bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of High Temperature Exposure on the Mechanical Properties and Moisture Absorption Kinetics of Graphite/Epoxy Laminates
Authors: Aktas Levent , Vu Nam Hoang , Altan M. Cengiz
Published: April 2008

This study investigates the effect of exposure to elevated temperatures on the mechanical properties and moisture absorption kinetics of a graphite/epoxy composite laminate. 16-ply unidirectional AS4/3501-6 laminates are cured in an autoclave. The temperature profile during cure cycle involves a ramp of 5°C/min followed by a 3-hour hold at 177°C (350°F). The test samples obtained from these laminates are subjected to 150, 200, 250, 275, 300 and 325°C for 30min. Flexural strength and stiffness of the samples are characterized by three-point bending tests before and after the temperature exposure. These samples are then immersed into distilled water at 80°C and weighed at regular intervals to characterize their moisture absorption kinetics. Stiffness remained nearly unaffected from exposure to elevated temperatures except for 300 and 325°C. At 300 and 325°C, up to 21% and 58% reductions in flexural stiffness with respect to the control samples is observed, respectively. On the other hand, flexural strength displayed slight reduction at 250°C and resulted in over 60% and 88% deterioration for 300 and 325°C, respectively. Exposure to 150 and 200°C did not result in significant changes in mechanical properties. However, moisture absorption experiments indicated an increase in the rate of diffusion even if the mechanical properties are unaffected. The diffusion coefficient displayed an increase of 27% for 150°C, 75% for 200°C, reaching a maximum increase of 600% for 300°C exposure.
Experimental Study of Transient Heat Transfer Process in a Submerged Radial Jet
Authors: Cely Maria , Bula Antonio , Ramos Antonio
Published: April 2008

A transient cooling process using a submerged radial water jet is considered. The experiment set up consists of a submerged radial jet exiting from a nozzle located over a thin plate. The plate is made out of aluminum alloy and it has two discrete heat sources located symmetrically at the opposite side of the impinging surface. The temperature variation in the plate is captured using a data acquisition system. The plate is allowed to reach a stable temperature before the radial jet system is generated. The results obtained present the temperature distribution for the plate and the heat transfer coefficient at the fluid-solid interface, for different nozzle heights and initial plate temperature.
Development of a More Efficient Defrost Control System for Heat Pumps
Authors: Yilmaz Emin
Published: April 2008

The purpose of this research project was to design a more efficient defrost control system for residential heat pumps. Defrost systems are used to melt the accumulated ice on evaporator coils of outdoor units. The purpose of the new control system is to prevent the initiation of defrost cycle when there is no substantial ice accumulation on the outdoor unit. Two of the envisioned ice accumulation sensing methods were (a). Increase in pressure loss across the evaporator coil and (b). Resistance change across two electrodes when ice bridges the electrodes. A differential pressure sensor was used to sense an increase in pressure loss across outdoor coil for this research project. Results indicate that, although maximum time interval of 90 minutes was used, about 55% of defrost cycles initiated were not necessary since there was no ice to melt. An ASYST based data acquisition system was used to monitor, measure and store key parameters. It is expected that with the new control system one can improve efficiency by about 3%. A similar project has been undertaken on a heat pump recently installed on our HVAC experimental unit as an undergraduate research project. Installation of temperature and humidity controlled enclosure, and thermocouples have been completed. Some results were reported here. If any additional progress is made, results of this project will be reported at the meeting.
Evaluation of a Model for the Evaporation of Fuel From a Liquid Pool in a CFD Fire Code
Authors: Brown Alexander L. , Vembe Bjorn Erling
Published: April 2008

A pool model has been developed to predict the evaporation of a liquid fuel from a surface in response to a fire. The model exists in the Fuego, Kameleon, and Vulcan fire codes. The model solves for the mass evolution based on what are thought to be the dominant input boundary conditions. Some empirical assumptions are made to predict the behavior of lower order physics. The performance of the model is evaluated by comparing predicted results with measurements for a variety of test cases in Fuego. Qualitative performance of the model is found to be reasonable. The model is found to yield quantitative results of mixed accuracy, suggesting the worth of considering improvements to the model. Evidence from the study helps indicate the future direction for improving this class of model.
A Fast Convergence Scheme for Coupled Energy Domains Simulation of MEMS
Authors: Guo J. , Querin Q. M.
Published: April 2008

Due to the massive demands from industry, the black-box based coupled energy domains simulation plays a more and more important role in the design of MEMS devices, and many numerical techniques have been developed so far for it. This paper presents a fast convergence scheme for coupled energy domains simulation of MEMS. This scheme is based on the relaxation approach but employs the Steffensen's acceleration technique to speed up the convergence procedure. In this paper, the details of this scheme are described as well as the relaxation and the multilevel Newton methods. The numerical examples show that the proposed scheme has equivalent convergence performance, sometimes even more efficient, as the multilevel Newton method, and much better than the relaxation method, especially for strong coupled or nonlinear situations, while keeping the advantage of easy programming.
Predictive Evolution of Fuel From a Liquid Pool Fire: Phenomenology Identification and Ranking Exercise
Authors: Brown Alexander L. , Gill Walter , Lopez Carlos
Published: April 2008

