bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimum Shape of Constant Stress Toroidal Shells
Authors: Truong Vu Vu
Published: March 2013

The paper presents the optimization of toroidal shell cross-sections under internal pressure. The wall thickness distribution along a circular centerline is derived in an analytical form. In membrane solution, this cross-section gives a constant Mises stress all over the shell. Therefore, it leads to material saving and contained volume increase in comparison with the traditional cross-section of circular constant thickness. The optimum shapes are designed for two states of shell, one is elasticity and the other is up to destruction. The maximum material saving can reach 70% in some configurations of toroid. Results of the proposed method are as good as or better than those found in literature.
Calculating the Optimum Angle of Filament-Wound Pipes in Natural Gas Transmission Pipelines Using Approximation Methods
Authors: Reza Khoshravan Azar Mohammad , Emami Satellou Ali Akbar , Shishesaz Mohammad , Salavati Bahram
Published: March 2013

Given the increasing use of composite materials in various industries, oil and gas industry also requires that more attention should be paid to these materials. Furthermore, due to variation in choice of materials, the materials needed for the mechanical strength, resistance in critical situations such as fire, costs and other priorities of the analysis carried out on them and the most optimal for achieving certain goals, are introduced. In this study, we will try to introduce appropriate choice for use in the natural gas transmission composite pipelines. Following a 4-layered filament-wound (FW) composite pipe will consider an offer our analyses under internal pressure. The analyses’ results will be calculated for different combinations of angles 15 deg, 30 deg, 45 deg, 55 deg, 60 deg, 75 deg, and 80 deg. Finally, we will compare the calculated values and the optimal angle will be gained by using the Approximation methods. It is explained that this layering is as the symmetrical.
Diffusion-Welded Microchannel Heat Exchanger for Industrial Processes
Authors: Sabharwall Piyush , Clark Denis E. , Mizia Ronald E. , Glazoff Michael V. , McKellar Michael G.
Published: March 2013

The goal of next generation reactors is to increase energy efficiency in the production of electricity and provide high-temperature heat for industrial processes. The efficient transfer of energy for industrial applications depends on the ability to incorporate effective heat exchangers between the nuclear heat transport system and the industrial process. The need for efficiency, compactness, and safety challenge the boundaries of existing heat exchanger technology. Various studies have been performed in attempts to update the secondary heat exchanger that is downstream of the primary heat exchanger, mostly because its performance is strongly tied to the ability to employ more efficient industrial processes. Modern compact heat exchangers can provide high compactness, a measure of the ratio of surface area-to-volume of a heat exchange. The microchannel heat exchanger studied here is a plate-type, robust heat exchanger that combines compactness, low pressure drop, high effectiveness, and the ability to operate with a very large pressure differential between hot and cold sides. The plates are etched and thereafter joined by diffusion welding, resulting in extremely strong all-metal heat exchanger cores. After bonding, any number of core blocks can be welded together to provide the required flow capacity. This study explores the microchannel heat exchanger and draws conclusions about diffusion welding/bonding for joining heat exchanger plates, with both experimental and computational modeling, along with existing challenges and gaps. Also, presented is a thermal design method for determining overall design specifications for a microchannel printed circuit heat exchanger for both supercritical (24 MPa) and subcritical (17 MPa) Rankine power cycles.
Beam-Mode Buckling of Buried Pipeline Subjected to Seismic Ground Motion
Authors: Mitsuya Masaki , Sakanoue Takashi , Motohashi Hiroyuki
Published: March 2013

During seismic events, buried pipelines are subjected to deformation by seismic ground motion. In such cases, it is important to ensure the integrity of the pipeline. Both beam-mode and shell-mode buckling may occur in the event of compressive loading induced by seismic ground motion. In this study, the beam-mode buckling of a buried pipeline that occurred after the 2007 Niigataken Chuetsu-oki earthquake in Japan is investigated. A simple formula for estimating the critical buckling strain, which is the strain at the peak load, is derived, and the formula is validated by finite-element analysis. In the formula, the critical buckling strain increases with the pipeline diameter and hardness of the surrounding soil. By comparing the critical strain derived in this study for beam-mode buckling with the critical strain derived in a past study for shell-mode buckling, the formula facilitates the selection of the mode to be considered for evaluating the earthquake resistance of a pipeline. In addition to the critical buckling strain, a method to estimate the deformation caused by seismic ground motion is proposed; the method can be used to evaluate the earthquake resistance of buried pipelines. This method uses finite-element analyses, and the soil–pipe interaction is considered. This method is used to reproduce the actual beam-mode buckling observed after the Niigataken Chuetsu-oki earthquake, and the earthquake resistance of a buried pipeline with general properties is evaluated as an example.
Applicability of Equivalent Constant Amplitude Loading for Assessing the Fatigue Life of Pipelines and Risers and the Influence of Compressive Stress Cycles
Authors: Iranpour Mohammad , Taheri Farid
Published: March 2013

