bluuebunny/crossref_metadata_2025 huggingface dataset:
Method for Obtaining Thermal Conductivity From Modified Laser Flash Measurement
Authors: Lin Bochuan , Ban Heng , Li Chao , Scripa Rosalia N. , Su Ching-Hua , Lehoczky Sandor L.
Published: April 2008

Laser flash method is commonly used to measure the thermal diffusivity of solids. In the original thermal analysis, adiabatic boundary conditions were used and the time for sample rear surface temperature to reach 50% of maximum value was used to calculate the thermal diffusivity. Later other boundary conditions were included in the analysis to compensate for the heat loss. The laser flash method can be modified to determine the thermal conductivity by comparing the temperature rise of the sample with a standard sample, both of which are coated to ensure identical surface emissivity. In our previous studies of applying the laser flash method to semiconductor melts, we have shown that it is possible to obtain thermal conductivity, specific heat capacity and thermal diffusivity from the experimental data. In these studies, the melt sample was sealed in a specially-designed fused silica cell. The heat transfer between melt sample and the fused silica cell allows the thermal conductivity to be included in the analysis. Therefore, the temperature response of the melt sample was controlled not only by the thermal diffusivity and conductivity of sample, but also by the thermal properties of fused silica cell. Using a computational fitting process, we obtained both thermal diffusivity and thermal conductivity of the sample. In this paper, an analytic solution for the transient heat transfer inside the sample and fused silica cell was developed. The influence of fused silica cell was included and the heat transfer to fused silica cell had a significant effect on the time-temperature response of the sample. Therefore, the rear surface temperature of the sample, described by an analytical solution, could be used to obtain both thermal diffusivity and thermal conductivity of the sample with known properties of the fused silica cell. The results indicated that this method was applicable for a wide range of sample and cell properties. The original solution for laser flash method became an extreme case in the current theory
Thermal-Mechanical Analysis of a Flip-Chip VCSEL (Vertical-Cavity Surface-Emitting Laser) Package With Low-Temperature Lead-Free (SnBi) Solder Joints
Authors: Lau John , Dauksher Walter
Published: April 2008

To perform Failure Analysis of an 1657CCGA package on PCB with OSP (Organic Solderability Preservative) surface finish.
Thermal and Hydrodynamic Modeling of Fully-Developed Convection in Anode-Supported Planar Solid Oxide Fuel Cells
Authors: Magar Yogesh N. , Manglik Raj M.
Published: April 2008

Uniform supply of volatile species to an active surface along with the oxidant flow to sustain the surface electrochemical reaction, and its effective cooling in an anode supported solid oxide fuel cell (SOFC) is modeled. Three-dimensional nonlinear partial differential governing equations for the conservation of mass, momentum, energy, species, and electrochemical kinetics for both the anode and cathode ducts for steady laminar, incompressible flow are solved computationally. A planar, tri-layer SOFC module, which consists of porous anode and cathode layers, solid electrolyte and rectangular flow ducts, is considered. The homogenous porous electrode layers are characterized by constant porosity, permeability, and thermal conductivity, and the fluid in these porous layers is considered to be in thermal equilibrium with the solid matrix. The computational results highlight the influence of fuel and oxidant flow duct aspect ratio and porous anode-layer depth on the friction factor and Nusselt number for typical electrochemical loads, and the consequent thermal signatures of the SOFC.
Real Time Optimal Task Allocation in Highly Dynamic Environments
Authors: Schneider David R. , Campbell Mark
Published: April 2008

Of the methods developed for Optimal Task Allocation, Mixed Integer Linear Programming (MILP) techniques are some of the most predominant. A new method, presented in this paper, is able to produce identical optimal solutions to the MILP techniques but in computation times orders of magnitude faster than MILP. This new method, referred to as G*TA, uses a minimum spanning forest algorithm to generate optimistic predictive costs in an A* framework, and a greedy approximation method to create upper bound estimates. A second new method which combines the G*TA and MILP methods, referred to as G*MILP, is also presented for its scaling potential. This combined method uses G*TA to solve a series of sub-problems and the final optimal task allocation is handled through MILP. All of these methods are compared and validated though a large series of real time tests using the Cornell RoboFlag testbed, a multi-robot, highly dynamic test environment.
Conceptual Design of a Testing Facility to Assess Trucks Maneuvering Performance
Authors: Romero Jose´ A. , Ortiz Wenceslao , Lozano Alejandro
Published: April 2008

Road safety is influenced by the dynamic performance of heavy trucks during emergency maneuvers that involve abrupt changes in direction and velocity. In this context, rating of trucks performance under such situations becomes crucial to promote safer roads. Present test methods to evaluate trucks performance during braking and lane change maneuvers involve substantial monetary and time investments, and are limited to certain critical trucks and cargo. A more general methodology to evaluate a wider range of vehicles under diverse situations is thus necessary. In this paper the conceptual design of a truck testing facility is proposed to characterize and compare the dynamic performance of the vehicles under emergency maneuvering, as a function of the components’ properties, payload conditions and overall truck design. The equipment consists of a moving platform on which the vehicle is mounted, including load cells to measure tire loads. The motion of the platform can simulate steering maneuvers by providing lateral and yaw excitations.
Effect of Blade Thickness on High Frequency Gust Response
Authors: Lysak Peter D.
Published: April 2008

