bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibration Behavior and Fatigue Strength of Mocked-Up Piping System
Authors: Hayashi M. , Tanaka I. , Iida K. , Matsuda F. , Sato M.
Published: February 2008

For the purpose of investigating vibration characteristics and fatigue strength of a socket-welded joint, a piping system was mocked-up by assembling a straight pipe of 350 mm nominal diameter and a long pipe of 20 mm nominal diameter consisting of straight pipes and elbows. The one end of the small-diameter piping is connected to the large-diameter pipe at its longitudinal midpoint by socket welding, and the rest is supported at several supporting points, the locations of which are changed as an experimental parameter. The materials of the small-diameter piping are carbon and stainless steels. The small-diameter piping was subjected to nearly resonant vibration with the frequency of about 11 Hz by a sinusoidal vibration load applied to the large-diameter pipe. The vibrating displacement amplitude measured on the actual piping was basically 0.05 mm in resonant condition; but the displacement was changed to obtain an S-N curve for the socket-welded joint in the fatigue life range of 104 to 107 cycles. In the mocked-up specimens, fatigue cracks were initiated from the toe of the socket-fillet welds at higher stress amplitude, but from the fillet root at lower stress amplitude. Comparative fatigue tests of straight shape socket-welded specimens fabricated with 20 mm nominal diameter pipe of the same material as used in the mocked-up specimen were carried out under four-point bending condition. The fatigue strength of the socket-welded joint in the mocked-up specimen was about 15 percent lower than that of the simple specimen fatigued by four-point bending load. The reason for this difference is probably due to the triaxial stress condition and three-dimensional restraint condition. The strain gage measurement showed that the shear stress was about 40 percent of the bending stress in the case of the mockedup specimen. In addition, vibration tests of the piping system showed good agreement between experimental and analytical results of vibration behavior.
Stresses and Strains in High-Pressure Composite Hoses
Authors: Nair S. , Dollar A.
Published: February 2008

A simple mechanical model for a high-pressure hose made of ethylene-propylene rubber reinforced with two helical steel wires and a layer of fabric is analyzed. The model assumes perfect bonding between the different constituents and the torsional effect due to the right-handed helical wires is neglected. Both linear and nonlinear stress-strain relations are considered for the rubber which is assumed to be incompressible. Stresses and strains of the constituents are obtained for different internal pressures and geometrical parameters.
A Re-Examination of Propane Tank Tub Rockets Including Field Trial Results
Authors: Miller T. , Birk A. M.
Published: February 2008

When a tank containing a pressure-liquefied gas fails, one mode of failure involves the tank being propelled large distances by the released two-phase material. This mode of failure is called a tub rocket and it can pose a severe hazard to the public because of its unpredictability. Field tests were recently conducted to study the effect of explosive devices on propane tanks. The tests included tanks of various sizes up to 2000 L (500 gal).In most cases, the tests resulted in punctured tanks with transient two-phase jet releases. In some cases, the jet releases were sufficient to propel the tanks over considerable distances. In a small number of tests involving 470-L tanks, the explosive device resulted in the clean removal of a tank end, and this resulted in near-ideal launches of tub rockets. In one case, the rocket was launched vertically, and in another, the rocket was launched near 45 deg elevation angle giving a tub range of 370 m. In other cases, the explosive devices resulted in punctures, and in some of these, the resulting two-phase jet propelled the tanks over considerable distance. These examples gave a good opportunity to re-examine tub rocket models for tanks containing liquefied gases. This paper describes a theoretical model involving two-phase critical flow propulsion of cylindrical tanks. Three different critical flow models are compared, including the homogeneous equilibrium model (HEM), the homogeneous frozen model (HFM), and the Henry-Fauske model (HFK). Range predictions are compared with existing data and a model previously developed. Model predictions are calibrated to the field trial results described in the foregoing and then used to predict realistic ranges for various sizes of storage and transport tanks.
Analysis of Fire-Induced Ruptures of 400-L Propane Tanks
Authors: Kielec D. J. , Birk A. M.
Published: February 2008

A series of fire tests were conducted to study the thermal rupture of propane tanks. The tests involved 400-L ASME automotive propane tanks filled to 80 percent capacity with commercial propane. The tanks were brought to failure using torches and pool fires. The resulting thermal ruptures varied in severity from minor fissures, measuring a few centimeters in length, to catastrophic failures where the tank was flattened on the ground. The catastrophic failures would typically be called boiling liquid expanding vapor explosions (BLEVEs). The objective of this work was to develop a correlation between the failure severity and the tank condition at failure. The deformed propane tanks were measured in detail and the extent of deformation was quantified. The tank failure severity was found to be a complex function of a number of tank and lading properties at failure. This paper presents the measured data from the tanks and a step-by-step description of how the correlation was determined.
Axisymmetric Guided Wave Scattering by Cracks in Welded Steel Pipes
Authors: Zhuang W. , Shah A. H. , Datta S. K.
Published: February 2008

