bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Stress of a Liquid Metal Target Container Under Pulsed Heating
Authors: Ni L. , Bauer G. S.
Published: February 2008

In this report, the dynamic response of a liquid metal target container for pulsed spallation neutron sources have been simulated using both a commercial code and a self-developed program. The main features and differences of both programs are presented. A transient thermal analysis was first examined with coupled and uncoupled heat equations. Temperature distribution results showed that the coupling effect between two pulses can be neglected. Stress waves due to direct pulsing have been calculated on the target container, investigating the effects of loading rate and structure thickness. Results from the transient thermal-structural analysis showed that, due to inertia effects, the dynamic stress in the target container is contributed mainly from direct heating in the initial time stage, and later from the pressure wave in the target liquid as it reaches the container wall.
NDE of a 3-D Surface Crack Using Closely Coupled Probes for DCPD Technique
Authors: Saka M. , Hirota D. , Abe´ H. , Komura I.
Published: February 2008

A procedure of applying the d-c potential drop technique using the closely coupled probes to NDE of a 3-D surface crack is newly developed. The calibration equation for three sensors which differ in the distance between the probes is derived. Experiments validated the use of the calibration equation for the NDE of cracks. The method to use the three sensors properly based on the measuring sensitivity is shown.
Localized Autofrettage as a Design Tool for the Fatigue Improvement of Cross-Bored Cylinders
Authors: Segall A. E. , Tricou C. , Evanko M. , Conway J. C.
Published: February 2008

An investigation was launched into the feasibility of improving the fatigue life of thick-walled cylinders with cross-bores by using a localized autofrettage technique. This technique utilized the high stress concentration at the cross-bore to induce localized residual stresses using relatively low internal pressures. An elastic-plastic finite-element analysis indicated that the resulting residual stresses in the vicinity of the cross-bore were predominately compressive and not sufficient in magnitude to induce reverse plasticity. When the resulting residual stresses were used with an elastic fracture-mechanics assessment of a quarter-circular crack at the intersection of the cylinder and cross-bore inner diameter, a significant extension of fatigue life was shown to be possible. In addition to prolonging the useful life of the cylinder, the localized residual stresses were shown to be possible at pressures below the yield threshold for the thick-walled cylinder. Thus, reverse plasticity, permanent deformations, and the need for post-autofrettage machining operations that could inadvertently lessen the beneficial results of a traditional autofrettage were avoided.
J-R Curves From Circumferentially Through-Wall-Cracked Pipe Tests Subjected to Combined Bending and Tension—Part II: Experimental and Analytical Validation
Authors: Miura N. , Wilkowski G. M.
Published: February 2008

In Part I (Miura and Wilkowski, 1998) of this paper, the theory of the two η-factor solutions for circumferentially through-wall-cracked pipes subjected to combined bending and tension due to internal pressure was presented. These solutions seemed to give reasonable predictions by comparing with the existing simplified J-estimation scheme. It was also ascertained that the J would be underestimated if the effect of the internal pressure was not properly considered. Consequently, this paper presents the application of these solutions to full-scale pipe tests. The tests were performed at 288°C (550°F) under combined bending and internal pressure. The materials used for the tests were both carbon steel and stainless steel. The effect of combined loading on the J-R curves was determined and compared to C(T) specimen J-R curves. The solutions were then verified by using three-dimensional finite element analysis.
Experimental Data on Seismic Response of Piping Components
Authors: Slagis G. C.
Published: February 2008

Experimental data from the EPRI Piping and Fitting Dynamic Reliability Program are evaluated. High-amplitude, seismic time history loads were applied to 32 piping components in a cantilevered configuration. Components included elbows, tees, reducers, a reinforced fabricated tee, a nozzle, and lugs. The test levels were about 2 to 8 times Level D. The seismic capability of elbows is shown to be remarkable. The seismic performance of lugs is judged to be poor. The tests demonstrate that collapse is a potential failure mode, particularly in low-frequency systems. The tests also demonstrate that a fatigue failure in a single, high-level, seismic event is possible. Of the 15 nonelbow tests that failed by fatigue, six (40 percent) failed during the first high-level seismic test. Design and fabrication details are crucial to seismic performance. Trends in the data need to be assessed to determine appropriate Section III stress limits for seismic loads. In particular, the impact of component frequency on seismic capability has to be quantified.
Experimental Studies of Natural Convection in Partitioned Enclosures With a Trombe Wall Geometry
Authors: Warrington R. O. , Ameel T. A.
Published: February 2008

Natural convection heat transfer was investigated in a scaled test facility of a Trombe wall geometry. A silicone oil was employed as the convecting medium to obtain large Rayleigh numbers (up to 1.5 × 1010, based on enclosure height) characteristic of full-scale Trombe wall in a passive solar building. The main objectives were to study effects of Trombe wall nonisothermality and location on heat transfer, fluid temperature and fluid flow patterns. As expected, Nusselt numbers were slightly larger on the Trombe wall space side than on the living space side. Nusselt numbers increased slightly as the mass transfer gaps in the Trombe wall were increased. The results were verified, for the zero gap case, by comparing with previous studies. Physical understanding of the convection process was enhanced by flow visualization data. The information obtained should be useful to designers in optimizing overall building performance for passive solar heating.
Yearly Thermal Analysis of a Residential Earth-Tube Heat Exchanger
Authors: Millette J. , Galanis N.
Published: February 2008

