bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Study of the Heat Transfer Rate in a Helical Static Mixer
Authors: Rahmani Ramin K. , Keith Theo G. , Ayasoufi Anahita
Published: April 2008

In chemical processing industries, heating, cooling and other thermal processing of viscous fluids are an integral part of the unit operations. Static mixers are often used in continuous mixing, heat transfer, and chemical reactions applications. In spite of wide spread usage, the flow physics of static mixers is not fully understood. For a given application, besides experimentation, the modern approach to resolve this is to use powerful computational fluid dynamics (CFD) tools to study static mixer performance. This paper extends a previous study by the authors on an industrial helical static mixer and investigates heat transfer and mixing mechanisms within a helical static mixer. A three-dimensional finite volume simulation is used to study the performance of the mixer. The effects of different flow conditions on the performance of the mixer are studied. Heat transfer rates for a flow in a pipe containing no mixer is compared to that with a helical static mixer.
Evaluation of Modified Oscillatory Shear Index and Recirculation Zone in a Deployed Coronary Stent
Authors: Rajamohan Divakar , Ibrahim Ashraf A. , Back Lloyd H. , Jog Milind A. , Banerjee Rupak K.
Published: April 2008

A major consequence of stent implantation is restenosis which occurs due to neointimal formation. There are several factors affecting restenosis among which wall shear stress plays a significant role. The present computational study of developing pulsatile flow through the entrance region of a deployed Palmaz stent in a coronary artery analyzes the local wall shear distribution and its effect on restenosis. A variation from low positive wall shear stress of around 10 dyn/cm2 at the upstream of stent strut intersection to a very high positive wall shear stress of 300 dyn/cm2 at strut intersection and then to a negative wall shear stress of −10 dyn/cm2 at the downstream of strut intersection was observed. Modified oscillatory shear index was calculated which showed persistent recirculation at the downstream of strut intersection indicating it as a highly prone region to restenosis.
Asymptotic Force Control of Hydraulic Actuators With Friction: Theory and Experiments
Authors: Sekhavat P. , Sepehri N. , Wu Q.
Published: April 2008

This paper documents the development, theoretical analysis and experimental evaluation of a Lyapunov-based nonlinear control scheme for asymptotic force regulation of hydraulic actuators with friction. The complete discontinuous model of actuator friction, servo-valve dynamics, and nonlinear hydraulic functions are all included in the theoretical solution and stability analyses of the resulting nonsmooth system. The frictionless contact force is modeled as a linear stiffness. Filippov’s solution theory and the extension of LaSalle’s invariance principle to nonsmooth systems are employed to prove the asymptotic convergence of the system trajectories towards equilibria. Experiments complement the theoretical analysis in providing a solid foundation for implementation of the proposed control scheme for asymptotic force regulation of the hydraulic actuators despite friction effects.
Detection for Parametric Form Features in Surface Meshes
Authors: Singh Prabhjot , Dutta Debasish
Published: April 2008

Reverse Engineering refers to the construction of solid models from existing parts. The process is initiated by taking dense surface measurements using an optical range sensor. These are then approximated to form a surface mesh representation. Polygonal surfaces meshes form the input for solid model construction. However, the C0 continuous meshes are devoid of high level form feature information which conveys design intent or engineering significance. Currently, only partial solutions to detect such features are known in literature. In this research we present algorithms to segment polygonal surface meshes into functional surface features. The first part of the paper deals with simple shape primitives based on 1st and 2nd order surfaces and combinations thereof. In the second part of the paper we propose methods to detect instances of parametric freeform surfaces. Detection is enabled by clustering and pattern recognition techniques. Algorithms and examples are presented. Future research directions are suggested.
Poking Cells in Cell-Gel Constructs: A Potential Way of Measuring Fluid Pressure in Cells
Authors: Srinivasan Jayendran , Kish Vincent , Salihu Sydha , Ayyalasomayajula Madhavi , Mukherjee Nilay
Published: April 2008

In this study, fluorescently labeled ATDC5 and bone marrow derived preosteoblastic cells were embedded in agarose gel and poked with a micropipette under a confocal microscope. Image stacks of cross sections of cells were taken before and after poking and the largest cross sectional areas were analyzed. After adjusting for photobleaching effects by equalizing the area of a nearby unpoked cell (by adjusting threshold values of the images) the area of the poked cell before and after poking was measured and the percentage change in area was calculated. The percentage change in cross sectional area was 25 ± 15% for ATDC5 cells and 31 ±13% for bone marrow derived cells (n= 5 for each type of cell). The decrease in area was statistically significant for each cell type (p<0.05). There was no difference in the reduction in areas between the two types of cells (power >80%). These results are consistent with the theory that some of the cell water is free and some are structured or restricted. This method can be utilized to determine fluid pressure in cells. This is significant because it is believed that changes in intracellular fluid pressure can play a role in cellular mechanotransduction.
Microstructure Evolution During Alternating-Current-Induced Fatigue
Authors: Keller R. R. , Geiss R. H. , Cheng Y.-W. , Read D. T.
Published: April 2008

