bluuebunny/crossref_metadata_2025 huggingface dataset:
Construction and Startup Performance of the Miamisburg Salt-Gradient Solar Pond
Authors: Wittenberg L. J. , Harris M. J.
Published: January 2010

The largest salt-gradient solar pond in the U. S. occupies an area of 2020 m2 and was installed for only $35/m2. The pond has a storage layer of 1.6 m consisting of 18 percent sodium chloride, a l-m gradient zone and a 0.4-m top convective zone. After 1.5 yr of operation, the storage temperature reached a maximum of 64°C in July and a minimum of 28°C in February. During July-September 1979, 143.5 GJ (136 million Btu) of heat was utilized. Under steady-state conditions, the pond is conservatively predicted to deliver over 1015 GJ/yr (962 million Btu) of heat to be used principally for heating an outdoor swimming pool in the summer and an adjacent recreation building from October to December each year. Based upon a 15-yr depreciation of the installation costs, the cost of this heat, $8.95/GJ ($9.45/million Btu) is already below the cost of heating with fuel oil. Maintenance of water clarity, corrosion of metallic components, and the assurance of the containment of the pond water have been the principal operational concerns and will require further study.
Second Law Analysis and Synthesis of Solar Collector Systems
Authors: Bejan A. , Kearney D. W. , Kreith F.
Published: January 2010

The second law of thermodynamics is used to analyze the potential for exergy conservation in solar collector systems. It is shown that the amount of useful energy (exergy) delivered by solar collector systems is affected by heat transfer irreversibilities occurring between the sun and the collector, between the collector and the ambient air, and inside the collector. Using as working examples an isothermal collector, a nonisothermal collector, and the design of the collector-user heat exchanger, the optimum operating conditions for minimum heat transfer irreversibility (maximum exergy delivery) are derived.
Overview of Wind Energy Systems: Issues in Development and Application
Authors: Moretti P. M. , Thresher R. W.
Published: January 2010

An overview of the current status of wind energy technology and system development is presented with major emphasis placed on the key issues which face the commercialization of wind technology. The basic fundamentals of the technology are reviewed and the direction of current development is outlined. Economic considerations are discussed both from a machine development point of view and the utility-industry cost-of-service approach. In addition, the problems associated with wind turbine performance testing are discussed and a short review of operational experience is provided. These topics are all considered in the context of providing the reader with an understanding of wind system technology, a general knowledge of current problems, and the expected trends for the future. Many of these important issues are still under intensive investigation, and in some cases, a clearly superior solution has not emerged. In these circumstances, the value judgments are properly left to the reader.
Effect of Corrugated Cover Directional Transmittance on the Thermal Performance of a Solar Collector
Authors: Smith T. F. , Chaidar S.
Published: January 2010

The benefits of light weight, structural strength, and reduced costs without significant reduction of transmission of solar energy of a corrugated fiberglass composite cover promise wide utilization of this cover in solar collectors to suppress convective and radiative heat losses from the absorber panel. In order to evaluate the thermal performance of a collector with a corrugated cover, the directional transmittance of the cover must be available. A study was undertaken to develop a model for the directional transmittance of a corrugated cover as represented by a sinusoidal periodic function. As an application of this model, hourly and daily thermal efficiencies of a solar collector with a corrugated cover are presented.
The Effects of Regional Insolation Differences upon Advanced Solar Thermal Electric Power Plant Performance and Energy Costs
Authors: Latta A. F. , Bowyer J. M. , Fujita T.
Published: January 2010

This paper presents the performance and cost of four 10-MWe advanced solar thermal electric power plants situated in various regions of the continental U.S. Each region has different insolation characteristics which result in varying collector field areas, plant performance, capital costs, and energy costs. The paraboloidal dish, central receiver, cylindrical parabolic trough, and compound parabolic concentrator (CPC) comprise the advanced concepts studied. This paper contains a discussion of the regional insolation data base, a description of the solar systems’ performances and costs, and a presentation of a range for the forecast cost of conventional electricity by region and nationally over the next several decades.
Analytical Dynamic Modeling of Line-Focus Solar Collectors
Authors: Wright J. D.
Published: January 2010

Solar thermal electric power and industrial process heat systems may require a constant outlet temperature from the collector field. This constant temperature is most efficiently maintained by adjusting the circulating fluid flow rate. Successful tuning of analog or digital controllers requires a knowledge of system dynamics. Models relating deviations in outlet temperature to changes in inlet temperature, insolation, and fluid flow rate illustrate the basic responses and the distributed-parameter nature of line-focus collectors. When plotted in dimensionless form, the frequency response of a given collector is essentially independent of the operating conditions, suggesting that feedback controller settings are directly related to such easily determined quantities as collector gain and fluid residence time.
Simulation of Thermal Performance of Solar Collector Arrays
Authors: Fanney A. H. , Thomas W. C.
Published: January 2010

