bluuebunny/crossref_metadata_2025 huggingface dataset:
Photopolymerizable Liquid Crystal Monomer-Oxide Nanoparticle Composites
Authors: Wellinghoff S. T. , Nicolella D. P. , Hanson D. P. , Rawls H. R. , Norling B. K.
Published: May 2008

Methacrylate and acrylate terminated monomers can be rapidly polymerized to polymer glasses useful in biomaterials, photolithography and rapid prototyping, optical coatings and composites. Unfortunately, polymerization shrinkage results in loss of tolerance and the development of internal stresses which can be especially critical in the case of highly crosslinked glasses. Structurally complicated oligomeric mixes of dimethacrylate monomers that exhibit a nematic liquid crystal to isotropic transition above room temperature have been synthesized in a low cost one pot synthesis to surmount the problem of polymerization shrinkage and the propensity of single component monomers to crystallize from the liquid state. Photopolymerization from the ordered liquid crystal state into a less ordered glass minimizes volumetric shrinkages to between 1–2% at greater than 90% polymerization conversion. These polymer glasses exhibited elastic bending moduli of 1.2 GPa to 1.5GPa, fracture strengths of 70–100MPa and fracture toughness of K=0.3–0.4 (MPa)1/2. In some cases the glasses exhibited ductile behavior which is unusual for highly crosslinked materials. Room temperature viscosities of 100P–2000P permit facile processing of the liquid crystal monomers with inorganic particles to make dental restorative composites.
Deposition of YSZ Thin Films by Liquid Fuel Combustion Chemical Vapor Deposition
Authors: Xu Zhigang , Sankar Jag , Wei Qiuming , Lua Jim , Yamolenko Sergey , Pai Devdas
Published: May 2008

Thin film of YSZ electrolyte is highly desired to reduce the electrical resistance in SOFCs. YSZ thin Films have been successfully produced using liquid fuel combustion chemical vapor deposition (CCVD) technique. Nucleation of the YSZ particles were investigated based on two processing parameters, i.e., substrate temperature and total-metal-concentration in the liquid fuel. An optimum substrate temperature was found for highest the nucleation density. The nucleation density was increased with the total-metal-concentration. Microstructure evolution of the YSZ particles in the early stage in film growth was also studied. It was found that the particle growth rate was linear with processing time, and the particle orientation was varying with the time in the early stage of the film processing. To enhance the film growth rate, the effect of thermophoresis was studied. By increase the temperature gradient towards substrate, the effect of thermophoresis was enhanced and the film growth is also increased.
Synthesis and Characterization of Metal-Ceramic Thin Film Nanocomposites With Improved Mechanical Properties
Authors: Kumar D. , Sudhir N. , Yarmolenko S. , Wei Q. , Sankar J. , Narayan J. , Pennycook S. J.
Published: May 2008

Thin films composite materials consisting of metallic nanocrystals embedded in an insulator host have been synthesized using alternating-target pulsed laser deposition of Fe/Ni and Al2O3. The evaluation of structural quality of the thin film composites using high resolution transmission electron microscopy and scanning transmission electron microscopy with atomic number contrast has revealed the formation of a biphase system with thermodynamically driven segregation of Ni and alumina during pulsed laser deposition. The best hardness values of the thin film composites, measured using nanoindentation techniques, was found to 20–30% larger than pure alumina films fabricated under identical conditions. The improvement in values of hardness of Al2O3 thin films by embedding metal nanocrystals is related to the evolution of a microstructure which efficiently hinders the manipulation and movement of dislocation and the growth of microcracks, which in turn, is achieved by grain boundary hardening.
Novel Nanocrystalline Composites
Authors: Narayan J.
Published: May 2008

We have developed a novel processing technique to fabricate tungsten carbide (WC) nanocomposites with uniform grain size. In this method, pulsed laser deposition of WC in conjunction with a few monolayers of nickel aluminide (NiAl) is used to control the grain size of nanocrystalline composites. The grain size of WC was controlled by the thickness of tungsten carbide and the substrate temperature. The role of NiAl is to ensure the nucleation of tungsten carbide islands, and it is relatively insoluble in WC. Using this approach, we have fabricated nanocomposites of grain sizes ranging from 6 nm to 35 nm. The hardness of the composite increases with the decrease in grain size, following approximately Hall-Petch relationship. Below a critical value, we observed a softening behavior which has been modeled to be related to intragrain deformation or grain boundary shear. The role of NiAl in grain boundary deformation is of particular interest in strengthening and stabilizing against the grain growth of nanocrystalline composites. The new WC-NiAl composite is expected to have superior high-temperature strength compared to conventional microcrystalline WC-Co composites.
Novel Nanostructural Biomaterial Composites
Authors: Narayan R. J.
Published: May 2008

