bluuebunny/crossref_metadata_2025 huggingface dataset:
Exergy-Based Environmental Design of a Computer Room Air Conditioning Unit
Authors: Lettieri David J. , Shah Amip J. , Carey Van P.
Published: July 2010

The growing environmental footprint of data centers suggests the need for comprehensive models that enable designers and operators to optimize deployment configurations. In this paper, we discuss an exergy-based approach to the environmental design of one component of a data center, the computer room air conditioning (CRAC) unit. Previous work has examined the lifetime exergy consumption of the server technology portion of a data center. In this work we construct a lifetime exergy model for a direct expansion CRAC unit which when combined with the computer server model provides a more complete picture of the environmental impact of a data center. The lifetime model includes the material and energy consumption of the raw materials, transportation, manufacturing processes, operation and disposal. The application of the model is then explored under a variety of design configurations and utilization scenarios. Key parameters that affect the environmental footprint of the CRAC unit (as predicted by the lifetime exergy model) are identified. Case studies are performed to illustrate how variations in these key parameters can lead to significant differences in the lifetime exergy consumption of the CRAC unit. The paper concludes by recommending strategies to reduce the lifetime exergy consumption.
On Motion Switchability in a Two Degree of Freedom, Friction-Induced Oscillator Traveling on Constant Speed Belts
Authors: Luo Albert C. J. , Mao Tingting
Published: July 2010

In this paper, all possible stick and non-stick motions in such a friction-induced oscillator are discussed and the corresponding analytical conditions for the stick and non-stick motions to the traveling belts are presented. The mapping structures are introduced and the periodic motions of the two oscillators are presented through the corresponding mapping structure. Velocity and force responses for stick and non-stick, periodic motions in the 2-DOF friction-induced system are illustrated for a better understanding of the motion complexity in such many degrees of freedom systems.
Optimization of a MCFC Hybrid System for Combined Production of Electricity and Hydrogen
Authors: Verda Vittorio , Nicolin Flavio
Published: July 2010

In this paper, a hybrid plant obtained by integrating a molten carbonate fuel cell stack with a micro gas turbine and a steam reformer is considered. The system also produces hydrogen through a pressure swing absorption system. The aim of this work is the multi-objective optimisation of the system, considering energy and economic objective functions. Possible off-design operating conditions accounting for degradation of the fuel cell performance and time variation in the biogas composition are considered, as well as variation in the ambient temperature. The results show that the operating temperature of the fuel cell is a crucial design parameter as its value strongly affects the plant efficiency, its lifetime and the unit cost of electricity.
Postbuckling Analysis of Variable Stiffness Composite Panels Using a Finite Element Based Perturbation Method
Authors: Rahman T. , IJsselmuiden S. T. , Abdalla M. M. , Jansen E. L.
Published: July 2010

In earlier research the authors optimized variable stiffness panels for maximum buckling load, using lamination parameters. The aim of the present research is to analyze those optimized panels in the postbuckling regime so that further improvement can be achieved in the future with respect to its postbuckling performance. Because the incremental-iterative nonlinear analysis in the postbuckling regime is not feasible within an optimization loop a finite element based perturbation method (Koiter type) is used to compute postbuckling coefficients, which are in turn used to make a quick estimate of the postbuckling stiffness of the panel and to establish a reduced order model. The proposed perturbation method has been implemented in a general purpose finite element code. In the present work the postbuckling analysis of variable stiffness panels carried out using the reduced order model is presented and the potential of the approach for incorporation within the optimization process is demonstrated.
Proximity-Based Passive Current Sensors for Real-Time Monitoring of Power Usage in Low and Mid-Voltage Applications
Authors: Sherman Christopher , Leland Eli S. , Pullin Andrew , White Richard M. , Wright Paul K.
Published: July 2010

Traditional monitoring of current flow in power lines involves breaking the circuit for through-the-sensor type monitoring or separating individual wires for around-the-conductor “clamp” metering. Such techniques for measurement are invasive and disruptive for many applications. Using 0.9 cm diameter permanent magnets attached to piezoelectric bimorph elements in conjunction with the fluctuating magnetic fields generated by alternating currents, sensors have been developed that enable in-situ, self-powered measurement of current flow without the need to encircle or disconnect the wire being measured. Whereas previous development [1, 2] of these devices has focused on two-wire applications for low (<600V) voltages, single-wire configurations for higher-voltage (up to 15kV) applications are also considered here. Outputs have been found to be linear through a wide ranges of current (0–200A on 0.6–120V AC), with resolution limited primarily by sensor distance from the target wire (3cm or less from wire edge). Sensitivity studies have been performed on conductors of varying dimensions (18 gauge to 4 gauge) and geometries (single conductor and two-wire) for known sensor placements and current flows. Initial integration has been performed with a wireless radio device to produce a self-contained sensor package 8cm by 10cm by 3cm that can sample data at 2 kHz and transmit results to a base station for further analysis. Initial numerical modeling of the magnetic field gradients around current-carrying wires has been performed to optimize sensor placement. Potential applications include customer (home, business, industry) and distribution grid-level monitoring.
Enhancement of Temperature Blending in Convective Heat Transfer by Motionless Inserts With Variable Segment Length
Authors: Tanbour Emad Y. , Rahmani Ramin K.
Published: July 2010

