bluuebunny/crossref_metadata_2025 huggingface dataset:
Life Cycle Impacts and External Costs for Various Hydrogen Pathways
Authors: Tupper Kendra , Kreider Jan F.
Published: October 2008

Hydrogen is an energy vector of considerable recent interest because of its perceived environmental benignity. Aspects of the hydrogen economy are addressed in this article by quantifying associated impacts and costs. For the first time, important questions are addressed in a comprehensive way. Impact assessments and external cost analyses investigate whether hydrogen should replace standard fuels and which production technologies are preferred. Finally, the life cycle stages of that contribute the largest impacts are identified. If external costs are to be minimized in the operation of a U.S. hydrogen economy, it is recommended that hydrogen (H2) be produced from solar thermochemical (STC) cycles and wind electrolysis, with the possible use of steam methane reforming (SMR). The external costs associated with biomass gasification are shown to be comparable with those for wind electrolysis. Thus, biomass-produced hydrogen could also be a viable alternative, especially in areas ideally suited to the growth of energy crops. Finally, the most influential life cycle stages are the Construction of the Fuel Cell Vehicle (FCV) and Hydrogen Production (except for the environmentally benign wind electrolysis). For the wind/electrolysis case, the majority of impacts come from plant construction.
Influence Factors of Energy Consumption in All Cold Outdoor Air Systems
Authors: Wei Bing , Li Li , Lu Jiang , Zong Luxiang , Wang Zhiwei
Published: October 2008

Nowadays the safety of the air conditioning systems is paid more attention to. All cold outdoor air systems due to their particular advantages such as credible safety, better indoor air quality, saving more building space and being in favor of the energy conservation in some given conditions [1] are discussed in this paper. The composing of all cold outdoor air system is outlined and the mathematical models of energy consumption evaluation are presented. With an actual example by using the method of equivalent weight full load operation time, the influence factors to the annual primary energy consumptions in all cold outdoor air systems, such as: the dew point temperature, the COP (Coefficient of Performance) of chiller, the equivalent weight full load operation time of chiller and the efficiency of enthalpy exchanger etc. are compared and analyzed. And the optimal application modes for energy conservation of all cold outdoor air systems are proposed. These can be good references for the application of all cold outdoor air systems.
The Indoor Thermal Environment Simulation and Analysis of an Emporium With Atrium
Authors: Wei Bing , Gao Yuefen , Wang Xiangning , Wang Zhiwei , Li Li
Published: October 2008

In most emporiums with atrium the phenomena of vertical temperature nonuniformity are very severe, especially in winter. In this paper with an example of emporium with atrium the actual data are measured and by using the method of CFD simulation the indoor thermal environment of the atrium and surrounding area are simulated. The three-dimensional flow fields are studied, the temperature and velocity fields under different air flow organization modes are gained, the effect of the atrium to the whole building is discussed and the corresponding correction method to the indoor space loads, especially the space loads in the upper and lower stories are proposed. The results above will be good references for the design of the emporiums with atrium. The use of the correction method will help to obtain a comfortable and stable indoor thermal environment, and also will be good to the building energy conservation.
Hybrid Solar Lighting May Have Another Utility: Solar Water Heating
Authors: Zemke Peter E. , Wood Byard D.
Published: October 2008

Hybrid solar lighting (HSL) has been successfully demonstrated as a means of collecting sunlight and transferring it through optical fibers into a building. The collected solar energy is primarily intended for illumination purposes. However, this technology may have an application in solar water heating. For a traditional solar water heating system, energy is required to pump the water to the roof and collected solar energy is lost to the environment through the collector and plumbing. If such a system is to be used in climates where the temperature falls below freezing, complexity is added resulting in lower system efficiencies. If, rather than pumping water to the roof to absorb solar energy, the solar radiation is “piped” into the hot water store, a solar water heating system may be much less complex and potentially more efficient. HSL technology can be used to collect solar radiation and transport it through optical fibers into a hot water store. Since the water remains in the tank, it is not exposed to freezing temperatures and heat loss through plumbing. The efficiency of the system would not be dependent on the outside temperature or the temperature of the water as traditional systems are, but solely on the efficiency in which solar radiation is transferred into the water. This paper will outline the major advantages of using HSL technology for solar water heating over traditional systems. The approximate efficiencies of a flat-plate collector, 2-axis solar tracking collector, and a system using HSL technology are compared using F-Chart for locations in the Southwestern and Northeastern United States. It is shown that improvements in efficiency are obtained using HSL technology if the system is capable of collecting and transferring the visible and infrared spectrum of solar radiation.
Economic Evaluation of a Solid Adsorption Solar Refrigerator
Authors: Anyanwu Emmanuel E. , Ogueke Nnamdi V.
Published: October 2008

A procedure is developed for assessing the economic viability of a solid adsorption solar refrigerator in terms of its life cycle saving over a conventional vapour compression refrigerator. The life cycle saving is expressed in generalized form. Economic factors considered include property tax rate, inflation rate, banks interest rate and yearly rate of increase of energy and maintenance cost. Results obtained indicate that the first cost of the solid adsorption solar refrigerator is usually quite high. However over time, the investment in it will be justified, especially in regions with high insolation level without grid connected electricity.
Mathematical Simulation of a Solar Bi-Ejector Refrigeration System
Authors: Zhang Bo , Dong Jianhua , Shen Shengqiang
Published: October 2008