Hydrogen-free diamondlike carbon (DLC), with hardness values close to that of diamond, possess many desirable biocompatible properties for a variety of biomedical applications. The DLC coatings can be applied to joints prostheses, heart valves, and other medical devices. Unfortunately, hydrogen-free DLC coatings have a large compressive stresses which result in poor adhesion and wear characteristics. In this paper, we present results on silver doping of DLC to alleviate internal stresses as well as create DLC-Ag nanocomposites where Ag is in the form of nanoparticles. The Ag nanoparticles are expected to impart antimicrobial properties by providing sources of electrons. In the second part of the paper, we have created DLC and nanotube composites where nanotubes grow normal to the surface. This novel architecture not only alleviates internal stresses, but DLC + Nanotube composites have enhanced hardness and unique antimicrobial properties. Finally, we discuss novel multilayer DLC and hydroxyapatite (HA) composite where HA and DLC films are deposited sequentially at room temperature. The HA films with composites close to that of bone is considered very desirable for biocompatibility and integration with base structures. We discuss novel processing, characterization, hardness and bioeompatible properties of all these composites in detail.
Evaluation of the Performance of Piezoceramic Materials at Moderately Elevated Temperatures
Authors: Schulz Mark J. , Sundaresan Mannur J. , McMichael Jason , Clayton David
Published: May 2008

Piezoceramic materials used for the actuating and sensing of smart structures are limited in the temperature range in which they can operate. Operation at temperatures above ambient is desired for many applications including aircraft, turbine engine housings and others. The decrease in actuation and sensing capability with increasing temperature is due to the loss of stiffness of the adhesive used to bond piezoceramic patches to structures, and the loss of the piezoceramic properties through partial depoling of the lead zirconate titanate material. This paper examines the performance of piezoceramic patch actuators at moderately elevated temperatures.
An Averaging Approach for Noisy Strongly Nonlinear Periodically Forced Systems
Authors: Choi Seunggil , Sri Namachchivaya N.
Published: May 2008

The purpose of this work is to develop a unified approach to study the dynamics of single degree of freedom systems excited by both periodic and random perturbations. The near resonant motion of such systems is not well understood. We will study this problem in depth with the aim of discovering a common geometric structure in the phase space, and to determine the effects of noisy perturbations on the passage of trajectories through the resonance zone. We consider the noisy, periodically driven Duffing equation as a prototypical single degree of freedom system and achieve a model-reduction through stochastic averaging. Depending on the strength of the noise, reduced Markov process takes its values on a line or on graph with certain gluing conditions at the vertex of the graph. The reduced model will provide a framework for computing standard statistical measures of dynamics and stability, namely, mean exit times, probability density functions, and stochastic bifurcations. This work will also explain a counter-intuitive phenomena of stochastic resonance, in which a weak periodic force in a nonlinear system can be enhanced by the addition of external noise.
Modeling for Mass Transfer and Thermal Stress of Silicon Carbide PVT Growth
Authors: Ma R.-H. , Zhang H. , Dudley M. , Ha S. , Skowronski M.
Published: May 2008

The growth of SiC bulk crystal is studied using a physical model including chemical reactions, mass transfer and growth kinetics. The thermal stress distribution in an irregular shaped growing crystal is predicted using a two-dimensional anisotropic stress model. The growth and stress models are integrated into an existing global heat transport model to investigate variation of thermal field, growth rate and the shape of the as-grown crystal as well as the thermal stress distribution during a real time growth processes. The onset of dislocation is also correlated with thermal elastic stress qualitatively using the CRSS model. The simulated results are compared with experimental measurement. The effects of the growth system geometry are also discussed.
Thermal Intumescent Characteristics of Heated Sodium Silicate
Authors: Otaka Takeshi , Asako Yutaka
Published: May 2008

A fire barrier material is made of a rubber in which intumescent materials are mixed. Sodium silicate is one of the intumescent materials which intumesces at low temperature. In this report, the thermal intumescent characteristics of water glass and sodium metasilicate are investigated. Thermal intumescent ratio of water glass and sodium metasilicate were measured using a thermo-gravimetry (TG/DTA) with the heating rate in the range from 1 K/min to 99.9 K/min. As the result, it is clarify that thermal intumescent characteristics depend on the heating rate. Thermal intumescent ratio increases with increasing the heating rate. No intumescence was observed under the condition that the heating rate ranges from 1 K/min to 20 K/min.
Packing Characteristics and Its Effect on Heat Transfer Characteristics in Melting of Granular Packed Bed Subject to Horizonal Forced Convection
Authors: Hao Y. L. , Tao Y.-X.
Published: May 2008

A series of experiments are conducted to investigate the characteristics and its effect on the melting and heat of a packed bed consisting of melting ice particles to horizontal forced convection. The volumes and situations of the melting ganular packed beds are by the visualization observations and measurements digital camcorders within the range of Re = 71 ~ 2291, Gr/Re2 = 1.48×10−5 ~ 17.32, and Ste = 0.0444 ~ 0.385, respectively. The mass of ice particles is measured at the time interval during the melting process. Two types of pattern can be found under the different conditions. The different types of heat transfer characteristics emerge in type of packing pattern. The correlations for each type of pattern are obtained based on the experimental results.
Fluid Flow and Lateral Fluid Dispersion in Bounded Granular Beds
Authors: Soleymani Azita , Takasuo Eveliina , Zamankhan Piroz , Polashenski William
Published: May 2008

