bluuebunny/crossref_metadata_2025 huggingface dataset:
Cooling Performance of Plain-Plate-Fin Heat Sinks With Slot Jet Impingement
Authors: Wu M. C. , Lee Y. C. , Peng C. H. , Fang C. J. , Hung Y. H.
Published: April 2008

An experimental investigation on the thermal performance of slot jet impinging onto fully-confined and partially-confined heat sinks with plain-plate fins (ppf) is presented. The relevant parameters influencing the convective cooling performance with slot jet impingement include the ratio of heat sink height to jet separation distance (Hs/H), ratio of heat sink height to nozzle width (Hs/Wj) and jet Reynolds number (Rej). The thermal performance of fully-confined ppf heat sinks (Hs/H=1) is experimentally investigated. Besides, an effective theoretical model based on a developing channel flow with an impinging effect is successfully proposed to predict the average Nusselt numbers of fully-confined ppf heat sinks. Furthermore, a new correlation of average Nusselt numbers in terms of Hs/Wj and Rej is proposed for the cases of fully-confined ppf heat sinks. For partially-confined cases, a normalized Nusselt number, [Equation]Nuj/[Equation]Nuj,Hs/H=1, is showed only dependent on Hs/H in the present study. A new correlation of [Equation]Nuj/[Equation]Nuj,Hs/H=1 in terms of Hs/H is proposed. This result manifests that the Nusselt numbers of partially-confined ppf heat sinks can properly be evaluated with the Nusselt numbers of fully-confined heat sinks and the normalized [Equation]Nuj/[Equation]Nuj,Hs/H=1 ratios. Finally, a generalized correlation of average Nusselt numbers in terms of Hs/H, Hs/Wj and Rej, which can be applied to both fully-confined and partially-confined heat sinks, is proposed. The maximum and average deviations between the correlations and the experimental data are 19.7% as well as 4.6%, respectively.
Pressure Drop and Heat Transfer Characteristics for Partially-Confined Heat Sinks in Ducted Flow
Authors: Chen H. T. , Wu T. Y. , Chen P. L. , Chang S. F. , Hung Y. H.
Published: April 2008

The pressure drop and heat transfer characteristics for partially-confined heat sinks with different fin types, including plain-plate fin, pin-fin array and strip-fin array, in ducted flow are investigated. The main focus of the experimental results is on pressure drop and heat transfer characteristics of generalized heat sink in ducted flow with considering the flow top- and side-bypass effects. The parameters controlled in the study are the heating load (Qt), inlet flow velocity (Ui), the ratio of heat sink height to duct height (Hs/Hc), and the ratio of heat sink width to duct width (Ws/Wc). The ranges of parameters studied are Ui=2~12m/s, Qt=10~30W, Ws/Wc = 0.6~1, and Hs/Hc = 0.5~1. In the present study, an effective friction factor related to the overall pressure drop is defined; and a new experimental correlation for the effective friction factor for generalized heat sinks in ducted flow with top- and side-bypass effects is presented. A satisfactory agreement between the experimental data and the theoretical predictions is achieved with the maximum and average deviations of 17.2% and 9.6%, respectively. As for convective heat transfer performance, the average Nusselt number is not significantly affected by Grashof number; while, it increases significantly with increasing Reynolds number. Furthermore, the thermal performance increases with increasing top or side confinement ratio (Hs/Hc or Ws/Wc). The best thermal performance occurred at the fully-confined condition, i.e., Hs/Hc=1, Ws/Wc = 1. Based on all the experimental data for three types of partially-confined heat sinks, a generalized correlation of average Nusselt number for partially-confined heat sinks in ducted flow in terms of Re, Hs/Hc and Ws/Wc is presented. The maximum and average deviations of the results obtained by the experimental data from the theoretical prediction are 12.4% and 7.5%, respectively.
Phase-Field Modeling of Microstructure Formation of Polycrystalline Materials in Various Cooling Conditions
Authors: Shu Y. , Li B. Q.
Published: April 2008

This paper presents a discontinuous finite element computational framework for the numerical solution to the phase-field equations during the solidification of polycrystalline materials. An important feature of the discontinuous method is that the continuity across the elements within the calculation domain is only weakly enforced, rather than rigorously enforced as done in conventional finite element method. The mathematical formulation and computational implementation are briefly described. Numerical simulations are conducted to study the interactions between the grains and the nuclei that are initially located close to or away from the boundary of the bulk grain. The phase-field evolutions during solidification in various cooling conditions are presented. Results indicate the dependence of grain growth behavior and its interface morphology on the undercooling temperature suppressed to the liquid pool. And this dependence is not so much related to the distance between the grain and nuclei.
Spatial Resolution Enhancement and Reconstruction of Mixed Convection Data Using Kriging Method
Authors: Cekli H. E. , Gunes H.
Published: April 2008

