bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic Antiplane Interaction of Subsurface Circular Cavities in a Semi-Infinite Piezoelectric Medium
Authors: Song Tianshu , Merhej Tamman , Shang Qingna , Li Dong
Published: July 2010

In the present work, dynamic interaction is investigated theoretically between several circular cavities near the surface in a semi-infinite piezoelectric medium subjected to time-harmonic incident anti-plane shearing. The analyses are based upon the use of complex variable and multi coordinates. Dynamic stress concentration factors at the edges of the subsurface circular cavities are obtained by solving boundary value problems with the method of orthogonal function expansion. Some numerical solutions about two interacting subsurface circular cavities in a semi-infinite piezoelectric medium are plotted so as to show how the frequencies of incident wave, the piezoelectric characteristic parameters of the material and the structural geometries influence on the dynamic stress concentration factors.
Steam Turbine Driving Compressor for Gas-Steam Combined Cycle Power Plant
Authors: Liu Wancai , Zhang Hui
Published: July 2010

Gas turbine is widely applied in power-generation field, especially combined gas-steam cycle. In this paper, the new scheme of steam turbine driving compressor is investigated aiming at the gas-steam combined cycle power plant. Under calculating the thermodynamic process, the new scheme is compared with the scheme of conventional gas-steam combined cycle, pointing its main merits and shortcomings. At the same time, two improved schemes of steam turbine driving compressor are discussed.
Friction Law for Bingham Fluid Flow in Channels of Arbitrary Cross-Section Shapes
Authors: Letelier Mario F. , Siginer Dennis A. , Stockle Juan S. , Vera Carlos
Published: July 2010

In many biomedical and industrial technological applications it is necessary to drive fluids that exhibit plastic or elasto-plastic behaviour. Particularly for cases in which fast results are demanded, or only small fluid samples are available, micro-channels are used. These normally have cross-section geometries determined by the manufacturing procedures and may be of square, rectangular, triangular and other shapes. In order to obtain the expected results, such as protein separation, particle concentrations, and the like, the rate of flow and time-dependent pattern of it must be carefully determined. In this paper it is presented an analytically rigorous method for calculating the friction coefficient in channels of arbitrary cross-section contours for plastic flow that may be conveniently described by the Bingham model. Results are presented for a variety of shapes and for different values of the yield stress.
Design of PID Controller for Control of Speed of the Robotic Fish Modeled by Lighthill’s Large Amplitude Elongated Body Theory in Linear Path
Authors: Shahi Mohammad , Meghdari Ali
Published: July 2010

Design of robotic fish based on hydrodynamics is presented and Lighthill’s Large Amplitude Elongated Body Theory (LAEBT) is used for modeling of the robotic fish in linear path. A PID controller for control of speed in linear path is designed and simulations are presented which shows its effectiveness for speed control of the robotic fish. It has been shown that in perspective of used approximate LAEBT model, the used control law maintains kinematic parameters and therefore, the associated efficiency will be maintained.
Energy Dynamics of Green Buildings: An Alternative to the Traditional Heating Ventilating and Air Conditioning Course
Authors: Naraghi Mohammad H. , McGough Michael T.
Published: July 2010

This paper describes a Mechanical Engineering Senior Undergraduate and/or early Graduate level course in sustainable building mechanical systems. This course can be an alternative to the traditional HVAC course and a part of energy concentration for undergraduate and/or graduate Mechanical Engineering. The course runs for a semester involving fourteen weeks of lecture — at most three hours of lecture per week. The course is primarily for Mechanical Engineering students. It is however, encouraged to be taken by Civil, Environmental and Architectural Engineering majors. A good part of the course is a group semester-long project. Attempt is made to form multidisciplinary groups involving Mechanical and other Engineering majors.
Viscoplastic Model Verification for SnPb Solder Based on Creep Tests
Authors: Han Changwoon , Park Noh-Chang , Oh Chul-Min , Hong Won-Sik , Song Byeongsuk
Published: July 2010

Heat sink assembly for a main board in a server station is built on printed circuit board by an anchor system, mounted by eutectic SnPb solder. Constant high temperature condition in the station keeps solder creeping and makes it failed eventually. To calculate the stress and predict the life of soldered anchor in the station, an FE model of anchor system is built. As viscoplastic behavior of solder depends on several factors such as microstructure of solder, temperature, load, and loading rate, model characteristics should be verified before applying it to life prediction. In this study, Anand unified constitutive equation is adapted for solder modeling and its creep behavior is calibrated and verified based on creep tests.
Elastic Properties of (Cu,Ni)6Sn5 Ternary Crystal Structure Using First-Principle Approach
Authors: Gao Feng , Qu Jianmin
Published: July 2010

