bluuebunny/crossref_metadata_2025 huggingface dataset:
Notch and Temperature Effects on Crack Propagation in SS 304 Under LCF Conditions
Authors: Merah N. , Bui-Quoc T. , Bernard M.
Published: February 2008

Crack growth behavior at room temperature and at 600°C of SS 304 plates with a central circular hole is studied using linear elastic and elastic-plastic fracture mechanics concepts. Due to large local plastic zone at the hole edge, short fatigue crack propagation is strongly affected by closure phenomena; and the extension rate of a short crack could not be adequately expressed in terms of stress intensity factor ΔK. However, the parameter ΔK would be appropriate for investigating the behavior of long cracks. Crack acceleration due to temperature increase is discussed and a strain-based normalization factor for ΔK is suggested for long cracks. The J-integral obtained from a finite element analysis is successful in establishing the propagation rate of both short and long cracks; simple power relations exist between da/dN and cyclic J-integral (ΔJf) at room temperature and at 600°C. With the modified J-integral, using the actual flow strain, the temperature effect could be incorporated in the correlation between da/dN and ΔJf.
Fatigue Strength Reduction Factors for Welds Based on Nondestructive Examination
Authors: Hechmer J. L. , Kuhn E. J.
Published: February 2008

Based on the author’s hypothesis that nondestructive examination (NDE) has a major role in predicting the fatigue life of pressure vessels, a project was initiated to develop a defined relationship between NDE and fatigue strength reduction factors (FSRF). Even though a relationship should apply to both base metal and weld metal, the project was limited to weld metal because NDE for base metal is reasonably well established, whereas NDE for weld metal is more variable, depending on application. A matrix of FSRF was developed based on weld type (full penetration, partial penetration, and fillet weld) versus the NDE that is applied. The NDE methods that are included are radiographic testing (RT), ultrasonic testing (UT), magnetic particle testing (MT), dye penetrant testing (PT), and visual testing (VT). The first two methods (RT and UT) are volumetric examinations, and the remaining three are surface examinations. Seven combinations of volumetric and surface examinations were defined; thus, seven levels of FSRF are defined. Following the initial development of the project, a PVRC (Pressure Vessel Research Council) grant was obtained for the purpose of having a broad review. The report (Hechmer, 1998) has been accepted by PVRC. This paper presents the final matrix, the basis for the FSRF, and key definitions for accurate application of the FSRF matrix. A substantial amount of additional information is presented in the PVRC report (Hechmer, 1998).
A High-Order Theory for Dynamic Buckling and Postbuckling Analysis of Laminated Cylindrical Shells
Authors: Eslami M. R. , Shariyat M.
Published: February 2008

Using a high-order Reisner-Mindlin-type shear deformation theory in a power series form, the general large deformation form of the Green strain tensor for imperfect cylindrical shells is introduced. Then, based on Hamilton’s principle, the equations of motion are derived for laminated composite shells. Related constitutive equations are also proposed. In this formulation, temperature dependency of material properties is considered, too. No simplifications are made in solving the coupled nonlinear equations of motion. Finally, few examples of the well-known references are reconsidered for comparison purposes.
Analytical Solutions of Openings Formed by Intersection of a Cylindrical Shell and an Oblique Nozzle Under Internal Pressure
Authors: Cai H. , Sun B. , Koplik B. , Tavantzis J.
Published: February 2008

This paper presents the analytical solutions of local circumferential and longitudinal stresses due to internal pressure on a cylindrical pressure vessel at the juncture of an opening formed by a nozzle with various intersecting angles in the case of thin wall vessels. First, we present the exact mathematical expression for the shell-nozzle intersection curve in mid-surface, and then solve the equations for the desired stresses using Fourier series methods. The resulting stresses are then normalized into stress concentration factors by means of the circumferential pressure stress. The influence of thickness is considered for stresses that have linear distribution along the thickness from inside to outside because of the thin wall vessel. For the ratio of nozzle radius/shell radius β = 0.4 and the ratio of shell radius/shell thickness γ = 40, the numerical calculations were performed for the stress concentration factors in both circumferential and longitudinal directions along the symmetric axes, and then plotted and tabulated for the intersection angles of 90, 75, 60, 45, and 30 deg, respectively. Numerical stress results indicate that the stresses for 30 deg intersection have the largest value. When the intersection angle is 90 deg, the results are in good agreement with the existing literature.
Deformation of Metal Pipe due to Underwater Shock Wave
Authors: Itoh S. , Kira A. , Liu Z.-Y. , Nagano S.
Published: February 2008