A liquid pool fire evaporates the liquid fuel at a rate that is governed by heat and mass transport. Predictive evolution of vaporized fuel from a pool can be obtained only by applying the correct boundary conditions and modeling the significant physics of the pool. However, pool fires can occur in a variety of configurations, and the significant physics of a fire change depending on the environment of the fire. Sandia National Laboratories has invested in fire experiments and modeling for a wide variety of scales and configurations over the last 40 years, and an accumulation of this knowledge can be applied to assessing the relative importance of various phenomena. This paper consolidates existing knowledge in the context of phenomena identification and ranking in order to guide future efforts aimed at improving the quantitative predictive capabilities of liquid fuel pool models. Ultimately, the intent is to converge to a predictive model of a liquid pool fire that can be implemented in a CFD model and confidently applied to risk assessment studies.
A Stochastic Model of Oxidation Mechanism on High Temperature Corrosion of Stainless Steel
Authors: Chen Huajun , Chen Yitung , Hsieh Hsuan-Tsung
Published: April 2008

To interpret the role of diffusion and reaction process, a cellular automaton model, which combines the surface growth and internal oxidation, was developed to explain the oxidation mechanism of stainless steels in high temperature corrosive liquid metal environment. In this model, three main processes, which include the corrosion of the substrate, the diffusion of iron species across the oxide layer and precipitation of iron on the oxide layer, are simulated. The diffusion process is simulated by random walk model. Mapping between present model and Wagner theory has been created. The gross features concerning the evolution of the involved process were founded.
CO2 Flow Boiling Heat Transfer and Flow Pattern at Low Temperatures in Horizontal Smooth Tubes
Authors: Park C. Y. , Hrnjak P. S.
Published: April 2008

In this study, flow boiling heat transfer coefficients and flow patterns CO2 are examined in horizontal smooth tubes with inner diameter 6.1 and 3.5 mm at low temperatures. In order to measure the heat transfer coefficients, the test tube was heated by two brass pieces maintained a higher temperature than CO2 by a secondary fluid. Flow visualization was carried out at adiabatic conditions. This research was performed at evaporation temperatures of -15 and -30 °C, mass flux from 100 to 400 kg/m2 s, and heat flux from 5 to 15 kW/m2 for vapor qualities ranging from 0.1 to 0.8. The CO2 heat transfer coefficients for the 6.1 and 3.5 mm tubes had nucleate boiling dominant heat transfer characteristics such as the strong dependence on heat fluxes. However, enhanced convective boiling contribution was presented for the 3.5 mm tube at 400 kg/m2 s. The presented heat transfer coefficients indicated the reduction of heat transfer coefficient as mass flux increased at low quality regions and also showed that dryout did not occur until the high quality region of 0.8, for mass fluxes of 200 and 400 kg/m2 s. The measured heat transfer coefficients were compared with predicted values with some general correlations to predict flow boiling heat transfer coefficients. The pictures of visualized flow patterns were presented and the flow patterns were compared with a flow pattern map. They were used to explain the relation between the flow boiling heat transfer coefficient and vapor quality at the mass flux of 100 kg/m2 s.
Exergy and Entropy Thermodynamic Concepts for Nonlinear Control Design
Authors: Robinett Rush D. , Wilson David G.
Published: April 2008

This paper develops a novel control system design methodology that uniquely combines: concepts from thermodynamic exergy and entropy; Hamiltonian systems; Lyapunov's direct method and Lyapunov optimal analysis; electric AC power concepts; and power flow analysis. Relationships are derived between exergy/entropy and Lyapunov optimal functions for Hamiltonian systems. The methodology is demonstrated with two fundamental numerical simulation examples: 1) the classic van der Pol nonlinear oscillator system and 2) a Multi-Input-Multi-Output (MIMO) planar 2 Degree-Of-Freedom (DOF) robot that employs PID tracking control. The control system performances and/or appropriately identified terms are partitioned and evaluated based on exergy generation and exergy dissipation terms. Traditionally, almost all modern control design is based on forcing the nonlinear systems to perform and behave like linear systems, thus limiting its maximum potential. These are also known as mainly passive-type control systems. This novel nonlinear control methodology results in both necessary and sufficient conditions for stability of nonlinear systems.
Mechanical Properties of CrN Films Deposited by Magnetron Sputtering Method
Authors: Jayatissa A. H. , Wagner D. , Sorin S. , Randall N. X.
Published: April 2008

