bluuebunny/crossref_metadata_2025 huggingface dataset:
Expansion of a Modified Transient Liquid Crystal Method for Thin Plates of Different Materials
Authors: Reed Alison K. , Van Treuren Kenneth
Published: April 2008

The purpose of this research is to apply a modified transient liquid crystal method to a thin flat plate to determine the local temperature distribution and heat transfer coefficient. This research examines three different plates: 1) 1/8 inch thick Plexiglas plate, 2) 1/2 inch thick Plexiglas plate, and 3) 1/8 inch thick aluminum plate. Each plate is approximately 6 inches in length by 3 inches in width. The temperature distributions on a flat plate are viewed over time using a liquid crystal thermography (LCT) technique. The plates are coated with a wide band liquid crystal (R30C5W) and fixed in a vertically oriented wind tunnel. For any thickness plate, the speed of the tunnel was adjusted for a Reynolds number within the range of approximately 22100 and 23100. For the theoretical analysis, the thin flat plate used a convective surface boundary condition and a 2-D transient finite-differencing conduction scheme. An initial local heat transfer coefficient distribution is selected based upon flat plate theory and is used to calculate an initial streamwise temperature distribution. The local heat transfer coefficient distribution is readjusted until the theoretical temperature distribution matches the experimental temperature distribution over the center surface of the plate. This technique allows a wider application of transient LCT and for heat transfer coefficients to be mapped on thin surfaces of different materials.
A Flow Visualization Study of Axial Turbine Tip Desensitization by Coolant Injection From a Tip Trench
Authors: Rao Nikhil M. , Camci Cengiz
Published: April 2008

The effect of coolant injection from a tip trench was investigated in a large-scale rotating turbine rig. Coolant is injected into the tip gap from discrete injection holes, located in a tip trench and directed towards the pressure-side. Surface flow patterns are visualized by a mixture of oil and paint. The mixture is applied on the blade pressure-side and allowed to seep onto the tip platform. Injection rates of 0.4%, 0.5%, 0.6%, and 0.7%, at a gap height of 1.40% blade height were investigated. Flow patterns for a gap height of 0.72% blade height are compared to the larger clearance gap. The flow visualization technique successfully identifies flow features like pressure-side edge separation, and reattachment and recirculation on the tip surface. The location of the reattachment line from the pressure-side edge varies little along the length of the blade and occurs at about two gap heights from the pressure-side edge. At the large gap height the tip gap flow is fully separated over the last 5% of the blade axial chord. Surface oil flow lines are directed almost normal to the camberline along most of the tip surface. Flow patterns with injection indicate that the ejected coolant effectively blocks the leakage flow. The coolant jets are turned towards the blade suction-side and appear to form a film on the tip surface. Some of the visualization material is carried by the leakage flow into the passage and is deposited on the blade suction surface, thereby giving an indication of the inception and growth of the leakage vortex. Suction surface patterns with injection indicate that leakage flow may be entering the adjacent passage at multiple locations.
Characterization and Attenuation of Sandwiched Deadband Problem Using Describing Function Analysis and Its Application to Electro-Hydraulic Systems Controlled by Closed-Center Valves
Authors: Liu Song , Yao Bin
Published: April 2008

Sandwiched deadbands can be seen in a wide variety of systems, such as electro-hydraulic systems controlled by closed-center valves. In such a system, the deadband is between the plant and actuator dynamics and therefore can not be compensated directly like an input deadband. Though this sandwiched deadband problem may be attenuated to certain degree through sophisticated advanced control techniques, the increased cost and the necessity of actuator state feedback prohibit their widespread application in the industry. An economical and popular method is to add an inverse deadband function in the controller to cancel or compensate the highly nonlinear behavior of the deadband. However, such a solution requires that the dynamics before the deadband (eg. the valve dynamics) is fast enough to be neglected — a requirement that can not be met in reality unless the closed loop bandwidth of the overall system is limited very low. To raise the achievable closed loop bandwidth for a much improved control performance, it is essential to be able to precisely characterize the effect of this sandwiched deadband on the stability and performance of the overall closed-loop system, which is the main focus of the paper. Specifically, a describing function based nonlinear analysis will be conducted to predict when the instability will occur and how the resulting limit cycle depends on the actuator dynamics and the targeted closed-loop bandwidth. Based on the analysis, the optimal closed-loop bandwidth can be determined to maximize the achievable overall system performance. The technique is applied to an electro-hydraulic system controlled by closed-center valves to optimize the controller design.
Automated Outcomes-Based Assessment Process for Traditional and Project-Based Engineering Instruction
Authors: Schmidt Philip S. , Jones Theresa L.
Published: April 2008

An outcomes-based assessment process called QQI, an acronym for Quantity-Quality-Improvement, has been developed and pilot-tested in several courses, both traditional and project-based, in mechanical engineering at the University of Texas at Austin. An online version of the QQI survey instrument has been created which automates collection of data and rapid generation of reports to faculty. The QQI process, including the instrument and report generator, research and design basis, and results of pilot testing, are described and department-wide implementation plans are discussed.
Aerodynamic High Speed Feeding Systems: Flexible and Reliable
Authors: Nyhuis Peter , Fiege Torsten
Published: April 2008