The Cu6Sn5 intermetallic compound (IMC) is an important interfacial reactive product in electronic packaging. The properties of Cu6Sn5 have been demonstrated to be crucial to the interface reliability at the solder interconnections. Due to the element inter-diffusion between the packaging side and PCB (printed circuit board) side during soldering process, a ternary Cu6Sn5-based Cu-Ni-Sn intermetallic compound is often generated. This ternary phase exhibits a similar crystal structure as Cu6Sn5 phase, in which the Ni atoms are regarded as the solubility by replacing the Cu atoms. Therefore, this Cu-Ni-Sn ternary phase is labeled as (Cu6−x, Nix)Sn5. It has been found that the Cu6Sn5 unit cell consists of 44 atoms, in which 24 atoms are Cu and 20 atoms are Sn. The 24 Cu atoms occupy 4a, 4e, 8f1 and 8f2 sites, while 20 Sn atoms occupy 4e, 8f1 and 8f2 sites. The reported experimental results are quite sparse and thus a fundamental calculation is required. In this paper, the elastic stiffness of (Cu6−x, Nix)Sn5 crystal structure is calculated based on the first-principle approach within density functional theory. The results indicate that Cu6Sn5 phase show a nearly isotropic elasticity. However for the phase Cu5Ni1Sn5 (x = 1) where Ni atom at 4a space site, the elasticity shows slightly anisotropic. With the Ni solubility increase (x=2), the anisotropic elasticity of Cu4Ni2Sn5 phase becomes profound. The density of states (DOS) and partial density of states (PDOS) from individual element contributions, as well as the hybridization between the element states are simulated herein to reveal the mechanism of the anisotropic elasticity of (Cu6−x, Nix)Sn5 phase due to the occupancy of Ni atoms.
Simulation of a Small Scale Pellet Boiler
Authors: Teixeira J. C. F. , Vasconcelos B. N. , Ferreira M. E. C.
Published: July 2010

A Computational Fluid Dynamics model, implemented in the FLUENT code, has been used to describe with detail the combustion inside the furnace of a 15 kW pellet boiler. The solid biomass is modeled by the reaction of the volatile mater. The air supply is split into two regions with varying AF ratios. It was also observed that the NO formation in the combustion chamber is essentially due to the fuel-NO path and therefore the variations of excess air did not affect the concentration levels of NO at the exit of the combustion chamber. However by increasing the air supply in the vicinity of the grate (by moving the secondary air supply closer to the primary air supply) the NO levels increased. The emissions of the flue gases were measured and compared with the computed results. The results enable the optimization of the combustion chamber design and the efficient fine tuning of a pellet boiler for a wide range of power levels.
Dynamic Modeling of a Piezo-Driven Compliant Mechanism Using Modal Analysis
Authors: Darki Ali Akbar , Zohoor Hassan , Shahidi Ali Reza , Sanikhani Hamed
Published: July 2010

Dynamic modeling of piezo-driven compliant mechanisms is necessary to predict dynamic behavior of nanopositioning systems, and also to optimize their controlling methods. Dynamic tests on a real system or dynamic analyses on a FEM model is very time consuming when they must be carried out iteratively. According to previous works, obtaining static specifications of model is possible within a reasonable error margin. But all geometric dimensions and mass distribution details of the whole moving parts should be considered to calculate dynamic specifications of the model. In this paper, a functional method is described to obtain dynamic specifications of an planar compliant mechanism, by means of a reference Frequency Response Function (FRF) diagram. On the other hand, an equivalent analytical FRF is derived from the Mass-Spring model. A Genetic Algorithm optimization process is performed on the mass matrix for matching of the two FRF diagrams. Results show that a diagonal 3-by-3 mass matrix can nearly follow dynamic behavior of FEM model. It also is verified that results from the optimized dynamic model and the FEM model will have similar response to step excitation.
Global Active Control of Transmitted Sound Into Acoustic Cavity With Speakers and Piezoelectric Patch Actuators
Authors: Hanifzadegan Masih , Ohadi Abdolreza
Published: July 2010

In this work modeling of a vibro-acoustic system and global sound field control with both acoustic and structural actuators have been studied. The model of the system consists of a 3D rectangular cavity with five acoustically rigid walls and a flexible plate on the top of cavity. First, modeling of the vibro-acoustic system has been acquired and subsequently the mode shapes and natural frequencies of the coupled system have been calculated. Plane waves on the plate surface are the main sources of disturbances in this system. Undesired sound (noise) which is propagated into the enclosure is controlled by mounted piezoelectric patch actuators on the plate and acoustic piston sources (speakers) inside cavity. The global active control is designed to minimize the acoustic potential energy inside the cavity. The control performance has been investigated by acoustic and structural actuators separately and simultaneously.
Heat Transfer Characteristics of Swirling Impinging Jets
Authors: Brown Karl J. , Murray Darina B. , Persoons Tim , O’Donovan Tadhg S.
Published: July 2010

