Showing papers in "Journal of Energy in 1981"

Wingmill: An Oscillating-Wing Windmill

Abstract: This article describes an analytical and experimental investigation of a windmill which utilizes a harmonically oscillating wing to extract wind energy. In particular, the wing's span is horizontally aligned and the airfoil is a chordwise-rigid symmetrical section. The whole wing oscillates in vertical translation and angle-of-attack, with prescribed phasing between the two motions. A theoretical analysis was developed utilizing unsteady-wing aerodynamics from aeroelasticity and the results guided the design of a working model for wind-tunnel experiments. For the cases tested, theory and experiment compared favorably, and showed the wingmill to be capable of efficiencies comparable to rotary designs.

Retorting and Combustion Processes in Surface Oil-Shale Retorts

Abstract: Lawrence Livermore's mathematical model for a batch oil-shale retorting process has proved useful in understanding in situ retorting in a bed of oil-shale rubble. This model is based on an improved understanding of the physical and chemical processes involved in retorting. It has since been modified to calculate the retorting of shale moving through a retort, as required for a continuous process in surface equipment. Calculations were made in which the retorting process that releases oil from raw shale is physically separated from the combustion process that recovers energy from spent shale by burning the residual carbon. Calculations were also made with the retorting and combustion processes combined in one unit. Results of the calculations illustrate the advantages and disadvantages of inert-gas and combustion retorts. Temperature control and the efficient use of energy from the nonliquid products of pyrolysis are key problems in surface retorting processes. The amount of gas produced by the combustion of char with air is insufficient to retort shale without steep temperature gradients which, in turn, may make the temperature difficult to control and result in the loss of oil yield. 13 figures, 3 tables.

Liquid Droplet Radiators for Heat Rejection in Space

Abstract: A radiator for heat rejection in space is described which utilizes a stream of liquid droplets to radiate waste heat. The large surface area per mass makes the liquid droplet radiator at least an order of magnitude lighter than tube and fin radiators. Generation and collection of the droplets, as well as heat transfer to the liquid, can be achieved with modest extensions of conventional technology. Low vapor pressure liquids are available which cover a radiating temperature range 250-1000 K with negligible evaporation losses. The droplet radiator may be employed for a wide range of heat rejection applications in space. Three applications - heat rejection for a high temperature Rankine cycle, cooling of photovoltaic cells, and low temperature heat rejection for refrigeration in space illustrate the versatility of the radiator.

Comparison of field and wind-tunnel Darrieus wind-turbine data

Abstract: A 2-m-dia Darrieus Vertical Axis Wind Turbine with NACA-0012 blades was extensively tested in the Vought Corporation Low Speed Wind Tunnel. This same turbine was installed in the field at the Sandia National Laboratories Wind Turbine Test Site and operated to determine if field data corresponded to data obtained in the wind tunnel. It is believed that the accuracy of the wind tunnel test data was verified and thus the credibility of that data base was further established.

Organic Working Fluids in Rankine Engines

Abstract: This paper provides a compilation of data on the use of organic working fluids in operational Rankine engines in the United States and other countries. Primary emphasis is placed on the maximum temperatures, and on the identification of thermal instability and chemical reaction problems related to these temperatures. Data are presented for 2150 operational Rankine engines from 20 different manufacturers and using 16 different working fluids.

Aerodynamic Performance of the DOE/Sandia 17-m-Diameter Vertical-Axis Wind Turbine

Abstract: The aerodynamic performance of the DOE/Sandia 17-m-diam Darrieus wind turbine is presented for two rotor configurations: 1) two strutted composite structure blades using a NACA-0012 airfoil section with a 21-in. (0.533-m) chord; and 2) two unstrutted extruded aluminum blades with a 24-in. (0.610-m) chord NACA-0015 section. Significant increases in overall performance were obtained for the extruded blades which represent a currently viable low cost blade construction technique applicable to the Darrieus wind turbine.