This paper presents a mathematical simulation of the dynamic thermal behavior of an innovative solar bi-ejector refrigeration system with a capacity to produce cooling water. In the bi-ejector refrigeration system, the mechanical circulation pump is replaced by a vapor-liquid ejector, in order to further reduce the electricity consumption and reinforce the system feasibility. Freon R123 is the working fluid at condensing temperature of 30°C generating temperature of 85°C and evaporating temperature of 8°C The generator heat load is 10kW and an obtained evaporator cooling load is around 3kW. The whole year simulation results are presented.
Mathematical Modeling of Solar-Hydrogen System for Residential Applications
Authors: Deshmukh Sachin S. , Boehm Robert
Published: October 2008

A possible future approach to home and personal vehicle energy needs is to combine solar power generation on the structure with hydrogen production and use. In this paper, performance of a solar-hydrogen system for residential application is simulated. Included in the main components of the solar-hydrogen system are photovoltaic panels, electrolyzer, fuel cell, compressor, and storage tank. The solar-hydrogen system is assumed to be installed on the standard house (1600 sq ft), to be a part of a grid-connected system where the house can receive energy from both grid as well as PV panels and fuel cell based on the energy requirements of the house. Using yearly weather data for Las Vegas, net grid interaction as well as stand alone (off grid) performance is considered as part of the analysis. The effect of component sizing aspects is examined.
Solar Tubular Reformer With Molten-Salt Thermal Storage: Design Modification of the Reactor Tube and Testing
Authors: Kodama Tatsuya , Hatamachi Tsuyoshi , Nakano Daisuke , Igarashi Youhei , Gokon Nobuyuki
Published: October 2008

For thermal storage in solar tubular reformers, high-temperature composite materials with alkali carbonate and magnesia have been examined. The new concept of “double-walled reactor tube” was previously proposed to use in solar tubular reformers, which involves storing the molten-salt/ceramic composite material in the annular regions between an internal catalyst tube and the exterior solar absorber wall. The shape and structure of the reactor tube can be modified to match with design of a solar tubular reformer. In this paper, the interior structure of the reactor tube has been modified for use in cavity-type reformers using straight reactor tubes. The Na2CO3, K2CO3 and Li2CO3 composite materials with magnesia were prepared, and tested on heat-discharge mode performances for CO2 reforming of methane in the modified reactor tube of a laboratory scale.
Interrelations of Hourly and Daily Global Illuminance
Authors: Ravikumar P.
Published: October 2008

It has been found that the values of ratio of hourly global illuminance to daily global illuminance, rvt, are very close to the corresponding values for global solar radiation, rt, examined from the measured data of six IDMP [1] (International Day light Measurement Programme) locations. This has been further confirmed by examining the values for rvt and rt as calculated from TMY2 [2] (Typical Metrological Year) data base for primary locations. Based on this, it has been proposed that the correlations available in literature to predict rt can be employed to predict rvt. Adequacy of the correlation due to Collares-Pereira and Rabl [3] available for rt has been examined to predict rvt as obtained from TMY2 data base for the 56 primary locations. It has been found that the values of rvt obtained from measured illuminance data of six locations have been predicted within a rms difference of 2.71% and within a rms difference of 4.3% for the 56 primary locations of TMY2 data when the correlation due to Collares-Pereira and Rabl for rt has been employed.
Ray Trace Analysis for Concentrating Sunlight Onto an Optical Fiber Bundle
Authors: Sadasivuni Cherishma , Dye Dan , Wood Byard
Published: October 2008

A two-axis concentrating solar collector/receiver is being designed to concentrate visible solar irradiance and distribute it inside a building for daylighting via a bundle of polymer optical fibers. This paper is concerned with the optics that will provide uniform illuminance of the visible spectrum on the entrance of the fiber optic bundle. A fiber optic bundle made of 3mm diameter fibers and a non-imaging device along with the solar collector’s primary and secondary mirrors has been modeled in a ray-tracing software package, TracePro 3.3. Fiber optic bundles of two different geometries were considered, viz. a square bundle with 225 fibers and a round bundle consisting of 126 fibers. The purpose of this research is to determine the optimum length of the non-imaging device that could provide uniform illuminance on the entrance area of the fiber optic bundles. Sensitivity analyses are conducted to see the variations in the output due to different possible off-set conditions, such as distance between the primary and the secondary mirror, the secondary mirror off-set from the primary mirror optical axis, and misalignment due to tracking error. The results of the sensitivity analyses are presented, and recommendations are made for the design of the non-imaging device. It is shown that the square non-imaging device and fiber bundle is superior to the round non-imaging device and fiber bundle.
Early Results From the Long-Term Testing of Inverters
Authors: Lynn Kevin , Wilson William
Published: October 2008