Fatigue life assessment of pipelines and risers is a complex process, involving various uncertainties. The selection of an appropriate fatigue model is important for establishing the inspection intervals and maintenance criteria. In offshore structures, the vortex-induced vibration (VIV) could cause severe fatigue damage in risers and pipelines, resulting in leakage or even catastrophic failure. The industry has customarily used simple fatigue models for fatigue life assessment of pipelines and risers (such as the Paris or Walker models); however, these models were developed based on constant amplitude loading scenarios. In contrast, VIV-induced stress-time history has a variable amplitude nature. The use of the simplified approach (which is inherently non conservative), has necessitated the implementation of large safety factors for fatigue design of pipelines and risers. Moreover, most of the experimental investigations conducted to date with the aim of characterizing the fatigue response of pipelines and risers have been done based on incorporation of constant amplitude loading (CAL) scenarios (which is unrealistic), or converting the variable amplitude loading (VAL) scenarios to an equivalent CAL. This study demonstrates that the use of such approaches would not be lead to accurate assessment of the fatigue response of risers subject to VIV-induced VAL. The experimental investigation performed in this study will also clarify the underlying reasons for the use of large safety factors by the industry when assessing the fatigue life of pipelines and risers. In addition, an experimental investigation was also conducted to highlight the influence of the compressive portion of VIV stress-time history on the fatigue life of such components. It is shown that the compressive stress cycles significantly influence the fatigue crack growth response of risers, and their presence should not be ignored.
A Molecular Dynamics Simulation for Thermal Conductivity Evaluation of Carbon Nanotube-Water Nanofluids
Authors: Javanmardi M. J. , Jafarpur K.
Published: March 2013

A nanofluid model is simulated by molecular dynamics (MD) approach. The simulated nanofluid has been a dispersion of single walled carbon nanotubes (CNT) in liquid water. Intermolecular force in liquid water has been determined using TIP4P model, and, interatomic force due to carbon nanotube has been calculated by the simplified form of Brenner's potential. However, interaction between molecules of water and atoms of carbon nanotube is modeled by Lennard-Jones potential. The Green–Kubo method is employed to predict the effective thermal conductivity of the nanofluid, and, effect of temperature is sought. The obtained results are checked against experimental data, and, good agreement between them is observed.
Slip Effects on the Peristaltic Motion of Nanofluid in a Channel With Wall Properties
Authors: Mustafa M. , Hina S. , Hayat T. , Alsaedi A.
Published: March 2013

This article looks at the peristaltic flow of nanofluid in a channel with compliant walls. Brownian motion and thermophoresis effects are taken into consideration. Mathematical model is formulated by using long wavelength and low Reynolds number assumptions. The analytic expressions of temperature and nanoparticles concentration are developed by homotopy analysis method (HAM). The solutions are validated through the numerical solutions obtained by employing the built in routine for solving nonlinear boundary value problem via shooting method through software mathematica. Special emphasis is given to the role of key parameters including the Brownian motion parameter (Nb), thermophoresis parameter (Nt), Prandtl number (Pr), Eckert number (Ec) on temperature, and nanoparticles concentration. It is observed that both temperature and nanoparticles volume fraction increase when the Brownian motion and thermophoresis effects intensify. Moreover, the heat transfer coefficient is increasing function of Nb and Nt.
Heat Transfer in Rotating Multipass Rectangular Ribbed Channel With and Without a Turning Vane
Authors: Lei Jiang , Li Shiou-Jiuan , Han Je-Chin , Zhang Luzeng , Moon Hee-Koo
Published: March 2013

This paper experimentally investigates the effect of a turning vane in hub region on heat transfer in a multipass rectangular channel with rib-roughed wall at high rotation numbers. The experimental data were taken in the second and the third passages (aspect ratio = 2:1) connected by an 180 deg U-bend. The flow was radial inward in the second passage and was radial outward after the 180 deg U-bend in the third passage. The square-edged ribs with P/e = 8, e/Dh = 0.1, and α = 45 deg were applied on the leading and trailing surfaces of the second and the third passages. Results showed that rotation increases heat transfer on the leading surface but decreases it on the trailing surface in the second passage. In the third passage, rotation decreases heat transfer on the leading surface but increases it on the trailing surface. Without a turning vane, rotation reduces heat transfer on the trailing surface and increases it on the leading surface in the hub 180 deg turn region. After adding a half-circle-shaped turning vane, heat transfer coefficients do not change in the second passage before-turn while they are different in the turn region and after-turn region in the third passage. Regional heat transfer coefficients are correlated with rotation numbers for multipass rectangular ribbed channel with and without a turning vane.
Influence of Condenser Conditions on Organic Rankine Cycle Load Characteristics
Authors: Erhart Tobias G. , Eicker Ursula , Infield David
Published: March 2013

