premixed GDL has been a process of optimization within these several mutually exclusive constraints, resulting in an overall efficiency of 0.1 -1.0%. Early in the development of the GDL it was suggested that the mixing of the carbon dioxide and catalyst after expansion to low static temperature and pressure would reduce the collisional loss of stored vibrational energy and provide greater flexibility of operating conditions. Vibrational energy can thus be frozen into the pure nitrogen donor gas well upstream of the nozzle throat at levels near the stagnation conditions. Calculations for stagnation conditions of 2000 K, 10 atm show a 1% loss of vibrational energy in the expansion of pure nitrogen as compared to the 40-50% loss that occurs principally in the throat region of a conventional nitrogen/carbon dioxide/catalyst GDL expansion. Mixing of the excited nitrogen with cold carbon dioxide is accompanied by near resonant collisional transfer of the vibrational energy to the lasing gas molecules, resulting in a population inversion with respect to the two laser levels. The thermal excitation of the nitrogen with subsequent turbulent mixing of the carbon dioxide and catalyst allows an increase in stagnation temperature to above 4000 K before molecular dissociation becomes important. The stored vibrational energy can be raised by an order of magnitude to the premixed case as seen in Fig. 1. The kinetic constraints on vibrational freezing are not as critical without the carbon dioxide and catalyst in the primary gas stream, allowing the use of larger nozzle throats resulting in lower viscous losses. The flexibility of operation with various mixtures of nitrogen, carbon dioxide, and catalyst permits more efficient extraction of power in the cavity region. These characteristics enable the mixing GDL to attain 5-10 times the efficiency of the conventional premixed GDL. Overall efficiencies of as high as 6% have been reported for the mixing GDL. The origins of the mixing gasdynamic laser can be found in the early research of Patel concerning energy transfer from nitrogen excited in a low-pressure electric discharge to carbon dioxide mixed subsonically 20 cm away from the discharge. His subsonic mixing laser was 10 times as efficient as the contemporary conventional CO2 discharge laser. Several other mixing lasers excited by electric discharges were subsequently developed' using both subsonic and supersonic

Concentration Ratios for Flat-Plate Solar Collectors with Adjustable Flat Mirrors

Abstract: Flat mirrors are frequently used to increase the heat output from flat-plate collectors. They are generally oriented in an east-west direction and are mounted below and/or above the collector panels. The annual performance of a mirror-boosted system can be improved by allowing periodic adjustments of the mirrors alone or of the panel-mirror units. In order to compare different mirror-panel configurations their solar flux concentration ratios are averaged over a yearly period using the solar elevation angle time probability function. AH configurations have the same ratio of mirror area to panel area. In general, it is found that the mirror orientations are more important than the panel orientations. Seasonal adjustments of the mirrors suffice to maintain acceptable values of the concentration and there is relatively little advantage in providing for collector panel adjustments. For year-round collection configurations with semiannual mirror adjustments provide a marked increase in output relative to fixed configurations. A double-mirror system (adjustable trough) provides higher concentrations than a single-mirror system for equal mirror area. Adjustable trough configurations with zero acceptance angle provide higher annual average concentration ratios than those with non-zero acceptance angles.

Fuel Property Effects on Life Characteristics of Aircraft Turbine Engine Combustors

Abstract: Results of a program to determine the effects of fuel properties on the life characteristics of two USAF/General Electric aircraft turbine engine combustors are presented. Thirteen test fuels were evaluated in an older technology cannular combustion system (J79) and in an advanced-technology, virtually smokeless, compact, annular combustion system (F101) over wide ranges of simulated engine operating conditions. Fuel variables were hydrogen content, aromatic structure, volatility, and distillation end point. Significant increases in combustor liner temperatures were observed as fuel hydrogen content was decreased. With fuel hydrogen contents of 14.5,14.0,13.0, and 12.0, the resulting relative combustor liner cyclic life predictions are 1.00, 0.78, 0.52, and 0.35 for the J79 combustor and 1.00, 0.72, 0.52, and 0.47 for the F101 combustor, respectively. Based upon these findings, it is concluded that improved liner cooling design features will be needed in most currenttechnology combustors to accommodate the projected lower hydrogen contents of future fuels.

Jet Membrane Process for Aerodynamic Separation of Mixtures and Isotopes

Abstract: The Jet Membrane aerodynamic separation concept is based upon preferential penetration of background gases into a free jet with collection of the enriched species by a downstream facing collector probe. Mass spectrometric measurements of light species upflow and separation or enrichment factors obtained using this method are presented for gas mixtures and the isotopes of sulfur (SF6) and uranium (UF6), using gaseous and condensible jet fluids (N2, CO2, and FC-43) in the continuum range of plume Knudsen numbers (A>i<0.05). Comparison with available theoretical models is also shown. In addition, the results of exploratory experiments to investigate certain aspects of transforming the Jet Membrane concept into a viable industrial process are presented. A cost model has been developed that predicts, using the results of the experiments and theory, a cost of enriched uranium for small [300,000 separative work units per year (SWU/yr)] Jet Membrane plants approximately 40% of that using the gas centrifuge process in a similar sized plant. Alternatively, the cost of enriched uranium from the small Jet Membrane plant will be the same as the cost from a 3,000,000 SWU/yr centrifuge plant.