The deformation process of the metal pipes, accelerated by underwater shock wave resulting from the underwater detonation of explosive inside the metal pipe, was investigated by means of both the optical observation experiment and the numerical calculation. The expanding deformation of metal pipes was experimentally viewed by both framing and streak photographic means. A computer code based on the arbitrary Lagrangian and Eulerian (ALE) method was used to perform the numerical simulation on this problem. It has confirmed that the deformations of the metal pipes obtained from the streak photographs agree quite well with those obtained by the numerical calculation. The experimental and numerical results both show that the expanding velocity along the radial direction in aluminum pipe is larger than that in copper pipe, under the same loading conditions; and also, the time needed to reach the maximum radial velocity is shorter in aluminum pipe than in copper pipe. The calculations clearly indicate that the metal pipes are able to acquire a maximum expanding velocity along the radial direction in a very short time after the beginning of the action of underwater shock wave, and also this maximum velocity value only decreases a little in the later time period.
Calculation of Stress Intensity Factors for Elliptical Cracks in Finite Bodies by Using the Boundary Weight Function Method
Authors: Ma C.-C. , Shen I-K.
Published: February 2008

In this study, mode I stress intensity factors for a three-dimensional finite cracked body with arbitrary shape and subjected to arbitrary loading is presented by using the boundary weight function method. The weight function is a universal function for a given cracked body and can be obtained from any arbitrary loading system. A numerical finite element method for the determination of weight function relevant to cracked bodies with finite dimensions is used. Explicit boundary weight functions are successfully demonstrated by using the least-squares fitting procedure for elliptical quarter-corner crack and embedded elliptical crack in parallelepipedic finite bodies. If the stress distribution of a cut-out parallelepipedic cracked body from any arbitrary shape of cracked body subjected to arbitrary loading is determined, the mode I stress intensity factors for the cracked body can be obtained from the predetermined boundary weight functions by a simple surface integration. Comparison of the calculated results with some available solutions in the published literature confirms the efficiency and accuracy of the proposed boundary weight function method.
Damage Tolerance of Large Shell Structures
Authors: Minnetyan L. , Chamis C. C.
Published: February 2008

Progressive damage and fracture of large shell structures is investigated. A computer model is used for the assessment of structural response, progressive fracture resistance, and defect/damage tolerance characteristics. Critical locations of a stiffened conical shell segment are identified. Defective and defect-free computer models are simulated to evaluate structural damage/defect tolerance. Safe pressurization levels are assessed for the retention of structural integrity at the presence of damage/defects. Damage initiation, growth, accumulation, and propagation to fracture are included in the simulations. Damage propagation and burst pressures for defective and defect-free shells are compared to evaluate damage tolerance. Design implications with regard to defect and damage tolerance of a large steel pressure vessel are examined.
An Efficient Asymptotic Approach for Assessing Fatigue Reliability
Authors: Tang J.
Published: February 2008

By applying the cumulative fatigue damage to the random process reliability problem, and the introduction of a proposed concept of unified equivalent stress mean level in fatigue life prediction, a technical reliability model for the random process problem under fatigue failure is proposed. The technical model emphasizes efficiency in the design choice and focuses on the accuracy of the results. Based on this model, an asymptotic method for fatigue reliability under random process loading is developed. The proposed method uses the recursive iteration algorithm to achieve results which include reliability and its corresponding mission life. The method reconciles the requirement of accuracy and efficiency for the random process reliability problems under fatigue failure. The accuracy and analytical and numerical efforts required are compared. Through numerical example, the advantage of the proposed method is demonstrated.
The Measurement of Fluidelastic Effects at Low Reduced Velocities Using Piezoelectric Actuators
Authors: Caillaud S. , de Langre E. , Piteau P.
Published: February 2008

Fluidelastic effects which are responsible for fluidelastic instabilities may be indirectly measured through the analysis of the vibrating motion of a system under flow. In this paper, piezoelectric actuators are used to increase the vibratory level when buffeting forces which excite tube vibration are low, and to improve the measurement of fluidelastic forces. The proposed method based on an added excitation allows the study of the added mass and provides a better accuracy on the measurement of the vibrating characteristics and, thereby, of the fluidelastic forces. This added excitation method is compared with a standard indirect approach on a tube underwater crossflow. The influence of the level of piezoelectric excitation forces is discussed, as well as the range of application of this technique.
On the Evaluation of Dynamic Stresses in Pipelines Using Limited Vibration Measurements and FEA in the Frequency Domain
Authors: Moussa W. A. , AbdelHamid A. N.
Published: February 2008

A practical technique is investigated for the determination of dynamic stresses in pipelines through the use of finite element method (FEM) and field measurement vibrations at selected points. Numerical simulation of a harmonically loaded pipeline structure is used to establish the validity of the technique in the frequency domain. The analysis is carried out for a fixed-hinged pipe model. The results show that lack of coincidence between the vibration measurement points (VMPs) and the exciting force, or the use of only translational vibration measurements (TVMs) produce an approximate stress picture. The extent of the “error” in these cases is found to depend on the density of the VMPs and the proximity between these points and the exciting force location. A safety-related risk assessment is applied to find the minimum distance between measuring points that is needed to meet design codes reliability specifications.
Prediction of Failure Behavior of a Welded Pressure Vessel Containing Flaws During a Hydrogen-Charged Burst Test
Authors: Bhuyan G. S. , Sperling E. J. , Shen G. , Yin H. , Rana M. D.
Published: February 2008

