bluuebunny/crossref_metadata_2025 huggingface dataset:
Description and Investigation of Size Effects in the Scaling of a Hot Forging Process and a Milling Tool Into the Microscale
Authors: Wulfsberg J. P. , Brudek G. , Lehmann J. , Terzi M.
Published: April 2008

From the general trend towards higher miniaturization and functional integration results an increasing demand for metallic parts of smallest dimensions (down to 100 μm). Industrial realization of these parts and the further breakthrough of products containing microparts require suitable production technologies with respect to accuracy, productivity, efficiency and reliability. This aspect is still a significant limitation. The problems which occur at the production of microparts with scaled, conventional processes will be expound by means of a process (microforging) and a microtool (micro diamond milling cutter). The application of metal forming technologies to the production of metallic microparts is limited by problems arising from size effects related to the small dimensions e.g. the influence of the microstructure becomes an important aspect to consider. An approach to these problems is the laser assistance of the microforming process. Laser light is used to increase the temperature of the material during forming, to increase the formability in the required area of the part and to reduce the flow stress and anisotropy of the material. To enable the transmitting of laser light into the workpiece, sapphire tools are used. Experimental investigations have shown that the use of sapphire tools in laser-assisted microforming processes is a suitable method for the production of microparts. Further investigations aim at modeling the material behavior and size effects in microforming processes and the integration of these models into FE simulations in order to extend its application to microproduction processes. The increasing requirements on form and surface qualities for milling tools used in micromanufacturing increasingly become more difficult to fulfill with conventional manufacturing processes. Alternative methods, for example Chemical Vapor Deposition (CVD) based procedures, could offer advantages. They do not only make smallest dimensions possible, but also allow the desired manufacturing tolerances of the tools to be met. As an example of a diamond growth process the development and testing of diamond side milling cutters for application in microtechnology are described [1, 2, 3, 4].
Design of a Workstation Table With Improved Crashworthiness Performance
Authors: Parent Daniel P. , Tyrell David C. , Rancatore Robert , Perlman Benjamin
Published: April 2008

Work is currently underway to develop strategies to protect rail passengers seated at workstation tables during a collision or derailment. Investigations have shown that during a collision, these tables can present a hostile secondary impact environment to the occupants. This effort includes the design, fabrication, and testing of an improved workstation table. The key criteria for the design of this table are that it must compartmentalize the occupants and reduce the risk of injury relative to currently installed tables. Strengthening the attachments between the table and the passenger car body will ensure compartmentalization. Employing energy-absorbing mechanisms to limit and distribute the load imparted on the abdomen of the occupant will reduce injury risk. This paper details the design requirements for an improved workstation table, which include service, fabrication, and occupant protection requirements. Service requirements define the geometry of the table, the performance of the table under normal service loads, and the maintenance of the table over the period of installation. Fabrication requirements define the limitations on material usage and construction costs. Occupant protection requirements define the ability of the table to reduce injury risk to the occupants under collision loads. The table must also conform to federal regulations pertaining to interior structures on passenger rail equipment. Four design concepts are evaluated against these design requirements. These concepts present different modes of deformation or displacement that absorb energy during impact. These concepts have been evaluated, and the highest-ranking concept involves a crushable foam or honeycomb table edge attached to a rigid center frame. Preliminary results from a computer simulation demonstrate the effectiveness of this concept in reducing the injury risk to the occupants.
Development of a Passenger Wheel Standard
Authors: Gordon Jeff , Stone Daniel H.
Published: April 2008

The American Public Transit Association (APTA) is seeking to develop specifications to ensure that wheels used in passenger applications perform safely under the service conditions to which they are exposed. To this end, an approach has been developed which will address this need at two levels. First, a variant on the Association of American Railroads (AAR) S-660 standard [1] is proposed with loading requirements that more realistically represent typical conditions in passenger operations. This is considered a design standard and is to be applied to identify wheel designs not susceptible to fatigue cracking in the wheel plate and hub suitable for use by transit and commuter agencies. Second, an application standard (or more precisely, a recommended practice) has been conceived which is designed to assist transit agencies (or original equipment manufacturers) in the appropriate choice of an “approved” wheel design based on the expected service environment. This technique will identify wheel designs which, under normal operating conditions, should not result in thermal damage to the wheel tread.
Forging the Way to a Better Axle
Authors: Miller Amy L. , Strayer David S. , Williams Todd
Published: April 2008