Enhancement of natural and forced convection heat transfer has been the subject of numerous academic and industrial studies. Stationary inserts can be efficiently employed as enhancement devices for heat transfer and temperature blending in the heat convection systems. Generally, a stationary heat transfer enhancement insert consists of a number of equal (or similar) motionless segments, placed inside of a pipe in order to control flowing fluid streams. An ideal insert, for temperature blending in compressible flow applications, provides a smaller standard deviation of temperature with minimized pressure drop and required space. The ratio of temperature uniformity to the pressure drop can be used to determine the efficiency of an insert design. It is possible to use different segment lengths for a given insert design to maximize this ratio. Numerical simulation for heat transfer in turbulent flow is employed to simulate the flow and thermal fields for streams of cold and hot gases flowing across stationary inserts with variable segment length and to study the impact of the segment length on the performance of the insert. It is shown that the insert with variable segment length is more effective in temperature blending for two compressible streams.
Parametric Study of Ultrafiltration
Authors: Zhou Nina , Nnanna A. G. Agwu
Published: July 2010

The performance of cross flow hollow fiber ultrafiltration (UF) membrane with molecular weight cut off (MWCO) 100 kDaltons was studied in order to effectively remove suspended solids in wastewater. Experiments were carried out to investigate the influence of the several factors such as cross flow velocity, transmembrane pressure (TMP), water temperature, and concentration of suspended solids on the membrane performance. Several cleaning methods were applied to remove the fouling. The experimental results showed that increasing TMP, temperature and cross flow velocity all resulted in increasing permeate flux. It is observed that high TMP aggravated the fouling while high cross flow velocity alleviated the fouling. High concentrations of suspended solids led to the reduction of permeate flux. It is also found that both combination of chemical, back- and forward-washing as well as soaking cleaning methods effectively removed fouling and achieved high flux recovery. The suspended solids were effectively removed by our UF system, and the water quality is significantly improved after ultrafiltration.
Effect of Relocation of Functional Units of a Non-Uniformly Powered Microprocessor on Thermal and Device Clock Performance
Authors: Karajgikar Saket , Agonafer Dereje , Ghose Kanad , Sammakia Bahgat , Amon Cristina , Refai-Ahmad Gamal
Published: July 2010

Integration of different functional components such as level two (L2) cache memory, high-speed I/O interfaces, memory controller, etc. has enhanced microprocessor performance. In this architecture, certain functional units on the microprocessor dissipate a significant fraction of the total power while other functional units dissipate little or no power. This highly non-uniform power distribution results in a large temperature gradient with localized hot spots that may have detrimental effects on computer performance, product reliability, and yield. Moving the functional units may reduce the junction temperature but can also affect performance by as much as 30%. In this paper, multi-objective optimization is performed to minimize the junction temperature without significantly altering the computer performance. From the results, the minimum and the maximum temperature was 56.6°C and 62.2°C with a corresponding penalty on the performance of 14% and 0% respectively. The numerical analysis was performed for 90 nm Pentium® IV Northwood architecture at 3 GHz clock speed.
A Micromachined Manifold Microchannel Cooler
Authors: Boteler Lauren , Jankowski Nicholas , Geil Bruce , McCluskey Patrick
Published: July 2010

An improved MEMS fabricated, manifold microchannel cooler has been developed for single phase liquid, forced convection. The manifold design uses multiple channel sizes to minimize pressure drop, maximize heat transfer, and improve temperature uniformity across the area of the cooled device. A significant reduction is achieved in thermal resistance between the device and the cooling fluid. This is a critical need in modern electronic components because of the increasing demand for higher power levels and packaging densities. This paper discusses improvements in fabrication, alignment procedure, and packaging in comparison to our previously published work. A wide range of microchannel dimensions have been fabricated and tested to show the effect of channel size on performance. Testing results of the thermal transfer rates will be presented using silicon diodes as heat sources. A 25 mm × 8 mm × 3 mm (thick) silicon cooler was fabricated to cool two 6 mm square devices. The cooler was microfabricated with a silicon three wafer stack and the channels were etched using standard MEMS processing techniques including DRIE. This new device has modified the authors previously published work in a number of ways. First, fabrication sequence has been modified for better depth uniformity and a new alignment technique has been used that incorporates micro ball bearings as passive alignment pins. Second, triangular shaped inlets have been incorporated to further reduce pressure drop. Third, an aluminum nitride layer was incorporated into the layer stack to achieve electrical isolation between the device and the fluid. Finally, thermal characterization has been improved by using aluminum nitride chip resistors as surrogate heat sources with improved reliability and temperature uniformity over the heated area. Dimensional improvements have also been made to improve fluidic performance and lessen the potential of clogging. The manifold channels are 500 μm wide and 1mm deep with a 50 μm fin width. The microchannels are 150 μm deep with a width of 80 μm and a fin width of 40 μm. The aluminum nitride is bonded onto the top of the silicon channels then the chip resistors are bonded with a silver polyimide paste onto the aluminum nitride. The devices fluidic and thermal performance was measured. We have demonstrated an improvement over the previously published manifold microchannel cooler while also demonstrating the use as a multichip module. The manifold microchannel design minimizes the pressure drop across the channel while maximizing cooling potential and temperature uniformity across the area of the device. The experimental results have shown very promising thermal performance of this multi-chip manifold microchannel cooler. Thermal resistances less than 0.4 C/W were measured at flow rates of 400 ccm with a pressure drop of 5.6 psi. Tests were performed with heat fluxes up to 331 W/cm2 with a measured chip temperature rise of only 53C. The results of the testing show very good thermal performance of this device.
Computational Studies of EHD-Enhanced Condensation Heat Transfer on a Downward-Facing Horizontal Plate
Authors: Sharifi Payam , Esmaeeli Asghar
Published: July 2010