The Florida Solar Energy Center (FSEC) has partnered with Sandia National Laboratories (SNL), the Southwest Technical Development Institute (SWTDI), and the California Energy Commissions Public Interest Energy Research (CEC PIER) in an effort to characterize the performance of PV inverters operating over extended periods of time. As part of this characterization, SNL executed an initial performance characterization in the laboratory to be repeated at one or two year intervals. These inverters were then sent distributed to the above test facilities for installation and long-term testing. To perform this long-term testing, FSEC built an inverter test facility made up of a configurable 10.1 kW PV array and four test beds. Each test bed was set up to monitor the following parameters: DC voltage, DC current, AC Voltage, AC Power and inverter temperature. Solar irradiance, ambient temperature, and several PV array temperatures were recorded by a separate, synchronized datalogger. Three inverters are currently being tested: the Fronius IG 3000, the Xantrex GT 3.0, and the SMA Sunny Boy 2500U. The three inverters were loaded with a PV array close to the maximum power limit allowed by the inverter, and the array power supplied to each inverter was within 100 W of one another. Since the PV array for each inverter used identical PV modules mounted in the same orientation, it was easier to develop a model to compare inverter performance based on energy output. In addition to energy output, other parameters were obtained such as inverter efficiency. An attempt was made to compare the results obtained at FSEC to those results compiled by the California Energy Commission.
A Review of PV System Performance and Life-Cycle Costs for the SunSmart Schools Program
Authors: Lynn Kevin , Szaro Jennifer , Wilson William , Healey Michael
Published: October 2008

In January of 2003, the Florida Department of Environmental Protection/Florida Energy Office (DEP/FEO) allocated $600,000 in hardware funds toward the installation of photovoltaic (PV) solar systems on Florida schools. As a result of this program, grid-connected PV systems less than six kilowatts in size were installed on 29 schools in the State of Florida. The Florida Solar Energy Center (FSEC) has monitored these systems for approximately one year of operation. The performance of 28 of these systems was analyzed using standard performance parameters such as the performance ratio, PV array efficiency, inverter efficiency, and PV system efficiency. In addition, a life-cycle cost analysis was conducted using new cost data values and updated market assumptions. These data will serve as a benchmark to compare against future systems with respect to performance vs. installed system cost.
Thermodynamic Analysis of Mixed-Metal Ferrites for Hydrogen Production by Two-Step Water Splitting
Authors: Allendorf Mark D. , Diver Richard B. , Miller James E. , Siegel Nathan P.
Published: October 2008

A thermodynamic analysis of the two-step water splitting process for the production of hydrogen is reported in this paper. Calculations simulating the preparation of ferrite samples, their thermal reduction to form a mixture of metal oxides, and subsequent reoxidation with steam to produce hydrogen were performed. Mixed-metal spinel ferrites of the general form MFe2O4, where M = Co, Ni, or Zn, are compared with iron spinel, Fe3O4. The results indicate that of the four ferrites examined, nickel spinel has the most favorable combination of properties for use in two-step water splitting.
Efficient Solar Thermal Processes From Carbon Based to Carbon Free Hydrogen Production
Authors: Sattler Christian , Roeb Martin , Monnerie Nathalie , Graf Daniela , Mo¨ller Stephan
Published: October 2008

The potential of hydrogen to be the energy carrier of the future is widely accepted. Today more than 90% of hydrogen is produced by cost effective technologies from fossil sources mainly by steam reforming of natural gas and coal gasification. But hydrogen is not important as an energy carrier yet — it is mainly a chemical. To finally benefit from hydrogen as a fuel it has to be produced greenhouse gas free in large quantities. Therefore these two tasks have to be connected by a strategy incorporating transition steps. Solar thermal processes have the potential to be the most effective alternatives for large scale hydrogen production in the future. Therefore high temperature solar technologies are under development for the different steps on the stair to renewable hydrogen. This paper discusses the strategy based on the efficiencies of the chosen solar processes incorporating carbonaceous materials as well as processes based on water splitting. And the availability of the technologies. A comparison with the most common industrial processes shall demonstrate which endeavors have to be done to establish renewable hydrogen as a fuel.
Experimental Analysis of Heat Transfer From Ice Rink Floors
Authors: Mun Jung , Krarti Moncef
Published: October 2008

This paper describes an experimental set-up to evaluate the refrigeration loads for ice rink floors under controlled conditions. The ice-rink set-up was instrumented to measure the temperatures along various locations within the ice-rink floor including the water/ice layer. In addition, the energy used to freeze the water is monitored over the entire charging cycle to evaluate the performance of the ice rink floor for various insulation thermal resistance values (or R-values). Four floor insulation configurations are considered in the experimental analysis of R-0 (no insulation), R-4.2, R-6.7 and R-10 (in IP unit: hr.ft2.°F/Btu). The impact of the air temperature above the ice rink is also evaluated. The experimental results confirm that the addition of the thermal insulation beneath the ice-rink floor reduces the refrigeration load, decreased the time required to freeze the water above the ice rink, and helps maintain lower average ice temperature.
Impact of Shape on Building Energy Use in Tunisia
Authors: Ouertani Kais , Krarti Moncef
Published: October 2008

