bluuebunny/crossref_metadata_2025 huggingface dataset:
Photocatalytic Degradation of Rhodamine B by TiO2/ZnO Nanofibers Under Visible Light Irradiation
Authors: Pei Carina Chun , Leung Wallace Woon-Fong , Yang Lijun , Hung Chi-ho
Published: August 2012

Photocatalytic reduction of contaminants in wastewater or polluted water can be enhanced by finding a suitable catalyst with property that utilizes an extended light adsorption spectrum, reducing the recombination of electron-hole pairs, and casting the catalyst into a form with large surface-to-volume ratio to be in contact with the contaminants. Based on these objectives, Zn-doped TiO2 nanoparticles with high photocatalytic activity were synthesized by the sol–gel assisted nozzle-less electrospinning technique followed by calcining the precursor Ti(OiPr)4/ZnAc/PVP nanofibers in air in the temperature range of 450–650°. The thermal decomposition behavior was studied by thermogravimetric analyser and differential scanning calorimeter (TGA–DSC), and the morphology and crystal structure were monitored by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). With the different concentration of zinc acetate in the precursor solution, the diameter of fibers ranged from 80–130 nm. The photocatalytic degradation of rhodamine B dye under visible light irradiation was also studied. It is found that the photosensitized degradation activity can be optimized by doping an appropriate amount of Zn (0.30 wt. %). Hence, the enhanced photodegradation of dyes with a new photocatalyst nanofiber under visible irradiation can be realized, which can take better use of solar energy.
Minimizing the Wick Thickness in a Planar Microscale Loop Heat Pipe Using Efficient Thermodynamic Design
Authors: Dhillon Navdeep S. , Cheng Jim C. , Pisano Albert P.
Published: August 2012

Theoretical and numerical thermodynamic analysis of the evaporator section of a planar microscale loop heat pipe is presented, to minimize the permissible wick thickness in such a device. In conventional cylindrical loop heat pipes, a minimum wick thickness is required in order to reduce parasitic heat flow, and prevent vapor leakage, into the compensation chamber. By taking advantage of the possibilities allowed by microfabrication techniques, a planar evaporator/compensation chamber design topology is proposed to overcome this limitation, which will enable wafer-based loop heat pipes with device thicknesses on the order of a millimeter or less. Thermodynamic principles governing two-phase flow of the working fluid in a loop heat pipe are analyzed to elucidate the fundamental requirements that would characterize the startup and steady state operation of a planar phase-change device. A three dimensional finite element thermal-fluid solver is implemented to study the thermal characteristics of the evaporator section and compensation chamber regions of a planar vertically wicking micro-columnated loop heat pipe. The use of in-plane thermal conduction barriers to reduce parasitic heat flow into the compensation chamber is demonstrated.
Introducing Energy Efficiency Metrics for Server and Data Centers
Authors: Beitelmal Abdlmonem H. , Fabris Drazen
Published: August 2012

New servers and data center metrics are introduced to facilitate proper evaluation of data centers power and cooling efficiency. These metrics will be used to help reduce the cost of operation and to provision data centers cooling resources. The most relevant variables for these metrics are identified and they are: the total facility power, the servers’ idle power, the average servers’ utilization, the cooling resources power and the total IT equipment power. These metrics can be used to characterize and classify servers and data centers performance and energy efficiency regardless of their size and location.
Improvement of Dye Sensitized Solar Cells With Nanofiber-Based Anode
Authors: Yang Lijun , Leung Wallace Woon-Fong
Published: August 2012

Dye Sensitized Solar Cell (DSSC) has great advantages over conventional silicon-based photovoltaics as it is inexpensive, flexible, and transparent. Sun energy is used to excite the electron of the organic (ruthenium-polypyridine) dye from which the electron from the dye is injected into the anode made of titanium dioxide (TiO2). The excited electron enters the conduction band of the TiO2 and gets transmitted across the TiO2 nanoparticles (anode) to the FTO (Fluorine-doped tin-oxide) glass/electrode, which in turn go to the external circuit powering the electrical load. The electron returns to the device via the counter electrode coated with a platinum catalyst to the electrolyte, typically iodide/tri-iodide, wherein the iodide ions carry the electron back to regenerate the dye attached to the TiO2 nanofibers. Improvement can be made by using 60–120 nm diameter TiO2 nanofibers produced in our lab, for which electrons can be directly transferred to the FTO reducing the recombination rate. Also, the large surface-to-volume ratio of the nanofibers allows numerous sites for attachment of the organic dye molecules, thereby increasing the capture of sunlight. In order to achieve high conversion efficiency, several critical parameters need to be optimized with the nanofiber-based DSSC. In this study, we investigate the thickness of the anode (TiO2 nanofiber) on the conversion efficiency. The conversion efficiency of the DSSC in our laboratory can reach more than 7%. Other improvements are believed to further boost this efficiency.
Numerical Modeling and Experimental Investigation of Improved Mixing From Both Coriolis Effect and Go¨rtler Vortices in Rotating Zigzag Microchannel
Authors: Ren Yong , Leung Wallace Woon-Fong
Published: August 2012

