bluuebunny/crossref_metadata_2025 huggingface dataset:
Rapid Consolidation of Hf Doped NiTi for High Transformation Temperatures
Authors: Wang Gang , Wereley Norman , Dai Liyang , Wuttig Manfred , Sahul Raffi , Tasovski Vasil
Published: April 2008

The objective of this study is to develop high transformation temperature shape memory alloys (SMAs) for actuation applications at elevated temperatures. We developed a process to consolidate NiTi micron powders doped with Hf using Material Modification Inc.’s (MMI) proprietary Plasma Pressure Compaction process (P2C). NiTi and NiTiHf samples were characterized to identify the material’s microstructure and composition using Scanning Electron Microscopy (SEM) and Energy Dissipative Spectroscopy (EDS) for both as consolidated and heat treated materials. Chemical and porosity analyses were also conducted to track impurities and microstructure (grain size and porosity). Extensive thermo-mechanical testing of the NiTi and NiTiHf samples were conducted to determine phase transformation temperatures and mechanical properties (Young’s Modulus). An acoustic elastometer was used to obtain the phase transformation temperatures for both NiTi and NiTiHf samples. By doping the SMA powder with 10% Hf (atomic percent), we were able to realize an increase in the austenite finish temperature to over 160 C.
Magneto-Rheological Parameter Identification From Viscometric Flow Curves Using Genetic Algorithms
Authors: Chaudhuri Anirban , Wereley Norman M. , Radhakrishnan R.
Published: April 2008

The primary objective of this study is to estimate the parameters of models characterizing the rheological properties of nanoparticle-based magnetorheological fluids. Experiments were carried out for suspensions of nanometer sized iron and cobalt particles. Shear stresses and the strain rates have been calculated for different magnetizing currents. The MR fluid was characterized using Bingham-Plastic and Herschel-Bulkley constitutive models. Both these models have two regimes: a rigid pre-yield behavior for shear stress less than a field-dependent yield stress, and viscous behavior for higher shear rates. Determination of model parameters is a complex problem due to the non-linearity of the model of the large amount of scatter in the experimentally observed data. To estimate the rheological parameters, we used a genetic algorithm and carried out a global optimization. The genetic scheme produces results with trends comparable to the gradient-based techniques and is more accurate. The Herschel-Bulkley fluid model is seen to fit the data with lower errors over a larger range as compared to the Bingham-Plastic model.
Application of X-Ray Diffraction for Residual Stress Determination in Mechanical Components
Authors: Belassel M. , Pineault J. , Brauss M.
Published: April 2008

X-ray diffraction has been applied to the measurement of residual stresses in mechanical and structural components for decades. It has been applied non-destructively in the laboratory on small and large components as well as in the field on very large components and structures. The technique is well suited to a wide variety of applications. Some examples include: process development and evaluation (including machining, heat treatment, welding and assembly), quality control, screening of non-conforming components and verifying the health of components during service at different intervals and at the end of life. Both residual stress levels and the associated work-hardening generated can be characterized using the shift and the broadening of the x-ray diffraction peak respectively. Since x-ray diffraction uses the atomic lattice spacing (d-spacing) as a strain gage it is thus only applicable to crystalline materials. In this paper, examples of x-ray diffraction applications on different materials subjected to various processes are illustrated. The effect of residual stresses on the fatigue lifetime of components is also considered.
Macroscopic Modeling of Turbulent Mass Transport in Heterogeneous Porous Media
Authors: Mesquita Maximilian S. , de Lemos Marcelo J. S.
Published: April 2008

In this work, results for a macroscopic mass transport model are presented for a parallel plate channel filled with a fluid saturated heterogeneous porous medium. The numerical methodology herein employed is based on the control volume approach. Turbulence is assumed to exist within the fluid phase. High and low Reynolds k-e models were used to model such non-linear effects. The flow equations at the pore-scale were numerically solved using the SIMPLE method applied to a non-orthogonal boundary-fitted coordinate system. Integrated mass fraction results were compiled leading to correlations for the mass dispersion coefficients in the x and y directions. Application of the macroscopic model using the proposed correlations showed the role of dispersion mechanism in the overall transport in porous media.
Automated Sizing Procedure of Servo-Driven Robot for Pallettes Handling
Authors: Andersen Torben Ole , Hansen Michael R.
Published: April 2008

A procedure for the automated sizing of spatial servo mechanisms is presented. The design performance is measured by means of a work task moving a payload from one point to another within a certain time. The design variables are composed of continuous and discrete parameters with the latter associated with the servo motor and planetary gears making up the servo drive. The costs are identified as the main objective for minimization whereas a number of side constraints related to accuracy, fatigue, vibrations and thermal conditions are presented and formulated mathematically. The two-level design procedure generates design from a motor and gear database that a subsequently subjected to minimization with a view to eliminate any constraint violations. The least costly of the feasible design are considered the optimal.
Multi Criteria Design Improvement of Commercial Loader Crane
Authors: Hansen Michael R. , Andersen Torben Ole , Ebbesen Morten Kjeld
Published: April 2008