A finite element program has been written to solve the three-dimensional Fourier equation for the periodic annual temperature field in the ground surrounding an earth tube connected to the heated basement of a residence situated in a northern community. The results indicate that the presence of the earth tube has a marginal influence on the heat losses from the basement to the ground. They also show that the continuous operation of the earth tube throughout the year is not recommended for the climatological conditions under consideration. An appropriate control strategy is therefore formulated. Correlations for the heat gain during winter operation and heat rejection during summer operation are presented in terms of the relevant design characteristics.
The Energy Impact of Air Leakage Through Insulated Walls
Authors: Bhattacharyya S. , Claridge D. E.
Published: February 2008

Infiltration is customarily assumed to increase the heating and cooling load of a building by an amount equal to the mass flow rate of the infiltration times the enthalpy difference between the inside and outside air—with the latent portion of the enthalpy difference sometimes neglected. An experimental and analytical investigation has been conducted on the actual energy impact of air leakage on a well-characterized insulated stud-cavity wall specimen. Calorimetric measurements conducted on the specimen with measured amounts of air leakage introduced under a variety of controlled conditions and configurations verify earlier test cell measurements showing that infiltration heat exchange can lead to a much smaller change in the energy load due to infiltration than is customarily calculated and show the dependence of infiltration heat exchange on flow rate and path length. An analytical model based on fundamental heat and mass transfer principles has been developed and the predicted values of Infiltration Heat Exchange Effectiveness, ε, as a function of air flow rates and effective path length for five stud-cavity wall specimen test configurations were consistent with the experimental results. Significant experimental results include: (i) ε values in the 0.16–0.7 range in the stud-cavity and (ii) ε values of 0.16 to 0.34 for air exiting the stud-cavity directly across from the entry. These results indicate that significant heat recovery is probable for most leakage occurring through insulated stud cavities.
Natural Convection and Conduction in Massive Wall Solar Collectors With Honeycomb and Without Vents
Authors: Lakhal E. K. , Bilgen E. , Vasseur P.
Published: February 2008

Steady heat transfer by natural convection and conduction is numerically studied in passive solar collector systems consisting of a massive wall with honeycomb structure and without vents. The boundary conditions are constant heat flux on the wall and fins, isothermal on the vertical bounding sides, and adiabatic on the horizontal sides. The governing parameters are the Rayleigh number (106 ≤ Ra ≤ 5 × 109), the aspect ratio of the enclosures (0.4 ≤ A = H′/L′ ≤ 1.4), the dimensionless lengths of the fins (0 ≤ B = l′/Ll′ ≤ 1), the aspect ratio of the microcavities (0.05 ≤ C = h′/L′ ≤ 1), the wall thickness (0.008 ≤ w = w′/L′ ≤ 0.033). The fin thickness (e = e′/H′ = 0.06) and the Prandtl number (Pr = 0.72) were constant, and the conductivity ratio was variable (10−4 ≤ kr ≤ 5 × 106). Local and average Nusselt numbers along the long sides are calculated as a function of various parameters. Streamlines and isotherms are produced. Effects of various parameters on the heat transfer are examined and heat transfer correlations are derived.
Effect of Operating Conditions on the Performance of Two-Bed Closed-Cycle Solid-Sorption Heat Pump Systems
Authors: Zheng W. , Worek W. M. , Nowakowski G.
Published: February 2008

The effect of two operating parameters, the regeneration temperature and the ambient temperature, on the performance of two-bed, closed-cycle solid-sorption heat pumps is investigated. The results show that increasing the regeneration temperature can improve both the COP and cooling capacity, and the effect on cooling capacity is more significant than the COP. Increasing the regeneration temperature from 180°C to 260°C, the cooling capacity increases by 50 percent and the COP improves 20 percent. When the ambient temperature drops, the system performance increases significantly. When the ambient temperature decreases by 10°C from the design point of 35°C, the COP and cooling capacity increases by 50 percent and 40 percent, respectively. Also, the bed cycling speed should be increased to achieve the optimum system performance when the regeneration temperature is higher or the ambient temperature becomes lower.
Prediction of Wind Turbine Rotor Loads Using the Beddoes-Leishman Model for Dynamic Stall
Authors: Pierce K. , Hansen A. C.
Published: February 2008