An industry-government collaborative program was carried out with an aim to promoting the acceptance of fracture mechanics-based fitness-for-service assessment methodology for a service-damaged pressure vessel. A collaborative round robin exercise was carried out to predict the fracture behavior of a vessel containing hydrogen damage, fabrication-related lack-of-fusion defects, an artificially induced fatigue crack, and a localized thinned area. The fracture assessment procedures used include the U.S. ASME Material Property Council’s PREFIS Program based on the British Standard (BS) Published Document (PD) 6493, ASME Section XI and The Central Electricity Generating Board (CEGB) R6 approach, The Welding Institute (TWI) CRACKWISE program (based on BS PD6493 Level 2 approach), a variant of the R6 approach, J-tearing instability approaches, various J-estimation schemes, LEFM approach, and simplified stress analysis. Assessments were compared with the results obtained from a hydrogen-charged burst test of the vessel. Predictions, based on the J-tearing approach, compared well with the actual burst test results. Actual burst pressure was about five times the operating pressure.
Fatigue Crack Growth Testing of Sub-Clad Defects
Authors: Jones D. P. , Leax T. R.
Published: February 2008

Fatigue crack growth tests were performed on four-point bend specimens with cracklike defects intentionally placed in A302B low-alloy pressure vessel steel clad with 308/309L weld-deposited stainless steel. The defects were placed in the base metal under the cladding by machining a cavity from the side opposite the cladding, electric-discharge machining a very sharp flaw, fatigue precracking the flaw, and then filling up the cavity by a weld repair process. The specimens were stress relieved before fatigue testing. The specimens were fatigue cycled at positive load ratios until the defects broke through to the surface. The specimens were then fractured at liquid nitrogen temperatures to reveal the fracture surfaces. Seven different sub-clad flaw specimens were tested in room temperature air and each test provides a record of cycles to defect breakthrough. Changes in defect size and shape as a function of applied load cycles were obtained by beach-marking the crack at various stages of the load history. The results provide a set of embedded defect data which can be used for qualifying fatigue crack growth analysis procedures such as those in Section XI of the ASME Boiler and Pressure Vessel Code. A comparison between calculated and measured values shows that the ASME B&PV Section XI fatigue crack growth procedures conservatively predict cycles to defect breakthrough for small sub-clad defects.
Numerical Analysis of Nonstationary Thermal Response Characteristics for a Fluid-Structure Interaction System
Authors: Muramatsu T.
Published: February 2008

Nonstationary thermal response analysis for a fundamental sodium experiment simulating thermal striping phenomena was carried out using a quasi-direct numerical thermohydraulics simulation code with a third-order upwind scheme for convection terms and a boundary element method code for thermal response evaluation of structures due to random sodium temperature fluctuations developed at Power Reactor and Nuclear Fuel Development Corporation (PNC). Discussions centered on an applicability of the numerical method for the damping effects of the temperature fluctuations in the course of heat transfer to the inside of structures from the fully turbulent region of sodium flows through the comparisons with the experiment. From these comparisons, it was confirmed that the numerical method has a sufficiently high potential in accuracy to predict the damping effects of the temperature fluctuations related to the thermal striping phenomena. Consequently, it is concluded that the numerical prediction by the method developed in this study can replace conventional experimental approaches using 1:1 or other scale model aiming at the simulation of the thermal striping phenomena in actual liquid metal fast breeder reactor (LMFBR) plants. Furthermore, economical improvements in the FBR plants can be carried out based on the discussions of optimization and rationalization of the structural design using the numerical methods.
Application of Equivalent Elastic Methods in Three-Dimensional Finite Element Structural Analysis
Authors: Jones D. P. , Gordon J. L. , Hutula D. N. , Holliday J. E. , Jandrasits W. G.
Published: February 2008

This paper describes use of equivalent solid (EQS) modeling to obtain efficient solutions to perforated material problems using three-dimensional finite element analysis (3-D-FEA) programs. It is shown that EQS modeling in 3-D-FEA requires an EQS constitutive relationship with a sufficient number of independent constants to allow the EQS material to respond according to the elastic symmetry of the penetration pattern. It is also shown that a 3-D-FEA submodel approach to calculate peak stresses and ligament stresses from EQS results is very accurate and preferred over more traditional stress multiplier approaches. The method is demonstrated on the problem of a transversely pressurized simply supported plate with a central divider lane separating two perforated regions with circular penetrations arranged in a square pattern. A 3-D-FEA solution for a model that incorporates each penetration explicitly is used for comparison with results from an EQS solution for the plate. Results for deflection and stresses from the EQS solution are within 3 percent of results from the explicit 3-D-FE model. A solution to the sample problem is also provided using the procedures in the ASME B&PV Code. The ASME B&PV Code formulas for plate deflection were shown to overestimate the stiffening effects of the divider lane and the outer stiffening ring.
Experimental Study of the Flow in the Suction Pipe of a Centrifugal Pump at Partial Flow Rates in Unsteady Conditions
Authors: Bolpaire S. , Barrand J. P.
Published: February 2008