An experimental method is described for simulating the useful energy supplied by collector arrays during tests of solar water heating systems. The method uses an electric heat source to simulate the absorbed solar energy in series with nonirradiated collectors to simulate the concurrent heat losses. This configuration maintains the collector-loop flow characteristics which are important for system tests. Expressions are developed for programming the heat source for collector arrays connected in parallel and series combinations with the heat source located either upstream or downstream from the nonirradiated array. Thermal modeling of representative arrays is used to investigate the consequences of using linearized collector efficiency curves to program the heat source and of using nonirradiated collectors to simulate heat losses. The absence of absorbed solar radiation in collector covers indoors is shown to partially cancel the effects of generally higher windspeed and increased longwave radiation loss in the outdoor environment. In typical situations, the analytical model showed that the use of nonirradiated collectors in series with an electric heat source may give up to 10 percent higher useful energy output as compared to an irradiated array. The difference, however, can be reduced by closely matching indoor and outdoor environmental conditions and by locating the heat source downstream from the nonirradiated collector array. The results of experiments to verify the performance of a nonirradiated array with a downstream electric heat source are presented. Day-long tests of a domestic solar hot water system with irradiated collectors were repeated using a nonirradiated array with a downstream heat source. The measured useful energy in the two cases was consistent with the results of the analytical investigation.
Frequency Response Analysis of Fluid Control Systems for Parabolic Trough Solar Collectors
Authors: Schindwolf R.
Published: January 2010

Previous studies of solar collector fluid control systems have utilized computer simulations of collector and piping dynamics to evaluate stability and response characteristics. To obtain reasonable simulation accuracy requires substantial computer memory and time and is well beyond the capability of small, desk-top computers. This paper derives a linearized steady-state frequency response for parabolic trough collectors and for connecting piping, which can be used in standard gain-phase analyses to evaluate system stability and closed loop frequency response. The frequency response characteristics of a typical collector string and piping are used in a gain-phase analysis to get some insight into the effect on system stability of various system parameters such as controller gain, sensor and controller time constants, and sensor location.
Ammonia Condensation on Smooth and Fluted Aluminum Tubes
Authors: Domingo N. , Michel J. W.
Published: January 2010

Experiments relative to heat exchangers for ocean thermal energy conversion (OTEC) systems have been completed for ammonia condensing on the outside of four aluminum tubes of three types: a smooth tube, a single (external) fluted tube, and two double (internal/external) fluted tubes. Composite heat transfer coefficients (coefficients that include vapor-side plus wall resistance) are reported for a smooth tube condensing horizontally and at various tilt angles, and for a single-fluted tube condensing vertically. Overall heat transfer data are given for both double-fluted tubes. The primary conclusions from this study were as follows: (a) smooth tube condensing performance was maximum for the horizontal orientation, where, for a given heat flux, composite coefficients were 2.1 times vertical smooth tube (1.2 m long) values; (b) a vertically oriented, single-fluted tube gave the highest performance among the tubes studied with composite condensing coefficients, at a given heat flux, up to 5.2 times the vertical smooth tube values; (c) overall performance for a tube with inside and outside flutes was 25 percent greater than observed for a tube having identical outside flutes but a smooth inside surface; (d) overall performance was virtually unchanged for a double-fluted aluminum tube as the number of external flutes was reduced from 45 to 36; and (e) overall heat transfer results from Oak Ridge National Laboratory (ORNL) double-fluted, vertical, single-tube tests were in approximate agreement with vertical, double-fluted condenser tube bundle data obtained by the Argonne National Laboratory (ANL).
Predictions of Low-Frequency and Impulsive Sound Radiation From Horizontal-Axis Wind Turbines
Authors: Martinez R. , Widnall S. E. , Harris W. L.
Published: January 2010

This paper develops theoretical models to predict the radiation of low-frequency and impulsive sound from horizontal-axis wind turbines due to three sources: (i) steady blade loads, (ii) unsteady blade loads due to operation in a ground shear, (iii) unsteady loads felt by the blades as they cross the tower wake. These models are then used to predict the acoustic output of MOD-I, the large wind turbine operated near Boone, N. C. Predicted acoustic time signals are compared to those actually measured near MOD-I; good agreement is obtained.
Heliostat Operation at the Central Receiver Test Facility, 1978–1980
Authors: Holmes J. T.
Published: January 2010

The operations and maintenance data and conclusions presented in this report are for the 222 heliostats that have been in use at the Central Receiver Test Facility (CRTF) from 1978 through 1980. The CRTF beam produces a total power of 5.5 MWth and a peak intensity of 2250 kW/m2 near solar noon. Improvements in the targeting accuracy have been made. The mirror reflectance is maintained near 80 percent by cleaning with rain or snow. The CRTF heliostats logged almost 300,000 operating hrs by the end of 1980.
Thermal Analysis of a Solar Pond Power Plant Operated With a Direct Contact Boiler
Authors: Sonn A. , Letan R.
Published: January 2010