Due to recent progress in automation technology, production systems can be realized which are able to assemble more than 600 parts per minute. The greatest problem at these high speeds is not machining itself, but the handling of the often disordered individual parts. When the individual workpieces are delivered in bulk, they have to be separated and oriented. This is done by feeding systems. The conventional feeding systems have weaknesses as far as process speed and reliability are concerned. Therefore a new technology has been developed, with which workpieces can be separated and oriented at the necessary speed with high process reliability. In this method, air flows are used to separate the workpieces and, in several process steps, orient them correctly by making use of their typical features. This technology is called aerodynamic feeding. The article describes the two fundamental procedures, aerodynamic separation and aerodynamic orientation and the structures of these systems.
Smart Thin Sheet Batteries Made With Ionic Polymer Metal Composites (IPMC’s)
Authors: Shahinpoor Mohsen
Published: April 2008

Presented is some experimental results and theoretical modeling pertaining to thin (30 microns) paper-like sheets of ionic polymer metal composites (IPMC’s) as paper batteries. These materials can generate electrical power by means of mechanical flexing, normal pressure and motion in general and they are smart because they are self-powered but rechargeable by moisture. Thin sheets or paper-like labels of IPMC’s can be bonded, glued or attached to any flexible or rigid substrate or can be laminated and can generate power by the motion of that substrate or any normal or oblique pressure exerted on that substrate through the IPMC sheet, label or laminate. A good example of these materials is perfluorinated sulfonic or carboxylic ionic polymers, which are suitably made into a functionally graded composite with a conductive phase such as graphite, conductive polymers or metals. These materials can also act as distributed nanosensors and distributed nanoactuators if moderate electrical field strength of about 10 volts per millimeter (10V/mm) is imposed on them through printed or interdigitated electrodes.
Impact of Product Mix Variations on Material Handling for Cellular Manufacturing
Authors: Bhandwale Amit , Kesavadas Thenkurussi
Published: April 2008

The identification of part families and machine groups that form the cells is a major step in the development of a cellular manufacturing system. The primary input to cell formation algorithms is the machine-part incidence matrix, which is a binary matrix representing machining requirements of parts in various part families. One common assumption of these cell formation algorithms is that the product mix remains stable over a period of time. In today’s world, the market demand is being shaped by consumers, resulting in a highly volatile market. This has given rise to a class of products characterized by low volume and high variety, which presents engineers with lots of problems and decisions in the early stages of product development. This can have an adverse effect on manufacturing like high investment in new machinery and material handling equipment, long setup times, high tooling costs, increased intercellular movement and excessive scrap which increases the cost without adding any value to the parts. Any change to the product mix results in a change in the machine-part incidence matrix, which may change the part families and machine groups, which form the cells. The manufacturing system needs to be flexible in order to handle large product mix changes. This paper discusses the impact of product mix variations on cellular manufacturing and presents a methodology to incorporate these variations into an existing cellular manufacturing setup.
An Exact Theoretical Solution for Predicting the Apparent Poisson’s Ratio of Articular Cartilage: A Charged-Hydrated Biological Tissue — The Triphasic Paradigm
Authors: Wan Leo Q. , Miller Chester , Guo X. Edward , Mow Van C.
Published: April 2008

The triphasic theory has been successfully used to model the mechano-electrochemical behaviors of soft charged hydrated tissue such as articular cartilage. However, the general equations describing such materials are highly complex and nonlinear. In this study, we have linearized these equations with respect to small strains, and using regular perturbation and similarity methods, analytic solutions have been obtained for the lateral expansion of a cylindrical specimen during the unconfined at both steady state, and at short times. Our results showed that the variation of apparent Poisson’s ratio is only dependent on an important governing parameter ζ, defined by the ratio of osmotic pressure change due to compression to the elastic stress change. From the short-time solution, the lateral expansion decreased with the square root of time.
Models for Joule Heating Dispersion in Complex Electrophoretic Separation Microchannels
Authors: Wang Yi , Lin Qiao , Mukherjee Tamal
Published: April 2008

This paper presents an analytical and parameterized model for analyzing the effects of Joule heating on analyte dispersion in electrophoretic separation microchannels. We first obtain non-uniform temperature distributions in the channel resulting from Joule heating, and then determine variations in electrophoretic velocity, based on the fact that the analyte’s electrophoretic mobility depends on the buffer viscosity and hence temperature. The convection-diffusion equation is then formulated and solved in terms of spatial moments of the analyte concentration. The resulting model is validated by both numerical simulations and experimental data, and holds for all mass transfer regimes, including unsteady dispersion processes that commonly occur in microchip electrophoresis. This model, which is given in terms of analytical expressions and fully parameterized with channel dimensions and material properties, applies to dispersion of analyte bands of general initial shape in straight and constant-radius-turn channels. As such, the model can be used to represent analyte dispersion in microchannels of more general shape, such as serpentine- or spiral-shaped channels.
Stress Assisted Controlled Fabrication of Nano Channels and Their Flow Characteristics
Authors: Mani Sathyanarayanan , Saif Taher M.
Published: April 2008