Impinging jets are used in a wide number of industrial cooling applications due to their high heat and mass transfer abilities. The current research is concerned with the effect of swirl on the heat transfer characteristics of jet impingement cooling. Two inserts were designed order to generate swirling flow. These two designs, “Swirl Insert A” and “Swirl Insert B”, were tested at various Reynolds numbers, between 8000 and 16000 inclusive, and at H/D = 0.5 and 1. The jet was directed downwards onto a 25μm thick stainless steel foil which was ohmically heated. Images were recorded using a thermal imaging camera focused on the underside of the foil. These images were then analysed using Matlab and the Nusselt number profile was obtained. It was found that, while both swirl inserts establish an improvement in the heat transfer by comparison to that of a jet with no swirl, the “Swirl Insert B” design performed better that the “Swirl Insert A” design for high Reynolds number at H/D = 0.5 and consistently for H/D = 1. It was also discovered that, while both the “No Insert” and “Swirl Insert B” results did not change dramatically with an alteration in H/D, “Swirl Insert A” decreased by ∼10%.
Efficient Heat Transfer in a Laminar Flow System by Hydrodynamic Manipulation
Authors: Olayiwola Bolaji O. , Walzel Peter
Published: July 2010

The effects of flow manipulation on the heat transfer performance of a laminar flow system were investigated. The combination of series of fins and oscillating flow was used due to its inherent advantage of triggering very complex transient interaction of eddies and flow deflection within the system. The investigations were performed with fluids providing Prandtl numbers Pr > 10. Steady Reynolds number in the range of 50 < Re < 1200 were studied. The duct with a hydraulic diameter Dh = 15 mm contains series of non-conducting fins. All geometrical parameters remain constant. Low frequency oscillation f < 100 Hz was used in order to obtain oscillation effects mainly dominated by oscillation velocity, and to avoid attenuation of the oscillation amplitude A in the device. Based on the experimental data, a correlation equation was developed. The energy dissipation as a result of applied oscillation was also determined by phase resolved measurements of the pressure difference and liquid displacement. The heat transfer coefficients were found to be dynamically controlled by the oscillations. The results show efficient heat transfer within the system due to the applied oscillation especially at low flow rates. At higher flow rates, the effect of the flow oscillation on the heat transfer performance of the system diminishes. With oscillating finned flow, the influence of the geometrical parameter Dh/L is not significant due to enhanced fluid mixing and repeated thermal boundary layer rearrangement as a result of the flow oscillation. The predictions of the correlation are reasonable. The results of the CFD show that for the fin spacing to be significant on the effectiveness of the finned system, the oscillating flow velocity must be higher than the mean flow velocity. Enhanced heat transfer performance is possible with increasing fin height but theoretically, this yields high pressure drop and increased pumping power. The calculated power input due to oscillation is comparatively low and decreases towards increasing net flow rates where the pulsating flow has a diminishing effect and the system approaches non-pulsating flow behaviour.
Experimental Characterization of Slug Flow Velocity Distribution in Two Phase Pipe Flow
Authors: Goharzadeh Afshin , Rodgers Peter
Published: July 2010

This paper presents an experimental study of gas-liquid slug flow inside a horizontal pipe. The influence of air bubble passage on liquid flow is characterized using Particle Image Velocimetry (PIV) combined with Refractive Index Matching (RIM) and fluorescent tracers. A physical insight into the velocity distribution within slug flow is presented. It was observed that the slug flow significantly influences the velocity profile in the liquid film. Measured velocity distributions also revealed a significant drop in the velocity magnitude immediately upstream of the slug nose. These findings aim to aid an understanding of the mechanism of solid transportation in slug flows.
A Two-Dimensional Numerical Investigation on Forced Convection in Channels With Transversal Ribs
Authors: Manca O. , Nardini S. , Ricci D.
Published: July 2010

Conventional sources of energy have been depleting at an alarming rate, which makes future sustainable development of energy use very difficult. Thus, heat transfer enhancement technology plays an important role and it has been widely applied to many applications as in refrigeration, automotive, process industry and solar energy heater. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility for increasing heat transfer with gas is to employ extended surfaces. Transversal ribs in a channel work as fins, increasing the heat transfer area and break the laminar sub-layer creating local wall turbulence. The heat transfer rate is improved but pressure drops increased as well. In this paper a numerical investigation is carried out on forced convection in channels heated by a constant heat flux. Also conductive effects are taken into account. The fluid is air and properties are assumed as function of temperature and flow is turbulent. Ribs of the same material of the channel walls are introduced and several arrangements and shapes are analyzed. The investigation is accomplished by means of the Fluent code. Results are presented in terms of temperature and velocity fields, average heat transfer coefficients and friction factor profiles. The aim of this study is to find arrangement of ribs such to give high heat transfer coefficients and low pressure drops. The maximum Nusselt number and friction factor have been detected for dimensionless pitches equal, respectively, to 12 and 10 for square and rectangular ribs, 10 and 8, for triangular ones.
Analysis and Experimental Visualization of the Flow Behavior Between Parallel Separated Cross-Corrugated Plates
Authors: Luna J. M. , Romero-Mendez R. , Hernandez-Guerrero A. , Luviano-Ortiz J. L.
Published: July 2010