Scattering of axisymmetric guided waves by cracks and weldments of anisotropic bonding material in welded steel pipes is investigated in this paper by a hybrid method employing finite element and modal representation techniques. The study is motivated by the need to develop a quantitative ultrasonic technique to distinguish flaws and bonding materials in welded cylindrical structures. Numerical results for reflection coefficients are presented for a steel pipe with cracks and V-shaped weldments with and without cracks at the interface between the weldment and the steel pipe. It is shown that as the frequency increases, the coefficients of reflection exhibit resonant peaks at the cutoff frequencies of higher guided modes. These peaks become increasingly pronounced as the slope and the length of the crack increase. Numerical results presented have important applications in quantitative nondestructive evaluation.
Damage Assessment and Management in Reformer Furnaces
Authors: da Silveira T. L. , Le May I.
Published: February 2008

The mechanisms of damage accumulation and methods of life assessment in reformer furnaces are discussed. Such furnaces are key elements in petrochemical plants, receiving a mixture of hydrocarbons and steam and producing a hydrogen-rich reaction gas in the presence of a catalyst. At the operating conditions of 800 to 900°C, high-temperature damage takes place in the reformer columns inside the furnace radiation chamber, as well as in the external outlet pipes. The damage mechanisms and methods of assessment are described for the various components involved.
Low-Speed Impact Damage in Filament-Wound CFRP Composite Pressure Vessels
Authors: Matemilola S. A. , Stronge W. J.
Published: February 2008

Quasi-static and impact tests were conducted on filament-wound carbon fiber composite pressure vessels to study factors that affect burst pressure. Observed damage included fiber microbuckling, matrix cracking, and delamination. Fiber microbuckling of the outer surface layer near the impact point was the main factor that reduced the burst pressure of the vessels. This type of damage was visually detectable on the surface. For similar levels of missile kinetic energy, the impact damage to filament-wound composite pressure vessels depends on size and shape of the colliding body in the contact area. Burst pressure for a damaged vessel decreases with the ratio of axial length of damaged fibers 1, to vessel wall thickness h, up to a ratio 1/h = 3; beyond this length of damaged section the burst pressure was independent of length of damage. Strain measurements near the region of loading showed that damage related to fiber microbuckling is sensitive to strain rate. At locations where impact damage was predominately due to fiber microbuckling, the failure strain was about six times the strain for microbuckling during quasi-static loading.
Stress Concentration, Stress Intensity, and Fatigue Lifetime Calculations in Autofrettaged Tubes Containing Axial Perforations Within the Wall
Authors: Parker A. P. , Endersby S. N. , Bond T. J. , Underwood J. H. , Lee S. L. , Higgins J.
Published: February 2008

Elastic, elastic-plastic and experimental stress analyses, and fatigue lifetime predictions are presented for thick cylinders containing multiple, axial holes within the wall. The holes are generally semi-elliptical (including semi-circular), and the cylinders are autofrettaged after introduction of the holes and are subsequently subjected to cyclic pressurization of the bore. Two potentially critical failure locations are identified; a fracture-mechanics based design methodology is proposed; elastic and elastic-plastic finite element (FE) analyses are undertaken. The elastic FE analysis predicts hoop stresses at the bore resulting from internal pressurization which are some 7 percent higher than those for the equivalent plain tube. For a given hole size and location and for nominal overstrains of 40 percent or greater, the residual compressive stress at the bore is reduced by approximately 15 percent below the value for a plain tube of the same radius ratio. Two experimental investigations are reported, one based upon X-ray diffraction, to measure residual stresses and stress gradients, and the other based upon radial tube slitting, to measure opening angle. They confirm most features of the residual stress profiles predicted from FE analysis with the exception of high compressive residual stresses and stress gradients immediately adjacent to the hole boundaries. Appropriate use of the residual stress information permits prediction of tube lifetimes for cracks emanating from the bore and from the hole. For the geometry and loading under consideration, the more critical location is predicted to be the hole boundary, the lifetime for failures originating from this point being some 60 percent of the lifetime for cracks originating at the bore.
An Investigation on the Properties of Underwater Shock Waves Generated in Underwater Explosions of High Explosives
Authors: Itoh S. , Liu Z. , Nadamitsu Y.
Published: February 2008

A cylinder expansion test for high explosives was carried out to determine JWL parameters. Using the JWL parameters, we carried out numerical simulations of the underwater shock waves generated by the underwater explosion of the high explosives. Our results showed that the behavior of the underwater shock waves at the vicinity of the explosives differs greatly from that far from the explosives. Especially, the strength of the underwater shock wave nearby the explosive rapidly decreases due to the effect of the expansion of the gas products.
Round Robin Calculations of Collapse Loads—A Torispherical Pressure Vessel Head With a Conical Transition
Authors: Yamamoto Y. , Asada S. , Okamoto A.
Published: February 2008