The operational range and the performances of pumps are limited by the occurrence of backflow and prerotation in the suction pipe as the flow rate is reduced. This paper presents the study of static pressure measurements and visualizations in the suction pipe, near the inlet of a centrifugal pump, at partial flow rates, in steady conditions, and during a fast start-up of the pump. The tests were carried out in water on the DERAP© test loop of the ENSAM Lille laboratory. Standard methods allowed to determine the recirculation critical flow rate. A visualization method showed that the axial extent of the recirculation and the prerotation with the flow rate is considerably reduced during a fast start-up compared to steady conditions.
The Interaction of Two Parallel Semi-Elliptical Surface Cracks Under Tension and Bending
Authors: Moussa W. A. , Bell R. , Tan C. L.
Published: February 2008

Multiple cracks are often observed in engineering structures; and their interaction and coalescence may significantly affect their life. Knowledge of the behavior of interacting cracks is very limited. A major component of any linear fracture mechanics model for fatigue crack growth is the calculation of the crack-tip stress intensity factor, SIF. In this paper, a parametric study is presented for two parallel surface cracks in an infinite plate subjected to remote tension or to pure bending loads. The stress intensity factors for these cracks as a function of the crack-front position, depth, shape, and plate thickness are calculated using three-dimensional (3-D) finite element, (FE) analysis. The ratios of crack depth to plate thickness, a/t, and to crack length, a/c, range from 0.1 to 0.62 and 0.1 to 1.0, respectively. Where possible, a comparison of 3-D with 2-D results is also considered.
Simplified Analyses of a Fiber-Reinforced Plastic Joint for Filament-Wound Pipes
Authors: Estrada H. , Parsons I. D.
Published: February 2008

A simplified analysis procedure is described for a fiber-reinforced plastic (FRP) stubflanged joint which addresses some of the problems with current FRP joints. The joint consists of a tapered hub that is filament-wound with the pipe. A separate stub is used to connect the two halves of the joint. This system avoids material discontinuities at the flange-pipe intersection and pull-back of the flange. The joint is modeled following the Taylor Forge approach used in metallic joint analysis. The analytical model is verified using finite element analysis; the results are in excellent agreement.
Fatigue Behavior of Line Pipes Subjected to Severe Mechanical Damage
Authors: Hagiwara N. , Oguchi N.
Published: February 2008

Fatigue behavior of electrically resistance welded (ERW) line pipes with a gouge in a dent was experimentally investigated. After denting and machining a gouge, fluctuating internal pressure was applied to line pipes. The fatigue behavior differed above and below the threshold Q(Qth), as a function of defect size and fracture toughness. When Q < Qth, ductile crack growth was observed with a consequent decrease in fatigue life. On the contrary, fatigue crack growth was observed when Q ≧ Qth. Fatigue life was predictable with an experimentally based power law equation incorporating dent depth, gouge depth, and hoop stress amplitude when Q ≧ Qth.
Effect of Internal Pressure on Elastic-Plastic Behavior of Pipe Elbows Under In-Plane Bending Moments
Authors: Shalaby M. A. , Younan M. Y. A.
Published: February 2008

The purpose of this study is to investigate the effect of pressure on the strain and stress analysis of pipe elbows subjected to in-plane bending moments. A finite element model for the bend was constructed and loaded with a pressure of 1200 psi and end moments taking geometric and material nonlinearities into account using (ABAQUS) nonlinear finite element code. The pressure changes the effective stress distribution and location of the initial yielding from the inside surface of the elbow crown to the outside surface for the closing moment case and increases the moment of yielding. For the opening moment case, yielding starts at the inside surface of the elbow crown with and without pressure. The pressure changes the location of the maximum axial strain at instability for the closing and opening cases, and it also changes the ovality of the cross section in both cases.
Dynamic Behavior of a Clamped Plastic Beam With Cracks at Supporting Ends Under Impact
Authors: Chen F. L. , Yu T. X.
Published: February 2008

This paper examines a projectile impact on a rigid-plastic beam with cracks at the fully clamped ends. By assuming the cracked sections yield immediately after impact, a three-hinge/two-hinge mechanism for the response process is constructed so that a complete solution considering the interaction between bending moment M and axial force N is derived. The key of the formulation is to find a complementary equation concerning the axial force N. To predict accurately the stability of the initial cracks, the J-integral criterion is extended to involve the contribution of the axial force. All the governing equations are nondimensionalized and rearranged, ready for Runge-Kutta integration procedure. The numerical results demonstrate that the mass ratio and the axial force have significant influence on the final deformation, energy partition, and the value of J-integral near the crack tip. The J-integral is not very sensitive to the depth of the initial cracks, but the presence of initial cracks in a beam may alter the failure behavior of the beam after impact, that is, from a strength-type failure to a fracture-type failure.
Modeling of Deepwater-Type Rectangular Tuned Liquid Damper With Submerged Nets
Authors: Kaneko S. , Yoshida O.
Published: February 2008