A method to fabricate nano channels narrower than 50nm without the need for any nano lithography is presented. The nano channels are formed by cracking a thin film of silicon dioxide on a silicon substrate by residual stress alone. However, for controlled initiation of cracks on oxide, stress raisers are planted on a silicon substrate by deep RIE. These channels are used to study capillary driven fluid flow through nanochannels. Experimental analysis suggests that the flow rate is inversely proportional to the square root of time, which is in agreement with the theoretical model. From the theoretical plot that fits the experimental data the value of the proportionality constant is determined. From this value it is possible to back calculate the meniscus contact angle if we know the surface energy of the fluid or vice versa.
Heat Transfer Analysis of Turbulent Flow in Rectangular-Sectioned U-Bends
Authors: Etemad Sassan , Sunde´n Bengt
Published: April 2008

The turbulent flow in rectangular-sectioned U-bend ducts with bend mid-line radius 3.35 and with aspect-ratios AR=0.5, 1, 2, and 4 were explored using linear and non-linear high- and low-Re k-ε turbulence models at a Reynolds number of 56000. The impact of the cross-section aspect ratio on the flow field and the associated thermal field was studied. Experimental data were found [1–3] for the square-sectioned cross section (AR=1) and this case was chosen as the reference case for comparison and validation with experimental data. The other cases were evaluated in relation to the square-sectioned case. The predicted data for AR=1 agreed well with the experimental data. The velocity profile upstream the bend has fundamental influence on the strength of the secondary flow and heat transfer. Complex secondary motion was detected for all cases but in particular for AR=1. The mixing process due to the secondary flow decreased in general with increasing aspect ratio.
Operational Wear and Friction in MEMS Devices
Authors: Subhash Ghatu , Corwin Alex D. , de Boer Maarten P.
Published: April 2008

Friction and wear are extremely important issues in micromachined surfaces in design applications that allow rubbing. A polysilicon surface-micromachined inchworm device has been developed to obtain detailed in-situ information on these properties under well-controlled loading conditions. Here, we investigate the inchworm operational wear and the evolution of friction coefficient as a function of the number of imposed wear cycles. A test procedure was developed to monitor various functional parameters such as the travel distance of the inchworm under an imposed drag force for a fixed number of steps and the friction coefficient. While subject to this drag force, the travel distance decreased gradually until the foot of the device became permanently lodged in the grooves created by the wear-track. Meanwhile, it was found that the friction coefficient increased from 0.2 on a virgin surface to 3 when the accumulated number of wear cycles reached around 200,000. The friction test itself was found to interact with the wear processes. By minimizing the number of friction tests performed during the wear test, the operational life of the device was extended well beyond 700,000 cycles. Microscopic observation of the wear surfaces revealed that the early wear is characterized by the blunting of the sharp peaks on the poly silicon grains and then flattening of this fine wear debris on the surface. Evidence of plastic deformation was inferred by the spread of the wear debris over several grains. With increased number of wear cycles, material removal through scratches induced by the wear debris was observed. The device failure occurred due to a large volume of material removal (severe wear) in localized regions.
Performance Benefits of R718 Turbo-Compression Cycle Using 3-Port Condensing Wave Rotors
Authors: Kharazi Amir A. , Akbari Pezhman , Mu¨ller Norbert
Published: April 2008

A number of technical challenges have often hindered the economical application of refrigeration cycles using water (R718) as refrigerant. The novel concept of condensing wave rotor provides a solution for performance improvement of R718 refrigeration cycles. The wave rotor implementation can increase efficiency and reduce the size and cost of R718 units. The condensing wave rotor employs pressurized water to pressurize, desuperheat, and condense the refrigerant vapor — all in one dynamic process. In this study, the underlying phenomena of flash evaporation, shock wave compression, desuperheating, and condensation inside the wave rotor channels are described in a wave and phase-change diagram. A computer program based on a thermodynamic model is generated to evaluate the performance of R718 baseline and wave-rotor-enhanced cycles. The detailed thermodynamic approach for the baseline and the modified cycles is described. The effect of some key parameters on the performance enhancement is demonstrated as an aid for optimization. A generated performance map summarizes the findings.
Flow Resistance of Surface Micromachined Microfluidic Channels
Authors: Galambos Paul
Published: April 2008

In this paper measured pressure vs. flow and flow resistance are compared with theoretical predictions (Poiseuille flow) for surface micromachined microfluidic channels with thin-film deformable covers. Three sets of data are compared. In data set 3 the channel width is narrow, channel deflections are relatively small, and there is very little deviation from the theoretical flow resistance prediction. In data sets 1 and 2 there is significant deviation from Poiseuille flow predictions—with flow resistances as little as 1/2 the predicted values that decrease with increasing pressure. Two hypotheses to explain this discrepancy are discussed: (1) channel cover deflection leading to deeper, lower resistance flow channels, and (2) an observed two-phase, air/water, flow phenomena leading to reduced effective wall friction in the channel.
Punch Shear Damage Behavior of Composite Laminates With and Without Pre-Defined Delaminations
Authors: Gama Bazle A. , Rahman Mostafezur , Gillespie John W.
Published: April 2008