The Beddoes-Leishman model for unsteady aerodynamics and dynamic stall has recently been implemented in YawDyn, a rotor analysis code developed at the University of Utah for the study of yaw loads and motions of horizontal axis wind turbines. This paper presents results obtained from validation efforts for the Beddoes model. Comparisons of predicted aerodynamic force coefficients with wind tunnel data and data from the combined experiment rotor are presented. Also, yaw motion comparisons with the combined experiment rotor are presented. In general the comparisons with the measured data are good, indicating that the model is appropriate for the conditions encountered by wind turbines.
A New Solar Receiver Thermal Store for Space-Based Activities Using Multiple Composite Phase-Change Materials
Authors: Gong Zhen-Xiang , Mujumdar A. S.
Published: February 2008

A new solar receiver latent thermal energy storage module for space-based activities is proposed. It is different from a conventional module (which uses a single phase-change material (PCM)); this module uses a composite configuration of multiple PCMs. A finite element model is presented which simulates the transient cyclic thermal process involved. Computations have been carried out to investigate the potential advantages of a composite multi-PCM store over a single PCM store. Numerical results indicate that variation of the fluid outlet temperature can be significantly reduced by appropriate selection of multiple composite PCMs.
Measured Performance and Modeling of an Evacuated-Tube, Integral-Collector-Storage Solar Water Heater
Authors: Mason A. A. , Davidson J. H.
Published: February 2008

An experimental study of an evacuated-tube, integral-collector-storage water heater was conducted in an indoor solar simulator. Useful collected energy, radiation-induced stratification and draw-induced mixing are characterized in eight trials in which test duration, initial tank water temperature, flow rate during withdrawal of heated water from the collector, withdrawal pattern and reflectance of the back-plane were varied. All tests were performed at nominal irradiance of 900 W/m2, normal incidence, and collector slope of 45 degrees. The capability of the TRNSYS integral collector storage model to predict performance for operating conditions for which data are assumed to be unavailable was assessed. Using data from one experimental trial, optical efficiency (τα) of the collector was determined by matching predicted useful energy gain to measured gain. Effectiveness of the calibrated model was based on a comparison of predicted gains to measured values obtained in the remaining seven trials. For five of seven trials, predicted performance is within nine percent of measured performance and less than experimental error. For the other two trials, predicted performance is within 15 percent of measured performance. The higher discrepancies may be partially due to experimental conditions not modeled such as heating of the piping connecting the collector to the test facility and inadequate characterization of back-plane reflectivity. The model does not predict radiation-induced stratification. Although the effect of mixing during draws can be approximated by specifying the number of fully mixed volume segments in the tanks, selection of number of nodes requires knowledge of the behavior of the system. The number of nodes selected has minimal impact on total energy gain, but does affect the temperature of water delivered to the load.
Gas Heat Conduction in Evacuated Flat-Plate Solar Collectors: Analysis and Reduction
Authors: Beikircher T. , Benz N. , Spirkl W.
Published: February 2008

In stationary heat-loss experiments, the thermal losses by gas conduction of an evacuated flat-plate solar collector (EFPC) were experimentally determined for different values of interior gas pressure. The experiments were carried out with air and argon in the pressure range from 10−3 to 104 Pa. For air, loss reduction sets in at 100 Pa, whereas at 0.1 Pa heat conduction is almost completely suppressed. Using argon as filling gas, gas conduction is reduced by 30 percent (compared to air) at moderate interior pressures of 1000 Pa. With decreasing pressure this reduction is even greater (50 percent reduction at 10 Pa). A theory was developed to calculate thermal losses by gas conduction in an EFPC: Fourier’s stationary heat conduction equation was solved numerically (method of finite differences) for the special geometry of the collector. From kinetic gas theory a formula for the pressure dependency of the thermal conductivity was derived covering the entire pressure range. The theory has been validated experimentally for the gases air and argon. Calculations for krypton and xenon show a possible gas conduction loss reduction of 60–70 percent and 75–85 percent (with respect to air, depending on gas pressure), corresponding to a reduction of the overall collector losses of up to 40 percent.
Exergy Analysis of a Solar Heating System
Authors: Liu Geng , Cengel Y. A. , Turner R. H.
Published: February 2008

Exergy destruction associated with the operation of a solar heating system is evaluated numerically via an exergy cascade. As expected, exergy destruction is dominated by heat transfer across temperature differences. An energy analysis is also given for comparison of exergy cascade to energy cascade. Efficiencies based on both the first law and second law of thermodynamics are calculated for a number of components and for the system. The results show that high first-law efficiency does not mean high second-law efficiency. Therefore, the second-law analysis has been proven to be a more powerful tool in identifying the site losses. The procedure used to determine total exergy destruction and second law efficiency can be used in a conceptual design and parametric study to evaluate the performance of other solar heating systems and other thermal systems.
An Alternative Desiccant Cooling Cycle
Authors: Kettleborough C. F. , Waugaman D. G.
Published: February 2008

A computer analysis of the thermal performance of a desiccant cooling cycle in which the cooled air, passing to the space to be conditioned, has not been in contact with the desiccant. It is shown that an important factor is the efficiency of the desiccant tower. Only liquid desiccants are considered.
On Thermoeconomics of a Sensible Heat, Thermal Energy Storage System
Authors: Badar M. A. , Zubair S. M.
Published: February 2008