An analytical model for describing the effectiveness of deepwater-type tuned liquid damper (TLD) with submerged nets for suppressing horizontal vibration of structures is proposed. TLD is a damping device for suppressing the vibration of long-period structures such as high-rise buildings, tall towers, the pylons of cable-stayed bridges, and so on. The damping force is created by the hydrodynamic force caused by the sloshing of water contained in rectangular tanks located on top of such structures. In this study, we proposed the dynamical model for analyzing deepwater-type TLD (DTLD) where the liquid depth is deep compared with the length of the rectangular tank. In particular, the effect of hydraulic resistance produced by submerged nets installed in the tank is examined intensively. In the analysis of DTLD, employing finite amplitude wave theory, we obtained the hydrodynamic force and the dissipation energy by using Galerkin method, taking the effect of submerged nets into account. The calculated results thus obtained are compared with experimental results, by which the validity of the modeling methodology is confirmed. Finally, the case in which DTLD with nets is installed on an actual structure is investigated both theoretically and experimentally and the performance of DTLD is illustrated.
Bauschinger Effect Design Procedures for Autofrettaged Tubes Including Material Removal and Sachs’ Method
Authors: Parker A. P. , Underwood J. H. , Kendall D. P.
Published: February 2008

Autofrettage is used to introduce advantageous residual stresses into pressure vessels and to enhance their fatigue lifetimes. The Bauschinger effect serves to reduce the yield strength in compression as a result of prior tensile plastic overload and can produce lower compressive residual hoop stresses near the bore than are predicted by “ideal” autofrettage solutions (elastic/perfectly plastic without Bauschinger effect). A complete analysis procedure is presented which encompasses representation of elastic-plastic uniaxial loading material behavior and of reverse-loading material behavior as a function of plastic strain during loading. Such data are then combined with some yield criterion to accurately predict elastic-plastic residual stress fields within an autofrettaged thick cylinder. Pressure for subsequent reyielding of the tube is calculated. The numerical procedure is further used to determine residual stress fields after removal of material from inside diameter (i.d.) and/or outside diameter (o.d.), including the effects of any further plasticity. A specific material removal sequence is recommended. It is shown that Sachs’ experimental method, which involves removing material from the i.d., may very significantly overestimate autofrettage residual stresses near the bore. Stress ranges and stress intensity factors for cracks within such stress fields are calculated together with the associated fatigue lifetimes as such cracks propagate under cyclic pressurization. The loss of fatigue lifetime resulting from the Bauschinger effect is shown to be extremely significant.
A Novel Nonconcentrating Reactor for Solar Water Detoxification
Authors: van Well M. , Dillert R. H. G. , Bahnemann D. W. , Benz V. W. , Mueller M. A.
Published: February 2008

The photocatalytic degradation of organic compounds using titanium dioxide is a promising method for the clean up of polluted water, especially if the sun is used as the light source. In this paper a novel double-skin sheet reactor made of Plexiglas®, able to use diffuse as well as direct sunlight, is introduced. To characterize this novel photochemical reactor for solar water detoxification, degradation experiments were performed using dichloroacetic acid as a model compound and varying the type of catalyst and its concentration. Moreover, the content of molecular oxygen of the suspension was varied systematically. Photonic efficiencies up to 13 percent were achieved in these experiments in very good agreement with those of corresponding experiments performed under idealized laboratory conditions. Photocatalytic detoxification experiments with ground water contaminated with nitro aromatic compounds from a World War II ammunition plant proved that this reactor can indeed be employed for the solar detoxification of realistic contaminated water.
Multiobjective Optimal Unit Sizing of a Grid-Connected Photovoltaic System in Consideration of Its Probabilistic Characteristics
Authors: Yokoyama Ryohei , Ito Koichi , Sakashita Mitsukuni , Matsumoto Yoshikazu , Yuasa Yoshiro
Published: February 2008

A probabilistic approach is presented to optimal unit sizing of a grid-connected photovoltaic system without storage batteries. In consideration of probabilistic characteristics of solar insolation and electricity demand, the surface area of photovoltaic array, capacity of receiving device, and electric contract demand are determined so as to minimize the expected values of annual total cost and annual energy consumption subject to the annual loss of power supply probability. This optimization problem is considered as a multiobjective one, and a discrete set of Pareto optimal solutions is derived numerically using the weighting method. A case study is carried out on an on-site system with the option of reverse power flow into the grid, using data on solar insolation obtained through real measurement. The trade-off relationship between the two objectives are clarified and optimal values of the above design items are determined in relation to the annual loss of power supply probability and the capital unit cost of photovoltaic array. Results by this probabilistic approach are compared with those by a deterministic approach.
Heat Pump Using a Solar Collector With Photovoltaic Modules on the Surface
Authors: Ito Sadasuke , Miura Nakatsu , Wang Jin Qi , Nishikawa Miwako
Published: February 2008

