bluuebunny/crossref_metadata_2025 huggingface dataset:
Operating Thresholds of Solar Collection Systems
Authors: Ward D. S.
Published: January 2010

A solar collector subsystem operating threshold is defined as the minimum solar insolation rate at which useful heat can be collected when collector loop piping heat losses and parasitic power requirements are considered. This paper discusses the quantitative effect of these energy flows on the operating threshold of the solar subsystem (and thus on the overall system efficiency), and briefly considers the effects of different installation and design procedures.
Computational Dynamic Modeling of Thin Film Evaporators and Condensers
Authors: Yao Shi-chune , Westerberg A. W. , Chao Nien-Hua
Published: January 2010

The steady and dynamic behavior of thin film evaporators and condensers are simulated with a general thin film heat exchanger model. The dynamics of the gravity-controlled falling laminar film on horizontal and vertical tubes are studied in detail. For a first approximation or for a slow transient a single-lumped model can be used. For a refined simulation or for a severe transient a grouped model is proposed. The grouped model preserves the important feature of delay-time and wave-distortion of a transient, which was observed in a separate precise analysis [9]. The thin film heat exchanger models are used in the dynamic simulation computer programs ODSP3 and OSCAR which were established for OTEC systems. Typical results are presented to demonstrate the capability of the model.
Comparative Study of Solar Optics for Paraboloidal Concentrators
Authors: Wen L. , Huang L. , Poon P. , Carley W.
Published: January 2010

Different analytical methods for computing the flux distribution on the focal plane of a paraboloidal solar concentrator are reviewed. An analytical solution in algebraic form is also derived for an idealized model. The effects resulting from using different assumptions in the definition of optical parameters used in these methodologies are compared and discussed in detail. These parameters include solar irradiance distribution (limb darkening and circumsolar), reflector surface specular spreading, surface slope error, and concentrator pointing inaccuracy. The type of computational method selected for use depends on the maturity of the design and the data available at the time the analysis is made.
Flow Field Analysis and Performance of Wind Turbines Employing Slotted Diffusers
Authors: Loeffler A. L.
Published: January 2010

Operation of diffuser-augmented wind turbines (DAWTs) utilizing slotted walls for tangential blowing as a boundary layer control measure has been analyzed using the method of singularities (MOS). The diffuser wall and the drop in total pressure through the turbine are represented by a series of ring vortices along the diffuser surface and along the wake boundary. Diffuser included angles of 60 to 80 deg are considered, in contrast to the conventional range of 7 to 10 deg. Agreement with Grumman Research Department experimental data with respect to overall performance and pressure and velocity distributions is reasonably good. In particular, the existence of the observed large pressure reduction at the diffuser exit plane is predicted. A consequence of this agreement is that Reynolds number scaling effects are small for slotted DAWTs, so that MOS analyses hold promise for other innovative diffuser designs and flow problems.
Design, Evaluation, and Testing of a Moderately Concentrating, Nontracking Solar Energy Collector
Authors: Olvera A. , Bannerot R. B.
Published: January 2010

The thermal performance of a moderately concentrating, nontracking, trough-like solar energy collector is predicted based on a series of experimental evaluations of its components. Four reflector designs were constructed and tested. Two were one-facet side wall (reflector) designs; two were two-facet designs. Six simple tubular, nonevacuated receiver designs were tested. A collector utilizing one of the reflector designs, geometric concentration ratio of 2.6, and one of the receiver designs was constructed and tested. The predicted performance (an effective overall heat loss coefficient of 4.6 W/m2–°C, an optical efficiency of 0.71 and a heat recovery factor of 0.95) closely approximated the actual thermal performance of the collector. The component evaluations are discussed in such detail that the analysis could easily be extended to other designs by the reader.
Design Improvements in LiBr Absorption Chillers for Solar Applications
Authors: Grossman Gershon , Bourne Joseph R. , Ben-Dror Jonathan , Kimchi Yigal , Vardi Isaiah
Published: January 2010

The present article describes a theoretical evaluation of two design improvements made in a lithium bromide absorption chiller which contribute substantially to its performance in solar applications. One is the addition of a solution preheater which allows for a considerable reduction in generator size and cost, and improves performance at part load. The other is the addition of an auxiliary generator which enables the chiller to operate at nominal capacity or higher at all times, while utilizing to a maximum the solar radiation available at the time, however small. This is an effective solution to the problem of backup required in all solar-powered systems. The evaluation has been performed by computer simulation and results are presented for the performance of the unit with different configurations of the above systems. The results indicate the limitations on the part of the load to be supplied by the preheater. They point toward the advantage of using an auxiliary generator in a separate shell from the solar-powered generator and with a separate condenser. Operating curves for the chiller with the design improvements are given.
Optimal Control of Mass Flow Rates in Flat Plate Solar Collectors
Authors: Winn R. C. , Winn C. B.
Published: January 2010