In this paper we investigate the use of Kriging method in order to reconstruct and enhance the resolution of mixed convection data. Direct numerical solutions are performed for mixed convection in a two-dimensional partially open rectangular cavity with a flush-mounted discrete heat source on a heat conducting vertical board. An external airflow enters the cavity through an opening in the left vertical wall and exits from the opposite opening in the right vertical wall. Kriging is a statistical tool useful in many disciplines such as geology, thermo-fluid systems, process engineering, environment and medicine. Kriging is used to estimate unknown values from data observed at known locations. A variogram is usually constructed to account for the spatial variation of known data. Kriging gives an unbias estimate for the unknown value using a weighted linear combination of the available data. In this paper, we investigate the capabilities of Kriging procedure for transitional mixed convection flows. Particularly, the effect of various types of variograms (e.g. polynomial, exponential and spherical functions, etc.) on the effectiveness of the Kriging procedure has been studied in detail. The use of Kriging for the resolution enhancement and for the reconstruction of large missing zone (black zone) is investigated. It is found that the gappy data for both periodic and non-periodic (quasi-periodic) flows can be remarkably recovered by the method. While we apply the method for DNS data in order to assess its effectiveness, the method should be particularly very useful for experimental data, where some enhancement/smoothing is generally required.
A New Type of Nanoengineered Heat Transfer Fluids: Nanoemulsion Fluids
Authors: Yang Bao , Han Zenghu
Published: April 2008

Thermal management in the next decade of microelectronics and optoelectronics will require heat transfer fluids with improved performance over those currently available. The strategy of adding SOLID particles to fluids for improving thermal conductivity has been pursued for nearly a century. In this work, a novel concept of using LIQUID nanodroplets for enhancing thermal conductivity has been developed and was experimentally-demonstrated in water-in-FC72 suspensions, called "nanoemulsion-fluids". The thermal conductivity of FC72 is found to be increased by up to 52% for a nanoemulsion-fluid containing 12vol% water nanodroplets of radius 9.8nm. Such types of nanoemulsion-fluids possess long-term stability and can be mass produced because of no needs for SOLID nanoparticles. The development of nanoemulsion-fluids would open a new direction for thermal fluids studies.
Convective Heat Transfer With Nanofluids in a Single 1.02-mm Tube
Authors: Lai W. Y. , Duculescu B. , Phelan P. E. , Prasher R. S.
Published: April 2008

Nanofluids are heat transfer liquids which contain small volume fractions of suspended nanoparticles, with sizes smaller than 100 nm, in colloidal solutions. Numerous experiments on the static thermal conductivity of these fluids have revealed a greater-than-expected effective thermal conductivity, and thus there is interest in utilizing nanofluids for heat transfer applications. The nanofluid thermal performance under convective heat transfer conditions is of even greater interest. Therefore, we report here our initial convection experiments with nanofluids. Our experimental test section consists of a single millimeter-size, stainless steel tube subjected to constant wall heat flux. The cooling nanofluids, flowed through the test tube, consist of Al2O3 nanoparticles and deionized water. Both wall temperature and fluid temperature are measured. Compared with base fluid, the Nu of 20-nm Al2O3-deionized water nanofluids had 8% enhancement for φ = 1 vol% but only 3% for φ = 0.5 vol% at Re = 270. Based on the results, the utility of convective heat sinks containing nanofluids are evaluated for contemporary uses.
Thermal Conductivity Measurement of Aluminum Oxide Nanofluids Using the 3-Omega Method
Authors: Oh Dong-Wook , Jain Ankur , Eaton John K. , Goodson Kenneth E. , Lee Joon Sik
Published: April 2008

Nanofluids, which are suspensions of nano-sized solid particles in a liquid medium, show remarkable enhancement in thermal conductivity compared to the base fluid. Nanofluids are a promising candidate for advanced heat transfer applications such as microelectronics cooling. While the thermal conductivity of nanofluids has been measured in the past using conventional techniques such as the transient hot wire method, this work presents the application of the 3-omega (3-ω) method for this purpose. The theoretical model for 3-ω response of a heater device with de-ionized (DI) water is verified by comparing with experimental measurements. Following this validation, the effective thermal conductivity of Al2O3 nanofluids in DI water and ethylene glycol are measured. The measured values are found to be in good agreement with previous works. In addition, interesting effects in the thermal response due to agglomeration and sedimentation of nanoparticles are observed.
Fire Safety Concern for Green or Sustainable Buildings With Natural Ventilation Provision
Authors: Chow W. K.
Published: April 2008

New architectural concepts and features are designed to give green or sustainable buildings for having a better environment in the future. These new concepts and features, especially those with glass facades, might have difficulties in complying with the fire safety codes, especially in those countries with only prescriptive codes. Performance-based design has to be applied. However, engineering performance-based fire codes are still under development and even the performance-based concept has not yet been accepted in some cities such as Hong Kong. There is fire safety concern in buildings with natural ventilation provision driven by wind action. In this paper, Computational Fluid Dynamics (CFD) will be applied to study natural ventilation in a small flat under wind action. Indoor air flow for a flat in a typical building will be simulated for windows at different locations. Mixing of heat due to a fire inside the building will be studied. The CFD tool selected is PHOENICS.
Flow and Heat Transfer Analysis Through a Brake Disc: A CFD Approach
Authors: Reddy S. Manohar , Mallikarjuna J. M. , Ganesan V.
Published: April 2008