This study aims to investigate the effect of uniform electric fields on the enhancement of condensation heat transfer from a downward facing horizontal plate by direct numerical simulations. The governing equations of fluid flow and electric field are solved using a front tracking/finite difference technique in the framework of Taylor’s leaky dielectric model. The electric force comprises of the dielectrophoretic and the Coulomb forces. Both forces act on the phase boundary and their relative magnitude and directions affect the condensation rate. For the results shown here, the condensate drops are more elongated compared to the those in zero-electric field. It is shown that the electric field enhances the condensation rate in two ways: by increasing the number of the drops that are generated per unit surface due to destablizing the interface and by increasing the frequency of drop generation and pinch off. The mechanism of elongation of the condensate drops are explained by detailed examination of the distribution of the electric field at the phase boundary.
The Effect of Film Thickness on EHD-Driven Instability of Interface Separating Two Liquids
Authors: Sharifi Payam , Esmaeeli Asghar
Published: July 2010

Most of the studies conducted so far on EHD-driven instability of superimposed fluids have been concerned with liquid layers of modest depths. In many applications, however, the liquid layers can be very thin. Since the dynamics in thin films is generally governed by lubrication equations rather than full Navier-Stokes equations, it is expected that the interface dynamics will be quite different from that of the liquids with modest depths. The objective of this study is to explore the effect of initial liquid thickness on the dynamics of the phase boundary. To do this end, we perform Direct Numerical Simulations (DNS) using a front tracking/finite difference scheme, in conjunction with Taylor’s leaky dielectric model. For the physical parameters used here, it is shown that for sufficiently thick liquid layers, the interface instability leads to formation of liquid columns that merge together to form a big column. However, for thin layers, the interactions between the columns are weaker and lead to a short and a longer column that are connected by a thin liquid film.
Unsteady Buoyant Convection and Liquid-Solid Phase Change in a Power Law Fluid Within a Differentially Heated Square Cavity
Authors: Silva Luis A. , Moraga Nelson O. , Ortega Alfonso
Published: July 2010

In the thermal processing of canned foodstuffs, a problem that frequently arises is related to the heating or cooling time required to process the contents of a can. The liquid-solid phase change phenomenon in a non-Newtonian fluid undergoing transient natural convection in a square cavity is the fundamental problem that is investigated. The unsteady Navier-Stokes equations and the convection-diffusion equation are the required mathematical formulation. Phase change effects are introduced through an apparent specific heat model. Because the fluid is initially at rest, the buoyant motion is transient, leading to a complex problem with unsteady fluid motion, temperature dependent rheology, and eventually phase change. A Finite Volume method was used to discretize the governing equations. Transient temperature and velocity fields were obtained for varied non Newtonian power index n. It was found that the motion of fluid is augmented when n increases. This power law index also influences the final shape of the solid/liquid interface.
Effect of Structural Design Parameters on Wafer Level CSP Ball Shear Strength and Their Influence on Accelerated Thermal Cycling Reliability
Authors: Lakhkar Nikhil , Viswanadham Puligandla , Agonafer Dereje
Published: July 2010