The optimal flat plate collector fluid flow rate is determined for several combinations of objective functions and system models. The method of implementing the control strategy for one of the problems considered, that which maximizes the integral of the difference between the collected solar power and fluid moving power, is described. The performance of the solar energy collection system in Solar House II at Colorado State University using this optimal controller is discussed and compared with the same system using bang-bang control. In addition, the dependence of the collector efficiency factor on flow rate is considered and its effect on the optimal control is determined.
Design Procedure and Application of Solar-Assisted Series Heat Pump Systems
Authors: Svard C. D. , Mitchell J. W. , Beckman W. A.
Published: January 2010

A general design procedure is presented for solar-assisted series heat pump systems used for space and process water heating. The procedure accounts for the variable efficiency and rate of energy delivery by the heat pump. The fraction of the required energy supplied by solar and the fractions supplied by work and auxiliary are determined. The performance results from this design procedure are compared against detailed computer simulations on a monthly and seasonal basis. For low temperature space heating applications, the maximum difference between the design procedure and computer simulations is three percent on a seasonal basis and 12 percent on a monthly basis. For high temperature process water heating systems, the maximum differences are three to six percent on a seasonal basis and six to 12 percent on a monthly basis, with the accuracy dependent upon the control strategy used. This design procedure is used to investigate high temperature series heat pump systems for providing hot water for industrial processes. Various system parameters are evaluated in terms of the overall effect that each has on system performance and design. Recommendations are given for high temperature series heat pump system design.
Natural Convection and Sidewall Losses in Trapezoidal Groove Collectors
Authors: Iyican L. , Witte L. C. , Bayazitoglu Y.
Published: January 2010

Experimental data for heat transfer across air-filled inclined trapezoidal enclosures are reported for a Rayleigh number range of ∼2 × 103 to ∼5 × 107. The large side was cooled to uniform temperature while the opposing small side was electrically heated. The enclosures were completed by two aluminum sidewalls which simulated the reflective surfaces in moderately-concentrating solar collectors. The experiments show that conductive heat losses up the sidewalls can be very large even when the sidewalls are thermally insulated from the top and bottom surfaces. However, the conductivity of the sidewalls has only a small effect on convective heat transfer across the groove. Natural convection heat transfer in the groove can be correlated reasonably well by an equation of the form Nu = C Ra0.345.
An Analysis of the Influence of Geography and Weather on Parabolic Trough Solar Collector Design
Authors: Treadwell G. W. , Grandjean N. R. , Biggs F.
Published: January 2010

The potential performance of single-axis tracking parabolic trough solar collectors as a function of optical energy distribution and receiver size has been calculated for 11 sites using typical meteorological year input data. A simulation based on the SOLTES code was developed which includes the three-dimensional features of a parabolic trough and calculates the thermooptical tradeoffs. The capability of the thermo-optical model has been confirmed by the comparison of calculated results with the experimental results from an all-day test of a parabolic trough. The results from this 11 site analysis indicate a potential performance superiority of a north-south horizontal axis trough and, in addition, a high quality (optical error, σsystem≤0.007-radian) collector should be of the same geometric design for all of the sites investigated and probably for all regions of the country.
Review, Evaluation, and Improvement of Direct Irradiance Models
Authors: Bird R. E. , Hulstrom R. L.
Published: January 2010

A study was performed to: (1) define the relative significance of the various atmospheric constituents to the depletion of the direct solar beam irradiance; (2) compare and evaluate several simple models versus a complex SOLTRAN-model; and (3) develop an improved, easy to use model. The results indicate that for a reasonable range of atmospheric conditions the broadband direct beam energy is attenuated by atmospheric constituents in the following order: aerosols attenuate the most; molecular scattering is next in importance; and water vapor absorption is third. Attenuation by O3, O2, and CO2 is minor. The total irradiance from various models agree to within ±10 percent at small zenith angles, but diverge significantly at large zenith angles.
Glass as Encapsulation for Low-Cost Photovoltaic Solar Arrays
Authors: Bouquet F. L.
Published: January 2010

In photovoltaic systems, the encapsulant material that protects the solar cells should be highly transparent and very durable. Glass satisfies these two criteria and is considered a primary candidate for low-cost, photovoltaic encapsulation systems. In this paper, various aspects of glass encapsulation are treated that are important for the designer of photovoltaic systems. Candidate glasses and available information defining the state of the art of glass encapsulation materials and processes for automated, high volume production of terrestrial photovoltaic devices and related applications are presented. The desired characteristics of glass encapsulation are (a) low degradation rates, (b) high transmittance, (c) high reliability, (d) low-cost and (e) high annual production capacity. The glass design areas treated herein include the types of glass, sources, prices, physical properties and glass modifications, such as antireflection coatings.
Mini-OTEC Operational Results
Authors: Owens W. L. , Trimble L. C.
Published: January 2010