The mechanical properties of CrN films coated by radio frequency (rf) magnetron sputtering method were investigated. CrN films were coated on stainless steel, silicon wafer and glass substrates using sputtering of a Cr target in nitrogen ambient. The films were coated by varying the deposition temperature, nitrogen partial pressure and rf power density. The films coated were characterized by nanoindentation method, microhardness, optical, and corrosion tests. In order to use CrN as mechanical coating material, the surface roughness, hardness and adhesion properties have to be determined. The film properties were measured using atomic force microscopy and nanoindentation method and analyzed as a function of deposition conditions. It was found that these properties can be varied by changing the deposition conditions.
A Scheduled Control Framework for Electrospinning Process in Nanofiber-Based Textile Fabrication
Authors: Hiremath Sandeep , Jalili Nader
Published: April 2008

The piezoelectric property exhibited by certain polymers such as polyvinylidene fluoride (PVDF) has been effectively utilized in developing piezoelectric-based film sensors and actuators with application to acoustic transducers, smart fabric and nanomanipulator controllers. The PVDF-based fabric, made of nonwoven nanofibers, is produced by "electrospinning" process in which a jet is ejected in the form of Taylor cone with the application of high voltage to a polymer droplet suspended at the tip of a nozzle. A simple physical model of the fluid jet to investigate the variation of fiber diameter with variation in system parameters is presented in this paper. It is observed that the major parameters that influence the fiber properties are magnitude of the electrostatic field, distance between the nozzle tip and collector grid, infusion rate, concentration of the polymer solution and design of the collector. Presently, the parameterization results from open loop experiments correspond exactly to equations obtained from the model. An image-based feedback control of the electrospinning process based on this model is thus proposed to optimize the nonwoven fiber properties (e.g. fiber diameter). The feedback control is achieved by obtaining and processing images of the jet formation from a high speed camera and analyzing the fiber thickness and jet stability shape.
Performance of an Electrokinetic Shuttle Polymerase Chain Reactor
Authors: Chen Pin-Chuan , Chen Jifeng , Nikitopoulos Dimitris E. , Soper Steven A. , Murphy Michael C.
Published: April 2008

An alternative polymerase chain reactor (PCR) driven by electrokinetic flow was developed and tested. A single straight microchannel and a double-T intersection were designed for injection of DNA samples and thermal cycling by shuttling between constant temperature zones. Thermal performance of the device was studied using numerical and analytical models to understand the temperature distribution. Devices were made on a polycarbonate substrate by hot embossing with a micromilled brass mold insert. A PID control system, with a tolerance of ± 0.2°C, was used to maintain the temperatures in each zone during experiments. Power consumption in each zone was predicted using thermal simulations. Molecular diffusion of 500 bp DNA was evaluated using two methods, an empirical equation and an analytical model, and the diffusion length after 20 cycles from both models was 100 μm with a 0.97 μm difference. Electroosmotic flow (EOF) was minimized by using dynamic coating and Joule heating was reduced by decreasing the KCl component in the DNA cocktail. Successful amplification of 500 bp DNA fragments at shuttle velocities of 1mm s-1 (620 seconds), 2mm s-1 (310 seconds), and 3mm s-1 (207 seconds) was demonstrated for 20 thermal cycles. The amplification efficiencies were 31%, 28%, and 18%, respectively. Unintentional flows resulting from siphoning phenomenon due to hydrostatic pressure, and Laplace pressure due to surface tension, may be responsible for the reduced amplification performance.
Laser Melt Processing of H13 Tool Steel
Authors: Parishram P. , Malshe Ajay P. , Fulton Arnie
Published: April 2008

H13 has been widely used in hot and cold work tooling applications and the thermal processing of H13 has important industrial significance particularly where longer tool life is important. This paper presents some results of the CO2 laser assisted processing of H13 tool steel. A block of preheated H13 tool steel was laser processed at six different parameters. Laser power (P) and Scan speed (V) were chosen as the primary variables. The processed region was characterized for geometry, micro hardness and microstructure. The block temperature was monitored using an alumel-chromel thermocouple. Optical observations indicated that the aspect ratios of the processed zone increased with power. Microhardness observations indicate that higher cooling rate parameters had higher hardness values. Finer dendrites were visible at higher power values. These observations were corroborated by magnitude of thermal change predictions made using the Rosenthal equation
The Effect of Computational Delay on Performance of Adaptive Control Systems
Authors: Orzechowski Pawel Konrad , Tsao Tsu-Chin , Gibson James Steve
Published: April 2008

In many adaptive control applications, especially where the recursive-least-squares (RLS) algorithms are used, the real-time implementation of high order adaptive filters for estimating the disturbance dynamics is computationally intensive. The delay associated with the computational burden is usually either underestimated as no delay or overestimated as one sample delay in the control system design and analysis. For a stochastic disturbance dynamics, the H2 optimal control performance for the case of one-step delay is worse than that of no delay due to the nonminimum phase plant zero introduced by the delay. The optimal performance for a fractional delay is bounded between these two extremes. The paper investigates the effect of the fractional computational delay on a variable order adaptive controller based on a recursive least-squares adaptive lattice filter. The trade-off between the adaptive filter order and the computational delay is analyzed and evaluated by an example.
Dynamic Operation of a MEMS Thermal Switch
Authors: Cho J. H. , Richards C. D. , Bahr D. F. , Richards R. F. , Jiao J.
Published: April 2008