The experimental visualization of the flow patterns developed in a channel formed by parallel separated cross-corrugated plates is presented in this work. The flow visualization was carried out by seeding reflective micro-particles in water. The cross-corrugated plates were characterized by corrugations with sinusoidal profile, 0.083 m wavelength and 0.075 m amplitude, placed at ±45° relative to the main flow direction. While the wavelength-amplitude aspect ratio was kept fixed, both the uniform spacing between plates and Reynolds number were varied. The essential feature of the flow is the secondary swirling motion developed by the furrow flows because of the crossing among streams. Three flow regimes were found: steady, unsteady and chaotic mixing. At some critical Reynolds numbers, depending upon the separation between plates, the flow becomes unsteady and chaotic mixing appears first in the outlet of the channel. Chaotic mixing moves closer to the inlet of the channel as the Reynolds number is increased. The results show that the onset of chaotic mixing occurs at larger Reynolds numbers as the spacing is increased. The flow pattern of this channel configuration is compared to that reported for the chevron arrangement.
Characteristics of Hydro-Dynamically and Thermally Developing Liquid Flow With Micro-Encapsulated Phase Change Material
Authors: Sabbah Rami , Yagoobi Jamal , Al Hallaj Said
Published: July 2010

This numerical investigation explores the hydrodynamic and thermal boundary layers characteristics of a liquid flow with Micro-Encapsulated Phase Change Material (MEPCM). Unlike pure liquids, the heat transfer characteristics of MEPCM slurry can not be simply presented in terms of corresponding dimensionless controlling parameters such as Peclet number. In the presence of phase change particles, the controlling parameters’ values change significantly along the tube length due to the phase change. As a result, the hydrodynamic and thermal boundary layers are significantly affected by the changing parameters. The numerical results reveal that the growth of the thermal boundary layer for MEPCM slurries is different than for pure liquids. The presence of MEPCM in the working fluid slows the growth of the thermal boundary layer and extends the thermal entry length. The local heat transfer coefficient strongly depends on the location of the melting zone interface.
Cultivation of Engineering Soft Skills Within the Constraints of a Prescribed Curriculum
Authors: Panthalookaran Varghese
Published: July 2010

Engineering soft skills are required of an engineer to excel in his/her career and profession. For engineering education institutions affiliated to a central university and working with a prescribed curriculum, it is often difficult to find time for real-world training of students in soft skills. The current paper summarizes the programs designed for undergraduate engineering students of an affiliated engineering institution in order to circumvent this problem. They integrate training in engineering soft skills with the regular academic schedule exerting minimal extra-loading for the students and ensuring individual attention. The distribution of training programs in time also facilitates natural and gradual development of the values, attitudes and soft-skills. Further, integration of soft skill training programs into regular academic schedule enhances the interest of students in academics.
Combined Impeller-Diffuser Design and the Influence of Slotted Guide Vanes on the Performance of Radial Diffusers
Authors: Epple Philipp , Miclea Mihai , Ilic Caslav , Delgado Antonio
Published: July 2010

Radial diffusers are devices to increase the static pressure of a radial impeller-diffuser-unit (IDU) and in many cases also its efficiency. A new design method for the coupled Impeller-Diffuser-Layout is proposed. This new design method is presented and the resulting theoretical differences of the vaned and vaneless diffusers are shown. It is known, also, that at high flow rates, the vaned diffusers will choke, i.e. the maximum flow rate of an IDU will be much less as the one of the impeller alone or an IDU with vaneless diffuser. In order to avoid the flow rate decrease in the vaned diffuser due to this blockage or choking, a new kind of diffuser is proposed: the slotted diffuser. The theoretical principles of chocking and the solution with the slotted diffusers are explained. In order to have an in depth understanding of its working principle, three IDU are numerically examinated: with vaneless diffuser, regular vaned diffuser and the new slotted diffuser. In general the slotted diffuser delivers approximately the same pressure and efficiency but a substantial higher flow rate than the vaned diffuser. The vaneless diffuser has the highest flow rate, but the lowest pressure. An in detail analysis of the gap losses between the exit of the impeller and the entry of the vaned regular and slotted diffusers is presented, unrevealing an major loss source in vaned IDU. Flow patterns of the different diffuser types are shown illustrating in a clear manner the working principle of these diffusers and their respective advantages and disadvantages. Finally, in order to validate the theoretical and numerical results, prototypes were built and measurements performed at a norm test rig according to DIN 24 163. Pictures of the prototypes as well as of the test rig are shown. The experimental results are in good agreement with the predictions of the numerical simulations confirming the theoretical and numerical investigations.
Heat Transfer and Pressure Drop of Periodically Fully Developed Swirling Laminar Flows in Twisted Tubes With Elliptical Cross Sections
Authors: Bishara Fady , Jog Milind A. , Manglik Raj M.
Published: July 2010