The flow pattern and mixing performance in different geometries of microchannels are investigated. A study for the zigzag shape channel under both stationary and rotation condition was investigated. The results are compared to the straight channel. Both numerical model via CFD and experiments are agreeing with each other. It is found when the channel is under rotation, the mixing performance is better than the stationary condition due to rotation induced Coriolis effect. As the rotation speed increases from 300rpm to 900rpm, an improved mixing performance can be further obtained. Our study results also demonstrate that zigzag channel can provide relatively better mixing, because the successive bending design can lead to secondary flow in the cross sectional directions due to Go¨rtler vortices generated from centrifugal effect as the flow negotiates the “turns” or “bends” of the channel, and this adds to mixing in addition to that due to aforementioned Coriolis effect. An analysis reveals that zigzag shape channel requires more pressure drop when compared with the straight channel in order to maintain the continuous throughflow due to the pressure/head loss as the flow encounters each bend and these losses become additive. This adds to the cost for the improved mixing from the Go¨rtler vortices.
Rheological Study of Y2O3 Nanofluids
Authors: Tesfai Waka , Singh Pawan K. , Masharqa Salim J. S. , Chiesa Matteo , Shatilla Youssef
Published: August 2012

This paper investigates the effects of shear rate and temperature on rheological behavior of Yttria (Y2O3) based nanofluids experimentally. These nanofluids are potentially useful in high electric field and high temperature environment as well as for nuclear applications. The nanofluids are prepared by two step method. The particle size of nanofluids is characterized by electro-acoustic spectroscopy. Rheology measurements of these nanofluids show typical Newtonian behavior for several volume fractions of Yttria for shear rates above 1s−1. Below 1s−1 shear rate the nanofluids show shear thinning behavior that depends on particles concentration. Generally, the effective viscosity of Yttria nanofluids is found to increase linearly up to 44% with particle loading of 5 vol%. The viscosity of these nanofluids follows Arrhenius type relationship with temperature similar to the base fluid behavior. The relative viscosity of these nanofluids has a temperature dependence behavior which contradicts reported observations in literature and can be attributed to the contribution from particle-particle interaction at higher concentrations. This temperature dependence was more pronounced with an increase in concentrations, which indicates that the viscosity increment of nanofluids is not only governed by the base fluid temperature dependence.
Integral Medicine: Cure and Organic Regeneration to Nano-Metric Level by Quantum Medicine Methods Programming Path Integrals
Authors: Bulnes Francisco , Bulnes Francisco H. , Herna´ndez Eduardo , Maya Juan
Published: August 2012

In the last years into the alternative medicine, have arise methods into the context of the quantum medicine and the generalization of the homeopathic methods that establish principles of holistic and causal cure in a deep level of cure, correcting and restoring the conscience of cure of the proper body. In this work that is the recompilation of some important results published, it considers and develops quantum methods of cure and organic re-generation, realizing actions of restoration and alignment of the vital field and their programming by means of intelligence codes of cure by path integrals.
Commercial Tree Chipper Safety Control Bar Activation Analysis
Authors: Brickman Dennis B.
Published: August 2012

This paper addresses the ability of a human worker to activate safety devices to stop and reverse the mechanical infeed system inside a commercial tree chipper infeed hopper. Studies were performed using a tray equipped commercial tree chipper incorporating a safety control bar and safety cables to stop and reverse the mechanical infeed system. The test results indicate that the human test subject was able to successfully activate the safety control bar and the safety cables from a variety of body positions around and within the tree chipper infeed hopper.
An Investigation Into the Acoustic Response of Diseased Arterial Pulse Waveforms
Authors: Al-Rawi M. A. , Al-Jumaily A. M. , Lu J. , Lowe A.
Published: August 2012

Aneurysm is a major contributing factor to death and disability worldwide. This research explores the concept of using computational fluid dynamics (CFD) as a cost effective and non-invasive method to detect the location and condition of diseased segments of blood vessels. In this study, 12 different abdominal aortic aneurysms cases and a controlled case of 3D coupled fluid–structure interaction scheme (FSI) are modeled. Pulse waves travelling through these segments are analyzed with a focus on the reflected waves at diseased region and the brachial artery. A commercial software ANSYS 12.1® is used to solve FSI models. An invasive catheter pulsatile pressure waveforms data is imposed at the inlet and the four outlets of the aorta and also used to validate the presented models. The results show that an increase in the diameter of aneurysmal artery will have an effect on the systolic and diastolic pressure at the brachial artery. The systolic pressure increases due to the forward pulse wave resulting from aneurysm. However, diastolic pressure decreases due to the delay of the backward waves which reach at the brachial artery. These models show that the forward and backward waves, which can be attributed to changes in the diameter of the abdominal aorta, may be useful in diagnosing cardiovascular diseases non-invasively.
Modal Based Geometric Stiffening Formulation for Dynamics Simulation of Multibody Systems
Authors: Wang Fengxia
Published: August 2012