The first at-sea ocean thermal energy conversion (OTEC) power was produced by Mini-OTEC on Aug. 2, 1979. The powerplant was mounted on a barge located approximately 2.2 km off Keahole Point on the Kona Coast of Hawaii. Ammonia was employed as the working fluid in a closed-cycle (Rankine) powerplant, which produced approximately 50 kW of gross electrical power at an average seawater temperature difference of 21°C. Parasitic pumping power requirements for seawater and ammonia resulted in a net electrical power of approximately 15 kW. Cold seawater was drawn from a depth of approximately 670 m through a 0.61 m dia polyethylene pipe, which formed part of a single-point tension leg mooring system. The longest period of continuous operation was 10 days, terminated by the conclusion of the program on Nov. 18, 1979.
Design Optimization of Sinusoidal Glass Honeycomb for Flat Plate Solar Collectors
Authors: McMurrin J. C. , Buchberg H.
Published: January 2010

The design of honeycomb made of sinusoidally corrugated glass strips was optimized for use in liquid-heating, single-glazed flat plate solar collectors with nonselective black absorbers. Cell dimensions maximizing daily-averaged solar collector efficiency and heat output per unit cost were estimated from present materials costs and postulated production methods for corrugated glass honeycomb cover assemblies. Efficiency of a cost-optimized honeycomb collector was predicted to be up to 60 percent at 100°C above ambient, and stagnation temperature up to 230°C above ambient (1000 W/m2 insolation), with lower cost per unit output than selective-absorber collectors similarly optimized.
One Viewpoint Concerning Unit Size in the Development of Wind Turbines
Authors: Howell W. E. , Todd C. J.
Published: January 2010

The size of wind machines best adopted for early penetration toward large-scale use is affected by the size of the national interim windpower goal (170 GW average power by 2000 AD) and the experience rate coupling cost of power to number of machines produced. Windpower mission studies made in 1976 are modified in the light of various goal-size and experience-rate assumptions, resulting in a rather flat cost minimum near 0.3–0.6 MW, suggesting that other considerations may be decisive. Several of these assumptions are discussed, leading to the conclusion that, although larger machines may prevail in the long run, moderate sizes are best suited to the early commercialization phase.
OTEC Gas Desorption Studies
Authors: Chen F. C. , Golshani A.
Published: January 2010

Seawater deaeration is a process affecting almost all proposed ocean thermal energy conversion (OTEC) open-cycle power systems. If the noncondensible dissolved air is not removed from a power system, it will accumulate in the condenser, reduce the effectiveness of condensation, and result in deterioration of system performance. To explore ways to mitigate these effects, a test loop was constructed and experiments were carried out in three areas: (a) vacuum deaeration in a packed column using Raschig rings or plastic pall rings, (b) deaeration in a barometric water intake system, and (c) noncondensibles disposal through hydraulic air compression. Preliminary subsystem analyses based on the experimental data have shown that, as compared to the previous baseline study, a 10 percent reduction both in deaeration cost and pumping power can be realized with a combination of barometric intake and packed column deaeration. The design and operation of the gas desorption loop and the experimental and computer simulation results are presented. The implications for OTEC open-cycle power systems are discussed.
A Methodology for Assessment of Wind Turbine Noise Generation
Authors: Kelley N. D. , Hemphill R. R. , McKenna H. E.
Published: January 2010

The detailed analysis of a series of acoustic measurements taken near several large wind turbines (100 kW and above) has identified the maximum acoustic energy as being concentrated in the low-frequency audible and subaudible ranges, usually less than 100 Hz. These measurements have also shown any reported community annoyance associated with turbine operations has often been related to the degree of coherent impulsiveness present and the subsequent harmonic coupling of acoustic energy to residential structures. Thus, one technique to assess the annoyance potential of a given wind turbine design is to develop a method which quantifies this degree of impulsiveness or coherency in the radiated acoustic energy spectrum under a wide range of operating conditions. Experience has also shown the presence of annoying conditions is highly time dependent and nonstationary, and, therefore, any attempts to quantify or at least classify wind turbine designs in terms of their noise annoyance potential must be handled within the proper probabilistic framework. A technique is described which employs multidimensional, joint probability analysis to establish the expected coincidence of acoustic energy levels in a contiguous sequence of octave frequency bands which have been chosen because of their relationship to common structural resonant frequencies in residential buildings. Evidence is presented to justify the choice of these particular bands. Comparisons of the acoustic performance and an estimate of the annoyance potential of several large wind turbine designs using this technique is also discussed.
Lightning Protection of Wind Turbines
Authors: Dodd C. W.
Published: January 2010

Because many areas of favorable locations for wind turbines coincide with high thunderstorm activity, a lightning protection system for wind turbines is essential to prevent losses due to strikes. Damage can occur to blades, bearings, mechanical linkages, electrical equipment, power interconnections, and electronics. This paper discusses how often a wind turbine may receive a strike, what damages can be expected, and how protection can be provided.
The Development and Design of Steam/Water Central Solar Receivers for Commercial Application
Authors: Durrant O. W. , Capozzi T. J. , Best R. H.
Published: January 2010