Turbomachinery rotor blades experience gust loading due to both inflow turbulence and circumferential variation in the mean velocity. The unsteady lift forces that result from these velocity disturbances can be a source of unwanted vibration and radiated noise. For incompressible flows, the blade gust response is often modeled using the well-known Sears function, which acts as a transfer function between a sinusoidal component of the gust and the fluctuating lift. However, the Sears function has a relatively slow high frequency roll-off and overpredicts the unsteady lift when the gust wavelength becomes much smaller than the blade chord. A more accurate model can be obtained by including the effect of blade thickness, which causes the gust to become distorted as it approaches the leading edge. This distortion results in attenuation of the higher-frequency components of the gust near the leading edge, which subsequently leads to reduced unsteady lift. In this paper, a model for the thickness effect is developed based on rapid distortion theory. Numerical calculations are made for a step-function gust encountering an elliptical leading edge with several thickness-to-chord ratios. The unsteady lift is calculated in the time domain, and a Fourier transform is used to obtain the frequency response. The results indicate that the gust response of a thick blade can be closely approximated by modifying the Sears function to include an exponential decay factor based on the thickness.
A Thermal Model of a Fiber Optic Bundle for a Hybrid Solar Lighting System
Authors: Cheadle Michael J. , Nellis Gregory F. , Klein Sanford A. , Beckman William A.
Published: April 2008

Hybrid solar lighting (HSL) systems distribute natural sunlight to luminaires located in office or retail buildings in order to reduce energy consumption associated with conventional lighting systems. HSL systems reduce energy consumption directly by reducing the lighting energy and indirectly by reducing the associated cooling loads. A key component of the HSL system is the fiber optic bundle (FOB) that transmits the light from the collector to the luminaire. The observed thermal failure of the FOB when exposed to concentrated sunlight has motivated the development of a thermal model of this component. This paper describes the development of a predictive thermal model of the heat transfer in an FOB for an HSL system. The model is verified experimentally against temperature measurements obtained in the lab under controlled conditions and provides a powerful design tool that can be used to evaluate alternative thermal management strategies.
Convective Heat Transfer From a Stationary or Rotating MCM Disk With a Unconfined Round Jet Impingement
Authors: Kuo Y. M. , Fang C. J. , Wu M. C. , Peng C. H. , Hung Y. H.
Published: April 2008

A series of experimental investigations with stringent measurement methods on the studies related to fluid flow and transient mixed convection from a horizontally unconfined stationary or rotating ceramic-based MCM disk with unconfined jet impingement have been successfully conducted. The relevant parameters influencing fluid flow and heat transfer performance are (1) mixed convection due to jet impingement and buoyancy: steady-state Grashof number, jet Reynolds number, and ratio of jet separation distance to nozzle diameter; and (2) mixed convection due to jet impingement, disk rotation and buoyancy: steady-state Grashof number, jet Reynolds number (Rej), rotational Reynolds number (Rer), ratio of jet separation distance to nozzle diameter (H/d). The thermal behavior explored includes the transient temperature distribution on the MCM disk surface, transient heat flux distribution of input power, transient convective heat flux distribution of chips, and transient chip and average heat transfer characteristics on the MCM disk surface. Besides, two new correlations of transient stagnation and average Nusselt numbers in terms of Rej, H/d and t are presented for the cases of stationary MCM disk. For the cases of rotating MCM disk, a new empirical correlation to classify two regimes of heat transfer modes such as disk rotation mode and jet impingement mode is presented; and a complete composite correlation of steady-state average Nusselt number for mixed convection due to jet impingement, disk rotation and buoyancy is proposed. As compared with the steady-state results, if the transient chip and average heat transfer behaviors may be considered as a superposition of a series of quasi-steady states, the transient chip and average Nusselt numbers in all the present transient experiments can be properly predicted by the existing steady-state correlations when t > 6 min in the power-on transient period.
Radiation Transfer in Whispering-Gallery Mode Microcavities
Authors: Quan Haiyong , Guo Zhixiong
Published: April 2008

