bluuebunny/crossref_metadata_2025 huggingface dataset:
Modified Laser Flash Method for Thermal Property Measurements and the Influence of Heat Convection
Authors: Lin Bochuan , Zhu Shen , Ban Heng , Li Chao , Scripa Rosalia N. , Su Ching-Hua , Lehoczky Sandor L.
Published: May 2008

This study examined the effect of natural convection in the modified laser flash method for the measurement of thermo physical properties of semiconductor melts. Common laser flash method uses a laser pulse to heat the front surface of a thin circular sample and measures the temperature transient of the rear surface. Thermal diffusivity is calculated based on the analysis of the transient heat conduction process. For semiconductor melts, the sample is contained in a specially designed quartz cell with optical windows. When the laser pulse heats the melt front surface, the resulting natural convection can introduce errors in the calculation of thermal diffusivity based on the heat conduction model. The effect of natural convection was evaluated by Computational Fluid Dynamics (CFD) simulations in this study. The results indicated that natural convection can decrease the time needed for the rear surface to reach its peak temperature, and can also decrease the peak temperature slightly. Based on our experimental data for Tellurium, the calculation using only heat conduction model resulted in a thermal diffusivity about 3% greater than that using the heat transfer model with natural convection.
Vibrations Generated by Pressure Oscillations for Improving Neonates Breathing
Authors: Al-Jumaily A. M. , Manilal P. I. , Prime N.
Published: May 2008

In this paper a structural analysis approach is developed to explain the relationship between the exciting pressure signals generated by the bubble continuous positive airway pressure (CPAP) devices and the vibration generated in the respiratory walls. It is demonstrated that the natural frequencies of the central airways in infants fall within the exciting frequency range, which helps in relaxing the respiratory walls, and gives them a better chance of faster recovery.
Optimal Thermal Design for PPF Heat Sinks
Authors: Chen Han-Ting , Horng Jenn-Tsong , Hung Ying-Huei
Published: May 2008

An effective method for predicting and optimizing the thermal performance of Parallel-Plain Fin (PPF) heat sinks that satisfy given design constraints has been successfully developed in the study. The thermal and hydrodynamic performance analyses for PPF heat sinks have been conducted. The Response Surface Methodology (RSM) is applied to establish analytical models of the thermal resistance and pressure drop in terms of the design variables with a Central Composite Design (CCD) experimental design. A constrained optimization technique, Sequential Quadratic Programming (SQP), is employed to efficiently seek the optimal designs; and the comparisons between these predicted optimal designs and those evaluated by the theoretical calculations are made with a satisfactory agreement.
Temperature-Dependence of Water Bridge Formation in Atomic Force Microscopy
Authors: Nelson Brent A. , Poggi Mark A. , Bottomley Lawrence A. , King William P.
Published: May 2008

When an Atomic Force Microscope (AFM) is operated in air, capillary condensation induces meniscus formation between the AFM tip and substrate. At present, no models account for the temperature-dependence of meniscus formation. This paper describes experiments measuring capillary forces between an AFM tip and mica at various temperatures and times. At low humidity, the capillary force decreases with increasing surface temperature in a manner unaccounted for by merely the dependence of water surface energy on temperature. We propose that this is due to water evaporation off the heated surface. The adhesion is also shown to decrease significantly with time until stabilizing after approximately an hour of experiments. Localized heating of the surface by the AFM laser is proposed as the cause of adhesion decrease. The decrease in force occurring at high surface temperatures implies a reduction in meniscus size that may potentially improve the resolution of AFM-based nanolithography techniques.
An Intelligent Ultrasonic Based Neuro-Navigation System for Improved Image Guided Neurosurgery
Authors: Akers Jennifer , Ray Probir Kumar , Mahajan Ajay , Lal Sumeer
Published: May 2008

This paper shows the feasibility of using an accurate 3D ultrasonic position estimation system for realtime image guided neurosurgery. Current image guided systems use camera based technology that is space-intensive, have an accuracy of about 2mm, and are prone to occasional failures. The 3D system presented in this paper eliminates the space intensive camera, has an accuracy better than 2mm in the operating range of about 20–40cm, makes the system independent of line-of-sight occlusion problems, and is expected to pave the way for accurate fusion models of MRI and ultrasonography to account for brain shifts during surgery. This paper presents the system formulation, optimal placement of receivers using an innovative genetic algorithm approach, a scheme for automatic installation and calibration, and finally some preliminary experimental results within a laboratory environment.
Radiation Heat Transfer Analysis of the Monolith-Type Solid Oxide Fuel Cell
Authors: Murthy Sunil , Fedorov Andrei
Published: May 2008