It is known that the higher the evaporation temperature, the higher the coefficient of performance of a heat pump for hot water supply. Flat-plate solar collectors which were insulated on the back and bonded with flexible polycrystalline silicon-type photovoltaic modules on the upper surfaces were used in a heat pump system as the evaporator in order to increase the coefficient of performance and to generate electric power. The total area of the collectors was 3.24 m2 and the photovoltaic modules covered 76 percent of the area. The characteristics of the photovoltaic array and the thermal performance of the heat pump were studied experimentally. The results indicated that a coefficient of performance (COP) of the heat pump as high as six could be obtained at 40°C of the water temperature at the inlet of the condenser in the daytime in winter. The peak electric power generated was 120 W. It was found that the photovoltaic modules on the collectors did not influence the performance of the heat pump appreciably. When there was little solar radiation, the COP of the heat pump became two which was very low. This defect was improved by using an evaporator, which had a high convective heat transfer coefficient, arranged in parallel with the fiat-plate collectors.
Performance Evaluations of LiCl and LiBr for Absorber Design Applications in the Open-Cycle Absorption Refrigeration System
Authors: Kim K. J. , Ameel T. A. , Wood B. D.
Published: February 2008

Both LiCl and LiBr solutions were considered for potential use in a solar-driven Open-Cycle Absorption Refrigeration (OCAR) system. A vertical falling film absorber was proposed and built to evaluate the performance of LiCl and LiBr as an absorbent. Absorption experiments were performed and the results are reported for typical operating conditions of nonabsorbable concentrations, solution concentration, solution temperature, cooling water temperature, absorber pressure, and solution flow rate, in terms of mass transfer rate. In general, LiBr outperformed LiCl in terms of effective absorption rate. Based upon experimental results, the required absorber area was estimated for both LiCl and LiBr. The small chemical potential of LiCl relative to LiBr leads to a larger absorber area. The cost for the required solution storage for three-ton cooling capacity of the present OCAR system was found to be high for both LiCl and LiBr. The pumping cost was estimated to be less than 0.1 kW for both.
Performance and Modeling of Thermosyphon Heat Exchangers for Solar Water Heaters
Authors: Dahl S. D. , Davidson J. H.
Published: February 2008

Determining the performance of indirect solar heating systems that use thermosyphon heat exchangers requires knowledge of how thermosyphon flow rate and heat exchanger performance vary with operating conditions. In this paper, measured performance of a two-pass, tube-in-shell, double-wall heat exchanger is discussed in terms of modeling issues. Thermosyphon heat exchangers may operate in the developing, mixed convection regime where natural convection effects can significantly influence overall heat transfer and friction coefficients. Existing models which assume the thermal and hydraulic behaviors of thermosyphon heat exchangers are only functions of the thermosyphon and collector flow rates may not be suitable for all heat exchanger types. For example, the overall heat-transfer coefficient-area product for the two-pass, tube-in-shell heat exchanger is best expressed as a function of Reynolds, Grashof, and Prandtl numbers on the thermosyphon side of the heat exchanger. It is proposed that annual simulations of solar water heaters with thermosyphon heat exchangers use this type of relationship to characterize heat transfer in the heat exchanger.
Study on a New Solid Absorption Refrigeration Pair: Active Carbon Fiber—Methanol
Authors: Wang R. Z. , Jia J. P. , Zhu Y. H. , Teng Y. , Wu J. Y. , Cheng J. , Wang Q. B.
Published: February 2008

Our experiments show that active carbon fiber (ACF) might be a good substitute for activated carbon (AC) as the refrigeration capacity Qf and adsorption time of ACF are three times more and 1/5 ∼ 1/10 of those of normal activated carbon (AC), respectively. The COP for ACF-methanol could be 10 percent ∼ 20 percent higher than that of AC-methanol. Thus ACF-methanol might be a good adsorption refrigeration pair for constructing adsorption refrigerators, especially those for household applications.
Analysis of Freezing in an Eccentric Annulus
Authors: Zhang Yuwen , Faghri A.
Published: February 2008

Freezing in an eccentric annulus is investigated numerically by using a temperature transforming model. Since the effect of the heat conduction along the circular direction on the growth of the freezing layer is very small, an analytical solution by employing integral approximate method is proposed. The freezing rate obtained by the analytical solution agreed very well with that of the numerical solution, although the analytical solution is much simpler than the numerical solution. The effects of the eccentric annulus geometric structure on the freezing process is also investigated.
Influence of Pitch, Twist, and Taper on a Blade’s Performance Loss due to Roughness
Authors: Tangler J. L.
Published: February 2008

The purpose of this study was to determine the influence of blade geometric parameters such as pitch, twist, and taper on a blade’s sensitivity to leading edge roughness. The approach began with an evaluation of available test data of performance degradation due to roughness effects for several rotors. In addition to airfoil geometry, this evaluation suggested that a rotor’s sensitivity to roughness was also influenced by the blade geometric parameters. Parametric studies were conducted using the PROP93 computer code with wind tunnel airfoil characteristics for smooth and rough surface conditions to quantify the performance loss due to roughness for tapered and twisted blades relative to a constant-chord nontwisted blade at several blade pitch angles. The results indicate that a constant-chord nontwisted blade pitched toward stall will have the greatest losses due to roughness. The use of twist, taper, and positive blade-pitch angles all help reduce the angle-of-attack distribution along the blade for a given wind speed and the associated performance degradation due to roughness.
Desirable Airfoil Characteristics for Large Variable-Speed Horizontal Axis Wind Turbines
Authors: Gigue`re P. , Selig M. S.
Published: February 2008