Periodically fully-developed swirling laminar flows in twisted tubes with elliptical cross sections are computationally simulated. The tubes are helically twisted and their geometry is described by the 180° twist ratios y of 3.0, 4.5 and 6.0, and ellipse cross-section aspect ratio of 0.7. Constant-property flow of water (nominal Pr = 3.0) with a Reynolds number range of 10 to 1200 is considered. The analysis quantifies the improvement in the Nusselt number as well as the increase in friction factor in order to map the effective heat transfer enhancement due to the twisted-tube-geometry-induced swirl flows. To this effect, the numerical results are compared with the baseline cases having a twist ratio of y = infinity, or straight elliptical cross-section tubes for which well established correlations are available. Numerical results show that the friction factor and the Nusselt number are a strong function of the twist ratio and the Reynolds number. The increase in fRe and Nu is higher as the twist becomes tighter (lower values of y). For Reynolds numbers below about 100, the heat transfer results do not deviate significantly from the straight-tube values, but at higher values of Re, significant enhancement in heat transfer is evident for all twist ratios considered here. The friction factor and Nusselt number results provided in this paper will help practicing engineers in integrating twisted elliptical tubes in various heat transfer applications.
Buckling Pressures of Metal Tanks With Variable Thickness Using a Reduced Stiffness Approach
Authors: Jaca Rossana C. , Godoy Luis A.
Published: July 2010

The Reduced Stiffness approach to compute lower bounds to buckling loads in shells has been employed by a number of researchers during the last thirty years as a convenient way to evaluate unstable behavior in imperfection-sensitive shells using simple eigenvalue analysis and without having to perform incremental nonlinear analysis. Recent applications by the authors and other researchers have shown ways to compute lower bounds using finite element analysis, in which a modified eigenvalue analysis is constructed by neglecting the membrane contributions to the matrix containing the initial stresses. This paper illustrates the application of the methodology within the context of finite element analysis to cases of shells with thickness changes in the meridional direction. A special purpose semi-analytical finite element code has been employed for uniform pressures acting on aboveground steel tanks. The tanks are representative of those constructed for the oil industry, with radius to thickness ratios of the order of 1500, and height to radius ratios lower than one. The results illustrate that the membrane contribution should not be completely eliminated in order to obtain lower bounds to buckling pressures and good estimates of buckling modes.
ASME Open Source Project: Prototype Re-Design and Conclusion of a Human Powered Water Purification Device
Authors: Schmaltz Kevin
Published: July 2010

The Western Kentucky University Mechanical Engineering program partnered with ASME to host an Open Source student design project to develop a prototype water purification device in 2008. The project was funded by an ASME grant and is part of a continuing initiative by ASME to extend the relevance of their annual Student Design Competitions (SDC) and link student projects to societal concerns. The Open Source Project extended the 2007 SDC which required students to design and construct human-powered devices to purify water. The design challenge was inspired by Hurricane Katrina-like temporary disasters, but also addresses one of the National Academy of Engineering’s Grand Challenges for Engineering: provide access to clean water. Affordable and practical solutions are needed to provide drinkable water to people who do not have the equipment, power or other resources necessary to assure safe water supplies. During the spring and early summer of 2008, five students from various SDC teams qualifying for the 2007 SDC finals used their competition experience to develop a new design for a human powered water purification system. Team members were distributed at universities from Sweden to Venezuela to New Mexico, and therefore interacted via internet and teleconferences to refine the design. Ongoing work was posted to the ASME website, allowing people external to the team a chance to critique or contribute to the design. The team met at WKU in May to construct and test a prototype of the design. The initial prototype was able to purify water at 10 times the rate of any SDC devices, using a combination of passive sand filtration, solar heat collection and mechanical friction heating. While this was a marked improvement, the reality is that the human effort to purify this water is still excessive. The second generation prototype was completed by faculty, staff and students at WKU during the 2009 summer with the information learned and experiences gained from the initial prototype of the distributed team. This paper will discuss the evolution of the project design from the SDC to through the second prototype and the impact of the open source approach to the design process. The project represents ASME’s first attempt at executing an “Open Source” project, providing a forum for mechanical engineers around the world to contribute to solutions of critical social, economic and environmental problems. If the final design proves technically feasible, the Open Source team will seek support from the ASME Center for Engineering Entrepreneurship and Innovation to commercialize the design.
Influence of the Thermal Properties of the Driving Components on the Performance of a Thermoacoustic Engine
Authors: Zink Florian , Vipperman Jeffrey S. , Schaefer Laura A.
Published: July 2010

Thermoacoustic energy conversion is based on the Stirling cycle. But rather than using pistons to create mechanical work, it utilizes sound waves. The most basic design of a thermoacoustic engine utilizes a simple resonance tube in which a regenerative unit (the stack) is placed. When the stack is subject to a temperature gradient, minute pressure disturbance in the resonator can be amplified to yield an intense sound wave as output. This amplification of the sound waves is the equivalent of mechanical work. Currently, this technology is limited by low energetic efficiency and the size of commercially available devices. The design of such devices is largely based on the hydraulic properties of the driving components. However, as the operation of thermoacoustic devices is based on the presence of temperature gradients across solids, thermal properties must be considered in the design phase. To date, this topic is underrepresented in the literature. This work will illustrate the influence of the thermal properties of the stack material on the thermoacoustic effect. The design of a thermoacoustic test setup is discussed. Measurements were conducted on stacks assembled with five feasible material choices, ranging from ceramic, with very low thermal conductivity, to copper, with high thermal conductivity. Results from the investigation highlight implications for device design and their miniaturization. In addition, the heat losses to the surroundings are estimated using data taken from the experiments. It is concluded that the thermal properties of the thermoacoustic stack are important design criteria and should be considered in future device designs.
Examination of Water Diffusion Process Within a Low Temperature Polymer Fuel Cell Membrane
Authors: Myles Timothy D. , Grew Kyle N. , Peracchio Aldo A. , Chiu Wilson K. S.
Published: July 2010