Subjecting electronic interconnect lines to high-density, low-frequency alternating current creates cyclic thermomechanical stresses that eventually cause electrical failure. A detailed understanding of the failure process could contribute to both prevention and diagnostics. We tested unpassivated Al-1Si traces on the NIST-2 test chip; these are 3.5 μm wide by 0.5 μm thick by 800 μm long, with a strong (111) as-deposited fiber texture and an initial average grain diameter of approximately 1 μm. We applied rms current densities of 11.7 to 13.2 MA/cm2 at 100 Hz. Resistance changes in the lines indicated that such current densities produce temperature cycles at 200 Hz with amplitude exceeding 100 K. Open circuits occurred in under 10 minutes, with substantial surface damage seen after only one minute. A few failures initiated at lithography defects initially present in the lines, but most were produced by the current alone. In one detailed example presented in this paper, we monitored the damage process by interrupting the current at 10, 20, 40, 80, 160, and 320 s in order to characterize an entire line by scanning electron microscopy and automated electron backscatter diffraction (EBSD); failure took place after 697 s. Results are described in terms of deformation, grain growth, and orientation changes.
Preliminary Investigation of Boiling and Transpiration of Water in a Porous Media Cooled With an Air Flow
Authors: Schubert Alexis , Keffler John , Ortega Alfonso
Published: April 2008

This paper describes a study focused on heat and mass transfer through various porous media involving both boiling and transpiration. Heat was supplied to a porous structure immersed in water. Water was boiled at the base of the porous material and in some cases advected from the porous structure by air blown over its surface. The porous media was expected to provide higher heat fluxes than those attained during pool boiling by providing additional surface area and by increasing the number of nucleation sites. The behavior was studied from just below the boiling point and into the nucleate boiling regime. The experimental apparatus consisted of a 2.5 cm square jet impinging onto a 2.5 cm square porous sample. A total of four copper foam samples and one carbon graphite foam sample were tested. The foam sample was placed in contact with a 2.5 cm square heated surface. Water was supplied through the sides of the porous sample and was able to leave the system as a vapor through the top surface of the sample, where it was advected away. It was determined that the presence of an impinging jet had no noticeable effect on heat flux. Up to 60% enhancement in heat flux was observed, compared to boiling of the plain surface. Contact resistance was significant and mitigated the affects of sample thermal conductivity.
Principle and Algorithm for Tomography-Based 3-D Anisotropic Elastography
Authors: Liu Yi , Wang Ge , Sun L. Z.
Published: April 2008

Pathological changes often alter the elastic properties of the tissues and organs. To quantify the biomedical material properties and assist diagnosis of cancerous tumors, elastography has been developed to quantitatively visualize distribution of the elastic modulus in biological media, incorporating measurements of displacement and force.
Feasibility Study on the Use of Temperature-Dependent Liposomes for Variable Concentration Profiles in Drug Delivery Applications
Authors: Lee Eunice S. , Munoz Christel M. , Simmons Blake A. , Ellis C. R. Bowe , Davalos Rafael V.
Published: April 2008

A novel methodology for delivering variable drug concentration profiles utilizes a combination of liposomes that destabilize at different rates at body temperature (37° C). Liposomes serve as the mobile drug delivery vehicle and release drugs into the body upon destabilization. Liposome destabilization is studied by monitoring the absorbance spectrum of fluorescent dyes. By combining liposomes of various compositions, concentration profiles that are optimized and tailored to specific patients and applications are feasible.
Web-Based Mechanical Engineering Design Education Environment Simulating Design Firms
Authors: Chen Zhiqiang , Siddique Zahed
Published: April 2008

Mechanical design education focuses on teaching students with fundamental design theory and methodology. Educators systematically introduce design theories, processes, and tools to help students solve design problems. Companies and professional organizations expect that students will be equipped with basic understanding of the engineering practice, and be able to effectively perform independently and in a team environment. Senior capstone design courses, particularly with industry sponsored projects, are widely used to satisfy both education and professional needs of students. This paper presents an education system, which can further facilitate students to acquire design skills in a real-time collaborative, and practical environment. The web-based system helps student teams to: (1) specify the design process for their team projects, (2) organize and distribute tasks among different team members to simulate industry design environment, and (3) get instantaneous access to models, analysis, etc. related to their design. The developed web-based system also contains a knowledge-base that provides students with instructions to setup the design process for projects, and to perform different design tasks. A virtual design organization is created in the system, which is managed by students. In this paper different components of the web-based design education system are presented.
Design a Product That Can Stimulate a Developing Nation’s Economy: Grain Mill
Authors: Faurote Shawn , Curtis Carrol , Jones Daniel , Otterson Andrew , Meyer Kevin , Guccione Leia , Lineberry Kristopher , Shedek Thomas , Bina Daniel , Hansen Robert , Maas Patrick , Wakefield Abby
Published: April 2008