This paper investigates the impact of the architectural form on the energy performance of residential buildings in Tunisia. A relative compactness is defined as one indicator of a building shape. The results of the analysis indicate that a significant decrease in heating and cooling energy requirements can be obtained by minimizing the relative compactness of detached residential houses. A simplified analysis tool, suitable for early design process, is developed to assess the impact of building form on its energy performance for several cities in Tunisia.
PV Operated HVAC for Southwest States
Authors: McCabe Joseph
Published: October 2008

This report analyzes energy usage and associated utility capacity requirements for compressor based air-conditioning compared to evaporative cooling supplied by electricity from photovoltaics (PV). Two novel scenarios are presented, two stage evaporative coolers with grid tied PV, and two stage evaporated coolers supplied with direct current (DC) electricity from PV. The two scenarios are complimentary; where a grid tied system can tap DC for air-conditioning purposes (see Figure 1). 8% PV system gains can be achieved by eliminating the inverter for powering such a DC heating, ventilating and air-conditioning (HVAC) system. A PV system directly coupled to high efficiency evaporative cooler can remove the air-conditioner peak demand from a utilities load profile. Typical cities energy comparisons are presented. Incentive and public goods programs are not necessarily designed for this optimized, direct utilization of DC approach.
Video Scanning Hartmann Optical Testing of State-of-the-Art Parabolic Trough Concentrators
Authors: Wendelin Tim , May Ken , Gee Randy
Published: October 2008

Significant progress has been made recently in solar parabolic trough technology development and deployment. Part of this success is due to the changing world energy scenario and the recognition that viable renewable energy technologies can play a role in supplying world energy needs. Part is also due to ongoing collaborative efforts by industry and the Department of Energy’s (DOE) Concentrating Solar Power Program (CSP) to enhance the state of the technology in terms of both cost and performance. Currently, there are two trough concentrator projects which the DOE CSP program is supporting. One company, Solargenix, is developing a design to be used in a 64MW plant outside of Boulder City, Nevada. This design is based on the original LUZ LS-2 trough concentrators employed at the Solar Electric Generating Systems (SEGS) plants in Southern California. Another company, Industrial Solar Technology (IST), is working on a scale-up of their design used historically for process heat applications. Very different from the LS-2 approach, this design is still in the research and development stages. One way in which the DOE CSP parabolic trough program assists industry is by providing optical testing and qualification of their concentrator designs. This paper describes the Video Scanning Hartmann Optical Test System (VSHOT) used to optically test both of these designs. The paper also presents the results of tests performed in the past year and what impact the testing has had on the developmental direction of each design.
Fabrication and Characterization of High Temperature Resin/Carbon Nanofiller Composites
Authors: Ghose Sayata , Watson Kent A. , Elliott Holly A. , Working Dennis C. , Criss Jim M. , Dudley Kenneth L. , Siochi Emilie J. , Connell John W.
Published: October 2008

As part of ongoing efforts to develop multifunctional advanced composites, blends of PETI-330 with multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNF) were prepared and characterized. The effect of nanofiller loading level on melt viscosity was determined. The resulting powders were characterized for degree of mixing, thermal, and rheological properties. Select samples were scaled up for processing and continuous strands of nanocomposites were extruded. Based on the characterization results, samples containing 10 and 15 wt% MWCNT and 30 and 40 wt% CNF were scaled up to ∼300 g and used to fabricate moldings 10.2 cm × 15.2 cm × 0.32 cm in size. The moldings were fabricated by injecting the mixtures at 260–280 °C into a stainless steel tool followed by curing for 1 h at 371 °C. The tool was designed to impart substantial shear during the injection process in an attempt to achieve some alignment of nanofillers in the flow direction. Moldings were obtained that were subsequently characterized for thermal, mechanical, electrical and EMI shielding properties. The degree of dispersion and alignment of nanofillers were investigated using high-resolution scanning electron microscopy. Preparation and preliminary characterization of PETI-330/MWCNT and PETI-330/CNF composites will be discussed.
AFM Capabilities in Characterization of Particle Nanocomposites: From Angstroms to Microns
Authors: West Paul , Starostina Natasha
Published: October 2008

Scanning Probe Microscopy has been routinely employed as a surface characterization technique for nearly 20 years. Atomic Force Microscopy, the most widely used subset of SPM, can be performed in ambient conditions with minimum sample preparation. AFM is able to measure three-dimensional topography information from the angstrom level to the micron scale, with unprecedented resolution. This paper reviews the most common examples of nanoparticle composite evaluation with an AFM. AFM is well suited for dispersion strengthened composite characterization. A standard set of measured parameters includes: volume, In general, AFM nanocomposite characterization is both cost and time effective, as well as easier to use than electron microscopy. The resolution of AFM is greater than or comparable to SEM/TEM, and the strong advantages of AFM for nanoparticle composite characterization include morphology measurement along with direct measurements of height, volume and 3D display.
Characterization of Polyaniline Nanocomposite Using AC Electrochemical Impedance Spectroscopy
Authors: Hu Jianxun , Wang Dongyan
Published: October 2008