Results are presented from a numerical study examining the flow of a viscous, incompressible fluid through random packing of nonoverlapping spheres at moderate Reynolds numbers (based on pore permeability and interstitial fluid velocity), spanning a wide range of flow conditions for porous media. By using a laminar model including inertial terms and assuming rough walls, numerical solutions of the Navier-Stokes equations in three-dimensional porous packed beds resulted in dimensionless pressure drops in excellent agreement with those reported in a previous study (Fand et al., 1987). This observation suggests that no transition to turbulence could occur in the range of Reynolds number studied. For flows in the Forchheimer regime, numerical results are presented of the lateral dispersivity of solute continuously injected into a three-dimensional bounded granular bed at moderate Peclet numbers. Lateral fluid dispersion coefficients are calculated by comparing the concentration profiles obtained from numerical and analytical methods. Comparing the present numerical results with data available in the literature, no evidence has been found to support the speculations by others for a transition from laminar to turbulent regimes in porous media at a critical Reynolds number.
Impingement Heat Transfer of Free-Surface Liquid Jets
Authors: Tong Albert Y.
Published: May 2008

The problem of convective heat transfer of a circular liquid jet impinging onto a substrate is studied numerically. The objective of the study is to understand the hydrodynamics and heat transfer of the impingement process. The Navier-Stokes equations are solved using a finite-volume formulation. The free surface of the jet is tracked by the volume-of-fluid method. The energy equation is modeled by using an enthalpy-based formulation. Detailed flow fields as well as free surface contours and pressure distributions on the substrate have been obtained. Local Nusselt number variations along the solid surface have also been calculated. The effects of several key parameters on the hydrodynamics and heat transfer of an impinging liquid jet have been examined. It has been found that the jet-inlet velocity profile and jet elevation have a significant effect on the hydrodynamics and heat transfer, particularly in the stagnation region, of an impinging jet. The numerical results have been compared with experimental data obtained from the literature. The close agreement supports the validity of the numerical study.
Turbulent Flow Over a Backward-Facing Step Using Penalty and Equal-Order Finite Element Methods
Authors: Akberov Roald , Pepper Darrell W. , Chen Yitung
Published: May 2008

Two-dimensional steady incompressible turbulent flow over a backward-facing step was calculated using equal-order and penalty function Emite element methods. The standard k–ε turbulence model with wall functions was applied. Results from both of the methods for pressure-velocity coupling look similar to each other. The greatest discrepancy was observed for the velocity vector plots behind the step. While the equal order method showed physically correct behavior of velocity near the walls, the penalty function method gave oscillations for the velocity component parallel to the wall.
Numerical Simulation of Turbulent Heat Transfer to Near-Critical Water in a Curved Pipe
Authors: Zheng B. , Lin C. X. , Ebadian M. A.
Published: May 2008

Numerical simulations are performed to investigate the developing turbulent flow and heat transfer characteristics of water near the critical point in a curved pipe. The Reynolds stress model is employed to simulate the turbulent flow and heat transfer in a curved pipe at a constant wall temperature with or without buoyancy force effect. Due to the great variation in physical properties of water near the critical point, the turbulent heat transfer can be significantly altered as compared with the pure force convection in the curved pipe. This study explores the influence of the near-critical pressure on the development of fluid flow and heat transfer along the pipe. Based on the results of this research, the development of velocity, temperature, and heat transfer coefficient along the pipe are presented graphically and analyzed.
Heat Transfer in a Suddenly Expanded Turbulent Flow Past a Porous Insert Using Linear and Non-Linear Eddy-Viscosity Models
Authors: de Lemos Marcelo J. S. , Assato Marcelo
Published: May 2008

This work presents numerical results for heat transfer in turbulent flow past a backward-facing-step channel with a porous insert using linear and non-linear eddy viscosity macroscopic models. The non-linear turbulence models are known to perform better than classical eddy-diffusivity models due to their ability to simulate important characteristics of the flow. Parameters such as porosity, permeability and thickness of the porous insert are varied in order to analyze their effects on the flow pattern, particularly on the damping of the recirculating bubble after the porous insertion. The numerical technique employed for discretizing the governing equations is the control-volume method. The SIMPLE algorithm is used to correct the pressure field. Wall functions for velocity and temperature are used in order to bypass fine computational close to the wall. Comparisons of results simulated with both linear and non-linear turbulence models are presented.
Heat Transfer Augmentation in an Oscillating Flow
Authors: Holst A. , Lundgren E. , Marksten U.
Published: May 2008