Punch shear tests have been proven to simulate most of the damage mechanisms observed under ballistic impact. A phenomenological model has been developed to quantify the elastic and absorbed energies as a function of displacement during punch. This model is used to quantify the damage mechanisms of thick-section composites as a function of displacement, and number of pre-defined delamination planes. It has been identified that different damage mechanisms as a function of displacement can be correlated with the load-displacement curve of punch shear tests. Three significant damage mechanisms are identified. Energy absorbed by these damage mechanisms are partitioned and quantified for a thick-section composite made from plain-weave S-2 glass and toughened API epoxy SC15 resin. The effect of pre-defined delamination planes on energy absorption and damage mechanisms are also quantified.
Numerical Simulation of a High Pressure Supersonic Multiphase Jet Flow Through a Gaseous Medium
Authors: Lagumbay Randy S. , Vasilyev Oleg V. , Haselbacher Andreas , Wang Jin
Published: April 2008

Computational Fluid Dynamics (CFD) analysis is used to numerically study the structure and dynamics of a high-pressure, high-speed jet of a gas/liquid mixture through a gaseous medium close to the nozzle region. The complex structure of the jet near the nozzle region is captured before it breaks-up downstream. A new multiphase model based on a mixture formulation of the conservation laws for a multiphase flows is used in the simulation. The model does not require ad-hoc closure for the variation of mixture density with pressure and yields thermodynamically accurate acoustic propagation for multiphase mixtures. The numerical formulation has been implemented to a multi-physics unstructured code “RocfluMP” that solves the modified three-dimensional time-dependent Euler/Navier-Stokes equations for a multiphase framework in integral form. The Roe’s approximate Riemann solver is used to allow capturing of shock waves and contact discontinuities. For a very steep gradient, an HLLC scheme is used to resolved the isolated shock and contact waves. The developed flow solver provides a general coupled incompressible-compressible multiphase framework that can be applied to a variety of supersonic jet flow problems including fuel injection systems, thermal and plasma spray coating, and liquid-jet machining. Preliminary results for shock tube analysis and gas/liquid free surface jet flow through a gaseous medium are presented and discussed.
Experimental Investigation of Dynamic Response of RF-MEMS Switches
Authors: Ozdoganlar O. Burak , Epp David S. , Dyck Christopher W.
Published: April 2008

Ohmic and capacitive switches constitute an important segment of radio frequency microelectromechanical systems (RF-MEMS) components. The main function of these switches is to provide very rapid opening and closing of electrical contacts. To fulfill this requirement, the structural dynamics and coupled-physics response of candidate switch designs must be thoroughly understood. This paper presents a set of dynamic experimentation of two RF-MEMS ohmic switches with different geometries to determine their natural frequencies, mode shapes, and damping characteristics at pressures spanning from vacuum to atmospheric. The experimental facility used for the tests is also described in detail.
Processing of Composite Cathode and YSZ Coatings for Solid Oxide Fuel Cells
Authors: Xu Zhigang , Pai Devdas , Sankar Jag
Published: April 2008

In our research, composite cathodes of strontium-doped lanthanum manganite (LSM) and yttria-stabilized zirconia (YSZ) were produced by using slurry casting and sintering procedures. The slurry was prepared using ball milling. The time of ball milling was studied in terms of particle size and homogeneity of the powder in the slurry. The effect of the composition of the slurry on the microstructure was studied to obtain cathodes with desired porosity. The sintering process was also optimized to compromise the porosity, grain size, and strength of the cathodes. The YSZ coating was implemented using electrophoretic deposition in liquid phase. Different charging methods of the YSZ powder in the suspension was used and their results were compared. The microstructures of cathodes and YSZ coatings were characterized using scanning electron microscope (SEM).
A Depth-Averaged Model for Electrokinetic Flows in a Thin Microchannel Geometry
Authors: Lin Hao , Storey Brian D. , Santiago Juan G.
Published: April 2008

We have developed a generalized electrokinetic model suitable for the study of microchannel flows with conductivity gradients and shallow channel depths. An asymptotic analysis was performed with channel depth-to-width ratio as the smallness parameter, and three dimensional transport equations are reduced to a set to depth-averaged equations governing flow dynamics in the streamwise-spanwise plane of a shallow channel. The momentum equation uses a Darcy-Brinkman-Forchheimer type formulation, and the convective-diffusive transport of the conductivity field in the depth direction manifests itself as a dispersion effect on in-plane motion. Accuracy of the model was assessed by comparing the numerical results with direct numerical simulations. These depth-averaged equations provide the accuracy of three-dimensional modeling with a convenient quasi-two-dimensional equation set applicable to a fairly wide class of microfluidic devices.
Marker-Less Measurement and Analysis of Collagen Uncrimping, Orientation, and Local Deformation Patterns Under Controlled Loads
Authors: Doehring Todd C.
Published: April 2008