The purpose of this project was to design a product that would improve the standard of living, as well as stimulate the economy of a developing nation. Increasing food production was determined to be one of the greatest needs in emerging economies. Initial market research of indigenous grinding methods and diets of several developing nations pointed to a need for grain mills in Central and South America. In order to design a grain mill to meet this need, grain mill machines currently available in industrialized nations were first analyzed in order to determine the technical aspects that would be needed to construct an appropriate grain mill. The initial grain mill designed as well as prototyped weighs 40 pounds and can be assembled without any tools. The grain mill is able to efficiently grind corn into fine flour using a two-step grinding process. Using the two-step process, 1.5 pounds of grain can be milled in an hour. In addition, the grain mill can be easily disassembled for cleaning and transportation when necessary. Through analysis of the potential market’s income as well as looking at the production process, the price per grain mill is expected to be $50, a cost that is within the budget of many families and communities in the Americas.
CFD Analysis of the Combustion of Hydrogen in a Simulated Two Dimensional Scramjet Engine
Authors: Rencher J. K. , Massoudi A. H. , Guillaume D. W.
Published: April 2008

The purpose of this research is to accurately simulate combustion in a scramjet engine using a CFD (Computational Fluid Dynamics) software package called Fluent and to validate the results with existing experimental data from NASA Langley Research Center[1]. The use of a particular engine characteristic called compression ramp injection was used to increase the mixing of air and fuel inside the combustion duct as well as provide the necessary compression of the fuel/air mixture. The duct length and other pertinent dimensions were also determined by published data from NASA [1]. The engine model used is relatively small and, at this stage, can be thought of as a two dimensional combustor duct rather than a true engine. The scope of this project involves the simultaneous calculations and analysis of both combustion and high-speed compressible flow. Thermodynamic data was used to create hydrogen fuel in a Fluent module called prePDF (probability density function), which calculates the look-up tables and chemical reactions for the fuel. Non-premixed combustion at Mach 2 was carried out using various equivalence ratios, (ratio of actual fuel/air mixture to stoichiometric fuel/air mixture) ranging from .4 to 1.4. The basic characteristics of the numerical model are as follows: steady state; non-premixed combustion; hydrogen fuel PDF model with 4 species; k-epsilon viscous model. Results of the numerical analysis include a comparison of combustion efficiencies for various equivalence ratios to the combustion efficiencies and equivalence ratios obtained by NASA in their experimental ground test facility at Langley Research Center [1].
Towards High-Speed Near-Field Scanning Optical Microscope
Authors: Wang Yuan , Sun Cheng , Fang Nicholas , Zhang Xiang
Published: April 2008

Recently, near-field scanning optical microscopy (NSOM) and its variations, which combine the scanning probe technology with optical microscopy, have been intensively applied in the study of biology, material science, surface chemistry, information storage, and nanofabrication. However, due to the serial scanning nature, the speed at which NSOM can successively records highly resolved images is rather limited. This hampers the applications of NSOM in characterizing dynamic response of particular samples. In this article, we perform systematic investigation of NSOM system parameters, which include scan rate, signal detector amplification, and illumination intensity. In this work, a model of signal flow for the NSOM system has been established to quantitatively investigate the interplay of the key process parameters and to further explore the technique solutions for high-speed NSOM imaging. The model is in good agreement with experimental results and the optimized conditions for high speed NSOM imaging are suggested.
Micro-Pneumatic Logic
Authors: Henning Albert K.
Published: April 2008

Advances in silicon membrane and microvalve technology continue to be made. Microvalves utilizing membranes have always encompassed the attribute of an on-off switch, thereby suggesting a logic element, although their main application has been arguably as a proportional flow control device. Recently, an analogy has been suggested between a microelectronic, p-channel MOSFET, and a microvalve. The analogy includes a qualitative comparison between the flow vs. pressure relationship for the microvalve, and the current vs. voltage relationship for the MOSFET. It also includes a simple, small-signal frequency analysis of microvalve flow, based on a ‘saturation’ flow behavior chosen arbitrarily to be similar to that in a MOSFET. In this work, a quantitative and rigorous model for the flow vs. pressure relationship for a microvalve is presented. The model couples the mechanical behavior of a silicon membrane, with the fluid mechanical behavior facilitated by the membrane’s motion. The model is substantiated by measurements. The model is compared by analogy to the related MOSFET model equations. The pneumatic model is then applied to both a normally-closed microvalve, and a normally-closed poppet valve. The normally-closed microvalve is analogous to a p-MOSFET. The normally-closed poppet microvalve is analogous to an n-MOSFET. By appropriate physical coupling of these two devices, a fully complementary pneumatic NOR gate results. The quantitative pneumatic flow model is applied to this structure, and the logic transfer function is obtained. The ramifications of the results for scaled, micro-pneumatic logic devices will be discussed.
Thermophysical Properties of a Slurry of Distilled Water and Microencapsulated Phase-Change Materials
Authors: Scott David A. , Baliga B. Rabi
Published: April 2008