Round robin calculations of collapse loads for a pressure vessel were made by 16 teams in Japan. The model is composed of a cylinder and a torispherical head with a conical transition. The structure is an example in which the stress classifications specified in the ASME Code are not strictly applicable. The calculations were performed to clarify the issue of the evaluation procedure using the limit analysis method specified in the ASME Code, Sect. III, and to check the sensitivity of calculation models and programs. It is found that the stress in the knuckle region has certain characteristics of secondary stress, yet still dominates the collapse of the vessel. Using the limit analysis to prove the validity of stress classifications is recommended. The sensitivity of the calculation methods is not so significant. Therefore, it is concluded that the limit analysis can be used as a standard procedure in regulations.
Free Vibrations of Transversely Isotropic Cylinders and Cylindrical Shells
Authors: Chen W. Q. , Ying J. , Yang Q. D.
Published: February 2008

Three displacement functions are introduced to decompose three displacement components so that the three-dimensional equations of motion of a transversely isotropic body are uncoupled. Expanding these functions in terms of orthogonal series, the equations of free vibration problem of a transversely isotropic cylindrical shell with ends simply supported are further simplified to be readily dealt with. As contrast to previous works, modified Bessel function solution with complex arguments is directly adopted for the case of complex eigenvalues. Moreover, for solid cylinders, (modified) Bessel functions of the first kind, even with pure imaginary arguments, are used because of their peculiar properties. Two numerical examples are given to check the correctness of the present method by comparing the results with those of others. Because no assumption is introduced in the paper, the method developed is completely three-dimensionally exact.
Analysis and Optimization of Bellows With General Shape
Authors: Koh B. K. , Park G. J.
Published: February 2008

A bellows is a component in piping systems which absorbs mechanical deformation with flexibility. Its geometry is an axially symmetric shell which consists of two toroidal shells and one annular plate or conical shell. In order to analyze the bellows, this study presents the finite element analysis using a conical frustum shell element. A finite element analysis program is developed to analyze various bellows. The formula for calculating the natural frequency of bellows is made by the simple beam theory. The formula for fatigue life is also derived by experiments. A shape optimal design problem is formulated using multiple objective optimization. The multiple objective functions are transformed to a scalar function with weighting factors. The stiffness, strength, and specified stiffness are considered as the multiple objective function. The formulation has inequality constraints imposed on the natural frequencies, the fatigue limit, and the manufacturing conditions. Geometric parameters of bellows are the design variables. The recursive quadratic programming algorithm is utilized to solve the problem.
Cracks Emanating From an Erosion in a Pressurized Autofrettaged Thick-Walled Cylinder—Part II: Erosion Depth and Ellipticity Effects
Authors: Perl M. , Levy C. , Fang H.
Published: February 2008

In Part I of this paper, the effects of constant depth erosion on the mode I stress intensity factor (SIF) were determined for a crack emanating from the erosion deepest point in a pressurized, autofrettaged, thick-walled cylinder. The erosion geometries investigated included semi-circular erosions and several arc erosions of various radii of curvature. Due to the trends found in that portion of the study, erosion depth and ellipticity are believed to have equally important impact on the SIFs. The present paper delves further into these two parameters using the following configurations: (a) semi-circular erosions of relative depths of 1–10 percent of the cylinder’s wall thickness, W; and (b) semi-elliptical erosions with ellipticities of d/h = 0.3 – 2.0. Deep cracks are found to be practically unaffected by the erosion, similar to the results presented in Part I of the paper. The effective SIF for relatively short cracks is found to be dramatically enhanced by the stress concentration factor (SCF), which encompasses the depth of the erosion as well as its radius of curvature at the tip. As a result of the increased effective SIF, a significant decrease in the vessel’s fatigue life of up to an order of magnitude may occur.
Validation of PSAs for Use in Risk-Monitoring Applications
Authors: Fleming K. N.
Published: February 2008

The purpose of this paper is to examine the use of probabilistic safety assessment (PSA) tools for evaluating the risk significance of changing plant configurations. The focus of this examination is the ability of current PSA technology to evaluate time-dependent variations in risk quantities. Recent results from the South Texas Project (STP) PSA are used to quantify the magnitude of changes in initiating event frequencies. Issues associated with interpreting the results of risk monitors are discussed.
Strain-Rate-Dependent Constitutive Equations for Concrete
Authors: Tedesco J. W. , Ross C. A.
Published: February 2008

This paper summarizes the results of a comprehensive experimental study to quantify the effects of strain rate on concrete compressive and tensile strengths. Direct compression and splitting tensile tests were conducted at quasi-static rates (between 10−7/s and 10−5/s) in a standard MTS machine to establish the “static” properties. These same tests were conducted at high strain rates (between 10−1/s and 103/s) on a split-Hopkinson pressure bar (SHPB) to determine the dynamic material properties. A statistical analysis was performed on the data and strain-rate-dependent constitutive equations, both for compression and tension, were developed. These constitutive equations were subsequently employed to modify an existing quasi-static, nonlinear concrete material model.
Equivalence for Two Interacting Parallel Cracks
Authors: Kuang J. H. , Chen C. K.
Published: February 2008