This paper describes the numerical simulation of the flow and heat transfer around a ventilated brake disc. The aim of this investigation is to provide more insight on ventilated brake disc flow phenomena with a view to improve heat dissipation. Analysis of brake disc has been carried out using FLUENT (CFD code based on the Finite Volume Method). Numerical predictions of the flow and heat transfer are compared with available experimental data in the literature [2]. In the present work validation of numerical results are discussed in two parts. In the first part, the optimum grid was found from the grid independence test and in the second part the effect of turbulence models on flow field development was studied. Three rotors have been considered with each of 36, 40 and 45 number of vanes. Each rotor of two flow passages has been considered for the analysis. An isothermal analysis has been carried out to analyse the heat transfer. From the grid independence test it was found that the grid with 300,000 cells is seems to be the appropriate. SST k-ω turbulence model was able to predict the flow field with an accuracy of 3% and 1% in predicting tangential velocity and radial velocity respectively. From the isothermal rotor analysis it is found that the geometry having 45 vanes dissipates 7.7% and 5% more heat compared to geometries having number of vanes 36 and 40 respectively.
Submicron Thermal Imaging of High Power Slab Coupled Optical Waveguide Laser (SCOWL)
Authors: Chan Paddy K. L. , Sathe Amul D. , Pipe Kevin P. , Plant Jason J. , Swint Reuel B. , Juodawlkis Paul W.
Published: April 2008

Nonradiative power dissipation within and near the active region of a high power single mode slab coupled optical waveguide laser is directly measured by CCD-based thermoreflectance, including its variation with device bias. By examining the high spatial resolution temperature profile at the optical output facets, we quantify heat spreading from the source in the active region both downward to the substrate and upward to the metal top contact.
The Miniaturization of a Refrigeration Vapor Compression System and Application to the Cooling of High Power Microelectronics
Authors: Chiriac Victor , Chiriac Florin
Published: April 2008

The study develops an analytical model of an optimized small scale refrigeration system using ejector vapor compression, with application to the cooling of the electronic components populating a Printed Circuit Board (PCB) in a High-Power Microelectronics System. The authors' previous studies [1 - 3] evaluated a vapor compression system using an off-the-shelf mechanical compressor and associated components, focusing mainly on the thermal feasibility of the mechanical refrigeration system and on-chip system-level incorporation. Present investigation focuses on the miniaturization of the various components of the vapor compression system (targeting the alternative ejector vapor compressor), with the intent to establish a cooling system for high power microelectronics, designed to fit smaller packages populating PCB, yet using a different approach for the vapor compression process. The previous study [1] evaluated several optimized evaporator designs for the mechanical compression system. The current design with miniaturized ejector is evaluated to address similar power dissipation ranges as before. In the final section of the study, the efficiency of the proposed ejector vapor compression system is compared to mechanical compression designs at same cooling powers. It is the intent of the authors to present an alternative vapor compression system and identify the pros and cons of implementing such a system to real-life microelectronics applications.
Simulation of Flow, Heat and Mass Transfer in a Curing Oven
Authors: Soni Somesh , Neeley Thomas S. , Murthy Jayathi Y.
Published: April 2008

Flow, heat and mass transfer in a paint curing oven are studied numerically with a view to improving the energy efficiency of the oven and to control pollution. Painted products traverse the paint curing oven at a constant rate and in a fixed trajectory, and are heated by hot air jets which control the part temperature to ensure paint curing. Steady simulations are performed to compute the air flow and temperature fields. Computed air temperatures match experimentally measured values to an accuracy of 19% (temperatures calculated relative to the room temperature). Assuming thermal equilibrium between the painted part and the local gas flow, positiondependent smoke release rates due to paint curing are computed from the part temperature using experimentally measured cure rates. Smoke is modeled as a gas-phase species in a dilute mixture with air and its concentration and distribution in the oven are computed. The thermal behavior of the oven is captured in a parameter called the thermal performance index. The exhaust air mass flux is shown to have large impact on this index. Smoke loss to the outside environment is computed to quantify the degree of pollution. The impact of air seals on the thermal performance index and smoke release to the environment are quantified. Finally the effect of the thermal mass of the parts is considered and the convective and radiative effects are studied.
Modeling and Testing a Cold Plate
Authors: Wilcox Bryan R. , Mueller Donald W. , Abu-Mulaweh Hosni I.
Published: April 2008