Deformation, crimp, and alignment patterns of collagen fibers in soft tissues have been measured using a novel testing system combining controlled loading with synchronized high-resolution imaging. Marker-less feature tracking was used to measure 2-D local deformations, and a radon transform was used to compute quantitative maps of crimp patterns and local tissue fiber orientation. We found highly nonuniform deformation and crimp patterns, with the highest strains near the clamps, and the lowest strains in the midsubstance region.
Experimental and Fundamental Analysis of Flow in Corners: Favorable and Adverse Pressure Gradients
Authors: Phillips Michael , Deutsch Steve , Fontaine Arnie , Yavuzkurt Savas
Published: April 2008

Three dimensional instantaneous velocity data were taken in a turbulent corner flow with smooth walls under zero, a favorable, and an adverse pressure gradient. The favorable pressure gradient was −26.5 Pa/m (K = 0.15E−6) and the adverse gradient was 34.9 Pa/m (K = −0.20E−6). This paper will concentrate on effects of the favorable and adverse pressure gradients. Zero pressure gradient results were published in an earlier manuscript [1]. Experiments were carried out in air with a free stream inlet velocity of 13 m/s and an axial Reynolds number of about one million. The data were collected using a three-component LDV system that was configured in a nearly orthogonal setup. Measurements were made down to a y+ of approximately 5, and should provide a valuable data set in developing models and predictive codes. Data were collected at two axial locations, 0.93 and 1.26 m measured from the virtual origin. The boundary layer thickness was 20.90 mm and 24.91 mm respectively at these locations for the zero gradient case. The favorable gradient had thicknesses of 19.35 mm and 22.53 mm respectively, whereas the thicknesses of adverse pressure gradient were 28.89 mm and 36.81 mm. At each position, instantaneous velocity profiles were measured at 6.35, 12.7, 20.6, 41.2, 82.3, 121.9, 164.5, 184.8, and 205.1 mm from the corner. The centerline profiles agree well with classical flat plate data. Three mean velocity and six Reynolds stress components have been calculated. The instantaneous velocity field data set is sufficient to compute higher order correlations. The data will be very valuable for development of computer codes and models for corner flows of all kinds and for heat transfer studies in the internal cooling channels of gas turbine blades and turbine end wall flow. An analysis of the data is presented and will provide a detailed database for this complex three dimensional flow fields.
Study on a PCM Heat Storage System for Rapid Heat Supply
Authors: Wei Jinjia , Kawaguchi Yasuo , Hirano Satoshi , Takeuchi Hiromi
Published: April 2008

A thermal energy storage system employing phase change material (PCM) for rapid heat discharge was studied numerically and experimentally. In the numerical studies, paraffin wax FNP-0090 (product of Nippon Seiro Co. Ltd.) was used as the PCM and was encapsulated in four different capsules (sphere, cylinder, plate and tube) for investigating the effects of geometrical configurations. The capsules filled with PCM were placed in a rectangular tank. Water was used as the working fluid in a rectangular tank. Water was used as the working fluid in the circulation system to discharge the storage tank. A one-dimensional model was used for solving the water temperature distribution along the flow direction in the tank and a conductive one-dimensional phase change model was used for simulating the solidification process of the PCM inside the capsules. The effects of the capsule diameter and shell thickness and the void fraction on the performance of the heat storage system were also investigated. Results shown include the variation of the outlet water temperature of the storage tank with time, the temperature and heat release distributions of the PCM along the flow direction in the tank at different times, etc. A plate heat exchanger was used as a heat storage tank for experimental study. FNP-0090 was filled into the channels (the space between two plates) of one side of the heat exchanger and water flowed in the channels of the other side of the heat exchanger. The effect of flow rate and initial temperature on the outlet fluid temperature and heat release was investigated. The numerical results and the experimental data agreed within 10%.
Integrating Fundamental STEM Material in a Laboratory Based Dynamic Systems Course
Authors: Avitabile Peter , Hodgkins Jeffrey , Van Zandt Tracy
Published: April 2008

A Dynamic Systems course generally involves material from previous undergraduate courses related to Differential Equations, Mathematical Methods for Engineers, Dynamics, etc. These underlying courses are basic building blocks that are critical to the students understanding of dynamic systems material. However, students often consider material in earlier courses as irrelevant since immediate practical application is not implemented in the previous courses. A traditional Dynamic Systems course, with traditional class lecture/homework/test scenario is destined to the same fate as these earlier courses if taught in the same manner. A new variation of this course has been implemented which has individual projects which address various analytical approaches using closed-form analytical solutions with MATLAB and SIMULINK computer software to completely address 1st and 2nd order systems. In addition, a laboratory based component is added to collect measured data for these systems to be used to further develop the analytical representation of these systems. Students work in groups and collect data to develop these models and prepare detailed reports summarizing their efforts. The project is described along with lab experiments performed. Student comments regarding the project are presented. Assessments of the first two semesters of the project clearly indicate that the students enjoyed the hands-on based project and clearly felt that they understood the material in much greater depth as a result of the project.
Effect of Viscosity on Gaseous Flow in a Micro-Nozzle
Authors: Murakami Shintaro , Asako Yutaka
Published: April 2008