Historically, rail “axles” for the center truck of Low Floor Mass Transit Cars have been manufactured and supplied by European companies. The industry standard is a fabricated assembly comprised of forged ends welded to a structural steel center of various shapes. Several factors have enticed one domestic supplier to look for a better way to manufacture the axle in the United States. The word axle will be used in this paper, although technically the word “support” is more valid as an “axle” is assumed to rotate and this “support” does not. Currently, Penn Machine is producing its latest support, a one piece forged axle with the properties of the previous welded assembly. Many considerations, including material type, manufacturability, stress and deflection, weight, and dimensional fit, were made prior to approval of the final design. Because previous models were designed and manufactured overseas, European design criteria and materials had to be considered, and in some cases modified for the domestic market. The analysis approach began with a European calculation method. Additional analysis was performed to evaluate modifications. Finite Element Analysis was conducted to refine the design and to investigate material reducing options. The proposed paper outlines the design process used in bringing this new and innovative concept off the boards and into reality. It is the hope of the authors that others will recognize domestic opportunities by observance of the process used to create the new axle. To date, the new axle is being proposed for use on two new transit systems. The cars will be tested with the new axle to insure safety and performance.
Characterizing Naphthalene via Material Flow Analysis
Authors: Ciocci Richard C.
Published: April 2008

An Environmental Protection Agency-funded project centers on the material flow analysis of naphthalene-containing products in an effort to eliminate, reduce, or replace the sources of naphthalene. The analysis commences with manufacturers who use naphthalene-containing products in their processes. Also, the analysis works in reverse by starting with the naphthalene user, as the material will be traced to the source in an effort to identify elimination/reduction opportunities throughout the material’s life cycle. A particular focus is the potential for removal of naphthalene from the primary processor’s raw material. A completed material flow accounting of naphthalene in the United States is the product of this work. The paper highlights the preliminary part of the study. It identifies the basic characteristics of naphthalene as one of the largest polynuclear aromatic hydrocarbons that is released to the environment. Included are likely sources of naphthalene emissions and releases as they are identified for further investigation.
A Room-Temperature Bonding Technique Using Ultrathin PDMS as an Intermediate Layer for Fabrication of Micron and Submicron Channels
Authors: Sung Yonduck , Zhao Yongjun , Lin Qiao
Published: April 2008

We present a new room-temperature bonding technique using a submicron-thick PDMS as an intermediate adhesive bonding layer for fabrication of micron and submicron-scale channels. The ultrathin bonding layers were created with spin-coating of PDMS dissolved in toluene at various weight ratios from 1:4 to 1:18 (PDMS:toluene) to obtain layer thicknesses from 1.65 μm to 0.10 μm, respectively. Bonding of discrete parts of microchannel was formed under pressure with a clamping vise at room-temperature. Tensile bonding strength test on this new technique showed excellent bonding strength. We have achieved 310 kPa for a 0.1 μm-thick layer with the aid of oxygen plasma treatment. To demonstrate its utility in micron and submicron channel fabrication, we created channels (970 μm × 60 μm × 0.97 μm) and performed leakage tests. The bonding showed no leakage at pressures up to 210 kPa.
Fluid Flow and Heat Transfer Induced by a Window Air Conditioner Unit and Associated Thermal Comfort
Authors: Begdouri Hamza , Rosario Luis , Rahman Muhammad M.
Published: April 2008

This study considers airflow simulations to evaluate the impact of different window air-conditioner locations on the thermal comfort in an office rooms (OR). This paper compares the air distribution for an office room by using computational fluid dynamics (CFD) modeling. The air distribution was modeled for a typical office room window air conditioning unit, air supply from a high pressure on the top and the low pressure exhaust on the bottom considering the existing manufacturing ratios for surface areas. Calculations were done for steady-state conditions including an occupant and a light source. The discharge angle for the supply grill of the AC unit was varied from 20 to 40 degrees. The position of the air conditioner was also varied and studied at 60%, 75% and 90% of the total height of the room. In addition the location of the occupant within the office room was varied. Predictions of the air movement, room temperature, room relative humidity, comfort level, and distribution of contaminants within the office room are shown. Analysis of these simulations is discussed. The positions of the air-conditioner unit, the inlet angle and the occupant position in the office room have shown to have important impacts on air quality and thermal comfort. Results are in good agreement with available experimental data.
Double Adjustable Magnetorheological Dampers for a Gun Recoil System
Authors: Choi Young-Tai , Yoo Jin-Hyeong , Wereley Norman M.
Published: April 2008

This paper examines a double adjustable magnetorheological (MR) damper that can produce high damper force and substantial dynamic force range (the ratio of the field-on to the field-off damper force), particularly over a high speed piston range. To this end, a double adjustable MR damper is configured and its hydraulic model is theoretically constructed. From this hydraulic model, the governing equation for the double adjustable MR damper is derived using the nonlinear pressure-flow relationship. The damper characteristics of the double adjustable MR damper are theoretically evaluated and compared with those of a conventional flow-mode MR damper. To investigate the effectiveness of the double adjustable MR damper in mitigating shock of a gun recoil system, a mechanical model of the recoil system using a double adjustable MR damper is theoretically constructed and the dynamic equation for the recoil system is derived. The shock mitigation performance of the MR gun recoil system with no-field and constant magnetic field inputs is numerically evaluated. A simple on-off control algorithm is proposed to improve the shock mitigation performance of the passive MR gun recoil systems. Finally, the shock mitigation performance of the MR gun recoil system using no-field, constant field, and on-off control algorithm is analyzed and compared with those of a conventional gun recoil system under nominal firing forces, as well as a 30% perturbation from nominal.
A Model of Shear Viscosity for Under-Fill Flows
Authors: Yang R. , Sun D. C. , Park Seungbae
Published: April 2008

