bluuebunny/crossref_metadata_2025 huggingface dataset:
Displacement Analysis of Spatial Six-Link, 5R-C Mechanisms: A General Solution
Authors: Ju Xu Li , Duffy J.
Published: January 2010

Four angular displacement equations are derived for the spatial 5R-C hexagon from which an input-output equation of 16th degree in the tan-half-angle of the output angular displacement for each of the RCRRRR, RRCRRR mechanisms and the yet unsolved RRRRRC2 mechanism can be obtained by the elimination of two unwanted variables in a single operation. This novel problem formulation is a general solution for all 5R-C mechanisms. Results are verified by a numerical example.
Improved Centerpoint Curve Generation Techniques for Four-Precision Position Synthesis Using the Complex Number Approach
Authors: Chase T. R. , Erdman A. G. , Riley D. R.
Published: January 2010

A method for predetermining the properties of a centerpoint curve of the Burmester curve pair which will result from an arbitrary set of four precision positions is introduced. The method is based on the discovery that the shape of any Burmester curve is dependent on the Grashof type of the associated compatibility linkage. Three improvements over the existing theory result. First, the exact range of the independent parameter which will generate solution dyads may be determined, eliminating the need to search for solutions on a trial-and-error basis. Second, the composition of the centerpoint curve may be predicted in advance, enabling improved plotting techniques. Third, the points comprising the centerpoint curve can be generated in their natural sequential order. These techniques may be readily programmed for automatic computation.
The Elliptic Polarity of Screws
Authors: Lipkin H. , Duffy J.
Published: January 2010

The nature and invariant properties of the elliptic polarity of screws in Euclidean space is established using a novel series of mappings, central to which is a quaternion representation. The role of the elliptic polarity in modeling constrained motion is detailed and illustrated by way of an example which has application in the control of robot manipulators. Ball’s planar representation of the two system of screws is generalized and is shown to be a representation on a complex plane where the elliptic polarity is a conformal mapping.
Simple Stress Formulae for a Thin-Rimmed Spur Gear. Part 1: Derivation of Approximation Formulae for Tooth Fillet and Root Stresses
Authors: Chong Tae Hyong , Kubo A.
Published: January 2010

Using the finite element method, influences of chordal tooth thickness at the critical section of tooth, radius of curvature of fillet, rim thickness, and supporting condition of a thin-rimmed spur gear on the tooth fillet and root stresses are investigated. Summing up a lot of FEM calculated results, a set of approximate formulae is derived for the calculation of tooth fillet and root stresses of a thin-rimmed spur gear. A comparison between the FEM calculated stress values and the values from these approximation formulae has shown good agreement.
Simple Stress Formulae for a Thin-Rimmed Spur Gear. Part 2: Tooth Fillet and Root Stress Calculation of a Thin-Rimmed Internal Spur Gear
Authors: Chong Tae Hyong , Kubo Aizoh
Published: January 2010

A method to apply the approximation formulae [1] for tooth fillet and root stresses of a thin-rimmed spur gear to the calculation of stress state of an internal spur gear is introduced, for the case of an internal spur gear which is fixed by bolts and/or supported by pinned coupling similar to geared coupling. By this method, reliable stress state at tooth fillet and root areas in the whole internal gear can be easily calculated.
Dynamic Load Factors in Internal Spur Gear Drives
Authors: Pintz A. , Kasuba R.
Published: January 2010

A comprehensive computer-based methodology was developed exclusively for the static and dynamic load analysis of internal spur gear (ISG) drives. An iterative procedure was applied to solve the statically indeterminate problem of multitooth pair contacts, load sharing, and operational contact ratios as influenced by both the gear mesh and the radial deflections of components. This methodology can be applied to involute and noninvolute spur gearing as well as to the very high contact ratio gearing. The performd parametric studies indicate that internal spur gear drives have considerably better dynamic performance (lower dynamic load factors) over equivalent external spur gear drives. Much of this improvement is due to the inherently higher contact ratios in the ISG drives.
On the Dynamic Gear Tooth Loading of Planetary Gearing as Affected by Bearing Clearances in High-Speed Machinery
Authors: Bahgat B. M. , Osman M. O. M. , Dukkipati R. V.
Published: January 2010

The paper studies the effect of bearing clearances in the dynamic analysis of planetary gear mechanisms in high-speed machinery. For this purpose, an analytical model is developed based on the interdependence between kinematics and kinetic relationships that must be satisfied when contact is maintained between the journal and its bearing. The contact mode is formulated such that the bearing eccentricity vector must align itself with bearing normal force at the point of contact. The analysis mainly relies on determining the direction of the bearing eccentricity vector defined as the clearance angles βi at the bearing revolutes for each contact mode of the gear teeth. The governing equations of the clearance angles are developed using the geometrical constraints of the contact point location and the velocity ratio. The clearance angles and their derivatives are used to systematically evaluate kinematic and dynamic quantities. A rigid planetary spur gears with two revolute clearances is analyzed to illustrate the procedure.
Optimal Design of Disk Springs
Authors: Metwalli S. M. , Shawki G. S. A. , Elzoghby A. A.
Published: January 2010