Silicate minerals have been found to improve physical and mechanical properties of polymers significantly through clay/polymer nanocomposites. This class of materials uses smectite-type clays, such as hectorite, montmorillonite, magadiite, and synthetic mica, as fillers to enhance the properties of polymers. One of the most important properties of smectite-type clays is their layered structure, in which each layer is constructed from tetrahedrally coordinated Si atoms fused into an edge-shared octahedral plane of either Al(OH)3 or Mg(OH)2. The layers exhibit excellent mechanical properties parallel to the layer direction due to the nature of the bonding between these atoms. It has been found that Young’s modulus in the layer direction is 50 to 400 times higher than that of a typical polymer [1–5]. The layers have a high aspect ratio and each one is approximately 1 nm thick, while the diameter may vary from 30 nm to several microns or larger. Hundreds or thousands of these layers are stacked together with weak van der Waals forces to form a clay particle. With such a configuration, it is possible to tailor clays into various different structures in polymer [1,6,7].
Characterizing Interfacial Friction Damping in Nano-Composite Materials
Authors: Koratkar Nikhil
Published: October 2008

Purified multiwalled carbon nanotubes are dispersed in polycarbonate matrices using a novel solution mixing technique and dynamic load tests are performed to characterize the storage and loss modulus. Tests are also performed with pristine polycarbonate (no carbon fillers), to compare the response of the two materials. The test results indicate that as the strain amplitude is increased, the storage modulus decreases in conjunction with an increase in the loss modulus. This suggests that at large strain levels the adhesion between the nanotubes and polymer is not strong enough to prevent interfacial slip, resulting in frictional sliding at the tube-polymer interfaces. This debonding at the filler-matrix interface is responsible for the observed decrease in storage modulus and increase in loss modulus. The nanotube-polymer sliding energy dissipation mechanism shows potential to reliably and efficiently deliver high levels of structural damping to polymer structures.
The Concept of Strain Tensor at Atomic Level
Authors: Pyrz Ryszard
Published: October 2008

An atomic strain concept is formulated that allows calculation of continuum quantities directly within a discrete atomic (molecular) system. The concept is based on the Voronoi tessellation of the molecular system and calculation of atomic site strains, which connects continuum variables and atomic quantities when the later are averaged over a sufficiently large volume treated as a point of the continuum body. The atomic strain tensor is applied to investigate deformation of regular and disordered molecular systems. It is shown that disordered systems exhibit significant non-affine deformations which can be captured by a proper correction of the strain tensor.
Critical Issues and Application Potentials in Nanofluids Research
Authors: Kostic Milivoje M.
Published: October 2008

Development of many industrial and new technologies is limited by existing thermal management, and need for high-performance cooling. Nanofluids, stable colloidal mixtures of nanoparticles (including nanofibers and functional nanocomposites) in common fluids, have a potential to meet these and many other challenges. Colloidal nano-mixtures with functionally-stable and active-like nanostructures that may self-adjust to the process conditions, require systematic surface-chemistry study and enhancements (coatings with functional layers, surfactants, etc), in addition to investigation of thermo-physical characteristics and phenomena. A comprehensive, systematic and interdisciplinary experimental research program is necessary to study, understand and resolve critical issues in nanofluids research to date. The research must focus on both synthesis and a careful exploration of thermo-physical characteristics. Development of new-hybrid, drag-reducing nanofluids may lead to enhanced flow and heat transfer characteristics. The nanoparticles in these fluids yield increased heat-transfer while the long-chain polymers are expected to enhance flow properties, including active and functional interactions with nanoparticles, thus providing potential for many applications yet to be developed and optimized.
Structural Damping Enhancement of Nanocomposites With Engineered Vapor Grown Carbon Nanofiber Paper
Authors: Gou Jihua , Gu Haichang , Song Gangbing
Published: October 2008

Due to their nanometer size and low density, the surface area to mass ratio of carbon nanotubes and carbon nanofibers is extremely large. In addition, the large aspect ratio and high elastic modulus of carbon nanotubes and carbon nanofibers allow for large differences in strain between the constituents in the nanocomposites, which could enhance the interfacial energy dissipation ability. While there are many reported benefits of carbon nanotubes and carbon nanofibers in the nanocomposites, the potential of carbon nanotubes and carbon nanofibers to enhance the structural damping properties of nanocomposites has not been fully explored. This paper presents a novel process to manufacture multifunctional and cost-effective hybrid nanocomposites through integrating engineered carbon nanofiber paper into traditional fiber reinforced composites to improve the structural damping properties. The vacuum-assisted resin transfer molding (VARTM) process was employed to fabricate the nanocomposites by using engineered carbon nanofiber papers as inter-layers or surface layers of traditional composite laminates. To characterize the structural damping properties, the influence of frequency dependence was analyzed through the experiments conducted using the nanocomposite beams. It was found that there is up to 200–700% increase of the damping ratios at higher frequencies. It was found that the connectivities between carbon nanofibers and short glass fibers within the carbon nanofiber paper were responsible for the significant energy dissipation in the nanocomposites during structural vibration applications.
Minimization of Through Thickness Flaws in Tungsten-Doped Diamond Like Carbon Thin Film
Authors: Abou-Hanna Jeries , Lozano Jose´ , Abuzaid Wael , Gaikwad Raghu , Carlson John
Published: October 2008

