bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Characterization of a Microscale Hydrogen Combustor Recuperator and Oil Heat Exchanger
Authors: Haley David B. , Narayanan Vinod
Published: August 2012

Experiments on a novel design of a microscale hydrogen combustor heat exchanger (μCHX) are presented. The experimental study demonstrates proof of concept for the design and examines the effect of varying selected fluidic and geometric conditions on the overall efficiency of the μCHX. A unit cell consisting of a combustion channel, a recuperator channel and an oil heat exchange channel is tested. This unit cell device has the potential to be scaled up to a reactor in the tens of kilowatts range required for practical heating applications. Combusted gases flow back through the device in a cross-flow configuration between the combustion channel and the oil channel, preheating the inlet gas stream and transferring heat to the oil. Platinum has been selectively deposited on the stainless steel inner wall of the combustion channel to facilitate heterogeneous combustion of hydrogen and air. The performance of the μCHX is characterized based on a global efficiency, defined as the ratio of the energy transferred to the oil stream compared to the energy rate of the supplied hydrogen gas. The effects of residence time, equivalence ratio, and average oil temperature, have been investigated. Hydrogen conversion rates in excess of 95 percent were achieved for residence times between 20–25 ms. Efficiencies in excess of 90 percent were obtained for equivalence ratios greater than 0.5 and for average oil temperatures between 63 °C and 105 °C. Experiments were also performed on two different lengths of catalyst with a higher efficiency being demonstrated by the catalyst with the longer length.
A Reliability-Based Energy Approach for Design Optimization of Blast Resistant Composites
Authors: Sheyka Michael P. , Kim Jung J. , Altunc Arife B. , Reda Taha Mahmoud M.
Published: August 2012

In the last three decades, significant efforts have been conducted for developing blast-resistant composites. Some of these efforts were focused on enhancing the stiffness and the strength of the composite materials. Here, an energy approach aiming at maximizing energy absorption in composite layers is used. The optimization is based on combining two materials A and B. While material A is strong, material B is ductile, thus a mechanism of energy reflection and absorption is developed within the composite layers. In this study, a simplified dynamic model is first developed to simulate the elastoplastic behavior of a composite plate subject to blast load. For an uncertain blast event, the probability of failure of each layer is evaluated using Monte Carlo method. By assigning a relatively high probability of failure (low target reliability index) of the energy absorbing layer and a relatively low probability of failure (high target reliability index) to the strong layer, the thickness of the composite layers is optimized. A case study for the design of a two layer composite plate made of Aluminum and Titanium subjected to an uncertain blast event is simulated and presented. A finite element model of the optimal Titanium and Aluminum composite plate is developed using explicit blast simulation to confirm the efficiency of the proposed design approach.
Nonlinear Flexural Modeling for Epoxy Resin Materials
Authors: Yekani Fard Masoud , Liu Yingtao , Chattopadhyay Aditi
Published: August 2012

Polymer composite structures are usually subjected to large flexural loadings, so the flexural behavior of these structures and their constituents are critical to their use. A novel approach for polymeric materials with strain softening model in tension and compression is developed to investigate the flexural behavior of Epon E 863. The tension and compression model consists of a bilinear ascending curve in pre-peak, strain softening followed by constant plastic flow in the post-peak response. The effects of softening localization on flexural response are considered. Local stress strain tension and compression responses, using digital image correlation system, are used for material characterization. Closed form expressions for flexural behavior are developed. The structural response of beams under three and four point bending and round plate on three symmetrical supports are studied experimentally and analytically. Results show that direct use of uniaxial tension and compression stress strain models underestimates the flexural load carrying capacity. Flexural over-strength factor obtained from inverse analysis of beam under three point bending is conservative and it could be used to modify the constitutive models for analyzing a structural system.
Heat Transfer Performance of a Dual-Chamber Finned Solar Absorber for Concentrating Solar Evaporator Applications
Authors: Sunter Deborah A. , Carey Van P.
Published: August 2012