In an effort to define the desirable airfoil characteristics for large variable-speed wind turbines, a systematic study was performed using a series of airfoils designed to have similar aerodynamic properties, except for the amount of lift, which varied over a wide range. For several airfoil combinations, blade shapes were designed for a 750-kW wind turbine with a 48.8-m diameter rotor using the optimization code PROPGA together with PROPID, which is an inverse design method for horizontalaxis wind turbines. Roughness effects, including the consideration of dirty-blade performance in the blade-shape optimization process, were also considered and are discussed. The results and conclusions reveal practical design implications that should aid in the aerodynamic blade design of not only large but also other sizes of variable-speed wind turbines.
The Effects of Static and Dynamic Imbalance on a Horizontal Axis Wind Turbine
Authors: Borg J. P. , Kirchhoff R. H.
Published: February 2008

In this note the differences between static and dynamic balancing of a wind turbine rotor are addressed. The paper begins with a definition of each type of balancing. It is demonstrated that even if a horizontal axis wind turbine rotor is in static balance, the rotor can still be dynamically imbalanced. Dynamic imbalance can result in a yaw and/or teeter producing torque. A turbine rotor is only in a state of dynamic balance when the principle axes of inertia are aligned with the angular velocity vector. This criteria is illustrated with a point mass model.
Heat Transfer for Slab-on-Grade Floors With Prescribed Heat Flux
Authors: Choi S. , Krarti M.
Published: February 2008

The general solution of soil temperature distribution is developed for a slab-on-grade floor with a known heat flux distribution at the slab surface. The Interzone Temperature Profile Estimation (ITPE) technique is applied to determine the steady-state variation of temperature within the ground. A water table at constant temperature is assumed to exist at a given depth below the soil surface. As a first application of the general solution, the optimum thermal insulation distribution is obtained for a slabon-grade floor. A second application of the solution developed in this paper consists of a diagnostic method to determine the configuration and the R-value for the thermal insulation of the slabon-grade floor based on measured data for the heat flux at the slab surface. A parametric analysis is conducted to determine the effects of heat flux profiles and water table depths on the required insulation distribution at the slab surface.
Experimental Measurements of Heat Transfer Coefficient in a Partially/Fully Opened Tilted Cavity
Authors: Chakroun W. , Elsayed M. M. , Al-Fahed S. F.
Published: February 2008

An experimental investigation was carried out to determine the heat transfer coefficient from a rectangular tilted cavity to the ambient due to the buoyancy driven flow in the cavity. The cavity is partially or fully open from one side. All the walls of the cavity are adiabatic except the wall facing the cavity opening which is heated at a constant heat flux. Air was used as the cavity fluid and the experiments were carried out at a flux Grashof number of 5.5 × 108. The tilt angle of the cavity, measured from the vertical direction, was changed between −90 deg to +90 deg in 15 deg increments. Also, geometries of aspect ratio (height-to-width of cavity) of 1.0, 0.5, and 0.25 and of opening ratio (opening height to cavity height) of 1.0, 0.5, and 0.25 were considered in the study. The results are presented in terms of the average Nusselt number for different values of the above experimental parameters. Conclusions are derived for the effect of changing the tilt angle, the aspect ratio, or the opening ratio of the cavity on the average heat transfer coefficient between the cavity and the ambient air.
A 50-kW Module Power Station of Directly Solar-Pumped Iodine Laser
Authors: Choi S. H. , Lee J. H. , Meador W. E. , Conway E. J.
Published: February 2008

The conceptual design of a 50 kW directly solar-pumped iodine laser (DSPIL) module was developed for a space-based power station which transmits its coherent-beam power to users such as the moon, Martian rovers, or other satellites with large (>25 kW) electric power requirements. Integration of multiple modules would provide an amount of power that exceeds the power of a single module by combining and directing the coherent beams to the user’s receiver. The model developed for the DSPIL system conservatively predicts the laser output power (50 kW) that appears much less than the laser output (93 kW) obtained from the gain volume ratio extrapolation of experimental data. The difference in laser outputs may be attributed to reflector configurations adopted in both design and experiment. Even though the photon absorption by multiple reflections in experimental cavity setup was more efficient, the maximum secondary absorption amounts to be only 24.7 percent of the primary. However, the gain volume ratio shows 86 percent more power output than theoretical estimation that is roughly 60 percent more than the contribution by the secondary absorption. Such a difference indicates that the theoretical model adopted in the study underestimates the overall performance of the DSPIL. This fact may tolerate more flexible and radical selection of design parameters than used in this design study. The design achieves an overall specific power of approximately 5 W/kg and total mass of 10 metric tons.
Ammonia-Water Low-Temperature Thermal Storage System
Authors: Rizza J. J.
Published: February 2008