Ball shear testing is typically conducted in Wafer level chip scale package (WLCSP) fabrication to estimate the strength of the solder ball attachment. Generally, the solder ball shear strength is dependent on the solder ball size, pad size, solder/pad interface treatment, reflow temperature and time. Solder ball strength is also a function of ram speed and height at which the ball is sheared with respect to the wafer. Recent investigations suggest that ball shear test is being used as an indicator for board level reliability of assemblies. In current market lead time for launching a new product is very short. Unfortunately, it takes several weeks to qualify a new product by board level qualification process. If there is a methodology through which one can predict the board level performance by extrapolating the wafer level test, it will save great amount of resources in testing and millions of dollars worth of testing time. In the first part of this study, we conducted a wafer level ball shear test. A DOE was created for varying wafer level structural parameters like solder ball size and type. Ball shear tests and Accelerated thermal cycling have similar failure signatures of compression on inner side and tension on outer side. Thus, for specific cases there is a possibility of correlating the two failure methodologies based on their failure signatures. Strain rate for ball shear test was determined based on shear speed and solder pad diameter. Strain rate for accelerated thermal cycling was determined based on difference in CTE between board and package. In this paper, results from ball shear test and accelerated thermal cycling are compared to find correlations for specific cases. The correlations derived from this study are statistical and empirical.
Design Concepts and Development of Elastomer Heat Engines/Pumps
Authors: Gerlach David W.
Published: July 2010

Although ideal elastomer thermodynamics has been described by many authors, their use in heat engines/pumps remains a theoretical and pedagogical curiosity. Because elastomers can generate large forces with small temperature changes, they may be useful in low delta T heat engines for energy recovery and bottoming cycles. In addition, the greater density of solid versus gas or two-phase working substances may enable a more compact system. Elastomer heat engines described in the literature are reviewed and compared. Most designs use an eccentric wheel design presenting design problems in sealing and physically separating the hot and cold sides. In addition, a variety of designs for rotary motors using the linear contraction of a solid that have been developed for thermoelastic shape memory alloy and mechanochemical systems are also pertinent. Several heat pump prototypes were constructed where an ideally isothermal process was performed by stretching in contact with a hot and a cold heat transfer plate. However, the sliding friction on the plates prevented any measured cooling effect. Designs utilizing a continuous elastomer belt winding over various configurations of rollers or pulleys appear to be most suited to elastomer systems due to the flexibility of placement of the hot and cold reservoirs. A simplified two wheeled design is described.
Thermal Characterization of Planar Interconnect Architectures Under Transient Currents
Authors: Barabadi Banafsheh , Joshi Yogendra K. , Kumar Satish , Refai-Ahmed Gamal
Published: July 2010

The quality and reliability of interconnects in microelectronics is a major challenge considering the increasing level of integration and high current densities. This work studied the problem of transient Joule heating in interconnects in a two-dimensional (2D) inhomogeneous model. The transmission line matrix (TLM) method was implemented with link-resistor (LR) and link-line (LL) formulations, and the results were compared with a finite element (FE) model that was developed in LSDyna. This comparison showed that the overall behavior of the TLM models were in good agreement with the FE model while, near the heat source, the transient TLM solutions developed slower than the FE solution. The steady-state results of the two models were identical. The two TLM formulations yielded slightly different transient results, with the LL result growing slower particularly at the source boundary and becoming unstable at short time-steps. It was concluded that the LR formulation is more accurate for transient thermal analysis. Computational efficiency of the TLM method and its ability to accept non-uniform 2D and 3D mesh and variable time-step makes it a good candidate for multi-scale analysis of Joule heating in the interconnects.
Stabilization of a Four-Wheel Mobile Robot From Kinematic Model to Dynamic Model by Feedback Passivation of Cascades Using Chained Form
Authors: Mohammadi Hossein , Haghpanah Arash , Eghtesad Mohammad
Published: July 2010

In this paper, a novel approach for dynamics based stabilization of a four-wheel mobile robot is presented. One of the well-known and well-established approaches for stabilization of mobile robots is converting the kinematic model of the robot to a chained form. In order to extend this method to dynamic based stabilization, kinematic and dynamic subsystems of the mobile robot state-space model can be considered as two subsystems of a cascade and then feedback passivation of cascades can be utilized for stabilization of the whole system dynamics.
Boundary Control of Temperature Distribution in a Rectangular FGM Plate
Authors: Rastgoftar Hossein , Gharib Shirangi Mehrdad , Eghtesad Mohammad
Published: July 2010

In this paper an analytical method and a PDE-based solution to control temperature distribution in FGM plates is introduced. For the rectangular FGM plate under consideration, it is assumed that the material properties such as thermal conductivity, density, and specific heat capacity, vary in the width direction (y); and the governing heat conduction equation of the plate is a second-order partial differential equation. Since there has been little control synthesis work for PDE-based systems as compared to the abundance of control design techniques available for ordinary differential equations (ODEs), most of the proposed control approaches for continuous domain rely on discretizing the PDE model into a set of ODEs. Using Lyapunov’s theorem, we will show that with applying controlled heat flux through the boundary of the domain, the temperature distribution of the plate will approach to the desired distribution of Td (x, y). Finally, numerical methods are used to analyze transient heat transfer as distributed temperature T (x, y, t) converge to desired one of Td (x, y).
Research on General Model of Hot Runner Mould for Transparent and Complex Plastic Knobs
Authors: Ge Xiaohong , Wu Shaolan , Li Hui , Huang Hongwu
Published: July 2010

