bluuebunny/crossref_metadata_2025 huggingface dataset:
Spline Functions Applied to the Synthesis and Analysis of Nonrigid Cam-Follower Systems
Authors: Tsay D. M. , Huey C. O.
Published: January 2010

A general, systematic procedure for the synthesis and analysis of cams is presented. The method accounts for the nonrigid behavior of the follower system and can be readily implemented as a computer aided design tool. It employs spline functions to interpolate motion constraints in the synthesis of output motion programs. It applies the spline collocation method for the solution of the differential equations in determining the cam profile and in analyzing the follower system response. The development presented is based on a single degree-of-freedom (DOF) follower model. It offers the advantage over other methods of greater generality yet requires only routine application procedures. An example is provided to illustrate the complete synthesis/analysis procedure. The results from the example are compared to those obtained using a conventional polynomial approach.
Model Based Rigid Body Guidance in Presence of Nonconvex Geometric Constraints
Authors: Ku T. S. , Ravani B.
Published: January 2010

This paper presents an efficient algorithm for guidance of a convex rigid body in-between nonconvex polygonal objects in a Computer-Aided Design (CAD) environment. A shrinking procedure is used that separates the kinematic from the shape constraints by reducing the problem to that of guidance of a line segment in an expanded environment. A slicing technique together with an algorithm for decomposition of the interface channel between the nonconvex objects is used to generate the motion program for the line segment. The results can be applied to model based guidance of mobile robots or automatic motion planning for robot manipulators.
Workspace Analysis of Multibody Mechanical Systems Using Continuation Methods
Authors: Jo Doo-Yearn , Haug E. J.
Published: January 2010

A new approach to numerical analysis of workspaces of multibody mechanical systems is presented, based on manifold theory and computational continuation methods. Generalized coordinates that define the kinematics of a system are classified and interpreted from an input-output point of view. Boundaries of workspaces, which depend on the classification of generalized coordinates, are defined as sets of points for which Jacobian matrices of the kinematic equations are row rank deficient. This criterion generalizes the conventional determinant criteria for applications with square Jacobian matrices. Numerical methods for tracing families of one dimensional trajectories on a workspace boundary are outlined. Open and closed loop manipulator examples are analyzed, using a manifold mapping computer program.
Tolerance Volume Due to Joint Variable Errors in Robots
Authors: Lee Woo-Jong , Woo T. C.
Published: January 2010

The locational uncertainty of a manipulator is largely due to the errors of the joint variables. But these errors cannot be easily compensated for because they are dependent on the operation (i.e., robot-configuration). Motivated by the need to conduct precision engineering and the intellectual curiosity of geometric uncertainty, the probabilistic tolerance volume due to joint errors is investigated. By defining the locational uncertainty in Cartesian space as a tolerance volume, the investigation focuses on the automatic generation of the tolerance volume from a given confidence level. For this purpose, the linear mapping form Δq space to Δd space through Jacobian matrix is analyzed probabilistically. Probabilistic approach is advantageous since the tolerance volume by the deterministic approach is found to be unnecessarily large. With the assumption of normality of joint variables, this paper begins with the computation of the confidence level for a given tolerance volume. A fast analytic procedure, which gives a considerable time-reduction compared to the commonly used Monte-Carlo simulation, is presented. Based on the monotonic relation between confidence level and tolerance volume, the procedure is used to generate the tolerance volume covering the desired confidence level. The scheme is tested with the six degrees-of-freedom Stanford manipulator and shows a significant (more than 5 times) reduction in the size of the tolerance volume with a 0.3 percent probability of error.
Computations with Imprecise Parameters in Engineering Design: Background and Theory
Authors: Wood K. L. , Antonsson E. K.
Published: January 2010

A technique to perform design calculations on imprecise representations of parameters has been developed and is presented. The level of imprecision in the description of design elements is typically high in the preliminary phase of engineering design. This imprecision is represented using the fuzzy calculus. Calculations can be performed using this method, to produce (imprecise) performance parameters from imprecise (input) design parameters. The Fuzzy Weighted Average technique is used to perform these calculations. A new metric, called the γ-level measure, is introduced to determine the relative coupling between imprecise inputs and outputs. The background and theory supporting this approach are presented, along with one example.
Euler Parameters in Computational Kinematics and Dynamics. Part 2
Authors: Nikravesh P. E. , Kwon O. K. , Wehage R. A.
Published: January 2010

In this paper a methodology for formulating kinematic constraint equations and equations of motion for constrained mechanical systems is presented. Constraint equations and transformation matrices are expressed in terms of Euler parameters. The kinematic velocity and acceleration equations, and the equations of motion are expressed in terms of physical angular velocity of the bodies. An algorithm for solving the constrained equations of motion using a constraint stabilization technique is reviewed. Significant reduction in computation time can be achieved with this formulation and the accompanying algorithm as compared with the method presented in Part 1.
An Adaptive Constraint Violation Stabilization Method for Dynamic Analysis of Mechanical Systems
Authors: Chang C. O. , Nikravesh P. E.
Published: January 2010