A closed-form model for the second-law-based thermoeconomic optimization of a sensible heat storage system, in which the energy is stored in a large liquid bath from a hot-gas source, is discussed with an example problem. The results are compared with those obtained from Bejan’s analysis to illustrate usefulness of the present approach. The influence of important parameters on the optimum number of heat transfer units Ntu,opt, and dimensionless charging time θopt, are presented in a graphic form.
Investigation of Cold Filling Receiver Panels and Piping in Molten-Nitrate-Salt Central-Receiver Solar Power Plants
Authors: Pacheco J. E. , Ralph M. E. , Chavez J. M.
Published: February 2008

Cold filling refers to flowing a fluid through piping or tubes that are at temperatures below the fluid’s freezing point. Since the piping and areas of the receiver in a molten-nitrate salt central-receiver solar power plant must be electrically heated to maintain their temperatures above the nitrate salt freezing point (430°F, 221°C), considerable energy could be used to maintain such temperatures during nightly shutdown and bad weather. Experiments and analyses have been conducted to investigate cold filling receiver panels and piping as a way of reducing parasitic electrical power consumption and increasing the availability of the plant. The two major concerns with cold filling are (1) how far can the molten salt penetrate cold piping before freezing closed, and (2) what thermal stresses develop during the associated thermal shock. Cold fill experiments were conducted by flowing molten salt at 550°F (288°C) through cold panels, manifolds, and piping to determine the feasibility of cold filling the receiver and piping. The transient thermal responses were measured and heat transfer coefficients were calculated from the data. Nondimensional analysis is presented which quantifies the thermal stresses in a pipe or tube undergoing thermal shock. In addition, penetration distances were calculated to determine the distance salt could flow in cold pipes prior to freezing closed.
On the Analysis of Surface Error Distributions on Concentrated Solar Collectors
Authors: Johnston G.
Published: February 2008

The distribution of surface normal deviations from an ideal shape on concentrating solar surfaces is used to define the optical quality of a reflector. These distributions can be modeled by considering them to ideally follow a two-dimensional, circular Gaussian distribution. However, the measurement of these deviations in experimental systems usually defines only that component of the surface normal that deviates from the ideal surface normal direction, and ignores the rotational component of the normal vector in the plane perpendicular to the ideal direction. To compare the measured one-dimensional radial distribution with the expected two-dimensional model, we must transform the two-dimensional model into the appropriate radial distribution. The following analysis describes this transformation, and presents results gained from an application of the analysis to measured surface normal data from a mirror panel used in the reflecting surface of the 400 m2 paraboloidal (“Big Dish”) concentrator constructed at the ANU.
A Complex Frequency Domain Model of Wind Turbine Structures
Authors: So̸rensen P. , Larsen G. C. , Christensen C. J.
Published: February 2008

The present paper describes a frequency domain model of the structure of an operating horizontal axis wind turbine with three or more blades. The frequency domain model is implemented along with an analogous time domain model in a PC code. This PC code is used to verify the frequency domain model comparing loads on the structure calculated with the frequency domain model both to loads calculated with the time domain model and to measured loads.
What are the Potential Benefits of Including Latent Storage in Common Wallboard?
Authors: Stovall T. K. , Tomlinson J. J.
Published: February 2008

Previous work has shown that wallboard can be successfully manufactured to contain up to 30 percent phase-change material (PCM), or wax, thus enabling this common building material to serve as a thermal energy storage device. The PCM wallboard was analyzed for passive solar applications and found to save energy with a reasonable payback time period of five years. Further evaluations of the wallboard are reported in this paper. This analysis looks at potential applications of PCM wallboard as a load management device and as a comfort enhancer. Results show that the wallboard is ineffective in modifying the comfort level but can provide significant load management relief. In some applications the load management strategy also serves to save a small amount of energy, in others there is a small energy penalty.
Design, Development, and Testing of an Automated Window Shade Controller
Authors: Luecke G. R. , Slaughter J.
Published: February 2008

An approach to the design of active window shades is developed to control the direct solar gain through a window. Using simple actuation hardware and sensors, a control strategy is presented that automatically adjusts window shades to save HVAC energy by controlling direct solar radiation passing through a window. The control algorithm is based on a simple approach that admits direct light in the winter and blocks the direct light in the summer, while providing shade adjustment that affords maximum visibility through the window. Cloudy skies or indirect sun result in horizontal placement of the shades, and the shades close at night. The implementation uses two thinfilm photovoltaic cells as sensors and a control algorithm that is independent of the window orientation, latitude, or solar time, so that it operates properly in any installation location. Preliminary analytic and test results show significant energy savings when the automatic window shades are compared with a window without shades, and with a window outfitted with fixed horizontal shades.
Thermodynamic Analysis of Solar Energy Utilization Combined With the Exploitation of the LNG Physical Exergy
Authors: Bisio G. , Pisoni C.
Published: February 2008