Water transport in fuel cells is of interest since the hydration state of the electrolyte is strong related to its conductivity. This study focuses on one part of water transport in fuel cell membranes, namely diffusion. In order to study diffusion processes in a fuel cell membrane a computer model has been developed. It is validated using information reported for the electrolyte membrane material Nafion. When the model is compared to experimental data from the literature a maximum error of 24.7% is observed. Two effects in addition to molecular diffusion have been studied; interfacial absorption and desorption of water at the membrane surface, and convective mass transfer. The effect of convective mass transfer is shown to be negligible while the effects of absorption and desorption are significant. By completing this validation it allows for the additional studies in the future of diffusion in other types of proton exchange membranes and the improvement of fuel cell performance.
Experimental Analysis of a Counter-Rotating Wind Turbine
Authors: Gregg Jason R. , Merchant J. Shane , Van Treuren Kenneth W. , Gravagne Ian A.
Published: July 2010

Increases in wind turbine efficiency have helped to provide cost-effective power to an ever-growing portion of the world. This paper explores the possibility of increasing power production using two counter-rotating sets of wind turbine blades. A review of design characteristics, such as number of blades, blade angle of twist, chord length, and generator efficiencies, resulted in the design of a counter-rotating wind turbine incorporating three different National Renewable Energy Laboratory (NREL) cross-sectional blade profiles along the span of the blades. A three-blade front system and two different three-blade rear systems were studied. The blade prototypes were modeled in SolidWorks®, produced using a Dimension SST 3D printer, and then tested using two Parallax™ four-pole stepper motors as generators in a model 406B ELD wind tunnel. Testing was performed between 15 mph and 40 mph in 5-mph increments. Preliminary results indicate that a counter-rotating assembly is promising for increasing energy extraction from a column of air. The counter-rotating system reached its optimum operating efficiency in wind tunnel testing at 25 mph using an exact reflection for the rear fan. At these test conditions 0.40% of the energy in the air column was converted into usable power. This outcome compares to a 0.21% power conversion when testing only the front-blade system. Additional testing will be completed using flow visualization in a ELD 502 water tunnel along with CFD analysis. The purpose of this testing is to discover air column behavior behind the upstream and downstream blade systems to optimize the design and increase total system efficiency. An appropriate scaling method must also be found. Currently, an energy model is being used to scale from the wind tunnel to the water tunnel. These tests would make it possible to design blade sets to create a maximum total efficiency at a specific wind speed. It would also be valuable to determine if counter-rotating systems could expand the range of possible turbine locations by lowering the required wind speed for significant power generation.
Design of a Variable Radius Piston Profile Generating Algorithm
Authors: Cole Gregory A. , Van de Ven James D.
Published: July 2010

One of the main sources of efficiency loss in heat engines is the inability of a sinusoidally displaced piston engines to approximate the ideal heat volumetric cycles the engines require. While attempts have been made to address this issue in the past, recent developments in Stirling engine technology utilizing rolling diaphragm seals on the cylinders has offered an opportunity to greatly increase the correlation between an engines volume-time profile to the ideal profile. By changing the radius of the piston used to drive the rolling diaphragm connection over its length, the piston can effectively be used as a “transfer function” translating the sinusoidal displacement of the crankshaft into a near ideal heat cycle volumetric displacement. This work presents a methodology for determining the ideal shape of such a piston, and a model used to most effectively match a desired input linear displacement profile with output volumetric displacement profile, without compromising the operating conditions required to maintain the diaphragm itself.
Characterization of Lead-Free Solder Interconnects Reliability Under Torsional Loads
Authors: Srinivas Vikram , Al-Bassyiouni Moustafa , Osterman Michael , Pecht Michael
Published: July 2010

Mechanical torsion loads often arise in portable electronics under life cycle conditions. With increased market pressure, drive to reduce time to market, and varying use conditions, it is critical to develop accelerated tests to evaluate reliability quickly. Mechanical torsion testing can provide a rapid assessment technique to characterize solder interconnect durability. This paper presents an evaluation of select lead-free solders, SAC305 (96.5Sn-3.0Ag-0.5Cu) and SN100C (99.25Sn-0.7Cu-0.05Ni+Ge), under mechanical torsion loading. For comparison, SnPb (63Sn-37Pb) solder was also evaluated. Common test vehicles with resistor 2512 packages were used for these tests. For the mechanical cycle tests, no statistical difference in reliability was observed between SAC305 and SnPb solder paste while SN100C solder pastes were found to exhibit lower durability during Weibull analysis.
Analysis of Thermal Response of a Portable Blood Cooling Device
Authors: Ho Son H. , Rahman Muhammad M. , Elsheikh Mutasim , Sunol Aydin K.
Published: July 2010