Two-dimensional compressible momentum and energy equations are solved numerically to obtain the effect of viscosity on gaseous flow in a micro converging-diverging nozzle. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian (ALE) method. The numerical computations were performed for a wide range of the diverging angle and throat height and for no-heat conduction flow. The results are compared with one-dimensional analytical solutions for flow in a conventional sized nozzle and the effects of the viscosity on gaseous flow in the micro-nozzle are discussed.
Convective Instabilities of Electrokinetic Flows in a Cross-Shaped Microchannel
Authors: Posner Jonathan D. , Santiago Juan G.
Published: April 2008

Electrokinetic instabilities (EKI) in cross-shaped channels are relevant to injections for field amplified sample stacking, flow intersections in multi-dimensional assay devices, and electrokinetic systems with indeterminate sample chemistry. Electrokinetic instabilities are generated by a coupling of electric fields and ionic conductivity gradients. This coupling results in an electric body force in the bulk liquid that can generate temporal, convective, and absolute flow instabilities. In this work, we perform a parametric experimental study of convective instabilities in cross-shaped microchannels using epifluorescence microscopy and digital imaging. We report coherent flow structures and show that the critical electric field for instability is both a function of center-to-sheath conductivity ratio and applied field ratio. Finally, we quantify the degree of mixing rate of electrokinetically unstable flows with time-average probability density functions of concentration profiles.
Estimation of Buoyancy Change of an NTE Capsule Using PCM
Authors: Yamaguchi Yoshiyuki , Takanashi Koji
Published: April 2008

A new device which has negative thermal expansion behavior has been developed. One of the authors named it “NTE capsule” for short. The NTE capsule is expected to enhance the heat transfer moving up and down in a top-heated water tank. Recently the authors developed a new NTE capsule using Phase Change Material (PCM). The motion of it in a top-heated water tank has already been analyzed by numerical calculation and its motion has already been observed by operation experiment. In this study, the propriety of primitive design model was discussed. For this purpose, the buoyancy change of a NTE capsule using PCM was measured and compared to an estimated value by a primitive design model. As the result, the correction of the design model which gave the prediction of the more precise buoyancy change was shown.
Numerical Simulations of a Hydrogen-Enriched Methane Fueled Spark Ignition Engine
Authors: Matham V. , Majmudar K. , Aung K.
Published: April 2008

The use of alternative fuels such as natural gas (methane) in spark-ignition (SI) engines is beneficial to the environment as it reduces emissions of pollutants such as NOx from these engines with slight penalty on the performance. This paper investigated the use of methane and hydrogen/methane mixtures in an SI engine by numerical simulations. The numerical simulations were based on the models of finite heat release, cylinder heat transfer, pumping losses, and friction losses. Simulations were carried out to evaluate the effects of compression ratio, equivalence ratio, ignition timing, and engine speed on the performance of the SI engine. The results showed that the current model could satisfactorily predict the performance of an SI engine fueled by gaseous fuels.
Selection of Optimal Tool Geometry and Cutting Conditions in End Milling With Graphite as a Solid Lubricant
Authors: Reddy N. Suresh Kumar , Rao P. Venkateswara
Published: April 2008

Coolants dissipate the heat generated during machining and hence improve productivity, machinability, etc. However, the use of cutting fluids in machining operations may seriously degrade the quality of environment. So, in recent years researchers have started machining with the use of solid lubricants with the aim of improving machining performance and overcome some of the limitations that arise with the use of cutting fluids or while machining dry. This paper deals with an investigation on using graphite as a solid lubricant to reduce the heat generated at the milling zone for improving the surface roughness of the machined AISI 1045 steel. An experimental setup has been developed to maintain constant flow rate of graphite powder continuously on to the workpiece and tool interface zone. The experimental studies have been conducted to see the effect of tool geometry (radial rake angle and nose radius) and cutting conditions (cutting speed and feed rate) on the machining response such as surface finish in solid lubricant assisted machining using four fluted solid TiAlN coated carbide cutters. Results indicate that there is a considerable improvement in the performance of milling AISI 1045 steel using graphite as a solid lubricant when compared with machining with cutting fluids. An attempt has also been made to select optimum tool geometry and cutting conditions in end milling with graphite as a solid lubricant by using the prediction model obtained from these experimental results.
Application of Controllable Electric Coolant Pump for Fuel Economy and Cooling Performance Improvement
Authors: Cho Hoon , Jung Dohoy , Filipi Zoran S. , Assanis Dennis N. , Vanderslice John , Bryzik Walter
Published: April 2008