In this paper the optimal disk spring is defined. Spring resilience is used as an objective function in order to attain maximum utilization of material. Various constraints on stress and/or deflection are considered. Results indicate that the radially tapered section represents the optimal realistic disk spring which maximizes the objective function and satisfies stipulated constraints. Optimal design parameters for radially tapered disk springs are thus considered and compared with those for uniform-section disk springs.
Optimal Design of a Class of Welded Structures Based on Design for Latitude
Authors: Sandgren E. , Gim G. , Ragsdell K. M.
Published: January 2010

The minimization of the sensitivity of a design to variations in uncontrollable parameters is illustrated. The procedure is applied to the design of a class of welded beam structures which results in a low-cost design with minimal sensitivities. Dominant constraints are chosen which contain variations of the uncontrollable parameters. A dual objective function is formed and tradeoff curves are presented from which the optimal solution is selected. The minimization is carried out using the generalized reduced gradient method and other applications are presented.
On the Reliability of Some Numerical Methods in Kinematic Analysis
Authors: Di Benedetto A. , Pennestri` E.
Published: January 2010

A numerical finite differences algorithm, given by a first differentiation formula and that can be used for repeated differentiations, has been deduced on the basis of an approximation technique that makes use of Gram’s orthogonal polynomials. The algorithm itself has been compared with other numerical procedures suggested by other authors. It has been demonstrated how the calculus reliability discussed is foreseeable when transfer functions of the algorithms are considered.
The Synthesis of Point Contact Restraint of a Rigid Body
Authors: Kerr D. R. , Sanger D. J.
Published: January 2010

This paper outlines the background of work in the area of kinematic restraint and the associated aspects of screw and vector theory, and presents methods for the synthesis of any required state of kinematic restraint of a rigid body, using point contacts. The applications of the theory are discussed, and an example is given.
An Analysis of Traction Drive Torsional Stiffness
Authors: Rohn D. A. , Loewenthal S. H.
Published: January 2010

An analysis of the tangential compliance of elastic bodies in concentrated contact is applied to traction drive elements to determine their torsional stiffness. Both static loading and rotating conditions are considered. The effects of several design variables are shown. The theoretical torsional stiffness of a fixed ratio multiroller traction drive is computed and compared to experimental values. The analysis shows that the torsional compliance of the traction contacts themselves is a relatively small portion of the overall drive system compliance. Comparison is also made to theoretical gear mesh stiffness.
Kinematic Synthesis of Spherical Two-Gear Drives With Prescribed Entire-Motion Characteristics: Unlimited Crank Rotations and Optimum Transmission. Part 1: Theory
Authors: Lee T. W. , Akbil E.
Published: January 2010

This investigation is concerned with the determination of the rotatability of the input and output cranks and the optimization of transmission characteristics of spherical two-gear drives. Algebraic solutions are shown to be feasible only in a few special cases. In general, numerical synthesis procedures, involving either optimization or parameter scanning processes, are essential and they are developed from the general theory presented in this paper. The results, including conditions that can be regarded as an extension of the Grashof’s rule to the class of spherical geared mechanisms, are useful for the rational design of mechanisms. Applications of the theory to practical mechanisms design are given in Part 2.
Analytic Determination of Slip and Efficiencies of Rolling Contact C.V.T.’s With Experimental Verifications
Authors: Modrey J. , Younes Y. K.
Published: January 2010

Rolling contact continuously variable transmissions (C.V.T.) transmit forces through a highly viscous spot between rolling-slipping contacts. The mechanics of the spot are characterized by complex elastohydrodynamic conditions and fluid properties only partially determinable at the extreme pressures of operation. A computer simulation of the spot mechanics based on extensions of research in less complex elastohydrodynamic situations was developed. Comparisons with parallel tests on a commercial C. V. T. verify that the simulation described in a good guide to design of this class of transmissions.
Optimum Profile Modifications for the Minimization of Static Transmission Errors of Spur Gears
Authors: Tavakoli M. S. , Houser D. R.
Published: January 2010

A procedure for computing static transmission errors and tooth load sharing was developed for low and high contact ratio internal and external spur gears. A suitable optimization algorithm was used to minimize any combination of the harmonics of gear mesh frequency components of the static transmission error. Different combinations of tip and root relief may be used to achieve optimization. These include varying the starting point of relief and varying the magnitude of relief, and selecting the gear and/or the pinion teeth to be tip and/or root-relieved. Also, there exists an option for using either linear or parabolic relief. In addition to the presentation of optimal profile modifications, the effects of off-design loads, nonoptimum modifications, and random spacing errors are presented.
Dynamics of High Mobility Track Vehicles
Authors: McCullough M. K. , Haug E. J.
Published: January 2010