Crack failure prediction is a prerequisite to assess the safety margin for pressure vessels with interacting parallel cracks. Therefore, an alternating iteration method with approximated image traction is employed in this study to assess the stress intensity factors of two stacked parallel cracks. The predicted crack intensity factors for these parallel cracks correlate well with the recent available solutions in literature. Maximum-energy-release-rate criterion is also utilized for converting problems of multiple cracks into a single crack in mode I. Results demonstrate that a shorter secondary parallel crack may enhance the equivalent crack primarily in the regions 0 < h/2a1 ≤ 0.8 and −1 ≤ t/a1 ≤ 1. The predicted results can be used to evaluate the conformability of simple proximity rules suggested by ASME Boiler & Pressure Vessel Code (ASME B&PV Code).
The Production of Liquid Fuel by Fast Pyrolysis of Biomass
Authors: Czernik S. , Scahill J. , Diebold J.
Published: February 2008

The NREL Fast Ablative Pyrolysis Technology was employed to generate oils from various biomass feedstocks. The oil yield from wood (64 percent) was higher than from herbaceous species (51 percent). Biomass oils have potential to be used as fuel though their properties are different from those of petroleum derived oils. They are multicomponent mixtures containing various groups of organic compounds such as sugars, aldehydes, acids, and phenolics. The density of the oils is about 1.2 g/ml and the pH is in the range 2.5–3.7. The viscosity of 20–80 cP (at 45°C) corresponds to that of No. 6 fuel oil. The high heating value for the biomass oils is in the range of 22.5–24.4 MJ/kg on a water-free basis. Considering the highest oil yields, it corresponds to approximately 65 percent of the wood heating value transferred to the oil.
Performance Optimization of Rotary Dehumidifiers
Authors: Zheng W. , Worek W. M. , Novosel D.
Published: February 2008

A rotary dehumidifier consists of a rotating porous matrix made of a desiccant with mechanically supporting materials. The dehumidification performance of a rotary dehumidifier wheel depends on its rotational speed, the sorption properties of the desiccant, the heat and mass transfer characteristics of the matrix, and the size of the dehumidifier. The effect of the rotational speed on the dehumidification performance of a rotary dehumidifier has been investigated by Zheng, Worek, and Novosel (1993). This paper extends that previous work and investigates the effects of desiccant sorption properties, the heat and mass transfer characteristics, and the size of the rotary dehumidifier on the dehumidification performance. The results show that the using desiccant materials in a rotary dehumidifier with different adsorption characteristics results in a wide variation in dehumidification performance. However, the maximum performance of a rotary dehumidifier occurs for a desiccant material having an isotherm shape that can be characterized to have a separation factor of 0.07. Also, as the desiccant moisture uptake increases, the dehumidifier performance also increases. However, the performance improvement for a desiccant matrix having a maximum moisture uptake of larger than 0.25 by weight is not significant. The heat and mass transfer properties and the size of a rotary dehumidifier are characterized by the number of transfer units NTU. Generally, the larger the NTU, the better dehumidification performance. However, similar to the maximum moisture uptake, when the NTU is larger than 12, the performance will not improve significantly. Also, the dehumidifier with the most favorable adsorption characteristic has a slowest rotational speed, which results in a lower power requirements to rotate the desiccant wheel and smaller carry-over losses.
An Off-Axis Cassegrain Optimal Design for Short Focal Length Parabolic Solar Concentrators
Authors: Roman R. Jose , Peterson J. E. , Goswami D. Y.
Published: February 2008

The present work addresses an off-axis Cassegrain optical concentration system. The specific primary collector analyzed, a short focal length parabolic concentrator, is at the University of Florida’s Energy Park. A secondary hyperbolic reflective element was designed to redirect the solar radiation from the primary focal plane to an off-axis target on the polar axis of the primary concentrator. This ground level target will be required for planned experimental work. The analysis was performed using a numerical ray tracing procedure that incorporates both random and systematic errors due to slope and surface irregularities. The optimization process varied secondary element size, curvature, and offset angle, and yielded information required for optimum design. As a single secondary element was found impractical, three elements were designed for use at various times of the year. The numerical analysis predicts that typically 70 to 75 percent of the solar flux incident on the primary concentrator aperture was focused within a 0.5-meter radius. During the design, it was found that this type of compact concentration system is a practical alternative. The optical system is also shown to have advantages that are generally applicable for problems involving short focal length primary concentrators, or when the solar apparatus is to be placed outside the primary collector aperture.
A Procedure for Testing the Ability of Whole Building Energy Simulation Programs to Thermally Model the Building Fabric
Authors: Judkoff R. D. , Neymark J. S.
Published: February 2008