The objectives of this work were to build and test a liquidcooled cold plate, and then to develop a numerical model to describe the thermal characteristics of the cold plate. An important parameter of interest was the total thermal resistance of the cold plate which is defined as the maximum temperature difference divided by the net heat flow rate. A cold plate was constructed by machining nine parallel, rectangular channels into an aluminum base (1.65 cm × 7.6 cm × 40 cm) upon which an aluminum cover plate was then welded. Twelve thermocouples were used to measure the temperature of the plate (surface and fin tip) and the circulating fluid at the inlet, outlet, and mid-plane. The working fluid was a 50/50 ethylene glycol-water mixture. Three heater blocks were mounted to the cold plate, and the assembly was insulated so that heat loss to the surroundings was minimized. Four runs were performed with flow rates ranging from 56 g/s to 95 g/s, and after steady-state conditions were reached the temperatures were recorded. Using these temperature measurements, the total thermal resistance was calculated. The thermal resistance of the cold plate was also calculated using a one-dimensional numerical model; agreement between the experimental measurements and model predictions is good. The methods described and results presented in this paper are useful to applied thermal engineers.
System Level Thermal Performance Evaluation of New Inverted Exposed Pad Packages for Automotive Applications
Authors: Chiriac Victor Adrian , Lee Tien-Yu Tom
Published: April 2008

An extensive 3-D conjugate numerical study is conducted to assess the thermal performance of the novel 54 lead SOIC (with inverted exposed Cu pad) packages for automotive applications. The thermal performance of the modified designs with exposed pad are investigated, ranging from smaller die/flag size to larger ones, with single or multiple heat sources operating under various powering conditions. The thermal performance is compared to other existing packages with typical application to the automotive industry. The impact of the lead frame geometrical structure and die attach material on the overall thermal behavior is evaluated. Under one steady state (4W) operating scenario, the package reaches a peak temperature of 117.1°C, corresponding to a junction-to-heatsink thermal resistance Rjhs of 4.27°C/W. For the design with a slightly smaller Cu alloy exposed pad (Cu Alloy), the peak temperature reached by the FETs is 117.8°C, slightly higher than for the design with the intermediate size flag. In this case, the junction-to-heatsink thermal resistance Rj-hs is 4.45°C/W. The worst case powering scenario is identified, with 1.312W/FET and total power of 10.5W, barely satisfying the overall thermal budget. The variation of the peak (junction) temperature is also evaluated for several powering scenarios. Finally, a comparison with a different exposed pad package is made. The impact of the higher thermal conductivity (solder) die attach is evaluated and compared to the epoxy die attach in the 54 lead SOIC package. Several cases are evaluated in the paper, with an emphasis on the superior thermal performance of new packages for automotive applications.
Design Methodology for Branching Fluid Network Heat Sinks
Authors: Moreno R. M. , Tao Y.-X.
Published: April 2008

In this paper recent works from the areas of entropy generation minimization and constructal theory are extended and combined with previous works from the area of physiological transport geometry prediction. From this a design methodology is developed which can be applied to branching fluid networks having the objective of maximizing the removal of heat from a given volume while minimizing the pumping power required. The methods are essentially a set of equations that serve as a resource for designers incorporating branching fluid networks as components within fluid-thermal systems that have the goal of transferring and remove heat while minimizing the entropy generation or destruction of available work.
Energy Flow in the Information Technology Stack: Introducing the Coefficient of Performance of the Ensemble
Authors: Patel Chandrakant D. , Sharma Ratnesh K. , Bash Cullen E. , Beitelmal Monem H.
Published: April 2008

The information technology industry is in the midst of a transformation to lower the cost of operation through consolidation and better utilization of critical data center resources. Successful consolidation necessitates increasing utilization of capital intensive "always-on" data center infrastructure, and reducing the recurring cost of power. A need exists, therefore for an end to end physical model that can be used to design and manage dense data centers and determine the cost of operating a data center. The chip core to the cooling tower model must capture the power levels and thermo-fluids behavior of chips, systems, aggregation of systems in racks, rows of racks, room flow distribution, air conditioning equipment, hydronics, vapor compression systems, pumps and heat exchangers. Earlier work has outlined the foundation for creation of a "smart" data center through use of flexible cooling resources and a distributed sensing and control system that can provision the cooling resources based on the need. This paper shows a common thermodynamic platform which serves as an evaluation and basis for policy based control engine for such a "smart" data center with much broader reach - from chip core to the cooling tower. Computational Fluid Dynamics modeling is performed to determine the computer room air conditioning utilization for a given distribution of heat load and cooling resources in a production data center. Coefficient of performance (COP) of the computer room air conditioning units, based on the level of utilization, is used with COP of other cooling resources in the stack to determine the COP of the ensemble. The ensemble COP represents an overall measure of the performance of the heat removal stack in a data center.
Optimal Ratio of Heat Removal Rate to Pumping Power for PCM Emulsion Fluids: Low Reynolds Number Limits
Authors: Maloji P. , Tao Y.-X.
Published: April 2008