This paper explores the performance advantages of a novel design of an evaporator-superheater for Rankine solar applications. The solar absorber device consists of a dual-chamber design in which the outer chamber contains fins for enhanced heat transfer allowing for multi-pass working fluid to accomplish both single phase and multiphase heat transfer in a simple low-cost manner. Analytical models to predict heat transfer performance and frictional losses in this design are described. Nondimensional analysis compares multiple strip-fin configurations for the outer chamber to establish optimal constructions. Predicted performance of the dual-chamber design is compared to traditional single chamber solar absorber tube for a 10 kW case study. The design analysis indicates that the concentric dual-chamber design minimizes heat loss to the surroundings providing a high level of evaporator performance.
Optimization Device for Grinding Media Performance Parameters
Authors: Phan Andrew M. , Summers Michael P. , Parmigiani John P.
Published: August 2012

The investment casting industry relies heavily on the use of grinding media during manufacturing. Typically, grinding media, when used in this application, have very short effective lifetimes. Determining the optimum life of grinding media is a key cost-containment and manufacturing-efficiency issue. However, current methods for determining optimum life as well as evaluating new grinding media products and optimum operating parameters are highly subjective and often is a matter of operator opinion. This subjectivity can lead to the premature retirement or overuse of grinding media, increasing cost and decreasing efficiency. A means of objectively and efficiently evaluating grinding media for optimum life and operating conditions, as well as evaluating new grinding-media products is needed. The approach taken in this work is to create a relatively low-cost test apparatus that uses grinding equipment, media, and specimens typically seen in the casting industry and measures key parameters. Also, the apparatus produces the fundamental motions and application forces typical of human operators. The resulting apparatus simultaneously moves a specimen in three orthogonal directions while applying a user-defined grinding force. Applied force, electric power input, grinding-motor rotational speed, test-specimen surface temperature and material removal are recorded. All operations of the device are autonomously performed through LabVIEW. The apparatus was constructed using standard commercial products for less than $15,000. Data comparing applied load versus material removal rate, surface temperature, and total material removed can be collected for different materials and grinding media. The device has been used to grind inconel specimens subjected to 10 to 70 pounds (45–312 N) of contact force corresponding to material removal rates of 0.26 to 5.26 grams/s at temperature changes of 90 to 210 degrees Fahrenheit (32.2–98.9 degrees Celsius). This data was used to determine a correlation between changes in performance parameters and a drop in material removal rate, total material removed, and belt life. No significant difference was found between the material removal rate of saw-cut and flame-cut Inconel specimens, dispelling a commonly held belief. Knowing key parameters that identify the effective lifetime of grinding media is significant to the casting industry. Methods described in this paper can be used to optimize grinding media life and determine optimum operating parameters.
Smart Fasteners and Their Application in Flanged Joints
Authors: Eslami Babak , Ganye Randy , Bunai Chris , Thamire Chandrasekhar
Published: August 2012

Fasteners are widely used in many industrial applications. Their function in many cases is to provide a leak-proof joint at the flange interface. To accomplish this function, fasteners must be clamped with appropriate force. In practice, it is difficult to measure such forces, intermittently or continuously. While measurement using load cells or strain gages is an available option, it tends to be expensive or infeasible due to the constraints imposed by the application. When tightening the fasteners initially or during maintenance, a less accurate method of specifying the bolt-tightening torque for achieving the necessary bolt force is widely followed in industry. These torque values are calculated using published design correlations [1]. Many factors affect such calculations: friction between the threads and collar and flange, age of the fasteners, assumptions about rigidity of the clamped components, being a few among those. Since specific values applicable for individual application are not always be known, fasteners are often over-tightened, resulting in increased stresses in the assembly elements or under tightened, resulting in leakages at the flange interfaces. In the current paper, we introduce the concept of smart fasteners that can visually indicate the tension they are subjected to, and validate it for a widely used industrial fastener size. Results from numerical and experimental studies conducted are presented for UNC 1/2 -13 × 4 1/4″ smart fasteners. Lastly, relationship between bolt-tightening torque and color intensity of the smart fasteners is provided.
Virtual Product Design Using Innovative Mechatronic Techniques for Global Supply Chain
Authors: Shetty Devdas , Manzione Louis , Campana Claudio
Published: August 2012