The flow of a dense slurry between two parallel walls is modeled in this paper. The flow behavior of the dense slurry is governed by the particle-particle and particle-wall interactions. Fluid film lubrication theory is used to find the unit solutions of interaction between two particles. The unit solutions are applied to a simple case of slurry flow densely packed with neutrally buoyant particles. The dependence of the effective viscosity of the slurry on packing parameters is revealed. The shear viscosity so obtained is intended for use in the analysis of under-fill flows of encapsulant induced by surface tension. An ongoing under-fill flow experiment aimed at validating the shear viscosity model is described.
A Two Parameter Robust Linear Parameter Varying Repetitive Control Approach to Variable Speed Electronic CAM Follower Problem
Authors: Wang Junqing , Tsao T. C.
Published: April 2008

Electronic cam follower motion control is a class of master-slave type mechanism where the slave axis motion must follow the master axis coordinate (process variable) according to a given cam profile while the master axis motion has a time varying speed. Time-domain repetitive control design can be well applied to the electronic cam slave control under constant nominal master’s axis speed. This approach won’t perform well when the master’s axis nominal speed varies, however. Recent research has suggested transforming the slave dynamics into the angle domain. By treating the rotational speed as a parameter which can be measured in real time, the resulting angle domain time varying plant is modeled as an affine linear parameter varying system. A continuous two parameter robust linear parameter varying repetitive controller with modified repetitive signal generator is proposed and compared with the time varying model reference approach. Simulation results show perfect asymptotic tracking performance with piecewise constant parameter profiles and graceful performance degradation with continuously varying parameter profiles.
Life Cycle Cost Analysis of a Novel Cooling and Power Gas Turbine Engine
Authors: Malhotra Vaibhav , Lear W. E. , Khan J. R. , Sherif S. A.
Published: April 2008

A Life cycle cost analysis (LCCA) was performed to compare life cycle costs of a novel gas turbine engine to that of a conventional microturbine with similar power capacity. This engine, called the High Pressure Regenerative Turbine Engine (HPRTE) operates on a pressurized semiclosed cycle and is integrated with a Vapor Absorption Refrigeration System (VARS). The HPRTE uses heat from its exhaust gases to power the absorption refrigeration unit which cools the high-pressure compressor inlet of the HPRTE to below ambient temperatures and also produces some external refrigeration. The life cycle cost analysis procedure is based on principles laid out in the Federal Energy Management Program (FEMP). The influence of different design and economic parameters on the life cycle costs of both technologies is analyzed. The results of this analysis are expressed in terms of the cost ratios of the two technologies. The pressurized nature of the HPRTE leads to compact components resulting in significant savings in equipment cost versus those of a microturbine. Revenue obtained from external refrigeration offsets some of the fuel costs for the HPRTE, thus proving to be a major contributor in cost savings for the HPRTE. For the base case of a high-pressure turbine (HPT) inlet temperature of 1373 K and an exit temperature of 1073 K, the HPRTE showed life cycle cost savings of 7% over a microturbine with a similar power capacity.
Thermal Stress Analysis for Differential Pressure Sensors
Authors: Chiou J. Albert , Chen Steven
Published: April 2008

Pressure sensors should be capable of measuring pressure accurately and consistently without being disturbed by the temperature environment. With silicon’s better thermal material properties, silicon micormachined pressure sensors are mass-produced and widely used. However, a silicon pressure sensing element has to be packaged and protected. The thermal mismatching between the sensing element and packaging may generate stresses on the transducer of a sensing element and create thermal hysteresis and voltage shift during temperature cycling. The induced thermal stresses can easily deteriorate performance reliability. In this paper, finite element analyses and experimental tests were conducted to reduce the thermal stress and thermal hysteresis. With the glass substrate to isolate the stress from plastic housing, the thermal hysteresis can be significantly improved. The die placement and dispense pattern can be also optimized to further improve the thermal hysteresis.
Wet SMA Actuator Array With Matrix Vasoconstriction Device
Authors: Flemming Leslie , Mascaro Stephen
Published: April 2008