Central tower solar receivers have many similarities to fossil-fuel-fired boilers in design, manufacturing, and construction. Babcock & Wilcox has designed several types of steam/water solar receivers. A typical DOE approach is to design, construct, and test in sequence a Subsystem Research Experiment (SRE) and a pilot plant, and then to scale it up to commercial sizes. In contrast, the normal approach of boiler manufacturers, and specifically Babcock & Wilcox, has been to design a sectionalized receiver and modularized components so they can be assembled in various sizes, capacities, and geometries to meet the requirements of the system and characteristics of the collector field. A receiver design having such features and using commercial-size and shop-assembled modules is described. Special design features are described to overcome the unbalance of north-to-south field flux ratios, effect of partial and transient cloud patterns, and a large number of thermal cycles. A parametric study to determine the maximum allowable heat flux on the heat transfer surface components is also described.
A Computer Model to Simulate Solar and Solar-Dehumidification Lumber Drying
Authors: Helmer W. A. , Chen P. Y. S. , Vaidya M. B.
Published: January 2010

A computer simulation model was developed for a solar lumber drier and a solar-dehumidification drier. Experimental data taken on an existing solar and solar-dehumidification drier compared well with the computer prediction. The solar-dehumidification lumber drier is able to dry wood about as fast as a conventional drier and yet use less than 50 percent of the fossel fuel energy at the site.
Effect of Circumsolar Radiation on Performance of Focusing Collectors
Authors: Rabl A. , Bendt P.
Published: January 2010

Circumsolar radiation is one of several factors, along with optical errors (contour, tracking, etc.), that determine the size and shape of the solar image at the receiver of a concentrating collector. The sensitivity of a collector to circumsolar radiation depends on insolation conditions and on collector parameters; it increases with geometrical concentration ratio and decreases with threshold. In this paper the Lawrence Berkeley Laboratory (LBL) circumsolar data are used to calculate the effect of circumsolar radiation on both the instantaneous and the long-term average performance of focusing collectors. To speed up the computations, the optical properties of the concentrator are expressed in terms of an angular acceptance function. The angular acceptance function and the brightness distribution of the sun are then convoluted, a procedure which requires, for each circumsolar scan, only 56 multiplications and additions (one for each of the angular intervals at which the brightness has been measured by the LBL circumsolar telescope). While the formalism is applicable to all focusing collectors, only parabolic troughs and dishes are evaluated explicitly in this paper. The instantaneous performance corresponding to particular circumsolar scans is of interest for the analysis of test results of collectors with high concentration. For most predictions of long-term average performance a far simpler approach will, however, be adequate. For this purpose a standard synthetic circumsolar scan has been developed that describes the brightness distribution of the solar disk (“limb darkening”) and of the circumsolar region. The radiation intercepted by a receiver is calculated once for the solar portion and once for the circumsolar portion of this standard sun shape. The long-term average radiation intercepted by the receiver is then obtained by averaging the solar and the circumsolar intercept factors, weighted according to the long-term average circumsolar ratio for the location and period under study. Tested against hour-by-hour simulations, this simple approach was found to have an rms error of only 0.2 percent, negligible compared to typical uncertainties in system performance calculations. This analysis points out the usefulness of the long-term average circumsolar ratio as a simple measure of circumsolar radiation.
Modeling of the Surface Convective Layer of Salt-Gradient Solar Ponds
Authors: Cha Y. S. , Sha W. T. , Schertz W. W.
Published: January 2010

A one-dimensional numerical model is developed to predict the diurnal variations of vertical temperature and concentration profiles in salt-gradient solar ponds. The model employs augmented thermal and mass diffusivities due to turbulent wind mixing and double-diffusive convection. Numerical results indicate that the thickness of the surface convective layer increases with wind speed (or the wavelength of the surface wave). Double-diffusive convection is, in the absence of wind, capable of sustaining a mixed layer at the surface when strong cooling occurs over the pond. In field ponds, the surface convective layer is probably maintained as a result of the combined action of wind-generated turbulent mixing and double-diffusive convection.
Appropriate Sizing of Solar Heating Systems
Authors: Bendt P.
Published: January 2010

It is generally assumed that a solar heating system should be sized by minimizing its life-cycle cost. This study shows, however, that the uncertainty in future economic trends makes the results of such a procedure questionable. The design conditions for minimum cost are extremely broad and all practical systems have a solar fraction within the limited range of 30 to 90 percent. Thus, by choosing only three collector areas that give systems within this range, one is assured of selecting a nearly optimal system for any realistic economic scenario. Selecting one of these three systems is essentially equivalent to economic optimization, but simpler. Procedures are derived in this paper for determining the sizes of the three systems. The conclusion is that the collector areas should be about 1/8, 1/5, and 1/3 of the building floor area. This rule of thumb eliminates the need to design solar systems individually, allowing the possiblity of mass-produced homes with standardized solar heating systems.
The Effect of Inlet and Exit Losses on Free Convective Laminar Flow in the Trombe Wall Channel
Authors: Tichy J. A.
Published: January 2010