Fully Developed Laminar Heat Transfer in Triangular Passages

Abstract: The problem of determining the Nusselt number for fully developed, laminar flow in a duct of triangular cross section has been addressed. The particular application to solar collector plate design is considered for which the collector plate forms heat-transfer passages of triangular cross section. The cases for which heat transfer occurs over all three surfaces and for which the back surface is insulated are both addressed. The two boundary conditions of a uniform peripheral flux and a uniform peripheral temperature are examined for the case of uniform axial heating rate, while the uniform peripheral temperature boundary condition is examined for the case of a uniform axial temperature specification. Solutions are obtained using the finite-element method to solve the momentum and energy conservation equations. Numerical results are presented over the entire range of corner half-angle.

Optimization of Liquid Desiccant Systems for Solar/Geothermal Dehumidification and Cooling

Abstract: Two efficient design configurations of a liquid desiccant cooling/dehumidification system that can be powered by low grade solar or geothermal energy and promise low parasitic power requirements for blowers and pumps are proposed and analyzed in this work. A mathematical model for each component in this system has been developed and synthesized for system simulation. The system performance is predicted and optimized through parametric studies using the computer code LIQSYS. It is shown that the exhaust recirculation mode (ERM) gives better performance at full capacity while the process recirculation mode (PRM) produces cooler and drier air.

Heat and Mass Transfer in MHD Channels

Abstract: Accurate estimates of convective and radiative heat transfer in the magnetohydrodynamic channel are provided by simultaneousl y solving the radiation transport equation and the quasi-three-dimensional gasdynamic equations. Carbon dioxide, water vapor, and potassium atoms are considered as the principal constituents participating in gas radiation. Calculations performed for a base load-size channel indicate that heat transfer by gas radiation almost equals that by convection for smooth walls, and amounts to three-fourths as much as the convective heat transfer for rough walls. The evolution of slag particles by homogeneous nucleation and condensation is also investigated. The slag particle size spectrum is computed as a function of the ash carryover rate from the combustor to channel. The average particle size is found to increase and the total number density to decrease with ash carryover rate.

Aerodynamic Interference Between Two Darrieus Wind Turbines

Abstract: The effect of aerodynamic interference on the performance of two curved bladed Darrieus-type vertical axis wind turbines has been calculated using a vortex/lifting line aerodynamic model. The turbines have a tower-to-tower separation distance of 1.5 turbine diameters, with the line of turbine centers varying with respect to the ambient wind direction. The effects of freestream turbulence were neglected. For the cases examined, the calculations showed that the downwind turbine power decrement (1) was significant only when the line of turbine centers was coincident with the ambient wind direction, (2) increased with increasing tipspeed ratio, and (3) is due more to induced flow angularities downstream than to speed deficits near the downstream turbine.

Experiments on an Oscillating Aerofoil and Applications to Wind-Energy Converters

Abstract: Forces measured on a two-dimensional NAG A 0012 aerofoil oscillating in pitch and combined pitch-heave are presented. Amplitudes of pitch were up to 34 deg and heave up to 0.2 chord. Reynolds numbers ranged from 0.7 x 10 to 3.3 x 10 and reduced frequency wc/2 V up to 0.45. The application of this data to the prediction of Darrieus turbine performance, by approximating blade-wind interaction to a pure pitch oscillation, showed some significant differences from steady aerofoil predictions. The use of an aerofoil oscillating in combined heave-pitch as a wind-energy converter is treated briefly.

Dependence of efficiency of shallow junction silicon solar cells on substrate doping

Abstract: Experimental evidence is provided to support a modification of solar cell theory to include the field-enhanced junction recombination dark current. This term is shown to become more important in limiting shallow junction solar cell efficiency as base resistivity is decreased. The anomalously high-diffusion dark current in the /i-region is also significant in limiting open-circuit voltage. This excess dark current is shown to result from high-surface recombination at the metallic contacts on the front surface (STa = 4 x 10 cm/s, SCr = 7 x 10 cm/s) along with bandgap narrowing and high Auger volume recombination in the diffused /i-region caused by high donor density. It is also pointed out that the effective thickness of the /i-region is substantially less than the junction depth. Methods are proposed for reducing the magnitude of both dark currents to improve overall cell performance.