For combustors a heat transfer augmentation of two to five times higher than expected has been reported. Experiments, where the temperature profile in the tail pipe of the pulse combustor has been measured, give no indication why the heat transfer should be augmented. The objective is to study the heat transfer of an oscillating flow between two parallel plates. A set of governing equations is formulated from first principles. Analytical solutions can then be obtained for both the velocity and temperature fields for the special flow considered. The heat conduction vector can so be determined and the heat transfer at the plates over one cycle is found to be dependent of the frequency of the oscillations as well as the phase difference between the pressure and temperature oscillations. From the analysis it is found that for certain intervals of the phase difference and the frequency of the oscillations an augmented heat transfer can be found. This means that an augmented heating (or cooling) process can be arranged in a steady flow by superimposing oscillations.
Numerical Prediction of Enhanced Heat Transfer Using Oval Tubes and Delta Winglets
Authors: Maurya D. , Tiwari S. , Biswas G. , Eswaran V. , Saha A. K.
Published: May 2008

Unsteady three-dimensional laminar flow and heat transfer in a channel with a built-in oval tube and delta winglets have been obtained through the solution of the complete Navier-Stokes and energy equations using a body-fitted grid and a finite-volume method. The geometrical configuration represents an element of a gas-liquid fin-tube cross flow heat exchanger. The air-cooled condensers of the geothermal power plants also use fin-tube heat exchangers. The size of such heat exchangers can be reduced through enhancement in transport coefficients on the air (gas) side, which are usually small compared to the liquid side. In a suggested strategy, oval tubes are used in place of circular tubes, and delta winglet type vortex generators in common-flow-down configuration are mounted on the fin-surface in front of the tubes, while another delta winglet pair in common-flow-up configuration is mounted downstream of the first set of winglets. An evaluation of this augmentation strategy is attempted in this investigation. The investigation was carried out for a winglet angle of attack of 40 degrees to the incoming flow. The structures of the velocity field, and the heat transfer characteristics have been presented. The results indicate that vortex generators in conjunction with the oval tube show definite promise for the improvement of fin-tube heat exchangers.
Shaping the Complexity of a Design
Authors: Rodri´guez-Toro Carlos , Tate Susan , Jared Graham , Swift Kenneth
Published: May 2008

This paper presents an introduction to concepts of complexity in support of assembly-oriented design, to guide the designer in creating a product with the most effective balance of manufacturing and assembly difficulty. The goal is to provide the designer with such information throughout the design process so that an efficient design is produced in the first instance. In this paper, the range of definitions and applications of the term ‘complexity’ are reviewed and then definitions appropriate for the situation are selected. The metrics required for comparison of variants of different complexity is discussed. Finally, a research agenda is presented for development of the proposed metrics within the Designers’ Sandpit project.
Analysis and Design for Two-Handed Heavy Part Assembly Methods
Authors: Wongwanich Yodyot , Sturges Robert H.
Published: May 2008

In spite of advances in industrial automation, manual assembly tasks continue to be an important feature of many industrial operations. In heavy part assembly, some pieces of raw material or equipment are too heavy to be safely handled by just one operator. Material handling devices such as Jib cranes or overhead cranes are employed to help operators work safer and, in some cases, faster. However, during full-load productions, access to these devices could become limited due to insufficient resources and hence, delay or extend the cycle times. The authors studied how people perform the assembly and subsequently applied Fitts’ Index of Difficulty to develop a model which indicates factors that increase the task difficulty. This model can also be used as an assembly time predictor. Since improving the efficiency of an overhead crane could significantly reduce the total cycle times and production costs, the authors modified the crane by adding a spring between the hook and the gripper to help support the weight. Two sets of experiments were conducted. The first set was to investigate the effect of spring stiffness on assembly time. The result indicated that using a spring that was too soft could create a parasitic oscillation, which increases the assembly time. The objective of the second set was to compare the assembly time of using the regular crane to that of the modified crane in situations where the part weights and the task difficulty vary. As a result of the modifications, assembly performance tended to increase by approximately 250% from using the modified crane.
Geometric Variation Prediction for Automotive Aluminum Welded Assemblies
Authors: Xiong C. H. , Rong Y. , Koganti R. P. , Zaluzek M. J. , Wang N.
Published: May 2008

Assembly error prediction is one of the key problems in quality control. The objective of this paper is to develop the statistical error analysis model for assembling, to derive measures of controlling the geometric variations in assembly with multiple assembly stations, and to provide a statistical tolerance prediction/distribution toolkit integrated with CAD system for responding quickly to market opportunities with reduced manufacturing costs and improved quality. First the homogeneous transformation is used to describe the location and orientation of assembly features, parts and other related surfaces. The desired location and orientation, and the related fixturing configuration (including locator position and orientation) are automatically extracted from CAD models. The location and orientation errors are represented with differential transformations. Then the statistical error prediction model is formulated and the related algorithms are integrated with the CAD system so that the complex geometric information can be directly accessed. In the prediction model, the manufacturing process (joining) error, induced by heat deformation in welding, is taken into account. Finally case studies are presented to verify the prediction algorithms. The proposed model has following characteristics: 1) variety error elements of both design and process aspects are taken into account; 2) assembly error prediction and control can be dealt with for multiple assembly stations and multiple fixtures in each station; and 3) the technical approach is integrated with CAD system.
A Clustering-Based Approach for Failure Mode Identification
Authors: Arunajadai Srikesh G. , Stone Robert B. , Tumer Irem Y.
Published: May 2008