A 7 MWth combined heat and power plant (CHP) based on an organic Rankine cycle (ORC) with 5.3 MWth and 1 MWel nominal output is analyzed. A district heating system serves as heat sink; the entire system is heat-led. Two examples for winter and summer operation are shown. The observed characteristics of the condenser are compared to results of a theoretical model. Variable mass flows, temperature levels (72 °C–95 °C) and temperature spreads result in varying condensation temperatures and pressure levels in the condenser (90 mbar to 150 mbar). High mass flows on the secondary side and related low temperature spreads improve the heat transfer and increase the condensation rate in the condenser. The monitoring data support the findings of a steady-state condenser model. As a consequence, advantageous load profiles according to the pressure characteristic of the system can be reached. Live steam pressure, pressure difference across the turbine, and flow rate increase. The effect on the electric efficiency is one percentage point in summer and 1.5 percentage points in winter, which translates to a difference in the electric yield of the cycle of about 10%. Furthermore, the data show that the transient sink conditions cause unsteady operation for the entire cycle.
Design, Simulation, and Construction of a Test Rig for Organic Vapors
Authors: Spinelli Andrea , Pini Matteo , Dossena Vincenzo , Gaetani Paolo , Casella Francesco
Published: March 2013

A blow-down wind tunnel for real-gas applications has been designed, validated by means of dynamic simulation, and then built. The facility is aimed at characterizing an organic vapor stream, representative of the expansion taking place in organic Rankine cycle (ORC) turbines, by independent measurements of pressure, temperature, and velocity. The characterization of such flows and the validation of design tools with experimental data, which are still lacking in the scientific literature, is expected to strongly benefit the performance of future ORC turbines. The investigation of flow fields within industrial ORC turbines has been strongly limited by the unavailability of calibration tunnels for real-gas operating probes, by the limited availability of plants, and by restricted access for instrumentation. As a consequence, it has been decided to design and realize a dedicated facility, in partnership with a major ORC manufacturer. The paper thoroughly discusses the design and the dynamic simulation of the apparatus, presents its final layout, and shows the facility “as built”. A straight-axis planar convergent-divergent nozzle represents the test section for early tests, but the test rig can also accommodate linear blade cascades. The facility implements a blow down operating scheme, due to high fluid density and operating temperature, which prevent continuous operation because of the prohibitive thermal power required. A wide variety of working fluids can be tested, with adjustable operating conditions up to maximum temperature and pressure of 400 °C and 50 bar, respectively. Despite the fact that the test rig operation is unsteady, the inlet nozzle pressure can be kept constant by a control valve. In order to estimate the duration of the setup and experimental phase, and to describe the time evolution of the main process variables, the dynamic plant operation, including the control system, has been simulated. Design and simulation have been performed with both lumped-parameter and 1D models, using siloxane MDM and hydrofluorocarbon R245fa as the reference working fluids, described by state-of-the-art thermodynamic models. Calculations show how experiments may last from 12 seconds up to several minutes (depending on the fluid and test pressure), while reaching the experimental conditions requires few hours, consistently with the performance of daily-based experiments. Moreover, the economic constraints have been met by the technical solutions adopted for the plant, allowing the construction of the facility.
Evaluation of the Energy Performance of an Organic Rankine Cycle-Based Micro Combined Heat and Power System Involving a Hermetic Scroll Expander
Authors: Oudkerk Jean-François , Quoilin Sylvain , Declaye Sébastien , Guillaume Ludovic , Winandy Eric , Lemort Vincent
Published: March 2013

This paper evaluates the performance of an organic Rankine cycle (ORC) based micro- combined heat and power (CHP) unit using a scroll expander. The considered system consists of a fuel boiler coupled with an ORC engine. As a preliminary step, the results of an experimental campaign and the modeling of a hermetic, lubricated scroll compressor used as an expander are presented. Then, a fluid comparison based on several criteria is conducted, leading to the selection of R245fa as working fluid for the ORC. A simulation model is then built to evaluate the performance of the system. The model associates an ORC model and a boiler model, both experimentally validated. This model is used to optimize and size the system. The optimization is performed considering two degrees of freedom: the evaporating temperature and the heat transfer fluid (HTF) mass flow rate. Seasonal simulation is finally performed with a bin method according to the standard PrEN14825 for an average European climate and for four heat emitter heating curves. Simulation results show that the electrical efficiency of the system varies from 6.35% for hot water at 65 °C (high temperature application) to 8.6% for a hot water temperature of 22 °C (low temperature application). Over one entire year, the system exhibits an overall electrical efficiency of about 8% and an overall thermal efficiency around 87% without significant difference between the four heat emitter heating curves. Finally, some improvements of the scroll expander are evaluated. It is shown that by increasing the maximum inlet temperature (limited to 140 °C due to technical reasons) and using two scroll expanders in series, the overall electrical efficiency reaches 12.5%.
Dynamic Modeling of Organic Rankine Cycle Power Systems
Authors: Casella Francesco , Mathijssen Tiemo , Colonna Piero , van Buijtenen Jos
Published: March 2013