There are many applications where high heat transfer removal rate in a limited tight space are required. The applications include mini and micro-scale channels flows in compact heat exchangers. The increase in heat transfer rate often requires the significant increase in fluid velocity and therefore the increase in the pumping power. One option is to utilize Phase Change Materials (PCM). This study contributes to the further understanding of performance enhancement of an improved heat transfer fluid by studying the optimal ratio of heat removal rate to the fluid pumping power. PCMs have the unique characteristics that can increase the thermal capacity of heat transfer fluids by providing latent heat capacity at a temperature different than the melting point of the carrier fluid. The ratio of heat transfer rate (Q) to fluid pumping power (P) is about twice as that for using pure water without PCM particles. The effectiveness factor (compared to water without PCM) is also doubled. It has been observed that as Re decreases the effective factor increases and Q/P ratio increases, which is also true if the concentration of PCM increases. In this experimental study focuses are on the heat transfer enhancement effects for very low Reynolds number (Re < 180 of pure water velocity) and PCM concentration slurry flow of 10% to 20%. Experimental investigations relevant to PCM slurry flows are carried out. Experimental results indicate that PCM slurry's heat transfer coefficient and apparent specific heat are affected significantly by the phase change process and the slurry mass fraction. It is found that the Q/P ratio primarily is a function of Reynolds number.
Evaluation of Energy Usage for a Teaching and Research Complex
Authors: Feng M. , Tao Y.-X. , Inclan E. , Bartra R.
Published: April 2008

The evaluation of energy performance for a teaching and research complex located in South Florida was carried out by auditing the energy bills, on-site data monitoring, and numerical simulation by computer. To facilitate the process of on-site data monitoring, a remotely controlled, wireless thermal monitoring system was deployed in the building. The system can automatically collect the temperature, relative humidity ratio, illumination intensity, and building electricity usage data for analysis. The contribution and savings potential of each energy consumption component is analyzed for the whole building. From the audit result it is obvious that laboratory equipment is the dominant electricity consumption factor. The fluctuation pattern of electricity usage due to artificial lighting demonstrates the effectiveness of occupancy sensors for energy saving during evenings, weekends and holidays. The trend of HVAC chilled water consumption rate follows closely with the indoor and outdoor temperature difference. Since the HVAC coil load represents the building's total cooling requirement, the ratio between chilled water rate and temperature difference reflects the building's comprehensive thermal resistance. This coefficient can be used as a new building energy index for future energy audits of similar buildings. Finally, computer software simulates several proposed energy saving scenarios, e.g. reducing the HVAC fresh air percentage, adding energy wheel to recycle the wasted cooling, etc. The result shows that installing energy wheel can save more cooling load than other methods, however such benefit is compromised by its extra motor electricity usage.
Heat Transfer Enhancement of Separated Convection Flow Adjacent to Backward-Facing Step With Baffle
Authors: Nie Jianhu , Chen Yitung , Sun Lijian , Hsieh Hsuan-Tsung
Published: April 2008

Simulations of three-dimensional laminar forced convection adjacent to inclined backward-facing step in rectangular duct are presented to examine effects of the baffle on flow and heat transfer distributions. The step height is maintained as constant. A baffle is mounted onto the upper wall and its distance from the backward-facing step is varied. The inlet flow is hydrodynamically steady and fully developed with uniform temperature. The bottom wall is heated with constant heat flux, while other walls are maintained as being thermally adiabatic. Velocity, temperature, Nusselt number, and friction coefficient distributions are presented. A baffle mounted onto the upper wall increases the magnitude of maximum Nuselt number at the stepped wall. One segment of the xu-line developing close to the backward-facing step becomes shorter with the decrease of the distance of the baffle from the backward-facing step. It becomes more relatively uniform in the spanwise direction as the distance decreases. The other segment developing adjacent to the sidewall moves further downstream as the baffle moves in the streamwise direction. The maximum Nusselt number does not appear at the center of the duct, as one may expect. It develops near the sidewall, and it moves further downstream as the location of the baffle moves in the streamwise direction. The friction coefficient at the stepped wall decreases as the distance of the baffle from the inlet increases.
A Methodology for Blast Furnase Hearth Wear Analysis
Authors: Zhang Yu , Deshpande Rohit , Huang D. , Chaubal Pinakin , Zhou Chenn Q.
Published: April 2008

The wear of a blast furnace hearth and the hearth inner profile are highly dependent on the liquid iron flow pattern, refractory temperatures, and temperature distributions at the hot face (the interface between the liquid iron and refractory or the skull). A 3-D CFD hearth model has been developed for predict the hearth erosion and its inner profile. The detailed computation results show that the hot face temperature is location dependant. Based on these discoveries, a new methodology along with new algorithms is established to calculate the hearth erosion and its inner profile. The methodology is to estimate the hearth primary inner profile based on 1-D heat transfer, and to compute the hot face temperature using the 3-D CFD hearth model according to the 1-D pre-estimated and re-estimated profiles. After the hot face temperatures are converged, the hot face positions are refined by a new algorithm, which is based on the difference between the calculated and measured results. The finalized CFD prediction temperatures are in good agreement with the experimental results except at or near the corner and taphole regions. In this paper, the detailed methodology and the new algorithm are presented along with the examples of hearth erosion and inner profile predictions.
New Electrochemical Cell Designs and Test Methods for Corrosion Testing of the Components in Integrated Circuit Liquid Cooling Systems
Authors: Chang Je-Young , Kim Choong-Un , Michael Nancy , Pathangey Balu , Gwin Paul , Prasher Ravi
Published: April 2008