In this paper we present the design, fabrication, and characterization of a MEMS thermal switch. Three switch designs are considered: one in which the conductive material is in the form of liquid-metal micro droplets, one in which the conductive material consists of aligned carbon nanotube arrays, and one in which solid silicon contacts are used. The ratio of thermal resistance in the on and off conditions is used to characterize performance. Based on these measurements the switch incorporating liquid-metal droplets is superior to the other two switches. The liquid-metal switch has a thermal resistance off to on ratio of 168 and can provide heating rates of 905 °C/s.
Accurate Interpretation of Magnetic Shape Memory Alloy Experiments Utilizing Coupled Magnetostatic Analysis
Authors: Lagoudas Dimitris C. , Kiefer Bjoern , Broederdorf Alicia J.
Published: April 2008

In order to build a reliable constitutive model for magnetic shape memory alloys (MSMAs) the availability of accurate experimental data for calibration and validation purposes is essential. However, the demagnetization effect and the resulting sample shape-dependent difference between the applied field and the internal field makes measurements of MSMAs properties difficult to interpret. Since for non-ellipsoidal specimen the internal magnetic field and thus the induced magnetization is nonuniform, standard demagnetization factors can not be applied without evaluation of the expected error. Following up on previous work by the authors this paper describes a methodology by which experimental data can be interpreted more accurately. The procedure involves the numerical solving of nonlinear magnetostatic boundary value problems for MSMAs in which the stress-dependent magnetic properties of the material are predicted by the constitutive model. New results of this analysis presented here include a parametric study of the sample shape dependence of the demagnetization effect when accounting for the nonlinear magnetization properties of MSMAs.
Vehicle Longitudinal Ride Comfort Control in Stop-and-Go Traffic
Authors: Koo Shiang-Lung , Tan Han-Shue , Bu Fanping , Tomizuka Masayoshi
Published: April 2008

Ride comfort at low vehicle speed is often overlooked but is very important to vehicle control applications (e.g. the latest stop-and-go function in Adaptive Cruise Control). Most control strategies that address passenger comfort simply utilize the bounds of jerk and acceleration of the vehicles. In general, they have several major limitations when applied to low-speed applications: (I) frequency-domain comfort requirements are not integrated and (II) the vehicle models are simplified too far to capture the tire and suspension dynamics that may impact comfort significantly at low speeds. This paper develops a control scheme for ride quality under stop-and-go situations. The scheme is based on optimal control and it ensures smooth acceleration during vehicle maneuvers. A two-degree-of-freedom control strategy is used to approximate the optimal control law. Experimental results demonstrate the effectiveness of this control scheme.
Theoretical and Numerical Solution of Momentum and Energy Equations for Flow of Air Over an Oscillating Horizontal Heated Plate
Authors: Kouhi Esfandyar , Hessami Mir-Akbar
Published: April 2008

Study of the hydraulic and thermal boundary layers is a major part of the investigation of any heat transfer problem. In the case of free and forced convection over a surface, heat transfer can be improved significantly by altering the fluid's flow within the boundary layer with the objective of reducing the boundary layer thickness. The technique which is used in this study for this purpose is the oscillation of the heated plate. The two important variables are therefore the oscillation velocity and frequency. In this article, first forced convection heat transfer over a stationery plate is studied for a fixed flow velocity to verify the accuracy of the calculations and to determine the details of the numerical computations in terms of grid distribution and convergence. Using the conclusions of this part of the study, forced convection over an oscillating heated plate is then investigated for a range of oscillation frequencies and velocities. The results of these numerical computations are compared with our theoretical results. Good agreement between these results is reported.
Sensitivity of Non-Uniform Beams in Depositing Mass Process
Authors: Caruntu Dumitru I.
Published: April 2008

This paper deals with the mass deposition influence on the natural frequencies of nonuniform cantilever resonator sensors of linear and parabolic thickness. Resonator sensitivity, defined as fraction of change in frequency per fraction of change in thickness deposition and relative density, was found. A constant thickness mass deposition on all four lateral surfaces of the cantilever of rectangular cross-section was assumed. Euler-Bernoulli theory was used, so only slender beams were considered. Mass deposition on the free end surface of the beams was neglected. The film thickness was considered very small compared to any beam dimension. The film had no contribution to the beam stiffness, only to the mass. Results show that for the same thickness deposition, the sensitivity in the first mode of beams of linear thickness is 2.5 to 3.5 higher when compared to uniform beams. For beams of parabolic thickness variation the relative sensitivity ranges between 1.5 and 2.1.
Developing Pod Over the Complex Plane to Form a Data Processing Tool for Finite Element Simulations of Steady State Structural Dynamics
Authors: Georgiou Ioannis T. , Papadopoulos Christos I.
Published: April 2008