Wind Turbines for Irrigation Pumping

Abstract: Irrigation pumping using modern wind turbines has been the objective of research at Bushland, Texas. A vertical-axis and a horizontal-axis turbine were tested in a mechanical wind-assist mode and a horizontal-axis, electrical-output turbine was tested in an electrical-assist mode. Data from all turbines indicated that power produced was normally less than expected, but was adequate for irrigation pumping. Many operational problems were encountered, but all were overcome with little difficulty. The Southern Great Plains have sufficient winds to power irrigation pumps when a mixture of winter and summer crops are grown. One of the major advantages of wind-assist pumping for the irrigation farmer is that he can easily retrofit the wind turbine to his existing irrigation system. Results indicated that as much as 40% of the present energy consumed in irrigation pumping can be generated by wind power.

Thermal Performance of a Solar Still

Abstract: A simple periodic analysis of a basin-type solar still (both single as well as double), mounted on a stand, has been presented. The effect of dye injected into the water of a single-basin still has been explained. Numerical calculations have been carried out using parameters corresponding to stills with which experiments have been carried out at the Indian Institute of Technology, Delhi. It is found that the present theory quite satisfactorily explains the thermal performance of basin-type solar stills.

Projected Costs for Electricity and Products from OTEC Facilities and Plantships

Abstract: The vast ocean thermal resource of the tropics can be used to serve all areas of the U.S. through the production at sea of fuels or energy-intensive products that can be transported to market by ship. This paper addresses ammonia, liquid hydrogen, methanol, and liquid methane, which could be sold as fuels or chemicals or used as hydrogen sources for onshore fuel-cell power systems. Estimated costs of their production on 325-MWe ocean thermal energy conversion (OTEC) plantships and their delivery to U.S. ports and inland cites are presented. The most promising product is ammonia, first for use in fertilizers and the chemical industry, and later as the least costly carrier of hydrogen for use in fuel cells. Estimated costs of delivering OTEC electricity by undersea cables from moored offshore plants to U.S. islands and Gulf Coast states are compared with costs of electricity from OTEC ammonia and from coal and nuclear power. Commercial viability for both OTEC approaches by the 1990-1993 period is indicated. The potentials for private cost-sharing in the initial 40-MWe demonstration facilities and plantships also are discussed.

Convective and radiative heat transfer in MHD radiant boilers

Abstract: A combined convection-gas radiation, two-zone flow model is formulated for study of the heat transfer characteristics of MHD radiant boilers. The radiative contributions of carbon dioxide, water vapor, potassium atoms, and slag particles are included in the formulation, and are determined by solving the radiation transport equation using the Pj approximation. The scattering and absorption cross section of slag particles are calculated from Mie theory. The model is used to analyze the scale-up of heat transfer in radiant boilers with refractory thickness, wall emissivity, and boiler size, under conditions of a gas composition and slag particle spectrum typical of coal-fired MHD combustion. A design procedure is suggested for sizing radiant boilers so as to achieve required heat extraction rate and to provide a flow residence time that is adequate for decomposition of NOX to acceptable levels.

Low Maintenance Lead-Acid Batteries for Energy Storage

Abstract: The maintenance costs of conventional industrial batteries over their operating life are similar to the initial cost. To reduce these costs and improve the reliability of such batteries, a line of low-maintenance lead-acid batteries suitable for both deepand shallow-cycle applications has been developed. When deep-cycled on a daily basis, these batteries need water addition every 100-125 cycles compared to every 5-10 cycles in the case of conventional industrial batteries. The low-maintenance characteristic is achieved by the use of a positive grid alloy that contains only 1.5% Sb coupled with an Sb-free negative grid alloy. This hybrid grid alloy combination has all of the advantages of an Sb-free combination (low gassing on overcharge, stable gassing characteristics over life, excellent capacity retention on open-circuit stand) and none of the disadvantages (low active material utilization, relatively poor deep-cycle performance). The features of this new low-maintenance battery are discussed with emphasis on grid alloys and charge characteristics. In tests with 400 A-h cells, it was found that the optimum charge regime for minimum water loss and maximum capacity retention is 5% overcharge at a maximum cell voltage of 2.55 V with a periodic 10% equalization charge.