New promising applications of organic Rankine cycle (ORC) technology, e.g., concentrated solar power, automotive heat recovery and off-grid distributed electricity generation, demand for more dynamic operation of ORC systems. Accurate physically-based dynamic modeling plays an important role in the development of such systems, both during the preliminary design as an aid for configuration and equipment selection, and for control design and optimization purposes. A software library of modular reusable dynamic models of ORC components has been developed in the MODELICA language and is documented in the paper. The model of an exemplary ORC system, namely the 150 kWe Tri-O-Gen ORC turbogenerator is validated using few carefully conceived experiments. The simulations are able to reproduce steady-state and dynamic measurements of key variables, both in nominal and in off-design operating conditions. The validation of the library opens doors to control-related studies, and to the development of more challenging dynamic applications of ORC power plants.
Convective Motion and Heat Transfer in a Slowly Rotating Fluid Quasi-Sphere With Uniform Heat Source and Axial Gravity
Authors: Anguiano-Orozco Gerardo , Avila Ruben , Shoaib Raza Syed
Published: March 2013

The laminar natural convection of a rotating fluid quasi-sphere in the presence of an axial gravity field and uniform heat source is presented. The influence of the Rayleigh number Ra and the Taylor number Ta on the flow pattern and heat transfer rate from the fluid quasi-sphere is discussed. The governing nonsteady, three-dimensional Navier–Stokes equations for an incompressible fluid, formulated in a Cartesian coordinate system, have been numerically solved by using the h/p spectral element method. It is shown that for a given Ta number, as the Ra number is increased, the heat transfer on the northern hemisphere is enhanced whereas the average Nusselt number on the southern hemisphere is reduced. On the other hand for a given Ra number, as the Ta number is increased, the heat transfer is a function of the convective motion intensity. It has been found that for low and high Ra numbers the heat transfer rate slightly depends on the rotation rate. However at intermediate Ra numbers, the net effect of an increased rotation rate is a reduction of the heat transfer through the wall, hence an increase of the maximum temperature of the fluid sphere is observed. We show that the net effect of the Coriolis force is to damp the convective motion and to allow a redistribution of the vorticity field.
Development of Infrared Microscopy for Measuring Asperity Contact Temperatures
Authors: Le Rouzic Julian , Reddyhoff Tom
Published: March 2013

Surface temperature measurements within sliding contacts are useful since interfacial heat dissipation is closely linked to tribological behavior. One of the most powerful techniques for such measurements is in-contact temperature mapping whereby a sliding contact is located beneath an infrared microscope. In this approach, one of the specimens must be transparent to infrared and coated such that radiation components can be distinguished and isolated from background values. Despite its effectiveness, a number of practical constraints prevent this technique from being applied to rough surfaces—a research area where temperature maps could provide much needed two-dimension input data to inform mixed and boundary friction models. The research described in this paper is aimed at improving the infrared temperature mapping technique in terms of validity, robustness, and spatial resolution, so that measurements of rough surfaces contacts can be made. First, Planck's law is applied in order to validate the use of surface coating as a means of removing background radiation. Second, a refined method of calibration is put forward and tested, which negates the need for a soft aluminum coating and hence enables rough surfaces to be measured. Finally, the use of super-resolution algorithms is assessed in order extend spatial resolution beyond the current limit of 6 μm.
The Effect of Triangle-Shaped Surface Textures on the Performance of the Lubricated Point-Contacts
Authors: Wang Wen-zhong , Huang Zhixiang , Shen Dian , Kong Lingjia , Li Shanshan
Published: March 2013

It has been recognized that purposefully designed surface texturing can contribute to the improvement of tribological performance of elements and friction reduction. However, its optimal parameters may depend on the operating conditions. This paper investigated the effect of a triangle-shaped dimples array on the tribological performance of the lubricated point-contacts under different lubrication regimes, based on the rotational sliding experiment of a patterned steel disk against smooth steel balls. The dimples arrays were produced by laser process and characterized by the 3D profilometer. A series of tests were conducted with different dimple parameters including depth, coverage ratio, size, and direction. Stribecklike curves were obtained to depict the transition of lubrication regimes, and the electrical contact resistance was utilized to qualitatively characterize the lubrication status. The test results showed that the dimples arrays with different sizes, depths and coverage ratios had a distinct effect on the friction behaviors. Compared with the nontextured surfaces, when the dimple depth decreased from 30μm to zero with fixed coverage ratio and size, the friction coefficient firstly decreased, and then increased. The friction coefficient finally approached that of the nontextured surface, during which the lowest value appeared at the dimple depth of approximately 10∼15μm. The coverage ratio of texture showed the similar effect on the friction coefficient. Usually, the coverage ratio of approximately 10% resulted in the lowest friction coefficient. The dimple size and direction also had obvious effects on the friction coefficient. Thus, it can be concluded that there exists a set of optimal values for the dimple depth, coverage ratio, size, and direction to realize the friction reduction.
An Integrated Mechanical–Thermal Predictive Model of Thermal Contact Conductance
Authors: Hong Jun , Peng Junfeng , Li Baotong
Published: March 2013