To analyze the steady state response of structural dynamical systems with multi-field response (example, Timoshenko shearable rod) given complex-valued databases (finite element simulations of complexified equations of motion), we have developed a Complex Proper Orthogonal Decomposition (CPOD) transform. Like the regular multi-field POD, the development of the C-POD is based on the primitive space and frequency auto-correlation operations. These data fusion operations give rise to complex Hermitian operators whose solution determines the C-POD transform. The eigen-values of the complex Hermitian operators are strictly positive and it is shown that they represent the energy fractions of the auto-correlation energy contained in the POD modes. The POD modes have both amplitudes and shapes that are complex-valued scalar functions. The C-POD transform is verified by applying it to characterize the finite element simulations of the steady state dynamics of planar beams and arches. It turns out that the real part of the shape of a POD mode coincides with the shape of the linear POD; whereas its amplitude is a localized function of frequency at a critical frequency which is identical to a natural frequency.
Spall Strength of S2-Glass Fiber Reinforced Polymer Composites
Authors: Yuan Fuping , Tsai Liren , Prakash Vikas
Published: April 2008

The utilization of layered heterogeneous material systems in the development of armor provides a potential for a great improvement in ballistic performance in a variety of lightweight armor applications. Some of the notable recent examples demonstrating the success of synthetic heterogeneous material systems include composite materials with organic matrices reinforced by glass fibers to achieve lightweight and enhanced ballistic resistance. In the present study, a series of plate impact experiments were performed on two S2-glass fiber reinforced polymer composites (GRP) with different resin content for their promising potential in future combat vehicle defense system. GRP has excellent strength along its fiberglass directions, however, the cohesion between fiberglass layers and its resin matrix is not strong and spall usually occurs during a typical impact process. The objective of the present study is to investigate: (a) dispersion and attenuation of shock-waves in two GRP composites; (b) the spall (delamination) strength of the two GRP composites both under compression and pressure-shear shock wave conditions. The GRP specimens were shock loaded by utilizing A1 7075-T6 flyer plates to around 2 GPa; the thickness of flyer and target for each experiment was carefully designed to produce a state of tension near the center of the GRP target plates. Normal plate impact, and combined pressure and shear experiments with skew angles ranging from 12o to 20o, were performed to study the effects of normal compression and combined compression and shear on the GRPs' spall strength. The measured spall strength as a function of the applied shear strain and the normal stress was used to develop a 3-dimensional failure surface. The results indicate that the spall strength of GRP decreases with increasing compressive stress; the addition of shear stress was found detrimental to the spall strength of GRP.
Noise Modeling and Characterization of Piezoresistive Transducers
Authors: Nishida Toshikazu , Dieme Robert , Sheplak Mark , Bosman Gijs
Published: April 2008

This paper presents detailed results on noise modeling and experimental characterization applicable to piezoresistive MEMS transducers using a piezoresistive MEMS microphone as an example. To accurately model the lower limit of the dynamic range of piezoresistive MEMS transducers, a detailed noise equivalent circuit, piezoresistor noise model, and experimental noise measurements are needed. From the sensitivity and the total root-mean-square output noise, the minimum detectable signal (MDS) may be computed. Key experimental results include comparison of the DC bridge and AC bridge noise measurement techniques and use of the AC measurement technique when the piezoresistive transducer output noise is less than the low frequency DC setup noise.
A Method to Estimate the Friction Coefficient and Tire Slip Angle Using Steering Torque
Authors: Hsu Yung-Hsiang J. , Laws Shad , Gadda Christopher D. , Gerdes J. Christian
Published: April 2008

Knowledge of tire forces is important for vehicle control systems that aim to enhance vehicle handling and passenger safety. This paper introduces a nonlinear observer that estimates the coefficient of friction and tire slip angle, both of which are key factors in characterizing the vehicle's lateral tire forces. The observer estimates the friction coefficient and slip angle based on sensor measurements available on many production vehicles. This includes steering torque measurements readily available in steer-by-wire or electric power steering (EPS) systems. Experimental results on a steer-by-wire research vehicle (Fig. 1) demonstrate the observer's ability to provide accurate estimates out to the limits of handling.
Testing and Modeling of a Semi-Closed Gas Turbine Cycle Integrated With a Vapor Absorption Refrigeration System
Authors: Khan J. R. , Lear W. E. , Sherif S. A. , Howell E. B. , Crittenden J. F. , Meitner P. L.
Published: April 2008