In order to improve the manufacturing efficiency and product quality of transparent and complex plastic knobs, a hot runner injection mold is introduced in this paper. Based on a shared hot runner system and a module combination of the mold holders, inserts and the beryllium-copper cored cooling components, an effective general model for hot runner injection molding is developed. The beryllium copper insert extrusion process is employed to copy with the requirements of great variety, high quality, low price and short producing cycle for knob products. The results of CAE analysis and production validation for typical knobs and insert extrusion process demonstrate the effectiveness of the newly developed hot runner injection molding and that the product quality fulfill the requirements of real manufacturing process.
A Combined Power Cycle Using Refuse Incineration and LNG Cold Energy With Use of Regasified LNG
Authors: Mahdavi Hamid , Meratizaman Mosa , Jazayeri S. Ali
Published: July 2010

The objectives of this paper are to develop a combined power generation cycle using refuse incineration and LNG cold energy, and to conduct parametric analysis to investigate the effects of key parameters on the thermal and exergy efficiencies. The combined cycle consists of an ammonia–water Rankine cycle with refuse incinerator and a LNG cold energy cycle with use of regasified LNG as the extra fuel in the incinerator. The combined cycle is compared with the conventional steam Rankine cycle.
The Force on Intruder in Vibration Granular Bed
Authors: Liu Chuanping , Wang Li , Jia Min
Published: July 2010

In this paper, a column is put in a vibrated bed as an intruder to study the force of bed by changing intruder’s mass and vibration strength. Our result indicates that the granular material is completely different with conventional fluid, which the force on intruder does not satisfy with Archimedes Law. The force is strongly influenced by its position in bed, as well as its size, shape and vibration strength. The deeper the intruder immerges, the bigger the force is. Because of the different forces, the interesting phenomena granular separation, that the intruder can not only rise to the top, but also sink to the bottom, and even keep in the middle of the bed, are present.
New Radial-Based Flow Configurations for PEMFCs
Authors: Perez-Raya Isaac , Hernandez-Guerrero Abel , Juarez-Robles Daniel , Gutierrez-Rivera M. Ernesto , Rubio-Arana J. C.
Published: July 2010

This work presents the results of a study of a new radial configuration proposed for the gas flow field for a PEM fuel cell. The objective of this study is to understand the effects of this configuration on the fuel cell performance. The results are compared with the radial designs proposed in previous analysis. The proposed designs on this work show an improvement on the cell performance, with a better use of the reaction area compared with a flow free radial design. The results also show that the effect of channeling the flow inside these radial configurations helps to improve the fuel cell performance.
Effects of Warping Constraints and Lateral Restraint on the Buckling of Thin-Walled Frames
Authors: Pignataro Marcello , Ruta Giuseppe , Rizzi Nicola , Varano Valerio
Published: July 2010

We present the effect of warping constraints on the buckling of a thin-walled two-bar (‘Roorda’) plane frame subjected to a ‘dead’ load at the joint. The hinges with the ‘ground’ allow rotation with axis perpendicular to the frame plane; the joint is constrained in the same direction to simulate a 3D-frame. Warping constraints are considered; the restraint at the joint is first supposed rigid and fixed, then is supposed linear elastic to account for different lateral restraint. Critical loads are evaluated numerically; an analysis of the post-buckling behaviour will be part of future investigations.
Modeling of Ultrafast Phase Change Processes in a Thin Metal Film Irradiated by Femtosecond Laser Pulse Trains
Authors: Huang Jing , Zhang Yuwen , Chen J. K. , Yang Mo
Published: July 2010

Ultrashort laser pulses can be generated in the form of a pulse train. In this paper, the ultrafast phase change processes of a 1-μm free-standing gold film irradiated by femtosecond laser pulse trains are simulated numerically. A two-temperature model coupled with interface tracking method is developed to describe the ultrafast melting, vaporization and resolidification processes. To deal with the large span in time scale, variable time steps are adopted. A laser pulse train consists of several pulse bursts with a repetition rate of 0.5∼1 MHz. Each pulse burst contains 3∼10 pulses with an interval of 50 ps ∼ 10 ns. The simulation results show that with such a configuration, to achieve the same melting depth, the maximum temperature in the film decreases significantly in comparison to that of a single pulse. Although the total energy depositing on the film will be lifted, more energy will be transferred into the deeper part, instead of accumulating in the sub-surface layer. This leads to lower temperature and temperature gradient, which is favorable in laser sintering and laser machining.
The Effectiveness of Mechanical and Manufacturing Engineering Technology Programs for Full-Time Employed Industry Students
Authors: Peter Geoffrey J.
Published: July 2010