A solar pond power plant operated with a direct contact boiler was thermally analyzed. A binary cycle system of concentrated brine, and an organic working fluid were considered. Brine temperature of 80°C, condensation at 30°C, a 75 percent efficient turbine, and 70 percent efficient pumps were specified for the analysis. The current study involved six working fluids: butane, pentane, hexane, and refrigerants R113, R114, R12. Each of these fluids exhibited a maximum efficiency of the system at characteristic operating conditions of the boiler. The system efficiency increased as the boiler pressure approached that of the pond. Net electrical outputs of 7–8.4 percent of the heat inputs were obtained for the low pressure fluids, such as pentane, hexane, and R113. Gravity flow of brine to boiler made the system efficiency approach the thermal efficiency of the power cycle. A single component vapor to turbine was considered, as the generated organic vapor appeared to contain less than 1.5 percent of water vapor for the fluids examined. Solute losses in brine by direct contact in boiler were estimated for pentane, as 120 kg per year per km2 of pond, or 60 kg/MWe•year, based on 2 MWe/km2 net electrical output. Such losses are practically negligible; however, selection of the working fluid has to be determined on an economic basis.
The Simulated and Experimental Performance of a Solar Heat Generating System
Authors: Cooper P. I. , Sheridan J. C.
Published: January 2010

There is little information in the literature on the results of comparing the simulated and experimental performance of solar heat generating systems, yet available detailed simulation packages such as TRNSYS [1] are used as benchmarks against which simplified design procedures are compared. A pilot-sized experimental facility located at the CSIRO Division of Energy Technology was used to generate experimental data for comparison with simulated results. The system consisted of 86.4 m2 of double-glazed solar collectors connected to a 9500-1 water storage tank from which energy was rejected at a controlled rate via a heat exchanger and cooling tower. The facility was comprehensively instrumented to measure and record system forcing functions and variables, such as solar radiation, ambient temperature, collector temperatures and flow rates, and load temperatures and flow rates. A series of experimental runs were carried out to compare simulated and experimental performance over a range of operating conditions. An aggregate of approximately 70 days of performance data was collected at 5 or 10 min intervals. The simulated and measured performance of the collectors and the entire system were compared at hourly and daily intervals. The predicted total energy delivered by the system for all data was found to be within 1 percent of the measured value. Agreement on other bases was not quite as close but was good enough to conclude that simulation with TRNSYS is satisfactory for the design of similar solar heat generating systems.
Comparison of Transient Performance Predictions of a Solar-Operated Diffusion-Type Still With a Roof-Type Still
Authors: Elsayed M. M.
Published: January 2010

A new type of solar-operated diffusion still is proposed. The still is powered directly by solar radiation and is easy to operate and maintain. Analyses of the proposed diffusion still and the conventional roof-type still are carried out to predict the transient performance of both stills at various operating and design conditions. Comparison of the performance of both stills on four sample days through the year is considered. The comparison shows that, although the diffusion still has a higher cover temperature, (i.e., larger heat loss to ambient) than the roof-type still, the diffusion still is superior to the roof-type still in both production rate and operation efficiency. The results also show that an increase in ambient temperature improves the performance of both stills.
The Transient, Steady-State, and Stability Behavior of a Toroidal Thermosyphon With a Parallel-Flow Heat Exchanger
Authors: Mertol A. , Greif R. , Giz A. T.
Published: January 2010

The transient and steady-state heat transfer, fluid flow, and stability of a toroidal thermosyphon have been studied theoretically. The thermosyphon is heated over the lower half and cooled over the upper half by an annular parallel-flow heat exchanger. Under some conditions the system becomes unstable and the interaction between the fluids in the thermosyphon and in the heat exchanger is of special interest. Indeed, two neutrally stable curves are obtained for the same heat exchanger conditions. Detailed results and discussion are presented for the stability of the system as well as for the temperature, velocity, pressure drop, and efficiency.
Bubble Nucleation and Growth in Open-Cycle OTEC Subsystems
Authors: Bugby D. C. , Mills A. F. , Wassel A. T.
Published: January 2010

Bubble nucleation and growth in the evaporator, condenser, upcomers, and feedwater distribution systems of open-cycle ocean thermal energy conversion (OTEC) power plants are examined. The phenomenon that will probably have the most impact on system design is cavitation in the warm water feed near the entrance of the evaporator. The critical bubble size for cavitation is about 105 μm. Sources of bubbles in the warm water feed are those entering from the ocean, those nucleating on suspended particles, and those nucleating on the upcomer wall. Analyses of bubble growth induced by changes in hydrostatic pressure, mass transfer, and coalescence are presented. Using available information for bubble size distribution in seawater at California locations, it is shown that cavitation will probably have a significant impact on evaporator performance unless a debubbler is provided upstream of the evaporator entrance.
A Numerical Study of Transient Mixed Convection Flows in a Thermal Storage Tank
Authors: Chan A. M. C. , Smereka P. S. , Giusti D.
Published: January 2010