A mechanical system superelement that represents spatial dynamics of high mobility track vehicle suspension systems is derived. Using results from a companion paper [1], the equations of motion for a suspension system with an arbitrary number of road wheels are systematically derived. Track is represented as a complex internal force element that acts between ground, wheels, and the chassis of the vehicle. Track tension is computed from a relaxed catenary relationship and track bridging effects are modeled. Numerical results for driver acceleration and absorbed power, as well as track tension are presented. A factor of 90 decrease in compute time is achieved over a comparable multibody model of the same vehicle.
Computer-Aided Design and Machining of Composite Ruled Surfaces
Authors: Ravani B. , Chen Y. J.
Published: January 2010

This paper develops the basic framework for Computer-Aided Design and Machining of composite ruled surfaces. Such surfaces are constructed by blending several patches which are segments of ruled surfaces. Taking advantage of the fact that a ruled surface is a one-parameter family of straight lines, methods are developed for blending of ruled patches. A new subdivision algorithm is also presented for generating sequences of cutter movements for machining of ruled patches.
Dynamic Behavior of a Hydraulically Actuated Mechanism. Part 2: Nonlinear Character
Authors: Venkatraman V. , Mayne R. W.
Published: January 2010

The first of these papers considering a hydraulically actuated mechanism presents the common oscillating cylinder arrangement and sets of equations which describe the dynamic system. It then defines dimensionless groups that characterize the actuator-mechanism and explores the quasi-linear behavior of the system. This present paper focuses on the nonlinear nature of the system. Effects of transmission angle, mechanism geometry and loading are considered as well as the range of operation in which the small perturbation behavior provides an adequate description of the dynamic response. The paper closes by identifying a new parameter which plays an important role in characterizing the dependence of the system transient response on mechanism geometry.
Incidence-Angle Modifier and Average Optical Efficiency of Parabolic Trough Collectors
Authors: Gaul H. , Rabl A.
Published: January 2010

The incidence-angle modifier for parabolic troughs is investigated in order to clarify the connection between collector tests and prediction of long-term energy delivery by collector arrays. The optical efficiency of a parabolic trough collector decreases with incidence angle for several reasons: the decreased transmission of the glazing and the absorption of the absorber; the increased width of the solar image on the receiver; and the spillover of the radiation from troughs of finite length. In order to be able to apply test results from a short collector module to collector arrays of arbitrary length, it is necessary to separate analytically the end loss from the first two effects. This analysis is applied to several collectors that have been tested at Sandia Laboratories and at the Solar Energy Research Institute (SERI). The measurements of the incidence-angle modifier at SERI were, carried out at low temperature with an open water test loop for improved accuracy. The results are presented in two forms: as a polynomial fit to the data; and as a single number, the all-day average optical efficiency for typical operating conditions.
Measurement of Heliostat Performance Characteristics
Authors: Thornton J. P. , Waddington D.
Published: January 2010

A key milestone in the development of any solar collector is the comparison of actual performance data with predicted data. During a series of tests at the Martin Marietta solar test facility during 1976 and 1977, the performance of four full-size, prototype heliostats with different types and sizes of glass mirrors were measured and subseqeuently shown to compare closely with the predicted performances.
The Sensitivity of Solar Transmittance, Reflectance and Absorptance to Selected Averaging Procedures and Solar Irradiance Distributions
Authors: Lind M. A. , Pettit R. B. , Masterson K. D.
Published: January 2010

The sensitivity of the solar weighted optical properties of selected materials to different terrestrial solar spectral irradiance distributions and computational techniques has been investigated. The spectral transmittance, reflectance, and absorptance of typical materials employed in solar thermal conversion systems were used for the calculations. The values obtained for several different solar irradiance distributions and calculational methods show only small differences. A single terrestrial solar irradiance distribution is recommended for use as a standard.
Stochastic Predictions of Solar Cooling System Performance
Authors: Anand D. K. , Deif I. N. , Bazques E. O. , Allen R. W.
Published: January 2010

The use of computerized system simulations for sizing and performance predictions of various solar systems requires some form of weather input to act as a system stimulus. When actual weather data are used, simulations run on an hourly basis are expensive and require considerable data handling. For many design procedures, however, hourly information is not needed, and simpler methods are desirable. One such method employs a probabilistic approach. This method involves the use of an algorithm that generates a probabilistic matrix, and an analytical formulation which is used to generate synthetic weather data. The approach has been found to be satisfactory. This work uses the stochastic (probabilistic) method to produce representative weather for five geographic regions in the U.S. for the summer months. Parallel runs are conducted with real and stochastic weather. A comparison of the results clearly shows that the probabilistic approach can satisfactorily substitute for real weather for the purpose of system simulation, at reduced cost and data handling.
Performance Predictions for Adiabatic Desiccant Dehumidifiers Using Linear Solutions
Authors: Mathiprakasam B. , Lavan Z.
Published: January 2010