Research has shown that nearly 80% of the costs and problems are created in product development and that cost and quality are essentially designed into products in the conceptual stage. Currently failure identification procedures (such as FMEA, FMECA and FTA) and design of experiments are being used for quality control and for the detection of potential failure modes during the detail design stage or post-product launch. Though all of these methods have their own advantages, they do not give information as to what are the predominant failures that a designer should focus on while designing a product. This work uses a functional approach to identify failure modes, which hypothesizes that similarities exist between different failure modes based on the functionality of the product/component. In this paper, a statistical clustering procedure is proposed to retrieve information on the set of predominant failures that a function experiences. The various stages of the methodology are illustrated using a hypothetical design example.
Feature Based Costing (FBC) of Welded Assemblies: A Genetic Approach
Authors: Subbarao Gautam , Philpott Michael L. , Schrader R. Sebastian , Holmes Dale E.
Published: May 2008

A genetic algorithm based welding planner capable of using parametric features to determine the manufacturing cost of welded assemblies has been developed. Parametric weld feature information obtained from a CAD system is translated to a hybrid traveling salesman problem. A genetic algorithm is used to search for a sequence of welds that minimizes the cost of the welded assembly. Emphasis is placed on developing a mechanistic, feature based DFM tool, with the aim of rapidly providing welded assembly cost feedback to the designer in a CAD environment, while maintaining a balance between accuracy and computational speed.
An Algorithm for Design of Multi-Stage Molds for Multi-Material Objects With Complex Interfaces
Authors: Gupta S. K. , Li X. , Priyadarshi A.
Published: May 2008

This paper describes an algorithm for automated design of multi-stage molds for manufacturing multi-material objects using multi-shot injection molding process. The algorithm described in this paper is a significant improvement over our previous algorithm [15] that worked on multi-material objects with simple planar interfaces. In the multi-stage molding process, the desired multi-material object is produced by carrying out multiple molding operations in a sequence, adding one material in the target object in each mold-stage. Each mold-stage can add only one type of material. Therefore, we need a sequence of mold-stages such that (1) each mold-stage adds a single-material component either fully or partially, and (2) the molding sequence completely produces the desired object. We expect that our algorithm will provide the necessary foundations for automating the design of multi-stage molds and therefore will help in significantly reducing the mold manufacturing lead-time.
Measurement of the Silicon Nanowire Thermal Conductivity
Authors: Li Deyu , Majumdar Arun , Wu Yiying , Yang Peidong , Kim Philip , Shi Li
Published: May 2008

One-dimensional (1D) materials such as various kinds of nanowires and nanotubes have attracted a lot of attention recently because of their potential applications in nanoelectronic and energy conversion devices [1–3]. As the size of low dimensional materials is confined to be comparable to the phonon mean free path, the thermal conductivity can be reduced due to boundary scattering. A theoretical study [4] further suggests that as the diameter of a Si nanowire becomes smaller than 20 nm, the phonon dispersion relation can be modified due to the boundary confinement and the phonon group velocities will be less than that of the bulk, which will also tend to reduce the thermal conductivity. A molecular dynamics (MD) simulation [5] has shown that for nanowires of cross sections ranging from 2.58 to 28.62 nm2, the thermal conductivity could be two orders of magnitude smaller than those of bulk Si crystals in a temperature range from 200 K to 500 K. In their paper, the authors also solved the Boltzmann transport equation (BTE) and showed that the MD results fit reasonably well with the BTE solutions. It is very important to experimentally verify the theoretical predictions and provide experimental data for the device design in nanoelectronic and nanoscale energy conversion devices. However, no systematic experimental studies of the size effect on the nanowire thermal conductivity have been published.
Initial Assessment of Small Systems (MEMS and NEMS) Course Taught in an Undergraduate and Graduate Classroom
Authors: Paquette Jason W. , Kim K. J.
Published: May 2008