A numerical solution for two-dimensional free convective laminar flow in the Trombe wall channel has recently been presented by Akbari and Borgers [1]. Their analysis assumed no flow losses in the channel entrance and exit, other than the exit dynamic head (loss coefficient k = 1), however the actual coefficient for combined inlet and exit losses is probably 2 < k < 5. In the present study, the convective terms of the momentum and energy equations are linearized through an Oseen-type approximation. A closed-form series solution to the resulting partial differential equations is obtained. Results are presented for dimensionless temperature and velocity field, flow rate and heat transfer; in terms of loss coefficient, surface temperature ratio, and Grashof number. As expected, vent loss reduces flow rate significantly: for loss coefficient k = 5, flow rate is reduced by ∼70 percent relative to k = 1. Surprisingly, at high Grashof number, vent loss can cause a significant (∼60 percent) increase in heat transfer. Reduction in flow rate occurs entirely due to flow velocity decrease in the region near the channel center, which contributes negligibly to the total heat delivery.
Thermal Performance Predictions and Sensitivity Analysis for a Parallel Flow Solar Regenerator
Authors: Gandhidasan P.
Published: January 2010

One of the efficient methods of regenerating the weak absorbent solution using solar energy is the forced flow regeneration system. This paper describes a forced flow solar regenerator in which the absorbent solution to be concentrated flows as a thin film over the absorber and the water evaporating from the solution due to absorption of solar energy is removed by forced air stream, which flow parallel to the liquid film. A theoretical model, which includes the variation of rate of evaporation of water along the flow length of the regenerator, has been used to examine the thermal performance of the regenerator. Changes in thermal performance are reported in terms of the ratio of solution flow rate to air flow rate and the amount of water evaporated from the absorbent solution.
Algorithm for Evaluating the Hourly Radiation Utilizability Function
Authors: Clark D. R. , Klein S. A. , Beckman W. A.
Published: January 2010

A computationally simple algorithm is presented for evaluating the hourly utilizability function, φ, defined as the fraction of the long-term, monthly-average, hourly solar radiation incident on a surface which exceeds a specified threshold intensity. The algorithm was developed by correlating values of φ obtained by numerical integration of hourly radiation for three locations. The algorithm is shown to compare well both with a more complex analytical expression for φ developed recently and with results obtained numerically using many years of hourly horizontal radiation measurements in nine U.S. locations. In addition, the algorithm is shown to be applicable for surfaces of any orientation.
A Numerical Model to Describe the Layer Behavior in Salt-Gradient Solar Ponds
Authors: Meyer K. A.
Published: January 2010

A numerical model has been developed to describe the time-dependent behavior of the interfaces between the convecting and nonconvecting regions of a salt-gradient solar pond. Salinity and temperature profiles, as a function of time, are also determined by the model. The model utilizes empirical correlations from the oceanographic literature that describe the heat and salt fluxes across the interfaces. The model also contains a treatment of entrainment caused by wind-generated turbulence. We find agreement of the calculated behavior with observations made on laboratory-scale solar pond simulation experiments. The model is used to determine pond performance under various operating conditions.
A Halo-Thermal Simulation of the Dead Sea for Application to Solar Energy Projects
Authors: Vadasz P. , Weiner D. , Zvirin Y.
Published: January 2010

A one-dimensional numerical model is developed to predict the long-range variations of vertical temperature, density, and salinity profiles in the Dead Sea, which is a highly saline large water body. The model utilizes the continuity, momentum, energy, and mass transfer equations, while taking into account the influence of the wind. The partial differential equations were solved numerically by means of explicit finite differences method. Simulation results were verified by comparison to measured data. In addition, the algorithm evaluates the evaporation rate from the Dead Sea which is an important parameter in several engineering projects under planning, such as the Mediterranean-Dead Sea conduit and the construction of floating salt gradient solar ponds for power generation.
Design, Performance, and Economics of 50-kW and 500-kW Vertical Axis Wind Turbines
Authors: Schienbein L. A. , Malcolm D. J.
Published: January 2010

A review of the development and performance of the DAF Indal 50-kW vertical axis Darrieus wind turbine shows that a high level of technical development and reliability has been achieved. Features of the drive train, braking and control systems are discussed and performance details are presented. Details are also presented of a 500-kW VAWT that is currently in production. A discussion of the economics of both the 50-kW and 500-kW VAWTs is included, showing the effects of charge rate, installed cost, operating cost, performance, and efficiency.
An Algebraic Formulation of Grashof’s Mobility Criteria With Application to Linkage Optimization Using Gradient-Dependent Methods
Authors: Angeles J. , Callejas M.
Published: January 2010