Tungsten-doped diamond-like carbon (DLC) coatings have been magnetron sputtered onto 52100 steel with chromium and chromium/tungsten carbide dual interlayers. The surface finish (Ra) of the substrate before deposition was 0.102 to 0.203 μm for a set of blocks and 0.05 to 0.10 μm for another set of samples, called buttons. SEM and TEM analyses revealed that this substrate finish as well as surface contaminants resulted in the formation of significant size flaws that develop during the deposition process through the film thickness. On the other hand a perfect flawless film was seen with the smooth substrate in the coupons. It was also observed that the film amplifies the substrate roughness. These two findings impact the tribological performance of the film. Current efforts attempted to determine an optimum set of deposition parameters, such as temperature and buffering gas pressure that would minimize or eliminate the formation of such flaws, and consequently minimize the roughness of the film surface.
Electro-Machining (EM) Using Metal Coated Atomic Force Microscope Tip and Single-Walled Carbon Nanotube Buckypaper Films
Authors: Park Jin Gyu , Liu Qing , Zhang Chuck , Liang Richard , Wang Ben , Pignatiello Joseph , McBrearty Kevin , Wysk Richard A. , Cohen Paul H. , Brooks James
Published: October 2008

Using metal-coated atomic force microscope (AFM) tips and single-walled carbon nanotube (SWNT) BuckyPaper films, the authors have successfully explored the feasibility of electro-machining (EM) at the nanometer scale. Highly ordered pyrolytic graphite (HOPG) and thin metal films were used as a substrate (workpiece) and metal-coated (Cr/Au) Si AFM tips and BuckyPaper films were used as electrodes. A negative voltage pulse was applied to the AFM tip to fabricate holes as small as 30 nm in diameter on the HOPG surface. Using SWNT BuckyPaper films, the submicron holes were fabricated on a metal surface, demonstrating that SWNTs can work as electrodes.
A Shear-Lag Model for Nanotube-Reinforced Composite Systems Under Transient Heat Transfer
Authors: Salehi-Khojin Amin , Jalili Nader
Published: October 2008

Understanding the stress transfer between nanotube reinforcements and matrix is an important factor in determining the overall mechanical properties of nanotube-reinforced composites. The classical shear-lag model in which the fiber and the matrix are equally long can not be applied to nanotube-based composite structures. Recently, a shear-lag model under mechanical loading for a concentric composite cylinder embedded with a capped nanotube has been introduced as the representative volume element (RVE). In this study, using similar approach the shear lag model is extended for a system under both mechanical and thermal loadings. The outer surface of RVE is prescribed to heating and cooling conditions, and transient heat transfer concept is used to find the temperature distribution in the matrix and on the surface of the nanotube. Using constitutive, geometrical and equilibrium equations for a given RVE, new shear-lag model for a nanotube-reinforced composite is then derived. It is demonstrated that the proposed model at room temperature could reduce to the same results obtained previously. These equations can be used to predict the mechanical properties of nanocomposite systems in real applications.
Mechanical Performance of Matrix Filled Single-Walled Carbon Nanotube Reinforced Nanocomposites
Authors: Askari Davood , Ghasemi-Nejhad Mehrdad N.
Published: October 2008

Carbon nanotubes have been used as an additional reinforcement to enhance mechanical, thermal, and electrical properties of the structural composites. Thus, it is very important to investigate the mechanical behaviour of such nanocomposites when they undergo external load. In this paper, first, analytical exact solution for effective longitudinal Young’s modulus of a generally orthotropic 3-phase nanocomposite cylinder, representing the 3-dimentional model of a filled single-walled carbon nanotube embedded in another host material is formulated and then used to obtain the analytical exact solutions for displacements, strains, and stress distributions throughout the entire tubular structure corresponding to an axially applied load. The materials of all three cylinders constructing the 3-phase nanocomposite cylinder are considered to be cylindrically generally orthotropic. Next, analytical solutions are examined for a particular cylindrical geometry and material properties. Results are obtained through the thickness of the tubes, i.e., through the radius, and then discussed. To verify the analytical exact solutions, a 3-dimentional finite element analysis of an identical 3-phase nanocomposite structure is performed and some of the results are compared to those obtained analytically. Excellent agreement is achieved validating our analytical solutions.
Nano-Scale Stress: From Discrete to Continuum
Authors: Schjo̸dt-Thomsen Jan , Pyrz Ryszard
Published: October 2008