In this study, a modeling framework for heat and mass transport is investigated for a unit cell of the monolith type SOFC, with emphasis on quantifying the radiation heat transfer effects. The Schuster-Schwartzchild two-flux approximation is used for treating thermal radiation transport in the optically thin YSZ electrolyte, and the Rosseland radiative thermal conductivity is used to account for radiation effects in the optically thick Ni-YSZ and LSM electrodes. The thermal radiation heat transfer is coupled to the overall energy conservation equations through the divergence of the local radiative flux. A commercially available CFD software was used as a platform for the global thermal-fluid modeling of the SOFC and the radiation models were implemented through the user-defined functions. Results from sample calculations show significant changes in the operating temperatures and parameters of the SOFC with the inclusion of radiation effects.
Three-Mask Fabrication and Optimized Design of First-Level Free-Standing Interconnect for Microelectronics Application
Authors: Zhu Qi , Ma Lunyu , Lo George , Sitaraman Suresh K.
Published: May 2008

Advances in compliant off-chip interconnects have achieved great strides. G-Helix, an electroplated compliant chip-to-substrate interconnect has the potential for accomplishing low-cost, easy-to-fabricate, wafer-level packaging. In this work, the design, fabrication, optimization and reliability of the G-Helix compliant off-chip interconnects have been studied. A three-mask process was used to successfully fabricate the free-standing G-Helix compliant interconnect. The mechanical compliance and the electrical parasitics were studied through numerical and analytical models. Response Surface Methodology (RSM) was used to maximize the mechanical compliance and minimize the electrical parasitics as well as the stresses induced in the interconnect. It is also seen through the models that an array of interconnects will be able to withstand the die and the heat-sink weight without plastically yielding. Also, the G-Helix interconnect assembly on organic printed circuit board using lead-free solder will be able to withstand more than 1000 accelerated thermal cycles without the need for an underfill.
Robustness Analysis of Semi-Active Tuned Vibration Absorbers With Magneto-Rheological Dampers: An Experimental Study
Authors: Koo Jeong-Hoi , Ahmadian Mehdi , Setareh Mehdi , Murray Thomas M.
Published: May 2008

This paper offers an experimental robustness analysis of a semiactive tuned vibration absorber (TVA) as well as a passive TVA. A conventional passive TVA is only effective when it is tuned properly; otherwise, it may amplify the vibrations of the primary system. In many practical applications, inevitable off-tuning of a TVA often occurs because of system’s operating conditions or parameter changes over time. For example, adding or subtracting external mass on the existing primary system results in changes in the system’s natural frequency. The frequency changes of the primary system are responsible for “off-tuning” of TVAs. When TVAs are off-tuned, their effectiveness is sharply reduced. In our experimental robustness analysis, we focused on the dynamic performance of both the passive and the semiactive TVAs when the mass of the primary system changed (mass off-tuning). To this end, a test apparatus was built to represent a two-degree-of-freedom structure model coupled with a TVA. The semiactive TVA considered in this study employed a Magneto-Rheological (MR) damper as its damping element to enhance overall performance. Using this test apparatus, a series of tests were conducted to identify the optimal tuning parameters of each of the TVAs. The optimal tuning parameters were obtained based on equal peak transmissibility criteria. The mass off-tuning tests were then performed on the optimally tuned semiactive TVA and the optimally tuned passive TVA. In order to off-tune the primary mass, the mass of the primary system varied from −23% to +23% of its nominal mass. The experimental results showed that the semiactive TVA with MR dampers are more robust to changes in the primary mass (off-tuning) than the passive TVA.
Least-Volume Optimization of Finned Heat Sinks for Burn-in Air-Cooling Solutions
Authors: He Zhaojuan , Phelan Patrick E.
Published: May 2008

With the development and increasing use of high-density components with their high power dissipation needs, electronic packages have required the investigation of innovative techniques for the efficient dissipation of heat. One prevalent method is the use of forced convection heat spreaders, called heat sinks, which are also widely used in Burn-In (BI) ovens. There are some contradictions remaining in recent research on modeling and Nusselt number correlations of heat sinks in forced air convection. This paper begins by reviewing past research for different finned heat sink geometries with and without bypass flow over the heat sinks. A new method called Least Volume Optimization is then proposed to analyze the thermal performance of finned heat sinks for BI air-cooling solutions. The analysis shows that the volumetric heat dissipation of a parallel plate fin heat sink is higher than that of a pin fin heat sink, based on an optimal fin geometry.
Modelling and Simulation of a Breathing System
Authors: Al-Jumaily A. M. , Mithrarathne P. , Gradon L. , White D.
Published: May 2008

This paper presents the development of a dynamic model for an artificial breathing system designed to help patients with sleep related disorders. The system consists of a variable-volume-reciprocating compressor, reservoir, mask and a controller. These components are inter-connected by flexible tubes. The key feature of this system is to maintain a slightly positive air pressure in a mask attached to the person with breathing difficulties. This facilitates the patient with a reduced inhalation effort. Each component of the system is modeled as a lumped sub-system to describe the dynamic behavior. The mathematical models are simulated using SIMULINK™ in MATLAB™ environment. This gives a greater flexibility in changing parameters to investigate various control as well as operational scenarios. The model is computer simulated to investigate the response of the system for various input parameters including controller analysis.
A Numerical Simulation of Controlling Chaotic Vibration of a Maglev System by OGY Method
Authors: Xu Zhixiang , Feng Zhengjin , Seto Kunisato , Tamura Hideyuki
Published: May 2008