A procedure was developed for systematically testing whole building energy simulation models and diagnosing the sources of predictive disagreement. Field trials of the method were conducted with a number of detailed state-of-the-art programs by researchers from nations participating in International Energy Agency (IEA) Task 12 and Annex 21. The technique consists of a series of carefully specified test case buildings that progress systematically from extremely simple to relatively realistic. Output values for the cases, such as annual loads, annual maximum and minimum temperatures, peak loads, and some hourly data are compared, and used in conjunction with diagnostic logic to determine the algorithms responsible for prediction differences. The more realistic cases, while geometrically simple, test the ability of the programs to model such combined effects as thermal mass, direct solar gain windows, window shading devices, internally generated heat, infiltration, sunspaces, earth coupling, and deadband and setback thermostat control. The more simplified cases facilitate diagnosis by allowing excitation of particular heat transfer mechanisms. The procedure was very effective at revealing bugs, faulty algorithms, and input errors in a group of building energy simulation programs that may be considered among the world’s best. The output data from the simulation programs can be used as reference ranges for comparing and diagnosing other detailed or simplified design tools.
Building Energy Use Prediction and System Identification Using Recurrent Neural Networks
Authors: Kreider J. F. , Claridge D. E. , Curtiss P. , Dodier R. , Haberl J. S. , Krarti M.
Published: February 2008

Following several successful applications of feedforward neural networks (NNs) to the building energy prediction problem (Wang and Kreider, 1992; JCEM, 1992, 1993; Curtiss et al., 1993, 1994; Anstett and Kreider, 1993; Kreider and Haberl, 1994) a more difficult problem has been addressed recently: namely, the prediction of building energy consumption well into the future without knowledge of immediately past energy consumption. This paper will report results on a recent study of six months of hourly data recorded at the Zachry Engineering Center (ZEC) in College Station, TX. Also reported are results on finding the R and C values for buildings from networks trained on building data.
A Two-Dimensional Methodology to Predict Vertical Axis Wind Turbine Performance
Authors: Fortunato B. , Dadone A. , Trifoni V.
Published: February 2008

An accurate two-dimensional methodology, the COIN Lambda Fast Solver, for the computation of the flow field about a vertical axis wind turbine is presented. Such a technique determines the smooth flow field by integrating the compatibility conditions along the bicharacteristic lines. The time-averaged wind turbine effects are introduced by means of an actuator porous cylinder having the same radius of the wind turbine. A time-averaged flow field is determined. The computed vertical axis wind turbine performances are compared with other numerical results. A qualitative comparison with experimental data is also shown. Such comparisons prove the merits of the proposed methodology.
Aerodynamic Damping of Blade Flap Motions at High Angles of Attack
Authors: Hansen A. C.
Published: February 2008

The YawDyn computer code is used to calculate the aerodynamic damping for a typical teetering rotor configuration. The code has been modified to calculate the net work done by aerodynamic forces in one complete rotor revolution. All cases were run for a teetering rotor similar to the ESI-80 with a specified teeter angle motion in order to isolate the aerodynamic effects from the inertial and gravitational loads. Effects of nonlinear static stall, dynamic stall, dynamic inflow, and delayed static stall due to rotation are analyzed separately and in combinations to explain the stability of flap motions in high winds. Contributions of the various steady and unsteady aerodynamic effects are presented for two airfoils: the LS(1) and the NREL Thin Airfoil Family (S805A, S806, S807). Teeter stability is compared for a blade with 10 deg of linear twist and a blade with optimum aerodynamic twist.
Distillation of Ethanol in a Solar Still: Studies on Heat and Mass Transfer
Authors: Shawaqfeh A. T. , Farid M. M.
Published: February 2008

A single-basin solar still may be used for primary concentration of dilute ethanol produced from fermentation. In order to describe the simultaneous heat and mass transfer in the still, different models have been proposed and tested against some experimental measurements on a still having a 1 m × 1 m basin area. Measurements were based on steady-state operation using electrical heating and unsteady-state operation using solar energy. The proposed models were found to have similar trends even though their derivations were based on different approaches. The models were found to overpredict the mass fluxes of ethanol (Me) and water (Mw) at high basin temperature and ethanol concentration, with different degrees.
An Analytical Solution to Transient Heat Conduction in a Composite Region With a Cylindrical Heat Source
Authors: Gu Yian , O’Neal D. L.
Published: February 2008

An approximate analytical solution to the transient heat-conduction problem in a large composite region with an internal cylindrical source is presented. The generalized orthogonal expansion technique is utilized in deriving the solution. Such problems are encountered in the design or simulation of the ground-coupled heat exchangers used in ground-coupled heat pumps. Solutions are presented for the nondimensional temperature as a function of the ratios of the thermal conductivities and thermal diffusivities of the two materials in the layers. To verify the correctness of the solution, comparisons are made between the two-layer composite solution and the classical homogeneous cylindrical source solution and a finite difference solution.
Flux Mapping the 400 m2 “Big Dish” at the Australian National University
Authors: Johnston G.
Published: February 2008

Videographic flux mapping has been used to characterise the focal flux distribution of the 400 m2 solar concentrator located at the Australian National University. Peak fluxes in the focal region of 1.13 MW m−2 have been recorded, which corresponds to a concentration of 1790 suns normalized to 1000 W m−2 insolation and 100 percent mirror reflectivity. Comparisons with ray trace predicted fluxes incorporating surface normal errors indicates that the dish surface has a mean surface error standard deviation of 6 milliradian.
Power Augmentation of a Horizontal Axis Wind Turbine Using a Mie Type Tip Vane: Velocity Distribution Around the Tip of a HAWT Blade With and Without a Mie Type Tip Vane
Authors: Shimizu Y. , Imamura H. , Matsumura S. , Maeda T. , van Bussel G. J. W.
Published: February 2008