Micro-electro-mechanical systems (MEMS) and nanotechnology are a fast developing technology which combines very small mechanical structures with microelectronics circuits. These devices range in scale from nanometers (10−9 m) to several millimeters, and they are fabricated using the established techniques of microelectronics construction. Due to the increasingly large size and opportunities in these fields, it is becoming necessary to offer course work with small systems for students at the undergraduate and graduate level. A course in MEMS/NEMS small systems was taught at the University of Nevada, Reno in the spring of 2002. The course used the text written by Hsu [1] along with supplementary material. Problems and examples of applying fundamental principles from mechanics, electromagnetism, thermodynamics and optics among others to problems in MEMS design, fabrication and actuation were considered. The course is primarily designed to introduce both engineering undergraduate and graduate students to the possibilities of this exciting new engineering field. Also, current MEMS, NEMS, and microfluidic applications, such as sensors, actuators, heat exchangers, and chemical/biological analysis systems, were discussed. The course introduced a broad spectrum of topics related to small system development including basic engineering science for small system design, engineering mechanics, thermofluid engineering, scaling laws, materials for small systems, fabrication technologies, small system design, advanced nano-materials (molecular motors, nanotubes, polymer nanocomposites), standard characterization techniques: SEM, TEM, AFM, and applications (MEMS, NEMS and microfluidics).
Achieving Quality Teaching and Learning Through Integrating Proper Research Activities in Mechatronics Education
Authors: Du Winncy Y.
Published: May 2008

This paper addresses an approach to improve the quality of engineering education by incorporating research components into the teaching in the form of team projects. By reflecting the author’s experience on teaching an undergraduate junior course – ME106/EE106 Mechatronics, the feasibility and effectiveness of this approach is demonstrated. It is shown that integrating research activities, industry sponsored projects, lab construction, and national student design contests into teaching helps improving the quality of engineering education. Properly integrating research activities into classroom also helps the faculty to maintain the dynamic balance between the teaching and research.
Second Law Based Optimization of Falling Film Single Tube Absorption Generator
Authors: Jani Saeid , Saidi Mohamad H. , Heydari Ali , Mozaffari Ali A.
Published: May 2008

The objective of this paper is to provide optimization of falling film Li/Br solution on a horizontal single tube based on minimization of entropy generation. Flow regime is considered to be laminar, the effect of boiling has been ignored and wall temperature is constant. Velocity, temperature and concentration distributions are numerically determined and dimensionless correlations are obtained for predicting the average heat transfer coefficient and average evaporation factor on the horizontal tube. Thermodynamic imperfection due to passing lithium bromide solution is attributed to non-isothermal heat transfer; fluid flow friction and mass transfer irreversibility. Scale analysis shows that the momentum and mass transfer irreversibilities can be ignored at the expense of heat transfer irreversibility. In the process of optimization, for a specified evaporation heat flux, the entropy generation along with the developed heat and mass transfer dimensionless correlations is minimized and the optimal geometry and the optimum thermal hydraulic parameters are revealed. The investigation cited here indicates the promise of entropy generation minimization as an efficient design and optimized tool.
Stability of Bioconvection in Suspensions of Gyrotactic Microorganisms in Porous Media
Authors: Kuznetsov A. V. , Avramenko A. A.
Published: May 2008

In this paper, a model of bioconvection in a suspension of gyrotactic motile microorganisms in a fluid saturated porous medium is suggested. The microorganisms considered in this paper are heavier than water and gyrotactic behavior results in their swimming towards the regions of most rapid downflow. Because of that, the regions of downflow become denser than the regions of upflow. Buoyancy increases the upward velocity in the regions of upflow and downward velocity in the regions of downflow, thus enhancing the velocity fluctuations. The experiments performed by Kessler (1986) and the numerical results of Kuznetsov and Jiang (2001) indicate that if the permeability of porous medium is sufficiently small it will prevent the development of convection instability. However, for practical purposes, in order to maximize the flux of the cells in the upward direction it is desirable to have the permeability of the porous medium as high as possible. The aim of this paper is to investigate the value of critical permeability. If permeability is smaller than this critical value bioconvection does not occur and microorganisms simply swim in the upward direction.
Time-Dependent Diffusion in the Alveolar Region of the Lungs: Effect of Moving Red Blood Cells
Authors: Merrikh A. A. , Lage J. L.
Published: May 2008

Results from a preliminary numerical simulation of alveolar gas diffusion with moving capillary red blood cells (RBCs) are presented. The alveolar region is modeled with four basic constituents, namely the alveolus (or gas region), the tissue (a region lumping the alveolar and capillary membranes, and the interstitial fluid), the blood plasma (a liquid region) and the RBCs. A single, straight capillary with equally spaced RBCs moving together with the blood plasma is considered in this preliminary study. The numerical simulation attempts also to mimic the time-varying gas concentration in the alveolus region due to respiration. Realistic physical parameters (e.g., dimensions, diffusivities and RBCs speed) are used for simulating CO diffusion, in accordance to clinical tests for determining the lung diffusing capacity. Results are compared to published results obtained when the RBCs are fix in place (stationary). The RBCs moving effect, relevant at high hematocrit, is to increase the resulting lung diffusing capacity.
Application of the Principle of Minimum of Entropy Production to the Analysis of the Eutectic Solidification
Authors: Geskin Ernest S.
Published: May 2008