The governing equations for adiabatic desiccant dehumidifiers were linearized and solved. The linear model used applies both to the fixed bed type and to the rotating type dehumidifiers. The solutions obtained are compared with the numerical nonlinear solutions for a broad range of operating conditions and found to agree very well. The saving in computing time by using the linear model is very significant.
Heat Exchanger Performance in Latent Heat Thermal Energy Storage
Authors: Smith R. N. , Ebersole T. E. , Griffin F. P.
Published: January 2010

An experimental study was made of the heat transfer in a component of a low temperature thermal energy storage system using latent heat of fusion of a phase change material (PCM). Measurements were made of the temperature rise of water flowing in a channel adjacent to a container filled with a freezing PCM, Gulfwax 33. In addition, temperature measurements within the PCM provided the location of the liquid/solid interface as a function of time. A simple analytical prediction is compared with the data to provide a verification of the qualitative observations. Certain multidimensional effects which occur during the freezing (discharge) mode of operation are identified especially the enhancement of freezing rates when the PCM container sidewalls (those not in contact with the heat exhange fluid) are conducting and are closely spaced. One limitation to storage systems of this type is the resistance to heat transfer of the solid phase, requiring a significant temperature drop for acceptable discharge rates. The additional “heat path” provided by the conducting container walls is shown to significantly reduce this resistance. Some observations concerning the implications for design of actual storage components are also provided.
Determining The Optical Quality of Focusing Collectors without Laser Ray Tracing
Authors: Bendt P. , Gaul H. , Rabl A.
Published: January 2010

This paper describes a novel alternative to the laser ray trace technique for evaluating the optical Quality of focusing solar collectors. The new method does not require any equipment beyond that which is used for measuring collector efficiency; it could therefore become part of routine collector testing. The total optical errors resulting from imperfect specularity and from inaccuracies in reflector position or slope are characterized by an angular standard deviation σoptical, the rms deviation of the reflected rays from the design direction. The method is based on the fact that the off-axis performance of a concentrator depends on σoptical. An angular scan is performed; i.e., the collector output is measured as a function of misalignment angle over the entire range of angles for which there is measurable output (typically a few degrees). This test should be carried out on a very clear day, with the receiver close to ambient temperature (if the latter condition cannot be satisfied, appropriate corrections are necessary). The parameter σoptical is then determined by a least-squares fit between the measured and the calculated angular scan. We tested the method on a parabolic trough collector manufactured by Hexcel, and it is suitable for parabolic dishes as well.
Dynamics of Mixed Layer in a Nonuniformly Stratified Fluid Heated from Below
Authors: Behnia M. , Viskanta R.
Published: January 2010

Unsteady natural convection in a nonuniformly stratified, finite depth layer of water heated from below has been studied. Laboratory experiments were performed using the Mach-Zehnder interferometer as a diagnostic tool for measuring temperature. A shadowgraph technique was used for flow visualization. A simple thermal and a more detailed two-differential equation k–ε turbulence models are used to predict the dynamics of mixed layer which develops when the thermally stratified fluid is heated from below. The thermal model predictions for the mixed layer height agreed to within 5 percent and the mixed layer temperature to within 15 percent of the experimental data obtained in controlled laboratory experiments. Even better agreement between data and predictions were obtained with the k–ε turbulence model. The entrainment processes at the interface between the mixed layer and the stable region as well as turbulence in the layer must be better understood for more realistic modeling of turbulent natural convection in nonuniformly stratified fluids.
Solar Heating and Cooling System Efficiency as a Function of Design and Installation
Authors: Ward D. S.
Published: January 2010

The effects of design and installation features on the overall efficiency of solar heating and cooling systems are evaluated. Solar system piping and thermal storage heat losses and parasitic power requirements are quantitatively evaluated by considering different degrees of insulation and design configurations. It is demonstrated that these system variables have a very strong effect on the technical feasibility of solar heating and/or cooling systems.
Computer Simulation Results for Planar Reflectors and Flat Plate Solar Collectors
Authors: Rudloff F. A. , Swanson S. R. , Boehm R. F.
Published: January 2010

The benefits attributed to reflectors for increasing performance of flat plate collectors vary quite widely in the literature. In the present study, a detailed computer simulation is carried out to investigate the increase in performance. The results show that: Collectors should be placed at a higher tilt angle than usual; reflectors placed in front of the collectors can be tilted up 5 or 10 deg; and performance has a broad peak with respect to tilt angle. The system performance enhancement in Salt Lake City, Utah ranges from 1.16 for domestic hot water to 1.28 for space heating for equal reflector-collector areas, and the break even ratio of per area reflector to collector cost is from 16 to 28 percent for these systems.
A Design Method for Optimizing Collector Systems for Small Solar Central Receivers
Authors: Bannerot R. B. , Laurence C. L.
Published: January 2010