A novel cooling and power cycle has been proposed that combines a semi-closed cycle gas turbine called the High Pressure Regenerative Turbine Engine (HPRTE) with a vapor absorption refrigeration system (VARS). The refrigeration cycle (VARS) interacts with the power cycle (HPRTE) solely through heat transfer in the generator and the evaporator. Waste heat from the recirculated combustion gas of the HPRTE is used to power the absorption refrigeration unit, which cools the high-pressure compressor inlet of the HPRTE to below ambient conditions and also produces excess refrigeration, in an amount which depends on ambient conditions. Water produced as a product of combustion is intentionally condensed in the evaporator of the VARS, which is designed to provide sufficient cooling for three purposes: chilling the inlet air to the high pressure compressor, water extraction, and for an external cooling load. In a previous study, the combined cycle was modeled using zero-dimensional steady-state thermodynamics, with the specified values of efficiencies and pressure drops for the turbo-machinery and heat exchangers. The model predicts that the combined cycle with steam blade cooling for a medium-sized engine will have a thermal efficiency of 49%, in addition to the external refrigeration load generated in the cycle which is 13% of the net work output. It also produces about 1.4 kg of water for each kg of fuel (propane) consumed. A small experimental unit demonstrating the HPRTE/VARS combined cycle has been constructed and is currently being tested in the Energy & Gas-dynamic Systems Laboratory at the University of Florida. A 45 HP Rover 1S-60 engine is integrated with a NH3/H2O vapor absorption refrigeration unit having a capacity of 19 Ton Refrigeration. The engine flow-path has been significantly modified to include partial recirculation of exhaust products, turbocharging, and recuperation, thus implementing the HPRTE concept. In addition, a significant modeling effort has been undertaken to simulate the combined cycle operation under design and off-design conditions. Initial experimental results show good agreement with the model predictions, including overall efficiency and water extraction rates.
Flow Structure and Heat Transfer During Free Liquid Jet Impingement on a Hemispherical Plate
Authors: Rahman Muhammad M. , Hernandez Cesar F. , Lallave Jorge C.
Published: April 2008

The flow structure and convective heat transfer behavior of a free liquid jet impinging on a hemispherical solid plate of finite thickness have been examined using a numerical analysis. The simulation model included the entire fluid region (impinging jet and flow spreading out over the convex surface) and solid plate as a conjugate problem. Solution was done for both isothermal and constant heat flux boundary conditions at the inner surface of the hemispherical plate. Computations were done for jet Reynolds number (ReJ) ranging from 500 to 2000 and the dimensionless nozzle to target spacing ratio (β) from 0.75 to 3. Results are presented for local heat transfer coefficient and the local Nusselt number using the following working fluids: water (H2O), flouroinert (FC-77), and oil (MIL-7808) and for various solid materials namely aluminum, Constantan, copper, silicon, and silver. It was observed that plate materials with higher thermal conductivity maintained a more uniform temperature distribution at the solid-fluid interface. A higher Reynolds number increased the Nusselt number and local heat transfer coefficient distributions over the entire solid-fluid interface.
Numerical Analysis of Thermal Behavior in a Refrigerated Warehouse
Authors: Ho Son H. , Rosario Luis , Rahman Muhammad M.
Published: April 2008

This paper presents a study of thermal behavior in a refrigerated warehouse equipped with ceiling type refrigeration unit. A two-dimensional steady-state problem was solved by using computational fluid dynamics modeling and simulation. The computational model includes a refrigerated space at the center plane of an array of 4 piles by 3 stacks of palletized product packages with a evaporator fan refrigeration unit, in which the fan pull air through cooling coil and blow out into the space. A parametric analysis was done based on fourteen simulation cases of conditions including different locations of the refrigeration unit as well as different normal forced air velocities produced by the fan. Typical distributions of velocity and temperature are presented. From the results, it is found that better cooling effectiveness and uniformity of the refrigerated space can be achieved by using higher normal supply air speed or locating the refrigeration unit lower and closer to the array of stacks of product packages.
Mechanical Behavior of Individual Micro/Nano-Fibers Using a Novel Characterization Device
Authors: Kaul Pankaj , Prakash Vikas , Abramson Alexis
Published: April 2008

The present paper reports the development of a novel mechanical testing device that enables highly reliable mechanical tensile testing on individual micro-/nano-structures. The device features independent measurement of both force and displacement histories in the specimen with nanoNewton force and sub-picometer displacement resolutions, respectively. Moreover, the device is well suited for in-situ testing of micro-/nano- structures within a high resolution scanning electron microscope (SEM), which permits continuous high resolution imaging of the specimen during straining. The device comprises of two main parts: (a) a three-plate capacitive transducer that doubles up both as an actuator and a force sensor, and (b) a commercially available nano-manipulator that facilitates transportation and positioning of nanoscale structures with nano-precision. In order to conduct the mechanical tests, the two ends of the specimen are attached to the probe tips at the nanomanipulator and the transducer ends, using either electron-beam or ion-beam induced deposition (EBID/IBID). The working and capabilities of the testing device are illustrated by presenting results of nanomechanical tensile tests on electrospun polyaniline microwires. The engineering stress versus engineering strain curves exhibit two very distinct Young's moduli during the loading or the unloading segments of the applied displacement. Failure at the probe/sample weld junction occurred at ~ 67 MPa, suggesting that polyaniline microfibers exhibit a yield stress higher than most comparable bulk polymers.
Design of Automotive Torsion Beam Suspension Using Lumped-Compliance Linkage Models
Authors: Lyu Naesung , Park Jungkap , Urabe Hiroyuki , Tokunaga Hiroyuki , Saitou Kazuhiro
Published: April 2008