The Oregon Institute of Technology (OIT), Portland Center, has been offering Manufacturing Engineering Technology (MfgET) and Mechanical Engineering Technology (MET) undergraduate programs for students around the greater Portland Metropolitan area for the past ten (10) years. A Master’s degree in Manufacturing Engineering Technology (MMfgET) is also offered. These programs are extensions of programs offered at OIT main Campus in Klamath Falls. Portland Campus programs are designed specifically to cater to students employed full-time in industry. This paper discusses engineering technology programs and their direct application in training local company fulltime employees to become engineers and managers. Most of these employees have associate degrees and years of experience in their respective companies. A discussion of engineering-related, hands-on work experience and understanding of engineering principles and their applications presented. The effectiveness of special instruction techniques, custom-developed for students with limited time availability, while maintaining ABET accreditations is also discussed. Discussion-oriented learning and teaching models and the impact of adding dimensions to these instructional models, with the industry-experienced students in mind, is emphasized. Case studies are presented to show improvement in student engagement, curiosity, and application of new knowledge to actual day-to-day, work-environment problems. Advantages and disadvantages of night school are discussed.
Reliability of Structural Systems Under Wind Action
Authors: Augusti G. , Ciampoli M. , Petrini F.
Published: July 2010

The most rational way of assessing and reducing the risks of building constructions and infrastructures subject to natural and man-made hazards is Performance-Based Design, usually indicated by the acronym PBD; this applies to both design of new facilities and rehabilitation or retrofitting of the existing ones. The basic concept of PBD has been applied for almost 30 years in the nuclear power plant industry; later, PBD has been formalized and developed primarily in seismic engineering but has been extended to other engineering field, like Blast Engineering and Fire Engineering. Also wind engineering has appeared of great potential interest for further developments of PBD. The first steps in this direction go back to an Italian research project, in which the expression “Performance-Based Wind Engineering” (PBWE) was coined. In this paper, an approach to PBWE is illustrated and applied to an example case: the assessment of the collapse and out-of-service risks of a long span suspension bridge.
Supersonic Flow at Micro-Tube Outlet
Authors: Yoshida Yasuhiro , Hong Chungpyo , Asako Yutaka , Suzuki Koichi
Published: July 2010

The boundary layer is formed on micro-channel walls and its thickness becomes 0 at the exit of the channel. And, it plays a role of a wall of a converging and diverging nozzle and the flow becomes supersonic at the micro-channel outlet. Then outlet Mach number is beyond unity. This fact is not widely known. Therefore, experimental investigations on behavior of super sonic flow at the outlet of straight micro-tubes whose diameter ranges from 150 to 500 μm are conducted. The stagnation pressure ranges 379 from to 812 kPa. The successive expansion and recompression waves of under-expanded state were visualized by Schlieren method and a high-speed camera. The numerical investigations are also performed for straight micro-tubes with diameter ranging from 50 to 400 μm. Numerical methodology is based on the aribitary-Langrangian-Eulerian (ALE) method. The stagnation pressure was chosen in such a way that the Mach number at the tube outlet ranges from 1.0 to 1.6. The ambient back pressure is fixed at the atmospheric pressure. The flow at the tube outlet change from the over-expanded to the under-expanded state. It is observed that the recompression and expansion waves are alternately formed in downstream of the micro-tube outlet in both experiments and numerical computations. The experimental correlation for the distance from the micro-tube outlet to the Mach disk as a function of pressure at the outlet was proposed for the prediction of outlet pressure of micro-tube in under-expanded.
Computational Modeling of Convective Heat Transfer in Converging-Diverging Plate Channels With Fin-Wall Perforation
Authors: Huzayyin O. A. , Jog M. A. , Manglik R. M.
Published: July 2010

The convective heat transfer performance of converging-diverging plate channels with fin-wall perforations is computationally modeled. Covering a Reynolds Number range of 10 < Re < 1000 for air (Pr = 0.72) flows, a parametric study of the effect of the two dimensional duct geometry, which has symmetric fin wall corrugations of trapezoidal profile, are considered. The geometric variables are described by the divergent-plane’s inclination angle φ and the convergent-divergent amplitude ratio α. The wall perforations are modeled as uniformly distributed equi-size thin slots so as to render a porosity (ratio of perforated are to total surface area) β of 10% on the fin surface. The fin-wall transpiration (fluid injection in the divergent section and fluid suction in the convergent section) is seen to promote enhanced convective heat transfer by inducing cross stream mixing and periodic disruption of the boundary layer. As a result, the thermal-hydraulic performance is found to be characteristically unusual, where increase in heat transfer is accompanied with a reduction in frictional loss. The enhanced performance evaluated by both area goodness and volume goodness measures, is seen to render a substantially more compact heat exchanger.
Enhanced Instruction of Engineering Mechanics Using Curvature Experiments
Authors: Newberry Byron L.
Published: July 2010