This paper presents the three-dimensional (3D) modeling and simulation of heat transfer within a portable blood cooling system with respect to space and time. The cooling system under study includes a cooler box with two cooling cylinders and eight blood bags. The cooler has the shape of a rectangular box with walls made of thermal-insulation material. The cooling cylinders protrude into the inner space through the bottom of the cooler box. Eight blood bags are arranged around these two cooling cylinders. The cooling cylinders use desiccant absorbing agents in combination with evaporative processes under vacuum pressure to achieve the cooling effect. Transient thermal response of the system is simulated by employing a computational approach. The computational domain includes the air inside the cooler box and the blood inside the blood bags. Heat from the surroundings penetrating the system through the insulation walls of the cooler box is included in the model. It is assumed that initially the blood is at the uniform ambient temperature. Once the cooling cylinders are activated, they draw heat from the air and the blood inside the cooler box. A lumped-parameter model is used to model the heat drawn by the cooling cylinder. The resulting solution of temperature distribution within the blood bags and the air in the cooler box is presented in the form of graphical visualization. Representative temperatures within the blood bags are presented as functions of time during a period of 12 hours. The computational model and results will be useful for the development and optimization of the design of portable cooling devices for the transportation of blood and similar biological tissues such as an organ for transplant.
Four-Wheel Steering Autonomous Vehicles
Authors: Jazar Reza N. , Mahinfalah M. , Khazaei A.
Published: July 2010

Employing an independent four-wheel-steering (4WS) system, we introduce an autodriver algorithm to keep an autonomous vehicle on a given road. The kinematic condition of steering can be used to set the steer angles such that the kinematic center of rotation is at a desired point. The road and tire characteristics, along with the dynamics of a moving vehicle cause the vehicle to turn about an actual point that is not necessarily at the road curvature center. The position of the dynamic turning center can be controlled by adjusting the steer angles such that it coincides with the road curvature center. Such a vehicle will move on the desired road autonomously.
Investigation of Water Vapor Diffusivity Through GDL of a PEMFC
Authors: LaManna Jacob , Kandlikar Satish G.
Published: July 2010

Water transport through the gas diffusion layer (GDL) of a proton exchange membrane (PEM) fuel cell is of critical importance in the operation of the fuel cell. In this study, the transport of water vapor through the GDL is investigated. A one-dimensional, single-phase heat and mass transfer model is developed to investigate the diffusivity of water vapor through the GDL of a PEMFC. An experimental apparatus is developed to induce water vapor gradients across the GDL while varying humidity levels and flow rates comparable to actual fuel cell operational conditions. Experimental data is then used to extract an effective water vapor diffusivity from the numerical model. Effective diffusivity was found to be 0.104×10−4 m2/s and the overall mass transfer coefficient was found to be 0.019 m/s at a temperature of 40°C.
Integrated Power Take-Off and Virtual Oscillator System for the VIVACE Converter: VCK System Identification
Authors: Lee Jonghun , Chang Che-Chun , Xiros Nikolaos I. , Bernitsas Michael M.
Published: July 2010

The first step in the development of an integrated system encompassing Power Take-Off (PTO) with virtual Mass-Damping-Spring (VMCK) for the VIVACE Converter (Vortex Induced Vibration for Aquatic Clean Energy) is achieved. VIVACE converts hydrokinetic energy of ocean/river currents to mechanical energy using Vortex Induced Vibrations (VIV). Subsequently, its PTO converts the mechanical energy to electricity. The objective integrated system acts as VMCK to support the hydro-mechanical component of VIVACE. The second function of the system is to act as PTO to implement the electro-mechanical component converting the harnessed mechanical energy to electrical energy without suppressing the hydro-mechanical energy harnessing mechanism of VIV. Vortex Induced Vibrations (VIV) are motions induced on long elastic bodies with bluff cross-section placed with their long axis perpendicular to a fluid flow due to periodic irregularities in this fluid-structure interaction phenomenon. In this paper, a single cylinder of VIVACE is considered. Even in this simplest case, the underlying physics of this phenomenon is strongly nonlinear. Special care is needed in designing systems that either support or enhance VIV or harvest the energy of VIV oscillations. In the first physical model of VIVACE, a mass-damper-spring arrangement was employed in the Marine Renewable Energy Laboratory (MRELab) of the University of Michigan to transmit mechanically the power to an electrical generator, which converted it to useful electrical power. A Virtual mass-damping-spring (VMCK) mechanism is intended to substitute the existing physical elements in the MRELab consisting of an electric motor driven by a power electronic converter allowing for programmable mass, stiffness and damping values. The integrated VMCK system enables improved control of the mechanism originally generating and supporting VIV as well as improved power take-off efficiency and capability. The VMCK system employs advanced switching control of the power transfer process so that VIV for a given damping is not affected. The first step taken in this paper towards development of the integrated system consists of the identification of the VCK system. The mechanical transmission system consists of a belt and two pulleys. The cylinder in VIV is attached to one side of the belt causing it to oscillate and in turn drive the pulleys.
Bonding Strength and Microstructure of SnAg-Based Solid Liquid Inter-Diffusion Bonds
Authors: Ladani Leila J. , Razmi Jafar
Published: July 2010