An approach to systematically deriving the optimal use of operator-in-the-loop machinery is presented. The operation is considered as a set of design variables that similarly to classical design variables such as geometry and materials may be manipulated with a view to reach certain performances. The emphasis of the paper is on mobile loader cranes and an example on the development of the lifting capacity diagram of such a crane is used to illustrate the potential benefits of employing the presented approach. In general, physical data is not given for the loader crane due to limited space, however, the authors will be happy to provide more details for anyone interested.
IT-Tools Concept for Simulation and Design of Water Hydraulic Mechatronic Test Facilities for Motion Control and Operation in Environmentally Sensitive Application Areas
Authors: Conrad Finn , Pobedza Janus , Sobczyk Andrzej
Published: April 2008

This paper presents a proposed IT-Tools concept for modeling, simulation, analysis and design of water hydraulic actuators for motion control of machines, lifts, cranes and robots. The designed test rigs have tap water hydraulic components of the Danfoss Nessie® product family and equipped with a measurement and data acquisition system. Results of the mathematical modeling, simulation and design of the motion control test rigs are presented. Furthermore, the paper presents selected experimental and identifying test results for the water hydraulic test rigs.
Testing the Die Attach Quality of 3D Stacked Dies
Authors: Rencz M. , Sze´kely V. , Poppe A. , Courtois B. , Zhang L. , Howard N. , Nguyen L.
Published: April 2008

The paper presents the structure function based methodologies for testing the die attach quality of packages containing stacked dies. After the presentation of the theoretical background several measured test series are presented to demonstrate the use and the advantages of the method. The method is applicable for the fast diagnosis of the die-attach problems of stacked dies, and it does not require any additional circuit elements in any of the stacked dies.
Experimental Investigation of Pressure Wave Supercharging for SI Engine
Authors: Suzuki Takashi , Oguri Yasufumi , Uchida Keisuke , Yoshida Masatake
Published: April 2008

The objective of this paper is to find experimentally the suitable working conditions of a pressure wave supercharger (PWS) for SI engine. A belt-driven CVT was installed in order to drive the rotor of PWS to the appropriate speed regardless of engine speed. The maximum BMEP was achieved by changing speed of the PWS rotor at constant engine speed and throttle open ratio. From the experiment, the appropriate rotor speeds which led to maximum BMEP at every engine speed and throttle open ratio were achieved. The results showed that two power peaks existed during the range of the tested rotor speed. Since the drop in BMEP between these two power peaks was relatively small, the rotor speed range between these points was defined as effective rotor speed. At engine speed of 2000–4000rpm, the effective rotor speed was found at the engine-rotor ratio of 2.5. In addition, the maximum compression efficiency of PWS was 75% at engine speed of 3000rpm and the exhaust gas pressure reduced to the same level of commonly used turbochargers at all engine speed. Furthermore, results of the transient experiment showed that PWS had as good response as the small turbocharger, which was optimized for the tested engine.
Aneurysm Growth and Thrombus Formation in the Basilar Artery
Authors: Jou Liang-Der , Dispensa Brad , Saloner David , Young William L.
Published: April 2008

Modifying aneurysm hemodynamics may reduce the likelihood of aneurysm rupture. In this study, hemodynamics in a growing aneurysm and a thrombus-developing basilar aneurysm is studied. The locations of thrombus and growth were identified by co-registering MR images of aneurysms at two different times. The thrombus (~6mm) appeared at the superior side of the aneurysm, where the flow impinged on the wall, and aneurysm growth (~3mm) was found at the inferior side (lower part) of the aneurysm. The wall shear stress was calculated from flow simulations. The location of growth has a very low wall shear stress (< 0.01N/m2). The change of hemodynamics during thrombus development was not significant, but the thickest thrombus was shown to have a wall shear stress level between 0.2 and 1N/m2.
Velocity and Strain Distributions in Two-Dimensional Orthogonal Machining
Authors: Lee Seongeyl , Hwang Jihong , Shankar M. Ravi , Chandrasekar Srinivasan , Compton W. Dale
Published: April 2008

A study has been made of the primary deformation zone and tool-chip interface in two-dimensional (plane strain) orthogonal machining of commercially pure metals. The use of a high-speed, Charge-Coupled Device (CCD) imaging system in conjunction with an optically transparent, sapphire cutting tool, has enabled characteristics of the deformation field such as velocity, strain, and material flow, to be obtained at high spatial and temporal resolution. The velocity distributions in the primary deformation zone and along the tool rake face have been obtained by applying a Particle Image Velocimetry (PIV) technique to sequences of high-speed images of the chip-tool interface taken through the transparent tool, and of the primary deformation zone recorded from a side of the workpiece. A procedure is presented and demonstrated for determining the strain and strain rate distributions in the primary deformation zone. The measurements have provided data about the variations of strain, strain rate and velocity, in and around the cutting edge and primary deformation zone; confirmed the existence of a region of retarded sliding in the region of intimate contact between tool and chip; and highlighted the occurrence of a region of dead metal ahead of the cutting edge when cutting with a negative rake angle tool. The implications of these results to the use of machining as a controlled test for studying very large strain deformation, and for estimating material properties under extreme conditions of deformation are discussed.
Metal Microstructures in Four Dimensions
Authors: Nielsen S. F. , Gundlach C. , Lauridsen E. M. , Martins R. V. , Poulsen H. F. , Schmidt S. , Jensen D. Juul
Published: April 2008