Transient, two-dimensional, mixed convection flows in a thermal storage tank have been studied using a previously developed numerical technique based on the marker and cell method. The governing equations are the conservation equations for laminar, natural convection flow based on the Boussinesq approximation. Forced convection flow is superimposed through the use of appropriate boundary conditions (inflow and outflow conditions). The transient heat transfer and fluid flow characteristics are examined for different boundary conditions. Typical transient temperature and velocity distributions are presented. The effect of inflow and outflow configurations on the storage tank thermal performance is also investigated. It is found that the device can store energy at a faster rate when hot water is discharged into the tank from the top and colder water is extracted from the bottom. However, the discharge direction into and from the tank, which can be either vertical or horizontal, is found to have negligible effect on the thermal storage efficiency.
Numerical Simulation of the Performance of a Salt-Gradient Solar Pond
Authors: Panahi Z. , Batty J. C. , Riley J. P.
Published: January 2010

A one-dimensional mathematical model which simulates the dynamic performance of stratified solar brine ponds is described. The model simulates the upper convective zone, the middle nonconvective zone, and the lower convective zone. In addition to the energy flux, the model simulates the varying brine densities as a function of temperature and salt concentration, and thus is able to examine various pond stability criteria. On the basis of model operational studies, the following results are presented: (i) a study of overall pond efficiency in terms of the upper convective layer; (ii) an optimization study of the thickness of the nonconvective zone in terms of net energy transmission to the lower convective zone; (iii) an investigation of the heat storage efficiency and of the overall pond efficiency as a function of pond loading rate for a particular depth of storage zone.
Vibration Characteristics of an Elastic Linkage With Elastic Input and Output Shafts
Authors: Garcia-Reynoso A. , Seering W. P.
Published: January 2010

This paper develops a mathematical model of the linearized vibrations of a four-bar linkage with a flexible rocker link and flexible input and output shafts. The model assumes constant input velocity and includes inertial masses at the ends of the input and output shafts. The assumed modes technique is used to model the rocker link. Exact rocker mode shapes are derived from an analysis of the continuous parameter model and are then used in a lumped parameter model to predict system response. Finally, a dimensional analysis is presented which develops the concept of families of mechanisms whose dynamic behaviors are similar.
Approaching Finite Element Method in Acoustic Analysis
Authors: Drakatos P. A.
Published: January 2010

The use of the Finite Element Method in acoustic analysis is a new problem with theoretical and practical interests. Although acoustic analysis is similar to fluid and heat transfer analysis, there are some important differences introduced by compressibility, white noise, echo, and so forth. This paper approaches the problem by combining spectral and cepstral analysis with the Finite Element Method. Starting from the acoustic intensity on the boundary of the ambient space of an acoustic source, a suitable model consisting of discrete frequencies for the Finite Element Method is created.
Hertzian Damping, Tooth Friction and Bending Elasticity in Gear Impact Dynamics
Authors: Yang D. C. H. , Lin J. Y.
Published: January 2010

This investigation presents an analytical and computer-aided study on the dynamics of meshing gears with backlash. Based on the rotary gear impact model of Yang and Sun, a modified model with additional considerations of bending deflection, axial compression, and Coulomb friction is developed. Despite the complexity in gear geometry, formulas for modeling these phenomena are all analytically derived. A computer simulation package is developed for this model. Consequently gear impact dynamics and the relative importance among the included considerations are studied. Results show that the energy loss due to the Hertzian damping is usually larger than that from the Coulomb friction, and the axial compressive energy is negligible in comparison to tooth bending energy. It is believed that the model and the finding in this study contribute toward understanding of impact behaviors of high-speed geared systems with frequent stop-and-start or intermittent motions.
Parametric Stability of a Two-Degree-of-Freedom Machine System: Part I—Equations of Motion and Stability
Authors: Zadoks R. I. , Midha A.
Published: January 2010

An important question facing a designer is whether a certain machine system will have a stable operating condition. To date, the investigations which deal with this question have been scarce. This study treats an elastic two-degree-of-freedom system with position-dependent inertia and external forcing. In Part I, the nonlinear equations of motion are derived and linearized about the system’s steady-state rigid-body response. The stability of the linearized equations is examined using Floquet theory, and a computationally efficient method for approximating the monodromy matrix is presented. A specific example is proposed and the results are presented in Part II of this paper.
Resolving Degeneracy in the Generalized Reduced Gradient Method
Authors: Gabriele G. A. , Beltracchi T. J.
Published: January 2010