Power augmentation and velocity measurements in the wake of a HAWT blade with Mie type tip vane (a tip device on the main blade) are presented. The maximum Cp with a Mie type tip vane is found to be 15 percent larger than that without the Mie type tip vane. Power augmentation caused by the Mie type tip vane is mainly due to the reduction of tip vortex and the diffusing effect by the Mie type tip vane. The effects of a Mie type tip vane are quantitatively verified by the velocity distributions around the tip of the main blade. The velocity distribution was measured by three-dimensional hot wire probes, which measured the axial, radial, and tangential velocity components. The circulation distributions along the main blade with a Mie type tip vane and without a Mie type tip vane were obtained from the measured velocity distributions. A strong reduction of bound vorticity is found for the main blade tip without the Mie type tip vane, whereas the bound vorticity persists on the main blade tip with the Mie type tip vane.
Navier-Stokes Computations of the NREL Airfoil Using a κ — ω Turbulent Model at High Angles of Attack
Authors: Yang S. L. , Chang Y. L. , Arici O.
Published: February 2008

This paper presents a two-dimensional numerical simulation of the turbulent flow fields for the NREL (National Renewable Energy Laboratory) S809 airfoil. The flow is modeled as steady, viscous, turbulent, and incompressible. The pseudo-compressible formulation is used for the time-averaged Navier-Stokes equations so that a time marching scheme developed for the compressible flow can be applied directly. The turbulent flow is simulated using Wilcox’s modified κ — ω model to account for the low Reynolds number effects near a solid wall and the model’s sensitivity to the freestream conditions. The governing equations are solved by an implicit approximate-factorization scheme. To correctly model the convection terms in the mean-flow and turbulence model equations, the symmetric TVD (Total Variational Diminishing) scheme is incorporated. The methodology developed is then applied to analyze the NREL S809 airfoil at various angles of attack (α) from 1 to 45 degrees. The accuracy of the numerical results is compared with the available Delft wind tunnel test data. For comparison, two Eppler code results at low angles of attack are also included. Depending on the value of α, preliminary results show excellent to fairly good agreement with the experimental data. Directions for future work are also discussed.
FT-IR Measurements of Emissivity and Temperature During High Flux Solar Processing
Authors: Markham J. R. , Smith W. W. , Haigis J. R. , Carangelo M. D. , Cosgrove J. E. , Kinsella K. , Solomon P. R. , Best P. E. , Lewandowski A. , Bingham C. E. , Pitts J. R.
Published: February 2008

The experimental capability to generate and utilize concentrated solar flux has been demonstrated at a number of facilities in the United States. To advance this research area, the National Renewable Energy Laboratory (NREL) has designed and constructed a versatile High Flux Solar Furnace (HFSF). Research is ongoing in areas of material processing, high temperature and UV enhanced detoxification, chemical synthesis, high flux optics, solar pumped lasers, and high heating rate processes. Surface modifications via concentrated solar flux, however, are currently performed without the means to accurately monitor the temperature of the surface of interest. Thermoelectric and pyrometric devices are not accurate due to limitations in surface contact and knowledge of surface emissivity, respectively, as well as interference contributed by the solar flux. In this article, we present a noncontact optical technique that simultaneously measures the directional spectral emissivity, and temperature of the surface during solar processing. A Fourier Transform Infrared (FT-IR) spectrometer is coupled to a processing chamber at NREL’s HFSF with a fiber-optic radiation transfer assembly. The system measures directional emission and hemispherical-directional reflectance in a spectral region that lacks contribution from solar flux. From these radiative property measurements during solar processing, the spectral emittance and temperature at the measurement point can be obtained. The methodology, validation measurements, and in-situ measurements during solar processing of materials are presented. Knowledge of surface temperature during solar processing is an important parameter for process control. Based on validation measurements for spectral emittance, the temperature error associated with the novel instrument is less than ±5 percent for surfaces of mid-range emittance. The error decreases for surfaces of higher emittance. This is far better than optical methods which are “lost” in terms of knowing the appropriate emittance for conversion of measured radiant intensity to temperature.
Effects of a Nonabsorbable Gas on Interfacial Heat and Mass Transfer for the Entrance Region of a Falling Film Absorber
Authors: Ameel T. A. , Habib H. M. , Wood B. D.
Published: February 2008