Wind Characteristics Over Complex Terrain Relative to WECS Siting

Abstract: The phenomenon of flow over various terrain features has been systematically interpreted for siting WECS (wind energy conversion systems). Because of the limited data from field programs, most of the reported results are interpreted from laboratory or theoretical studies. The information presented cannot be utilized to compute highly accurate values of the wind power at a site nor to identify the exact optimum location for a WECS. The wind prospector can, however, use it to select locations where the wind field will be potentially higher than the synoptic wind. Information needed to identify and to avoid regions of low wind speed and of highly turbulent and periodic flow is also given. This information considers the effects of the geometries of terrain features, their surface conditions and atmosphere stratifications, as well as the history of wind approaching the WECS site. Basic guidance in practical WECS siting is thus presented.

Stabilization of Low Calorific Value Gases in a Cyclone Combustor

Abstract: This paper describes an experimental investigation in which the combustion of low calorific value gases in a cyclone combustor are simulated by dilute mixtures of natural gas and air O = 1.68). The flame front, so formed, is annular and located close to the chamber walls. Detailed measurements of the combustion aerodynamics and pollution characteristics of the burner are presented which show low flame front temperatures i.e., 1200 °C and negligible NO emissions throughout the cyclone chamber, in which complete burnout of fuel occurs. Refractory lining of the cyclone chamber is shown to improve performance by 40% with further increases possible by insulation of the inlet/outlet manifold and an increase in the strength of the annular recirculation zone. Comparison is made of the mean and fluctuating values of three components of velocity, measured by laser Doppler anemometry, for both isothermal and combustion conditions.

Catalytic Honeycomb Combustor: Steady-State Model and Comparison with Experiment

Abstract: A steady-state lean combustion model for monolithic catalytic combustors is given. The model, consisting of several semiglobal chemical reaction steps in the gas phase and on the surface, is capable of analyzing CO and THC emissions. In the model computation presented, the influence of operating and design parameters on the minimum combustor length is studied. Special attention is given to the effect of after-bed gas phase reaction space. Comparison with experimental data indicates good agreement in the range of parameters covered.

Falling-Bead Dry Cooling Tower

Abstract: A method of rejecting of heat from a power plant is discussed wherein the heat to be rejected is transferred to small metallic or glass-like beads which are dropped from the top of a structure This tower channels cooling air upward through the stream of falling beads The advantage is that the cooling process involves little or no water and is less costly than the fin-tube dry-cooling scheme The reduced cost allows the plant to operate at a lower effective rejection temperature which results in greater plant thermal efficiency An analysis is carried out which illustrates the aerodynamic characteristics of the heat exchanger and identifies the role of particle size and material properties The interaction between bead thermal behavior and duct flow characteristics permit the identification of the major system loss mechanisms: the power lost as a result of bead drag and the pumping power These losses are examined from the point of view of determining the optimum conversion-cycle rejection temperature and the resultant efficiency improvement This benefit and the reduced system cost could significantly lower power-generation costs at sites where water is not readily available