In this paper, we first introduced the Model-based OGY method for controlling chaos of nonlinear continuous time dynamical system, and then applied this Model-Based OGY Method to a repulsive maglev system to control its chaotic vibrations. From the numerical simulation results, we found out that the Model-based OGY Method is successfully applied to controlling chaotic vibrations of the repulsive maglev system, and hence the effectivity of Model-based OGY Method is demonstrated.
Band-Gap Engineering of Elastic Waveguides Using Periodic Materials
Authors: Hussein Mahmoud I. , Hulbert Gregory M. , Scott Richard A.
Published: May 2008

Within periodically heterogeneous materials, wave scattering takes place across constituent material interfaces in such a way that an overall wave attenuation effect arises at certain frequency ranges known as band gaps. This phenomenon can be utilized in developing structures with tailored dynamic characteristics. In this work, periodic materials are used to synthesize elastic waveguides within bounded structures. The underlying local-global design process is described, and the effect of the number of periodic cells used to form the guide “wall” is studied. Using forced vibration analysis, it is shown that with only three or four periodic unit cells, the desired wave attenuation capacity required to form a guide is attained.
Heat Flux Maps for Ovens: Concept of Baking Comfort Zones
Authors: Pierrel F. , Newborough M.
Published: May 2008

Achieving rapid baking in industrial tunnel ovens, while maintaining adequate product quality is a significant challenge. The application of excessive heat fluxes to a low-diffusivity heterogeneous food product can easily yield a product of poor quality (color, texture, flavour). It is desirable to optimize the application of heat on a transient basis during the baking process in order to minimize bake times and achieve an acceptable set of product responses (e.g. color, height, crust hardness, crumb moisture, weight loss). The magnitudes of the convective, radiative, condensing/evaporating and conductive heat fluxes dictate the quality of the baked product and the process efficiency. By mapping the applied fluxes with time a “baking comfort zone” can be established. The map can be developed to indicate minima and maxima flux values and/or to identify an optimal heating profile. The baking comfort zone for a given product provides a useful visual indicator, which can be related to a similar indicator of product responses to improve understanding of the baking process. Furthermore, provided adequate instrumentation is available, the baking comfort zone can be utilized (i) by the operator of an oven at the process control interface to ensure that an appropriate heating profile is being achieved in practice; and (ii) to replicate products in different ovens. This concept is based upon baking tests conducted on a high performance research oven manufactured by APV Baker (UK) and installed in their research centre in Peterborough England.
Numerical Study of Mixing in Microchannels With Patterned Zeta Potential Surfaces
Authors: Hong Seungbae , Thiffeault Jean-Luc , Fre´chette Luc G. , Modi Vijay
Published: May 2008

In a recent study, an effective means of mixing a low Reynolds number pressure-driven flow in a micro-channel was reported by Stroock et al. [10] using trenches on the lower wall that form a staggered herringbone pattern. In the present work numerical results are reported that indicate enhanced mixing using a similar herringbone pattern in the context of an electro-osmotically driven flow in microchannels. Instead of trenches, all walls are flush, making microfabrication easier. The lower wall would have lithographically deposited polymer coatings that exhibit a zeta potential of a sign opposite to that at the other walls. These coatings are chosen to form a herringbone pattern. If mixing can be achieved using purely electro-osmotic flows, then it becomes easier to scale the channel dimensions to smaller values without the penalty of a dramatic increase in pressure drop. Moreover, the possibility of mixing with purely electro-osmotic flows that do not require time varying electric fields leads to a simpler system with fewer moving parts. With current micro-fabrication techniques, it is difficult to produce periodic patterned coatings on all four walls of a rectangular microchannel. For this reason, this study limits its scope to coatings applied only on the lower surface of the microchannel, with a rectangular cross-section. Numerical simulations are used in order to elucidate the dominant mechanism responsible for mixing, which is identified as the blinking-vortex [3]. The flow regime chosen to illustrate these effects is the same as that used by Stroock et al. [10], characterized by Reynolds numbers that are O(10−2) and Pe´clet numbers that are of O(105). The presence of patterned zeta potentials in a microchannel violates conditions of ideal electro-osmosis [4] and hence the flows are necessarily three-dimensional. The efficiency of mixing is quantified by examining particle tracks at several downstream sections of the microchannel and averaging their concentration over boxes of finite size to model diffusion. It is found that the standard deviation of the concentration decays exponentially, and that the rate of decay is independent of the Pe´clet number when the latter is sufficiently large, indicating that chaotically-enhanced mixing is occurring.
On Proper Orthogonal Decomposition or K-L Expansion to Analyze Transient Sound Pressure Fields in Linear Acoustics
Authors: Georgiou Ioannis T. , Papadopoulos Christos I.
Published: May 2008