An analysis of a low-temperature thermal storage system using an ammonia-water solution both as a refrigerant and as a low-temperature thermal storage material is considered. The thermal storage is useable at a temperature of −27°C and higher. The proposed system is designed to shift electric demand from high to low-demand periods. The system utilizes a heat-operated absorption refrigeration system; however, the generator heat is supplied by a self-contained vapor compression heat pump. The heat pump is operated during the off-peak period to recover the low-temperature thermal storage by reprocessing the stored ammonia-water solution to a lower ammonia-water concentration. The ammonia vapor liberated from solution in the dephlegmator is used in the compressor to produce the generator heat. Three different configurations are considered, including a solar-assisted system. The results are compared to an eutectic salt storage system.
Parametric Study on the Operating Efficiencies of a Packed Bed for High-Temperature Sensible Heat Storage
Authors: Adebiyi G. A. , Nsofor E. C. , Steele W. G. , Jalalzadeh-Azar A. A.
Published: February 2008

A comprehensive computer model of a packed bed thermal energy storage system originally developed for storage media employing either sensible heat storage (SHS) materials or phase-change material (PCM), was validated for the sensible heat storage media using a rather extensive set of data obtained with a custom-made experimental facility for high-temperature energy storage. The model is for high-temperature storage and incorporates several features including (a) allowance for media property variations with temperature, (b) provisions for arbitrary initial conditions and time-dependent varying fluid inlet temperature to be set, (c) formulation for axial thermal dispersion effects in the bed, (d) modeling for intraparticle transient conduction in the storage medium, (e) provision for energy storage (or accumulation) in the fluid medium, (f) modeling for the transient conduction in the containment vessel wall, (g) energy recovery in two modes, one with flow direction parallel with that in the storage mode (cocurrent) and the other with flow in the opposite direction (countercurrent), and (h) computation of the first and second-law efficiencies. Parametric studies on the sensible heat storage system were carried out using the validated model to determine the effects of several of the design and operating parameters on the first and second-law efficiencies of the packed bed. Decisions on the thermodynamic optimum system design and operating parameters for the packed bed are based on the second-law evaluations made
A Transient Heat and Mass Transfer Model of Residential Attics Used to Simulate Radiant Barrier Retrofits, Part II: Validation and Simulations
Authors: Medina M. A. , O’Neal D. L. , Turner W. D.
Published: February 2008

A computer program was developed and used to implement the model described on Part I of this paper. The program used an iterative process to predict temperatures and heat fluxes using linear algebra principles. The results from the program were compared to experimental data collected during a three-year period. The model simulated different conditions such as variations in attic ventilation, variations in attic ceiling insulation, and different radiant barrier orientations for summer and winter seasons. It was observed that the model predicted with an error of less than ten percent for most cases. This paper presents model results for nonradiant barrier cases as well as cases for radiant barriers installed horizontally on top of the attic floor (HRB) and for radiant barriers stapled to the attic rafters (TRB). Savings produced by radiant barriers and sensitivity analyses are also presented. The model results supported the experimental trend that emissivity was the single most significant parameter that affected the performance of radiant barriers.
Thermally Regenerative Monolithic Rotor Dehumidifier for Adsorption Cooling System
Authors: Kuma Toshimi , Hirose Tsutomu , Goto Motonobu , Kodama Akio
Published: February 2008

A silica-base monolithic adsorbent was prepared by sol-gel synthesis with a corrugated ceramic fiber sheet as a matrix and assembled in an adsorptive dehumidifier of rotary type, which operates with a thermal regeneration cycle. High efficiency of dehumidification was confirmed at a regeneration temperature as low as 80°C when the rotation speed or cycle time was adjusted to the optimal value. A prototype air conditioning unit equipped with the balanced flow dehumidifier was examined in a direct pass ventilation mode. A satisfactory decrease in enthalpy of product air relative to room air was observed. Changes in the state of air during processing are discussed rather rigorously in terms of a humidity chart.
Mass and Aerodynamic Imbalance of a Horizontal Axis Wind Turbine
Authors: Borg J. P. , Kirchhoff R. H.
Published: February 2008

It is very common among wind turbines of all designs that a spectral analysis of operating variables, such as yaw motion, torque, or electrical power output has a large concentration of variance at the rotational frequency of the low speed shaft. This spike in the spectrum of the operating variables has come to be known as the once per revolution response or 1P. In addition to this 1P spike, three-bladed wind turbine spectral signatures usually include the harmonic integers 2P and 3P. The two main sources of IP are mass imbalance in the rotor plane and various aerodynamic performance imbalances of the rotor blades. This paper is dedicated to determining the specific contribution of each of these sources to 1P as well as their effects on the 2P and 3P harmonics. Mass imbalance and aerodynamic imbalance issues are addressed separately so that the relative contribution of each can be quantified. The nonlinear differential equations describing the coupled azimuth and yaw motion with mass imbalance were analytically solved using a perturbation technique. A blade strip element technique was used to determine the effects of aerodynamic imbalance on 1P, 2P, and 3P fluctuations. It was found that 60 percent of the 1P low-speed shaft torque (LSST) fluctuation is due to mass imbalance and 40 percent due to aerodynamic imbalance. These results compare quite favorably with the NREL 15 kW Combined Experiment wind turbine data.