A new mechanism for controlling arrays of Shape Memory Alloy (SMA) muscle wires has been developed. Similar to previous work, SMA wires on the order of 0.25 mm in diameter are embedded in a network of compliant fluid filled vessels on the order of 1 mm in diameter. Hot and cold water are delivered through the vascular network to convectively heat and cool the SMA muscles, causing them to contract and extend. By arranging the muscles or actuators in a 2D array, n2 actuators can be controlled using 2n valves, where the valves control the flow to and from rows and columns of actuators. However, unlike the previous Matrix Manifold and Valve system (MMV), the fluid flows to the actuators are now controlled using a Matrix Vasoconstriction Device (MVD). The MVD is capable of constricting combinations of the vessels, which are arranged in rows and columns. The MVD does not introduce any fluidic resistance to the network until constricted, allowing for larger flow rates and faster muscle cycling. The MVD system architecture also removes undesired dynamic effects stemming from fluidic capacitance which were suffered by the MMV. An array of 16 muscle wires has been experimentally implemented using an MVD with 8 control inputs. The MVD has been constructed in a 50 mm × 50 mm × 60 mm volume, and the overall length of the actuators is 500 mm. The system will drive each SMA wire at a rate of 2 Hz with a force of 10 N and a stroke of 10 mm. The system could control a robotic hand with up to 16 DOF and fit within the size of a human forearm.
Drop Test and Simulation of Array-Type Multilayer Ceramic Capacitor of Mobile Phone
Authors: Moon Yang Ho
Published: April 2008

MLCC (multilayer ceramic capacitor) is used as electrical parts of computer or mobile phone etc by surface mounting. Drop reliability analysis of MLCC is required for mobile phone because it can be dropped many times when mobile phone used. In this paper when the mobile is dropped, the strain and acceleration are measured and applied to boundary and load condition of simulation. From that result it can be found that the board flex during drop is a major factor that effects on stress in external electrode. From repeated board flex test, drop impact reliability can be estimated.
A Study on Optical Fiber Damage Due to Optoelectronic Assembly Processes
Authors: Nagarkar Kaustubh R. , Borgesen Peter , Srihari Krishnaswami
Published: April 2008

Optoelectronic assembly processes, such as laser and photodiode packaging, connector assembly, and splicing, tend to involve extensive handling of optical fibers. These processes offer considerable likelihood of inducing severe damage to the fibers. Such damage degrades the strength of optical fibers and could result in lower than expected lifetimes in service. The objective of this research was to investigate the impact of fiber-optic assembly processes on the mechanical performance of optical fibers. Certain applications such as fiber-optic splices, connectors, and optoelectronic packages require that the protective coating of the fibers be removed through a process called ‘fiber-stripping’. The process of ‘fiber-stripping’ was characterized to identify the primary sources of mechanical degradation. The related handling and cleaning steps were also evaluated. Further, the process steps in the assembly of fiber optic connectors were closely examined and the impact of assembling fibers into adhesives was tested. Qualitative and quantitative tools have been used to investigate the problems and have been discussed in this paper. Tensile tests were used to compare the mechanical performance of the fibers. Special fixtures and test set-ups were created that enabled the testing of the fibers. Characterization techniques, such as Scanning Electron Microscopy (SEM) analysis and optical microscopy, were also used. The results have enabled to identify the contributions of the individual assembly steps that impair the strength of optical fibers. This paper provides an understanding of the potential sources and mechanisms of degradation due to such processes.
Fundamental Concepts and an Innovating Approach for Extended Surface Heat Transfer
Authors: Razelos Panagiotis
Published: April 2008

In this work we re-examine the main fin equation qf = ηfAfΔT, proposed by Gardner [1] that has been used for the last sixty years to determine the performance of fins. The fundamental concepts of extended surface heat transfer are introduced, and their mathematical expressions are derived. The vital role of fin effectiveness, a term also introduced by Gardner [1] is established. It is shown that the effectiveness is inextricably linked in proving the validity of the simplifying assumptions that most of the fins’ endeavors are based on. It is also shown that the common practice of using the efficiency to predict the fin’s performance leads to serious errors. A novel approach to fin analysis, based on a proposed transformation of coordinates, is presented, which can be employed to considerably simplify the pertinent differential equations and obtain more friendly expressions describing the fin’s performance. The heat dissipation is expressed in a non-dimensional form and for several practical cases polynomial expressions have developed, that will help students to engage in rudimentary fin designs. It is also shown that, the one-dimensional approach can be used to obtain solutions involving extended surfaces made from anisotropic material. Three examples serve to illustrate the usefulness of our method.
Reducing Occupant Injury in Frontal Crashes for a Low-Floor City Bus
Authors: Sahraei Esfahani Elham , Darvish Kurosh , Parnianpour Mohamad , Bateni Akbar
Published: April 2008

In this research, the effect of beam buckling in a predefined direction is used to reduce occupant injuries in frontal crashes of an ultra-low-floor (ULF) city bus. In ULF buses, the floor structure consists of several longitudinal long beams, which in case of a frontal crash may buckle due to the axial impact. The direction of rotational acceleration of the driver seat due to buckling is highly affected by the position of the driver seat. A finite element model of an ULF bus was developed using LS-Dyna. The driver model, a Hybrid III 50th male dummy with deformable jacket and abdomen, was restrained to the seat with a 3-point belt. An Elastic-Plastic material model was used for the bus structure to investigate the buckling behavior of the beam elements. Using diagonal beams to guide the buckling in a desired direction, rewarding results were achieved in reducing the occupant injuries. For example, with an extra diagonal beam under the seat, the driver’s HIC15 was reduced from 739 to 415.7 and HIC36 from 791 to 700.6.
Polymer Tube Embedded In-Plane Micropump: Design, Analysis and Fabrication
Authors: Kole Ashutosh , Sin Jeongsik , Lee Woo Ho , Popaq Danq , Agonafer Dereje , Stephanou Harry E.
Published: April 2008