Sets of constraints on analytic functions of linkage parameters, equivalent to those of Grashof’s mobility criteria, are derived. These inequalities represent necessary and sufficient mobility conditions for the input and the output links of planar 4R linkages, as well as for its coupler link. The application of the foregoing constraint relations to linkage optimization using gradient-dependent methods is shown with an example that is fully solved resorting to Newton-Raphson’s method and an interior penalty function.
Parametric Stability of a Two-Degree-of-Freedom Machine System: Part II—Stability Analysis
Authors: Zadoks R. I. , Midha A.
Published: January 2010

In this paper, the equations developed in a companion paper (Part I) are adapted for use in developing stability charts. The nonlinear equations of motion were developed for a two-degree-of-freedom machine system in torsional vibration. Eigenvalues of the monodromy matrix, called Floquet multipliers, facilitate the examination of the solution to the linearized equations of motion. Two methods for producing the stability charts are presented here. A single-cylinder internal combustion engine is used as an example and sample results are included.
Rigid Body Location and Robot Workspaces: Some Alternative Manipulator Forms
Authors: Davidson J. K. , Hunt K. H.
Published: January 2010

Using an enumeration procedure for connectivity, the theoretically minimum number of actuators is identified for each of six types of point workspace. Robot dexterity is described using the omnidirectional, primary, and dexterous workspaces of a point. It is shown that only two plane workspaces are sufficient to provide all the mechanically achievable workspaces that are dual to the six point workspaces. Several manipulator structures are identified, and these provide equivalent dexterity to that achieved by a spherical wrist with three concurrent, sequentially orthogonal, and fully-rotatable hinge joints.
Configuration Optimization of Trusses Subject to Strength, Displacement and Frequency Constraints
Authors: Felix J. , Vanderplaats G. N.
Published: January 2010

Three-dimensional elastic trusses are designed for minimum weight, subject to constraints on member stresses, Euler buckling, joint displacements and system natural frequencies. Multiple static loading conditions are considered. The finite-element displacement method of analysis is used and eigenvalues are calculated using the subspace iteration technique. All gradient information is calculated analytically. The design problem is cast as a multilevel numerical optimization problem. The joint coordinates are treated as system variables. For each proposed configuration, the member sizes are updated as a suboptimization problem. This subproblem is efficiently solved using approximation concepts in the reciprocal variable space. The multilevel approach is shown to be an effective technique which conveniently takes advantage of the most efficient methods available for the member sizing problem. Examples are presented to demonstrate the method. The optimum configuration is shown to be strongly dependent on the constraints which are imposed on the design.
The Efficiency Limit of Belt and Cable Drives
Authors: Townsend W. T. , Salisbury J. K.
Published: January 2010

Compliant belt and cable drives cannot approach perfect efficiency. Some friction loss in the form of belt/pulley slippage must be present. Thermodynamic principles may be applied to a simple control volume drawn around a belt or cable drive to show that there is a limit on efficiency. This maximum efficiency applies to all belt and cable drives. Chain/sprocket drives, though similar to belt and cable drives, may not be limited to this efficiency. Consequences of the analysis relevant to belt and cable transmission design are that: (1) multiple transmission stages degrade the total efficiency, and (2) it is best to maximize the cable or belt speed and stiffness per unit length for a given power transmitted.
Probabilistic Optimal Design Using Second Moment Criteria
Authors: Belegundu A. D.
Published: January 2010

Probability-based optimal design of structures is presented. The emphasis here is to develop a practical approach to optimal design given random design parameters. The method is applicable to structures which are modeled using the finite element method. The Hasofer-Lind (H-L) second-moment design criterion is used to formulate the general design problem. A method for calculating the sensitivity coefficients is presented, which involves second-order design sensitivity analysis. The importance of second order derivatives is established. A nonlinear programming technique is used to solve the problem. Numerical results are presented, where stiffness parameters are treated as random variables.
Simulation of a Hydraulic Hybrid Vehicle Using Bond Graphs
Authors: Pease Grant , Henderson Jerald M.
Published: January 2010

A simulation of a hydro-pneumatic hybrid vehicle was developed using bond graphs. This simulation was verified and used as a design tool to optimize the performance and efficiency of the system.
Analysis and Design of the “Solar One” Thermal Storage Subsystem Heat Exchangers
Authors: Weiner F. R.
Published: January 2010

This paper describes the analysis and design of the five kinds of heat exchangers used in the thermal storage subsystem of the 10 MWe Solar Central Receiver Pilot Plant, now becoming more known as “Solar One.” The paper discusses the practices and standards used in the designs of the heat exchangers, lists the heat exchanger design requirements, and discusses the process conditions. The design assumptions and constraints, the geometrical considerations, and the tradeoff studies that were conducted to optimize the designs are also discussed. A description of each heat exchanger reveals the final design solution. Novel and unique features of a power plant that must operate on a daily sun-cycle are identified.
Overview of the Electrofluid Dynamic Wind-Driven Generator
Authors: Mitchell R. L.
Published: January 2010