A solar air collector system combined with LNG vaporization is analyzed in terms of energy and exergy.
Calculating Solar Radiation Received by Tubular Collectors
Authors: Perez R. , Seals R. , Anderson J. , Menicucci D.
Published: February 2008

Tubular absorbers installed inside evacuated tubes represent an increasingly common design for low-temperature solar collectors. Much work has been done on the subject of solar radiation received by flat-plate collectors; much less has been done for tubular collectors. In this paper we present an algorithm to estimate irradiance impinging on tubular arrays. Key examples are provided to illustrate the difference of energy collected between flat-plate and tubular collectors.
Photocatalytic Treatment of Wastewater From 5–Fluorouracil Manufacturing
Authors: Anheden M. , Goswami D. Y. , Svedberg G.
Published: February 2008

This paper presents some of the experimental results from a study conducted to demonstrate the potential use of photocatalytic oxidation for decolorization and COD reduction of wastewater from 5–fluorouracil manufacturing. A series of batch experiments, were carried out using diluted solutions of the wastewater with 0.1 percent w/v TiO2. Low pressure mercury lamps were used to simulate the UV part of sunlight. The experiments showed that a complete decolorization and a substantial reduction of COD was achieved within 20 hours with a 20 percent solution. During the reaction period, the pH was noted to decrease considerably, indicating formation of acids. Adding hydrogen peroxide to the solution was found to significantly increase the reaction rates. Adding 2400 ppm of H2O2 gave an 80 percent decrease in color in one hour and a 70-80 percent decrease in COD in 20 hours. The influence of UV-light intensity was also examined. This experiment showed that with a UV-intensity of 15 W/m2, i.e., a cloudy day, the decolorization rate was still considerable, while the COD reduction rate was very low.
A Two-Region Model for Gradient Modification of Salt-Gradient Solar Ponds by Radial Injection
Authors: Eghneim G. A. , Kleis S. J.
Published: February 2008

A combined experimental and numerical study was conducted to support the development of a new gradient maintenance technique for salt-gradient solar ponds. Two numerical models were developed and verified by laboratory experiments. The first is an axisymmetric (near-field) model which determines mixing and entrainment in the near-field of the injecting diffuser by solving the conservation equations of mass, momentum, energy, and salt. The model assumes variable properties and uses a simple turbulence model based on the mixing length hypothesis to account for the turbulence effects. A series of experimental measurements were conducted in the laboratory for the initial adjustment of the turbulence model and verification of the code. The second model is a one-dimensional far-field model which determines the change of the salt distribution in the pond gradient zone as a result of injection by coupling the near-field injection conditions to the pond geometry. This is implemented by distributing the volume fluxes obtained at the domain boundary of the near-field model, to the gradient layers of the same densities. The numerical predictions obtained by the two-region model was found to be in reasonable agreement with the experimental data.
Simulation of Solar Radiation Heat Flux Data for Energy Calculation
Authors: Panek A. , Lee Y. , Tanaka H.
Published: February 2008

The global (or total) and diffuse solar irradiation data are not always available in many areas of the world and they have to be estimated using some sort of empirical models. This paper describes how the sequence of hourly irradiation data can be simulated using some statistical parameters of the global solar radiation intensity such as the monthly average and variance of its daily maxima and autocorrelation time constant. The results of this simulation are compared with the measured data for two different locations, Ottawa, Canada and Warsaw, Poland (these two locations are chosen because of easy access to the radiation data). The comparison shows an acceptable level of agreement between the simulated and measured results.
Direct Steam Generation in Parabolic Trough Solar Power Plants: Numerical Investigation of the Transients and the Control of a Once-Through System
Authors: Lippke F.
Published: February 2008

Direct steam generation (DSG) in parabolic troughs was first studied in the early 1980s by Murphy (1982) and Pederson (1982). Intensive research on DSG then started in 1988, when Luz identified this technology as the desired system for a future generation of its power plants. These R&D activities were not terminated on Luz’s demise in 1991, but have been continued by several institutes and companies in Europe as well as in Israel (Dagan et al., 1991, Mu¨ller et al., 1992a, b, 1993, 1994). This paper concerns the dynamic reaction of the water-steam flow. In order to investigate this, a numerical simulation program was developed at the ZSW. The numerical approach, its verification, and results of an extended study concerning the reaction and the control (ability) of a once-through DSG system at different weather conditions are presented.
Solar Flux-Density Distribution due to Partially Shaded/Blocked Mirrors Using the Separation of Variables/Superposition Technique With Polynomial and Gaussian Sunshapes
Authors: Elsayed M. , Fathalah K. A.
Published: February 2008

In a previous work (El Sayed et al., 1994), the separation of a variable/superposition technique was used to predict the flux density distribution on the receiver surfaces of solar central receiver plants. In this paper further developments of the technique are given. A numerical technique is derived to carry out the convolution of the sunshape and error density functions. Also, a simplified numerical procedure is presented to determine the basic flux density function on which the technique depends. The technique is used to predict the receiver solar flux distribution using two sunshapes, polynomial and Gaussian distributions. The results predicted with the technique are validated by comparison with experimental results from mirrors both with and without partial shading/blocking of their surfaces.
Performance Analysis of an OTEC Plant and a Desalination Plant Using an Integrated Hybrid Cycle
Authors: Uehara Haruo , Miyara Akio , Ikegami Yasuyuki , Nakaoka Tsutomu
Published: February 2008