Global economic pressures have influenced industries to reduce budgets and look for innovative solutions. New product development procedures, especially in automotive, aerospace, industries today deploy increasingly sophisticated solutions to streamline and speed up product development as well as to improve overall product quality. With new digital factory layout tools and improved 3-D visualizations, manufacturers can digitally design and validate full factories in up to half the time previously required to do the job. Virtual product design procedures involving simulation of complex systems allows designers to develop system without finalizing the hardware. The simulation procedure can be as “what if” scenario when the hardware doesn’t exist. There are two critical issues to consider: speed and complexity. Trade-offs between simulation speed and the level of accuracy is necessary because of system resources available. As the simulation becomes faster with faster processors but the use of multicore systems help simulation. The interactive modeling is crucial to the design process, and it can occur in a mixed environment where real and virtual objects are combined. The key aspect of the virtual environments is that the visual representation of system partitioning and interaction lends itself to mechatronic applications. They also reduce system complexity from a developer’s standpoint, allowing concentration on the application details. Virtual simulations enable everyone to work on development before the first prototype is completed. Engineers can validate the entire operating cycle for the machine by driving the simulation with control system logic and timing. With industries leading all-digital design, validation, and commissioning of factory automation devices, virtual commissioning of factory-floor layout is becoming important. This paper will examine in detail the capability can offer manufacturers the ability to digitally design and layout either new factories or assembly lines much more quickly without putting any physical equipment into place, a method that can cut the time needed for such tasks. The paper discusses a strategy to take that virtual world into the physical world, but also being able to tie it back, so that information that would come from the shop floor could make it back to design.
A Support Tool for Teaching Grafcet: Engineering Students’ Perceptions
Authors: Lea˜o Celina P. , Soares Filomena O. , Machado Jose´ , de Moura Oliveira P. B. , Boaventura Cunha J.
Published: August 2012

Modeling discrete event systems with sequential behavior can be a very hard and complex task. Some formalisms are used in this context, such as: Petri Nets, Statecharts, Finite automata, Grafcet and others. Among these, Grafcet seems to be a good choice because it is easy: to learn, to understand and to use. Teaching Grafcet is then relevant within engineering courses concerned with Industrial Automation. A virtual laboratory, e-GRAFCET, developed and first tested in UTAD University; it is a new, easy-to-use multimedia e-educational tool to support the self-learning process of Grafcet. This paper, reports a study of e-GRAFCET use by the students of University of Minho. A questionnaire was prepared and students asked to fulfill it in a volunteer basis. The results were statistically analyzed and the scores compared. The overall objective is to understand how the tool helps students in their study, and consequently improve their learning off Grafcet, independently of their engineering background.
Flat Polymer Heat Spreader With High Aspect Ratio Micro Hybrid Wick Operating Under Adverse Gravity
Authors: Oshman Christopher , Li Qian , Liew Li-Anne , Yang Ronggui , Lee Y. C. , Bright Victor M.
Published: August 2012

We report the successful fabrication and application of a micro-scale hybrid liquid wicking structure in flat polymer-based heat spreaders to improve the heat transfer performance under gravitational acceleration. The hybrid wick consists of 100 μm high, 200 μm wide square electroformed high aspect ratio copper micro-pillars with 31 μm spacing for liquid flow. A woven copper mesh with 51 μm diameter and 76 μm spacing was bonded to the top surface of the pillars to enhance evaporation and condensation heat transfer. The exterior device geometry is 40 mm × 40 mm × 1.0 mm. The 100 μm thick liquid crystal polymer (LCP) casing contains a two-dimensional array of copper filled vias to reduce the overall thermal resistance. The device was tested with heat flux input of up to 63 W/cm2 at horizontal and vertical orientations. The difference in temperature between the evaporator and condenser was measured and compared to a copper reference block of identical exterior dimensions. The experimentally determined thermal resistance of the copper block remained nearly constant at 1.2 K/W. The thermal resistance of the flat polymer heat spreader at horizontal orientation was 0.55 K/W. The same device at −90° adverse orientation resulted in a thermal resistance of 0.60 K/W. These measurements indicate that this hybrid wicking structure is capable of providing a capillary pumping pressure that is effective at transferring at least 63 W/cm2 heat flux regardless of orientation. This work illustrates an important step to developing more effective thermal management strategies for the next generation of heat generating components and the possibility of developing flexible, polymer-based heat spreaders fabricated with standardized printed circuit board technologies.
Detailed Energy and Exergy Analysis for a Solar Lithium Bromide Absorption Chiller and a Conventional Electric Chiller (R134a)
Authors: Hu Yang , Schaefer Laura A. , Hartkopf Volker
Published: August 2012