The transient dynamic analysis of equations of motion for constrained mechanical systems requires the solution of a mixed set of algebraic and differential equations. A constraint violation stabilization method, based on feedback control theory of linear systems, has been suggested by some researchers for solving these equations. However, since the value of damping parameters for this method are uncertain, the method is to some extent unattractive for general-purpose use. This paper presents an adaptive mechanism for determining the damping parameters. The results of the simulation for two examples illustrate the improvement in reducing the constraint violations when using this method.
A Rotary Model for Spur Gear Dynamics
Authors: Yang D. C. H. , Sun Z. S.
Published: January 2010

We develop a dynamic model for a spur gear system with backlash. This model is circular and is geometrically different from the rectilinear gear model of Azar and Crossley. By taking advantage of involute tooth profile, we are able to take material compliance and energy dissipation into account. Furthermore, the complicated phenomenon of contact tooth pairs alternation between one and two during meshing is also included in the model. This model is believed to be closer to reality than the existing model and hopefully is useful in studying gears in high-speed and intermittent motions.
An Investigation of the Transient Thermal Analysis of Spur Gears
Authors: El-Bayoumy L. E. , Akin L. S. , Townsend D. P.
Published: January 2010

A finite element computer program has been developed for evaluating the transient behavior of surface temperature in high performance spur gears. The program is an extension of a previously developed code that was limited to steady-state behavior. The time dimension is implemented using two- and three-point finite difference schemes. The different schemes are provided to the user for the purpose of numerical stability and convergence studies. A detailed explanation of the gear cooling process leading to the establishment of a modified Blok model is also included. Other conventional models for approximating the heat transfer coefficients are available for comparison. Preliminary results are given showing snap shots of gear temperature contours at the initial stages of tooth engagement.
Efficiency of Nonstandard and High Contact Ratio Involute Spur Gears
Authors: Anderson N. E. , Loewenthal S. H.
Published: January 2010

A power loss prediction method previously developed by the authors was extended to include involute spur gears of nonstandard proportions. The method can now be used to analyze the effects of modified addendum, tooth thickness, and gear center distance in addition to the parameters previously considered which included gear diameter, pitch, pressure angle, face width, oil viscosity, speed, and torque. Particular emphasis is placed on high contact ratio gearing (contact ratios greater than two). Despite their higher sliding velocities, high contact ratio gears can be designed to levels of efficiency approaching those of conventional gears while retaining their advantages through proper selection of gear geometry.
Dynamic Analysis of Constrained System of Rigid and Flexible Bodies With Intermittent Motion
Authors: Khulief Y. A. , Shabana A. A.
Published: January 2010

A method for dynamic analysis of large-scale constrained system of mixed rigid and flexible bodies with intermittent motion is presented. The system equations of motion are written in the Lagrangian formulation using a finite set of coupled reference position and local elastic generalized coordinates. Equations of motion are computer generated and integrated forward in time using an explicit-implicit integration algorithm. Points in time at which sudden events of the intermittent behavior occur are monitored by an event predictor which controls the integration algorithm and forces a solution for the system impulse-momentum relation at those points. Solutions of impulse-momentum relations define the jump discontinuities in the composite velocity vector as well as the generalized impulses of the reaction forces at different joints of the mechanical system.
Kinematic Synthesis of Spherical Two-Gear Drives With Prescribed Entire-Motion Characteristics: Unlimited Crank Rotations and Optimum Transmission. Part 2: Applications
Authors: Lee T. W. , Akbil E.
Published: January 2010

The theory developed in Part 1 [1] as well as in a companion paper [2] has been applied to the kinematic synthesis of a special class of spherical two-gear drives, including the Rotary Step Mechanism, with prescribed entire-motion characteristics. Insight into the behavior of such mechanisms can be interpreted through the results of an analytical investigation of mechanism characteristics. A useful design procedure, a design table, and a set of design guidelines are presented. Examples are given to illustrate both the analytical synthesis and the computer-aided analysis procedures.
The Generalization of Line Trajectories in Spatial Kinematics to Trajectories of Great Circles on a Hypersphere
Authors: McCarthy J. M.
Published: January 2010

This paper examines the instantaneous kinematics of motion defined by a parameterized set of 4 × 4 orthogonal matrices, termed hyperspherical motion. The transformation equation defining the trajectories traced by planes through the origin of the moving hypersphere is presented. These planes intersect the hypersphere in great circles. This transformation takes the convenient form of “double spherical motion” with the introduction of matrices and vectors with double number elements. A limit process exhibits the kinematics of line trajectories in space and its dual number formulation as a special case of the kinematics of the hyperspherical trajectories of great circles.
Design and Application Criteria for Connecting Couplings
Authors: Rivin E. I.
Published: January 2010