This paper presents the design, analysis, and fabrication of a novel polymer tube embedded in-plane micropump. The key component of the proposed micropump is a Parylene polymer tube that is embedded into a silicon micromachined actuation structure. The advantages of embedding a Parylene polymer tube are biocompatibility, leakage free flow, and insulation from electrical and thermal contacts. The tube works as a diaphragm, which transfers the pumping motion from the silicon electrothermal actuators to fluid. In order to guide the design of the pump, FEM simulation was performed for structural analysis on Parylene tube and evaluation of the electrothermal actuator. Parylene was conformally deposited on the nickel coated DRIE processed silicon mold, and peeled off and two Parylene layers were bonded together to form a tube. The maximum deflection achieved from the Parylene diaphragm is 5.4μm and the computed flow rate of the pump is 160nl/min.
Finned Tube Gap Resistance for Compressor Inter-Cooler
Authors: Jaw Luis
Published: April 2008

This paper presents a rational analysis for predicting thermal-contact resistance in the compressor intercoolers where the hot air is on the finned side with cooling water in the tube side. It further includes a derivation of the maximum design temperature for the hot air or fluid for a zero thermal-contractor or gap resistance. At the elevated temperatures, a gap resistance is created by the differential thermal expansion between the fins and the tubes. This expansion completely relaxes the initial fabrication contact pressure that binds the fins to the tubes. The equations derived for the gap resistance and maximum design temperature are quite in good agreement in verifying the results. The results generally show that the gap resistance increases as hot air temperature increase, and that the lower cooling temperatures would tolerate higher design temperatures. It is interesting to note that the initial contact pressure is a major factor in restricting the formation of the gap resistance
The Surface Roughness Effect on the Dynamic Stiffness and Damping Characteristics of the Hydrostatic Thrust Spherical Bearing: Part 4 — Fitted Type of Bearings
Authors: Yacout A. W. , Ismaeel A. S. , Kassab S. Z.
Published: April 2008

Analytical solutions are not available for spherical bearing problems except for very specialized cases. However, this study offers a theoretical analysis, using the first order perturbations, to evaluate the frequency dependent stiffness and damping characteristics of compensated hydrostatic thrust spherical bearing including the surface roughness, the shaft rotation and the recess volume fluid compressibility effects. The dynamic stiffness and damping coefficients are presented for capillary tube and/or office compensated bearing. Results are obtained for various vibration frequencies or squeeze parameters (frequency parameters) and recess volume fluid compressibility parameters in addition to the other usual bearing design parameters. The study shows that both of the surface roughness and the centripetal inertia have slight effect on the stiffness and the damping coefficients while the recess volume fluid compressibility parameter has the major effect on the bearing dynamic characteristics.
Networked Assembly of Affine Physical System Models
Authors: Motato E. , Radcliffe C.
Published: April 2008

Engineering design is evolving into a global strategy that distributes model information through computer networks. This strategy requires companies to provide dynamic models of supplied components. Component models must be assembled to obtain the product dynamic model. Four characteristics are needed. Specifically, models require a unique standard format, the exchange of model information must be executed in a single-query transmission, the models must describe only external behavior, and the assembly process must be recursive. The Modular Modeling Method (MMM) [1], is a model assembly algorithm that satisfies these requirements. The MMM algorithm assembles linear physical systems models with dynamic stiffness matrices. This paper will extend MMM to nonlinear affine behavior. In an affine system, deviations in the inputs and outputs exhibit a proportional relationship, but the outputs of the system are not zero at zero input [2]. The main reason for developing a process to assemble affine systems is the possibility of using this method to assemble general differentiable nonlinear physical system models performing around a constant operating point.
Progressive Rate Steel Vehicle Suspension
Authors: Oledzki Wieslaw J.
Published: April 2008