Resistive strain gauges are the most commonly used experimental devices for stress analysis. Their versatility stems from their ability to directly measure local strain on the surface of a structure, almost regardless of geometry. This strength can represent an educational limitation, however. Measurements made using strain gauges tend to provide results without students assessing or understanding the global structural response; limiting the insight gained and the instructional value of the experiment. Herein a low-cost device is presented that allows accurate measurement of local curvature in a beam. Once the local curvature is known, the elastic equations governing the beam may be used to calculate the local strain, stress, and deflection. The educational strength of the device is that students are forced to understand the interrelation of stress, strain, and deflection to post-process the experimental results. The device, though limited to beam geometries, has proven effective in helping students master engineering mechanics. It also allows investigation of the entire beam without added expense; as the device is not permanently affixed to one location. This is a significant advantage compared to strain gauges that provide only point data and are single-use. Details of the device itself, how it has been incorporated into the curriculum, and data assessing its effectiveness within a junior-level course are presented.
Performance of Parallel-Flow Gas-to-Gas Micro-Double-Tubes-Heat Exchangers
Authors: Hong Chungpyo , Asako Yutaka , Suzuki Koichi
Published: July 2010

Heat transfer performance of two-stream parallel-flow gas-to-gas micro-double-tubes-heat exchangers was investigated numerically. The flow passages of the micro- double-tubes-heat exchanger are a circular tube for hot passage and a concentric annular tube for cold passage. A circular tube of r = 50 μm and a concentric annular tube of ri = 51 μm and ro = 71 μm with an identical cross-sectional area were chosen and the selected length was 20mm, respectively. Then, the partition wall is assumed to be a stainless steel tube with 1 μm in thickness. Numerical methodology is based on the arbitrary-Langrangian-Eulerian method. Computations were performed for wide flow range to find the effects of capacity ratio on the heat transfer characteristics of gas-to-gas micro-double-tubes-heat exchangers. The results are presented in form of temperature contours, bulk temperature, total temperatures and heat flux variation along the length. Also, the effectiveness and the number of transfer units approach and the estimation of the heat exchange rate were discussed.
Flow Investigation Through a 30° Turn Diffusing Duct in Subsonic Flow Regime
Authors: Sinha Prasanta K. , Haldar Biswajit , Mullick Amar N. , Majumdar Bireswar
Published: July 2010

Curved diffusers are an integral component of the gas turbine engines of high-speed aircraft. These facilitate effective operation of the combustor by reducing the total pressure loss. The performance characteristics of these diffusers depend on their geometry and the inlet conditions. In the present investigation the distribution of axial velocity, transverse velocity, mean velocity, static and total pressures are experimentally studied on a curved diffuser of 30° angle of turn with an area ratio of 1.27. The centreline length was chosen as three times of inlet diameter. The experimental results then were numerically validated with the help of Fluent, the commercial CFD software. The measurements of axial velocity, transverse velocity, mean velocity, static pressure and total pressure distribution were taken at Reynolds number 1.9 × 105 based on inlet diameter and mass average inlet velocity. The mean velocity and all the three components of mean velocity were measured with the help of a pre-calibrated five-hole pressure probe. The velocity distribution shows that the flow is symmetrical and uniform at the inlet and exit sections and high velocity cores are accumulated at the top concave surface due to the combined effect of velocity diffusion and centrifugal action. It also indicates the possible development of secondary motions between the concave and convex walls of the test diffuser. The mass average static pressure recovery and total pressure loss within the curved diffuser increases continuously from inlet to exit and they attained maximum values of 35% and 14% respectively. A comparison between the experimental and predicated results shows a good qualitative agreement between the two. Standard k-ε model in Fluent solver was chosen for validation. It has been observed that coefficient of pressure recovery Cpr for the computational investigation was obtained as 38% compared to the experimental investigation which was 35% and the coefficient of pressure loss is obtained as 13% in computation investigation compared to the 14% in experimental study, which indicates a very good qualitative matching.
Lessons Learned From the Use of the Laser Doppler Velocimeter and the Particle Image Velocimeter for Water Flow Bounded by a Layer of Oil
Authors: Wong K. V. , Samarajeewa H. , Itier B.
Published: July 2010

The objectives of this paper are to describe the learning of the use of the Laser Doppler Velocimeter (LDV) as well as the Particle Image Velocimeter (PIV), including the fine points in their usage for instructional purposes. The application is to measure the velocity distribution across a flow of water bounded by a layer of oil using lasers. The characteristics at the oil-water interface are very interesting. It would be significant to measure the velocity distributions around this region. Such a scenario occurs during oil spills and spills of oily chemical pollutants in the sea or open ocean. The LDV is a well established method for measuring both laminar and turbulent flows. In this method, tracer particles are used to assist in measuring velocity profiles. This method was pushed to the limit by measuring the velocity boundary layer in the open channel flow. The average free-stream velocity is measured by other conventional means as a check on the LDV measurements. The PIV method is an optical method used to obtain instantaneous velocity measurements and related properties in fluids. The fluid is seeded with tracer particles and it is the motion of these seeded particles that is used to calculate the velocity information of the flow being studied. The PIV produces two dimensional vector fields. The simple PIV system was pushed to the limit by using it to measure the velocities in the oil-water interface of an open channel flow bounded by oil on the surface. The major difference between the LDV and the PIV is that the LDV measurements are done at a point, whereas the PIV measures the velocity of a region. Furthermore, PIV produces two dimensional vector fields while the LDV produces only a velocity measurement.
Thermal Decomposition Modeling and Thermophysical Property Measurement of a Highly Crosslinked Polymer Composite
Authors: Brundage Aaron L. , Erickson Kenneth L. , Dowding Kevin J.
Published: July 2010