This paper introduces new electrochemical cells and testing methods that are ideal for characterizing corrosion risk assessment of the components used for liquid cooling system with high surface to liquid volume ratio. Two cell configurations are described in this paper and they use three electrode and two electrode cells. These cells have the identical structure except for the number of electrodes. These cells are made by sandwiching the working electrode plate (sample) and the counter electrode plate (graphite) with a spacer (gasket), and by filling the cavity with the liquid under interest. In case of the three-electrode cell, the reference electrode is inserted through the hole in the graphite. The three-electrode cell is ideal for the quantitative characterization of the corrosion rate by utilizing conventional electrochemical techniques such as a Tafel method. The use of the two-electrode cell is similar to the case of the galvanic corrosion characterization as it measures the cell current that flows between the dissimilar metals that are in contact with the liquid. When coupled with computer assisted data acquisition, the two-electrode cell configuration allows the characterization of long-term corrosion reliability of a component with a variation in a large number of test variables. It is particularly useful in finding corrosion inhibitors.
Simulation of Random Packing of Spherical Particles With Different Size Distributions
Authors: Shi Yu , Zhang Yuwen
Published: April 2008

A numerical model for a loose packing process of spherical particles is presented. The simulation model starts with randomly choosing a sphere according to a pre-generated continuous particle-size distribution, and then dropping the sphere into a dimension-specified box, and obtaining its final position by using dropping and rolling rules which are derived from similar physical process of spheres dropping in the gravitational field to minimize its gravity potential. Effects of three different particle-size distributions on the packing structure were investigated. Analysis on the physical background of the powder-based manufacturing process is additionally applied to produce optimal packing parameters of bimodal and Gaussian distributions to improve the quality of the fabricated parts. The results showed that higher packing density can be obtained using bimodal size distribution with particle-size ratio from 1.5 to 2.0 and the mixture composition around n2:n1=6:4. For particle size with a Gaussian distribution, the particle radii should be limited in a narrow range around 0.67 to 1.5.
Coupled Quantum-Scattering Madeling of Thermoelectric Properties of Si/Ge/Si Quantum Well Structures
Authors: Bulusu A. , Walker D. G.
Published: April 2008

Confined structures presumably offer enhanced performance of thermoelectric devices. 1) Interfaces and boundaries create scattering sites for phonons, which reduces the thermal conductivity. 2) Reduced dimensionality increases the local density of states near the Fermi level, which increases the Seebeck coefficient. From these two phenomena, the net effect should be an increase in ZT, the performance parameter used to evaluate different materials and structures. These effects have been measured and modeled, but none of the models attempts to quantify the electron-phonon coupled effects particularly in the regime where quantum and scattering influences are found. Using the non-equilibrium Green's function (NEGF) approach, quantum wells composed of Si and Ge are studied and the important physics isolated. Results show a competing effect between the decrease in the electrical conductivity due to scattering with the increase in electrical conductivity with doping, leading to 77% decrease in the value of the power factor for the case of electron-optical phonon scattering.
Integrated Multidisciplinary Design and Optimization Methodologies in Electronics Packaging: State-of-the-Art Review
Authors: Suwa Tohru , Hadim Hamid
Published: April 2008

Electronic packaging design is a process that requires optimized solutions based on multidisciplinary design tradeoffs, which usually have complicated relations among multiple design variables. Required numerical analyses such as thermal and thermo-mechanical have hampered this multidisciplinary optimization process because of their time intensive modeling and computation time. This paper presents a state-of-the-art overview of recent multidisciplinary design and optimization methodologies in electronics packaging. The reported methodologies are divided into tow groups: (1) integrated multidisciplinary CAD environment, and (2) automated design and optimization techniques. A semi-automated design environment, which includes graphical user interface, modeling, and simulation, enhances the design procedure in the first group. Fully automated design optimization methodologies are used for various design applications in the second group. In recent years, methodologies using (1) detailed numerical analysis models directly connected to optimization algorithms, (2) design of experiments (DoE), and (3) artificial neural networks (ANNs) have been proposed as new trends in this field. Advantages as well as disadvantages of these methods are discussed.
An Immersed Boundary and Material Point Methodology for Moving/Compliant Surfaces With Heat Transfer
Authors: Gilmanov A. , Acharya S.
Published: April 2008

Simulations of flow and heat transfer in complex geometries with flow-structure-interaction (FSI) require special treatment. In this paper, an approach that combines the immersed boundary method (IBM) for handling complex moving boundaries and the material point method (MPM) for resolving structural stresses and movement is presented as an approach for solving FSI problems. In the IBM, a Cartesian grid is generally defined, and the variable values at grid points adjacent to a non-Cartesian boundary are forced or interpolated to satisfy the boundary conditions. MPM is used to solve equations of solid structure (stresses and deflection) and communicates with the fluid through appropriate interface-boundary conditions. Several examples of using this combination of IBM&MPM are presented and the advantages and disadvantages of this approach are outlined.
An Evaluation of the Wicking Characteristics of Stochastic Open-Cell Nickel Foams
Authors: Sheehan Jessica , Queheillalt Douglas T. , Norris Pamela M.
Published: April 2008