The design methodology for the determination of the optimal heliostat field designs is presented in detail for a small solar central receiver. The optimization process is reviewed. Cost and performance models are discussed. To illustrate the design process a representative small solar central receiver system is optimized. Cost factors were developed from current prices. The individual heliostat design and cost data were taken from the design of the ten megawatt-electric Barstow Pilot Plant design. A north field configuration, steel guyed tower and a tilted, circular aperture, cavity receiver were utilized. It is demonstrated that solar central receiver systems are more cost effective at higher power levels, above those considered here. But this fact has nothing to do with relative cost effectiveness of competing small, stand-alone, power systems.
Comparison of Proportional and On/Off Solar Collector Loop Control Strategies Using a Dynamic Collector Model
Authors: Schiller S. R. , Warren M. L. , Auslander D. M.
Published: January 2010

Common control strategies used to regulate the flow of liquid through flat-plate solar collectors are discussed and evaluated using a dynamic collector model. Performance of all strategies is compared using different set points, flow rates, insolation levels and patterns, and ambient temperature conditions. The unique characteristic of the dynamic collector model is that it includes the effect of collector capacitance. Short term temperature response and the energy-storage capability of collector capacitance are shown to play significant roles in comparing on/off and proportional controllers. Inclusion of these effects has produced considerably more realistic simulations than any generated by steady-state models. Simulations indicate relative advantages and disadvantages of both types of controllers, conditions under which each performs better, and the importance of pump cycling and controller set points on total energy collection.
The Mediterranean-Dead Sea Project: A Mathematical Model and Dynamic Optimization of a Solar-Hydroelectric Power Plant
Authors: Weiner Dan
Published: January 2010

The Dead Sea, part of the Jordon Rift Valley, lies at an elevation of about 400 m below sea level at a distance of only 70 km from the Mediterranean. In this paper, a mathematical model is derived simulating the dynamic behavior of a solar-hydroelectric power plant, utilizing the difference in elevation between the Mediterranean Sea and the Dead Sea by conducting Mediterranean water to the Dead Sea, partly by tunnel. This model was applied to determine the optimal control of inlet water to the evaporation basin of the Dead Sea, through the entire life of the plant, by dynamic programming methods. The optimization results were also utilized for determination of plant engineering parameters such as the diameter and gradient of the sea water tunnel.
An Algorithm for Calculating Monthly-Average Radiation on Inclined Surfaces
Authors: Klein S. A. , Theilacker J. C.
Published: January 2010

An analytical method is developed for estimating R, the ratio of the long-term monthly-average daily radiation on an inclined surface to that on a horizontal surface. This method differs from the Liu and Jordan [1] method in the manner in which the beam radiation component is determined. The method is applicable for surfaces of any orientation. R values calculated in this manner and by the Liu and Jordan method are compared with integrated hourly calculations for 23 years in Madison, WI, Albuquerque, NM and Miami, FL; the comparisons show that the method described in this paper agrees more closely with the integrated hourly calculations, especially for surfaces facing east or west of south.
A Single-Stage Ammonia/Water Absorption Cycle With Integrated Heat Exchange Components
Authors: Johnston A. M. , O’Sullivan C. H.
Published: January 2010

Thermodynamic analysis of the single-stage ammonia/water cycle indicates the importance of close temperature approach in the counter-current heat exchanges of the cycle and of recovering useful heat from the vapor rectification process. A novel style of heat exchange equipment, constructed in a laboratory by photo-etching flow passages into stainless steel plates which are then diffusion-bonded together, is capable of both of these services. In air-conditioning applications, coefficients of performance of 0.75 to 0.85 (for sink temperatures of 50°C to 30°C) appear to be achievable.
Solar-Assisted Heat Pump and Swimming Pool Synergy for Domestic Heating
Authors: Galloway T. R.
Published: January 2010

In this study for a 150-m2 home, performance and economic advantages are shown for a solar-assisted heat pump providing domestic hot water and space heating and cooling when the pump uses a year-round solar-heated swimming pool (capitalized as a luxury) for a large, thermal energy reservoir. The pool can seasonally cycle between 18 and 31°C (64 and 88°F), allowing year-round swimming and providing an excellent water source for the heat pump and the low cost, low temperature, plastic solar collector panels operating at near-optimum efficiency. To optimize the system, we examined the performance and cost characteristics of different glazed and unglazed solar panels (28 to 150 m2 and horizontal to 60 deg tilt) at sites in the San Francisco Bay area and San Joaquin Valley. Actual experimental data on the pool and panels have been used together with numerical simulations for performance. The optimum system was found to use 75 m2 of a $44 m−2 unglazed panel at a 48 deg tilt, a 300-GJ yr−1 (30,000-BTU h−1) capacity heat pump, and a standard 50-m2 swimming pool with a solar blanket cover. Solar energy supplied about 85 percent of the energy requirements at $6.62 GJ−1 ($6.62/106 BTU) as of July 1979. With 20-yr life financing (15 percent interest), the break-even point was projected at 7 yr with a net savings of 42,701 dollars by the year 2000 (using the 55 percent California State Solar Tax Credit), compared with a conventional, all natural-gas system where the gas cost increases at 14 percent yr−1 from $3 GJ−1. Discounting these savings of 42,701 dollars back to July 1979, its present value of the savings of 6350 dollars would be equivalent to a 9.5 percent return on investment.
In Situ Biofouling of Ocean Thermal Energy Conversion (OTEC) Evaporator Tubes
Authors: Sasscer Donald S. , Morgan Thomas , Tosteson Thomas R. , Grannemann Glenn N.
Published: January 2010