An analytical solution is presented for the effect of air (nonabsorbable gas) on the heat and mass transfer rates during the absorption of water vapor (absorbate) by a falling laminar film of aqueous lithium bromide (absorbent), an important process in a proposed open-cycle solar absorption cooling system. The analysis was restricted to the entrance region where an analytical solution is possible. The model consists of a falling film of aqueous lithium bromide flowing down a vertical wall which is kept at uniform temperature. The liquid film is in contact with a gas consisting of a mixture of water vapor and air. The gas phase is moving under the influence of the drag from the falling liquid film. The governing equations are written with a set of interfacial and boundary conditions and solved analytically for the two phases. Heat and mass transfer results are presented for a range of uniform inlet air concentrations. It was found that the concentration of the nonabsorbable gas increases sharply at the liquid gas interface. The absorption of the absorbate in the entrance region showed a continuous reduction with an increase in the amount of air.
Load Models for Fatigue Reliability From Limited Data
Authors: Winterstein S. R. , Lange C. H.
Published: February 2008

Probability distributions of wind turbine loads are estimated from limited data. The impact of different models on fatigue damage is shown. Common one-parameter probability models, such as the Rayleigh and exponential, are found to give significantly different estimates of load distributions and damage. Greatest differences occur in materials with relatively high values of the S–N exponent b, such as composites. In such cases more accurate damage estimates are found by matching at least two moments of the load data (Weibull model), or still higher moments as well. For this purpose, a new, four-moment “generalized Weibull” model is introduced. For edgewise loads it appears a notable improvement over the basic Weibull model, while it supports the Weibull model in the flapwise case. Uncertainty in damage estimates is also quantified, along with the implied data needs.
Design and Measured Performance of a Solar Chimney for Natural Circulation Solar Energy Dryers
Authors: Ekechukwu O. V. , Norton B.
Published: February 2008

An experimental solar chimney consisted of a cylindrical polyethylene-clad vertical chamber supported by steel framework and draped internally with a selectively absorbing surface. The performance of the chimney which was monitored extensively is reported. Issues related to the design and construction of solar chimneys for natural circulation solar energy dryers are discussed.
Theoretical Performance of a Solar Pond With Enhanced Ground Energy Storage
Authors: Prasad R. , Rao D. P.
Published: February 2008

A method was proposed earlier by the authors for the enhancement of energy storage in the ground beneath solar ponds employing the trapezoidal-shaped trenches at the bottom of the pond. The theoretical performance of the solar pond with trapezoidal trenches is presented for constant and variable energy extraction patterns. The results indicate that the trenches could be effective in reducing the thickness of lower convective layer and hence the salt requirement of the pond. However, the effectiveness of the trenches seems to be dependent on the energy extraction pattern. For the constant extraction pattern of 63.9 W m−2, it is found that 36.5 percent reduction in the salt requirement can be achieved with 3-m deep trenches compared to the flat-bottom pond. For the variable extraction pattern, the reduction was only 21.5 percent.
Thermodynamic Optimization of Solar-Driven Refrigerators
Authors: Vargas J. V. C. , Sokolov M. , Bejan A.
Published: February 2008

This paper describes the thermodynamic optimization of a class of refrigerators without work input, which are driven by heat transfer from a solar collector. The model consists of a finite-size solar collector with heat loss to the ambient, and a refrigerator with three finite-size heat exchangers, namely, the evaporator between refrigeration load and refrigerant, the condenser between the refrigerant and the ambient, and the heat exchanger between the solar collector and the refrigerant. The total thermal conductance of the three heat exchangers is fixed. The solar collector heat loss to the ambient is proportional to the collector-ambient temperature difference. The first part of the paper reports the operating conditions for maximum refrigeration effect, specifically, the optimal collector temperature, and the optimal way of allocating the thermal conductance inventory to the three heat exchangers. For example, the optimal condenser conductance is equal to half of the total thermal conductance, and is independent of other operating parameters. The second part of the paper examines the changes in the optimal design when the price of the refrigeration load (pL) is different (higher) than the price of the heat input provided by the collector (pH). The optimal collector temperature and the optimal three-way allocation of the thermal conductance inventory are reported as functions of the price ratio pH/pL.
Thermodynamic Design of a Phase Change Thermal Storage Module
Authors: Conti M. , Bellecci C. , Charach Ch.
Published: February 2008

This paper analyzes the irreversibilities due to the heat transfer processes in a latent heat thermal storage system. The Thermal Storage Module (TSM) consists of a cylindrical shell that surrounds an internal coaxial tube. The shell side is filled by a Phase Change Material (PCM); a fluid flows through the inner tube and exchanges heat along the way. The most fundamental assumption underlying this study is that the exergy of the hot fluid stream in the active phase is discharged into the environment and completely destroyed, unless it is partially intercepted by the storage system. A numerical study is conducted to identify and to minimize the thermodynamic losses of the storage and removal processes. The dependence of the second-law efficiency of the system on various design parameters is investigated and discussed.
A Noncalorimetric Method for Heat-Transfer Coefficient Measurement of Building Thermal Envelopes
Authors: Liu Mingsheng , Claridge D. E.
Published: February 2008