A classification of couplings as rigid, misalignment-compensating, torsionally flexible, and combination purpose is proposed. Selection criteria for two basic subclasses of misalignment-compensating couplings are derived, some standard designs are analyzed, and modifications of Oldham and gear couplings in which compensatory motion is accommodated by internal shear in thin elastomeric layers instead of reciprocal sliding are described. The new designs demonstrate very high efficiency and exert substantially reduced forces on the connected shafts. Factors determining the influence of torsionally flexible couplings on transmission dynamics are formulated as reduction of torsional stiffness, enhancement of damping, modification of nonlinearity, and inertia distribution. Compensation properties of combination purpose couplings are investigated analytically and a “design index” is introduced. A comparison of important characteristics of some commercially available types of combination purpose couplings is performed, to facilitate an intelligent comparison and selection of various coupling types. A line of approach for the improvement of torsionally flexible / combination purpose couplings by using highly nonlinear elastomeric elements is suggested.
A General and Efficient Method for Dynamic Analysis of Mechanical Systems Using Velocity Transformations
Authors: Kim S. S. , Vanderploeg M. J.
Published: January 2010

This paper presents a new formulation for the equations of motion of interconnected rigid bodies. This formulation initially uses Cartesian coordinates to define the position of the system, the kinematic joints between bodies, and forcing functions on and between bodies. This makes initial system definition straightforward. The equations of motion are then derived in terms of relative joint coordinates through the use of a velocity transformation matrix. The velocity transformation matrix relates relative coordinates to Cartesian coordinates. It is derived using kinematic relationships for each joint type and graph theory for identifying the system topology. By using relative coordinates, the equations of motion are efficiently integrated. Use of both Cartesian and relative coordinates produces an efficient set of equations without loss of generality. The algorithm just described is implemented in a general purpose computer program. Examples are used to demonstrate the generality and efficiency of the algorithms.
Design of Horizontal Pressure Vessels Using the Decision Support Problem Technique
Authors: Nguyen N. , Mistree F.
Published: January 2010

A design method has been developed to determine systematically the system variables that will best achieve multiple design objectives involving both cost and damage tolerance of horizontal vessel design. The method is computer based, and is particularly suited for designing pressure vessels using multiple (conflicting) objectives. The method has been tested and validated against a computer program used extensively in industry. Better results by the new design method are demonstrated through case studies. The results indicate a wide range of vessel dimensions to which the design method can be applied. In general, application of the method will increase the efficiency of the design of horizontal pressure vessels.
Fatigue Life Analysis of a Turboprop Reduction Gearbox
Authors: Lewicki D. G. , Black J. D. , Savage M. , Coy J. J.
Published: January 2010

A fatigue life analysis of the Allison T56/501 turboprop reduction gearbox was developed. The life and reliability of the gearbox was based on the lives and reliabilities of the main power train bearings and gears. The bearing and gear lives were determined using the Lundberg-Palmgren theory and a mission profile. The five-planet-bearing set had the shortest calculated life among the various gearbox components, which agreed with field experience where the planet bearing had the greatest incidences of failure. The analytical predictions of relative lives among the various bearings were in reasonable agreement with field experience. The predicted gearbox life was in excellent agreement with field data when the material life adjustment factors alone were used. The gearbox had a lower predicted life in comparison with field data when no life adjustment factors were used or when lubrication life adjustment factors were used either alone or in combination with the material factors.
Thermoelectric Ocean Thermal Energy Conversion
Authors: Bohn M. S. , Benson D. K. , Jayadev T. S.
Published: January 2010

A novel thermoelectric OTEC concept is proposed and compared with the ammonia closed-cycle designs. The thermoelectric OTEC uses no working fluid and therefore requires no pressure vessel, working fluid pumps, or turbogenerator. These components are replaced by power modules which are heat exchangers integrated with thermoelectric generators. The thermoelectric OTEC concept offers several potential advantages including: higher reliability system performance through the use of a high level of redundancy and long-lived, solid-state thermoelectric generators with no moving parts, greater safety for crew and environment by elimination of the pressurized working fluid, and the possibility of comparable system costs, i.e., costs near $2000/kWe (net) in 1980 dollars.
An Average Slope Factor for Solar Insolation
Authors: Field R. L.
Published: January 2010

Design methods for solar collector sizing (such as f-chart) usually require a multiplying factor (the slope factor) to correct insolation data taken on the horizontal for the tilt angle of the solar collector. The slope factor is a function of the haze factor (KT) at each location which varies month to month. A simplification (with attendant error) can be made for space heating by taking the 6 month average winter haze factor as a constant to get a single set of slope factor curves. For hot water heating a 12 month average of the haze factor is used to find the correct slope factor chart. Available slope factor equations using average haze factors were plotted to result in a chart whose parameters are latitude and month of year. Correction charts for off-average locations are presented. The error in the given slope factor charts is estimated to be accurate ± 7 percent for most cities.
Numerical Simulation of Dual-Media Thermal Energy Storage Systems
Authors: Gross R. J. , Hickox C. E. , Hackett C. E.
Published: January 2010