The present work deals with a stress measure derived from a general atomic force field. Usually, stresses at atomic level are determined through the Clausius virial theorem for a fixed volume containing interacting particles. The present stress is derived on the basis of the first Brillouin zone, or equivalently the Voronoi cell, surrounding the atom. Thus, this is the smallest scale at which the stress measure makes sense. Obviously, the stress is discrete in nature since the Voronoi cells are discrete. In order for the stress to become continuous the finite element formalism is used in terms of interpolation functions from 3D Voronoi elements. The present stress measure is non-local, it is not necessarily symmetric in its indices and incorporates micro-deformations.
Zeta Potential Studies of Titanium Dioxide and Silver Nanoparticle Composites in Water-Based Colloidal Suspension
Authors: Azouri Assaf , Ge Ming , Xun Kun , Sattler Klaus , Lichwa Joe , Ray Chittaranjan
Published: October 2008

We determine the zeta potential (ZP) by using electrophoretic laser light scattering and Laser Doppler Velocimetry (LDV). Particle sizes are measured by photon correlation spectroscopy (PCS). We studied the ZP for colloidal suspensions of TiO2 and Ag metal particles in order to determine the kinetic interaction and charge exchange between the particles. We investigated the natural tendency of the particles for aggregation and varied the pH of the solution. It was found that the ZP versus pH curve for the mixed TiO2/Ag did not behave as the average of the individual TiO2 and Ag curves as one would expect, and instead there was a slight horizontal shift towards higher pH values which implies that the particles in the mixed TiO2/Ag colloid are interacting with the result of charge exchange. The average particle size was measured in terms of effective diameter, for the TiO2, Ag and the mixed TiO2/Ag particles. The results indicated an increase of approximately 100 nm in the effective diameter of the mixed TiO2/Ag particles size compared to the size of the individual TiO2 particles. This can be explained as the fact that 50 nm Ag particles are adsorbed on the surface of the TiO2 particles.
Colloidal Stability of Nanosoil/Nanofiber Aqueous Suspensions From Natural Environment in Hawaii
Authors: Azouri Assaf , Ge Ming , Xun Kun , Sattler Klaus , Lichwa Joe , Ray Chittaranjan
Published: October 2008

Nanoparticles from iron-oxide rich soil and nanofibers from bark of the plumeria tree in Hawaii have been studied using photon correlation spectroscopy (PCS). Particles with sizes of several hundred nanometers have been investigated in aqueous suspension. The zeta potentials have been determined as a function of pH for soil, fiber, and the soil/fiber mixture. It is found that all three suspensions have negative zeta potentials and no isoelectric point within the pH range from 4 to 11. This shows that the suspensions are stable over a wide range of conditions. Both soil and fiber samples have approximately constant zeta potentials within this range. However, the zeta potential changes significantly for the nanosoil/nanofiber mixture when the pH is varied. We conclude that the nanoparticles of soil and fiber interact in the suspension and that this depends on the pH value of the suspension.
Nanomodified Fibre Reinforced Polymer Composites and Adhesives: What Needs To Be Done?
Authors: Raja Manuri Venkata Gopalakrishna Rao
Published: October 2008

The discovery of C60 bucky balls by Richard E Smalley and team that won them the Nobel Prize 1996, and the pioneering work by Thomas Ebbesen and Pulickel M Ajayan from the lijima Lab, on bulk production of CNTs, paved the way to worldwide research, in nanotechnology. Studies of researchers like, Koral Schulte, F.H. Gojny and several others, resulted in nanotube modified epoxy composites with improved fracture toughness and stiffness properties. Ray Boughman and group’s work may be considered as the first in the direction of CNT modified fibrous composites, when they produced the toughest ever SWNTs from a PVA dope. Alan Windles and team carried out rapid production of continuous CNT fibres. All these efforts while laying the foundation for use of CNTs in composites of particulate type, strongly reveal a big gap to be filled by nanoscientists and engineers alike, in extending the use of CNTs in structural grade composites. In this paper, therefore, an attempt has been made, to highlight the above efforts and explicitly bring out, the need to focus on scientific and technological aspects pertinent to the Nanotube-modified FRP Composites and adhesives, recognizing that the best of CNTs for the structural–composites is yet to come.
Characterizations on Microscale Laser Dynamic Forming of Metal Foil
Authors: Cheng Gary J. , Pirzada Daniel
Published: October 2008

Laser dynamic forming (LDF) is a unique hybrid forming process, combining the advantages of laser shock peening, laser forming and metal forming, with an ultra high strain rate forming utilizing laser shock waves. In this paper, a hybrid forming technique based on laser dynamic forming will be demonstrated. The feasibility of laser dynamic forming will be discussed through experiments. The mechanical and microstructure of the formed 3D structures will be characterized. The grain microstructure and misorientation will be investigated quantitatively with Electron backscatter diffraction (EBSD). The residual stress distributions are measured using X-ray diffraction. We will describe the important factors that lead to improved micro-formability at high strain rate induced by high shock pressure. It is concluded that with further development, this may be an important microforming technology for various materials. LDF has great potential for meso-, micro- and nano scale forming since the laser provides high precision, highly-localized heating intensity, high repeatability, fast setup and superb flexibility.
Laser Cladding Based Solid Freeform Fabrication and Direct Metal Deposition
Authors: Qi Huan , Mazumder Jyotirmoy
Published: October 2008