This work concerns the implementation of nonlinear modal reduction to flexible multi-body dynamics. Linear elastic theory will lead to instability issues with rotating beamlike structures, due to the neglecting of the membrane-bending coupling on the beam cross-section. During the past decade, considerable efforts have been focused on the derivation of geometric nonlinear formulation based on nodal coordinates. In this work, in order to improve the convergence characteristic and also to reduce the computation time in flexible multi-body dynamics, which is extremely important for complicated large systems, a standard modal reduction procedure based on matrix operation is developed with essential geometric stiffening nonlinearities retained in the equation of motion. The example used in this work is a rotating Euler-Bernoulli beam, two nonlinear reduced models were established based on modal coordinates, the first reduced model created from theoretical bending and axial mode shapes by Galerkin method; the second reduced model is derived by the standard matrix operator from a full finite element model. Transient simulation results of lower degrees of freedom from above two reduced models are compared with those obtained from full nonlinear finite element model.
Numerical Modeling and Validation of Supersonic Two-Phase Flow of CO2 in Converging-Diverging Nozzles
Authors: Yazdani Miad , Radcliff Thomas D. , Alahyari Abbas A. , Farzad Mohsen
Published: August 2012

CO2 is an attractive alternative to conventional refrigerants due to its low direct global warming effects. Unfortunately, CO2 and many alternative refrigerants have lower thermodynamic performance resulting in larger indirect emissions. Effective use of ejectors to recover part of the lost expansion work, which occurs in throttling devices can close this performance gap and enable the use of CO2. In an ejector, the pressure of the motive fluid is converted into momentum through a choked converging-diverging nozzle, which then entrains and raises the energy of a lower-momentum suction flow. In a two-phase ejector, the motive nozzle flow is complicated by non-equilibrium phase change affecting local sonic velocity and leading to various types of shockwaves, pseudo shocks, and expansion waves inside or outside the exit of the nozzle. Since the characteristics of the jet leaving the motive nozzle greatly affect the performance of the ejector, this paper focuses on the details of flow development and shockwave interaction within and just outside the nozzle. The analysis is based on a high-fidelity model that incorporates real-fluid properties of CO2, local mass and energy transfer between phases, and a two-phase sonic velocity model in the presence of finite-rate phase change. The model has been validated against literature data for two-phase supersonic nozzles as well as overall ejector performance data. The results show that due to non-equilibrium effects and delayed phase change, the flow can choke well downstream of the minimum-area throat. Also, Mach number profiles show that, although phase change is at a maximum near the boundaries, the flow first becomes supersonic in the interior of the flow where sound speed is lowest. Shock waves occurring within the nozzle can interact with the boundary layer flow and result in a ‘shock train’ and a sequence of subsonic and supersonic flow observed previously in single-phase nozzles. In cases with lower nozzle back pressure, the flow continues to accelerate through the nozzle and the exit pressure adjusts in a series of supersonic expansion waves.
Structural Health Monitoring of High Temperature Composites
Authors: Salowitz Nathan , Li Yu-Hung , Kim Sang-Jong , Roy Surajit , Chang Fu-Kuo
Published: August 2012

High-temperature polymer-matrix composites (PMCs) are necessary and critical for the development of supersonic aircraft and orbital re-entry vehicles because of the need for light-weight design, high strength-to-weight ratios and high thermal stability in structures. Damage detection is a primary concern in composite structures because they are prone to multiple damage forms that can be hidden within the structure. Damage can include matrix cracking, fiber breakage, and delamination which can be caused by impacts, fatigue, or overloading. To overcome these shortfalls highly damage tolerant structures are employed to improve the safety of structures. Unfortunately this requires additional, potentially unnecessary, structural weight which is detrimental to aerospace structures. Acoustic ultrasound based structural health monitoring (SHM) has demonstrated the ability to overcome these problems by using arrays of Lead Zirconate Titanate piezoelectric transducers typically mounted on a flex circuit all of which is permanently affixed to, or embedded within, a structure [1] [2] [3] [4]. These transducers can excite and detect ultrasonic wave propagation in the structure and diagnostic algorithms, interpreting the signals, have been developed enabling real time inspection for damage. However, modern SHM systems are not capable of surviving the high temperatures experienced in the fabrication and service of High-temperature polymer matrix composites. In particular the Lead Zirconate Titanate piezoelectric elements typically depolarize and lose their functionality at around 200°C [5] [6]. Additionally, current SHM diagnostic algorithms are dependent on baseline data to compare signals to. These signals change with temperature and even just a few degree change can be detrimental to the system’s abilities. The current method for enabling functionality over a range of temperatures is to take numerous sets of baseline data at very high resolution across a range of temperatures. In order to adapt SHM for high temperature composites new piezoelectric materials must be developed capable of surviving elevated fabrication and operational temperatures. Small scale network components must be integrated to reduce detrimental effects of embedding SHM systems within the composite layup [7] [8] [9]. Additionally, methods for reducing the number of baseline data sets in the diagnostic algorithms must be developed. This paper presents development and testing of Bismuth Scandium Lead Titanate piezo ceramic transducers for high temperature SHM. These transducers are incorporated into a stretchable network system and mounted on a glass backing. Functionality is tested using a commercially available data acquisition system designed for SHM and intended for use with PZT transducers. Ongoing development of temperature compensation algorithms is also presented herein.
Design and Analysis of a Smart Composite Wing
Authors: Hasan Zeaid , Hammoudeh Hamzeh , Atmeh Ghassan
Published: August 2012