The Building Energy Data Book (2009) [1] shows that commercial and residential buildings in the U.S. consume 39.9% of the primary energy and contribute 39% of the total CO2 emissions. In the operation of buildings, 41.8% of building energy consumption is provided for building cooling, heating, domestic hot water, and ventilation for commercial buildings, while in residential buildings, this percentage increases to 58%. In energy system analysis, the energy approach is the traditional method of assessing the way energy is used in an operation. However, an energy balance provides no information on the degradation of energy or resources during a process. The concept of exergy combines the first law and second law of thermodynamics. The exergy analysis clearly quantifies the energy quality match between the supply and demand sides, and also addresses the exergy destruction (entropy generation) in each component. In this paper, a solar thermal driven absorption cooling system was analyzed for providing cooling to a building, the Intelligent Workplace South Zone at Carnegie Mellon University. The system includes a 52 m2 parabolic trough solar collector, and a 16 kW (4 tons) two-stage lithium bromide absorption chiller. The energy model and newly developed two-stage lithium bromide absorption chiller are programmed and integrated in Engineering Equation Solver (EES). The temperature, enthalpy, entropy, mass flow rate, and mass fraction of lithium bromide in the solar absorption system were presented in steady state operation. The exergy destruction in each component is calculated. The exergy destructions for the solar collector, generator, absorber, and heat exchangers were significantly higher than those in evaporator, condenser and expansion valves, the overall energy and exegetic efficiency were also calculated.
Experimental Validation of a CFD Model in a Thermal Environment Characterization
Authors: Teixeira Senhorinha , Oliveira Ricardo , Rodrigues Nelson , Miguel Alberto Se´rgio , Teixeira Jose´ Carlos
Published: August 2012

Comfort has a great influence on work performance and productivity. Creating a comfortable environment can be achieved by various routes: a good selection of clothing and a proper design of equipment and technical facilities that can render an appropriate acclimatization of the occupational environment. There are several methods for solving problems of thermal comfort, including computer simulation of the thermal system comprising the Human Body - Clothing - Environment. With the evolution of computer technology and CFD (Computational Fluid Dynamics) techniques one can now develop complete analysis of HVAC systems, with regard to the fields of flow velocity, temperature distribution, particularly in the vicinity of the human body. In this way a complete interaction of the human body with the surrounding air can be descried. The difficulty in modeling the human body arises from the complex geometric shape and its thermo-physiological properties, being important to include all these factors in the numerical simulation of the human body in a closed environment. In the current study a CFD model was developed to describe the fluid flow, heat transfer and mass transfer between the ventilation air and a human manikin inside a room. The computational model solves the heat, mass and momentum conservation equations in the computation domain using a finite volume discretization method and the resulting equations are solved in the ANSYS © environment and then validated with experimental data. The thermal characterization of the environment followed the Fanger index (PMV-PPD).
Effects of Treatments on Cellulosic Biomass Structure in Ethanol Manufacturing: A Literature Review
Authors: Zhang Qi , Zhang Pengfei , Pei Z. J. , Pei Linda
Published: August 2012

Ethanol made from cellulosic biomass is an alternative to petroleum-based liquid transportation fuels. Enzymatic hydrolysis uses enzymes to convert cellulosic biomass into sugars that are fermented into ethanol. In order to increase sugar yield, various treatments (such as biomass size reduction and pretreatment) are applied to cellulosic biomass before enzymatic hydrolysis. These treatments will alter structure parameters of cellulosic biomass, such as crystallinity index, degree of polymerization, particle size, pore volume, and specific surface area. There are currently no review papers on these structure parameters of cellulosic biomass in ethanol manufacturing. This paper reviews experimental investigations in the literature about effects of various treatments on the structure parameters of cellulosic biomass.
CNT Thin Film Network Failure due to Concentrated Current Loadings
Authors: Jack David A.
Published: August 2012

Polymer composite carbon nanotube (CNT) thin films have been hypothesized as a possible material for lightning strike protection for next generation aircraft structures. This study employs the author’s previously presented three-dimensional physics-based coupled thermal and electrical multi-scale model which constructs the non-deterministic nanostructure variations for a CNT thin film, and returns the bulk thermal and electrical response due to high electrical loadings. The key results of the present study are the presentation of a possible failure mechanism for CNT thin films under increasing electrical loadings. This paper discusses the nanoscale breakdown of the network conductivity using a quasi-static loading, and uses the nanoscale results in a macroscopic finite element model which couples resistive heating with thermal breakdown. The results are in reasonable agreement with those found in the literature for a similar system.
Indentation Depth Dependent Hardness in Polydimethylsiloxane
Authors: Han Chung-Souk , Wrucke Andrew J. , Majumdar Partha
Published: August 2012