This paper presents experimental measurements of some effective thermophysical properties of slurries consisting of microencapsulated phase change materials (MCPCMs) suspended in distilled water. The related apparatus and procedures are also presented and discussed. The MCPCMs considered here consist of a core of phase-change material (PCM), in this case a substance akin to octadecane, surrounded by a solid shell. The effective density of the slurries was measured using hydrometers. The effective thermal conductivity of the slurries was measured using an in-house designed apparatus. The effective kinematic viscosity of the slurries was measured using a series of glass capillary viscometers. A differential scanning calorimeter (DSC) was used to obtain the effective specific heat, melting and freezing temperatures of the core PCMs, and the latent heat of the slurries. Slurry concentrations between 0% (pure distilled water) and 20% by mass of the MCPCMs were considered in this investigation, at temperatures ranging from 5°C to 65°C. Where possible, the results have been compared to predictions obtained using available analytical expressions with properties of the constitutive materials as inputs.
Phase Change and Two Phase Flow in Cathode Porous Electrodes of Fuel Cells
Authors: Bradean R. , Promislow K. , Wetton B.
Published: April 2008

The steady state transport phenomena in the cathode porous electrode of a proton exchange membrane (PEM) fuel cell are investigated in a two-dimensional configuration near the outlet. The fuel cell is operated by hydrogen and humidified oxygen in a regime in which the porous cathode contains a two-phase two-component mixture of oxygen, water vapor and liquid water. Numerical results are presented for the liquid water, oxygen and temperature distributions through the cathode porous electrode. The phase change effect on the transport of reactant to the catalyst layer is found to be important.
Chaotic Oscillations of a Post-Buckled Beam Constrained by an Axial Spring: Part 1 — Experiment
Authors: Nagai Ken-ichi , Maruyama Shinichi , Sakaimoto Kazuya , Yamaguchi Takao
Published: April 2008

Experimental results are presented on chaotic oscillations of a post-buckled beam subjected to periodic lateral acceleration. A thin steel beam of thickness 0.198mm, breath 12.7 mm and length 106mm is used as a test beam. Both ends of the beam are clamped and one end is connected to an axial spring. First, natural frequencies of the beam are measured under an axial compression. Under the post-buckled configuration of the beam, characteristics of static deflection by a concentrated load on the beam are obtained. The post-buckled beam shows the soften-and-hardening characteristics of restoring force. The frequency regions of chaotic responses are inspected. The chaotic responses around these domains are examined carefully by time histories, the Poincare´ maps, the Fourier spectra, the maximum Lyapunov exponents and the principal component analysis. The predominant chaotic responses of the beam are generated by the jump phenomena. The chaotic responses are related to the sub-harmonic resonances of 1/2 and 1/3 orders with the lowest mode of vibration. The maximum Lyapunov exponent of the former chaotic response of 1/2 order is larger than that of the latter chaotic response of 1/3 order. Onsets of the chaotic responses are also confirmed by the Poincare´ projection in the variation of exciting frequency.
Verify Results of a Combustion Chamber Model for One Type of Fuel
Authors: Massoudi A. H. , Rencher J. K. , Guillaume D. W.
Published: April 2008

The focus of this paper is the validation of a Computational Fluid Dynamic (CFD) code with respect to combustion processes. To perform this validation, the emission results from a numerical model of a simple combustor are compared to experimental results obtained from a physical model that has the exact same dimensions and configuration as the numerical model. FLUENT was the numerical CFD code used for this study. Both the numerical model and the experimental apparatus are two-dimensional, vertical combustors that inject methane through a 2 mm slot at the combustor base. Air is injected through 6 mm slots placed 6 mm on each side of the fuel injection slot. The combustion chamber is a 300 mm long tube that has a wall thickness of 5 mm. For both the experimental and numerical results, the equivalence ratio was varied from 1 to 1.5 The results obtained at the exit of the chamber show that the temperature predictions match the model within 2.5%, the CO predictions match the model within 14.75%, and the CO2 predictions match the model within 15.91%. This study shows that the results from FLUENT are consistent with the experimental results. The percentage error shows a slight difference between the numerical and physical results, but these errors are acceptable because of the assumptions made and the nature of numerical modeling.
A Numerical and Experimental Study of the Thermal Management of LEDs
Authors: Chiang S. B. , Lu M. C. , Wu W. L. , Yen M. C. , Wang C. C.
Published: April 2008