It is well known that progressiveness of the damping characteristic of vehicle suspension is a highly desirable feature that substantially improves shock absorption transmitted from the road wheels to the body of a vehicle. It is also well known that progressive rate vehicle suspensions with smooth (i.e. differentiable) damping characteristic commonly in use are pneumatic and hydro-pneumatic ones. However, these suspensions are inferior to steel ones in many aspects such as strength, durability, reliability and cost, and their damping characteristic, being determined by the thermodynamic properties (adiabatic exponent) of the gas (air or nitrogen) they utilize, cannot be freely adjusted and is far from optimum. There are also some progressive rate vehicle suspensions fitted with steel springs, but they usually features inferior non-differentiable damping characteristic. The problem of constructing purely mechanical steel progressive rate vehicle suspension has been undertaken by many inventors, but none of such suspensions proposed in the past was a success. This is due to the fact that those suspensions used unreliable and perishable cam mechanisms to achieve required non-linearity of damping characteristic. In the present article we briefly discuss an innovative recently patented [1-4] vehicle suspension, that produces progressive rate smooth damping characteristic out of linear characteristic of steel spring of any kind, which damping characteristic can be adjusted to any specific requirements, and which features extraordinarily compact and robust structure. It is to be stressed that the suspension presented in this paper has yet not been tested in a vehicle, but some measurements has been made using a steel model of a "flat" version of the suspension mechanism proving general assumptions behind the design.
Smith Predictor Position Control for the Inlet Guide Vane of Centrifugal Air Compressors
Authors: Sodemann Angela , Li Yaoyu , Wu Xin , Lancaster Rick , Rucker Mark , Carnagie Jeff , Inman Andy , Lee Jay
Published: April 2008

Fast and accurate positioning of Inlet Guide Vane (IGV) is critical for flow regulation in centrifugal air compressors, especially for surge avoidance control. Both transport delay and external disturbance are present for IGV position control on a compressed air system. A Smith Predictor based control scheme with the process-model modification is applied to this problem. The adopted control scheme can both compensate for the time delay and effectively reject step disturbances present in the IGV system. Simulation was conducted using simple PI controller and a PI controller with the Smith Predictor with process-model modification. It showed that the proposed control scheme can achieve zero steady-state error with the presence of external disturbance and the settling time was shortened. Robust stability and performance of the system was discussed.
On-Line Monitoring Software and Diagnostic Tool for Centrifugal Compressor Performance Evaluation
Authors: Abidogun Kamorudeen B. , Al-Ghamdi Mohamed S. , Al-Ali Adel , Al-Yousef Khalid
Published: April 2008

In-house developed centrifugal compressor performance software was customized for PETROKEMYA (an affiliate of SABIC) Olefins III cracked gas compressor (CGC), the heart of ethylene plant. The software provides live performance analysis of the machine by calculating, per section, polytropic efficiency, polytropic head, and gas power using Lee-Kesler equation of state. Gas analysis is read online to reflect the minute changes in the composition on the calculated parameters. Actual operating parameters are plotted continuously and compared to the performance curves in order to predict possible performance deterioration before it becomes too late. Such information is useful in determining future maintenance requirements based on the actual performance of the machine rather than the traditional time-based maintenance. Moreover, it ensures proper timely action through optimization of wash oil or other chemical injection to help minimize fouling accumulation rate and maximize production and machine availability. Features are introduced to enable performance analysis of the compressor since commissioning to be carried out by click of a button, providing useful information for upgrading and troubleshooting. Unlike its commercially available counterpart with write-protected restrictions, the software is easily modified for additional features that are of interest to Engineers. Features planned for the future include adding intelligent system capability for predicting performance deterioration severity, auto-notifying agents etc. Performance evaluation of a 45 MW, five section process gas compressor before and after turnaround (T/A), clearly revealed the fouling prediction capability of the software.
Determination of Optimal Orientations and Volume Fractions of Nanotubes in a Polymer for Vibration Damping
Authors: Damu Mohan , Lumsdaine Arnold
Published: April 2008

Topology optimization has been used to maximize the damping performance of constrained damping layer structures with viscoelastic core [1-3]. Studies show that using nanotubes as reinforcements in polymer material might improve the damping and stiffness properties [4,5]. Experimental investigations using nanotube reinforcements in constrained damping layers showed a significant improvement in damping properties of the structure [6]. Optimizing the topology of structures involving nanotube reinforcements can further enhance the damping properties by making optimal use of the nanotubes as reinforcements. In preliminary studies performed with volume fraction of nanotubes as a design variable in the optimization [7,8] substantial improvements in the damping properties were observed. In this work, the topology of a cantilever beam structure involving nanotube reinforced polymer layers is optimized with the objective of maximizing the system loss factor for the first resonance frequency of the base beam. The volume fractions and orientations of the nanotubes in each finite element and the material fraction of the nanotube reinforced polymer (NRP) and the elastic material are the design variables in the optimization process. ABAQUS is used for the finite element modeling and an optimization code NLPQL which uses a sequential quadratic programming algorithm is used for the optimization.
Effect of Presence of Multi-Walled Carbon Nanotubes on the Creep Properties of Sn-Ag-Cu Solder
Authors: Nai S. M. L. , Wei J. , Gupta M.
Published: April 2008