Micro/nanoscale radiation transfer in whispering-gallery mode (WGM) microcavities is investigated. Each cavity consists of a waveguide and a microdisk coupled in a planar chip. In order to characterize the WGM resonance phenomena, studies of configuration parameters, specifically the microdisk size, the gap distance separating the microdisk and waveguide, and the waveguide width are numerically conducted. The finite element method is used for solving Maxwell’s equations which govern the propagation of electromagnetic (EM) field and the radiation energy transport in the micro/nanoscale WGM structures. The EM fields and the radiation energy distributions in the microcavities are then obtained. The scattering spectra for three different microdisk sizes are also obtained; and through which the WGM resonant properties such as the quality factor, the full-width at half maximum (FWHM), the free spectral range, and the finesse of the resonant modes are analyzed. It is found that the resonant frequencies and their free spectral ranges are predominantly determined by the size of the microcavity; while the FWHM, finesse, and quality factor are strong functions of the gap.
Repetitive Control for an Electrostatic Microbridge Actuator
Authors: Zhao Haiyu , Rahn Christopher D. , Canbolat Huseyin
Published: April 2008

Electrostatic microactuators are used extensively in MEMS sensors, RF switches, and microfluidic pumps. Due to high bandwidth operation, however, reduction of residual vibration using feedback control is diffcult to implement. This paper designs, proves stability, and simulates a feedforward repetitive controller for an electrostatic microbridge. Squeeze film damping ensures boundedness of the distributed transverse displacement. Offline processing using repetitive control algorithm updates a waveform generator’s parameters based on measured response to reduce errors between the desired and actual displacement distribution. Simulations show a 36% reduction in midspan overshoot.
Development of MATLAB Graphical User Interface for Teaching Statics
Authors: Al-Masoud Nidal
Published: April 2008

In this paper a Graphical User Interface (GUI) platform to supplement teaching and learning in Engineering Mechanics — Statics course is developed. The package encompasses several interrelated modules of the concepts introduced in a typical Statics class. The GUI provides a user-friendly interactive approach to solving problems and displaying the results both numerically and graphically in two- and three-dimensional spaces. In addition to visualization, GUI approach allows users to modify input data and observe the effect on the solution, thus providing students with additional insight to predict the behavior of structures under different loading scenarios.
Multi-Axis Maglev Positioner With High Resolution Over Large Travel Range
Authors: Kim Won-Jong , Verma Shobhit
Published: April 2008

This paper presents a novel multi-axis positioner that operates on the magnetic-levitation (maglev) principle. This maglev stage is capable of positioning at the resolution of a few nanometers over a planar travel range of several millimeters. A novel actuation scheme was developed for the compact design of this stage that enables 6-axis force generation with just 3 permanent magnets. We calculated the forces with electromagnetic analysis over the whole travel range and experimentally verified them with a unit actuator. The single moving part, namely the platen, is modeled as a pure mass due to the negligible effect of magnetic spring and damping. There are 3 laser interferometers and 3 capacitance sensors to sense the 6-axis position/rotation of the platen. A lead-lag compensator was designed and implemented to control each axis. A nonlinear model of the force was developed by electromagnetic analysis, and feedback linearization was applied to cancel the nonlinearity of the actuators over the large travel range. Various experiments were conducted to test positioning, loading, and vibration-isolation capabilities. This maglev stage has a moving mass of 0.267 kg. Its position resolution is 4 nm over a travel range of 5 × 5 mm in the x-y plane. It can carry and precisely position an additional payload of 2 kg. Its potential applications include semiconductor manufacturing, micro-fabrication and assembly, nanoscale profiling, and nano-indentation.
Simulation of Phonon Interfacial Transport in Strained Silicon-Germanium Heterostructures
Authors: Zhang Wei , Fisher Timothy S.
Published: April 2008

A nonequilibrium Green’s function (NEGF) method is used to simulate the phonon transport across a strained thin film between two semi-infinite contacts. The calculation of dynamical matrix, self-energy matrix and transmission function are discussed. Uncoupled Green’s functions are computed numerically using a block tridiagonal algorithm. The numerical role of the broadening constant is investigated. The bulk density of states in a single atomic chain is calculated and compares well with an analytical solution. The transmission function and thermal conductance across the thin film are evaluated for two different configurations (Ge-Si-Ge and Si-Ge-Si) and compared against homogeneous bulk systems (Si only and Ge only), indicating that heterogeneous interfaces reduce thermal conductance significantly.
The Enhancement Effect of Corona Discharge on Natural Convection Heat Transfer in Triangular Channels
Authors: Molki Majid , Harirchian Tannaz
Published: April 2008

A numerical research was conducted to investigate the effect of corona discharge on natural convection heat transfer in a triangular channel. The channel side walls were isothermal, the lower wall was adiabatic, and the fluid was air at the atmospheric pressure. The electric field was generated by a positive corona discharge from a charged wire electrode located at the center of the channel. The governing equations of the electric and flow fields were solved by a finite-volume technique. Three cases were considered: (1) natural convection; (2) corona-induced convection; and (3) combined natural and corona-induced convection. The computations encompassed Rayleigh numbers from 3,737 to 37,377 and applied voltages from 7 to 9 kV in the laminar regime. Computations for the applied voltage of 7.5 kV indicated that the heat transfer was enhanced from Nu/Nu0 = 1.01 to 1.04, or 1–4%, for different values of Ra. The enhancement at Ra = 3,737 and the applied voltage of 7 to 9 kV was Nu/Nu0 = 1.01 to 1.40, or 1–40%.
Grazing Bifurcation and Periodic Motion Switching in a Piecewise Linear, Impacting Oscillator Under a Periodical Excitation
Authors: Luo Albert C. J. , Chen Lidi
Published: April 2008