This paper presents a new method for efficiently and accurately modeling the elasto-kinematic behaviors of torsion beam suspension systems and of other similar classes of mechanical systems, and a design method utilizing the models. The torsion beam is represented as a linkage of lumped mass joined by nonlinear springs, bending and torsion, whose stiffness are identified via off-line computational experiments using nonlinear finite element simulations. A number of such computer experiments are conducted off-line for representative dimensions of torsion beams, and the results are stored in surrogate response models. During design iterations, these surrogate response models are utilized to automatically construct a lumped-compliance linkage model of a torsion beam and integrate it into a multi-body suspension system model that can be simulated using commercial software. Comparison with a nonlinear finite element analysis demonstrates much improved accuracy of the proposed model over commercial flexible multi-body simulation software, with comparable computational speed. Finally, an example is presented on the multi-objective optimization of the cross section of the torsion beam using the developed surrogate response models.
Development of a Brake System for Lightweight Vehicle
Authors: Lee Seok , Shim Taehyun , Cho Byung-Kwan
Published: April 2008

With a growing demand for improved fuel efficiency and reduced emissions, lightweight vehicles have gained strong attention in current automotive industry. This paper discusses the development of a brake system for a lightweight vehicle that has significant weight variations. A conventional brake system was first designed and its performance was assessed. In order to improve the brake efficiency and prevent wheel lockup under all loading cases, antilock brake system (ABS) is proposed in which a wheel slip controller based on sliding mode control and a solenoid valve actuator is modeled. In the wheel slip controller, Extended Kalman Filter (EKF) was used to monitor the brake forces and a pulse width modulation (PWM) technique was applied to control the solenoid valve. The overall brake performance was evaluated through simulation of 8 DOF nonlinear vehicle model. The proposed brake system showed significant improvement in brake efficiency.
Numerical Analysis of Local Heat Transfer From a Flat Plate to a Swirling Air Impingining Jet
Authors: Yan X. Terry , Kalvakota Rahul S.
Published: April 2008

Local heat transfer from a flat plate to a swirling circular air impinging jet is investigated numerically. Reynolds Averaged Navier-Stokes equations (RANS) and energy equation are solved for the axisymmetric, three dimensional flow. Eddy-viscosity based turbulence models, RNG and V2F, are used. Non-uniform meshes are used for the three dimensional flows and mesh independent solutions are obtained. The flow Reynolds number, which is based on the jet diameter, is kept at 23,000. In the analysis, local heat transfer coefficients are obtained for different swirl numbers, S = 0.21, 0.35 and 0.47 and jet-to-plate distance, L/D, ranging from 2 to 9. Investigation of the effect of swirl flow profile at the exiting plane of the jet on heat transfer is also presented. It is found that different swirl profiles with the same swirl number lead to very different heat transfer behaviors in the stagnation region of the impinging jet.
Numerical Analysis of Natural Convection Induced Oxygen Transport in Liquid Lead Bismuth Eutectic
Authors: Tan Xianfang , Chen Yitung , Chen Huajun , Tan Taide , Hsieh Hsuan-Tsung
Published: April 2008

Liquid lead bismuth eutectic (LBE) is very corrosive to steels. To mitigate structural corrosion of LBE systems, active oxygen control technique is developed. To enhance the speed of oxygen transport in liquid LBE, natural convection has been proposed. This paper numerically analyzes the oxygen transport in a natural convection induced LBE enclosure. Different temperature boundary conditions are added to the container. Both laminar and turbulent LBE flows which are distinguished by strength of flow measured are analyzed. Three laminar cases: (a) heated from the bottom and cooled from the top of the container; (b) heated from the sidewalls and cooled from the top of the container; (c) one sidewall heated and the opposite wall cooled, and one fully turbulent case with one sidewall heated and the opposite sidewall cooled are chosen. Oxidization in near wall areas and formation of oxide layers on container surfaces are considered. In each case, the characteristic velocity and oxygen diffusion time are estimated, the change of oxygen distribution with time are obtained, and the bulk concentration of oxygen and the efficiency of oxide layer formation on different liquid-solid interfaces are calculated. To obtain more information of oxygen transportation and distribution, three-dimension analysis of the laminar flow is done. Based on the analysis, several conclusions are finally obtained.
Three-Dimensional Modeling of Density Current in Confined and Unconfined Channels
Authors: Aram Ehsan , Firoozabadi Bahar
Published: April 2008