The Electrofluid Dynamic wind-driven generator has been investigated under government supported programs since 1975. The concept features the direct conversion of wind energy into electrical power with virtually no moving parts. Research on this concept has resulted in a detailed operational theory of electrofluid systems and a preliminary conceptual design of a full-scale generator. Analysis of the potential of this concept has established a range for the value indicators and an understanding of its optimization potential and uncertainty. A comparison is made between the value indicators for the Electrofluid Dynamic concept and those of several conventional WECS.
Design Optimization of Small Wind Turbines for Low Wind Regimes
Authors: Cromack D. E. , Oscar Debbie
Published: January 2010

The optimized design of a wind turbine depends on numerous parameters involving the entire machine (rotor, generator, etc.) and on the intended operating environment as described by the wind characteristics as well as on the load or application. This paper presents the design optimization process, identifies and discusses the influence of the various parameters, and then reviews the procedure by looking at two examples. The results of this process emphasize the relative importance of the design on rated wind speed, rotor rpm, generator size, and rotor blade characteristics. These results in general show that wind turbines have been designed for excessively high-rated wind speeds and generator capacities, except for those machines intended for wind farm applications and sites with particularly high winds. Machines designed for residential use should be sized to closely match the expected load and should be rated at a wind speed close to that value where the maximum energy contribution occurs. This wind speed is much lower than the rated wind speed for most currently available machines particularly for regions of relatively low annual mean wind speeds. Simplicity of design leads to a lower cost system, lower maintenance, and operating costs and greater reliability. It is this simply designed and optimized wind turbine that will have lasting success in the commercial market place.
An Experimental Technique for Testing Thermosyphon Solar Hot Water Systems
Authors: Fanney A. H.
Published: January 2010

An experimental technique for testing thermosyphon solar hot water systems is described which allows testing of the system indoors under nonirradiated conditions. The technique described is applicable to thermosyphon systems that utilize flat-plate solar collectors. Energy normally absorbed by the irradiated solar collectors is supplied by electric strip heaters attached to the back side of the absorber plates. Analytical expressions are developed that allow the power input to the strip heaters to be calculated for various environmental conditions. A description of the experimental apparatus and test procedure is given. Results are presented that show that the performance of a thermosyphon system tested under nonirradiated conditions using the electric strip heater technique closely duplicates system performance under outdoor irradiated conditions
Heat Pipe Thermodynamic Cycle and its Applications
Authors: Kobayashi Y.
Published: January 2010

A new type of thermodynamic cycle originating from extended application of the heat pipe principle is proposed and its thermal cycle is discussed from the viewpoint of theoretical thermal efficiency and Coefficient of Performance (COP). An idealized structure that will meet the basic function for thermal systems is also suggested. A significant advantage of these systems is their use with low-temperature energy sources found in nature or heat rejected from industrial sites.
Thermodynamic Analysis of a Solar Zeolite Refrigeration System
Authors: Chang S. C. , Roux J. A.
Published: January 2010

A solar zeolite-water absorption refrigeration unit was studied. Thermodynamic expressions were derived to predict the system performance. The operating range and optimum design parameters for the zeolite system were determined. The main parameters governing performance were: solar collector type, ambient temperature, and absorber properties. Results are shown for various solar collector types and various zeolite types. A desorption initiation temperature is shown to exist. The analysis is not based on empirical heat of absorption data, but rather on a zeolite properties relationship (log Pv versus 1/Tz) to determine system performance.
Second-Law Analysis of Solar Collectors With Energy Storage Capability
Authors: Chelghoum D. E. , Bejan A.
Published: January 2010

This is an analytical and numerical study of the exergy that can be delivered by a solar collector installation with temporary energy storage capability. In the first part of the study, the method of variational calculus is used to show that under conditions of time-dependent inlet and outlet flow rates, the total exergy delivered by the installation is maximum when the collector temperature is maintained at an optimum constant level throughout the insolation period. More realistic models of solar collectors with storage capability are analyzed in the second and third parts of the study. In each of the models considered, the analysis shows that the relative timing of the filling and discharge processes has a significant effect on the total exergy delivered by the installation. The main conclusion of the study is that the daily regime of operation of the collection/storage installation can be selected by design in order to maximize the harvesting of solar exergy per unit of collector area.
Structural Design and Life Assessment of a Molten Salt Solar Receiver
Authors: Narayanan T. V. , Rao M. S. M. , Carli G.
Published: January 2010