The grazing bifurcation and periodic motion switching of the harmonically forced, piecewise linear system with impacting are investigated. The generic mappings based on the discontinuous boundaries are introduced. Furthermore, the mapping structures are developed for the analytical prediction of periodic motions in such a system. The local stability and bifurcation conditions for specified periodic motions are obtained. The regular and grazing, periodic motions are illustrated. The grazing is the origin of the periodic motion switching for this system. Such a grazing bifurcation cannot be estimated through the local stability analysis. This model is applicable to prediction of periodic motions in nonlinear dynamics of gear transmission systems.
Periodic Motions in a Periodically Forced Oscillator Moving on the Oscillating Belt With Dry Friction
Authors: Luo Albert C. J. , Gegg Brandon C.
Published: April 2008

In this paper, periodic motion in an oscillator moving on a periodically vibrating belt with dry-friction is investigated. The conditions of stick and non-stick motions for such an oscillator are obtained in the relative motion frame, and the grazing and stick (or sliding) bifurcations are presented as well. The periodic motions are predicted analytically and numerically, and the analytical prediction is based on the appropriate mapping structures. The eigenvalue analysis of such periodic motions is carried out. The periodic motions are illustrated through the displacement, velocity and force responses in the absolute and relative frames. This investigation provides an efficient method to predict periodic motions of such an oscillator involving dry-friction. The significance of this investigation lies in controlling motion of such friction-induced oscillator in industry.
A Numerical Study of the Natural Convective Heat Transfer From a Partially Covered Recessed Isothermal Vertical Surface
Authors: Oosthuizen Patrick H.
Published: April 2008

A numerical study of natural convective heat transfer from a heated isothermal vertical plane surface has been considered. There are relatively short horizontal adiabatic surfaces normal to the isothermal surface at the top and bottom of this isothermal surface these horizontal adiabatic wall surfaces then being joined to vertical adiabatic surfaces. There is a thin surface that offers no resistance to heat transfer that is parallel to the vertical isothermal surface and which partly covers this surface. The situation considered is a simplified model of a window, which is represented by the vertical isothermal wall section, that is recessed in a frame, which is represented by the horizontal adiabatic surfaces, which is mounted in a vertical wall, which is represented by the vertical adiabatic surfaces, and which is exposed to a large surrounding room. The window is covered by a partially open plane blind which is represented by the vertical thin surface that offers no resistance to heat transfer. The flow has been assumed to be laminar and two-dimensional. Fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces. The governing equations, written in dimensionless form, have been solved using a commercial finite-element based code. Results have only been obtained for a Prandtl number of 0.7.
Motion of Nanoparticles in Nanofluids Under an Electric Field
Authors: Min Jung Yim , Jang Seok Pil , Choi Stephen U. S.
Published: April 2008

Nanofluids — fluids with unprecedented stability of suspension nanoparticles — have attractive features such as high thermal conductivities at very low nanoparticle concentrations, strongly temperature-dependent conductivity, and three-fold higher critical heat flux compared to base fluids. These features are not explained by traditional theories of solid/liquid suspensions, such as Maxwell’s theory or other macroscale approaches. Recently, Jang and Choi’s model has led to the discovery, primarily by extending Einstein’s theory of Brownian motion to energy transport in nanofluids, that Brownian motion of nanoparticles at the molecular and nanoscale level is a dominant mechanism governing their thermal behavior. In this paper we describe a theoretical model for controlling the motion of nanoparticles in nanofluids by means of an electric field and an analytical solution for particle motions in nanofluids. We show that the motion of nanoparticles can be controlled by use of an AC field and that the size and zeta potential of the nanoparticles are the key parameters to control nanoparticle motion beyond Brownian motion.
Micro EDM Deposition by Using Brass Wire Electrode in Air
Authors: Cao Guohui , Chi Guanxin , Jin Baidong , Wang Zhenlong , Zhao Wansheng
Published: April 2008