Dense underflows are continuous currents which move down-slope due to the fact that their density is heavier than that ambient water. In this work, 2-D and 3-D density current in a channel were investigated by a set of experimental studies and the data were used to simulate the density current. The velocity components were measured using Acoustic Doppler Velocimetry (ADV). The height of density current (current's depth) was also measured. In this study, the density current with a uniform velocity and concentration enters the channel via a sluice gate into a lighter ambient fluid and moves forward down-slope. A low-Reynolds number turbulent model (Launder and Sharma, 1974) has been applied to simulate the structure of 3-D density current in the confined (small width three dimensional density current) and unconfined (large width three dimensional density current) channels. The computed velocity profiles in unconfined channel were compared with the 3-D experimental data for verification. The height and velocity profiles of the confined current were also compared with 2-D experimental data. It was shown that by decreasing in width of the channel, the height of the current and the magnitude of maximum and average velocity increase and the confined current behaves as 2-D current after a distance. These factors prepare the conditions for minimizing sediment deposition and sedimentation rates can be greatly reduced. Although the k - ε Launder and Sharma model is applied here to a conservative density current, it seems that the analysis can be valid in general for turbidity current laden with fine particles.
The Fractal Model of Heat Conduction of Graphite Foam
Authors: Zhang Xinming , Chen Qinghua , Zeng Danling
Published: April 2008

Graphite foam is a new material for effective heat conduction, which possesses exceedingly good thermal physical properties, thus the investigation on it has absorbed wide attention of scientists and engineers. By using experimental method such a material was obtained in our lab, and the factors which influence the micro-structure of the material was preliminary discussed based on our experiments. However, the main focus of the present paper is placed on the determination of the effective thermal conductivity of the material. Firstly, in accordance with the microscopic structure of the material, a simplified geometric model was constructed. Based on it a heat conduction unit cell was proposed to calculate the effective thermal conductivity of the porous material. Then, a geometric transformation was carried out to transit the original simple model to the real fractal one. The effective thermal conductivity λ' and its averaged value λ'm for the bulk porous material were derived. Examples were provided to show the computational procedure and to confirm the availability of the method proposed. The influence factors on λm. in the fractal model were also discussed in detail.
Characterization and Modeling of Anisotropic Thermal Conductivity in Polymer Composites
Authors: Bahadur Raj , Bar-Cohen Avram
Published: April 2008

The thermophysical properties of a commercially available Polyphenylene Sulphide (PPS)-carbon fiber composite material are experimentally characterized and used to validate application of the Nielsen thermal conductivity model to this category of polymer matrix composites. The PPS-fiber thermal conductivity was measured in the three orthogonal directions, using the laser flash thermal diffusivity method, and found to display significant anisotropy. Thermal conductivity predictions based on the Nielsen model, and using E-SEM measured values of fiber dimensions and fiber orientation and carbon fiber mass content determined from TGA analysis, were found to be within 5% of the corresponding measurements. The close agreement between predictions and measurements permitted the determination of the morphological influence of fiber material, volume content and orientation, and resin and fiber thermal conductivities, on thermal conductivity to be parametrically investigated and optimized for a given formulation. The impact of this optimization on the thermal performance of a PPS-fiber pin fin is described.
Optimization of Single-Strap Composite Joints
Authors: Shahin Khaled , Taheri Farid
Published: April 2008

Adhesive joints are increasingly being utilized in joining primary structural components made of fiber reinforced polymer composites (FRP). While adhesively bonded joints transfer loads by means of shear stresses the eccentricity of the load path found in such joints results in the lateral deformation of the joint assembly and the creation of bending moments at the end portions of the adhesive layer. In the case of the single-strap joint, the magnitude of such bending moments can render the joint structurally inefficient. That said, in many practical situations, the single-strap joint leads to be the only feasible joint configuration; therefore, the understanding of its characteristics is of paramount importance. A detailed analytical investigation of the deformations of single-strap joints was carried out to better understand the dependence of edge moments on various parameters influencing the joint capacity and performance. Accurate expressions were also developed for evaluating the magnitude of the bending moment and shear forces at the ends on the adhesive layer. A complete solution is provided that can accurately predict the magnitude of the edge forces in both balanced and unbalanced single-strap joints. The edge forces obtained from the solution can be used as boundary conditions for the complete analysis of shear and peel stresses in the adhesive layer. The analytical expressions of the bending moment and shear forces can also be used to determine the upper and lower bounds of the magnitudes of the edge forces. These limits show that the efficiency of a single-strap joint can be easily made comparable to that of the commonly used single-lap joint. It will also be shown that on the other hand, a carelessly designed single-strap joint can be nothing more than a so-called "built-in stress concentration". The integrity of the analytical expressions was also verified by geometrically nonlinear finite element analysis. The results obtained from the proposed solution showed better agreement to the finite element results than those obtained from the currently available solutions cited in the literature.
Microcapsule Generation Using a Compound Jet Instability
Authors: Lee Sang-Youp , Snider Connie , Park Kinam , Robinson J. Paul
Published: April 2008

A new microcapsule generation technique is presented. The microcapsule system has been built based on conventional flow cytometry. The results show that the current system can control the jet diameters of each component solution comprising a compound jet, in addition to the resultant microcapsule diameter, using the pressure balance between adjacent fluids in the hydrodynamic focusing region. It has been also shown that the synchronized breakup of the compound jet is critical for the reservoir-type morphology of the microcapsules.