Size dependent deformation in polymers has been observed in various experiments including microbeam bending, foams, composites and indentation. For indentation depths from 100 microns down to hundreds of nanometers strong increases in the hardness has been observed where the hardness has been determined with a Berkovich indenter tip on polydimethylsiloxane. These observations are related to other existing experimental data of the literature and possible rationales for these indentation size effects are discussed.
A Bi-Level Multi-Objective Robust Design Optimization Method With Multiple Robustness Index Capabilities
Authors: Letcher Todd , Shen M.-H. Herman
Published: August 2012

A multi-objective robust optimization framework that incorporates a robustness index for each objective has been developed in a bi-level approach. The top level of the framework consists of the standard optimization problem formulation with the addition of a robustness constraint. The bottom level uses the Worst Case Sensitivity Region (WCSR) concept previously developed to solve single objective robust optimization problems. In this framework, a separate robustness index for each objective allows the designer to choose the importance of each objective. The method is demonstrated on a commonly studied two-bar truss structural optimization problem. The results of the problem demonstrate the effectiveness and usefulness of the multiple robustness index capabilities added to this framework. A multi-objective genetic algorithm, NSGA-II, is used in both levels of the framework.
Anisotropic Ductile Fracture of AA6260-T6 Al-Alloy Extrusions
Authors: Luo M. , Wierzbicki T. , Mohr D.
Published: August 2012

The anisotropic ductile fracture of AA6260-T6 extruded aluminum alloy profiles is studied within a phenomenological framework. A basic fracture testing program covering a wide range of stress states and three distinct material orientations (i.e. 0°, 45° and 90° with respect to the extrusion direction) is carried out. It comprises notched tensile specimens, tensile specimens with a central hole, butterfly shear specimens and circular punch specimens. The surface strain fields are determined using Digital Image Correlation (DIC), while a finite element simulation is performed of each experiment to determine the local stress and strain histories at the material point where fracture initiates. The experimental-numerical analysis reveals a strong anisotropy of the present material ductility/fracture, which cannot be approximated by existing isotropic fracture models. A new non-associated anisotropic fracture model is proposed incorporating the stress state dependent Modified Mohr-Coulomb (MMC) weighting function and a material direction sensitive damage rule. All seven fracture model parameters are identified for the present extruded aluminum using an inverse method. The good agreement of the model predictions with the results from fourteen distinct experiments demonstrates the remarkable predictive capabilities of the proposed model.
Simulation of Shock Response in a Lab-Scale Space Frame Structure Using Finite Element Analysis
Authors: Thota Jagadeep , Trabia Mohamed B. , O’Toole Brendan J.
Published: August 2012

Space frames are usually used to enhance the structural strength of a vehicle while reducing its overall weight. Impact loading is a critical factor when assessing the functionality of these frames. In order to properly design the space frame structure, it is important to predict the shocks moving through the members of the space frame. While performance of space frame structures under static loads in well-understood, research on space frame structures subjected to impact loading is minimal. In this research, a lab-scale space frame structure, comprising of hollow square members that are connected together through bolted joints which allow for quick assembly/disassembly of a particular section, is manufactured. Non-destructive impact tests are carried out on this space frame structure and the resulting acceleration signals at various locations are recorded. A finite element (FE) model of the lab-scale structure is created and simulated for the experimental impact loads. Acceleration signals from the FE model are compared with the experimental data. The natural frequencies of the structure are also compared with the results of the FE model. The results show a good match between the model and the experimental setup.
Time Integration Incorporated Sensitivity Analysis With Generalized-α Method for Multibody Dynamics Systems
Authors: Dong Guang , Ma Zheng-Dong , Hulbert Gregory , Kikuchi Noboru
Published: August 2012