By Three Dimensional X-ray Diffraction (3DXRD) microscopy it is possible to characterize microstructures non-destructively in 3 dimensions. The measurements are furthermore typically so fast that dynamics may be monitored in-situ, giving also the 4th dimension, namely the time. The 3DXRD technique is based on diffraction of high energy x-rays from third generation synchrotron sources. In the present paper the 3DXRD technique is described and it’s potentials are illustrated by examples relating to elastic and plastic strains, recovery, recrystallization and grain growth.
Estimation of Mass Transfer During Drop Formation: New Flow Expansion Model
Authors: Javadi A. , Bastani D.
Published: April 2008

Although there is extensive experimental, theoretical and numerical research on dynamics of drop formation in liquid-liquid systems, the evaluation of mass transfer during drop formation is rather complex and there has been little research on that. The various mathematical models developed for this problem are generally based on a solution of the diffusion equation without any allowance for circulation within the drop. This is the main reason for the poor prediction of these models in many cases for which internal convection has an important effect on mass transfer rate. In this paper an attempt was made to define a parameter related to the extent of the convective mixing within the growing drop. For this purpose it is assumed that the entrance of the dispersed flow into the growing drop from the nozzle is analogous to the entrance of the flow from a smaller channel to a larger one (the expanding drops). This transfer mechanism presented in this paper has been dubbed “flow expansion.” A global time-dependent Reynolds number was defined based on the equivalent diameter of growing drop as a length scale and also on a velocity scale, which is obtained using this flow expansion assumption. This time dependent Reynolds number of growing drop (Regd) has an important role on the mass transfer coefficient. The results of the model where predicting the effects of the nozzle diameter and dispersed phase flow rate on the mass transfer behavior showed good agreement with experimental data. This comparison demonstrates an improvement on famous models such as surface stretch and fresh surface elements for evaluation of mass transfer during drop formation.
Three-Dimensional High-Resolution Optical/X-Ray Stereoscopic Tracking Velocimetry
Authors: Lee David J. , Cha Soyoung S. , Ramachandran Narayanan
Published: April 2008

Measurement of three-dimensional (3-D) three-component velocity fields is of great importance in a variety of research and industrial applications for understanding materials processing, fluid physics, and strain/displacement measurements. The 3-D experiments in these fields most likely inhibit the use of conventional techniques, which are based only on planar and optically-transparent-field observation. Here, we briefly review the current status of 3-D diagnostics for motion/velocity detection, for both optical and x-ray systems. As an initial step for providing 3-D capabilities, we have developed stereoscopic tracking velocimetry (STV) to measure 3-D flow/deformation through optical observation. The STV is advantageous in system simplicity, for continually observing 3-D phenomena in near real-time. In an effort to enhance the data processing through automation and to avoid the confusion in tracking numerous markers or particles, artificial neural networks are employed to incorporate human intelligence. Our initial optical investigations have proven the STV to be a very viable candidate for reliably measuring 3-D flow motions. With previous activities are focused on improving the processing efficiency, overall accuracy, and automation based on the optical system, the current efforts is directed to the concurrent expansion to the x-ray system for broader experimental applications.
Fabrication and Testing of Micro Corona Motor and Micro Gas Bearings
Authors: Kim Daejong , Lee Sanghoon , Bryant Michael D.
Published: April 2008

The paper introduces fabrication processes of a micro corona motor and micro gas bearings via X-ray lithography. The micro corona motor was fabricated using a membrane-less built-on X-ray mask. The motor principle requires axially thick sharp stator electrodes. Therefore, X-ray lithography was adopted for precise, high aspect ratio characteristics. To minimize diffraction, a built-on X-ray mask (conformal mask) technique was employed with negative toned SU-8 photo resist. This technique may be suitable for fast fabrication of prototypes or very tall structures, which can be largely affected by printing gaps. Micro gas bearings were fabricated as a viable bearing system for the micro corona motor. Timembrane mask was fabricated to meet the strict performance requirements and geometric constraints of the micro gas bearing. Test results of the micro gas bearings and micro corona motor are also presented.
High-Resolution Radiography for Detecting and Measuring Micron-Scale Features
Authors: Morse Daniel H. , Antolak Arlyn J. , Mills Bernice E.
Published: April 2008