In this study, Sn-Ag-Cu based nanocomposites with multi-walled carbon nanotubes (MWCNTs) as reinforcements were successfully synthesized using the powder metallurgy technique. Varying weight percentages of MWCNTs were blended together with micron size lead-free solder particles. The blended powder mixtures were then compacted, sintered and finally extruded at room temperature. The extruded materials were then used to characterize the melting point and to prepare lap-shear samples for creep tests. Miniature creep samples were created using a specially designed fixture and static loading creep tests were carried out on the solder joint samples at room temperature at 24N and 36N loads. Creep results showed improved creep resistance with the addition of MWCNTs. An attempt is made in the present study to correlate the variation in weight percentages of reinforcement with the creep properties of the resultant nanocomposite materials.
Hydoroil-Based Micro Pin Fin Heat Sink
Authors: Kosar Ali , Kuo Chih-Jung , Peles Yoav
Published: April 2008

An experimental study on thermal-hydraulic performance of de-ionized water over a bank of shrouded NACA 66-021 hydrofoil micro pin fins with wetted perimeter of 1030-μm and chord thickness of 100 μm has been performed. Average heat transfer coefficients have been obtained over effective heat fluxes ranging from 4.0 to 308 W/cm2 and mass velocities from 134 to 6600 kg/m2s. The experimental data is reduced to the Nusselt numbers, Reynolds numbers, total thermal resistances, and friction factors in order to determine the thermal-hydraulic performance of the heat sink. It has been found that prodigious hydrodynamic improvement can be obtained with the hydrofoil-based micro pin fin heat sink compared to the circular pin fin device. Fluid flow over pin fin heat sinks comprised from hydrofoils yielded radically lower thermal resistances than circular pin fins for a similar pressure drop.
Mathematical Formulation of Transport Phenomena in Buoyancy-Driven Nanofluids
Authors: Routhu Manoha , Nnanna A. G. Agwu
Published: April 2008

This paper is concerned with the interaction between nanoparticles in buoyancy-driven flow. The nanoparticles suspended in a base liquid are driven to stochastic motion by rapidly fluctuating forces, this phenomenon is termed as 'thermal dispersion' resulting from the dissociation of the ambient solvent molecules taking place within the mixture. Such thermal dispersion is esteemed to play an aggressive role in the increase of energy exchange rates in the fluid. Under the influence of these forces, the suspended nanoparticles may experience interparticle collision and attachment of the colliding particles and form aggregates. The theme of the present work is to understand the thermal transport phenomena of buoyancy-driven nanoparticles as well as to analyze the enhancement mechanism of energy transport from the nanoparticles. By considering physical properties of both the base fluid and the nanoparticles, as well as the structure of the nanoparticles and aggregates, a mathematical model has been developed to predict the axial velocity and temperature of both the fluid and the nanoparticle arbitrarily moving inside the system. The model proposed is a two-equation model, one for the fluid and the other for the nanoparticles, which are later combined together to form a non-homogeneous equation in x- and y-direction respectively. The solutions to these equations are presented in this work.
Transport Properties of Alumina Nanofluids
Authors: Wong Kau-Fui , Bhshkar Tarun
Published: April 2008

Recent studies have showed that nanofluids have significantly greater thermal conductivity compared to their base fluids. Large surface area to volume ratio and certain effects of Brownian motion of nanoparticles are believed to be the main factors for the significant increase in the thermal conductivity of nanofluids. In this thesis, all the three transport properties, namely, thermal conductivity, electrical conductivity and viscosity were studied for Alumina nanofluid (Aluminum oxide nanoparticles in water). Experiments were performed both as a function of volumetric concentration (3 – 8%) and temperature (2°C – 50°C). Alumina nanoparticles with a mean diameter of 36 nm were dispersed in water. Transient hot wire method as described by Nagaska and Nagashima for electrically conducting fluids was used to test the thermal conductivity. In this work, an insulated platinum wire of 0.003 inches diameter was used as the hot wire for the thermal conductivity experiments. Initial calibration was performed using de-ionized water and the resulting data was within 2.5% of standard thermal conductivity values for water. The thermal conductivity of alumina nanofluid increased with both increase in temperature and concentration. A maximum thermal conductivity of 0.7351 W/mK was recorded for an 8.47% volume concentration of alumina nanoparticles at 46.6°C, the effective thermal conductivity at this concentration and temperature was observed to be 1.1501, which translates to an increase in thermal conductivity by 22% when compared to water at room temperature. Alumina being a good conductor of electricity, alumina nanofluid displays an increasing trend in electrical conductivity as volumetric concentration increases. A microprocessor based conductivity/TDS meter was used to perform the electrical conductivity experiments. After carefully calibrating the conductivity meters glass probe with platinum tip, using a standard potassium chloride solution, readings were taken at various volumetric concentrations. A 3457.1% increase in the electrical conductivity was measured for a meager 1.44% volumetric concentration of alumina nanoparticles in water. The highest value of electrical conductivity: 314 μS/cm was recorded for a volumetric concentration of 8.47%. For measuring the kinematic viscosity of alumina nanofluid, a standard kinematic viscometer with constant temperature bath was used. Calibrated capillary viscometers were used to measure flow under gravity at precisely controlled temperatures. The capillary viscometers were calibrated with de-ionized water at different temperatures, and the resulting kinematic viscosity values were found to be within 3% of the standard published values. An increase of 35.5% in the kinematic viscosity was observed for an 8.47% volumetric concentration of alumina nanoparticles in water. The maximum kinematic viscosity of alumina nanofluid: 2.90142 mm2/s, was obtained at 0°C for an 8.47% volumetric concentration of alumina nanoparticles.
Critical Heat Flux Measurement and Model for Refrigerant-123 Under Stabilized Flow Conditions in Microchannels
Authors: Kuan Wai Keat , Kandlikar Satish G.
Published: April 2008