In this paper, an integrated mechanical–thermal predictive model of thermal contact conductance (TCC) between two nominally flat metallic rough surfaces is developed. Asperities on rough surface were approximated as parabolas. The asperity height deviation and average asperity top radius were measured as surface parameters and then used for mechanical and thermal modeling. A 3D shoulder–shoulder contact deformation model was then extended, taking into account different degrees of misalignment of contact between asperities and three modes of deformation: elastic, elastoplastic, and plastic. The yielded normal contact pressure, which should be equal to the exterior load, was formulated as a function of the given mean separation between the contacting surfaces for given surfaces and material properties. Based on the contact deformation model, a regression correlation of thermal contact conductance of a single pair shoulder–shoulder contacting asperities was integrated to get total TCC as a function of material properties and mean separation. As contact pressure and thermal contact conductance are all monotonically correlated with the mean separation, the mapping between the pressure and thermal contact conductance can be established by integrating the two parts. Finally, the integrated mechanical–thermal predictive model was compared to an existing predictive model and a series of experimental data. The results were in good agreement, demonstrating the validity of the model.
Evolution of Maximum Contact Stresses in Amorphous Carbon Coated Silicon During Sliding Wear Against Si3N4 Ball
Authors: Cai T. X. , Zhang P. Y. , Diao D. F.
Published: March 2013

The evolution of the maximum contact stresses in amorphous carbon coated silicon during sliding wear against a Si3N4 ball was investigated. Amorphous carbon coating was prepared on a silicon substrate by the electron cyclotron resonance (ECR) plasma sputtering method. Surface morphologies of the coating and counterpart were measured by an atomic force microscope (AFM). The friction and wear behavior of the coating was studied by a ball-on-disk tribometer. The cross-sections of the wear tracks at different wear stages were observed with a scanning electron microscope (SEM). Maximum contact stresses with different coating thicknesses were calculated by the three-dimensional semi-analytical method (SAM). The results demonstrated that when taking surface asperities into consideration, maximum shear stress at the bonding interface and adjacent substrate showed a dramatic increase during wear and should be responsible for the initiation and propagation of the cracks observed at the final stage of sliding.
Influence of Surface Waviness on the Thermal Elastohydrodynamic Lubrication of an Eccentric-Tappet Pair
Authors: Wang J. , Venner C. H. , Lubrecht A. A.
Published: March 2013

The effect of single-sided and double-sided harmonic surface waviness on the film thickness, pressure, and temperature oscillations in an elastohydrodynamically lubricated eccentric-tappet pair has been investigated in relation to the eccentricity and the waviness wavelength. The results show that, during one working cycle, the waviness causes significant fluctuations of the oil film, pressure, and temperature, as well as a reduction in minimum film thickness. Smaller wavelength causes more dramatic variations in oil film. The fluctuations of the pressure, film thickness, temperature, and traction coefficient caused by double-sided waviness are nearly the same compared with the single-sided waviness, but the variations are less intense.
Investigation and Validation of Finite Element Analysis Material Modeling for Integrity Assessment of Indented Pipe Under Static and Cyclic Loading
Authors: Al-Muslim Husain M. , Arif Abul Fazal M.
Published: March 2013

Mechanical damage in transportation pipelines is a threat to its structural integrity. There are many parameters that affect the severity of the mechanical damage which are related to the pipe geometry and material properties, the defect geometry and boundary conditions, the loading cycle, and the pipe state of stress. To understand those effects, the utilization of numerical finite element analysis (FEA) has been used extensively to supplement the expensive; and thus, limited full-scale tests. The actual pipe material exhibits a number of special features including nonlinear elasticity, anisotropy, and cyclic softening which need advanced material modeling techniques. However, the success of the numerical material model to actually simulate the pipe material behavior could not be studied in detail previously due to the insufficient experimental data especially in cyclic pressure loading. The objective of this paper is to investigate the effect of material modeling using FEA on the integrity assessment of dented pipe under static and cyclic loading by simulating pipe denting followed by subsequent pressure cycles. Several material models are tested and calibrated against the measurements of full-scale tests to find the effects of material modeling assumptions (e.g. isotropy, yield point, hardening rule). The results show that a combined material model simulating all special features of nonlinear elasticity, anisotropy, and cyclic softening gives a very close representation of experimental data in terms of strain values and fatigue cycles to failure. Therefore, detailed material properties are needed to conduct accurate integrity assessments of dented pipes especially under cyclic conditions.
Prediction of Leak Rates Through Porous Gaskets at High Temperature
Authors: Grine Lotfi , Bouzid Abdel-Hakim
Published: March 2013