Heat pipes are a very efficient device which can be used for the rapid transfer of thermal energy. Small and microscale heat pipes are used in a variety of applications such as electronics and microprocessor coolers. As the size of the heat pipe devices increase, the volume and rate at which the working fluid is replenished in the evaporator region becomes an important parameter influencing the performance of the heat pipe system. Here, a stochastic open-cell nickel-foam has been evaluated for use as the wick material in heat pipes. The pore size of the open-cell nickel foam was modified via compression in the through thickness direction in order to evaluate its wicking characteristics and fluid flow resistance as a function of pore size. These properties are controlled by the effective pore size (controlled via through thickness compression) of the nickel foam. The equilibrium wicking height was measured by a simple flow experiment. The mass flow rate and the differential pressure of the crushed foams were measured at each thickness to generate a friction factor as a function of pore size. The equilibrium wicking height results were compared to a simple analytical model of a single capillary tube and found to be in reasonable agreement and the friction factor followed the same trend as the equilibrium wicking height. The experiments were used to evaluate the suitability of stochastic open cell nickel foams as wicks for heat pipe systems.
Thermal Enhancement of Stacked Dies Using Thermal Vias
Authors: Sung Baekyoung , Chepuri Krishnateja , Lee Yongjie , Agonafer Dereje , Agonafer Damena , Amon Cristina
Published: April 2008

Following Moore's law, the number of transistors on a die continues to rise and has recently exceeded a billion on high end processors. In light of the convergence of technology, power requirements is becoming a serious concern even on low density interconnect systems such as cellular phones and personal digital assistants. Also, in order to minimize foot prints, the recent trend in packaging is stacking. The stacking, however, creates challenges in cooling and especially if one is to include logic in the stack. The primary heat flow path for stacking is through the substrate and as the number of stacks increase, the cooling problem is amplified. Thermal vias are emerging as a viable technology for transferring heat and in effect creating a thermal short circuit from individual die to the substrate. Some of the authors of this paper earlier reported on the reliability of stacked memory dies. In a subsequent paper the thermal reliability that included geometrical stacking architecture (rotating, spacer, ..) and the inclusion of both logic and memory dies was addressed. In this present paper, the heat transfer enhancement using silicon vias on various stacking schemes is discussed. The CAD models required for this study were developed in Pro/Engineer® Wildfire™ 2.0 and for the result simulation ANSYS® Workbench™ 10.0 have been used. Packaging architectures that have been taken in to consideration are die, solder ball, substrate, mold cap and thermal vias.
Simulation and Experimental Validation of a Magnetocaloric Microcooler
Authors: Ghirlanda Simone L. , Kim Sangchae , Hernandez Cesar F. , Rahman Muhammad M. , Bhansali Shekhar
Published: April 2008

This research focuses on the simulation and experimental test and validation of a magnetocaloric microcooler that works under a small magnetic field obtainable by an electromagnet or a permanent magnet. The numerical simulation model of the cooler was constructed by finite element method. Three different kinds of bonded channel layers were used. The temperature change of the working fluid in the cooler was analyzed. The results from the simulation showed a clear fluid temperature difference between the outlet and inlet of the channel (ΔT) of 11 °C while the fluid average temperature ≈ 7.01 °C at the outlet of the microcooler. The microcooler was fabricated using the MEMS processes, and experimental setup was developed for testing of the microcooler. The cooling test was performed for coolers with different channel layers – only micro channel wafer, microchannels in Si-Si fusion bonded wafers and microchannels in glass-Si anodic bonded wafers. Simulated and experimental results of the cooler demonstrate the effect of the materials that were used for microchannels and intermediate plates, on the cooling characteristics.
Transient Heat Transfer Simulation of the Coupling 3-D Moving Piston Assembly-Lubricant Film-Liner System
Authors: Zhien Liu , Yankun Jiang , Guohua Chen , Wanli Yang
Published: April 2008

Transient heat transfer model of the coupling 3-D moving piston assembly-lubricant film-liner system is successfully developed for predicting the temperature distributions in the component system of internal combustion chamber, in which the effect of the friction heat generated at the piston ring/cylinder liner interfaces has been taken into account. The finite element method (FEM) is employed in the model for establishing the heat transfer relation among the moving piston assembly-lubricant film-cylinder liner. The 3-D discrete model of the coupling system is obtained by hypothesizing the lubricant film as 1-D thermal resistances and the friction heat as heat flux boundary conditions. The allocation and distribution model of friction heat on piston ring pack and liner are also established. The 3-D coupling heat transfer model has been used to analyze the heat transfer of a gasoline engine.
The diagnosis of longstanding groin pain: a prospective clinical cohort study
Authors: Bradshaw C J , Bundy M , Falvey E
Published: April 2008

Background:

Longstanding groin pain is a difficult diagnostic challenge for sports physicians, and the lack of consensus on diagnostic criteria and taxonomy makes comparison of published studies difficult.