This paper focuses on the design and analysis of a general aviation airplane wing which is fabricated of fiber reinforced composite laminates. The use of composite materials in commercial transport has continued to increase over the past 30 years. Composites materials are intended to be used more extensively as an alternative to aluminum structure in aircraft and aerospace applications. This is due to their attractive properties such as high strength-to-weight ratio and flexibility. The design of a general aviation aircraft is initially implemented in the first section. Using fiber-reinforced composite materials, an initial design of the wing box is assumed for the preliminary layout. The load carrying members of the wing are modeled as a rectangular box beam with taper while excluding the sweep angle. Aerodynamic analysis is conducted in order to extract the aerodynamic loads applied on the wing. These loads (lift, drag) are applied to the wing structure in order to conduct the proper stress analysis to attain the static structural behavior of the wing. An iterative procedure based on applying the stress analysis results to the appropriate macromechanical failure of composite materials (such as Tsai-Hill) is incorporated in order to evaluate the structural integrity of the wing against the applied loads. Moreover, static shape control of the composite wing is also considered using surface mounted and embedded piezoelectric actuators distributed along the wing span which have the capability to sense and take corrective actions under undesirable stimuli. The sequence of actuation of piezoelectric actuators embedded between the composite plies controls the elastic deformation response to loading of the composite wing. The analysis is conducted using the commercial finite element software Abaqus for several different types of piezoelectric actuators such as Lead Zirconate Titanate (PZT) and other piezoelectric fiber composites such as Active Fiber Composite (AFC) and Microfiber Composite (MFC). Finally, cost analysis of composite wings is briefly discussed.
Experimental Investigation of a Flat-Plate Oscillating Heat Pipe During High-Gravity Loading
Authors: Ma Hongbin , Thompson Scott M. , Hathaway Aaron A. , Smoot Chris D. , Wilson Corey A. , Young Robert M. , Greenberg Lawrence , Osick Brian R. , Van Campen Stephen , Morgan Brian C. , Sharar Darin , Jankowski Nicholas
Published: August 2012

The thermal performance of a miniature, three-dimensional flat-plate oscillating heat pipe (3D FP-OHP) was experimentally investigated during high gravity loading with non-favorable evaporator positioning. The heat pipe had dimensions of 3.0 × 3.0 × 0.254 cm3 and utilized a novel design concept incorporating a two-layer channel arrangement. The device was charged with acetone and tested at a heat input of 95 W within a spin-table centrifuge. It was found that the heat pipe operated and performed near-independent of the investigated hyper-gravity loading up to 10g. Results show that at ten times the acceleration due to gravity (10g) the effective thermal conductivity was almost constant and even slightly increased which is very different from a conventional heat pipe. The gravity-independent heat transfer performance provides a unique feature of OHPs.
Chaotic Vibrations of Functionally Graded Doubly Curved Shells With Internal Resonance
Authors: Alijani F. , Amabili M. , Karagiozis K.
Published: August 2012

Chaotic vibrations of functionally graded doubly curved shells subjected to concentrated harmonic load are investigated. It is assumed that the shell is simply supported and the edges can move freely in in-plane directions. Donnell’s nonlinear shallow shell theory is used and the governing partial differential equations are obtained in terms of shell’s transverse displacement and Airy’s stress function. By using Galerkin’s technique, the equations of motion are reduced to a set of infinite nonlinear ordinary differential equations with cubic and quadratic nonlinearities. A bifurcation analysis is carried out and the discretized equations are integrated at (i) fixed excitation frequencies and variable excitation amplitudes and (ii) fixed excitation amplitudes and variable excitation frequencies. In particular, Gear’s backward differentiation formula is used to obtain bifurcation diagrams, Poincare´ maps and time histories. Furthermore, maximum Lyapunov exponent and Lyapunov spectrum are obtained to classify the rich dynamics. It is revealed that the shell may exhibit complex behaviour including sub-harmonic, quasi-periodic and chaotic response when subjected to large harmonic excitations.
On 2D Forcespinning™ Modeling
Authors: Padron Simon , Caruntu Dumitru I. , Lozano Karen
Published: August 2012