The topology optimization method is extended for the optimization of geometrically nonlinear, time-dependent multibody dynamics systems undergoing nonlinear responses. In particular, this paper focuses on sensitivity analysis methods for topology optimization of general multibody dynamics systems, which include large displacements and rotations and dynamic loading. The generalized-α method is employed to solve the multibody dynamics system equations of motion. The developed time integration incorporated sensitivity analysis method is based on a linear approximation of two consecutive time steps, such that the generalized-α method is only applied once in the time integration of the equations of motion. This approach significantly reduces the computational costs associated with sensitivity analysis. To show the effectiveness of the developed procedures, topology optimization of a ground structure embedded in a planar multibody dynamics system under dynamic loading is presented.
Flexible Layer-by-Layer Self-Assembled Graphene Based Glucose Biosensors
Authors: Zhang Bo , Cui Tony Zhengyu
Published: August 2012

The manufacture and characterization of glucose biosensor based on layer by layer self assembled graphene are presented. Due to self assembly technique and flexible polymer substrate, the cost of the biosensor is very competitive. The resolution of the graphene based biosensor reaches down to 10 pM, which shows greater advantages over CNT based biosensor under the same conditions. The response time of graphene biosensor is less than 3 s, which is much faster than other materials and methods. This work demonstrates that graphene and polymers are very promising materials for the applications of low-cost glucose biosensors.
Microfluidic Study of Drainage and Imbibition in Porous Media: Definition of Amott Indices
Authors: Dressaire Emilie , Stone Howard A.
Published: August 2012

The wettability of reservoir rocks plays a critical role in oil recovery operations. This property is traditionally defined in terms of the contact angle between the fluid-fluid interface and the solid surface. In natural porous media, it has been preferred to characterize the wettability and its effects on fluid flow behavior in terms of Amott indices, through the capillary pressure-fluid saturation relationship. This “bulk” definition is based on the steady states reached by the two phases, the wetting one and the non-wetting one, upon drainage (removal of the wetting fluid) and imbibition (removal of the non-wetting fluid). These indices provide some indirect indication of the rock surface chemistry and porosity structure. Previous studies on Amott indices have mostly focused on numerical modeling of rocks. In this paper, we present an experimental study on two phase flow in regular lattices of glass microchannels. A wet etching technique is used to fabricate 2D networks composed of hundreds of repeat units. The repeat units are square, hexagonal, or triangular, with a lattice parameter of about 100 micrometers. Controlling and varying the microchannel wettability, network geometry, and fluid properties allow correlating the physical chemistry of the system and the characteristics of the multiphase flow. We perform drainage-imbibition cycles by controlling the pressure difference across the device. For each pressure difference, we record and characterize the distribution of the two phases at equilibrium. Our results capture the dependance of the Amott index on both fluid and network properties. The values obtained are consistent with previous studies on wetting phenomena at the pore level. The drainage-imbibition cycles also provide information on the patterns of invasion. We show that the study of the cycles can further predictability of Amott indices.
Turbulent Flow Over a Facing Step at Several Reynolds Numbers
Authors: Jimenez-Bernal Jose A. , Juarez-Montalvo Adan , Gutierrez-Torres Claudia del C. , Barbosa Saldan˜a Juan G. , Rodriguez-Jimenez Luis F.
Published: August 2012

An experimental study was performed over forward facing step (FFS). It was located within a transparent rectangular acrylic channel (1.4 m in length, 0.1 m in width and 0.02 m in height). The step is 0.01 m in height and 0.1 m in width, and was located 0.7 m downstream (fully developed region); a spanwise aspect ratio, w/h = 10 was used. The experiments were carried out using particle image velocimetry (PIV), which is a non intrusive experimental technique. The experimental water flow conditions include three Reynolds numbers based on the step height, Reh = 1124, 1404 and 1685. These flow conditions correspond to turbulent flow. Measurements were carried out in two zones; zone A begins at x = 8 cm (measured from the step base), and zone B starts at x = 0, y = 0, the visualization region corresponds to an area of 22.76 mm × 16.89 mm. 100 instantaneous velocity fields were obtained for each Reh. A temporal and spatial average was performed to obtain a velocity profile in zone A; likewise, the corresponding turbulence intensity and shear stress distribution were evaluated. The average velocity profile was evaluated for each Reh. Regarding the vortex center location, it was observed that as Reh increases, the y-direction coordinate moves towards bottom of wall channel. For zone B, it was also observed a reduction of the shear stress as Reh increases.
Brain Subarachnoid Space Architecture: Histological Approach
Authors: Saboori Parisa , Sadegh Ali
Published: August 2012