Identification of the most energetic spatio-temporal patterns that govern the low-frequency dynamics of an air cavity excited by noise sources could lead to significant design improvements of enclosures for noise reduction / isolation and / or sound quality. In this work we show how the Proper Orthogonal Decomposition (POD) method can be applied to identify optimum spatio-temporal patterns governing the dynamics of the sound pressure field developed inside an air cavity. The novel feature of this approach resides into the fact that the POD technique is utilized to process databases for acoustic variables produced by state of the art computational methods in acoustics, such as the finite element method. For a cavity with rigid walls and excited by a harmonic point source, the POD technique reveals that the sound pressure field is composed of a very small number of Proper Orthogonal Modes, which are unique since they are optimum by construction. The POD technique identifies the shapes or patterns of these modes.
2-D H-Adaptive Finite Element Method for Gas Gun Design
Authors: deBues Timothy T. , Pepper Darrell W. , Chen Yitung
Published: May 2008

The Joint Actinide Shock Physics Experimental Research (JASPER) facility utilizes a two-stage light gas gun to conduct equation of state experiments. The gun has a launch tube bore diameter of 28 mm, and is capable of launching projectiles at a velocity of 7.5 km/s using compressed hydrogen as a propellant. A numerical study is conducted to determine the effects that launch tube exit geometry changes have on attitude of the projectile in flight. A comparison of two launch tube exit geometries is considered. The first case is standard muzzle geometry where the wall of the bore and the outer surface of the launch tube form a right angle. The second case includes a beveled transition from the wall of the bore to the outer surface of the launch tube. An h-adaptive, Petrov-Galerkin finite element method is employed to model the axisymmetric compressible flow equations. Numerical solutions indicate that pressure variations occur on the back face of the projectile from case to case.
An Effective Unit Cell Approach to Compute the Thermal Conductivity of Composites With Cylindrical Particles
Authors: Ganapathy Deepak , Singh Kulwinder , Phelan Patrick E. , Prasher Ravi S.
Published: May 2008

This paper introduces a novel method to model the effective thermal conductivity of cylindrical-particle-laden composite materials. This modeling methodology is a combination of the effective medium theory and the finite differences method. Typically the curvature effects of cylindrical or spherical particles are ignored while calculating the thermal conductivity of composites containing such particles through numerical techniques. These particles are modeled as cuboids or cubes. Numerical modeling of circular/spherical geometries as cubes or cuboids will lead to wrong conclusions due to two reasons: (i) It does not capture the effect of curvature on heat flow, i.e., constriction of heat flux lines near the particles due to shape, (ii) It assigns higher effective conductivity to the particles as the cubes or the cuboids have larger volume and surface area. An alternative approach to mesh the particles into small volumes is just about impossible as it leads to highly intensive computational algorithms to get accurate results. On the other hand, effective medium theory takes the effect of curvature into account but it cannot be used at high volume fractions because it does not take into account the effects of percolation. In this paper, a novel model is proposed where the cylindrical particles are still treated as squares (cuboids) but to capture the effect of curvature, an effective conductivity is assigned to the particles by using the effective medium approach. The authors call this the effective unit cell approach. Results from this model for different volume fractions, on average, have been found to lie within ±5% of experimental thermal conductivity data.
Methodology for Selection of Rapid Tooling Process for Manufacturing Applications
Authors: Chung Chan W. , Hong Joon , Lee Alex , Ramani Karthik , Tomovic Mileta
Published: May 2008

Digital representation of geometry is transforming the methods for the manufacturing of products. Such transformations include a significant reduction in cost and leadtime to produce products and to increase the variety of products. The ability to produce tooling from material removal and additive processes has led to new methods to produce tooling from digital geometry representations. These include processes that are grouped together as fast-free-form-fabrication (FFFF) methods. In addition, other possibilities exist in modular tooling for generating variety and new processes/methods for producing such geometries. Also, conventional machining processes have improved significantly. As a result of these transformations, a tooling designer faces many choices of methods, materials, and lead-times to produce tooling. These decisions involve geometric reasoning coupled with other requirements based on production needs, cost constraints, and individual casting shop capabilities. This paper discusses a methodology for selection of rapid tooling (RT) processes based on a number of user-specified attributes and relative cost and lead-time comparisons across a wide spectrum of available RT processes. The method is based on a combination of weighted functionals and on the approximate mathematical models of metalcasting process costs and their lead-time. The method has been put on the Internet for easy access. It is currently limited to only several of the most common RT processes and materials. However, the database will be expanded in the future to include a majority if not all of the metalcasting processes.
Simultaneous Manipulator/Controller Design Optimization Using Multi-Objective Evolutionary Algorithms
Authors: Ravichandran T. , Heppler G. R. , Wang D. W. L.
Published: May 2008