An efficient numerical technique, originated by MacCormack, is used to predict temperature distributions in one-dimensional flow through a finite length packed bed. The method allows for temperature dependent properties, time varying inlet conditions, and nonuniform initial conditions. A thorough comparison with the classical Schumann model is presented, along with other examples which demonstrate the versatility of the numerical method. Calculations are also compared with results obtained from an experimental study of a pebble-bed thermal energy storage device.
ASHRAE 93-77 Instantaneous and All-Day Tests of the Sunpak™ Evacuated-Tube Collector
Authors: Mather G. R.
Published: January 2010

The results of ASHRAE 93-77 instantaneous and all day tests for two Sunpak™ evacuated-tube collectors are presented and discussed in terms of a simple dynamic response model and a biaxial incidence angle modifier approximation. The dynamic model predicts, and experimental results confirm, a residence time type of response rather than the exponential response that is assumed to characterize most collectors. The anisotropic geometries of the two collectors require that their optical properties be described by an incidence angle modifier that depends on both solar altitude and azimuth in the tilted aperture plane. The test results support the idea that this dependence can be characterized with sufficient accuracy by a biaxial approximation which requires that incidence angle modifiers be measured in each of two mutually perpendicular symmetry planes of the collectors. The all-day measurements are compared with the results to be expected from the ASHRAE 93-77 instantaneous tests, and excellent agreement is obtained when the dynamic model is used to account for the time variations in insolation and inlet temperature. It is concluded that the two Sunpak™ evacuated-tube models can be characterized adequately within the scope of ASHRAE 93-77, but that measurements over and above those actually required by this standard are necessary for a complete characterization. In addition, it is recommended that these collectors be tested on a tracking mount because of their long response times. Such instantaneous test results, in combination with the dynamic model, can be used to predict daily and long-term performance under most conditions.
Radiation and Free Convection Shield for Passive Thermal Control
Authors: Ortega J. K. E.
Published: January 2010

A radiation and free convection shield (RFS), when used with a thermal storage wall, can enhance the thermal performance of the storage wall and provide passive thermal control. In order to optimize the performance of the RFS, it is desirable to know how the impedance provided by the use of an RFS varies with the thermophysical properties of materials used to construct it. A numerical nodal thermal model was constructed to evaluate the impedance as a function of the thermophysical properties of the RFS. Two RFS thermophysical properties are identified as the most important in controlling the impedance from the storage wall to the room: thermal conductivity and total surface emissivity. A decrease in the RFS surface-to-surface thermal conductance, a decrease in the RFS total surface emissivity, or both, substantially increases the impedance from the storage wall to the room.
A Stochastic Analysis of a Solar Heated and Cooled House
Authors: Tanthapanichakoon Wiwut , Himmelblau D. M.
Published: January 2010

Monte Carlo simulation techniques have been used to characterize the stochastic responses of the components of a solar heated and cooled house. Random variables with specified ensemble means, standard deviations, and probability distributions were introduced as inputs and parameters into the model equations for the house, and the equations solved repeatedly to provide samples of the component outputs. The character of the frequency distributions of the outputs, their means and standard deviations, and time statistics are discussed as well as implications with respect to the design of similar systems.
Heliostat Characterization at the Central Receiver Test Facility
Authors: King D. L. , Arvizu D. E.
Published: January 2010

The Central Receiver Test Facility (CRTF) operated for the Department of Energy by Sandia Laboratories in Albuquerque, N. M. was constructed for the purpose of evaluating solar central receiver design concepts. At this facility working experience with the CRTF heliostat field has been gained and an extensive heliostat evaluation capability has evolved. Valuable information has been gained at the CRTF that will help in the future design and specification of heliostats. This paper summarizes the work that led to the current state of heliostat evaluation capability and includes; a description of the CRTF heliostat, measurements of environmental degradation of mirror reflectance, heliostat beam measurements with an instrumented sweeping bar, beam quality and tracking accuracy data obtained with the newly developed Beam Characterization System (BCS) and comparisons of measured beam data with the heliostat computer model HELIOS.
The Effect of Receiver Optical Properties on Solar Thermal Electric Systems
Authors: Call P. J. , Jorgensen G. J. , Pitts J. R.
Published: January 2010