The Puerto Rico Center for Energy and Environmental Research designed, constructed and operated a facility for measuring in situ biofouling of simulated Ocean Thermal Energy Conversion (OTEC) evaporator tubes of various materials. The system consisted of two 5052 aluminum alloy and two titanium experimental modules mounted on a Landing Craft, Utility moored in 1100 m of water at a potential OTEC site two miles south of Punta Tuna, Puerto Rico. Continuous flow of ocean surface water was maintained through all modules, and the fouling resistance (Rf) for each instrumented tube was monitored regularly. During the first eight months of operation the tubes were cleaned three times with manually operated M.A.N. brushes. Initially, the rate of increase in Rf was greater for the aluminum units, but after the third cleaning all units had fouling rates near 4×10−6 m2-K/W-day (2×10−5 hr-ft2-°F/Btu-day). Each cleaning of the tubes reduced Rf to values betwen 9×10−6 and 20×10−6 m2-K/W (5×10−5 and 11×10−5 hr-ft2-°F/Btu).
Temperature Variation in the Absorber Plate of an Air Heating Flat Plate Solar Collector
Authors: Diaz L. A. , Suryanarayana N. V.
Published: January 2010

A flat plate solar collector is modelled as a rectangular channel of high width to gap ratio with air entering the collector with a fully developed turbulent velocity profile. One plate of the collector is subjected to a uniform heat flux with the other plate heavily insulated. Experimental values of friction factor and heated plate temperature in the thermal entrance region are presented and compared with analytical predictions. It is shown that there will be significant plate temperature variation in the thermal entrance region particularly at low flow rates. It is also shown that neglecting conduction effects in the absorber plate will not lead to any significant errors in estimating absorber plate temperature variation. Tabulated values of dimensionless plate temperature for different values of the dimensionless distance from the leading edge for several Reynolds number are presented.
Performance of Storage Walls with Highly Conductive Covering Plates and Connecting Fins
Authors: Ortega J. K. E. , Bingham C. E. , Connolly J. M.
Published: January 2010

The thermal behavior of a storage wall, constructed of concrete, with highly conductive covering plates and connecting vertical fins, is investigated. The results demonstrate that, during the charging mode, the amount of energy released from the front surface is significantly reduced. A portion of the saved energy is stored for future discharge, but a large portion is transferred to the back surface and released. A selective front surface further reduces the energy released from the front surface, and this energy is stored. By properly selecting the fin spacing, plate-fin thickness, and plate-fin thermal conductivity, the rate and direction of thermal discharge can be controlled. The improved heat transfer capability and added thermal control provide new alternatives for interzonal heat transfer and multizone passive building designs.
The Interrelation between Recurrent and Capital Costs in a Solar Thermal Process Heat System
Authors: Lukens L. L. , Schimmel W. P.
Published: January 2010

The effect of operation and maintenance (O&M) costs on energy produced by solar collector systems is crucial to the market penetration of solar process heat as an alternative energy source. In the present paper, a particular O&M operation, regular collector cleaning, is considered in order to determine its effect upon annualized life cycle energy cost. A first-order model of mirror reflectance degradation as a function of time is constructed from experimental data taken at Albuquerque, N.M. This is used as input to a systems optimization model of a line-focus solar collector process heat installation. The energy cost variation is considered as a function of cleaning cost per unit of collector aperture and cleaning interval. Results are presented for a process heat temperature of 177°C.
A Numerical Model for the Flow Within the Tower of a Tornado-Type Wind Energy System
Authors: Ayad S. S.
Published: January 2010

The two-equation k–ε turbulence model is used to predict numerically the flow within the tower of a tornado-type wind energy system. Calculations are carried out for a tower in a uniform flow. Both cases of closed-bottom tower and simulated turbine flow with a variety of turbine-to-tower diameter ratios and turbine flow rates are considered. Calculated values of pressure for closed-bottom tower are compared with experimental values. Considerable reduction of the pressure drop is found due to the interaction of the nonrotating axial flow from the turbine with the vortex within the tower. Values of the maximum power that can be extracted by the turbine are estimated for a given set of tower flow boundary conditions. The optimum ratio of turbine-to-tower diameters was found to be around 0.4.
Preliminary Design of a 1-MWe OTEC Test Plant
Authors: Kajikawa T.
Published: January 2010