Proposed a new process technology of micro electrical discharge machining (EDM) beyond the traditional EDM concept. This method can deposit the brass wire tool electrode on the workpiece surface by pulse discharges between anode and cathode in air. At first, the basic machining parameters, which realize micro electrical discharge deposition, are prejudged according to the discharge phenomena in air and EDM basic theory. Afterwards, a lot of experiments were carried on an ordinary sinking-EDM machine tool. The results of experiments show that wire tool electrode materials, brass, can be deposited on steel workpiece surface. The diameter of micro fabricated cylinders is 100–240 microns, and the height is 1000–7350 microns. On some special machining parameters, a micro spiral structure can be deposited also, which is 100 micron in thread diameter and more than ten cycles. Excepting lots of experiments, the structure and properties of deposited substance were analyzed by SEM, spectroscopy analysis and micro hardness meter and so on. The results of analyzing the deposited cylinders show that the structure is multi-layer, which is beneficial for the further study of 3D scanning machining. The hardness is a little higher than the original metal. In this depositing process, element Zn of tool electrode is almost oxidized to ZnO. Element Cu is not oxidized, existing as solid Cu. Because the reactivity of Cu is weaker than that of Zn.
Strength and Damage Tolerance Analysis of a Fiber Reinforced Plastic(FRP) Multi Leafspring of a Light Passenger Vehicle Using Finite Element Analysis
Authors: Sairam K. , Jagadeesh K. A. , Senthilkumar M.
Published: April 2008

In the present scenario, strength of the structures has been the main focus of automobile manufacturers. The suspension leaf spring is one of the potential items for higher strength in automobiles as it accounts more than two times stronger than the conventional steel leaf spring. This helps in achieving more damping capacity, less fuel consumption and resistance against impact loads in the vehicle. The introduction of composite materials made it possible to avoid catastrophic damage due to sudden impact loads that are transferred to the chassis of light passenger vehicle through the leaf spring. In this work, an attempt has been made in replacing the design of a conventional multileaf leaf spring by a composite multileaf leaf spring based on strength ratio without any modification of the existing design of a light passenger vehicle. The materials adopted in the analysis of composite multileaf leaf spring are glass/epoxy, glass jute /epoxy, carbon jute/epoxy. The optimum material combination is determined based on the maximum induced bending stress, material availability and the contact pressure generated between each and every laminate which will influence the unsprung weight of the light passenger vehicle. Due to impact loads acting on the multileaf leaf spring damage tolerance work is also carried out in the composite material that has minimum contact pressure by creating artificial hemispherical damage for varying proportions. The optimum composite multileaf leaf spring is fabricated using filament winding technique. Modeling and contact analysis were carried out for both conventional and composite materials using ANSYS 8.1 software. From the investigations undergone, it is well proved that composite multileaf leaf spring made of glass/epoxy is found to be of higher strength comparing strength ratio, induced bending stress, contact pressure as well as with respect to cost, than the conventional leaf spring and the optimum damage radius due to sudden impact loads is also predicted in the composite multileaf leaf spring.
Flow Friction Behavior in Porous Channels
Authors: Jeng T. M. , Wu T. Y. , Chen P. L. , Chang S. F. , Hung Y. H.
Published: April 2008

A series of experimental studies on the flow friction behavior in a rectangular channel filled with various porous metallic foam materials have been performed. The rectangular channel has a cross-sectional area 60mm × 25.4mm with a length of 60mm. The parameters and conditions of interest in the study are the Reynolds number (Re) and medium porosity/pore density (ε/PPI). The ranges of the above-mentioned parameters are: Re=2058-6736 and ε=0.7-0.93/5-40PPI. Their effects on flow friction characteristics in such porous metallic foam channels have been systematically explored. In the study, the porous flow parameters including the Darcy number (Da), inertia coefficient (CF) and Darcy friction factor (f) are investigated. The combined effects of foam porosity and Reynolds number are examined in detail. From the results, the relevant new empirical correlations of Da and CF are proposed, respectively; and a new correlation of the friction factor in terms of ε, Da and Re is presented. Besides, the results reveal that all the ratios of f/fε=1 are much greater than unity and reach the orders of around hundreds to thousands. This manifests that it needs more pumping power to maintain the same flow rate as in a hollow channel. Finally, the experimental data of f/fε=1 is correlated in the study.
Thermal Deformation Prediction and Measurement of Space Optical Systems
Authors: Scott Mark I. , Sexton Mitra N. , Stubbs David M. , Hashemi Ab
Published: April 2008

A computational and experimental study of the thermal and thermally induced deformation of a plano mirror undergoing mW heat loading was performed to verify the capability to model the response of a representative imaging optic on the Space Interferometry Mission (SIM) spacecraft. Novel state of the art experimental and computational techniques provided milliKelvin and picometer precision in temperature and deformation prediction and experimental measurement. Mirrors of two different substrates, initially at ambient temperature under vacuum, were subjected to a thermal loading profile representing flight-like and overdrive thermal disturbance conditions. The experimental setup measured milliKelvin level temperature changes and picometer level deformation responses. I-deas / TMG was used to generate an integrated model to predict milliKelvin level changes in temperature of the mirror and picometer level deformation responses of the mirror surface. This paper focuses on the thermally induced deformation modeling and correlation to experimental data for the optical system. Comparison between experimental results and computational models for the deformation aspects of the test agreed well for the fused silica test mirror. In particular for the flight-like regime of primary interest, agreement between the experimental deformations and computational deformation results was within 18%. However the experimental results for the deformation of the Zerodur mirror presented challenges in prediction by the computational models. This is partly attributed to the low value of Zerodur CTE which affects numerical precision and partly due to non-homogeneity of the CTE which is neither modeled nor measured. Bi-material affect of coating was also investigated and found to be a potential source of discrepancy. Further studies regarding computational methods for Zerodur deformation are planned.
Effects of Inlet Position and Baffle Configuration on the Hydraulic Performance of Primary Settling Tanks
Authors: Firoozabadi B. , Tamayol A. , Ahmadi G.
Published: April 2008