A multi-objective design methodology that uses an evolutionary algorithm optimization process is presented and is applied to the simultaneous optimal design of a robotic manipulator/controller for performing point-to-point motion tasks. Dynamic performance measures, for the closed-loop system, are optimized by considering a nonlinear PD controller and quintic polynomial trajectories for point-to-point motions. Results of the simultaneous optimal design of a planar manipulator, a nonlinear controller, and some sample trajectories are presented to illustrate the efficacy of this methodology.
Rough Surface Effects on Film Cooling of the Suction Side Surface of a Turbine Vane
Authors: Bogard David G. , Snook Daniel , Kohli Atul
Published: May 2008

In-service turbine airfoils generally have surface roughness much greater than new airfoils due to deposition, erosion, and spallation. This surface roughness has the effects of promoting early transition and increasing surface friction and heat transfer rates. When film cooling is used on the airfoil, the surface roughness affects film cooling performance by changing the approach boundary layer flow, and by increasing the turbulent mixing downstream of coolant injection. Previous studies of surface roughness effects on film cooling performance have used flat surface wind tunnel facilities. The present study was unique in using a simulated vane test facility. Hence it is the first study of surface roughness effects on film cooling of a highly curved surface. In our experiments, effects of roughness upstream and downstream of coolant injection were studied. Combined effects of leading edge showerhead injection and high mainstream turbulence levels were also investigated. In this study, determination of the effects on film cooling performance was limited to measurements of adiabatic effectiveness. Each configuration was tested over a range of blowing ratios and with a density ratio of 1.6. In each case roughness caused a significant degradation in adiabatic effectiveness. Roughness was observed to have a much greater effect on adiabatic effectiveness on the vane geometry than previous studies had observed using flat surfaces.
Drop-Impact Reliability of Chip-Scale Packages in Handheld Products
Authors: Tian Guoyun , Liu Yueli , Lall Pradeep , Johnson R. Wayne , Abderrahman Sanan , Palmer Mike , Islam Nokib , Panchgade Dhananjay , Suhling Jeffrey , Crane Larry
Published: May 2008

The use of CSPs has expanded rapidly, particularly in portable electronic products. Many CSP designs will meet the thermal cycle or thermal shock requirements for these applications. However, mechanical shock (drop) and bending requirements often necessitate the use of underfills to increase the mechanical strength of the CSP-to-board connection. Capillary flow underfills processed after reflow, provide the most common solution to improving mechanical reliability. However, capillary underfill adds board dehydration, underfill dispense, flow and cure steps and the associated equipment to the assembly process. Corner bonding provides an alternate approach. Dots of underfill are dispensed at the four corners of the CSP site after solder paste print, but before CSP placement. During reflow the underfill cures, providing mechanical coupling between the CSP and the board at the corners of the CSP. Since only small areas of underfill are used, board dehydration is not required. This paper examines the manufacturing process for corner bonding including dispense volume, CSP placement and reflow. Drop test results are then presented. A conventional, capillary process was used for comparison of drop test results. Test results with corner bonding were intermediate between complete capillary underfill and non-underfilled CSPs. Finite element modeling results for the drop test are also included.
Optical (Camera-Based) Technology for Seismic Risk Assessment
Authors: Wischgoll Thomas , Hutchinson Tara C. , Kuester Falko
Published: May 2008

Due to an increasing bandwidth for data transport in recent computers, optical (camera-based) sensors with high frame rates and reasonable resolutions can nowadays be used with off-the-shelf computers. By monitoring buildings, bridges and other infrastructure with such sensors, they can greatly assist in risk assessment. In this paper, several field application examples are described, largely encompassing the areas of civil infrastructure monitoring. Optical (camera-based) systems can be particularly powerful for monitoring both local and global movements within a scene or environment. Therefore, natural hazards induced by such movements, for example during earthquake events, are an important application area for these new technologies. First, a clear definition of seismic risk assessment is provided. Subsequently, two important fields where cameras may be useful in seismic risk assessment are described. Specifically, the context of (i) early warning systems and (ii) post-earthquake assessment are addressed. An example of using the optical record from a series of large shake table tests is provided and comparison with other methods discussed.
The Effects of Grain-Refinement and Heat Treatment on the Properties of Ni-Alloys for LIGA Microsystems
Authors: Goods Steve , Graham Samuel , Kelly James
Published: May 2008

Electrodeposited Ni and Ni-alloys are being considered for use in a number of microelectromechanical systems (MEMS) applications employing LIGA processing technology. For these materials, research has shown that various organic and metallic alloying additives, often in combination with pulse plating techniques allows the development of microstructures with nanocrystalline to microcrystalline grain sizes [1–10]. This range of grain sizes yields widely varying material properties that may, at times, be exploited to tailor the performance of LIGA microsystems. In order to make use of this potential, a better understanding of the effect of processing on material properties such as elastic modules, yield strength, and electrical conductivity is required. In addition to analyzing the effects that material processing may have on initial properties of the nanostructured materials, it is also imperative to understand how exposures to thermal environments which may be seen in post-processing or service life may induce changes in these properties.
Error Causes and Magnitudes in Thermochromic Liquid Crystal Thermometry
Authors: Wiberg Roland , Lior Noam
Published: May 2008