The engine cooling system for a typical class 3 pickup truck with a medium duty diesel engine was modeled with a commercial code, GT-Cool in order to explore the benefit of controllable electric pump on the cooling performance and the fuel economy. As the first step, the cooling system model with a conventional mechanical coolant pump was validated with experimental data. After the model validation, the mechanical pump sub-model was replaced with the electric pump submodel and then the potential benefit of the electric pump on fuel economy was investigated with the simulation. Based on coolant flow analysis the modified thermostat hysteresis was proposed to reduce the recirculating flow and electric pump effort, thus enabling assessment of the full power saving potential. It was also demonstrated that the radiator size could be reduced without any cooling performance penalty by replacing mechanical pump with the electric pump and decoupling of the pump speed from engine speed. The predicted results indicate that the cooling system with the electric pump can dramatically reduce the pump power consumption during the FTP 74 driving schedule and that radiator can be down-sized by more than 27% of the original size under grade load condition.
A Systematic Evaluation of NOx Formation Pathways and Subgrid Scale Models in Turbulent Nonpremixed CO/H2/N2 Jet Flame Predictions
Authors: Desam Padmabhushana R. , Smith Philip J.
Published: April 2008

Numerical prediction of Nitrogen Oxides (NOx) from combustion processes has been a challenging task to the combustion community, yet necessary to reduce environmental impact. Turbulent nonpremixed combustion is characterized by wide ranges of overlapping length and time scales associated with the mixing and chemical reaction processes. In practice, averaged governing equations are solved with subgrid scale models to account for the unresolved scales and interactions among them. A validation study of subgrid scale models is made for a turbulent nonpremixed CO/H2/N2 jet flame. Numerical predictions of Nitric Oxide (NO) quantities are compared with experimental data to evaluate the accuracy of subgrid scale models. Factors significantly affect NO formation are identified and studied thoroughly. In addition to thermal NO pathway, N2O-intermediate pathway is also dominant for this fuel composition. Even though this flame has a very low radiant fraction, the heat loss has a significant effect on NO formation because of the highly temperature dependent NO formation rates. Superequilibrium O-atom & OH radical levels showed high sensitivity to the thermal NO formation in high-temperature zones. An order of magnitude differences are observed in thermal NO by neglecting subgrid scale fluctuations on NO formation with some what less sensitivity to NO formation by the N2O pathway. For reliable and accurate NO numerical predictions, the following should be accounted for; NO formation pathways, radiation effects, nonequilibrium O-atom & OH-radicals and subgrid scale turbulence effects. Overall, the Zeldovich mechanism predicted thermal NO very closely and overpredictions resulted from the N2O-intermediate pathway.
Dynamic Forces and Hole Quality in Drilling Process
Authors: Pirtini Muge , Lazoglu Ismail
Published: April 2008

Drilling is one of the most commonly used machining processes in various industries such as automotive, aircraft and aerospace, dies/molds, home appliance, medical and electronic equipment industries. Due to the increasing competitiveness in the market, cycle times of the drilling processes must be decreased. Moreover, tight geometric tolerance requirements in designs, drilled hole precisions must be increased in production. On the other hand, process engineers have to be conservative when selecting machining conditions with respect to metal removal rate in order to avoid undesirable cases such as drill breakage, excessive cutter deflection and undesirable hole profile problems. In this research, a new mathematical model based on the mechanics and dynamics of the drilling process is developed for the predictions of cutting forces and hole qualities in advance. A new method is also proposed in order to obtain cutting coefficients directly from a set of relatively simple calibration tests. The model is able simulate the cutting forces for various cutting conditions in the process planning stage. In structural dynamics module, measured frequency response functions of the spindle and tool system are integrated into the model in order to obtain drilled hole profiles. Therefore, in addition to predicting the forces, the new model allows to determine and visualize drilled hole profiles in 3D and to select parameters properly under the manufacturing and tolerance constraints. Extensive number of experiments is performed to validate the theoretical model outputs with the measured forces and CMM hole profiles. It is observed that model predictions agree well with the force and CMM measurements. Some of the typical calibration and validation results are presented in this paper.
Innovation in Engineering Mechanics Course Instructions: A Novel Practice
Authors: Huang Lihua , Wang Yuefang , Jiang Feng
Published: April 2008

The course innovation in Engineering Mechanics in the Civil and Hydraulic Engineering Department, Dalian University of Technology is reviewed in this paper. For several decades, a complete system of mechanics teaching has been built up in the University. However, some drawbacks have appeared showing the system not apt to the information-technology age. In order to improve the teaching of Mechanics subjects and make it more suitable for the modern college education, a course innovation has been carried out since 1997 in the Civil and Hydraulic Engineering Department. The innovation includes the following perspectives: the construction of a new Mechanics teaching system, the adoption of new teaching methods, the edition of textbooks and the enforcement of experiments and practices. After a long time of practice, a new teaching system has been formulated and a much class time has been saved. Meanwhile, the qualification-oriented education rather than the examination-oriented education is emphasized. It is demonstrated that students benefit from this course innovation for not only mastering the knowledge from textbooks better, but also for greatly improving their abilities of analyzing and solving engineering problems.
The Fractal Feature of the Liquid-Vapor Interface
Authors: Zeng Danling , Wang Deming , Liu Juanfang
Published: April 2008