Solid Liquid Inter-diffusion (SLID) is a new technology used as interconnects in high density and 3 dimensional packages. This manuscript investigates effect of process parameters, pressure, time and temperature on the strength of bonds and microstructure produced using this technology. A full factorial experiment is designed and implemented on the process with these 3 variables at 3 levels using Sn3.5Ag. Bonds’ strength were then measured using a micro-tester and load displacements were monitored. This analysis shows that SLID bonds form at temperatures much higher than melting temperature of the low melting material. It also shows that time is a significant factor. Bonds that are formed under 10 minutes of time do not show a significant amount of intermetallics. Although the elemental percentage of copper is high in the middle of the bond, it does not reach enough to form any of intermetallic compounds of this ternary system. The specimens fabricated under longer time around 1 hour showed a more brittle, intermetallic like behavior.
On an Approximate Theory for Nonlinear Dynamics of Rods
Authors: Luo Albert C. J.
Published: July 2010

In this paper, a nonlinear theory for a straight rod is presented in the Cartesian coordinate frame. The traditional treatises of nonlinear rods were based on the Cosserat’s theory (e.g., E. and F. Cosserat, 1896) or the Kirchhoff assumptions (e.g., Kirchhoff, 1859; Love, 1944). This paper extends the ideas of Galerkin (1915), and the nonlinear theory of rods is developed from the general theory of the 3-dimennsional deformable-body.
Numerical Simulation of Mixed Convection in a Rectangular Cavity With Multiple Heat Sources
Authors: Gunes Hasan , Cadırcı Sertac , Gocmen Kenan
Published: July 2010

A numerical study is presented for a mixed convection in a two-dimensional partially open rectangular cavity. The uniform heat-flux, discrete heat sources are flush-mounted on three identical heat conducting vertical boards, which are mounted on the bottom wall of a partially open cavity. An external airflow enters the cavity through an opening (inlet) in the left vertical wall and exits from the opposite opening (outlet) in the right vertical wall. In this paper, the effect of the number of boards on the flow and thermal field characteristics are investigated and compared with a single board case, where appropriate. The simulations are carried out for wide ranges of Reynolds number and Richardson number (buoyancy parameter, Ri = Gr/Re2) for a working fluid of air (Pr = 0.71). The solutions were found to be time-independent for only sufficiently low values of Re and Ri. For large Re and/or Ri, the oscillatory flow is analyzed by considering time-histories, frequencies and instantaneous snapshots for the field variables. The effect of the oscillatory flow on the heat removal from the heat source is discussed. It was observed that with the onset of oscillatory flow, the re-circulating cells set into motion and thus considerable reduction in the maximum dimensionless temperature is achieved, making the cooling with convection as an effective mode of heat transfer. The results also indicate that the Reynolds number and Richardson number have a strong effect on the temperature and velocity distributions as well as the average Nusselt number evaluated over the heat source.
Experimental Demonstration of Localized Flow Control in a Microchannel Using Induced-Charge Electroosmosis
Authors: Yazdi Shahrzad H. , Davison Scott M. , Sharp Kendra V.
Published: July 2010

In this paper we investigate the use of induced charged electroosmosis (ICEO) as a means of providing localized flow control within bulk pressure-driven flow. Conductive posts are positioned in a microchannel in such a way that an AC electric field can be applied across them. This AC field induces an electric double layer (EDL), leading to ICEO flow around the conductive object. A pressure gradient is applied across the length of the channel to drive a background flow past the ICEO region. The combination of AC and pressure-driven flow fields is expected to create recirculation regions around the posts which could be useful for trapping particles or focusing the flow, e.g. for lab-on-a-chip applications. Numerical models of ICEO flow were developed and used to provide guidance for the design of microfluidic devices. These numerical models were also used to explore the number, position and shape of the conducting posts to create useful flow patterns. However, this paper focuses on the fabrication of and experiments within a prototypical microdevice. The device was fabricated from silicon dioxide and conducting gold pillars positioned in the glass channel. Experimental results obtained from this device have demonstrated localized ICEO-based flow control. Specifically, wake regions devoid of particles are created behind the posts.
Consumer and Manufacturer Design Factors for Use of Compressed Natural Gas (CNG) in American Automobiles
Authors: Costarell Michael David , Wallace Darrell
Published: July 2010

Despite significant research and development during the past quarter century, there has been an insignificant transition to use of compressed natural gas (CNG) vehicles. Although CNG automobiles reduce harmful emissions and reduce consumption of foreign oil, the nation has not successfully transitioned away from gasoline and diesel fuels. Therefore, the pros and cons of owning and operating CNG vehicles are explored from the consumer’s perspective. Included in this paper are isentropic compression models for single stage, 4 stage isentropic, and 4 stage with a constant temperature increase between cylinders. The models are then used to predict charging times for both residential and industrial compressors for an energy basis of 1MMBtu (1.055 GJ). The impact of CNG vehicles on US air emissions is discussed, with qualitative comparisons of CNG and oil-based emissions.