Forcespinning™ is a novel method that makes used of centrifugal forces to produce nanofibers rapidly and at high yields. To improve and enhance this new nanofiber production method a model of the system is begun. The process is started by deriving the governing equations of the forcespinning™ sytem and the constraints associated it. A simple 2D model is then obtained using the derived governing equations for the inviscid case to determine the trends of fiber diameter and trajectories. Then, focus is given to the time-dependency of these equations, and the effects of parametric excitation of the system on fiber formation are analyzed. The equations are solved using a combination of the method of multiple scales and the finite difference method with slender-jet theory assumptions.
Low Voltage Electrohydrodynamic Micropump for Cooling of Electronic Device
Authors: Fandohan Comlan , Agwu Nnanna A. G.
Published: August 2012

To dissipate the high heat generated in microprocessors and electronic components, electrohydrodynamic (EHD) micropumps are often used. An EHD system involves the interaction of a flow field and an applied electric field; specifically, an ion-drag EHD micropump uses the interaction of an electric field with electric charges, dipoles or particles embedded in a dielectric fluid in order to generate a net flow. These EHD micropumps, require high voltage to drive the fluid, and as a result have not gained wide application. This study presents a systematic analytical method of reducing the high voltage requirement. The approach is to select a dielectric material such that flow rate is maximized with low electric potential. It is known that the dielectric maximum velocity is a function of the dielectric potential, dielectric permittivity, and viscosity. In this paper, a flow rate is assumed to be sufficient. The electric potential is decreased by selecting the appropriate fluid. Fluid of high permittivity and low viscosity will enhance the potential factor there by, decreasing the potential.
A Multibody Model for Computer Simulation of Molecular Structures on Supercomputers
Authors: Rudraraju Krishna Chaitanya , Duan Shanzhong Shawn
Published: August 2012

An efficient O(N) algorithm has been developed on the basis of the proper integration between an internal coordinate method (ICM) and a multibody molecular method. The method has been implemented for virtual prototyping of molecular systems with a simple chain structure and the results showed O(N) computational performance. This paper results the application of O(N) procedure to a large molecular chain and show the linear computational load relationship with the number of subsets. Initially, a brief introduction to O(N) procedure and the theoretical development of the algorithm is presented. Later focus will be turned to the implementation of the algorithm on the molecular structure. Finally, the motion behavior and the simulation time are analyzed for different computer systems.
Compliant Plate Seals for Turbomachinery Applications
Authors: Deo Hrishikesh V.
Published: August 2012

In this paper, a novel GE Compliant Plate Seal is proposed that consists of compliant plates attached to a stator in a circumferential fashion around a rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter, and an intermediate plate extends inwards into this slot from stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip-clearance. When the tip-clearance reduces below the equilibrium clearance, the hydrostatic lift forces cause the compliant plates to lift away from the rotor. Conversely when the tip-clearance increases above the equilibrium clearance, the hydrostatic blowdown forces cause the compliant plates to blow down towards the rotor. Due to this self-correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and non-contact operation even in the presence of large rotor transients. Simplified CFD models have been developed to predict the leakage flow rates and hydrostatic lift and blowdown forces, and a design philosophy is proposed to predict the feedback phenomenon from the CFD models. The proposed models are validated and self-correcting behavior is demonstrated through experimental testing.
Investigation of Several Turbulence Models in Simulation of an Axial PAT for a Small Hydropower Using as Renewable Source of Energy
Authors: Bozorgi A. , Riasi A. , Nourbakhshi A.
Published: August 2012

Small hydropower stations as one of the clean and renewable resources of energy have great capacity to generate electricity and with increasing energy demands, using such potentials is quite necessary. One of the suitable choices for utilizing small hydropower resources is using pump as turbine (PAT), which means using pump in reverse mode. Pumps are relatively simple and inexpensive machines, easy to maintain and readily available in many of developing countries. Several methods have been developed to predict operation of pumps running as turbines but their results are not in good coincidence with experimental data for all pumps. Therefore, study and investigation of hydraulic behavior of pumps in reverse mode can be useful. In this work, an axial pump is simulated in reverse mode by computational fluid dynamics. Reynolds-Averaged Navier–Stokes equations are solved using different turbulence models in NUMECA software environment. Characteristic curves of the reverse pump are obtained for each turbulence model and results are compared with experimental data. The results show that Spallart-Allmaras can predict operation of the axial PAT better than other models.
Fracture Strength of Laser Etched Glass
Authors: Browne Joshua D. , Rorrer Ronald A. L.
Published: August 2012

The effect of CO2 laser etching on the strength of soda lime plate glass has been investigated. The majority of common beverage glassware is comprised of soda lime glass. Laser etching is used to create patterns on such glassware for aesthetic reasons. Various etching conditions have been investigated in order to compare to the strength of un-etched glass. Three point bend tests were used to determine strength values. The resulting fracture strength of etched glass is based upon the flaws and resulting stress concentrations created during the laser ablation process. In addition to stress concentrations, the thermal history and residual thermal stresses play a role in the failure process. Samples were also cyclically washed to determine the effect of water and thermal cycling. Results were documented and compared via Weibull analysis. Nominal strength values were 114 MPA for unetched, 83 MPa for wash cycled, 43 MPa for etched, and 33 MPa for etched and wash cycled.
Cross Analysis of Metal Foam Design Parameters for Achieving Desired Fluid Flow
Authors: Hess Timothy , Morkos Beshoy , Bowman Mark , Summers Joshua D.
Published: August 2012