Ignition of Pulverized Coal with Arc Heated Air

Abstract: C powerplant practice, with suspension fired boilers, involves consumption of large quantities of premium fuel to accomplish ignition of pulverized coal. A new approach to coal ignition is described. A vortex stabilized electric arc heater was attached to a full-scale commercial pulverized coal burner. A continuous arc heated air jet was used as an ignition source. The equipment was operated in a powerplant where ignition of coal was demonstrated. Ignition was accomplished with igniter input power levels which are lower than conventional practice by a factor of six. Cost of an igniter system for a large commercial size coal burner was estimated; the arc igniter appears to be economically viable and competitive with conventional practice.

Concentration, Velocity, and Particle Size Measurements in Gas-Solid Two-Phase Jets

Abstract: An optical technique was developed and used to measure particle concentration profiles in dense two-phase axisymmetric jets. Gas velocity profiles of the single-phase jet were measured by a pitot probe. Particle size distribution across the jet was measured with isokinetic particle sampling probes. Schlieren photographs of shock waves in the jet were taken to study the influence of particles on shock-wave structure near the exit of the nozzle. The effect of nozzle configuration on the two-phase jet flow was also investigated. The measurements were made by seeding 1,3, and 5% by weight of 24 /xm mean diameter spherical fly ash particles into jets at Mach numbers of 0.2, 0.8, and 1.0. The particle concentration profiles showed that particles concentrate on the axis of the jet at the exit of the nozzle and the profiles are influenced by the seeding rate, the velocity of the jet, and the nozzle configuration. The particle size distribution is homogeneous in the jet. Schlieren photographs of shock waves in the jet showed that the normal shock wave near the exit of the nozzle was convexly curved with the addition of a suspension of particles in the jet.

Approximate Three-Dimensional Electric Solution for a Frame-Type MHD Generator

Abstract: An approximate technique to determine the potential distribution and integral performance characteristics of a frame-type MHD channel is presented. In addition to including the effect of the conducting sideframes, the model considers the effects of finite segmentation and the effects of variable plasma conductivity, Hall parameter, and velocity. In its simplest form, the approximate technique effects results for the threedimensional potential distribution by solution of an ordinary differential equation. The accuracy of the technique is demonstrated by comparison with results of more detailed calculations and by comparison with experimental results. These comparisons show good agreement both for the integrated generator performance and for the current distribution to the electrode frame. In contrast to the detailed calculation procedure, the approximate technique has modest solution times and can be incorporated in a MHD generator design and prediction code.

Power Takeoff Analysis for Diagonally Connected MHD Channels

Abstract: The electrical loading of the power take-off region of diagonally connected MHD channels is investigated by a two-dimensional model. The study examines the loading schemes typical of those proposed for the U-25 and U-25 Bypass channels. The model is applicable for the following four cases: (1) connection with diodes only, (2) connection with diodes and equal resistors, (3) connection with diodes and variable resistances to obtain a given current distribution, and (4) connection with diodes and variable resistors under changing load. The analysis is applicable for the power take-off regions of single or multiple-output systems. The general behaviors of the current and the potential distributions in all four cases are discussed. The analytical results are in good agreement with the experimental data. It is found possible to design the electrical circuit of the channel in the take-off region so as to achieve a fairly even load current output under changing total load current.

Lean Stability Augmentation for Premixing, Prevaporizing Combustors

Abstract: An experimental program was conducted to investigate techniques for improving the lean combustion limits of premixing, prevaporizing combustors applicable to gas turbine engine main burners. Augmented flameholders employing recessed perforated plates, catalyzed tube bundles, and configurations in which pilot fuel was injected into the wake of V-gutters or perforated plates were designed and tested. Stable operation of the piloted designs was achieved at equivalence ratios as low as 0.25; NOX emissions of less than 1.0 g/kg at simulated turbine engine cruise conditions were obtained. A piloted perforated plate employing 4°'o pilot fuel flow produced the best performance while meeting severe NOX constraints. Nomenclature d = diameter El = emission index, g/kg P = pressure, atm; ratio of pilot fuel flow to total fuel flow PPM = concentration in parts per million by volume T = temperature, K V = velocity, ms w = flow rate, kg/s rjc = combustion efficiency (chemical) 0 = equivalence ratio T = residence time, s Subscripts ad = adiabatic flame bo = blowout = design point = approach flow condition = pilot stream des o P