A performance analysis of an OTEC plant using an integrated hybrid cycle (I–H OTEC Cycle) has been conducted. The I–H OTEC cycle is a combination of a closed-cycle OTEC plant and a spray flash desalination plant. In an I–H OTEC cycle, warm sea water evaporates the liquid ammonia in the OTEC evaporator, then enters the flash chamber and evaporates itself. The evaporated steam enters the desalination condenser and is condensed by the cold sea water passed through the OTEC condenser. The optimization of the I–H OTEC cycle is analyzed by the method of steepest descent. The total heat transfer area of heat exchangers per net power is used as an objective function. Numerical results are reported for a 10 MW I–H OTEC cycle with plate-type heat exchangers and ammonia as working fluid. The results are compared with those of a joint hybrid OTEC cycle (J–H OTEC Cycle).
Destruction of Organic Compounds in Water Using Supported Photocatalysts
Authors: Zhang Yin , Crittenden J. C. , Hand D. W. , Perram D. L.
Published: February 2008

Photocatalytic destruction of organic compounds in water is investigated using tanning lamps and fixed-bed photoreactors. Platinized titanium dioxide (Pt-TiO2) supported on silica gel is used as a photocatalyst. Complete mineralization of influent concentrations of 4.98 mg/L tetrachloroethylene and 2.35 mg/L p-dichlorobenzene requires a reactor residence time less than 1.3 minutes. While for influent concentrations of 3.58 mg/L 2-chlorobiphenyl, 2.50 mg/L methyl ethyl ketone and 0.49 mg/L carbon tetrachloride, complete mineralization requires reactor residence times of 1.6, 10.5, and 16.8, minutes, respectively. A reactor model is developed using Langmuir-Hinshelwood kinetics and the model parameters are determined using a reference compound, trichloroethylene. Based on the results of experiments with trichloroethylene, the model predicts the mineralization of the aforementioned compounds from ultraviolet (UV) irradiance, influent concentration, hydroxyl radical rate constants, and the known physical properties of the compounds. The model is also able to predict organic destruction using solar insolation (which has a different spectral distribution from the tanning lamps) based on the UV absorption characteristics of titanium dioxide.
Darrieus Rotor Aerodynamics in Turbulent Wind
Authors: Brahimi M. T. , Paraschivoiu I.
Published: February 2008

The earlier aerodynamic models for studying vertical axis wind turbines (VAWT’s) are based on constant incident wind conditions and are thus capable of predicting only periodic variations in the loads. The purpose of the present study is to develop a mode capable of predicting the aerodynamic loads on the Darrieus rotor in a turbulent wind. This model is based on the double-multiple streamtube method (DMS) and incorporates a stochastic wind model The method used to simulate turbulent velocity fluctuations is based on the power spectral density. The problem consists in generating a region of turbulent flow with a relevant spectrum and spatial correlation. The first aerodynamic code developed is based on a one-dimensional turbulent wind model. However, since this model ignores the structure of the turbulence in the crossflow plane, an extension to three dimensions has been made. The computer code developed, CARDAAS, has been used to predict aerodynamic loads for the Sandia-17m rotor and compared to CARDAAV results and experimental data. Results have shown that the computed aerodynamic loads have been improved by including stochastic wind into the aerodynamic model.
Convective Heat Loss from Upward and Downward-Facing Cavity Solar Receivers: Measurements and Calculations
Authors: Leibfried U. , Ortjohann J.
Published: February 2008

Up to now, nearly all the experimental and theoretical work treating convective heat loss of cavity receivers had been effected for downward and sideward-facing receivers, as they are used in dish concentrators and solar power towers. With a test facility it was possible to show flow patterns and a temperature field in a hot cavity for a variety of parameter settings and over the whole range of tilt angles. Two types of geometries were examined: a spherical and a hemispherical cavity, both with an inner diameter of 400 mm, the aperture diameter ranging between 60 and 195 mm. Temperatures were varied between 573 K and 873 K. The dependence of losses on temperature, tilt angle, aperture-radius, geometry, ribs, and ventilation is reported. Special emphasis is invested to get an understanding of the air flow in an upward facing cavity. Based on the works of Clausing et al. (1987), and Stine and McDonald (1989), two algorithms are developed that allow the calculation of convective loss from upward-facing receivers. Over the whole range of tilt angles, calculated results are compared with measurements. Good agreement between the calculated and measured data is found.
Thermal and Structural Analysis of the Heat Receiver for the Solar Dynamic Ground Test Demonstrator
Authors: Strumpf H. J. , Avanessian V. , Ghafourian R. , Huang F.
Published: February 2008