This paper presents an experimental study of air flow through open cell metal foams for use as a thermal energy dissipating system. The goal of this paper is to identify the optimum configuration of metal foam design parameters for maximum flow. Four foam blocks were used in the study, representing a range of design parameters: material (copper or aluminum), pore size (5–10 pores per inch), and relative density (ε = 0.875–0.952). The effects of pore size were isolated by comparing air flow through three aluminum foam blocks with constant density and varied pore size. A series of wind tunnel tests were performed to measure the velocity of air flowing through the foam as a function of the free stream air velocity, ranging from 0 to 17.4 mph (7.5 m/s). Results indicated smaller pore sizes and larger densities decreased the amount of airflow through the foam. However, one foam sample produced results that did not fit this trend. Further investigation found this was likely due to the differences in the cross-sectional geometry of the foam ligaments. The ligament geometry, affected by density and manufacturing method, was not constant and not initially considered as a variable of interest. The cross-section shape of the ligaments was found to vary from a rounded triangular shape to a triangle shape with concave surfaces, increasing the amount of drag in the airflow through the sample.
Enhanced Pool Boiling Performance on Micro-, Nano-, and Hybrid-Structured Surfaces
Authors: Li Qian , Wang Wei , Oshman Chris , Latour Benoit , Li Chen , Bright Victor M. , Lee Yung-Cheng , Yang Ronggui
Published: August 2012

Thermal management plays an important role in both high power electronics and energy conversion systems. A key issue in thermal management is the dissipation of the high heat flux generated by functional components. In this paper, various microstructures, nanostructures and hybrid micro/nano-structures were successfully fabricated on copper (Cu) surfaces, and the corresponding pool boiling heat transfer performance was systematically studied. It is found that the critical heat flux (CHF) of hybrid structured surfaces is about 15% higher than that of the surfaces with nanowires only and micro-pillars only. More importantly, the superheat at CHF for the hybrid structured surface is much smaller than that of the micro-pillared surface (about 35%), and a maximum heat transfer coefficient (HTC) of about 90,000W/m2K is obtained. Compared with the known best pool boiling performance on biporous media, a much larger HTC and much lower superheat at a heat flux of 250W/cm2 have been obtained on the novel hybrid-structured surfaces.
Intensity-Dependent Dispersion in Nonlinear Phononic Layered Systems
Authors: Manktelow Kevin L. , Leamy Michael J. , Ruzzene Massimo
Published: August 2012

Phononic crystals are typically considered to operate in regimes where a linear constitutive relationship provides an adequate representation. For high intensity wave propagation, however, weak nonlinearities can affect performance. For example, a cubic nonlinearity gives rise to frequency shifting and thus a shift in band gap location. In the study of nonlinear optics, a cubic term has been treated using a quasi-linear constitutive relationship with intensity dependent properties. This technique is explored herein for generating nonlinear dispersion relationships for the elastic case. In addition, a perturbation method developed previously for discrete systems, used in conjunction with a finite element discretization, is proposed as an alternative dispersion analysis tool. Simulations of the fully nonlinear governing equations are provided as validation of the predicted dispersion curves.
Enhanced Capillarity in Microchannels Coated With Nanoscale Porous Titanium Dioxide
Authors: Zhang Bo , Zhang Min , Zhang Tao , Cui Tianhong
Published: August 2012

The enhanced capillarity in microchannels coated with nanoscale porous titanium dioxide (TiO2) by liquid phase deposition (LPD) is presented in this letter. To characterize the capillarity, the position of meniscus flow as a function of time was measured under calcinations and lightproof storage. The results from six groups of microchannels with the same width but different heights demonstrate that the porous surface of a titanium dioxide film enhances the capillarity stability significantly when the pore size is in the same order of magnitude to the channel height. This effect decreases as the channel height increases.
Electron Transport and Recombination in TiO2 Nanofiber Dye Sensitized Solar Cell
Authors: Li Jinwei , Shi Yong
Published: August 2012

Dye sensitized solar cells (DSSCs), a new type of photo-electrochemical solar cells, are a promising alternative to the silicon based photovoltaic because they hold advantages of low cost, simple manufacturing processes and higher conversion efficiency compared with other types of excitonic solar cell. DSSCs with conversion efficiencies of up to 11% have been achieved with a highly stable electrolyte under AM1.5G conditions. Recently, one dimensional (1D) electrospun TiO2 nanofibers have been used as the DSSC photoanode to improve the electron transport efficiency and enhance the light harvest efficiency by scattering more light in the red part of the solar spectrum. In this paper, stepped light induced transient measurement of photocurrent and voltage (SLIM-PCV) has been employed to study electron transport and recombination in DSSCs. Electron diffusion coefficients and electron lifetimes were measured with differing light intensities. The electron diffusion coefficients and electron lifetimes strong correlate with intensity, which indicates the trap limited diffusion process for electrons in the TiO2 nanofiber DSSC.
Monitoring Transportation, Air Pollution and Energy Demand in the Philippines Using LEAP
Authors: Ahanchian Mohammad , Biona Jose Bienvenido Manuel
Published: August 2012