This paper investigates experimentally and assesses the errors that may be incurred in the hue-based thermochromic liquid crystal (TLC) method, and their causes. The errors include response time, hysteresis, aging, surrounding illumination disturbance, direct illumination and viewing angle, illumination light intensity, TLC thickness, digital resolution of the image conversion system, and measurement noise. Some of the main conclusions are that (1) the 3×8 bits digital representation of the red, green and blue TLC color values produces a temperature measurement error of typically 1% of the TLC effective temperature range, (2) an 8-fold variation of the light intensity into the camera produced variations, which were not discernable from the digital resolution error, (3) this temperature depends on the TLC film thickness, (4) thicker films are less susceptible to aging and thickness nonuniformities.
Analysis of Transient Heat Transfer in a Microchannel Heat Exchanger During Magnetic Heating of the Substrate Material
Authors: Rahman Muhammad M. , Shevade Shantanu S. , Bethanabotla Venkat
Published: May 2008

The paper presents a systematic analysis of heat transfer processes during the heat up and cool down phases of a magnetic material when subjected to a magnetic field. As a first step towards the development of a MEMS magnetocaloric refrigerator for hydrogen liquefaction, a computer simulation of fluid flow and transient heat transfer in microchannels was carried out. The study considered microchannels with rectangular and square cross sections with heat generation in the substrate due to imposed magnetic field. The results computed were for gadolinium substrate and water as the working fluid. In order to achieve the liquefaction of a cryogen such as hydrogen, heat need to be removed from the working fluid by taking the advantage of the demagnetization of the material when the magnetic field is removed. The purpose of this study is to explore the transient heat transfer coefficient when the fluid is circulated through the substrate via microchannels. The application of the magnetic field was simulated by using the concept of volumetric heat source distributed uniformly over the entire solid material. Because of the relatively small size of the MEMS device, the magnetic field strength is expected to be uniform throughout the material. The strength of the source was calculated from energy balance during magnetization of the material. From the simulation results, plots of Nusselt number and heat transfer coefficient over the length of the channel as well as locally at different sections were obtained. A thorough investigation for velocity and temperature distributions were performed by varying channel aspect ratio, Reynolds number, and heat generation rate in the channel.
Oxygen Liquefier Using a Mixed Gas Refrigeration Cycle
Authors: Chakravarthy Vijayaraghavan , Weber Joe , Rashad Abdul-Aziz , Acharya Arun , Bonaquist Dante
Published: May 2008

This paper presents the design, selection of equipment, testing, and analysis of a 2 TPD (76 kg/hr) prototype oxygen liquefier that employs a mixed gas refrigeration cycle. Small scale oxygen plants (30–60 TPD) based on VPSA systems (Vapor Pressure Swing Adsorption) periodically require liquid back-up to provide uninterrupted supply of O2 gas to customers during planned plant maintenance. Supply of liquid for back-up, especially to customers in remote locations, is expensive and difficult. Economically designed MGR liquefiers will fulfill this market need. The 2 TPD prototype O2 liquefier is based on the dual loop MGR Rankine cycle (see Figure 1). The forecooler loop provides refrigeration at the warm end (233K). R507 is used as a refrigerant for the forecooler in the warm end loop. The main refrigeration loop uses a mixture of R218, R14 and N2. The main advantage of separating the refrigerants into two different loops is to avoid freezing of high boiling point refrigerants at liquid O2 temperatures in the main refrigeration loop. The process and mixture composition were optimized using the HYSYS process simulation package. Very useful insights were gained in terms of reducing the irreversibilities in the heat exchanger. Low cost innovative designs were adopted for the heat exchangers. For example: (1) plate-and-frame heat exchangers were successfully used for multiple gas streams, (ii) a spirally wound coiled heat exchanger was used to liquefy oxygen. Similarly, the compressors used in the forecooler and main cycle were low cost, off-the-shelf items used in conventional refrigeration systems. The liquefier unit was initially demonstrated and a liquid making capacity of 1.5 TPD at a unit power of 44 kW/TPD was achieved. Subsequent modifications to the heat exchangers resulted in meeting the design expectations at a unit power of 37 kW/TPD.
Development of a Silicon-Based Passive Gas-Liquid Separation System for Microscale Direct Methanol Fuel Cells
Authors: Hsieh C. C. , Yao S. C. , Alyousef Yousef
Published: May 2008