The importance of reducing the thermal emittance of the receiver surface on the cost effective operation of intermediate and high temperature (≥ 400 °C) solar thermal electric power plants is discussed. Computer codes for seven systems (point and line focus) are used to independently determine optimum operating conditions for selective (low emittance) and nonselective receiver surfaces. The detailed computer calculations show excellent agreement with numbers generated from a simplified analytical model indicating that system dynamics are a secondary effect in this sensitivity analysis. This study reveals that improvements in system cost effectiveness of 5 to 10 percent for desert environments can be produced by reducing receiver emittance from 0.95 to 0.3. The system operating temperature is determined not to be a critical parameter and little effect is observed on the system capacity factor.
Analytical Predictions of Liquid and Air Photovoltaic/Thermal, Flat-Plate Collector Performance
Authors: Raghuraman P.
Published: January 2010

Two separate one-dimensional analyses have been developed for the prediction of the thermal and electrical performance of both liquid and air flat-plate, photovoltaic/thermal (PV/T) collectors. The analyses account for the temperature difference between the primary insolation absorber (the photovoltaic cells) and secondary absorber (a thermal absorber flat plate). The results of the analyses are compared with test measurements, and therefrom design recommendations are made to maximize the total energy extracted from the collectors.
Mixed Layer Development in a Double-Diffusive, Thermohaline System
Authors: Poplawsky C. J. , Incropera F. P. , Viskanta R.
Published: January 2010

A double-diffusive, thermohaline system has been studied under laboratory conditions involving uniform heating from below. Shadowgraph visualization has been used with temperature and salt concentration measurements to investigate mixing layer development and the onset of diffusion layer instabilities. Such instabilities were observed to occur in two of the experiments and were approximately predicted by an existing stability criterion. Interfacial boundary layers which separated the mixing layers from the diffusion region ranged in thickness from 10 to 30 mm and were characterized by a nearly uniform temperature and a nonlinear vertical salt concentration distribution. The rate of mixing layer development decreased with increasing salt concentration.
Temperature and Heat Flow Measurements From an Insulated Concrete Bermed Wall and Adjacent Floor
Authors: Kuehn T. H.
Published: January 2010

Temperature distributions and heat flows in a bermed concrete wall and concrete floor have been recorded for two years at the Iowa State University Energy Research House. Annual variations are correlated using a third-order Fourier technique. The results for the wall show the importance of interior insulation, exterior insulation near the top, and vertical heat conduction. Seasonal heat transfer through the wall is comparable to that for a well-insulated frame wall of the same surface area above grade. Floor heat-loss is nearly constant but is larger in summer than in winter. Diurnal variation in bermed wall heat flux is caused primarily by changes of indoor air temperature and shows negligible correlation with ambient temperature fluctuations. An analytical model has been developed to predict the soil temperatures adjacent to the bermed wall and floor. Results from the model agree well with the data correlations.
Making the Most of Federal Tax Laws for WECS Development
Authors: Lotker M.
Published: January 2010

The last few years have seen the passage of a wide variety of federal and state legislation designed to encourage renewable energy technologies in general and wind power in particular. Key laws include: (a) The Public Utility Regulatory Policy Act of 1978, (b) The Crude Oil Windfall Profits Tax Act of 1980, (c) The Economic Recovery Tax Act of 1981, (d) The Wind Energy Systems Act of 1980. This paper reviews the most significant aspects of these laws from the perspective of wind power development. The paper then presents a discussion of one approach—use of a limited partnership and tax sheltered financing—as it would be applied to a wind park. Overall cash flows, returns, and tax implications of the hypothetical venture are presented.
Strategies for Minimizing Operational Impacts of Large Wind Turbine Arrays on Automatic Generation Control Systems
Authors: Reddoch T. W. , Barnes P. R. , Lawler J. S. , Skroski J. C.
Published: January 2010

A primary application of wind electric generation is expected to be large clusters or arrays of MW-size wind turbines connected to the utility transmission network. Array output power variations due to the uncontrolled nature of the wind resource can cause undesirable dynamic impacts on the utility system, such as excessive frequency and/or tie-line power flow deviations. As a consequence, spinning reserve, unloadable generation, and load following requirements and their associated economic penalties tend to increase as wind electric generation is added to the system. However, if array power variations are limited and/or anticipated, the associated operation and economic penalties can be significantly reduced. In this paper, a number of operational concepts are considered which have the potential to enhance the effectiveness of wind turbine arrays in the utility system.
Wind System Value Analysis for Electric Utilities: A Comparison of Four Methods
Authors: Harper J. , Percival D. , Flaim T. , Sullivan R. L.
Published: January 2010

There have been several studies of how much Wind Energy Conversion Systems (WECS) are worth to electric utilities. When attempting to compare the different results of these studies, questions arose concerning the effect of the different methodologies and models on the determined WECS values. This paper will report on the only known effort that used more than a single methodology for the value analysis of WECS to a specific utility. This paper will present and compare the WECS utility value analysis methodologies of Aerospace Corp., JBF Scientific Corp., and the Solar Energy Research Institute (SERI). Results of the application of these three methodologies were found for two large utilities. Breakeven values (the amount a utility can pay for a wind turbine over its lifetime and still breakeven economically) were found to be from $1600 to $2400 per kW of wind capacity in 1980 dollars. The reasons for variation in the results are discussed.
Operation and Performance of the Solar Steam System at the Johnson & Johnson Plant in Sherman, Texas
Authors: Brink D. F. , Youngblood S. B.
Published: January 2010