An ocean-based, 1-MWe (gross) test plant has been planned to establish the feasibility of OTEC (ocean thermal energy conversion) power generation in the revised Sunshine Project. The preliminary design of the proposed test plant employs a closed-cycle power system using ammonia as the working fluid on a barge-type platform with a rigid-arm-type, detachable, single-buoy mooring system. Two types each of titanium evaporators and condensers are to be included. The steel, cold-water pipe is suspended from the buoy. The design value of the ocean temperature difference is 20 K. The paper presents an overview of the preliminary design of the test plant and the tests to be conducted.
Evaluation of Reliability of Operational Solar-Energy Systems
Authors: Mavec J. , Wolosewicz R. , Waite E.
Published: January 2010

This paper presents a reliability study of two solar-energy systems using air as the heat-transfer medium. Failure modes and effects analysis are used to examine the controls of the systems for three operating modes. Principal components are identified for each mode, and a fault tree and reliability block diagram are constructed to structure the fault or failed sequence. Established failure rates are assigned to each component, and an exponential failure distribution is assumed. For components operating on demand at a given average frequency, the adjusted demand and normal operating failure rates are combined to reflect the total contribution. Representative operational times and component frequencies are found for each operating mode. A fault-tree computer code is used to determine minimal outsets to the top event, remove redundant events, and perform necessary calculations. The computer code obtains results at each level (component, cutset, and tree) using repairable and nonrepairable models.
Model Basin Tests of Ocean Wave Responses for a 40-MW OTEC Pilot Plant
Authors: George J. F. , Richards D.
Published: January 2010

A 1/30th-scale model of a floating 40-MW OTEC pilot plant has been subjected to wave conditions that the prototype would experience as a plant moored off Puerto Rico or Hawaii, or as a cruising plantship in the South Atlantic Ocean east of Brazil. The model, in its unmodified baseline configuration, survived the design wave conditions for the three sites, with more than adequate stability margins. A modified configuration was also tested to reduce the possibility of taking on “green water” which was a concern at the Puerto Rico and Hawaii sites. Additional data were obtained on seawater system parameters, cold water pipe motions, and mooring forces.
Comparison of Wind Turbine Performance Prediction and Measurement
Authors: Tangler J. L.
Published: January 2010

The purpose of this work was to evaluate the state-of-the-art of performance prediction for small horizontal-axis wind turbines. This effort was undertaken since few of the existing performance methods used to predict rotor power output have been validated with reliable test data. The program involved evaluating several existing performance models from four contractors by comparing their predictions for two wind turbines with actual test data. Test data were acquired by Rocky Flats Test and Development Center and furnished to the contractors after submission of their prediction reports. The results of the correlation study will help identify areas in which existing rotor performance models are inadequate and, where possible, the reasons for the models shortcomings. In addition, several problems associated with obtaining accurate test data will be discussed.
A Jet Condenser for Ocean Thermal Energy Conversion
Authors: Richter H. J. , Wallis G. B.
Published: January 2010

A novel idea to use a jet condenser for Ocean Thermal Energy Conversion (OTEC) plants is presented here. The jet condenser offers the advantage of a relatively simple device. It consists of a mixing section where the partially evaporated warm water and the cold water mix and condensation takes place. After the complete condensation, the water stream is employed to drive a water turbine. The basic thermodynamic principles are evaluated. Introducing realistic efficiencies for the jet condenser, about 20 to 25 percent of the available energy can possibly be expected to be converted into mechanical energy.
OTEC Plant Response and Control Analysis
Authors: Owens W. L.
Published: January 2010

An analysis is presented which allows prediction of closed-cycle OTEC power plant system response and control. Two basic operational control schemes are presented, which are primarily related to the type of seawater pumps employed. Variable flow seawater pumps allow optimization of the OTEC thermal-cycle state points for maximization of net generated power. Constant flow pumps are cheaper and simpler, but do not allow direct control over the evaporator and condenser operating temperatures. A system of nonlinear differential equations representing the basic elements of a constant seawater flow OTEC plant with turbine bypass flow control has been formulated for computer solution. Typical normalized response curves are presented for pressures, temperatures, mass flow rates, and generator speed for a small-scale, 50-kW OTEC plant design.
A Simple Tool for the Design of Passive Solar Buildings
Authors: Winn C. B.
Published: January 2010

The design tools that are presently available for use by designers of passive solar heating or cooling systems include detailed simulation codes, correlations derived from the detailed codes, and simulations that may be used for short-term analyses using programmable handheld calculators or desktop computers. An alternative method is based on classical frequency response techniques and yields results that are in close agreement with those that are obtained from detailed computer simulations. The method may be used to quickly determine the average temperature and the magnitude of the diurnal temperature variation in a passive solar building. The effects of parameter changes may also be quickly and easily determined by this method. The method is described in the paper and results are presented for a slab-on-grade building having a thermal storage wall and a thermal storage floor incorporating off-peak load management.
Second Law Analysis of Desiccant Cooling Systems
Authors: Lavan Z. , Monnier J.-B. , Worek W. M.
Published: January 2010