X-ray radiography has long been recognized as a valuable tool for detecting internal features and flaws. Recent developments in microfabrication and composite materials have extended inspection requirements to the resolution limits of conventional radiography. Our work has been directed toward pushing both detection and measurement capabilities to a smaller scale. Until recently, we have used conventional contact radiography, optimized to resolve small features. With the recent purchase of a nano-focus (sub-micron) x-ray source, we are now investigating projection radiography, phase contrast imaging and micro-computed tomography (μ-CT). Projection radiography produces a magnified image that is limited in spatial resolution mainly by the source size, not by film grain size or detector pixel size. Under certain conditions phase contrast can increase the ability to resolve small features such as cracks, especially in materials with low absorption contrast. Micro-computed tomography can provide three-dimensional measurements on a micron scale and has been shown to provide better sensitivity than simple radiographs. We have included applications of these techniques to small-scale measurements not easily made by mechanical or optical means. Examples include void detection in meso-scale nickel MEMS parts, measurement of edge profiles in thick gold lithography masks, and characterization of the distribution of phases in composite materials. Our work, so far, has been limited to film.
Dynamic Behavior and Simulation of Nanoparticle Sliding During Nanoprobe-Based Positioning
Authors: Tafazzoli Afshin , Sitti Metin
Published: April 2008

In this paper, the behavior of nanoparticles, manipulated by an atomic force microscope nanoprobe, is investigated. Manipulation by pushing, pulling or picking nanoparticles can result in rolling, sliding, sticking, or rotation behavior. The dynamic simulation of the nanoparticle manipulation, using atomic force microscope (AFM), is performed. According to the dynamics of the system, the AFM pushing force increases to the critical value required for nanoparticle motion. Nanoparticle positioning is designed based on when the nanoparticle is stopped by the AFM in order to move on the substrate. Simulation results for gold particles on a silicon substrate showed that sliding on the substrate is dominant in nanoscales.
Using Small X-Ray Beams to Understand Corrosion in Nuclear Fuel Cladding
Authors: Motta Arthur T. , Yilmazbayhan Aylin , Comstock Robert J. , Lai Barry , Cai Zhonghou
Published: April 2008

Uniform oxidation by the primary circuit water and associated may soon limit the service of Zr alloy fuel cladding in Light Water reactors. Understanding the differences in corrosion rate between alloys based on the microstructure of the protective oxide may allow us to design better alloying materials for severe duty cycle applications. The use of synchrotron radiation microbeam at APS allows the study of these oxide layers with an unique combination of the wealth of diffraction and fluorescence information and the level of spatial resolution obtained. We will discuss some of our experimental results and the potentials of these techniques in solving engineering problems.
Direct Synchrotron X-Ray Microdiffraction Measurements of Strain and Bending in Micromachined Silicon Devices
Authors: Evans Paul G. , Rugheimer Paul P. , Roberts Michelle , Lagally Max G. , Lee Chung-Hoon , Xiao Yanan , Lai Barry , Cai Zhonghou
Published: April 2008

The manipulation of strain in micromachined silicon structures is an important aspect of the design of emerging mechanical and electronic devices. Strain also has a fundamental role in the formation of devices through its effects on surface processes in epitaxial growth including diffusion and can be an important tool for studying these processes. Microfabricated silicon structures offer the opportunity to control the strain at length scales of less than one micron to several hundred microns. Synchrotron x-ray microdiffraction allows simultaneous independent measurements of the strain and bending in these structures. Microdiffraction measurements show that bending is the dominant source of strain in a prototypical microfabricated Si bridge loaded at its ends by silicon nitride thin films. The total strain difference between the top and bottom of the bent bridge exceeds 0.1% in our prototype structures and can potentially be increased in optimized devices.
Heat Pipe Optimization Team: The Heat Pipe Assisted Heat Sink Project
Authors: Agonafer Damena , Ibarra Juan , McGee Kendrick , Platt Frank , Harris Kendall , Aganofer Dereje
Published: April 2008

The Heat Pipe Assisted Heat Sink (HPAHS) team will be working on solving challenging thermal management problems for a device known as the base transceiver station (BTS); a device used to transfer cell phone calls. This problem was raised due to transfer cell phone calls. This problem was raised due to the high use of cell phone in recent years. According to 2002 Scarborough Research, the number of cell phones in US was 180 million (2/3 of population). Due to this high increase in demand for cell phone usage, Replacement Handset Shipments are projected to increase worldwide from Current 40% of total shipments to almost 85%. This will increase from 211 million in 2002 to 591 million by 2008 (Nokia). Cell phone calls are transferred via a device known as the base transceiver station (BTS). Cell phone companies are increasing the performance of the BTS by adding more electronics. Nokia is increasing the current BTS performance by adding another power amplifier. We will encounter the problem of designing the thermal solution to ensure optimal thermal performance, while meeting customer requirements of cost and manufacturing process.
Students Design Competition, Best Heat Sinks for Electronics Cooling
Authors: Sadeghipour Sadegh M. , Asheghi Mehdi
Published: April 2008