Interfacial phenomenon appears frequently in practice. It plays important roles in various fields of science and technology. In order to make a clear understanding on the characteristics of an interface, a molecular dynamics simulation (MDS) was performed. The simulation results show that there exists a transition layer between the coexisting phases in which thermodynamics properties changes continuously. On the other hand, according to the fractal theory it is considered that the interface is not a smooth surface but a fractal one. The fractal dimension of it is calculated in the paper by the aid of the general approach provided in fractal theory. Furthermore, a relation between interface tension and fractal dimension of the interface was advanced. The surface tension thus obtained agrees well with the experiments.
Forced-Convection Condensation of Ethylene Glycol on Integral-Fin Tubes
Authors: Namasivayam Satesh , Briggs Adrian
Published: April 2008

This paper reports new experimental data for forced-convection condensation of ethylene glycol on a set of five single, copper, integral-fin tubes. The five tubes had fin root diameter of 12.7 mm, fin height and thickness of 1.6 mm and 0.25 mm respectively. Fin spacings were 0.25, 0.5, 1.0, 1.5 and 2.0 mm. A plain tube of outside diameter 12.7 mm was also tested. The tests, which were performed at near constant pressure of approximately 15 kPa, covered vapor velocities between 10 and 22 m/s and a wide range of heat fluxes. The best performing tube was that with a fin spacing of 0.5 mm, which had an enhancement ratio (compared to the plain tube at the same vapor-side temperature difference and vapor velocity) of 2.5 at the lowest vapor velocity tested, increasing to 2.7 at the highest. The increase in enhancement ratio with increasing vapor velocity, which is the opposite trend to that found in most earlier experimental studies, was thought to be due to a slight reduction in condensate flooding between the fins due to increased vapor shear.
Multicriteria Design Optimization for an Artificial Hip Prosthesis
Authors: Toshimasa Ishida , Ikuya Nishimura , Hiromasa Tanino , Hiroshi Ito , Takeo Matsuno , Yoshinori Mitamura
Published: April 2008

A multiobjective optimization was executed to solve several failure problems of the cemented hip stem. The objective functions are several types of stresses in the cement mantle: largest maximum principal stress (PRINCIPAL), stem/cement interface shear stress (S/C shear), bone/cement interface shear stress (B/C shear), tensile stress at proximal-lateral section (TENSILE). Pareto maps were made in order to show the relationship between the objective functions. In the results, each objective function was reduced 44–62%. Trade-off appeared between PRINCIPAL and TENSILE.
A Piezoelectric Bidirectional Micropump for a Medical Application
Authors: Doll A. , Goldschmidtboeing F. , Heinrichs M. , Woias P. , Schrag H. J. , Hopt U. T.
Published: April 2008

In this work, we present recent developments of our novel artificial sphincter system. The highly integrated system consists of several inflatable balloons and a micropump. We will analyse the apparatus concerning the volumes that have to be moved and make a specification for a suitable pump. A bidirectional silicon micropump with active valves is used to meet the worked out requirements of the sphincter prosthesis. The fabrication of the pump is described and the working principle will be explained. A summary of an analytical lumped parameter approach to model the pump’s performance is given. Optimization measures derived from this model are pointed out. The driver electronics is described and energy consumption issues are discussed. Two different pump designs were realized. The measured pump performance concerning the flowrate and the achievable pressure were compared to the theoretical model. A good agreement between model and measured data was found. A maximum flowrate of 1.3 ml/min and a maximum backpressure of 40000 Pa was achieved. The realized pump performance is sufficient for first experimental studies with the artificial sphincter system.
Optical and Heat Transfer Characteristics in a Rapid Thermal Annealing System for LCD Manufacturing Procedures
Authors: Lee Seong Hyuk , Kim Hyoung June , Shin Dong Hoon , Choi Young Ki , Park Seungho , Lee Joon Sik
Published: April 2008

The objectives of this article are to suggest a way to evaluate the quality of polycrystalline silicon film from the thin film optics analysis and also to investigate the heat transfer characteristics in a rapid thermal annealing system for LCD manufacturing. The characteristic transmission matrix method is used to calculate the transmittance, and the predictions are compared with the experimental data for two different samples. The transient and one-dimensional conductive and radiative heat transfer equations are additionally solved to predict the surface temperatures of thin films. The two-flux method is also used for radiation and the ray-tracing method is utilized to consider the wave interference. As the film thickness increases, the peak transmittance increases and the wavelength for the peak becomes longer due to wave interferences. These characteristics can be used for in-situ and practical estimation of the silicon film quality during the crystallization process. From thermal analysis, it is shown that the selective heating in the multilayer film structure acts as an important mechanism during the annealing of silicon film deposited on the glass.