A solar dynamic ground test demonstrator space power system is being developed. The system comprises a complete Brayton engine—a heat receiver, concentrator, radiator, recuperator, heat rejection gas cooler, and turboalternator compressor. All of these components will be operated inside a vacuum tank. The engine is powered by simulated sunlight from an external bank of lights. Successful completion of the testing will indicate the readiness of solar dynamic power for space applications. This paper discusses the thermal and structural analysis of the heat receiver component. The analysis performed indicates that all components comfortably meet the life and cold start requirements, while maintaining the necessary overall performance.
Analytical Model to Predict Annual Soil Surface Temperature Variation
Authors: Krarti M. , Lopez-Alonzo C. , Claridge D. E. , Kreider J. F.
Published: February 2008

An analytical model is developed to predict the annual variation of soil surface temperature from readily available weather data and soil thermal properties. The time variation is approximated by a first harmonic function characterized by an average, an amplitude, and a phase lag. A parametric analysis is presented to determine the effect of various factors such as evaporation, soil absorptivity, and soil convective properties on soil surface temperature. A comparison of the model predictions with experimental data is presented. The comparative analysis indicates that the simplified model predicts soil surface temperatures within ten percent of measured data for five locations.
Solar Concentration of 50,000 Achieved With Output Power Approaching 1 kW
Authors: Jenkins D. , Winston R. , Bliss J. , O’Gallagher J. , Lewandowski A. , Bingham C.
Published: February 2008

We have achieved a 50,000 ± 3,000 times concentration of sunlight using a unique dielectric nonimaging concentrator in an experiment performed at the National Renewable Energy Laboratory. The scale of the experiment is several times larger than that of previous experiments. Total output power approaching 1 kW passes through a 4.6 mm diameter aperture. An extractor tip is added to the concentrator profile which allows measurement of flux levels using an air calorimeter. This new device has the potential to allow the use of dielectric concentrators at larger scale for thermal electric power generation. We report on the implications of this experiment for the future use of dielectric concentrators.
Photogrammetry: An Available Surface Characterization Tool for Solar Concentrators, Part I: Measurements of Surfaces
Authors: Shortis M. R. , Johnston G. H. G.
Published: February 2008

Close range photogrammetry is a sensing technique that allows the three-dimensional coordinates of selected points on a surface of almost any dimension and orientation to be assessed. Surface characterisations of paraboloidal reflecting surfaces at the ANU using photogrammetry have indicated that three-dimensional coordinate precisions approaching 1:20,000 are readily achievable using this technique. This allows surface quality assessments to be made of large solar collecting devices with a precision that is difficult to achieve with other methods.
Inherent Limitations of Volumetric Solar Receivers
Authors: Kribus A. , Ries H. , Spirkl W.
Published: February 2008

The flow in volumetric absorbers is investigated using a simple mathematical model. It is found that there are several restrictions and failure mechanisms that are inherent to the volumetric absorber, regardless of the precise structural details, material properties, etc. The heat that the absorber can extract safely is limited by flow-related constraints. Multiple steady solutions exist for certain parameter values: a “fast” solution corresponding to a low exit temperature, a “slow” solution which is unstable, and a “choked” solution for which the absorber is near to stagnation temperature. The existence of multiple solutions may lead to abrupt local “switching” and absorber failure. For a given irradiance applied to the absorber, the existence and the character of the solutions are determined by a single dimensionless parameter, the Blow parameter B. Neglecting the variation of the hydraulic resistivity with temperature may lead to a dangerous overestimate of the receiver’s ability to sustain irradiation. For reasonable efficiencies control of mass flow or outlet temperature of the absorber, rather than pressure control, may be required.
Analysis of Gas Heat Conduction in Evacuated Tube Solar Collectors
Authors: Beikircher T. , Spirkl W.
Published: February 2008

We investigated the gas heat conduction in two types of evacuated tubular solar collectors for a wide range of Knudsen numbers. For tube-in-tube collectors, we generalized a solution of the gas kinetic Boltzmann equation, which has been obtained by the four-momentum method, to polyatomic gases. The resulting equation coincides with Sherman’s interpolation formula. For a plate-in-tube collector, we measured the stationary heat loss for gas pressures varying between 10−2 and 104 Pa. The accuracy of an earlier experiment was improved. For analysis we applied the temperature jump method: a heat conduction equation with boundary conditions of the third kind involving the temperature gradient and the pressure was numerically solved. The results with the temperature jump method agree with the experimental values nearly within the error bands. We also applied Sherman’s interpolation formula and found, as expected, that the heat conduction as function of the pressure is too steep. For both types of collectors, the influence of geometric parameters was theoretically studied.
Evaluation of Different Radiation and Albedo Models for the Prediction of Solar Radiation Incident on Tilted Surfaces, for Four European Locations
Authors: Psiloglou B. E. , Balaras C. A. , Santamouris M. , Asimakopoulos D. N.
Published: February 2008