The Thermal Fluids Engineering, a junior course required by the mechanical engineering students at Carnegie Mellon University, is offered in the spring semesters. The students who take this course have previous background in thermodynamics, heat transfer, and fluid mechanics. Therefore, the emphases of this course are mainly on the applications, including design of the thermal systems. Included in the course is a design project competition for which the students design and manufacture a heat sink for electronic cooling. The heat sinks are then tested and ranked according to their performance in cooling a mock processor. Students are usually very excited about this competition and work very hard and zealously to present the best design and, they sometimes come up with very novel ideas. The design project has proven to be of great pedagogical value to the students. In this paper we will report on the competition of the spring semester 2004, which has been between twenty-seven student groups. We will review the competition as a whole and discuss in more detail the projects that particularly performed the best and the worst. We will share our observations about the educational benefits of the design projects, as well.
Analytical and Experimental Investigation of Different Synthetic Jet Actuator Configurations
Authors: Ugrina Sandra , Flatau Alison
Published: April 2008

The ultimate goal of this project is to actively control the flow over a micro air vehicle using smart materials. MAVs are a new type of aircraft operating at Reynolds numbers of about 50,000 that are one to two orders of magnitude lower than encountered in larger aircraft. The intention is to implement smart structures and couple them with fluids to improve the deteriorated aerodynamics of MAVs and help improve efficiency, stability and maneuverability of such vehicles. The actuators used in this work for artificially controlling the boundary layer are piezoelectrically driven synthetic jets. We theoretically investigated and predicted the behavior of the synthetic jet as we changed the geometry and material property parameters of the actuator. Analytical results were then compared to the results obtained from the experiments. It is crucial to be able to accurately design a strong unimorph to be implemented as an active component of a synthetic jet actuator and design the geometry configuration of the cavity that will best couple with the chosen membrane. A condenser microphone, a constant temperature anemometer (CTA) and a laser vibrometer were used to quantify actuator performance. It was observed that the size of the cavity and the size and shape of the exit nozzle were related and the performance of the actuator increased when the structure was tuned such that the resonant frequency of the diaphragm and that of the cavity were close to matching. A square unimorph made of PZT-5H and bonded to a 0.20- mm brass shim maximized jet velocity for the actuators studied. Optimum direction of change in the volume and the dimensions of the nozzle will strongly depend on the resonant frequency of the membrane in use. In this situation, increasing either the volume of the cavity or the thickness of the nozzle made the two frequencies move away from each other producing reduction in jet velocity. Increasing the area of the nozzle, made the structure behave more as needed and was taken as a key parameter for tuning the base geometry of the device.
Impact Test and Simulation of Portable Electronic Devices: An Assessment
Authors: Liu Sheng , Wu Xin , Gibson Ronald , Wang Xuefang , Zhang Hong Hai , Gan Zhiyin , Ren Jianwen , Chen Bin
Published: April 2008

Portable electronics devices are well known to be susceptible to drop impact which can cause various damage modes such as interconnect breakage, battery separation, possible cracking/debonding along interfaces, display damage, leaking in insulin pump, etc., Drop/impact performance of these products is one of important concerns of product design. Because of the small size of this type of electronics products, it is very expensive, time-consuming and difficult to conduct drop tests to directly detect the failure mechanisms and identify their drop behaviors. A brief review is given in terms of the development in testing standards, material modeling and structure modeling. Barriers and needs are given for both the measurement and modeling, with particular attention to the material rate dependent constitutive modeling, testing facilities development, and nonlinear contact mechanics modeling.
Modeling Nanoscale Thermal Transport via the Boltzmann Transport Equation
Authors: Amon Cristina H. , Murthy Jayathi Y. , Narumanchi Sreekant V. J.
Published: April 2008

In modern microelectronics, where extreme miniaturization has led to feature sizes in the sub-micron and nanoscale range, Fourier diffusion has been found to be inadequate for the prediction of heat conduction. Over the past decade, the phonon Boltzmann transport equation (BTE) in the relaxation time approximation has been employed to make thermal predictions in dielectrics and semiconductors at micron and nanoscales. This paper presents a review of the BTE-based solution methods widely employed in the literature. Particular attention is given to the problem of self-heating (hotspot) in sub-micron transistors. First, the solution approaches based on the gray formulation of the BTE are presented. In this class of solution methods, phonons are characterized by one single group velocity and relaxation time. Phonon dispersion is not accounted for in any detail. This is the most widely employed approach in the literature. The semi-gray BTE approach, moments of the Boltzmann equation, the lattice Boltzmann approach, and the ballistic-diffusive approximation are presented. Models which incorporate greater details of phonon dispersion are also discussed. This includes a full phonon dispersion model developed recently by the authors. This full phonon dispersion model satisfies energy conservation, incorporates the different phonon modes, and well as the interactions between the different modes, and accounts for the frequency dependence for both the phonon group velocity and relaxation times. Results which illustrate the differences between some of these models reveal the importance of developing models that incorporate substantial details of phonon physics.
Linear and Nonlinear Numerical Investigations of Regular Open Cell Structures
Authors: Luxner Mathias H. , Stampfl Juergen , Pettermann Heinz E.
Published: April 2008