Circulation regions always exist in the settling tanks. These regions reduce the tank’s performance and decrease effective volume of the tank. Recirculation zones would also result in short-circuiting and high flow mixing problems. Inlet position would also have effect on these, too. Using good baffle configuration may increase performance of settling tanks. One method for comparison of different tanks with each others is to use FTC. In this paper, by using FTC the effects of inlet position and baffle configuration on the hydraulic performance of primary settling tanks are studied. The best position of baffle is also determined.
Numerical Evaluation on the Heat Dissipation Capability of Liquid Metal Based Chip Cooling Device
Authors: Deng Zhong-Shan , Liu Jing
Published: April 2008

With the sharp improvement in computational speed of CPU, thermal management becomes a major concern in the current microelectronic industry. Conventional thermal management methods for CPU chip cooling are approaching their limit for quite a few newly emerging high integrity and high power processors. Therefore, liquid metal based chip cooling method has been proposed to accommodate to this request. In order to better understand the mechanisms of the cooling enhancement by the liquid metal based cooling technique, the three-dimensional heat transfer process thus involved in the cooling chip is numerically simulated in this study. A series of calculations with different flow rates and thermal parameters are performed. The cooling capability of the liquid metal is also compared with that of the water-cooling system. The results indicate that the liquid metal has powerful cooling capability, which is much better than that of the conventional liquid-cooling system.
A Simplified THD Model for the Steady State Journal Bearing Under Turbulent Flow
Authors: Mistry K. N. , Athre K.
Published: April 2008

Turbulence is an irregular fluid motion in which the various flow properties such as velocity and pressure show random variation with time and position. Because of this randomness the instantaneous value of flow properties has little practical significance and it is the average value of properties that is of interest. In turbulence the number of equations in the system available to characterize the flow remains the same as the laminar case. However, the additional unknown term, Reynolds shear stress, contributed due to mean flow and the turbulent fluctuations makes it difficult to solve purely on theoretical grounds. Thus certain assumptions concerning the character of the flow and experimental data are essential to solve the turbulence problem. The paper concerns the hydrodynamic turbulence motion in the lubrication layer, wherein, the thermo hydrodynamic analysis, the Reynolds and energy equations are decoupled and average value of eddy viscosity is used. Recirculation and mixing of the lubricant at inlet and parabolic distribution of temperature across film at the inlet is included in the analysis. Also, a parabolic distribution of temperature across film at the inlet is taken into account. The energy equation in the cavitation zone is treated with the empirical constants/weight age factors for the conduction and convection terms of heat dissipation. The heat generation in the cavitation zone term is neglected. The viscous sub layer is defined by an empirical equation, and the energy equation is treated separately for the viscous sub layer and turbulent core. The grid size is selected on the basis of the viscous sub layer thickness. The predicted results obtained by using the present model are compared with the experimental results.
Effects of Rotary Inertia and Shear Deformation on Nonlinear Vibration of Micro/Nano-Beam Resonators
Authors: Ramezani Asghar , Alasty Aria
Published: April 2008

In this paper, the large amplitude free vibration of a doubly clamped microbeam is considered. The effects of shear deformation and rotary inertia on the large amplitude vibration of the microbeam are investigated. To this end, first Hamilton’s principle is used in deriving the partial differential equation of the microbeam response under the mentioned conditions. Then, implementing the Galerkin’s method the partial differential equation is converted to an ordinary nonlinear differential equation. Finally, the method of multiple scales is used to determine a second order perturbation solution for the obtained ODE. The results show that nonlinearity acts in the direction of increasing the natural frequency of the doubly clamped microbeam. Shear deformation and rotary inertia have significant effects on the large amplitude vibration of thick and short microbeams.
Investigation of Extensional Actuation Strain in Ionomeric Polymer Transducers
Authors: Akle Barbar J. , Leo Donald J.
Published: April 2008