The ability of a gasket to maintain tightness under different operating conditions has been studied extensively in recent years. However, most of the research studies conducted on leakage predictions was performed at room temperature. The aim of this work is to predict leakage through gaskets taking into account the effect of the temperature on the fluid properties and gasket internal structural characteristics. The analytical model of slip flow regime to evaluate the mass leak rates through a porous gasket developed by Grine and Bouzid (2011, “Correlation of Gaseous Mass Leak Rates Through Micro and Nano-Porous Gaskets,” ASME J. Pressure Vessel Technol.) was used in this study. The results from the model were validated and compared with the experimental data obtained from tests conducted on the Universal Gasket Rig with two different gases (helium and nitrogen). The leak rates measured are in the range of 1 to 0.0001 mg/s, which are measurable using the pressure rise technique. As a second objective, the influence of the gasket displacements caused by stress and temperature on the flow leakage was studied. A relationship between displacement or void thickness and leakage is clearly demonstrated. The slip flow regime model is capable of predicting leakage at temperature with reasonable accuracy.
Cross-Weld Creep Comparison of Power Plant Steels CrMoV, P91 and P92
Authors: Tanner David W. J. , Sun Wei , Hyde Thomas H.
Published: March 2013

Results obtained from high temperature creep tests of ferritic steel CrMoV, P91 and P92 cross-weld specimens are compared. Data are presented normalized with the results of the corresponding parent metals in order to compare the materials tested at different temperatures and stresses, and to identify characteristic cross-weld material trends. All cross-weld failures occurred in the heat-affected zone (HAZ) adjacent to the parent metal, known as type IV, at earlier test durations than for the parent material specimens. The relative performance of the cross-welds was found to decrease with decreasing stress. The CrMoV cross-weld specimens showed by far the lowest weld strength reduction factors and greatest notch strengthening, determined by testing uniaxially loaded bars with semicircular circumferential notches located in the heat-affected zone. The P91 and P92 cross-weld specimens were found to have similar (high) weld strength reduction factors and showed little or no notch strengthening. The failure time of a P92 cross-weld specimen relative to the P92 parent material could be estimated using data from P91 cross-weld and relative parent material tests.
Nonlinear Electroosmosis Pressure-Driven Flow in a Wide Microchannel With Patchwise Surface Heterogeneity
Authors: Bhattacharyya S. , Bera Subrata
Published: March 2013

In this paper, we have studied the electrokinetics and mixing driven by an imposed pressure gradient and electric field in a charged modulated microchannel. By performing detailed numerical simulations based on the coupled Poisson, Nernst–Planck, and incompressible Navier–Stokes equations, we discussed electrokinetic transport and other hydrodynamic effects under the application of combined pressure and dc electric fields for different values of electric double layer thickness and channel patch potential. A numerical method based on the pressure correction iterative algorithm is adopted to compute the flow field and mole fraction of the ions. Since electroosmotic flow depends on the magnitude and sign of wall potential, a vortex can be generated through adjusting the patch potential. The dependence of the vortical flow on imposed pressure gradient is investigated. Formation of vortex in electroosmotic flow has importance in producing solute dispersion. The circulation of vortex grows with the rise of patch potential, whereas the pressure-assisted electroosmotic flow produces a reduction in vortex size. However, the flow rate is substantially increased in pressure-assisted electroosmotic flow. Flow reversal and suppression of fluid transport is possible through an adverse pressure gradient. The ion distribution and electric field above the potential patch are distorted by the imposed pressure gradient. At higher values of the pressure gradient, the combined pressure electroosmotic-driven flow resembles the fully developed Poiseuille flow. Current density is found to increase with the rise of imposed pressure gradient.
Up-Scaled Microfluidic Fuel Cells With Porous Flow-Through Electrodes
Authors: Fuerth D. , Bazylak A.
Published: March 2013

In this work, an experimental microfluidic fuel cell is presented with a novel up-scaled porous electrode architecture that provides higher available surface area compared to conventional microfluidic fuel cells, providing the potential for higher overall power outputs. Our proof-of-concept architecture is an up-scaled flow-through fuel cell with more than nine times the active electrode surface area of the flow-through architecture first proposed by Kjeang et al. (2008, “A Microfluidic Fuel Cell With Flow-Through Porous Electrodes,” J. Am. Chem. Soc., 130, pp. 4000–4006). Formic acid and potassium permanganate were employed as the fuel and oxidant, respectively, both dissolved in a sulfuric acid electrolyte. Platinum black was employed as the catalyst for both anode and cathode, and the performances of carbon-based porous electrodes including cloth, fiber, and foam were compared to that of traditional Toray carbon paper (TGP-H-120). The effects of catalyst loading were investigated in a microfluidic fuel cell containing 80 pores per linear inch carbon foam electrodes. A discussion is also provided of current density normalization techniques via projected electrode surface area and electrode volume, the latter of which is a highly informative means for comparing flow-through architectures.
Induced-Charge Electroosmosis Around Touching Metal Rods
Authors: Canpolat Cetin , Zhang Mingkan , Rosen William , Qian Shizhi , Beskok Ali
Published: March 2013