Preliminary Work Concerning the Near-Wake Structure of the Darrieus Turbine

Abstract: The work presented here in i s in tended t o p rov ide a p r e l i m i n a r y i n d i c a t i o n o f t h e na tu re o f t h e near wake s t r u c t u r e behind a Darr ieus t u r b i n e . A more impor tant aspect o f t h e work, however, i s t o examine t h e p o t e n t i a l o f a vor tex a n a l y t i c a l model i n making near wake p r e d i c t i o n s . Near wake p r e d i c t i o n s us ing t h i s model a re compared w i t h a f u l l s c a l e Darr ieus t u r b i n e o p e r a t i n g i n a n a t u r a l wind environment. The purpose o f t h i s paper i s t o present some p r e l i m i n a r y r e s u l t s w i t h regard t o u t i l i z a t i o n o f a vo r tex rode1 f o r p r e d i c t i n g wake s t r u c t u r e s . I n o rder t o p lace t h i s work i n proper perspec t i ve t h e f o l l o w i n g b r i e f rev iew i s g iven t o c h a r a c t e r i z e t h e s t a t e o f t h e a r t w i t h regard t o both a n a l y t i c a l and experimental i n v e s t i g a t i o n s which have been undertaken i n t h e pas t .

Catalytic Combustion of Hydrogen in Model Appliances

Abstract: Water-heater and space-heater designs were developed into working models that were laboratory-tested for performance in terms of self-starting capabilities for catalytic (Nameless) combustion; nearly complete combustion of the fuel gases (tank-grade hydrogen and reformed natural gas); efficient transfer of the heat of combustion to the fluid to be heated; and low or negligible pollutants in the products of combustion. The atmospheric catalytic-burner surfaces had to be designed so that the rate of heat generation is equal to the rate of heat dissipation when surface temperatures are below the autoignition temperature of H2 in air, 585°C (1085°F). This rate balance is accomplished by heat transfer to a heat sink (for example, water in a water heater or room air in a space heater). However, the heat-transfer rate to the heat sink from the combustion surface must be low enough during the low-temperature start-up period to allow the entire surface to reach its normal steady-state operating temperature. This must be accomplished in a relatively short period of time to avoid the release of significant amounts of unburned hydrogen during the start-up period. Measurements prove that, with proper catalyst loadings and burner configurations, over 91% of the fuel gas is reacted (catalytically combusted) to form water vapor. Thermal efficiencies exceeding 80% (based on the high heating value of hydrogen) were noted for water heating, and efficiencies exceeding 91% were noted for space heating with humidification. A major pollutant of general concern in combustion is N O X . Operating conditions permitted negligible addition of NOt to the ambient air, and in some cases, appliance operation reduced the level of NO_V in ambient air.

Experimental and Theoretical Studies of Nitrogen Oxide Production in a Turbulent Premixed Flame

Abstract: NO/sub x/ measurements have been performed in a high velocity, turbulent, premixed CH/sub 4/-air flame, where the combustion is initiated and stabilized by a parallel flow of burned gases This experimental study emphasizes the influence of the turbulence in the vicinity of the confluence between the two jets, as well as the homogeneous turbulence within the premixed stream Two theoretical calculations of the NO/sub x/ concentrations have also been attempted: the first involves a complicated chemical scheme but neglects the influence of turbulent fluctuations on the reaction rates; the second assumes a two parallel reaction scheme, but takes into account the effect of fluctuations by a ''presumed pdf'' approach It is concluded that the ''superequilibrium'' of O seems to be more important than the turbulent fluctuations 20 refs

Pulsed spray drop sizing

Abstract: A drop sizing technique based on the diffraction of light by spherical particles was modified to yield timeresolved drop size measurements in a pulsed spray. The diffraction pattern produced by passing a collimated HeNe laser beam through the fuel spray was measured with a photodiode located in the focal plane of a collection lens. The pulsed spray was operated at a frequency of 1670 cycles/min with a spray duration of 28 ms; measured drop sizes for these conditions varied from 106 pm at the start of injection to 75 /mi near the end of injection.

Behavior of OH and NO^ in a Mixing-Influenced Jet-Stirred Reactor

Abstract: Measurements of OH and NO^ in a premixed jet-stirred reactor are reviewed and interpreted in order to discern the influence of finite mixing and the formation of pollutants. The reactor conditions were P = 93 kPa, 4