Ionomeric polymer transducers have received considerable attention in the past ten years due to their ability to generate large bending strain and moderate stress at low applied voltages. Bending transducers made of an ionomeric polymer membrane sandwiched between two flexible electrodes deform through the expansion of one electrode and contraction of the opposite electrode due to cation displacement. This is similar to a bimorph type actuation. In this study we report actuation through the thickness of the membrane, leading to the potential of a new actuation mechanism for ionomeric polymer materials. Several experiments are performed to compare the bending actuation with the extensional actuation capability. The direct assembly method previously developed by the authors is used to fabricate ionic polymer transducers with controlled electrode dimensions and morphology. Electrodes with varying thickness are used to alter thickness of the active material. In the first experiment, the actuators are cut in beam shape and are allowed to bend in cantilever configuration. In the second configuration, bending is constrained by sandwiching the membranes between two solid metal plates and force is measured across the thickness of the actuator. A bimorph model is used to assess the effect of electrode thickness on the strain. An electromechanical coupling model presented by Leo et al. [1] determined the strain in the active areas as a function of the charge. This model is presented with a linear and a quadratic term that produces a 1st harmonic response for a sine wave actuation input. The quadratic term in the strain generates a zero net bending moment for ionic polymer transducers with symmetric electrodes. The linear term is also canceled in extensional actuation for symmetric electrodes. Experimental results demonstrates strain on the order of 110 μstrain in the thickness direction compared to 1700 μstrain peak to peak on the external fibers for the same transducer when it is allowed to bend under +/−2V potential at 0.5 Hz.
Optimized Excitation Signal Source for Efficient Measurement of E/M Impedance
Authors: Xu Buli , Giurgiutiu Victor
Published: April 2008

This paper presented an improved algorithm using digitally synthesized excitation signal sources for efficient and accurate measurement of the E/M impedance for structural health monitoring with PWAS (piezoelectric wafer active sensor) transducers. Instead of using a sinusoidal excitation to measure the structural E/M impedance at a single frequency at a time, the digitally synthesized signal sources get the entire structural E/M impedance spectrum immediately at one step through permanently attached PWAS. Digitally synthesized signal source is a time efficient way for E/M impedance spectrum measurement. Firstly, introduction of E/M impedance measurement and the concept of using transfer function to achieve admittance and impedance of PWAS were provided. Secondly, two ways of synthesizing signal sources were discussed. Thirdly, the characteristics and performance of the two signal sources for E/M impedance measurement were compared in simulation and examined by laboratory experiment of measuring a free PWAS impedance spectrum over a wide frequency range (100k~1MHz). Finally, the hardware implementation and measurement precision of the new impedance methods were discussed and concluded.
Experimental Study of Entrance Effects on Laminar Gas Flow Through Silicon Orifices
Authors: Knobloch Aaron J. , Hibshman Joell R. , Wu George , Saia Rich
Published: April 2008

This study summarizes a fundamental investigation of flow through an array of silicon micromachined rectangular slots. The purpose of the study is to evaluate the effect of entrance pressure, flow area, orifice thickness, slot length, and slot width of the orifice on flow rate. These orifices were fabricated using a simple frontside through wafer DRIE process on a 385 μm thick wafer and wafer bonding to create thicker orifices. The dies were then packaged as part of a TO8 can and flow tested. To complement the results of this experimental work, two simple flow models were developed to predict the effect of geometrical and entrance conditions on the flow rate. These models were based on macroscale assumptions that were not necessarily true in the case of thin orifices. One relationship was based on Pouiselle flow which assumes fully developed flow conditions. Calculation of the entry length required for fully developed flow indicate that in the low Reynolds Number regime (32-550) evaluated, the entry flow development requires 2-8 times the thickness of the thickest orifices used for this study. Therefore, calculations of orifice flow based on a Pouiselle model are an overestimate of the actual measured flow rates. Another model examined typical orifice relationships using head loss at the entrance and exit of the slots did not accurately capture the particular flow rates since it overestimated the expansion or constriction losses. A series of experiments where the pressure was varied between 75 and 1000 Pa were performed. A comparison of the Pouiselle flow solution with experimental results was made which showed that the Pouiselle flow model overpredicts the flow rates and more specifically, the effect of width on the flow rates. The results of these tests were used to develop a transfer function which describes the dependence of flow rate on orifice width, thickness, length, and inlet pressure.
Disjoining Pressure Effects in Ultra-Thin Liquid Films in Micropassages: Comparison of Thermodynamic Theory With Predictions of Molecular Dynamics Simulations
Authors: Carey V. P. , Wemhoff A. P.
Published: April 2008

The concept of disjoining pressure, developed from thermodynamic and hydrodynamic analysis, has been widely used as a means of modeling the liquid-solid molecular force interactions in an ultra-thin liquid film on a solid surface. In particular, this approach has been extensively used in models of thin film transport in passages in micro evaporators and micro heat pipes. In this investigation, hybrid μPT molecular dynamics (MD) simulations were used to predict the pressure field and film thermophysics for an argon film on a metal surface. The results of the simulations are compared with predictions of the classic thermodynamic disjoining pressure model. The thermodynamic model provides only a prediction of the relation between vapor pressure and film thickness for a specified temperature. The MD simulations provide a detailed prediction of the density and pressure variation in the liquid film, as well as a prediction of the variation of the equilibrium vapor pressure variation with temperature and film thickness. Comparisons indicate that the predicted variations of vapor pressure with thickness for these two models are in close agreement. A modified thermodynamic model is developed which suggests that presence of a wall-affected layer tends to enhance the reduction of the equilibrium vapor pressure. However, the MD simulation results imply that presence of a wall layer has little effect on the vapor pressure. Implications of the MD simulation predictions for thin film transport in micro evaporators and heat pipes are also discussed.
Study of the Effective Thermal Conductivity of Nanofluids
Authors: Shukla Ratnesh K. , Dhir Vijay K.
Published: April 2008