The design, fabrication, and performance characterization of a passive gas-liquid separation system is presented in this paper. The gas-liquid separation system is silicon-based and its fabrication is compatible with the existing CMU design of the microscale direct methanol fuel cell (DMFC). Both gas and liquid separators consist of staggered arrays of etched-through holes fabricated by deep reactive ion etching (DRIE). The gas separator is coated with a thin layer of hydrophobic polymer to substantiate the gas-liquid separation. To visually characterize the system performance, the gas-liquid separation system is made on a single wafer with a glass plate bonded on the top to form a separation chamber with a narrow gap in between. Benzocyclobutene (BCB) is applied for the low-temperature bonding. The maximum pressure for the liquid leakage of the gas separators is experimentally determined and compared with the values predicted theoretically. Several successful gas-liquid separations are observed at liquid pressures between 14.2 and 22.7 cmH2O, liquid flow rates between 0.705 and 1.786 cc/min, and CO2 flow rates between 0.15160 to 0.20435 cc/min.
Splice Loss Optimization of Single Mode Fiber and Erbium Doped Fiber—Experiments and Issues
Authors: Pradhan Salil , Arbulich John , Srihari K.
Published: May 2008

In metro and long haul networking applications, Erbium Doped Fiber Amplifiers (EDFAs) are used to amplify weak optical signals. Manufacturing of EDFAs is primarily a fusion splicing process in which both Single Mode Fibers (SMFs) and Erbium Doped Fibers (EDFs) are utilized. One of the critical operations is the splicing of an SMF to an EDF, a dissimilar fiber splicing process. Splice losses between these fibers need to be optimized, and the process is highly reliant on the properties of the EDF. Mode Field Diameter (MFD), spectral attenuation at peak wavelength and concentration of erbium along its length vary from batch to batch. The splice loss is dependent on some of these properties and must be taken into consideration. With this background, research was conducted to study the properties of EDFs and its applicability in the splicing process. Having considered the characteristics of the EDF in different wavelength regions, experiments were designed to optimize the losses between an SMF and an EDF. In the C-band (1525–1565 nm), erbium atoms absorb most of the transmitted power (in absence of a 980/1480 nm laser pump). Splice losses measured in these regions are dependent upon the absorption properties and would not depict a true picture of the splice loss. Since the incident power is absorbed, an alternate approach would be to launch extremely low power (<−27 dBm). In this case, the absorption losses should be minimal. As C-band is highly absorptive, launching power in the range of 1310 nm would be another possible scenario. The ‘cutback’ method was also employed to determine the losses in the C-band region. Statistical methods such as the Design of Experiments (DOE) were used to study the properties of the EDF and its response to various splicing parameters and wavelengths. Splice loss trends at various power levels were also investigated. The primary intent of these experiments was to translate the results and their utility into the manufacturing of EDFAs, wherein a multitude factors creep into the splicing scenario. The best method would be the one that consistently yields a low splice loss, since these are critical to minimize the noise figure of the EDFA.
A Mechanics Model of Skin Penetration
Authors: Shergold Oliver A. , Fleck Norman A.
Published: May 2008

Experiments are performed to show that sharp-tipped needles and high pressure liquid jets pierce skin and silicone rubbers by a similar penetration mechanism. The solid tears to form a crack, which opens to accommodate the punch. A model is presented for the penetration of soft solids, such as skin and rubber, by a sharp-tipped punch. Both the model and the experiments reveal that to penetrate the solid, the average pressure across the punch tip increases with diminishing punch radius. It is also shown that the penetration pressure increases for tougher solids with stronger strain hardening capacities.
Forecasting Manufacturing Quality and Optimizing Product Robustness Using Process Capability Data
Authors: Kern Daniel , Du Xiaoping , Sudjianto Agus
Published: May 2008

A company’s success is highly dependent on its ability to manufacture quality products. Designing products that can be manufactured to meet customer needs with an acceptable level of variation is challenging because design engineers are often unfamiliar with the company’s manufacturing capability or are unable to effectively use the capability data to improve a design. The authors present an approach to forecast the manufacturing quality of a product and optimize its robustness while it is being designed. The system comprises a database that stores process capability data and simulation models to simulate process capability data when actual, appropriate data are nonexistent. These data and tools are used with a new probabilistic approach through the inverse reliability strategy to optimize the robustness of a design by locating values of design parameters that enhance the performance of the design and are insensitive to manufacturing variation. Design engineers can use this approach to set design parameter values that will improve the functionality of the product while ensuring it can be produced with high capability. This approach is demonstrated with a design example of an engine valvetrain.
Transmission Microscopic Moire´ Interferometry for Nanoscale Deformation Measurements
Authors: Han C. W. , Cho S. , Han B.
Published: May 2008

Moire´ interferometry is a full-field optical method that has high displacement, strain and spatial resolution. The method has been used extensively for deformation analyses in the various fields of mechanics. Special considerations arise when deformation measurements of tiny specimens or tiny regions of larger specimens are sought. The relative displacements within a small field of view will be small (even if the strains are not small), so the number of morie´ fringes might not be enough for an accurate analysis.
Application of Various Combustion Models to a Generic Combustor
Authors: Jiang Lei-Yong , Campbell Ian
Published: May 2008