Thermophysical properties including density, specific heat, and thermal diffusivity of a poly (diallyl phthalate) inert filler composite material were characterized over a wide temperature range from room temperature to 800 °C. Over this temperature range, the material decomposition was approximated by a one-step process with first-order kinetics. Thermal kinetics data were obtained by thermal gravimetric analysis with Fourier transform infrared spectroscopy (TGA-FTIR) and thermophysical properties were obtained from differential scanning calorimetry (DSC) and laser flash diffusivity experiments. The response of the material to radiant heating was simulated with a computational heat transfer, multidimensional, finite element code. Additionally, the experimental uncertainty in the measurements was quantified to estimate the uncertainty in the reaction parameters due to heating rate and variability in inert filler-polymer composition in large sample sizes. Hence, the thermal response and the uncertainty were quantified for a complex decomposing material in a practical geometry for technologically important applications.
A Unified Method for Modeling 3 Phase Synchronous Machines
Authors: Snell Antony
Published: July 2010

The use of 3 phase synchronous machines (motor or generator) is becoming more widespread with the introduction of variable frequency drives, which allow the machines to be used very effectively as low maintenance alternatives to brushed DC commutator motors. However, mathematical modeling of these machines is often difficult to understand. Many textbooks on electro-mechanical machines introduce the synchronous machine using a phasor model of the voltages induced in the armature and the applied voltage. This yields some neat results of output torque as a function of the torque angle but fails to provide much insight into how this torque comes about. Furthermore, the method assumes that the resistance of the armature windings is negligible compared with armature reactance. The method falls apart when resistance must be included. Even when armature resistance is small, there is no insight into how efficiency is compromised by copper losses in the armature. The approach described in this paper is based on the same theory, which is usually used to explain the operation of DC commutator machines. This approach provides direct insight into how torque is developed. Losses introduced by armature resistance are included so reasonable efficiency estimates can be made. Meanwhile the neat results of the simple phasor model can be obtained as a special cases by setting armature resistance to zero.
A New Approach to Study and Compare the Annual Performance of Liquid and Solid Desiccant Cooling Systems
Authors: Esfandiari Nia Fatemeh , Phelan Patrick E.
Published: July 2010

Desiccant cooling systems, considered one of the sustainable air conditioning technologies, have been attractive for researchers to be studied for many years. In this paper, the modeling and simulation of a packed tower liquid dehumidifier and regenerator as well as a solid desiccant wheel are presented. The simplified equations that predict the air conditions after passing these systems are developed. This approach is quick and does not need a lengthy computer calculation and large memory capacity. Liquid and solid desiccant cooling cycles are presented and using this approach, the performance of these systems is calculated for weather data of a reference year and different climates in the United States. These systems are compared regarding their energy and water consumption based on this new approach. The first results show that liquid desiccant systems, without technology improvements, have the large sizes at lower capacities and have lower coefficients of performance than solid desiccant cooling systems.
Thermophysical Characteristics of Self-Assembled Ethanol/Polyalphaolefin Nanoemulsion Fluids
Authors: Xu J. J. , Liu X. , Yang B.
Published: July 2010

The strategy of adding solid particles to fluids for improving thermal conductivity has been pursued for more than one century. Here, a novel concept of using liquid nanodroplets for enhancing thermal performance has been developed and demonstrated in polyalphaolefin nanoemulsion fluids with dispersed ethanol nanodroplets. The ethanol/polyalphaolefin nanoemulsion fluids are spontaneously generated by self-assembly, and are thermodynamically stable. Their thermophysical properties, including thermal conductivity and viscosity, and impact on convective heat transfer are investigated experimentally. The thermal conductivity enhancement in these fluids is found to be moderate, but increases rapidly with increasing temperature in the measured temperature range from 35 oC to 75 oC. A very remarkable increase in convective heat transfer coefficient occurs in the nanoemulsion fluids due to the explosive vaporization of the ethanol nanodroplets at the superheat limit (i.e., spinodal states, about 122 oC higher than the atmospheric boiling point for ethanol). The explosive liquid-vapor phase transition is monitored using high speed camera. The fluid heat transfer could be augmented through the heat of vaporization (which intuitively raises the base fluid specific heat capacity) and the fluid mixing induced by the sound waves. The development of such phase-changeable nanoemulsion fluids would open a new direction for thermal fluids studies.