The diffuse radiation incident on an inclined surface is composed of both the sky diffuse radiation and the ground-reflected radiation. Depending on the model used to calculate the sky diffuse radiation and the estimated albedo value, it is possible to introduce a significant error in the prediction of the total radiation incident on a tilted surface. Twelve sky diffuse submodels associated with four different albedo submodels are used to estimate the total radiation on the tilted surface from data on the horizontal plane. The predicted total solar radiation values are compared with measured data on a south facing vertical surface, from four representative south and north European locations. Root mean square error, mean bias error, and a t-test are used to determine the intrinsic performance of each combination of diffuse tilt and albedo submodel. Accordingly, the various model combinations do not exhibit a statistically significant difference between measured and calculated values.
Frequency Domain Analysis of the Fatigue Loads on Typical Wind Turbine Blades
Authors: Sutherland H. J.
Published: February 2008

The fatigue analysis of a wind turbine blade typically depends on converting time-series data to a series of load cycles using one of several cyclic counting algorithms. However, many structural analysis techniques yield frequency-domain stress spectra, and a large body of experimental loads (stress) data is reported in the frequency domain. To permit the fatigue analysis of this class of data, a series of computational algorithms based on Fourier analysis techniques has been developed. The principle underlying these algorithms is the use of an Inverse Fast Fourier Transform (FFT) to transform the frequency spectrum to an equivalent time series suitable for cycle counting. In addition to analyzing the fatigue loads along the primary blade axes, this analysis technique also permits the examination of “off-axis” bending loads. These algorithms, which have been incorporated in the LIFE2 fatigue analysis code for wind turbines, are illustrated and evaluated with data from typical wind turbine blades.
Wind Tunnel Test of the S814 Thick Root Airfoil
Authors: Somers D. M. , Tangler J. L.
Published: February 2008

The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high maximum lift coefficient designed to be largely insensitive to leading-edge roughness effects. The 24 percent thick S814 airfoil was designed with these characteristics to accommodate aerodynamic and structural considerations for the root region of a wind-turbine blade. In addition, the airfoil’s maximum lift-to-drag ratio was designed to occur at a high lift coefficient. To accomplish the objective, a two-dimensional wind tunnel test of the S814 thick root airfoil was conducted in January 1994 in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory, The Netherlands. Data were obtained with transition free and transition fixed for Reynolds numbers of 0.7, 1.0, 1.5, 2.0, and 3.0 × 106. For the design Reynolds number of 1.5 × 106, the maximum lift coefficient with transition free is 1.32, which satisfies the design specification. However, this value is significantly lower than the predicted maximum lift coefficient of almost 1.6. With transition fixed at the leading edge, the maximum lift coefficient is 1.22. The small difference in maximum lift coefficient between the transition-free and transition-fixed conditions demonstrates the airfoil’s minimal sensitivity to roughness effects. The S814 root airfoil was designed to complement existing NREL low maximum-lift-coefficient tip-region airfoils for rotor blades 10 to 15 meters in length.
The Effects of Controls on Fatigue Loads in Two-Bladed Teetered Rotor Wind Turbines
Authors: Wu K. C. , De La Guardia R.
Published: February 2008

This paper presents a quantitative analysis of the fatigue loads in a down wind, yaw-controlled, fixed pitch, two-bladed teetered-rotor wind turbine using proportional-integral, full-state optimal, and fuzzy logic controllers. Time-domain simulation data is generated using the EASY5x/WT software developed at the University of Texas at El Paso. The simulation data reveal that the choice of controller type, or the controller dynamics, can play a very important role in the fatigue life of a wind turbine and should be considered early in the design process of the wind turbine. In summary, the fuzzy logic controller is the most robust controller under a wide regime of wind conditions. It provides the best overall performance in terms of power regulation capability and minimum fatigue loads. The optimal controller with a full-state Kalman filter observer provides a satisfactory performance interms of power regulation capability and loads when the operating condition is close to the design point at which the controller was optimized. It fails to regulate the power output when the actual operating point deviated too far, about 30 percent in our computer simulations, from the designed operating point. The PI controller provided satisfactory performance in power regulation. However, it produced the worst fatigue loads to the wind turbine among the three controllers.
Variable Speed Operation of Permanent Magnet Alternator Wind Turbines Using a Single Switch Power Converter
Authors: Venkataramanan G. , Milkovska B. , Gerez V. , Nehrir H.
Published: February 2008

Advantages of operating wind turbine generators at variable speed are well known. Various approaches have been proposed to extract maximum power from the turbines by operating them at the optimum tip-speed ratio. Often, they feature a three-phase controlled rectifier d-c link followed by a three-phase inverter type of power converter topology to deliver constant frequency a-c output power from a variable speed generator coupled to the turbine. However, in stand-alone power supply applications for remote sites, where the power level is a few kW or less, this approach is economically unjustifiable. This paper presents a single switch power electronic converter to regulate the power output of a permanent magnet alternator driven turbine feeding a battery, featuring minimal additional costs suitable for low power applications. Power converter operation and a control strategy to maintain optimum tip-speed ratio are discussed in the paper. Computer simulations of the complete system verifying the proposed concepts are presented.