The Generalized Reduced Gradient (GRG) method has proven to be one of the more robust and efficient algorithms currently available for solving nonlinear programming problems. The method divides the vector of design variables into two classes, nonbasic and basic variables, and employs the implicit function theorem to formulate a reduced, unconstrained problem in the nonbasic variables. In order to employ the implicit function theorem two assumptions are made: (1) The Jacobian matrix of the active constraints with respect to the basic variables is nonsingular; and (2) All basic variables are within their respective bounds. When the second condition is not satisfied then the current point is degenerate and further progress is not assured. Methods based on performing basis changes exist for resolving degeneracy. In this paper, we will describe a technique based on the method of feasible directions which has the advantage of requiring no basis changes to generate a new direction.
Fault Tree Approach for the Reliability Analysis of Gear Trains
Authors: Pan T. S. , Rao S. S.
Published: January 2010

The application of fault tree techniques to the analysis of gear trains is considered. The techniques involve the decomposition of the system into a logic diagram or fault tree in which certain basic or primary events lead to a specified top event which signifies the total failure of the system. The fault trees are used to obtain minimal cut sets from which the modes of system failure and, hence, the reliability measure for the top event can be calculated. The method of constructing fault trees and the subsequent estimation of reliability of the system is illustrated through a nine speed compound gear train and a five speed epicyclic gear train.
Piston Rod Design Using Johnson’s Method of Optimum Design
Authors: Onwubiko C.
Published: January 2010

Many of the available algorithms for solving the problems of nonlinear optimization have failed to yield results. This may be as a result of searching for solutions in an infeasible region or because the problem is ill-defined. In any case, there is no way for the designer to know that any of these situations exist ahead of time. However, Johnson’s method of optimum design is one algorithm that is capable of giving insight to the designer when a feasible solution may exist. This paper applies this method to the design of a piston rod. It is also demonstrated that using this method the designer can easily consider many types of materials in the design process without undue waste of time.
Thermal Performance of a Heat Storage Module Using Calcium Chloride Hexahydrate
Authors: Dietz D.
Published: January 2010

The thermal performance of an air-heated/cooled, phase-change, heat stoage module was tested and evaluated. The module (rated at 38.7 kWh) consist of 130 vertically oriented tubes filled with 729 kg (1607 lb) of calcium chloride hexahydrate and enclosed in a rectangular box. Heat transfer rates measured during charging and discharging decreased with time as a result of decreasing effective heat transfer area and increasing thermal resistance of the phase-change material. These two dominant effects are included in a proposed mathematical model that predicted the experimental data.
Physics Considerations of Solar Energy Conversion
Authors: Haught A. F.
Published: January 2010

A comparative analysis is presented of the conversion of radiant energy to useful work by thermal and quantum processes. The operation of thermal and quantum converters and the thermodynamic conversion efficiency of each are developed in terms of the mechanism of radiation-matter interaction in thermal and quantum systems. From the analysis the maximum conversion efficiency of a single-collector thermal converter with unconcentrated solar radiation and an ambient (reservoir) temperature of 300 K is 0.540; for the same conditions the maximum conversion efficiency of a single-collector quantum system is 0.309. The analysis is extended to consider the effects on the conversion efficiency of heat reject temperature, cascaded operation, in which the reject heat of the quantum converter is used as the input to a thermal bottoming cycle, and of concentration of the solar radiation. The results obtained represent the thermodynamic limits for radiant energy conversion by thermal and quantum processes, and calculations with solar input serve as a reference against which to judge the performance and capabilities of prospective solar energy conversion systems.
Solar-Powered/Fuel-Assisted Rankine-Cycle Power and Cooling-System: Simulation Method and Seasonal Performance
Authors: Lior N. , Koai K.
Published: January 2010

The subject of this analysis is a solar cooling system based on a novel hybrid steam Rankine cycle. Steam is generated by the use of solar energy collected at about 100° C, and it is then superheated to about 600° C in a fossil-fuel-fired superheater. The addition of about 20–26 percent of fuel doubles the power cycle’s efficiency as compared to organic Rankine cycles operating at similar collector temperatures. A comprehensive computer program was developed to analyze the operation and performance of the entire power/cooling system. Transient simulation was performed on an hourly basis over a cooling season in two representative climatic regions (Washington, D.C. and Phoenix, Ariz.). One of the conclusions is that the seasonal system COP is 0.82 for the design configuration and that the use of water-cooled condensers and flat-plate collectors of higher efficiency increases this value to 1.35.
Nongray-Radiative and Convective-Conductive Thermal Coupling in Teflon-Glazed, Selective-Black, Flat-Plate Solar Collectors
Authors: Edwards D. K. , Rhee S. J.
Published: January 2010