A solar system that produces 174° C (345° F) steam is in operation at the Johnson & Johnson manufacturing plant in Sherman, Texas. The system uses parabolic trough collectors to heat pressurized water which then flashes to steam in a flash boiler; this steam is fed into the plant steam main for use in several manufacturing processes. The facility’s performance has been monitored continuously since it began operation in January 1980. The collector field typically has delivered energy to the flash boiler at an average daily efficiency of 30 to 40 percent, with an hourly average efficiency ranging from 38 to 42 percent at peak insolation periods. The daily and hourly values for energy collected and steam generated on a clear day in September are presented, as well as a monthly summary for the first 13 months of operation.
Transient Simulation of Absorption Machines
Authors: Anand D. K. , Allen R. W. , Kumar B.
Published: January 2010

This paper presents a model for a water-cooled Lithium-Bromide/water absorption chiller and predicts its transient response both during the start-up phase and during the shutoff period. The simulation model incorporates such influencing factors as the thermodynamic properties of the working fluid, the absorbent, the heat-transfer configuration of different components of the chiller and related physical data. The time constants of different components are controlled by a set of key parameters that have been identified in this study. The results show a variable but at times significant amount of time delay before the chiller capacity gets close to its steady-state value. The model is intended to provide an insight into the mechanism of build-up to steady-state performance. By recognizing the significant factors contributing to transient degradation, steps can be taken to reduce such degradation. The evaluation of the residual capacity in the shut-off period will yield more realistic estimates of chiller COP for a chiller satisfying dynamic space cooling load.
Space Heating Through Isentropic Compression Utilizing Wind Energy
Authors: Noon R.
Published: January 2010

The following paper is a preliminary examination of using wind power to provide hot air for space heating using the shaft power of a wind turbine to isentropically compress air. Excluding mechanical losses, 71 percent of the shaft power supplied to a single stage compressor can be converted to internal energy gain, i.e., temperature rise. Approximate economic parameters indicate that such wind space heating systems are more economic than active solar systems when the average heating season available wind energy per collection area is 20 percent higher than that for solar.
Design of a Packed Bed Thermal Storage Unit for a Solar System
Authors: Kulakowski B. T. , Schmidt F. W.
Published: January 2010

A method for the design and sizing of a packed bed thermal storage unit for a hot air solar heating system is presented. A controlled bypass of the heat storage unit during the retrieval process is used in order to maintain the fluid temperature leaving the system at a constant value. The use of a bypass arrangement with a closed air circulation loop for the collector enables the storage unit to operate at a higher mean temperature and the system to utilize the maximum allowable pressure drop. This results in a greater heat storage per unit volume of storage material. The complete solar system is simulated numerically during both the heating and retrieval modes of operation to obtain a set of design charts for sizing the thermal storage unit. In the simulation, consideration is given to geographical location, composition of the storage bed and the maximum allowable pressure drop across the bed. A set of design curves for State College, Pennsylvania, is presented.
Systematic Rotation and Receiver Location Error Effects on Parabolic Trough Annual Performance
Authors: Treadwell G. W. , Grandjean N. R.
Published: January 2010

This report deals with the effects of certain systematic errors on performance and, therefore, their influence on the design of troughs. Systematic rotation error is the angle between the reflector vertex-focus axis and the vertex-sun axis; systematic receiver location error is the vectorial deviation of a receiver from focus. The existence of systematic rotation errors and systematic receiver location errors can have a significant effect on the annual performance of parabolic trough collectors. These systematic errors can exist in addition to errors which are random in nature and which, therefore, can be treated statistically. Systematic rotation errors of 16 milliradians result in annual performance degradation of greater than 30 percent. Systematic receiver location errors can have a similar effect depending upon magnitude. The technique for calculating the influence of systematic errors on performance is outlined and methods of identifying and minimizing these errors are suggested.
The Use of Ground-Coupled Tanks in Solar-Assisted 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 element, for solar-assisted heat-pump systems. As part of this research program, four buried tank experiments were operated between December 1978 and March 1981 in order to determine the feasibility of ground-coupled tanks in these systems. Heat was added to or removed from the tanks according to a weekly schedule derived from computer simulations of solar heat-pump systems in the local (New York) climate. Each tank was operated according to a different control strategy. This paper presents experimental results from these tank experiments for this period, and compares these results to those generated by a computer model, GROCS, developed at BNL. The model is found to be valid, for the most part, using undisturbed soil thermal properties which provide the best fit to the data most of the time. Its results are very sensitive to soil thermal conductivity during periods of large heat addition to the tanks. A ground coupled tank is found to be desirable in series solar-assisted heat-pump systems. However, no important carry-over of summer-collected heat to winter was observed.
An Economic and Performance Evaluation of Parabolic Trough Component Improvements
Authors: Gee R. C. , Murphy L. M.
Published: January 2010