This research is conducted to assess the present situation of energy demand and emission of air pollutants from road transportation sector in the Philippines along with the future forecasting of the environmental impacts from transportation sector. According to the published reports of the Department of Energy of the Philippines, transportation have the most energy-intensive sector amongst the sectors, which will account for the largest share in the country’s final energy demand registering an average of 34.5 percent. Hence, the past trend of energy consumption and emissions are applied in order to predict the future pattern. In addition, a model of transportation system using computer based software called “Long Range Energy Alternatives Planning (LEAP)” has been developed together with the associated Environmental Database (EDB) model. The framework of calculation utilized official transportation database, fuel consumption of certain vehicle type and corresponding emission of each vehicle type. The base scenario called as Business -As- Usual (BAU) is surveyed and other different alternative scenarios are presented and discussed. The model is run under the database of 2001 as the base year and extrapolated until 2030 to predict the impact of transportation. The main objective of this study is to achieve an optimal transportation policy which contributes in decline of energy demand as well as air pollution in the Philippines.
A Numerical Study of Natural Convective Heat Transfer From an Inclined Isothermal Plate Having a Square Wave Surface
Authors: Oosthuizen Patrick H. , Paul Jane T.
Published: August 2012

Natural convective heat transfer from a wide isothermal plate which has a “wavy” surface, i.e., has a surface which periodically rises and falls, has been numerically studied. The surface waves run in the horizontal direction, i.e., are normal to the direction of flow over the surface, and have relatively small amplitude. Attention has been restricted to the case where the waves have a rectangular cross-sectional shape. The plate is, in general, inclined to the vertical, consideration only being given to inclination angles at which the heated plate is facing upwards. The range of Rayleigh numbers considered extends from values that for a non-wavy vertical plate would be associated with laminar flow to values that would be associated with fully turbulent flow. The flow has been assumed to be steady and fluid properties have been assumed constant except for the density change with temperature that gives rise to the buoyancy forces, this being treated by means of the Boussinesq approximation. The Reynolds averaged governing equations in conjunction with a standard k-epsilon turbulence model with buoyancy force effects fully accounted for have been used in obtaining the solution. The governing equations have been solved using the commercial cfd code FLUENT. The solution has the following parameters: (i) the Rayleigh number based on the height of the heated plate, (ii) the Prandtl number, (iii) the ratios of the amplitude of the surface waviness and of the pitch of the surface waves to the height of the plate, and (iv) the angle of inclination of the plate to the vertical. Results have only been obtained for a Prandtl number of 0.74. The effects of the other dimensionless variables on the mean surface Nusselt number have been numerically studied.
Active Gearing System for Wind Turbines
Authors: McMullan Daniel , Dao Anh , Brooking Daniel , Weller J. Mark , Azzouz M. Salim
Published: August 2012

The purpose of this research paper is to investigate the possibility of improving the efficiency of wind turbines by taking advantage of the wind speed variability. An active epicycloids gearbox system allowing a variable speed at the input shaft and delivering a constant speed at the output shaft is proposed herein. The gearing system consists of an assembly of spur and ring gears run and controlled by an electrical motor. The system acts as a continuously variable transmission (CVT) between the wind turbine hub and the electricity generator which requires an entry speed corresponding to an electrical grid frequency of 60 Hz. The active gearing system is designed using CAD software, and the gearing design theory is used to dimension the proposed epicycloids system. The kinematic gearing theory is used to establish the different gearing ratios of the system, and the kinematic velocity relationships between the gearing system stages. The forces and torques acting on the gearing system are computed using the equilibrium equations. Ideally, the electrical power consumed by the regulating motor system is minimal so that a maximum percentage of the generated electrical power is supplied to the electricity grid. The advantage of this gearbox configuration is that the power consumed by the regulating motor will be theoretically close to zero when the wind speed is about 10.5 mph, which is the average wind speed for many areas where wind turbines are installed. As the wind speed moves away from its mentioned average, the gearbox electrical controls activate a regulating motor to secure a constant speed at the generator input. Currently, a prototype of the proposed system is under tests and experimental data has already shown the constancy of the angular velocity at the generator input. The measurements of the mechanical power distribution between the different components of the system are still underway. A prony-break system is currently used for this purpose. It is expected that within a defined range of the hub angular velocities, the power absorbed by the regulating motor remains a small fraction of the power delivered by the electricity generator.
Design Optimization Method for MR-Brake Actuators
Authors: Erol Ozan G. , Gurocak Hakan , Gonenc Berk
Published: August 2012