Aim:

To determine the usefulness and validity of the clinical classification proposed by Holmichet alin a primary care sports medicine population.

Design:

Prospective cohort study.

Setting:

Private sports medicine clinic in London, UK.

Participants:

218 consecutive cases presenting with longstanding groin pain.

Interventions:

Clinical assessment, diagnostic investigations and follow-up.

Results:

Groin pain patients (173 men, 45 women) presented from 23 sporting codes from professional athletes to the recreational exerciser. Men most commonly played soccer (football) (22%) and rugby (21%), while women were most often runners (40%). 12 month follow-up was successful in 65% of cases; an accurate diagnosis was made in 89% of cases. Hip pathology (50.4%) was the most common form of injury, with pubic pathology seen in 21% of cases. Pubic pathology was most often seen in kicking sports (58%), and straight line activities most often resulted in hip pathology (39%). Those patients diagnosed with hip pathology were less likely to return to pre-morbid levels of activity than those diagnosed with pubic pathology (28%vs15%).

Conclusion:

This series shows a different breakdown of injuries in a sporting population presenting with groin pain than previously reported. This reflects diagnostic difficulties in the area. The high incidence of hip pathology and the poor prognosis which this confers are worthy of note.
RESONANCES ATTACHED TO THE SINGULARITIES OF THE FUNCTION COUPLING TWO SIMPLE SYSTEMS TO A FIELD
Authors: BILLIONNET CLAUDE
Published: April 2008

We examine resonances for two systems consisting of a particle coupled to a massless boson's field. The field is the free field in the whole space. In the first system, the particle is confined inside a ball. We show that besides the usual energy levels of the particle, which have become complex through the coupling to the field, other resonances are to be taken into account if the ball's radius is comparable to the particle's Compton wavelength. In the second system, the particle is in a finite-depth square-well potential. We study the way the resonances' energy and width depend on the extent of the uncoupled particle's wave functions. In both cases, we limit ourselves to considering two levels of the particle only.
GIANT THIRD-ORDER NONLINEARITIES IN ANHARMONIC QUANTUM WELLS
Authors: WANG GUANGHUI , GUO QI
Published: April 2008

Third-harmonic generation (THG) and its origin are investigated in an anharmonic quantum well by the perturbation theory. The calculated results show that the nonlinear effect roots in an anharmonic oscillation of electrons deviate asymmetrically or symmetrically from an ideal harmonic oscillation, and the more the deviation is, the larger the nonlinearities will be. In addition, the nonlinear coefficient is also relative to the anharmonic-oscillation frequency in the model. The most important point is that the THG coefficient may be obtained over 10-10 (m/V)2, about ten orders of magnitude greater than those in bulk GaAs.
LEVEL CROSSING AND QUANTUM PHASE TRANSITION OF THE XY RING
Authors: JING JUN , MA H. R.
Published: April 2008

The ground state of a spin-1/2 ring in the Heisenberg XY model is investigated. The spatial correlation and concurrence between an arbitrary nearest-neighbor pair of spins are calculated with different coupling strength, anisotropic parameter and magnitude of the transverse field. Abrupt changes of the correlation and concurrence due to the competition between coupling and alignment are observed. The transition is found to be the direct result of the level crossing of a finite size spin system.
CHANGES OF ELECTRONIC NOISE INDUCED BY OSCILLATING FIELDS IN BULK GaAs SEMICONDUCTORS
Authors: ADORNO D. PERSANO , CAPIZZO M. C. , ZARCONE M.
Published: April 2008

A Monte Carlo study of hot-electron intrinsic noise in a n-type GaAs bulk driven by one or two mixed cyclostationary electric fields is presented. The noise properties are investigated by computing the spectral density of velocity fluctuations. An analysis of the noise features as a function of the amplitudes and frequencies of two applied fields is presented. Numerical results show that it is possible to reduce the intrinsic noise. The best conditions to realize this effect are discussed.
FREQUENCY-ENERGY VARIABILITY CHARACTERIZATION OF LOCAL REAL-TIME NOISY SEISMIC RECORDS
Authors: COLAK O. H. , DESTICI T. C. , OZEN S. , ARMAN H. , CEREZCI O.
Published: April 2008

In this study, we have presented a new approach to separate noisy components and to characterize frequency-energy variability for local real-time noisy earthquakes where epicentral distance is 0–10°. This approach is based on wavelet transform and deals with energy variations in different frequency bands. All records have been decomposed to approximation and detail components with using overlapping window design and wavelet transform. Energy components of each window were determined and highest energy component has been selected in all windows. When selected energy values have been associated in a vector, two different types of frequency-energy characteristics which include critical points to detect P (longitudinal) and S (transverse) waves have been obtained.