This study examines the thermofluids characteristics of a LED lighting device. It is found that the heat sources of the present LED lighting are from the PCB and from the LED itself. To effectively improve the overall performance of the LED device, it is suggested that these two heat sources should be dealt with separately. For efficient thermal management of the LED, it is recommended to use the insulators and separate sink. The former can effectively block the heat flow from the PCB to LED panel where the latter can maintain the temperatures of PCB and LED within tolerable limit.
A Swept Ellipse Offsetting Approach for Three-Axis Sculptured Surface Tool Path Generation
Authors: Jang Peter , Stori James A.
Published: April 2008

This paper presents a new offsetting approach for tool path generation in three-axis sculptured surface machining. The approach generates tool paths with scallop, curvature, and force characteristics which make them suitable for high speed machining. An ellipse in the parametric space is used to approximate the intersection between the ball-end mill and the scallop surface for any cutter contact point on the surface. The envelope formed by these swept ellipses of varying dimension and orientation creates a constant scallop curve which is used to generate offset paths. The offset is developed incrementally, utilizing post-processing techniques to eliminate high-curvature regions in the trajectory. The offsetting approach can generate continuous spiraling trajectories which offer the benefit of minimal tool retractions. Results are shown for spiraling paths generated from both convex and non-convex boundaries.
Micro-Guidance of Pick-and-Place Robots via Task-Space Sensing
Authors: Nejat Goldie , Benhabib Beno
Published: April 2008

In this paper, a line-of-sight-sensing based guidance methodology is proposed for the localization of robotic end-effectors in high-precision (i.e., micron or sub-micron accuracy) pick-and-place applications. The novelty of the overall system is its applicability to cases that do not allow for the direct proximity measurement of the end-effector’s pose. The proposed iterative guidance algorithm utilizes a pseudo-PD function to minimize the systematic errors of the end-effector, while allowing the pose of the end-effector to converge within the random noise limits. The system has been experimentally tested for a three-dof planar parallel manipulator.
A Study of the Assurance Life Prediction Method for Latch Spring of Vehicle Door Using the Modification of Shape Parameter
Authors: Lee Geunho , Kim Hyoungeui , Kang Bosik
Published: April 2008

This study was performed to develop the assurance life prediction method using modification of shape parameter for the latch spring of vehicle door. The shape parameter β is a main parameter with scale parameter, number of sample, confidence level, in determining the predicted assurance life and testing time. The proposed the modification of shape parameter is an approach to verify the life prediction procedures based on the life testing data and to improve the reliability assessment on the statistical distribution. The latch spring generally represent fatigue and fracture characteristics as a failure mode. Firstly, life distribution of latch spring was supposed to follow Weibull distribution and life test time was calculated under the conditions of average life (B5) 300,000 cycles and 95% confidence level for 60 test samples with value of shape parameter 2.07 from reference data. Secondly, after the life test, the value of shape parameter 2.26 can be obtained by using MINITAB. Finally, the assurance life of latch spring could be predicted by the relation of mean life and the scale parameter which is achieved also from the analysis of sample failure data.
The Exergy Cost of Information Processing: A Comparison of Computer-Based Technologies and Biological Systems
Authors: Carey V. P. , Shah A. J.
Published: April 2008

Processing information (analysis, storing, retrieving, sharing) is the primary function of modern computer-based information systems. Systems of this type generally require an input flow of exergy (available energy) to function. Information processing systems now are evolving in two directions. One direction is towards bigger and more sophisticated systems. The other is towards systems that are more compact and portable. In both cases, the energy efficiency is becoming an increasingly important design issue. This paper summarizes an exploration of the exergy cost of processing information at the component and system levels in state-of-the-art information processing systems. The energy efficiency characteristics of computer-based information technologies are also compared to estimates of the energy efficiency of biological information processing in brains of mammals. Energy efficiencies of processors and systems are quantified in terms of the ratio of MIPS to exergy input rate. Available data suggest that for recent generations of processors, this ratio has been increasing proportional to the square root of processor speed. Despite this increase, the energy efficiency of computer-based systems is currently substantially below the estimated efficiency of biological systems. The data also suggest that unless processor energy efficiencies are greatly increased, the development of information processing systems that match human brain performance will be hindered by the need for large power supplies and high-capacity heat rejection systems.
Effect of Wall Thermal Boundary Conditions on the Development of Three-Dimensional, Unsteady Natural Convective Flow in a Horizontal Enclosure With a Heated Strip on the Lower Surface
Authors: Oosthuizen Patrick H. , Paul Jane T.
Published: April 2008