Nanofluids, that is liquids containing nanometer sized metallic or non-metallic solid nanoparticles, show an increase in thermal conductivity compared to that of the base liquid. In this paper a model for thermal conductivity of nanofluids based on the theory of Brownian motion of particles in a homogeneous liquid combined with the macroscopic Hamilton-Crosser model is presented. The model is shown to predict a temperature and particle size dependent thermal conductivity. Comparison between the predicted and experimental results show that the model is able to accurately predict the temperature and volume fraction dependence of the thermal conductivity of water based alumina and gold nanofluids.
Systems Stability Using Weight Functions Method
Authors: Stroe Ion , Caruntu Dumitru I.
Published: April 2008

A new method for systems stability analysis is presented. This method is called weight functions method and it replaces the problem of Liapunov function finding with a problem of finding a number of functions (weight functions) equal to the number of first order differential equations describing the system. It is known that there are not general methods for finding Liapunov functions. The weight functions method is simpler than the classical method since one function at a time has to found. This method’s conditions of solution stability for linear and nonlinear systems are presented. Applications such as Lurie-Postnikov problem and controlled systems stability are presented as well.
Research of the Relationship Between the Clearance and Wear of Precise Micro Punch and Die
Authors: Lin Jui-Chang , Lee Kingsun , Lu Ming-Fang , Yen Chainming
Published: April 2008

The punch and die operation is widely used for forming and processing of both metal and non-metal sheets due to its ease-of-operation. Moreover, this method is characterized by a higher degree of cost-effectiveness and accuracy as compared to other processing modes, such as casting, forging and metal processing. The typical field of application covers parts manufacturing for timekeepers, vehicles, sheet metals or motors and various thin plates. With the development of IC (Integrated circuit) processing technology, passive components are being increasingly miniaturized, ranging from 0603 (0.06″ × 0.03″) chips to existing 0402 (0.04″ × 0.02″) and 0201 chips. Because of increasing miniaturization of passive components, the smaller aperture of composite paper bags for various IC will be required. The IC chips need to be packaged for sale. The packaging bag has many small apertures to store the chips. Micro punches and dies are use to punch this aperture. The accuracy of aperture for packaging bags, however, depends on the clearance between the punch and die. This study utilizes an Image Vision System to measure the clearance of micro dies and the burr size of processed composite materials in order to estimate which condition is better for micro dies. The relational expression was established between input parameters and outputs via a Neural Network. This can help to anticipate the burr size under any clearance, and contributes to the design and application of smaller punches in the future.
Transverse Vibration of Two Axially Moving Beams Connected by an Elastic Foundation
Authors: Gaith Mohamed , Mu¨ftu¨ Sinan
Published: April 2008

Transverse vibration of two axially moving beams connected by a Winkler elastic foundation is analyzed analytically. The system is a model of paper and paper-cloth (wire-screen) used in paper making. The two beams are tensioned, translating axially with a common constant velocity, simply supported at their ends, and of different materials and geometry. Due to the effect of translation, the dynamics of the system displays gyroscopic motion. The Euler-Bernoulli beam theory is used to model the deflections, and the governing equations are expressed in the canonical state form. The natural frequencies and associated mode shapes are obtained. It is found that the natural frequencies of the system are composed of two infinite sets describing in-phase and out-of-phase vibrations. In case the beams are identical, these modes become synchronous and asynchronous, respectively. Divergence instability occurs at the critical velocity; and, the frequency-velocity relationship is similar to that of a single traveling beam. The effects of the mass, flexural rigidity, and axial tension ratios of the two beams, as well as the effects of the elastic foundation stiffness are investigated.
Identification and Adaptive Control of the Uncertain Lorenz System
Authors: Pishkenari Hossein Nejat , Shahrokhi Mohammad
Published: April 2008

In this paper an identification method which can estimate the unknown parameters of a general nonlinear system based on three techniques (gradient, least-squares and rapid identification) has been developed. The stability of the proposed schemes has been shown using the Lyapunov stability theorem. The properties of each identification technique have been discussed briefly. Open loop identification of the Lorenz chaotic system is presented to show the effectiveness of the proposed approach. To illustrate the efficiency of the identification method for control purposes, it has been applied for controlling the well-known Lorenz system. By exploiting the property of the system a novel singularity-free controller is proposed. The stability of controller has been shown by a Lyapunov function. The designed controller coupled with the proposed identification technique can stabilize the uncertain Lorenz system. The effectiveness of the approach has been shown through simulation.