A noncalorimetric method for measuring the heat-transfer coefficient (UA) of building thermal envelopes is proposed and applied in an indoor test cell. The UA value measured by this method agrees closely with that measured by a calorimetric method. This method creates a Single input and a Single output data Pair (SSP) from the measured data sets by using digital filters. The filter output and physical criteria are used to determine the correct transfer function, which yields the measured UA value. This method seems to have the following advantages over calorimetric methods: it uses shorter measurement times, uses simpler test equipment, and has minimum thermal intrusion on normal operating conditions.
Developments to the TRNSYS Simulation Program
Authors: Fiksel A. , Thornton J. W. , Klein S. A. , Beckman W. A.
Published: February 2008

The TRNSYS simulation program is a sequential-modular transient simulation program which is widely used for both solar and nonsolar simulation studies despite its near 20-year-old origins. There have been many revisions to TRNSYS between its original release and the current version 13.1 but they have maintained the same sequential computational scheme for solving simultaneous algebraic and differential equations. TRNSYS 14 has recently been developed which implements a more robust method for solving simultaneous sets of nonlinear equations. The new computational scheme utilizes equation blocking to improve convergence properties and it handles discrete control decisions in a manner which promotes convergence in the iterative calculations. The new computational scheme allows TRNSYS 14 to solve problems which were either difficult or impossible to solve in previous versions as well as backwards problems, for which the output of a component is specified and the input must be determined. The computation scheme incorporated into TRNSYS 14 is described in this paper and its capabilities are illustrated with several examples.
High-Capacity Factor Wind Energy Systems
Authors: Cavallo Alfred J.
Published: February 2008

Wind-generated electricity can be fundamentally transformed from an intermittent resource to a baseload power supply. For the case of long distance transmission of wind electricity, this change can be achieved at a negligible increase or even a decrease in per unit cost of electricity. The economic and technical feasibility of this process can be illustrated by studying the example of a wind farm located in central Kansas and a 2000 km, 2000 megawatt transmission line to southern California. Such a system can have capacity factor of 60 percent, with no economic penalty and without storage. With compressed air energy storage (CAES) (and with a negligible economic penalty), capacity factors of 70–95 percent can be achieved. This strategy has important implications for the development of wind energy throughout the world since good wind resources are usually located far from major demand centers.
Thermal Performance Analysis of a Partly Closed-Open Solar Regenerator
Authors: Gandhidasan P. , Al-Farayedhi A. A.
Published: February 2008

This paper presents a modified open regeneration system suitable for humid climates. The upper part of the open regenerator is covered with a single glazing where the desiccant can be heated up without evaporation of water and the evaporation starts at the beginning of the open surface. For this type of regenerator, performance analysis has been made to predict the mass of water evaporated from the weak liquid desiccant to the atmosphere. The regeneration efficiency is obtained for various ratios of glaze surface area to the open surface area for different operating parameters.
Numerical Study of Melting of Large-Diameter Crystals Using an Orbital Solar Concentrator
Authors: Lan X. K. , Khodadadi J. M. , Jones P. D. , Wang L.
Published: February 2008

The melting of large-diameter crystals using an orbital solar concentrator is studied numerically. In the proposed configuration, a parabolic dish imaging concentrator is used to focus the sun’s radiation onto an ampoule which holds the solid charge material to be processed. The charge will start melting in the vicinity of the focal height, after which it is translated in order for the melt to resolidify as a single crystal. A ray-trace method has been developed to determine the incident concentrated solar heat flux on the ampoule’s surface for both perfectly aligned and misaligned configurations. For the perfectly aligned charge, a transient two-dimensional conduction problem with phase change is formulated, whereas once the perfect alignment of the charge’s symmetry axis with the sun’s incoming ray is perturbed, the problem becomes three-dimensional due to the complex surface heat flux boundary condition. The commercial code FIDAP is used to solve the governing transport equation. By ignoring the participation of the ampoule in the heat transfer process, preliminary results highlighting the feasibility of growing GaAs, Ge, and Si crystals with diameters of the order of 20 cm using the orbital solar concentrator concept are presented. The transient temperature fields within various charge materials during the heat-up process are quantified. The resulting melting pattern within the charge due to the uncolumnated beam is observed to be uniform along the charge when compared to the idealized limiting case of columnated beams. Finally, the effect of the misalignment angle on the melting process is quantified.
A Triple Hot-Wire System for Indoor Air Flow Measurements
Authors: Papadopoulos K. H. , Soilemes A. T. , Helmis C. G. , Asimakopoulos D. N. , Santamouris M. , Argiriou A. , Dascalaki E.
Published: February 2008

The application of a home made, triple hot-wire system in indoor air flow measurements is presented. Both the anemometer and sensor have been developed at Athens University with the aim to provide a reliable, research tool of reasonable cost, simple construction, and satisfactory performance. All three velocity components above a threshold of 10 cm s−1 can be measured. The system is also equipped with two thermometers for measuring the mean and fluctuating air temperature and for providing a means of temperature compensation of the hot wires’ signal. After evaluation of the system in the laboratory, it was used in the measurement of the velocity profile of flows driven by the temperature difference between two internal zones. The implied accuracy of the method allows for its integration with measurements of air volume exchange rates between internal zones, as estimated by tracer gas techniques.