An analysis is presented comparing Teflon film with glass for the inner glazing of a double-glazed selective-black, flat-plate solar collector. The effect of spacing between glazings and between the inner glazing and absorber plate is examined. It is shown that a 12.5-micron Teflon film is superior to glass for the inner glazing of a selective-black collector, because the advantage of its high solar transparency overwhelms the disadvantage of its infrared transparency. A too-small spacing between a selective-black absorber and its inner cover short-circuits the desirable thermal radiation resistance offered by a selective-black absorber plate. Account is taken of spectral variations in the radiation properties of glass, Teflon, and the absorber plate. Allowance is made for the fact that critical Rayleigh number is lower for a plastic film inner glazing than for a glass one.
Solar-Cell Interconnect Design for Terrestrial Photovoltaic Modules
Authors: Mon G. R. , Moore D. M. , Ross R. G.
Published: January 2010

An investigation of interconnect fatigue in photovoltaic systems has led to the development of useful reliability-design and life-prediction algorithms presented here. Experimental data gathered in this study indicate that the classical strain-cycle (fatigue) curve for the interconnect material fails to account for the broad statistical scatter, which is critical to reliability prediction. To fill this shortcoming, a functional form is fitted to experimental cumulative interconnect failure-rate data to yield statistical fatigue curves (with failure probability as a parameter) that enable (a) the prediction of cumulative interconnect failures during the design life of an array field, and (b) the unambiguous—i.e., quantitative—interpretation of data from field-service qualification (accelerated thermal-cycling) tests. Optimal interconnect cost-reliability design algorithms are derived, intended to minimize the cost of energy over the design life of the array field. This procedure yields not only the minimum break-even cost of delivered energy, but also the required degree of interconnect redundancy and an estimate of array power degradation during the design life of the array field. The usefulness of the design algorithms is demonstrated with realistic examples of design optimization, prediction, and service qualification testing.
On the Tracking Error of a Self-Contained Solar Tracking System
Authors: Baz A. , Sabry A. , Mobarak A. , Morcos S.
Published: January 2010

This paper deals with the analysis of the tracking errors of a self-contained solar tracking system that is totally powered by solar energy. The effect of the different design parameters of the system on its tracking error is studied in detail, in an attempt to define the important factors that influence the system’s performance. The obtained results present valuable design guides for this class of tracking system.
The Use of Serpentine Earth Coils in Ground Coupled Heat Pump Systems
Authors: Metz P. D.
Published: January 2010

A research program at Brookhaven National Laboratory (BNL) has studied ground coupling, i.e., the use of the earth as a heat source/sink or storage medium for solar-assisted and stand-alone heat pump systems. As part of this research program, five serpentine earth coil experiments were operated between December 1978 and September 1981. Heat was added to or removed from the earth coils according to weekly schedules based on computer simulations of solar-assisted and stand-alone, ground-coupled heat pump systems operated in the local (New York) climate. Each earth coil was operated according to a different control strategy. This paper presents experimental results from these experiments for the period December 1978 to April 1981, and compares these results to those generated by a comptuer model, GROCS, developed at BNL. The model is found to provide a reasonably good fit to the data, for the most part, using the experimental undisturbed soil thermal properties. In some cases, the use of a lower soil thermal conductivity provides a better fit, particularly during summer months when heat was added to the ground. Thus, given soil properties, GROCS can be used to predict earth coil performance. If given earth coil performance, the model can predict soil thermal properties. Serpentine earth coils are found to be suitable to provide auxiliary heat or heat rejection for solar heat pump systems. In fact, earth coil-based, stand-alone, ground-coupled heat pump systems can provide all heat needed for winter space heating and all heat rejection required for summer space cooling with no need for any auxiliary heating. Subfreezing winter operation is necessary for shallow earth coils in cold climates. No deleterious effects to the ground were observed from the long-term operation of these experiments.
Numerical Study of Flow and Temperature Stratifications in a Liquid Thermal Storage Tank
Authors: Guo K. L. , Wu S. T.
Published: January 2010

A two-dimensional, time-dependent mathematical model has been developed to investigate the flow and temperature stratification phenomena in a liquid thermal storage tank for a solar energy system. This model is based on the principles of both natural and forced convective heat transfer. To obtain the numerical solution for this set of nonlinear partial differential equations, an improved Alternative Direction Implicit (ADI) scheme was developed, which enables us to obtain solutions for very large Grashof and Reynolds numbers for the first time. In this analysis, we present the numerical results on the flow patterns and temperature distributions in a liquid storage tank for various Reynolds and Grashof numbers together with the numerical scheme.
Determination of Direct Normal Solar Radiation From Measured Global Values—Comparison of Models
Authors: Turner W. D. , Mujahid A. M.
Published: January 2010

The modeling of direct normal solar radiation from measured global solar radiation is discussed and a new direct normal model developed from the Mississippi County Community College solar monitoring station at Blytheville, Ark., is presented. Comparisons of several existing models, including the Aerospace model developed by Randall and Whitson, are made. The Blytheville model and the Aerospace model are compared using five recent solar radiation data bases. The Aerospace model proved to be superior to all the models for the data bases used; however, the Blytheville model was only slightly less accurate and much easier to use. The Blytheville model predicted the beam radiation accurately for several widely varying climatic locations.
Optimization and Design of Zone Heating Systems, Energy Conservation, and Passive Solar
Authors: Kirkpatrick A. , Winn C. B.
Published: January 2010