The present work is aimed toward understanding the effect of flow boiling stability on critical heat flux (CHF) with Refrigerant-123 (R-123) in microchannel passages. Experimental data and theoretical model to predict the CHF are the focus of this work. The experimental test section has six parallel microchannels with each having a cross sectional area of 1054 × 157 μm2. The effect of flow instabilities in microchannels is investigated using flow restrictors at the inlet of each microchannel to stabilize the flow boiling process and avoid the backflow phenomena. This technique resulted in successfully stabilizing the flow boiling process as seen through a high-speed camera. The present CHF result is found to correlate to mean absolute error (MAE) of 24.1% with a macroscale empirical equation by Katto [13]. A theoretical analysis of flow boiling phenomena revealed that the ratio of evaporation momentum to surface tension forces is an important parameter. For the first time, a theoretical CHF model is proposed using these underlying forces to represent CHF mechanism in microchannels, and its correlation agrees with the experimental data with MAE of 2.5%.
Control of the Continuum Model of a Large Flexible Space Structure
Authors: Salehian Armaghan , Seigler T. Michael , Inman Daniel J.
Published: April 2008

An analytical approach is presented here to develop a continuum model of a space radar antenna and the truss structure for the purpose of the control and vibration suppression. Kinetic and potential energy expressions are given for the equivalent homogenized 1-D model. Hamilton's principle is applied to find the governing partial differential equations for this structure. The equations for bending are similar to an extended Timoshenko beam model. A Linear, Quadratic, Regulator (LQR) problem is solved to find the optimal solution for feedback control design of the distributed parameter model. The control force designed this way is applied to a Finite Element Model (FEM) of the truss structure for the purpose of validation. Results from the FEM are shown to be in good agreement with the distributed parameter model.
Effect of Dwell Times and Ramp Rates on the Thermal Cycling Reliability of Pb-Free Wafer-Level Chip Scale Packages: Experiments and Modeling
Authors: Chaparala S. , Pitarresi J. M. , Meilunas M.
Published: April 2008

Lead-free (Pb-free) solder has seen increasing use in interconnect systems for electronic packages due to legislative and marketing pressures. The NEMI selected eutectic Sn3.9Ag0.6Cu alloy (or a close variation near eutectic Sn3.5Ag1.0Cu used in this study) is a leading Pb-free substitute for the Sn/Pb solder candidate. The reliability of this Pb-free solder alloy under accelerated thermal cycling and thermal shock testing as a function of testing parameters such as dwell time and ramp rate is critical in qualifying the performance of these Pb-free alternatives with the traditionally used Sn37Pb solder This paper presents the reliability of Pb-free solder joints in wafer level chip scale packages (WLCSPs), which are extensions of flip-chip packaging technology to standard surface mount technology, with external dimensions equal to that of the silicon device [1]. The reliability of these packages under both liquid-to-liquid thermal shock (LLTS) testing and accelerated air-to-air thermal cycling (AATC) conditions, as a function of dwell times and ramp rates is evaluated using extensive experimental testing in combination with finite element analysis. Besides, two asymmetric cycles in which the cold and hot dwell times differ at two temperature extremes were studied. Along with the Pb-free solder, some test vehicles were built using eutectic Sn-Pb solder and evaluated for comparison purposes. Experimental results show that an increase in ramp rate does not adversely affect the solder joint reliability in the case of Pb-free solder. The reliability of lead-free WLCSPs was highly dependent upon the dwell time at the temperature extremes, with this dependency being considerably greater for the lead-free allow than for Sn/Pb at 0°C and 100°C. Accelerated test results show that increasing the dwell time from 280 to 900 seconds reduced the N63.2 of the Sn/Pb samples by 12% and the Pb-free samples by 65%. Reliability during asymmetric cycles resulted in a trend that is similar in two cases studied. A predictive equation was developed to evaluate the characteristic life of the package with respect to the dwell time. Non-linear, finite element (FE) modeling was conducted using temperature dependent creep constitutive relations for the Pb-free solder to understand the experimental trends observed. The FE results predicted the same trend of the package reliability as observed experimentally, with respect to the changing dwell and ramp times. The finite element predictions demonstrated reasonable correlation with the experimental observations.