MR-brakes work by varying viscosity of a magnetorheological (MR) fluid inside the brake. This electronically controllable viscosity leads to variable friction torque generated by the actuator. A properly designed MR-brake can have a high torque-to-volume ratio which is quite desirable for an actuator. However, designing an MR-brake is a complex process as there are many parameters involved in the design which can affect the size and torque output significantly. The contribution of this study is a new design approach that combines the Taguchi design of experiments method with parameterized finite element analysis for optimization. Unlike the typical multivariate optimization methods, this approach can identify the dominant parameters of the design and allows the designer to only explore their interactions during the optimization process. This unique feature reduces the size of the search space and the time it takes to find an optimal solution. It normally takes about a week to design an MR-brake manually. Our interactive method allows the designer to finish the design in about two minutes. In this paper, we first present the details of the MR-brake design problem. This is followed by the details of our new approach. Next, we show how to design an MR-brake using this method. Prototype of a new brake was fabricated. Results of experiments with the prototype brake are very encouraging and are in close agreement with the theoretical performance predictions.
Multifield Analysis of a Piezoelectric Valveless Micropump
Authors: Sayar Ersin , Farouk Bakhtier
Published: August 2012

Coupled multifield analysis of piezoelectrically actuated valveless-micropump MEMS devices are carried out for liquid transport applications. We consider the three-way coupling between electrical, mechanical and fluidic fields in such systems where actuator deflection causes fluid flow through a micropump. Flow contraction and expansion (through a nozzle and a diffuser respectively) generates net fluid flow as the bilayer structural-piezoelectric membrane of the actuator deflects. The analysis involves structural and fluid field couplings in a sequential structural-fluid analysis of the microfluidic device. The effect of the driving voltage on silicon-PZT-5A membrane deflection and flow rate through the inlet/outlet is investigated via time averaging the predicted instantaneous velocity fields. At low actuation frequencies (below 10 kHz), the excitation voltage is a dominant factor on the flow rate of the micropump. The pressure, velocity and flow rate prediction models developed in the present study can be utilized to optimize the design of MEMS based micropumps.
Visualization and Characterization of the Flashing Spray of Cryogen R404a
Authors: Zhou Z.-F. , Wu W.-T. , Chen B. , Guo L.-J. , Wang Y.-S. , Wang G.-X.
Published: August 2012

Flashing spray of volatile liquids is a common phenomenon observed in many industrial applications such as fuel injection of engines, accidental release of flammable and toxic pressure-liquefied gases, failure of a vessel or pipe in the form of a small hole in chemical industry, and cryogenic spray cooling in laser dermatology. In flashing spray, the volatile liquid is depressurized rapidly at the exit of a nozzle (or a hole in a vessel) and becomes superheated. Such superheated liquid (in the form of either a jet or droplets) leads to explosive atomization, leading to fine droplet sizes and a short spray distance. This paper presents an experimental investigation of flashing spray of cryogen R404a. A photographic study of the spray is first conducted, providing visualization of spray formation and showing the dynamic characteristics of the spray. Then the R404a short spray is characterized by the phase Doppler particle analyzer (PDPA). The PDPA measurements provide the distributions of the diameter and velocities of liquid droplets in the spray., showing the dramatic dynamic variation of the liquid droplets due to explosive atomization of large droplets in the region near the exit of nozzle. The data finds that the average droplet axial velocity increases first to a maximum, followed by a gradual decrease, a typical variation expected for flashing spray. During the same time period, the average droplet diameter shows a quick decrease, from early large droplets of about 30 microns in diameter to fine droplet with about 10 microns within about 40 mm spray distance. This study provides quantitative data on droplet velocity and diameter in flashing spray, useful for model validation. The qualitative results help to have a better understanding of the flashing spray atomization mechanisms for volatile cryogens.
Interfacial Fracture Strength Measurement of Tissue-Biomaterial Systems
Authors: Khandaker M. P. H. , Li Yanling , Tarantini Stefano
Published: August 2012

The interfacial mechanics at the bone-implant interface is a critical issue for implant fixation and the filling of bone defects created by tumors and/or their excision. The present study is based on the hypothesis that the differences of the surface roughness at bone/ implant interface due to incorporation of micro and nano nanoparticle additives may have significant influence on the quality of bone/implant union. This research studied poly Methyl MethAcrylate (PMMA) bone cement with and without MgO additives as different implant materials. The aims of this research were to determine the influences of a magnesium oxide (MgO) additive particle size to PMMA bone cement on the bonding strength between bone and bone cement specimens. The scope of work for this study were: (1) to quantify elastic properties (Young’s modulus and Poisson’s ratio) of bone cement specimens, (2) to determine whether inclusion of MgO particles with PMMA has any influence on the interface strength between bone and PMMA, and (3) to quantify the effect of surface roughness on the interface fracture strength between bone and PMMA. This study found that the mean interface strength for bone-PMMA is significantly less than the mean interface strengths of bone-PMMA with microsize MgO particles and bone-PMMA with nanosize MgO particles.