This paper addresses the problem of determining the optimal mix of energy conservation, passive solar, and zone heating systems in residential buildings. Analytic solutions to constrained and global optimization problems are presented. This work draws upon the Lagrangian multiplier technique used in related studies of energy conservation and passive solar design. Graphs are presented showing the optimal cost fractions for energy conservation, passive solar, and a zone heater as a function of the initial cost constraint, for a reference building in Dodge City, Kansas. The use of a zone heater is shown to reduce the annual energy requirements for space heating, and increase the life cycle savings. Also presented are design curves for the required zone heater capacity as a function of the thermal time constant for a given zone, heater response time, and interzonal heat transfer. Finally, design curves for the zone mean radiant temperature as a function of zone size, zone heater temperature, zone heater area, and interzonal heat transfer are presented.
Solar Collector Parameter Identification From Unsteady Data by a Discrete-Gradient Algorithm
Authors: Hotchkiss G. B. , Burmeister L. C. , Bishop K. A.
Published: January 2010

A discrete-gradient algorithm is used to identify the parameters in a one-node and a two-node capacitance model of a flat-plate collector. Collector parameters are first obtained by a linear-least-squares fit to steady state data. These parameters, together with the collector heat capacitances, are then separately determined from unsteady data by use of the discrete-gradient algorithm with less than 10 percent deviation from the steady-state determination. All data were obtained in the indoor solar simulator at the NASA Lewis Research Center.
Electrical Wind-Assisted Water Pumping
Authors: Clark R. N. , Vosper F. C.
Published: January 2010

Most modern wind turbines are designed to generate utility compatible AC electric power. The easiest way to use these wind turbines for irrigation pumping is by intertying with the electric utility grid. However, because irrigation pumping requires large amounts of power during critical crop growth stages and minimum power during the nongrowing season, utilities have to supply power during peak load times and purchase power during off peak times. Five wind turbines having induction generators have been operated in water pumping experiments at Bushland, Texas. These turbines ranged in rated capacity from 25 to 100 kW and have included both horizontal and vertical-axis types. All units have operated at least 5000 hr, with one unit having been operated for over 20,000 hr. Performance curves, monthly energy production, percentage of run-time, and availability are given for each turbine.
Interannual Wind Speed Variations and Estimated Wind Turbine Generator Energy Output at Selected Sites in the Pacific Northwest
Authors: Baker R. W.
Published: January 2010

The hourly wind speed data collected over a six-year period at four wind power measurement locations are used to estimate the annual energy output of a large wind turbine generator. The interannual energy and wind speed variations are discussed. The estimated interannual energy output at each location is related to the mean annual wind speed variation. The data indicate that at three of the four locations the estimated interannual energy variation varied as the square of the mean annual wind speed variation. That is, a 10 percent increase in the mean annual wind speed resulted in a 20 percent increase in the annual energy output. At the fourth location there was an approximate linear relationship.
Energy Conservation Potential of Large Capacity Solar-Assisted Heat Pumps for Low Temperature IPH Applications
Authors: Chaturvedi S. K. , Murphy L. M.
Published: January 2010

Energy conservation and economic potential of large capacity (∼MWth) solar-assisted water-to-water heat pumps (SAHP) is evaluated for year round low temperature (<100° C) industrial process heating applications at four locations in the United States. The long-term thermal performance of the SAHP system is determined by a recently proposed utilizability method that accounts for the variable coefficient of performance of the SAHP system. The large SAHP system appears to be an attractive energy conservation alternative to fuel oil and electricity for locations with high solar resources and low electricity costs. In all but one location, the SAHP system was clearly superior to the solar only systems, such as flat plate and concentrating collectors, from the point of view of the annualized delivered energy cost. For the ranges of collector area and load temperatures considered in this study, the large SAHP system has clearly superior energy conservation potential at all four locations compared to other alternatives such as fuel oil or electricity. However, the practial suitability of SAHP cycle, as determined by the levelized cost of delivered energy, is unfavorable at all four locations when compared with fuel oil.
An Analytical Model for the Integrated Daily Performance of Solar Air Heating Systems
Authors: Hoerger C. R. B. , Phillips W. F.
Published: January 2010

An analytical Integrated Daily Performance Model (IDPM) is developed to predict the long term performance of solar air heating systems. The model is developed for systems using packed-bed energy storage and includes the effects of temperature stratification within the storage. The model makes use of the stratification coefficient approach to integrate the equations describing system performance. This analysis differs from similar previous analyses for water heating systems in that a control scheme more typical of air heating systems is used: collector output may go directly to either storage or the load. The IDPM is compared to simulations using a fully mixed model of storage and a single-phase model of storage. The comparisons show that the IDPM is more accurate than the mixed model and requires considerably less computation time than simulations using the single-phase model. In addition, the IDPM identifies several parameters that are important to system performance, but are not easily identified by non-analytical analyses.
Low-Concentration CPC’s for Low-Temperature Solar Energy Applications
Authors: Gordon J. M.
Published: January 2010