Linear and nonlinear Finite Element simulations of various regular three-dimensional cellular solids (lattice structures) with relative densities ranging from 10% and 20% are presented. The structures consist of polymeric struts with circular cross sections. Two different Finite Element modeling techniques are employed. Beam element based models and continuum element based models are utilized and their applicability is assessed. Beam element based models compromise about the numerical model size and the detail resolution of the problem. Continuum element based models are used for highly detailed unit cell analyses. For simulations of the overall behavior the structures are treated as infinite media by a periodic microfield approach. The entire overall elasticity tensors are computed for the constitutive characterization of the effective mechanical behavior of the micro-structures. Overall stress-strain curves are predicted for uniaxial compressive loading, taking into account finite strains and elasto-plastic strut material. The predicted properties are evaluated with respect to direction dependence and density dependence. Finite samples of specimens are modeled for comparison to experimentally obtained results.
A Micro State Dynamic Model and Compatibility Conditions for the One Dimensional Non-Stationary Compressible Flow in Pressure Wave Machines
Authors: Nour Eldin H. A. , El-Nashar I.
Published: April 2008

Shock tube like applications such as the pressure wave machines are subjected to the possible build up of moving discontinuities in the material, temperature and pressure. The method of characteristics offered a suitable platform to take these aspects into consideration. Jenny [1,2,3] has applied this method to obtain the direction and the corresponding compatibility conditions for the isentropic non-stationary one dimensional gas flow. Following Jenny’s derivation, it was possible to derive the general compatibility conditions [4–8] along the corresponding characteristic directions. The variable grid method [4–8] used a second order approximation of the direction and compatibility conditions. A system of non-linear equations [4–8] for the local states and the grid positions was obtained. In spite of the accurate results achieved by the variable grid method, the obligation to grid reorganization -while numerically tractable- have drawn the attention to the possibility that there may be persistent and inherent analytical/physical inadequacy with respect to the resulting compatibility equations that are numerically reflected by inhomogeneous build up of the variable grid. This paper, therefore, revisits the formulation of the dynamics of the one dimensional non stationary compressible flow and develops a new micro state dynamic model. The micro state equations of continuity, momentum and energy are derived. A micro state variable such as Θ or P represents the micro state dynamics, while the corresponding flow variables of temperature T or density ρ are to be regarded as observed measurement variables. Further, the micro state compatibility conditions are derived. The resulting micro state total differentials dS0 & dS± along the particle path & sound propagation ± Lines are linear functions of the micro state differentials. It is shown that dS0 is the total differential of the micro state energy equation along the particle path. It is proportional to the “Clausius”-entropy differential ds through the gas constant R and to the differential of the number of micro states dΩ* in “Boltzmann”-relation by the Avogadro number NA. For isentropic flow, dS± is proportional — through κ and the sound speed a — to the transformed micro state “Riemann”-differential dR±. Otherwise, the relation ±ΔbaR± = [Δ,baS± + ΔbaS0] holds along the ± Lines where ±ΔbaR± & ΔbaS± are the weighted change of the micro state differential of Riemann-Invariants and the change of dS± along the ± Lines respectively. δ baS0 is the “jump” along the ± Lines of dS0. Beside providing novel micro state compatibility conditions for the variable grid method, the presented formulation clears the existence as well as the sign of entropy change (reversibility/irreversibility) within the second law of thermodynamics.
Life Cycle Analysis of Conventional Manufacturing Techniques: Sand Casting
Authors: Dalquist Stephanie , Gutowski Timothy
Published: April 2008

Conventional manufacturing techniques have not been subject to much scrutiny by industrial ecologists to date. Many newer techniques and products draw more attention as they rise quickly from research to global scales, amplifying their environmental consequences. Despite the presence of new technologies and increased overseas production, casting activity continues to have a strong presence in the US, and represents a stable component in the national economy. Data from the US government, US industry groups, and UK mass balance profiles facilitate an understanding of sand casting and comparison across manufacturing processes. The figures in the US and UK are similar in terms of diversity of metals (where the US is 72%, 13%, 10% and the UK 76%, 13%, 8% for iron, aluminum, and steel, respectively), energy per ton of saleable cast metal (10.1 and 9.3 million Btu/ton in the US and UK), and overall emissions, with notable similarities in benzene and particulate emissions. One notable discrepancy is in sand use, where the US sends to waste 0.5 tons of sand per ton of cast metal, whereas the UK sends 0.25 tons to landfill.
Practical Study of Application of Thermal Network Method to Thermal Design of Electronic Equipment: An Example for the Thermal Design of a Compact Self-Ballasted Fluorescent Lamp
Authors: Ishizuka Masaru , Nakagawa Shinji , Koizumi Katsuhiro
Published: April 2008