The flow-field of a generic gas combustor with interior and exterior conjugate heat transfers was numerically studied. Results obtained from three combustion models, combined with the re-normalization group (RNG) k-ε turbulence model, discrete ordinates radiation model, and partial equilibrium NOx model are presented and discussed. The numerical results are compared with a comprehensive database obtained from a series of experimental tests. The flow patterns and the recirculation zone length are excellently predicted, and the mean axial velocities are in fairly good agreement with the experimental measurements, particularly at downstream sections for all three combustion models. The mean temperature profiles are also fairly well captured by the probability density function (PDF) and eddy dissipation (EDS) combustion models. The EDS-finite-rate combustion model fails to provide acceptable temperature field. In general, the PDF shows some superiority over the EDS and EDS-finite-rate models. NOx levels predicted by the EDS model are in reasonable agreement with the experimental measurements.
Wire Bond Failures in Power Modules
Authors: Ramminger S. , Wachutka G.
Published: May 2008

Power modules are key components for traction applications, railway locomotives, streetcars and elevators, all of which are equipped with Insulated Gate Bipolar Transistor (IGBT) modules. In this application field, a highly reliable system is of uppermost interest. Reliability tests show that wire bonding and soldering may cause the modules to fail. The packaging setup is a multilayer system in which different materials are soldered together. During a temperature swing caused by self-heating and/or by changes in the ambient temperature, the layers expand differently. This generally causes shear forces at the terminations of joint interfaces finally leading to material fatigue and shorter life. In this paper, we give an overview of the wire bonding technique used in power modules and discuss the mechanisms and failure modes associated with it.
Determination of Temperatures and Heat Fluxes on Surfaces and Interfaces of Multi-Domain Three-Dimensional Electronic Components
Authors: Dennis Brian H. , Han Zhen-Xue , Dulikravich George S.
Published: May 2008

A finite element method (FEM) formulation for the prediction of unknown steady boundary conditions in heat conduction for multi-domain three-dimensional solid objects is presented. The FEM formulation is capable of determining temperatures and heat fluxes on the boundaries where such quantities are unknown, provided such quantities are sufficiently over-specified on other boundaries. An inverse finite element program has been previously developed and successfully tested on 3-D simple geometries. The finite element code uses an efficient sparse matrix storage scheme that allows treatment of realistic three-dimensional problems on personal computer. The finite element formulation also allows for very straight-forward treatment of geometries composed of many different materials. The inverse FEM formulation was applied to the prediction of die junction temperature distribution in a simple ball grid array (BGA) electronic package. Examples are presented with simulated measurement that include random measurement errors. Regularization was applied to control numerical error when large measurement errors were added to the over-specified boundary conditions.
Structural Health Monitoring for Rotating Imbalance and Misalignment
Authors: Mattson S. G. , Pandit S. M. , Kubow S. A.
Published: May 2008

The dynamics of rotating machinery are dominated by responses due to shaft and drive train characteristics such as imbalance, misalignment, gear mesh, and bearings. These phenomena occur a fixed number of times every revolution, and are related to rotational speed. This paper presents a new method for condition monitoring of such phenomena. An autoregressive model used for condition assessment is fit to the pulse signal. Decomposition of the model yields its characteristic roots, which contain the frequency, damping value, and variance of the signal component. The model also provides an analytical spectrum yielding clear spectral peaks with extremely accurate levels. The illustrated results are based on an experiment built to simulate a rotating imbalance, shaft misalignment, or a combination of the two. Three areas of improvement are identified. The first is characterization of extra information in the speed signal, eliminating the need for an added measurement that must be related to the speed. The second development is a single number estimate of energies at defect frequencies, eliminating subjective interpretation of spectral plots. The third enhancement is the technique’s ability to make accurate spectral estimates based on limited data, allowing the technician to handle situations where rapid speed changes are unavoidable.
Teaching Environmentally Benign Manufacturing
Authors: Gutowski Timothy G.
Published: May 2008

Teaching Environmentally Benign Manufacturing (EBM) presents the general challenges of teaching an application rather than a discipline. This is not too different from the challenges of teaching manufacturing about ten years ago. In that case we could rely heavily on successful practice and then develop principles to explain those successes. The principal success at that time was the Toyota Production System. Even today people continue to observe and write about why it works and its limitations [1, 2, 3].
Thermo-Optical Behavior of Passively-Cooled Polymer Waveguides
Authors: Kim Kyoung-Joon , Bar-Cohen Avram
Published: May 2008

Polymer waveguides offer considerable promise as cost-effective transmission channels for optical signals. However, thermo-optic effects induced by the intrinsic absorption of light in the waveguide material can compromise their performance. The present study seeks to define the thermo-optical issues in Bragg grating polymer waveguides, including the effects and relative importance of temperature change, thermal strain, and thermally-induced stresses. Analytical and numerical solutions are obtained for the temperature, strain, and stress fields in the core of a polymer waveguide, heated by intrinsic light energy absorption, and used to evaluate the resulting Bragg wavelength shift and reflectivity variance.