We consider the feasibility of low-concentration CPC’s for low-temperature applications. A quantitative assessment of optical gains versus thermal losses, and of savings in reflector area, leads to the conclusion that low-concentration CPC’s of relatively small acceptance angle may be competitive with, or superior to, flat plates. Calculations of yearly collected energy and material requirements are presented, and comparisons are made with corresponding flat plate collectors.
Operation of a Small-Scale Salt-Gradient Solar Pond: Experimental Results
Authors: Elhadidy M. A. , Nimmo B. G. , Zubair S.
Published: January 2010

A small-scale sodium chloride salt gradient solar pond was operated outdoors in Dhahran over a period of nine months. Vertical temperature profiles in the pond and in the ground underneath the pond, density profiles and temperatures at fixed locations in the pond were measured. Variation of the bottom zone temperature with time over the operating period is presented as well as representative vertical pond temperature profiles taken in the morning and afternoon. From these profiles and additional temperature data taken from fixed locations in the bottom zone, some insight was gained regarding onset of bottom convection and the midday total energy collection. Evidence is shown which suggests that weak convective cells in the gradient zone will “self-heal” even when on the order of 5 cm in thickness.
Transmission of Solar Radiation Through a Random Medium of Water and Glass
Authors: Witte M. J. , Newell T. A.
Published: January 2010

Two models are presented for the prediction of solar radiation transmission through a random medium of glass and water. One model is based on two-dimensional radiation exchange through a rectangular lattice of glass and water. This model is also applicable for materials other than glass and water. The other model is a semi-empirical equation which expresses the transmission as an exponential function. Both models predict transmittances within 5–10 percent of experimental data.
Double Diffusive Natural Convection in Solar Ponds With Nonlinear Temperature and Salinity Profiles
Authors: Kirkpatrick A. T. , Gordon R. F. , Johnson D. H.
Published: January 2010

A solar pond can be used as a thermal energy source provided that convective instabilities do not occur. This paper experimentally examines the stability of a fluid layer with nonlinear salinity and temperature profiles. A nonlinear salt profile was set up in a fluid layer, and the water was heated by a solar radiation simulator. Three stability experiments were conducted. Instabilities occurred at the location of the weakest salinity gradient, and were confined to a thin region, as predicted by theory. A local length scale was used to produce a stability parameter, the ratio of thermal to solute Rayleigh numbers. It is shown that for nonconstant solute and temperature gradients, the appropriate length scale is based on the radius of curvature of the salinity distribution. With this chocie of a length scale, good agreement was found between theory and experiment for the onset of an instability.
Nonimaging Solar Energy Concentrators (CPC’s) With Fully Illuminated Flat Receivers: A Viable Alternative to Flat-Plate Collectors
Authors: Gordon J. M.
Published: January 2010

Low-concentration, stationary, nonimaging concentrators (CPC’s) with flat receivers illuminated on both sides are considered as viable alternatives to flat-plate solar collectors. Closed-form, analytic formulae are derived for the geometric characteristics of two concentrator types of greatest interest (i.e., stationary collectors for year-round energy delivery), which enable calculations of collectible energy without computer ray-tracing stimulations. The relative merits of these concentrators in terms of energy collection and production costs are assessed with respect to each other as well as to flat-plate collectors.
In-Line Sputtering System for Depositing CuInSe2/CdS Heterojunctions
Authors: Thornton J. A. , Lommasson T. C. , Cornog D. G.
Published: January 2010

An in-line deposition system for fabricating all-sputtered CuInSe2/CdS heterojunctions has been designed and fabricated. The system uses planar magnetron sputtering sources driven with direct currents. The apparatus consists of a vacuum interlock and four processing chambers. A vertically mounted frame containing four 25 mm × 25 mm substrates is introduced through a vacuum interlock and positioned at stationary deposition stations within each of the four processing chambers. One chamber is configured for depositing a metal base electrode. A second chamber contains a station for depositing CuInSe2 by reactive cosputtering from Cu and In sources in an H2Se-Ar atmosphere. The final two chambers are configured for depositing a CdS layer consisting of two sublayers such, for example, as (CdZn)S and In-doped CdS which are deposited by reactive sputtering from Cd-alloy targets in an H2S-AR atmosphere. The CuInSe2 deposition chamber is isolated from the base electrode and CdS deposition chambers by gate valves to minimize cross contamination. The system has now been operated for over a year with more than three hundred deposition runs having been made, using primarily the CuInSe2 deposition chamber. Solar cells with efficiencies up to 6 percent have been fabricated from reactive sputtered CuInSe2 layers deposited using the apparatus. The purpose of this paper is to describe the design and operation of the system.