Thermal design is one of the most important issues in the development of compact self—ballasted fluorescent lamps as the demand for small yet powerful lamps is mounting. This paper proposes a simulation method that is based on a thermal network model for which a set of equations are developed. Some of the coefficients of the thermal network equations were determined experimentally using a simulated model lamp. The calculated temperatures are in good agreement with the measured temperatures. The work illustrates the usefulness of the proposed methodology in the design of compact self—ballasted fluorescent lamps.
Nusselt Number and Friction Factor of Staggered Arrays of Low Aspect Ratio Micro-Pin-Fins Under Cross Flow for Water as Fluid
Authors: Prasher Ravi S. , Dirner John , Chang Je-Young , Myers Alan , Chau David , He Dongming , Prstic Suzana
Published: April 2008

Experimental results of the thermal and hydraulic performances of silicon-based, low aspect ratio micro-pin-fin cold plates under cross flow conditions are reported. The pins were both circular and square in shape with dimensions (diameter for circular and sides for square) ranging from 50 to 150 μm. The test chip contained 20 integral 75×75 μm temperature sensors which were used to determine the thermal resistance (K W-1) of the cold plates. The experiments were conducted using water, over a Reynolds number (Re) ranging from 40 to 1000. The data show that the average Nusselt number (Nu) based on the fin diameter varies as Re0.84 for Re < 100 and as Re0.73 for Re > 100, where Re is the Reynolds number based on maximum velocity and the fin diameter. Analysis of the Fanning friction factor (f) data shows that f varies as Re-1.35 for Re < 100 and as Re-0.1 for Re > 100.
Finite Element Modeling of Forced Convection Heat Transfer in Carbon Foams
Authors: Anghelescu Mihnea , Alam Khairul
Published: April 2008

Carbon foams are a class of porous materials with direct applications to thermal management of electronics. These foams have open cell structure that can be used to flow a coolant such that the foam ligaments act as heat exchanger fins. The heat transfer and fluid flow in carbon foams is particularly difficult to model due to the complex physical structure of the carbon foam. Several attempts have been made to model convection heat transfer in porous media employing the method of volume averaging in formulation of governing equations. However, this approach cannot describe the complex interaction at the micro level and its effect on the transport at the macro level. This paper presents an analysis of forced convection heat transfer in an accurate geometrical representation of three-dimensional features in a carbon foam.
Numerical Simulation of a Thermally-Driven Open Cavity With a Shrouding Wall
Authors: Franco Admilson Texeira , Ganzarolli Marcelo M.
Published: April 2008

Natural convection in a square open cavity with and without the presence of a shrouding wall is analyzed. One vertical wall is heated and the horizontal walls are adiabatic. The other vertical wall is open to the ambient or a fluid reservoir. A shrouding wall is placed in front of this open wall forming a vertical open channel. Laminar and two-dimensional flow is assumed for the Rayleigh number ranging from 103 to 107 and the problem is solved numerically by using the Finite Volume-SOLA method. The average Nusselt number is reported for different values of the Rayleigh number and the distance of the shrouding wall to the open cavity.
Effect of 3D Diffusion Over Vertical Thin Rectangular Geometries in Natural Convection Heat Transfer
Authors: Gursoy Mustafa , Arik Mehmet , Icoz Tunc , Yovanovich Michael , Borca-Tasciuc Theodorian
Published: April 2008

Natural convection over vertical plates is a very well known problem in heat transfer. There are many available correlations to predict Nusselt numbers for a wide range of Rayleigh numbers. These benchmark studies on natural convection for vertical plates were conducted on rather large surfaces leading to Rayleigh numbers in the range of 0.1 to 109. In natural convection the sole driving force of fluid motion is the change in fluid density, when the diffusive limit is small compared to convective heat transfer. However, conduction to air, as well as air entrainment from sides also contributes to the heat removal from heater surfaces. An experimental study has been carried out with small and large heaters compared to published data for 2×103<Ra<4×107. Square surfaces of 12.5 and 25.4 mm, and rectangular heaters of sizes 25.4×101.6 and 25.4×203.2 mm were tested for a range of heat inputs such that the surface temperatures are controlled between 30 °C and 80 °C. It is found that published correlations underpredict the Nusselt numbers as much as 20%. It is observed that widely known correlations underpredict the experimental values since the 3D conduction and side air drifts on heat transfer are not accounted for in these correlations. However, the cuboid model which includes the 3D diffusion term showed much better agreement with the experimental results.
Experimental Characterization of a Carbon Fiber Composite Material Heat Sink in Boiling Heat Transfer Using FC-72
Authors: Gandikota Venugopal , Chengalvala Harish , Fleischer Amy S. , Jones G. F.
Published: April 2008