Flow in a rectangular enclosure with a square vertical cross-section normal to the longitudinal coordinate direction and having a strip on the lower horizontal surface which is heated to a uniform high temperature has been numerically studied. Two wall thermal boundary conditions have been considered. In one, the longitudinal vertical side walls are cooled to a uniform low temperature and the horizontal top surface is adiabatic while in the other the longitudinal vertical side walls and the horizontal top surface are cooled to a uniform low temperature. In both cases, the square vertical end walls of the enclosure are adiabatic. It has been assumed that the flow is laminar and that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces. The unsteady, three-dimensional governing equations, expressed in dimensionless form, have been solved using a finite-difference procedure. The solution was started with no flow in the enclosure. The solution, in general, has the following parameters: the Rayleigh Number, Ra, the Prandtl number, Pr, the dimensionless longitudinal length of the enclosure relative to the size of the square cross-section, Ay, the dimensionless width of the heated strip on the lower surface relative to the size of the square cross-section, wH, and the thermal boundary condition on the upper surface. Results have only been obtained for a Prandtl number of 0.7 and only results for wH = 1/3 will be presented. Results have been obtained for values of Ay between 0.5 and 2 for Rayleigh numbers up to 5×105. In all cases, three-dimensional unsteady flow has been found to exist at the higher Rayleigh numbers. The conditions under which this unsteady flow develops and the effect of Ay on the variation of the mean Nusselt number with Rayleigh number and the effect of the wall surface boundary condition on these results has been investigated.
The Effect of Inclined Vertical Slats on the Free Convective Heat Transfer Rate From an Isothermal Heated Vertical Surface
Authors: Oosthuizen Patrick H. , Sun Lan , Naylor David
Published: April 2008

Free convective heat transfer from a wide heated vertical isothermal plate with adiabatic surfaces above and below the heated surface has been considered. There are a series of equally spaced vertical thin, flat surfaces (termed “slats”) near the heated surface, these surfaces being, in general, inclined to the heated surface. The slats are pivoted about their center-point and thus as their angle is changed, the distance of the tip of the slat from the plate changes. The temperature of the vertical isothermal surfaces has been assumed to be greater than the ambient temperature. Various cases have been considered to examine the effect of the geometry of the adiabatic surfaces above and below the heated plate, the effect of heat conduction in the slats and the effect of heat generation in the slats. The situation considered is an approximate model of a window with a vertical blind, the particular case where the window is hotter than the room air being considered. The heat generation that can occur in the slats is then the result of solar energy passing through the window and being absorbed by the slats. The flow has been assumed to be laminar and steady. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces. The governing equations have been written in dimensionless form and the resulting dimensionless equations have been solved using a commercial finite-element package. Because of the application that motivated the study, results have only been obtained for a Prandtl number of 0.7. The effect of the other dimensionless variables on the mean dimensionless heat transfer rate from the heated surface has been examined.
An Exergy-Based Control Strategy for Computer Room Air-Conditioning Units in Data Centers
Authors: Shah Amip J. , Carey Van P. , Bash Cullen E. , Patel Chandrakant D.
Published: April 2008

Recent compaction and miniaturization of electronic equipment has caused a dramatic increase in the amount of heat dissipated within data centers housing compute, network, and storage systems. The efficient thermal management of these systems is complicated by the intricate interdependence among the various components of the thermal architecture, including the heat-dissipating computer racks, the Computer Room Air-Conditioning (CRAC) units, and the physical airspace within the room. To account for this interdependence, an approach based on the thermodynamic metric of exergy has been proposed, which allows for prediction of an optimal CRAC operating point that corresponds to the point of minimal irreversibility for the overall system. To validate the formulated theory, predictions from the model have been compared with actual data center power consumption measurements. Initial comparisons indicate good agreement, suggesting that the proposed theory has great applicability for efficient data center thermal management.
Activation Energy Measurement in Thin Gold Film by MEMS-Based Tensile Testing Device
Authors: Han Jong H. , Saif Taher M.
Published: April 2008

In this paper, we report a methodology to measure activation energy for time-dependent stress-relaxation in a thin free-standing tensile specimen by utilizing a MEMS-based tensile testing device. An analytical model is developed to investigate its stress-relaxation behavior. Along with this analytical model of the MEMS tensile tester, Arrhenius relation is applied to estimate relaxation times for different temperatures of a free-standing sample beam. From the relation between relaxation time and temperature, the activation energy for the stress-relaxation is obtained. For a 200-nm Au film, we obtained the relaxation time of 250, 67, and 40 seconds for the corresponding temperatures of 295, 312, and 323 K, respectively. The activation energy for stress-relaxation was 0.544 eV. The experimental data is fitted with the analytical model to find the relaxation time. The thin film on the MEMS tensile tester is prepared by sputter-deposition. By optical lithography and ICP DRIE Si etching, the MEMS tensile tester with a free standing beam is fabricated.
Optimal Tool Orientation for Five-Axis Tool-End Machining by Swept Envelope Approach
Authors: Chiou John C. J. , Lee Yuan-Shin
Published: April 2008