Improved parabolic trough concentrating collectors will result from better design, improved fabrication techniques, and the development and use of improved materials. This paper presents and implements an easily applied methodology that quantifies the performance potential of selected parabolic through component improvements from a systems viewpoint and uses performance data to determine the economic value of each improvement. Specifically considered are evacuated receivers, silvered glass reflectors, improved receiver selective coatings, higher optical accuracy concentrators, and higher transmittance receiver glazings. Upper-bound costs for each improvement are provided as are estimates of the increased solar energy system rates of return made possible by these improvements. The performance and economic potentials of some of these improvements are substantial, especially at higher collector operating temperatures.
Conceptual Design of an Advanced Water/Steam Receiver for a Solar Thermal Central Power System
Authors: Wu S. F. , Narayanan T. V. , Gorman D. N.
Published: January 2010

This paper describes the conceptual design of an advanced water/steam receiver for a commercial-scale solar central receiver thermal power system. The objective was to develop a receiver concept featuring an optimum combination of cost, performance, and reliability. While interfaces with other major subsystems of the complete power plant were recognized, emphasis was on the design and and performance of the receiver. The baseline thermal rating of this receiver was 550 MW, and the steam outlet conditions were 12,860 kPa and 516 C. After technical and econmic evaluations, a quad-cavity, natural-circulation concept was selected as the preferred receiver design. It consists of four separate cavities in a single receiver unit, each cavity receiving concentrated solar energy from one quadrant of a surrounding heliostat field.
Convective Heat Losses From Flat-Plate Solar Collectors in Turbulent Winds
Authors: Kind R. J. , Gladstone D. H. , Moizer A. D.
Published: January 2010

This paper presents results for convective heat transfer coefficients on the surface of flat-plate solar collectors mounted on a single-family residential building and exposed to the wind. The results were obtained by testing a 1:32 scale model in highly turbulent nonuniform flows which simulated the natural wind. For full-scale conditions, the heat transfer coefficients are two to three times lower than those given by a commonly used correlation. The coefficients show some sensitivity to wind direction but are insensitive to the characteristics of the wind and to architectural details of the building.
Thermal Energy Storage Development for Solar Electrical Power and Process Heat Applications
Authors: Radosevich L. G. , Wyman C. E.
Published: January 2010

Development of thermal energy storage technologies for solar thermal systems has been conducted since the mid-1970s. This paper presents an overview of past and present experimental activities for electrical power and process heat applications both within and outside the United States. The factors affecting the selection of a storage technology for these applications, as well as the nature of those applications, are discussed. Future research needs are also described.
On the Weathering of Thin Plastic Films
Authors: Cheng H. , Bannerot R. B.
Published: January 2010

A program is described for the controlled degradation and evaluation of thin plastic film samples in a set of parallel (in time) exposures. The intent of the various exposures is to separate the effects of identifiable degradation mechanisms associated with each material’s use as a solar collector cover. The mechanisms considered were those due to: (i) environment less solar irradiation (chemical, abrasion, humidity, etc.); (ii) environment including solar irradiation; (iii) thermal effects and (iv) mechanical effects. The procedures described in the program are illustrated by presenting the details for the evaluation of two commonly used plastic films.
Correlations of Solar Insolation and Wind Data for SOLMET Stations
Authors: Randall D. E. , Grandjean N. R.
Published: January 2010

Correlations of direct solar insolation and windspeed data based upon a 12.5-year period are presented for 26 SOLMET stations distributed over the contiguous United States. These correlations indicate that for all 26 stations 97.5 percent of the available direct insolation occurs at windspeeds of 15 m/s (33.6 mph) or less for three different solar collector tracking apertures. These results imply that operational wind load design criteria for tracking collector devices may be less stringent than is required for survival criteria in the stow orientation. Additional selected frequency distributions for direct insolation, windspeed, and wind direction data spanning the 1952–1964 time frame are also presented.
Transient Behavior of a Rock-Bed Thermal Storage System Subjected to Variable Inlet Air Temperatures: Analysis and Experimentation
Authors: Shitzer A. , Levy M.
Published: January 2010