The principle of minimum entropy production is applied to the analysis of the formation of a solid structure in the course of the eutectic solidification. It is assumed that the liquid and solid phases are divided by the plane boundary and the solidification rate is constant. At these conditions solidification results in the development of the lamellar structure in the solid and the process is defined by the lamellar spacing and the rate of the motion of the liquid-solid interface. The variational equation describing system evolution is modified to describe the process in question. A solution of this equation determines the relationship between the solidification rate and the lamellar spacing. The obtained results complies with experimental data.
Thermodynamic Theory of Convective Drying Process of Porous Media
Authors: Li You-Rong , Zeng Dan-Ling
Published: May 2008

Based on non-equilibrium thermodynamic theory and combined with the conservation laws, a comprehensive theoretical model was established to describe heat and mass transfer during convective drying process, and numerical calculation was performed. The results show that: (a) the external convective heat and mass transfer may be treated as the conductive heat transfer with internal heat source and the molecular mass diffusion with internal mass source, respectively, and the ability of heat and mass transfer mainly depends on the strength of the heat source and mass source; the higher the temperature of the drying media, the lower the strength of the internal heat source, but the higher that of the internal mass sources; (b) the evaporation of internal water takes place inside the whole material, and the molecular mass diffusion of the internal vapor is in the direction of decreasing mass transfer potential, not along the decreasing partial pressure of vapor.
Heat Transfer and Pressure Drop Correlations for Double-Pass Solar Collector With and Without Porous Media
Authors: Sopian K. , Elradi Adam M. , Abdullah Shahrir , Wong K. V.
Published: May 2008

Correlations of transient heat transfer and pressure drop have been developed for air flowing through the porous media, which packed a double-pass solar air heater. Various porous media are arranged in different porosities to increase heat transfer, area density and the total heat transfer rate. Transient heat transfer experiments indicate that both the heat transfer coefficient and the friction factor are strong functions of porosity. The heat transfer coefficient and the friction factor are also strong functions of the geometrical parameters of the porous media. A test collector was developed and tested indoors by varying the design features and operating conditions using a halogen-lamp simulator as a radiation source. This type of collector can be used for drying and heat applications such as solar industrial processes, space heating and solar drying of agricultural products.
Analysis of Pulse Heating on a Fluid-Cooled Surface for Fluid Shear Stress
Authors: Cole Kevin D.
Published: May 2008

This paper is a report of an improved heat transfer model for rapid temperature variations caused by pulse heating of fluid-cooled surfaces, with application to fluid shear-stress measurement. The key improvement is the use of a fully-transient treatment of the heat transfer in the fluid flow as part of a combined convection-conduction model. Surface-temperature results are presented for several fluid/solid combinations for a two-dimensional heater located on the fluid-solid interface. A sensitivity study suggests that pulse heating may be better than steady heating for measurement of fluid shear stress, and that measurements downstream of the heater may also be important.
Numerical Analysis of Conduction in a Foam
Authors: Druma A. M. , Alam M. K. , Druma C.
Published: May 2008

Porous organic materials are being developed for use as insulation, heat spreaders, and compact heat exchanger cores. The bulk properties of such a porous medium are difficult to determine analytically, particularly for the case of high porosity or when the porous material is not isotropic or homogeneous. Models that predict thermal conductivity of foams often use an empirical parameter to account for the effect of pore shape and material microstructure on the conduction process. A finite element analysis has been developed to calculate the thermal conductivity of a porous medium containing micropores. The effective thermal conductivity and the empirical conduction parameter are evaluated by comparing the results of the analytical and numerical models.
Study on Boiling Heat Transfer in Mist Cooling: The Characteristics of Heat Transfer and Droplets in Mist Dispersed Flow
Authors: Ohtake Hiroyasu , Teruya Yoshihiro , Koizumi Yasuo
Published: May 2008

Recently, the dry/semi-dry machining without machining oil is proposed for ecology. The establishment of high heat removable technology is required in the future machining. In this study, as a proposal of the high heat removable technology, the boiling heat transfer in mist dispersed flow was investigated. In particular, the heat transfer in water mist for low droplet density, focusing on the heat transfer characteristics and behaviors of liquid film and droplets on a heating surface was examined experimentally. Furthermore, the velocities of droplets, the diameters of those and air velocity were measured by using LDV, immersion method and a fine Pitot tube, respectively. The heat transfer mechanism in the mist cooling was classified into three regions based on heat transfer characteristics and behaviors of the droplets and liquid film: non-boiling, evaporation/augmentation with the droplets and evaporation of the liquid film. Three correlations for the regions were developed with the microscopic parameters of two-phase flow, respectively.
A Method of Power Generation From Low Temperature Medium
Authors: Cai Qingjun , Chen Chung-Lung
Published: May 2008