The on-going trend towards increasing device performance while shrinking device size often results in escalating power densities and high operating temperatures. High operating temperatures may lead to reduced reliability and induced thermal stresses. Therefore, it is necessary to employ new and innovative thermal management techniques to maintain a suitable junction temperature at high power densities. For this reason, there is interest in a variety of liquid cooling techniques. This study analyzes a composite material heat sink. The heat sink consists of a very large number of small cross-section fins fabricated from carbon pitch fibers and epoxy. These carbon pitch fibers have a high thermal conductivity along the length of the fin. It is expected that the longer length will result in more heat transfer surface area and a more effective heat sink. This experimental study characterizes the thermal performance of the carbon-fiber heat sink in a two-phase closed loop thermosyphon using FC-72 as the operating fluid. The influence of heat load, thermosyphon fill volume, and condenser operating temperature on the overall thermal performance is examined. The results of this experiment provide significant insight into the possible implementation and benefits of carbon fiber heat sink technology in two-phase flow leading to significant improvements in thermal management strategies for advanced electronics. The carbon fiber heat sink yielded heat transfer coefficients in the range of 1300-1500 W/m2 K for heat fluxes in the range up to 3.2 W/cm2. Resistances in the range of 0.20 K/W – 0.23 K/W were achieved for the same heat fluxes. Condenser temperature and fill ratio did not show a significant effect on any of the results.
Numerical Simulation for Under Floor Air Distribution System With Swirl Diffusers
Authors: Wang Xiuling , Pepper Darrell W.
Published: April 2008

The Finite Volume RNG k-ε turbulent model was employed to simulate an Under Floor Air Distribution (UFAD) system consisting of 8 swirl diffusers. Initial mesh generation was conducted using Pro/E and GAMBIT. CFD results using FLUENT show both flow and thermal patterns for an actual instrumented laboratory room (Building Technology Laboratory - BTL) located at the University of Nevada Las Vegas. Simulation results for flow and thermal patterns are presented utilizing symmetrical boundary settings for the BTL. Stratification heights and clear zones are discussed. The application of CFD simulation provides insightful analyses in UFAD design and placement.
Numerical Modeling of Data Center Clusters: Impact of Model Complexity
Authors: Bhopte Siddharth , Iyengar Madhusudan K. , Sammakia Bahgat , Schmidt Roger , Agonafer Dereje
Published: April 2008

Data centers are facilities that house large numbers of computer servers that dissipate high power. With the rapid increase in the heat flux of such systems, their thermal management has become a challenge that needs to be addressed. Computational analyses using a CFD code is a very useful technique that helps the engineer to understand and solve the data center cooling problem. In this paper the state of the art of numerical modeling of data center is discussed. Representative systems are modeled using the two most prominent approaches. Variation in results with the addition of modeling details is presented. The effect of under floor parameters such as the conditioned chilled air supply flow rate, the under floor plenum depth, and the tile opening flow resistance, is discussed. Total flow rate delivered by the Computer Room Air Conditioning (CRAC) unit depends on blower and system characteristic curves, as specified by the vendor. Impact of plenum depth and tile resistance on total CRAC flow rate is discussed. Under floor blockages such as cables, pipes, and random materials, impede the flow of the cold air stream and yield unpredictable air flow patterns. Currently, models with idealized plenums are used for simulation of data centers. The effect of including blockages in CFD analyses is discussed. A novel approach that defines safe and critical paths under plenum for routing the blockages is presented.
Comparison Between the Performance of Binary Coding and Real Number Encoding in Genetic Algorithms Applied to the IHCP
Authors: Woodbury Keith A. , Duvvuri Suprasanna
Published: April 2008

In this paper a comparison between binary coding and real number encoding has been drawn for solving a one dimensional heat conduction equation with specified boundary conditions. A test problem is taken and solved using binary coding as well as real number encoding and the results obtained are compared to that of the test problem, based on which the conclusions are drawn.
Guidelines on Managing Under Floor Blockages for Improved Data Center Performance
Authors: Bhopte Siddharth , Sammakia Bahgat , Iyengar Madhusudan K. , Schmidt Roger
Published: April 2008

Due to the increase in computer rack equipment power in recent years, thermal management of data centers has become a challenging problem. Data center facilities with raised floor plenums are the most popular configuration from a thermal management perspective. Considerable ongoing research efforts focus on optimizing the room layouts and equipment design in order to achieve the desired cooling. However, the detrimental impact of under floor blockages, which occur widely, is seldom addressed. These blockages often take the form of chiller pipes, cabling, and wires. They impede the flow of cold air from the air conditioning units and yield unpredictable air flow patterns. This results in highly maldistributed tile flow rates which can create additional hot spots above the raised floors. In this paper the effect of such under floor blockages on data center performance is characterized in detail. A representative data center is modeled using commercial CFD code, with typical under floor blockages. Blockages are shown to have a significant impact on tile flow rates and rack inlet temperatures. A detailed parametric study is presented, to identify the locations under the floor, where blockages if installed, have minimal effect on data center performance. Case studies are presented to show that blockages, if installed with prior consideration, have a positive effect on overall data center performance. Finally guidelines are presented on how to rearrange existing blockages or to install new blockages, and still achieve an improvement in thermal performance, without any change to the room layout or cold air supply.