Induced-charge electroosmosis (ICEO) around multiple gold-coated stainless steel rods under different ac electric fields is analyzed using microparticle image velocimetry (micro-PIV) and numerical simulations. In the present investigation, the induced electric double layer (EDL) is in weakly nonlinear limit. The ICEO flow around multiple touching rods exhibits geometry dependent quadrupolar flow structures with four vortices. The velocity magnitude is proportional to the square of the electric field. The ICEO flow velocity also depends on the cylinder orientation. The velocity increases with increased radial distance from the rod’s surface, attains a maximum, and then decays to zero. Experimental and numerical velocity distributions have the same trend beyond 0.2 mm of the rod’s surface.
Multiresponse Optimization of Al Alloy-SiC Composite Machining Parameters for Minimum Tool Wear and Maximum Metal Removal Rate
Authors: Bhushan Rajesh Kumar
Published: March 2013

Optimization in turning means determination of the optimal set of the machining parameters to satisfy the objectives within the operational constraints. These objectives may be the minimum tool wear, the maximum metal removal rate (MRR), or any weighted combination of both. The main machining parameters which are considered as variables of the optimization are the cutting speed, feed rate, depth of cut, and nose radius. The optimum set of these four input parameters is determined for a particular job-tool combination of 7075Al alloy-15 wt. % SiC (20–40 μm) composite and tungsten carbide tool during a single-pass turning which minimizes the tool wear and maximizes the metal removal rate. The regression models, developed for the minimum tool wear and the maximum MRR were used for finding the multiresponse optimization solutions. To obtain a trade-off between the tool wear and MRR the, a method for simultaneous optimization of the multiple responses based on an overall desirability function was used. The research deals with the optimization of multiple surface roughness parameters along with MRR in search of an optimal parametric combination (favorable process environment) capable of producing desired surface quality of the turned product in a relatively lesser time (enhancement in productivity). The multi-objective optimization resulted in a cutting speed of 210 m/min, a feed of 0.16 mm/rev, a depth of cut of 0.42 mm, and a nose radius of 0.40 mm. These machining conditions are expected to respond with the minimum tool wear and maximum the MRR, which correspond to a satisfactory overall desirability.
Physics-Based Reasoning in Conceptual Design Using a Formal Representation of Function Structure Graphs
Authors: Sen Chiradeep , Summers Joshua D. , Mocko Gregory M.
Published: March 2013

This paper validates that a previously published formal representation of function structure graphs actually supports the reasoning that motivated its development in the first place. In doing so, it presents the algorithms to perform those reasoning, provides justification for the reasoning, and presents a software implementation called Concept Modeler (ConMod) to demonstrate the reasoning. Specifically, the representation is shown to support constructing function structure graphs in a grammar-controlled manner so that logical and physics-based inconsistencies are prevented in real-time, thus ensuring logically consistent models. Further, it is demonstrated that the representation can support postmodeling reasoning to check the modeled concepts against two universal principles of physics: the balance laws of mass and energy, and the principle of irreversibility. The representation in question is recently published and its internal ontological and logical consistency has been already demonstrated. However, its ability to support the intended reasoning was not validated so far, which is accomplished in this paper.
Effects of Polymer Binder in Electrolyte Slurries and Their Microtubular SOFC Applications
Authors: Hasan Zahir Md. , Suzuki Toshio
Published: March 2013

The electrolyte slurry was prepared by mixing Gd-doped CeO2(GDC), solvent (ethanol and toluene), a polymer (polyvinyl butyral (PVB)) binder, and a dispersant (an amine system). The slurries were processed by an atomization process and coated on the top of microtubular tubes. A very smooth (with no cracks) electrolyte surface was obtained when the PVB polymer content was 8 wt. % (regular solution); however, a unique natural patchwork-type nanoporous grain boundary was obtained when the polymer content was increased to 16 wt. % (excess solution) in the same slurries. The results of this study show that polymers (binders) can be used not only to fabricate a dense electrolyte but also to generate a nanoporous grain boundary. The fabricated electrolytes have been tested for solid oxide fuel cell (SOFC) applications in the intermediate-temperature region. The microtubular cell with dense electrolytes maintained a high performance even under 600 °C.
Characteristic Analysis of Wind Turbine Gearbox Considering Non-Torque Loading
Authors: Park Young-Jun , Lee Geun-Ho , Song Jin-Seop , Nam Yong-Yun
Published: March 2013