This paper presents a swept envelope approach to determining the optimal tool orientation for five-axis tool-end machining. The swept profile of the cutter is determined based on the tool motion. By analyzing the swept profile against the part geometry, four types of machining errors (local gouge, side gouge, rear gouge, and global collision) are identified. The tool orientation is then corrected to avoid such errors. The cutter’s swept envelope is further constructed by integrating the intermediate swept profiles, and can be applied to NC simulation and verification. This paper presents the explicit solution for the swept profile of a general cutter in five-axis tool-end machining. The relation of the swept profile, the part geometry, the tool motion, and the machining errors is developed. Therefore, the error sources can be detected early and prevented during tool path planning. The analytical results indicate that the optimal tool orientation occurs when the curvature of the cutter’s swept profile matches with the curvature of the local part surface. In addition, the optimal cutting direction generally follows the minimum curvature direction. Computer illustrations and example demonstrations are shown in this paper. The results reveal the developed method can accurately determine the optimal tool orientation and efficiently avoid machining errors for five-axis tool-end machining.
Innovations in Teaching: Engineering Drawing and 3D Visualization
Authors: Caulfield-Browne Mark
Published: April 2008

A fundamental course offered at The Petroleum Institute (PI) in Abu Dhabi, to all sophomore engineering students, is Engineering Graphics. One of the objectives of the Engineering Graphics course is to equip students with the basic drawing and visualization skills required of competent engineers. With English being a second language, a number of issues in developing such a course had to be addressed: proficiency in the English language, previous drawing experience, 3D visualization skills, judicious and appropriate use of technology. While some of our sophomore students cope adequately with learning in English, many struggle to understand the language used in technical courses. Further, the majority of our students have no prior drawing experience and generally have poorly developed 3D visualization skills. This paper will consider how the learning process can be enhanced through appropriate use of technology. The development and delivery of an innovative, bespoke Engineering Graphics and 3D Visualization course will be presented. The course concentrates on developing visualization skills by providing a web-based, independent-learning component. Interactive multimedia resources were developed to accompany the sketching part of the course. The 3-dimensional sketching examples given in the course notes were modeled using the CAD software the students would learn later in the course. It was anticipated that, by providing these powerful visualization tools, students would intuitively understand the concepts even without previous exposure to Engineering Graphics or fluency in the language of instruction. In this paper, the course structure will be presented, our findings will be outlined and recommendations discussed.
Review of Two Numerical Approaches to Predict Nonlinear Airfoil Response to High-Amplitude Incident Gust
Authors: Golubev Vladimir V.
Published: April 2008

In this work, two different numerical methods of time-accurate nonlinear analysis are reviewed and compared in application to the problem of nonlinear unsteady aerodynamic and aeroacoustic airfoil responses to a high-intensity impinging gust. The incident perturbation field is of finite amplitude relative to the mean flow so that in general, no assumption of a linear superposition of responses from each individual harmonic can be made. Thus, in addition to providing a comparison of two different approaches in computational aeroacoustics, the paper achieves the objective of obtaining verified solutions determining the limits of validity for linearized methods, universally accepted in studies of unsteady aerodynamics and aeroacoustics. The work investigates nonlinear near- and far-field responses of a Joukowksi airfoil in the parametric space of gust intensity and frequency.
Surface Wave Propagation of an Ultra Thin Liquid Film on a Rotating Disk
Authors: Wu Lin
Published: April 2008

We theoretically and numerically study the propagation of axisymmetrical long surface waves of an ultra thin liquid film on a rotating disk. When breaking condition is satisfied, shock waves form and propagate driven by the centrifugal and external shearing forces. The disjoining pressure due to van der Waals force provides diffusion to the system. The surface waves are planarized by the centrifugal force, external shearing force and the disjoining pressure.
A Simple Asymptotic Compact Model for Two-Phase Frictional Pressure Gradient in Horizontal Pipes
Authors: Awad M. M. , Muzychka Y. S.
Published: April 2008

A simple semi-theoretical method for calculating two-phase frictional pressure gradient in horizontal pipes using asymptotic analysis is presented. Two-phase frictional pressure gradient is expressed in terms of the asymptotic single-phase frictional pressure gradients for liquid and gas flowing alone. The proposed model uses an asymptotic correlation method to develop a robust compact model. The proposed model can be transformed into either a two-phase frictional multiplier for liquid flowing alone (φl2) or two-phase frictional multiplier for gas flowing alone (φg2) as a function of the Lockhart-Martinelli parameter, X. Single phase friction factors are calculated using the Churchill model which allows for prediction over the full range of laminar-transition-turbulent regions and to allow for pipe roughness effects. The proposed model is compared against published data for a number of pipe diameters. Effect of mass flux on two-phase frictional pressure gradient is also investigated. Comparison with other existing correlations for two-phase frictional pressure gradient such as the Chisholm correlation, the Friedel correlation, and the Mu¨ller-Steinhagen and Heck correlation, is also presented. Comparison with other existing correlations and experimental data for both φl and φg versus X is also presented.
Noise Analysis in Parametric Resonance Based Mass Sensing
Authors: Zhang Wenhua , Turner Kimberly L.
Published: April 2008