Three-dimensional additive manufacturing or solid freeform fabrication (SFF) techniques, originated in the rapid fabrication of non-functional physical prototypes in polymers (Rapid Prototyping), have matured to the manufacture of functional prototypes, short-run production products, and now even advanced engineering designs. Laser-based material deposition or laser cladding has been used as a SFF technique, in which a laser beam is used as a precise high-energy thermal source to melt preplaced or pneumatically delivered metal powders and make solidified deposits on a substrate. By using laser cladding techniques, three-dimensional fully dense components can be built line-by-line and layer-by-layer directly from a CAD model with tailored material properties. Laser cladding is essentially a fusion and solidification (thermal) process, which involves complicated interactions between the laser beam, metal powders, the base material (substrate), and processing gases. Maintaining a stable and uniform melt pool during laser cladding is critical to produce dimensional accuracy and material integrity. An effective control of energy (laser power) spatial and temporal distributions in either an open-loop or closed-loop laser cladding process is essential to achieve the high quality results. This paper reviews, from a laser-material interaction point of view, various laser cladding based SFF processes, and particularly the direct metal deposition technique.
The Optimization of Variable Blank Holder Force for Sheet Metal Stamping
Authors: Wang Wu-Rong , Chen Guan-Long
Published: October 2008

This paper focuses on the research of blank holding force (BHF) and proposes a new strategy to optimize the variable BHF and determine the drawing limit under the variable BHF. The optimization strategy is based on the analysis of BHF formability window and integrated into FEM code to obtain time or/and spatial optimal BHF that applies on binders. And then a stepped rectangular box of 60 mm drawing height with segmented binders and a cylinder cup without die bottom are adopted to validate the optimization strategy. Firstly, constant BHF FEM simulations through careful experiment design are conducted to discover the drawing limit height under maximum constant BHF. Secondly, FEM simulation combining the new BHF optimization strategy is carried and the optimal profile of variable BHF is determined for both step box and cylinder cup during the whole punch stroke. The result shows this stepped box could be formed successfully using 5754-0 aluminum alloy sheet, while the maximum drawing height under constant BHF is 45mm. And the drawing limit of cylinder box under optimal BHF could reach the drawing height of 61mm, which is greatly increased comparing with maximum of 47mm under constant BHF. Finally, the constant BHF experiment and the derived trajectory of optimal BHF of both geometries are verified on a multipoint variable BHF hydraulic press and the experiment results correspond well with those of FEM simulation. This new BHF optimization strategy not only helps to determine time and spatial optimal BHF for known geometry, but also assists to design maximum drawing height for unknown geometry, which makes it an effective method.
Failure Prediction in Hydroforming of Pre-Bent HSLA Tube Using an Extended Stress-Based Forming Limit Curve
Authors: Sorine M. , Simha C. H. M. , van Riemsdijk I. , Worswick M. J.
Published: October 2008

This paper examines the prediction of failure during the hydroforming of pre-bent HSLA350 tubes using the Extended Stress-Based Forming Limit Curve (XSFLC) [1]. The process of obtaining a strain-based forming limit curve (ε-FLC) for the tube and its application to the prediction of failure in tube hydroforming, utilizing the XSFLC, is presented in detail. The XSFLC was obtained from ε-FLC that was calibrated using the results of free expansion tube burst tests. Tube bending and hydroforming experiments were carried out and modeled using the dynamic explicit finite element code, LS-DYNA. An LS-DYNA user subroutine that utilizes the XSFLC to predict the onset of necking was used to model the tube material. The predicted failure location and pressure at the onset of necking were found to be in a good agreement with the experimental results.
Investigation on Coining of Micro-Features Using Pure Copper
Authors: Kim Gap-Yong , Koc¸ Muammer , Ni Jun
Published: October 2008

Recently, applied research activities on the miniaturization of conventional forming processes have received attention in search for mass production methods for micro-scale metallic parts. This study investigated the coining of micro-features by numerical analyses and experiments. Prior to conducting the experiments, finite element simulation was used to understand the effects of channel aspect ratio, workpiece thickness, channel number, channel geometry, and friction on the coining process. Experiments using pure copper specimens were performed to confirm the findings from the simulation and to study the effects of preform shape and grain size. It was found that the channel depth, workpiece thickness, and channel geometry had a significant effect on the final load, while the channel number did not influence the final load. It was also concluded that certain preform shapes induce favorable flow of the material and result in enhanced formation of the micro-protrusions. For the conditions used in the experiments, however, effects from the grain size were not observed.
Manufacturing of Porous Coatings With Micro-Scale Features for Improved Boiling Heat Transfer
Authors: Chen Peng , Koc¸ Muammer , Ni Jun
Published: October 2008

Several recent heat transfer studies indicated that porous surfaces with modulated porous surface features lead to an improved boiling heat transfer efficiency. Thus, the aim of this study is to develop a novel manufacturing process that will produce the modulated porous surfaces cost-effectively. In this study, compaction and sintering experiment were conducted to investigate the consolidation performance of the powder into micro-scale features. The effects of compaction force and sintering on the pore size and mechanical strength of the formed micro-features were investigated. It was found that sintering at 800°C for 20 minutes can significantly increases the strength of the compacted part, while the interconnected pore structure was maintained.