Fuel Character Effects on J79 and F101 Engine Combustor Emissions

Abstract: Results of a program to determine the effects of fuel properties on the pollutant emissions of two US Air Force aircraft gas turbine engines are presented. Thirteen test fuels, including baseline JP-4 and JP-8, were evaluated in a cannular (J79) and a full annular (F101) combustor. The principal fuel variables were hydrogen content, aromatic structure, volatility, and distillation end point. Data analysis shows that fuel hydrogen content is a key fuel property, particularly with respect to high power emissions (oxides of nitrogen and smoke), and that low power emissions (carbon monoxide and hydrocarbons) are more dependent on fuel atomization and evaporation characteristics.© 1980 ASME

High electrical conductivity and high Hall coefficient in MHD generator

Abstract: E have reported1'4 the observed recovery of the effective conductivity and the effective Hall coefficient in both Faraday and Hall nenequilibrium MHD generators in the regime of fully ionized seed. In our recent DISK-II power generation experiments with the magnetic field higher than in earlier experiments,4 we observed very high electrical conductivity and high Hall coefficient due to the reduction of ionization instability. In this Note, we report the main results of the experiments. The experimental apparatus and its operating conditions are described elsewhere.4 The operating conditions which are different from the earlier experiments are the higher magnetic field of 1.43 T and the higher seed fraction of 1.1 x 10 ~4. The voltage-current curve obtained in the present experiments is shown in Fig. 1. We can see in this figure the recovery of voltage and current in region A (load resistance R = 0.0094ft-0.48Q) and their reduction in region B (R>112). These results can be explained from the measured fluctuations of the Hall electric field, which are shown in Fig. 2. We can see from this figure the reduced fluctuations in region A (less than 10% for 0.39ft >jR>0.1Q). The electron temperature measured from the continuum recombination radiation intensities ranged 4400-5500 K, which coincided with the theoretical values predicted from the relation PCrit>Po (Pent—tne critical Hall coefficient for ionization instability and 00 =the ideal Hall coefficient). In region B, the electron temperature increased above 5500 K and initiation of argon ionization made the working plasma unstable. Here it should be noted that the Joule heating of electrons increases as the external load resistance increases in a Hall generator. We can also see from Fig. 1 that the stable region A is broader than in the earlier DISK-II experiments.4 This can be ascribed to the increasing voltage drop near electrodes against current: The voltage drop near electrodes increased from 8 to 41 V as the load resistance decreased from 0.39 to 0.0094ft. This implies that the total resistance of both the external load resistance and the working gas resistances near the electrodes does not decrease as rapidly as the load resistance and that, therefore, the decrease of electron temperature becomes small even though the load resistance decreases drastically from 0.39 to 0.0094ft. The effective conductivity aeff and the effective Hall coefficient j8eff in the present experiments are shown in Figs. 3 and 4, respectively. We can see from these figures that the highest aeff is 200 mho/m which is almost the ideal a0 and that the highest 0eff is 8.5 which is 80% of the ideal /30.

Optical Design of Solar Concentrators

Abstract: A generalized technique for the optical design of solar concentrators has been developed. The design technique considers limb darkening effects, collector placement errors, concentrator optical errors, and concentrator pointing errors. In addition to giving the designer the ability to explore the sensitivity of a design to these parameters, the technique also allows the designer to prescibe the heating distribution on the collector surface. A detailed derivation of the design technique and illustrative results are presented.

Performance Assessment of a Flettner Wind Turbine

Abstract: Introduction W the renewed interest in utilizing wind energy has stimulated a number of novel ideas and brought about considerable progress in conventional wind turbine technology, a system invented about 60 years ago which may have a significant economic advantage over propeller-type and Darrius machines has apparently been overlooked by the engineering community. Anton Flettner, who is often cited in fluid mechanics texts for his utilization of the Magnus effect to propel a sailing ship, devised and constructed a wind turbine using spinning rotors for blades. With the Magnus effect providing lift, the turbine functions aerodynamically in the same way as a propeller-type device does, as indicated in Fig. 1. Other than a brief description and photograph of the prototype (the turbine was 20 m in diameter and had four blades) in Flettner's autobiographical account, however, no citation of work on the concept either by Flettner or others could be found in the literature. With the blades spun by d.c. drive motors mounted in the blades, the Flettner turbine could be operated at constant rotational speed to drive an alternator, the mode of operation generally favored now for large conventional wind turbines. Control of the spin rate of the blades would provide simple, effective control of output torque and rotational speed. This study was undertaken to provide a preliminary assessment of the performance of the Flettner wind turbine, primarily from an aerodynamic standpoint. Hopefully, the results obtained can serve as a guide in the formulation of a complete preliminary design study to obtain a quantitative measure of the merits of the device. An analysis of optimum aerodynamic configuration and power output as a function of wind speed using the classical strip formulation is outlined in what follows, together with a limited performance analysis of a hybrid configuration. Aerodynamic aspects of control system and structural design are then discussed, and specific advantages and disadvantages of the Flettner concept which should be quantitatively assessed in a design exercise to determine economic viability are summarized.