For a long time, how to utilize waste heat to generate electricity has been an interesting and challenging field for energy scientists. This paper presents a new method, ferrofluid power generator (FPG), which takes advantage of waste heat or solar energy to generate electricity in a multiple heating and cooling tube with alternate ferrofluid slug and vapor bubble structures. Based on this method, a new device, a thermomagnetic engine (TME) composed of a straight vacuum tube, a current induced coil, and magnet & ferrofluid slugs (MFS), was designed. Experimental results show that the expanding vapor bubbles push MFSs to generate drastic and continuous oscillating movements under the effect of heat. The pulse voltage signals from the induced coil demonstrate that the TME has a practical structure, potentially higher power generating capacity, and a stable operation.
Study on the Air-Side Heat Transfer and Pressure Drop for Fin-Tube Heat Exchangers
Authors: Jeong Ji Hwan , Chang Keun Sun , Kweon Young Chel , Lee Sang Jae , Lee Min Kyu
Published: May 2008

Experimental measurements and numerical analysis have been carried out in order to investigate performances of air-side heat transfer and pressure drop for six types of heat exhcangers with various fin shapes. An air-enthalpy calorimeter is used in this work. Numerical analysis shows a good agreement with experimental measurements. Measurements for six types of heat exchangers at various air-velocity are compared with each other. Heat transfer per unit area appears to be nearly the same in the range of 0.7~0.9 m/s while it varies within 3% at 1.5 m/s. The numerical results show that most of heat transfer takes place through fins for all types and majority of heat transfer happens from the 1st row.
Characterization of Heat Sink Flow Bypass in Plate Fin Heat Sinks
Authors: Leonard W. , Teertstra P. , Culham J. R. , Zaghol Ahmed
Published: May 2008

Experimental testing has been performed on two plate fin heat sinks in order to examine flow bypass phenomenon. The present study examines pressure drop and thermal resistance as well as flow velocities within the heat sinks. Tests are performed for bypass channel/fin height ratios of 0.25, 0.5, 0.75 and 1 with approach velocities from 2 to 8 m/s. By examining flow behavior within the heat sinks and the bypass channel, a model for predicting flow bypass is presented that incorporates only the significant pressure drop mechanisms that affect the flow path. This model allows for a simple prediction of flow bypass for plate fin heat sinks based solely on geometry. For all of the heat sinks tested the agreement between model and experimental data is ∓8%.
Effect of Entrance Condition on Frictional Losses and Transition to Turbulence
Authors: Kandlikar Satish G. , Campbell Levi A.
Published: May 2008

In studying the fluid flow and heat transfer in microchannels, various claims have been made regarding transition at Reynolds numbers significantly below 2300. As a first step in identifying the reasons for such early transition, the effect of entrance geometry on the pressure drop and transition to turbulence is studied experimentally in a conventional channel of 1.9 cm inner diameter. Four types of entrance conditions have been studied with flow of oil in a closed loop. The experimental results show the effect of entrance conditions on local friction factor, hydrodynamic developing length, and transition Reynolds number. The study will be extended to microchannels in the future.
Anisotropic Thermal Diffusivity of Aligned Multiwalled Carbon Nanotube Arrays
Authors: Borca-Tasciuc Theodorian , Hapenciuc Claudiu L. , Wei Bingqing , Vajtai Robert , Ajayan Pulickel M.
Published: May 2008

This work employs a photothermoelectric technique to measure the anisotropic thermal diffusivity of an aligned multiwalled carbon nanotube array. A modulated laser beam incident to the front surface of the sample creates a thermal wave which is detected by a fast responding thermocouple formed between the back surface of the sample and the tip of a sharp metallic probe. The anisotropic thermal diffusivity values are obtained by fitting the radial and frequency dependent thermal signals with an anisotropic heat conduction model. The room temperature thermal diffusivity measured perpendicular to the alignment direction is 0.246×10−5m2/s, an order of magnitude smaller than thermal diffusivity along the CNTs alignment direction 4.4×10−5m2/s. However, the thermal diffusivity of the aligned multiwalled CNT is two orders of magnitude smaller than expected for an individual multiwalled CNT.
Microscale Flow Visualization
Authors: Sinton David , Li Dongqing
Published: May 2008

A combined experimental and numerical analysis technique for velocity profiles in liquid microchannel flows is described. The working fluids employed are aqueous solutions with caged fluorescent dyes. A sheet of fluorescent dye is photo-injected by briefly exposing a cross-section of the fluid to ultraviolet light. The transport of the resulting ‘band’ of fluorescent dye is imaged onto a CCD camera using an epi-illumination fluorescent microscope system. The velocity profile is calculated from images acquired and processed after each uncaging event. The analysis technique utilizes several images, to provide velocity data with an increased signal-to-noise ratio. This combined experimental/numerical technique can provide velocity data in the near-wall region as well as in the bulk. Results are shown to compare favorably to analytical solutions in both pressure-driven and electroosmotic flow in circular cross-section capillaries of 205μm and 102μm inner diameters, respectively. Near-wall resolution is verified through application to electroosmotic flows with thin electrical double layers.