An analytical solution to the transient thermal behavior of a rock-bed thermal storage system subjected to varying air inlet temperature is presented. The solution is obtained in terms of infinite double series which are based on Schumann’s solution, derived for a step change in air inlet temperature. In the present study, bed and fluid temperatures in response to arbitrary fluid inlet temperatures are calculated by means of Duhamel’s theorem. Results of this study were verified experimentally and compared to a numerical solution. Agreement in both these cases was very good. Pressure drop data were compared to values predicted by two previously published correlations. These correlations were found to underpredict the measured data by factors in the range 1.5–5. Reasons for this discrepancy are mainly due to the differences in the type and particularly the shapes of rocks used in the different studies.
High-Efficiency, Thin-Film GaAs Solar Cells
Authors: Zwerdling S. , Wang K. L. , Yeh Y. C. M.
Published: January 2010

The present research is directed toward demonstrating the feasibility of producing high-efficiency GaAs solar cells with high power-to-weight ratio by organo-metallic chemical vapor deposition (OM-CVD) growth of thin epi-layers on suitable substrates. Antireflection-coated, metal-oxide-semiconductor (AMOS), GaAs solar cells grown on bulk polycrystalline Ge substrates were initially studied, with the best efficiency achieved being about 9 percent AM1 (7 percent AM0). Subsequently, a new direct deposition method for fabricating ultra-thin top layer, epitaxial n+ /p shallow homojunction solar cells on (100) GaAs substrates (without anodic thinning) was developed by means of which large area (1 cm2) cells were produced with about 19 percent AM1 (15 percent AM0) conversion efficiency. An AM1 conversion efficiency of about 18 percent (14 percent AM0), or about 17 percent (13 percent AM0) with 5 percent grid coverage, was achieved for a single-crystal, GaAs, n+ /p cell grown by OM-CVD on a Ge wafer. These achievements led to the fabrication, for the first time, of thin GaAs epi-layers OM-CVD grown with good crystallographic quality, using a (100) Si-substrate on which a thin Ge epi-interlayer was first deposited by CVD from GeH4 and processed for improved surface morphology.
Solar Collector Durability Evaluation by Stagnation Temperature Measurements
Authors: Dawson A. G. , Thomas W. C. , Waksman D.
Published: January 2010

An analytical and experimental investigation was undertaken to evaluate an alternative method for measuring the thermal degradation of materials used in flat-plate collectors. This test method is based on measuring the temperature of the absorber under a no-flow condition before and after prolonged exposure. The primary material properties of interest are cover transmittance, solar absorptance and infrared emittance of the absorber, and thermal conductivity of insulation. The advantages and limitations of the proposed test method are compared with those for the currently used method, which is based on measuring the energy output from collectors. Experimental results from both outdoor and indoor tests are presented. Steady-state and transient analytical models are developed to evaluate the proposed test method and interpret experimental results. While the measurements required in the proposed method are simpler than those used to measure energy output, other factors, such as nonisothermal absorbers, variations in environmental conditions, and transient response, must be reconciled.
A New High-Temperature Solar Research Furnace
Authors: Diver R. B. , Carlson D. E. E. , Macdonald F. J. , Fletcher E. A.
Published: January 2010

A new highly concentrating solar research furnace has recently been completed at the University of Minnesota. The experimentally observed flux concentration ratio, at small aperture, of a cavity receiver is about 7000. The furnace embodies features which may be of interest to others in the solar energy community. This paper describes its construction and performance.
Diffuse Sky Measurements and Determination of Corrected Shadow Band Multiplication Factors
Authors: Turner W. D. , Mujahid A. M.
Published: January 2010

A meteorological monitoring station was operated at Blytheville, Arkansas, from April 1978 to April 1980. Direct normal, global, and diffuse sky radiation were monitored. From these data, models have been developed for the prediction of solar radiation, and discussions of several diffuse solar radiation models are included herein. Comparisons are made with these current diffuse models, and the correlation is quite good. In addition, instantaneous shadow band correction factors are presented which will allow a more accurate correction to be applied to the measured diffuse sky reading. The instantaneous correction factors are keyed to the global radiation measurement. Instead of applying a fixed correction factor to the diffuse measurement, regardless of sky condition, a variable factor can be applied. This will solve some of the current errors observed in diffuse measurements, because the current factors overpredict the diffuse radiation on cloudy days and underpredict the diffuse on clear days.
Performance of Solar Domestic Hot Water Systems at the National Bureau of Standards—Measurements and Predictions
Authors: Fanney A. H. , Klein S. A.
Published: January 2010

The thermal performance of six solar domestic hot water systems and a conventional hot water system have been carefully monitored by the National Bureau of Standards in Gaithersburg, Maryland. The system configurations include an evacuated-tube air system with a crossflow heat exchanger and two storage tanks, a single-tank direct system, a double-tank direct system, a single-tank indirect system with a wrap-around heat exchanger, a double-tank indirect system with a coil-in-tank heat exchanger, and a thermosyphon system. Results are presented for a one-year time interval commencing January 1980. This paper includes a detailed description of the hot-water systems, experimental test results, and comparisons with computer predictions using the f-chart method [1].