Mass sensing based on parametric resonance has shown high sensitivity and has many potential applications in chemical and biological sensing. We investigate noise effects on the sensitivity of mass sensing using parametric resonance. Temperature fluctuation noise, Johnson noise, and Brownian motion noise have been considered. Numerical simulation and experimental results show that noise affects the sensitivity of parametric resonance mass sensing in different mechanism from simple harmonic resonance based mass sensor and Brownian motion noise of the micro-oscillator has the major contribution to the frequency uncertainty at the boundary of parametric resonance area and the sensitivity in mass sensing.
Prediction of the Heat Transfer and Flow Characteristics in Rotary Combustor
Authors: Tanaka Takahiro , Mizuno Masayuki , Oguma Masahito
Published: April 2008

A numerical analysis model is developed to evaluate heat transfer and fluid flow characteristics of a through-flow-type-rotary system. The numerical domain is divided into three parts, waste layer, gas phase above the layer and rotary grate, and these are modeled, respectively. The analytical results of CO concentration in gas at outlet, peak temperature of rotary grate and heat-recovering rate correspond with the experimental those, which shows validity of the numerical model. The maximum temperature of the layer, heat recovering rate and NO concentration in gas at outlet rise in proportion to O2 concentration in air into combustion zone, and unburned carbon in combustion residue and CO concentration at outlet and decrease at a fixed rate. In case that flue gas is recirculated from the top of incinerator into combustion zone, NO concentration in gas at the outlet decreases in proportion to the flow rate of recirculating gas.
Micro T-Switches for Cell Sorting Applications
Authors: Ho Chen-Ta , Liu Cheng-Hsien
Published: April 2008

A new micro-T-switch actuated by electrochemical bubbles for cells sorting has been proposed and successfully demonstrated by MEMS micromachining technique. We take advantage of electrolysis-bubbles, which have the features of low operation temperature and high surface-tension force, to actuate the micro T- switches in our device. The micro-T-switch is placed at the junction of the T-shapes microchannel. The movable T-structure design makes cell sorting active and programmable compared with other passive cell sorting mechanism such as micro-filters. Furthermore, the low operation temperature for electrolysis - bubbles driving mechanism could minimize cell-damage that happens in conventional high electric-separation instruments, such as Flow Cytometry.
Wall Shear Stress in Development Process of Aneurysm Around Anterior Communicating Artery
Authors: Umezawa Kenichi , Torisu Akihiro , Kudo Susumu , Yamaguchi Ryuhei
Published: April 2008

In the present paper, the distribution of the wall shear stress around the apex of the anterior communicating artery (ACoA) in the development process of aneurysm has been studied in laminar steady flow. The anterior communicating artery composing the circle of Willis is one of the predilection sites where the cerebral aneurysm occurs frequently. Once the small aneurysm initiates around the apex in one anterior cerebral artery (ACA) with high flow rate, the distribution of the wall shear stress abruptly changes around the initial aneurysm. With the development of the aneurysm, the wall shear stress distinctly changes along the concaved surface of the aneurysm. The distribution of the wall shear stress in the development process of the aneurysm is physiologically discussed from the viewpoint of hemodynamics.
Convective Heat Transfer From Heated Extended Surfaces With a Confined Slot Jet Impingement
Authors: Liu L. K. , Wu M. C. , Fang C. J. , Hung Y. H.
Published: April 2008

A series of experimental investigations with stringent measurement methods on the studies related to mixed convection from the horizontally confined extended surfaces with a slot jet impingement have been successfully conducted. The relevant parameters influencing mixed convection performance due to jet impingement and buoyancy include the Grashof number, ratio of jet separation distance to nozzle width, ratio of extended surfaces height to nozzle width and jet Reynolds number. The range of these parameters studied are Grs = 3.77 × 105 – 1.84 × 106, H/W = 1–10, Hs/W = 0.74–3.40 and Re = 63–1383. In the study, the heat transfer behavior on the extended surfaces with confined slot jet impingement such as the temperature distribution, local and average Nusselt numbers on the extended surfaces has been systematically explored. The results manifest that the effect of steady-state Grashof number on heat transfer behavior such as stagnation, local and average Nusselt number is not significant; while the heat transfer performance increases with decreasing jet separation distance or with increasing extended surface height and jet Reynolds number. Besides, two new correlations of local and average Nusselt numbers in terms of H/W, Hs/W and Re are proposed for the cases of extended surfaces. A satisfactory agreement is achieved between the results predicted by these correlations and the experimental data. Finally, a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement and buoyancy is proposed. The comparison of the predictions evaluated by this correlation with all the present experimental data is made. The maximum and average deviations of the predictions from the experimental data are 7.46% and 2.87%, respectively.