A second law analysis of constant pressure open cycle cooling systems was performed in order to assess the potential performance of desiccant cooling systems. The results yield upper bounds which are independent of the nature of the desiccant. Calculations carried out for a wide range of operating conditions show that the performance of these open cycle systems strongly depends on the humidity ratio. For ARI conditions, the reversible COP is about 4.66, and it approaches infinity at very low outdoor humidity ratios.
Selection of a Working Fluid for an Organic Rankine Cycle Coupled to a Salt-Gradient Solar Pond by Direct-Contact Heat Exchange
Authors: Wright J. D.
Published: January 2010

An analysis was conducted of power production by an organic Rankine cycle engine coupled to a solar pond with direct-contact heat exchange. Use of a direct-contact boiler reduced the projected plant cost by 25 percent. The choice of a working fluid affects plant efficiency, turbine size, and working fluid losses. Pentane was shown to be the working fluid best suited to this application.
High-Temperature Ceramic Heat Exchanger Element for a Solar Thermal Receiver
Authors: Strumpf H. J. , Kotchick D. M. , Coombs M. G.
Published: January 2010

A study has been completed on the development of a high-temperature ceramic heat exchanger element to be integrated into a solar receiver producing heated air. A number of conceptual designs were developed for heat exchanger elements of differing configuration. These were evaluated with respect to thermal performance, pressure drop, structural integrity, and fabricability. The final design selection identified a finned ceramic shell as the most favorable concept. The ceramic shell is surrounded by a larger metallic shell. The flanges of the two shells are sealed to provide a leak-tight pressure vessel. The ceramic shell is fabricated by an innovative combination of slip casting the receiver walls and precision casting the heat transfer finned plates. The fins are bonded to the shell during firing. Fabrication of a one-half scale demonstrator ceramic receiver has been completed.
Transient Performance of Evacuated Tubular Solar Collectors
Authors: Behrendorff M. J. , Tanner R. I.
Published: January 2010

A computer program using a finite difference technique is developed to study the steady-state and transient performance of an evacuated solar collector suitable for applications in the 120–250°C temperature region. The collector is modeled as an equivalent flat plate collector, with water, oil, and air being the heat transfer fluids studied in detail. Nonflow and laminar flow conditions are considered for the three fluids, together with turbulent flow for air. Step and sinusoidal solar inputs are modeled. Experimental transient tests on a module of evacuated collectors were made and were used to show that the accuracy of the theoretical model developed is adequate for design purposes.
Analysis of Two-Phase Flow Solar Collectors With Application to Heat Pumps
Authors: Chaturvedi S. K. , Chiang Y. F. , Roberts A. S.
Published: January 2010

A thermodynamic model is developed to analyze the thermal performance of two-phase solar collectors. The well-known equilibrium homogeneous theory is used to model the two-phase flow in the solar collectors. The resultant set of coupled ordinary differential equations for saturated pressure and quality of working fluid in the collector tubes are solved by an iterative procedure using a fourth-order Runge-Kutta method. The results are then applied to determine the thermal performance of a solar assisted heat pump which uses two-phase flow collectors as the evaporator. The results indicate that even with the use of less expensive bare solar collectors as evaporator for the heat pump, the heating coefficient of performance (COPH) as high as 6 can be obtained under realistic ambient conditions provided a proper matching exists between the collector’s evaporative capacity and the compressor’s pumping capacity.
Hybrid Thermoelectric Solar Collector Design and Analysis
Authors: Roberts A. S. , Shaheen K. E.
Published: January 2010

A flat-plate solar collector is conceived where energy cascades through thermoelectric power modules generating direct-current electricity. The intent of this work was to choose a collector configuration and to perform a steady-state thermal performance assessment. A set of energy balance equations were written and solved numerically for the purpose of optimizing collector thermal and electrical performance. The collector design involves finned columns of thermoelectric modules imbedded in the absorber plate (hot junction) over a parallel array of vertical tubes. The thermoelectric power output is limited by the small hot-junction/cold-junction temperature difference which can be maintained under steady-state conditions. The electric power per unit tube pass area is found to have a maximum as a function of a geometric parameter, while electric power is maximized with respect to an electric resistance ratio. Although the electric power efficiency is small, results indicate that there is sufficient electric power production to drive a coolant circulator, suggesting the potential for a stand-alone system.
Convective Losses From Cavity Solar Receivers—Comparisons Between Analytical Predictions and Experimental Results
Authors: Clausing A. M.
Published: January 2010

Cavity solar receivers are generally believed to have higher thermal efficiencies than external receivers due to reduced losses. A simple analytical model was presented by the author which indicated that the ability to heat the air inside the cavity often controls the convective loss from cavity receivers. Thus, if the receiver contains a large amount of inactive hot wall area, it can experience a large convective loss. Excellent experimental data from a variety of cavity configurations and orientations have recently become available. These data provided a means of testing and refining the analytical model. In this manuscript, a brief description of the refined model is presented. Emphasis is placed on using available experimental evidence to substantiate the hypothesized mechanisms and assumptions. Detailed comparisons are given between analytical predictions and experimental results. Excellent agreement is obtained, and the important mechanisms are more clearly delineated.