In the design of wind turbine gearboxes, the most important objective is to improve the durability to guarantee a service life of more than 20 years. This work investigates how external loads caused by wind fluctuation influence both the load distribution over the gear tooth flank and the planet load sharing. A whole system model is developed to analyze a wind turbine gearbox (WTG) that consists of planetary gearsets. Two models for different design loads are employed to quantify how external loads acting on the input shaft of the WTG affect the load distribution of the gears and the load sharing among the planets under quasi-static conditions. One model considers only the torque for the design load, whereas the other model also considers non-torque loads. For two models, the results for the gear mesh misalignment, contact pattern, load distribution, and load sharing are different, and this leads to different gear safety factors. Therefore, the results indicate that it is appropriate to consider the non-torque loads in addition to the torque as the design load for a WTG, and that this is very important to accurately determine the design load that guarantee the service life of a WTG.
Flow Separation Control in an Annular to Conical Diffuser Using Two-Dimensional and Three-Dimensional Wall Steps
Authors: Lo Kin Pong , Elkins Christopher J. , Eaton John K.
Published: March 2013

Conical diffusers are often installed downstream of a turbomachine with a central hub. Previous studies showed that nonstreamlined hubs had extended separated wakes that reduced the adverse pressure gradient in the diffuser. Active flow control techniques can rapidly close the central separation bubble, but this restores the adverse pressure gradient, which can cause the outer wall boundary layer to separate. The present study focuses on the use of a step-wall diffuser to stabilize the wall boundary layer separation in the presence of core flow control. Three-component mean velocity data for a set of conical diffusers were acquired using magnetic resonance velocimetry. The results showed the step-wall diffuser stabilized the wall boundary layer separation by fixing its location. An axisymmetric step separation bubble was formed. A step with a periodically varying height reduced the reattachment length of the step separation and allowed the diffuser to be shortened. The step-wall diffuser was found to be robust in a range of core flow velocity profiles. The minimum distance between the core flow control mechanism and the step-wall diffuser as well as the minimum length of the step were determined.
Catalytic Steam Reforming of Glycerol Over Cerium and Palladium-Based Catalysts for Hydrogen Production
Authors: Ebshish Ali , Yaakob Zahira , Taufiq-Yap Y. H. , Bshish Ahmed , Shaibani Abdulmajid
Published: March 2013

In this work, catalytic steam reforming of glycerol for hydrogen production was performed over Ce/Al2O3 and Pd/Al2O3 catalysts prepared via the impregnation method. The catalysts were characterized by scanning electron microscopy (SEM-EDX), transmission electron microscopy (TEM), BET surface area, and X-ray diffraction (XRD). Two sets of catalytic reactions were conducted, one comparing 1% Pd/Al2O3 to 1% Ce/Al2O3 and the second comparing 1% Ce/Al2O3 loading to 10% Ce/Al2O3 loading. All catalytic reactions were performed using a fixed-bed reactor operated at 600 °C and atmospheric pressure. Aglycerol–water mixture at a molar ratio of 1:6 was fed to the reactor at 0.05 ml/min. In the first set of experiments, Pd/Al2O3 exhibited higher hydrogen productivity than Ce/Al2O3. A maximum hydrogen yield of 56% and a maximum selectivity of 78.7% were achieved over the Pd/Al2O3 catalyst. For the second set of experiments, the results show that the reaction conversion increased as the cerium loading increased from 1% to 10%. A total average hydrogen yield of 28.0% and a selectivity of 45.5% were obtained over 1% Ce/Al2O3, while the total average hydrogen yield and selectivity were 42.2% and 52.7%, respectively, for 10% Ce/Al2O3.
A Piezoelectric Servo Feed Drive for Electro Discharge Machining System Industrial Applications Using Linear Ultrasonic Motor
Authors: Shafik M. , Abdalla H. S. , Fransson P.
Published: March 2013

A new servo drive for electro discharge machining industrial applications is presented in this paper. The development processes of the servo feed drive have passed through three main stages. The first stage focused on design and development of a linear piezoelectric ultrasonic motor. The second one concentrated on development of an electronic driver and its embedded software. The integration, testing, and validation in electro discharge machining system, was the last stage of the development lifecycle. The linear piezoelectric ultrasonic motor consists of three main parts, the stator, rotor, and sliding element. The motor design process, basic configuration, principles of motion, finite element analysis, and experimental examination of the main characteristics are discussed in this paper. The electronic driver of the ultrasonic motor consists of two main stages, the booster and piezoelectric amplifier. The piezo amplifier consists of four output transistors, a push-pull and bridge, connected in order to achieve the necessary electrical parameters to drive and control the motor servo feed drive traveling speed. The essential experimental arrangement to implement and examine the developed ultrasonic servo feed drive in an electro discharge machining system was carried out. The initial results showed that the servo drive is able to provide: a reversible directional of motion, no-load traveling speed equal to 28 mm per s, maximum load of 0.78 N, a resolution <50 μm, and a dynamic time response <10 ms. The electron microscopic micro examination into the machined samples showed that: ultrasonic servo drive showed a clear improvement in the surface profile finish, a notable reduction in the stability, processing time, material removal rate, arcing, and short-circuiting teething phenomena. This was verified by assessing the electrode movements, the variations of the inter electrode gap voltage, current, and feedback control signals.