This paper discusses the structural integrity and creep-fatigue life assessment of a commercial size molten salt solar central receiver. The life evaluation is based on criteria that are a modified version of ASME Code Case N-47. These criteria are deemed conservative enough to provide a reasonable level of safety and reliability, and yet not so conservative as to impose severe economic penalties on the receiver. The justification for these criteria and their application to the receiver are discussed in detail.
Single-Pass Open-Loop Solar Thermal Energy Systems: On Maximum Energy Delivery by Variable Flow Rate
Authors: Gordon J. M. , Zarmi Y.
Published: January 2010

For single-pass open-loop solar thermal energy systems, in which the flow rate can vary with radiation but is constrained to have a given annual average, an upper bound is derived for the yearly energy delivery. Compared to the corresponding constant flow rate, single-pass open-loop system, the upper bound for additional yearly delivery is found to be negligible for solar systems with practical design parameters. This implies that the sophistication and expense involved in searching for, and implementing, optimal variable (radiation-dependent) collector flow rate strategies for these systems may not be worth the effort. The sensitivity of this upper bound to climatic and collector characteristics is determined analytically, and is illustrated by several numerical examples. The results derived are general in that they apply to all collector types.
Development and Performance of a Digital Image Radiometer for Heliostat Evaluation at Solar One
Authors: Blackmon J. B.
Published: January 2010

A review is presented of the development, performance, and operation of a digital image radiometer (DIR) used to evaluate and enhance heliostat optical and tracking performance at the Solar One 10 MWe pilot plant at Daggett, Calif. The system, termed the beam characterization system (BCS), is based on digitizing, calibrating, and computer-processing video images of heliostat-reflected beams displayed on four 30- by 40-ft targets located on the tower beneath the receiver. Additionally, the radiance distribution of the sun is simultaneously recorded by a separate, specially modified solar-tracking video camera. The basic theory and analytical techniques used to determine beam centroid error (i.e., heliostat pointing errors), the actual incident beam power, spillage power off the receiver, and solar radiance distribution are described. The computer system is presented including the automatic data acquisition mode, the interface with the heliostat array controller (HAC), and the data acquisition system (DAS). Data display for plant operator purposes and additional data acquired and stored for more detailed engineering evaluations are discussed. Advanced applications of the DIR such as determination of total incident flux on a receiver from a field of heliostats, reflectance monitoring, and measurement of atmospheric attenuation are presented.
Study of Thermal Oscillations at the Dryout Front in Half Heated Tubes
Authors: Samra S. S. , Dhir V. K.
Published: January 2010

In this work thermal oscillations at the dryout front in an electrically heated composite tube of inconel and glass have been studied experimentally and analytically. The tube has an inside diameter of 17.2 mm, and a heated length of 1913 mm. The thickness of the inconel half tube is 0.89 mm. In the experiments deionized water and Freon-113 were used as the test liquids while the pressure at the exit of the tube was one atmosphere. The dryout front was established at a predetermined height from the inlet. The frequency and magnitude of the wall temperature oscillations in the vicinity of the dryout front has been obtained from the temperature-time history. The most probable time period obtained from the probability distributions has been correlated with dimensionless groups formed with mass velocity, tube diameter and the physical properties of the test liquid. Normalized probability distributions for the time period have been found to be represented by a modified gamma-distribution. The magnitude and the nature of the temperature oscillations has been predicted by solving the energy equation for the heated tube and the mass conservation equation for the liquid film left on the wall during upward movement of the dryout front. The predictions have been compared with the data.
On the Highest Efficiency Windmill Design
Authors: Galetuse S.
Published: January 2010

A discussion concerning the effect of profile drag on induced velocities is presented. It is concluded that Glauert’s relations for the ideal windmill are also valid for a real windmill. Using these results, the optimum conditions for induced efficiency and power coefficient are obtained. The chord distribution and the twist of the blade are then given as a function of constant K2 for highest power coefficient.
A Conceptual Basis for the Design of Parabolic Troughs for Different Design Environments
Authors: Gu¨ven H. M. , Mistree F. , Bannerot R. B.
Published: January 2010

In this paper, a rational approach for multi-objective design and optimization of parabolic trough solar collectors for different design environments is presented. A macro and micro-level partitioning of the design problem is implemented. In this process, environmental goals, objectives, and limitations are accounted for at the macro-level of design. At the micro-level of design, subsystem designs that were developed at the macro-level design are integrated such as to maximize the collector all-day thermal efficiency. A seven-step procedure is developed to optimize the collector dimensions at the micro-level of design. The process is demonstrated through illustrative examples.
Digital Control of Working Fluid Flow Rate for an OTEC Plant
Authors: Nakamura M. , Egashira N. , Uehara H.
Published: January 2010

The role of control in operating an OTEC plant efficiently is of great importance. This paper describes digital control of working fluid rate based on an adaptive control theory for the “Imari 2” OTEC plant at Saga University. Provisions have been made for linkage between the software of the adaptive control theory and the hardware of the OTEC plant. We can obtain satisfactory control performance using this digital control system.