Human brain is suspended in the skull through three fibrous tissue layers, dura mater, arachnoid and pia mater, known as the meninges layer. The space between the arachnoid and pia mater is known as subarachnoid space (SAS). SAS consists of arachnoid trabeculae and cerebrospinal fluid (CSF), which stabilizes the shape and the position of the brain during head movements. Through solid-fluid interaction, it has been shown that subarachnoid space (SAS) trabeculae plays an important role in damping and reducing the relative movement of the brain with respect to the skull, thereby reducing traumatic brain injuries (TBI), (Zoghi and Sadegh 2010). While the functionality of the SAS is understood, the architecture, the histology and biomechanics of this important region has not been fully investigated. In their modeling of the head, previous investigators have over simplified this important region. This is due to the trabeculae’s complex geometry, abundance of trabeculae and lack of the material properties. These simplifications could lead to inaccurate results of finite element head studies. Killer HE, et al, (2003) investigated the trabecular histology of optical nerves and Alcoldo, et al (1986) used Scanning Electron Microscopy (SEM) to study the arachnid mater of the SAS. The result of these studies reveal that the arachnoid is a thin vascular layer composed of fibroblast cells interspersed with bundles of collagen and the trabecula is also a collagen based structure. However, the brain SAS trabecular architecture and histology has not been fully investigated. The goal of this study is to investigate the mechanotransduction of the head impacts to the brain with the emphasis on the role of material modeling and architecture of the subarachnoid space as it relates to Traumatic Brain Injuries (TBI). This goal was accomplished through three aims including experimental studies, material modeling and a 3D finite element model. In this paper, to present a global view of this investigation, brief descriptions of each aim are presented. It was concluded that the trabeculae contain collagen Type I with tree-shaped architecture and the validated material properties of SAS is approximately E = 1000 Pa.
Fabrication of Ceramic High Temperature Microsystems
Authors: Kellie Benjamin , Prakash Shaurya
Published: August 2012

This paper reports on recent advances in fabricating alumina-based ceramic microcombustors for applications in high temperature microsystems. We have fabricated alumina structures with critical dimensions on the order of 1 mm or less by using a gel-casting approach with poly(vinyl) alcohol (PVA) as a non-toxic polymeric binder. Polymer binder content, alumina weight ratio, and thermal cycling were varied systematically to develop microcombustors that can sustain stable flames in a spiral configuration allowing for better mixing of fuel and oxidizer streams for a more uniform heat output. The polymer binder and cross-linker content varied between 10 and 20% (w/v to DI water) and 50 and 100% (w/w to PVA) respectively to obtain an optimal binder content. The weight ratio of alumina (w/w 30–50%) in the binder solution was evaluated with 1.1 micron particles to observe the effect on the green body density. The green body was then fired in a high temperature furnace in air to burn-out the polymeric binder and sinter the ceramic. Heating and cooling rates, maximum operation temperature, and dwell times were evaluated to obtain high density ceramic structures with 50% or higher alumina content. Thermal stress and heating and cooling rates appear to be major parameters to control in order to obtain high-quality microcombustors.
Thermodynamics Applied to Geothermal Power Plants: Case Study—Unit 5, Cerro Prieto, Baja California Mexico
Authors: Campbell Rami´rez He´ctor Enrique , Montero Alpirez Gisela , Samaniego Ramos Margarita Gil , Valdez Salas Benjamin
Published: August 2012

Cerro Prieto Geothermal Power Plant has a capacity of 720 MW. The earliest 5 units are 23 years old, and unit 5 from Cerro Prieto Uno was restored in 2008. This paper presents a thermodynamic analysis on the effects that has the increase of non condensable gases content in geothermal steam. Results show that the cooling water temperature will rise due to the energy entering the system with the water flow of the new vacuum system that feeds the condenser. Normal operation would be limited and there exists a risk of not sustaining the condenser’s pressure. The new vacuum system, should extract from the condenser a flow 4 times larger, requiring 27% more steam at a higher pressure, as well as 4.5 times the quantity of cooling water. At this condition, the water returning to the condenser is 4.3 times larger than the original at a higher temperature, increasing in 218% the associated energy. A thermal behavior model was obtained for the cooling tower. In the most likely scenario the cooling tower exit temperature will be higher than the required, and to maintain the equilibrium it will be necessary to lower the condenser thermal load by reducing the steam flow to the turbine and accordingly, the power delivered.
Design and Simulation of a Hybrid Entrained-Flow and Fluidized Bed Mild Gasifier: Part 2—Case Study and Analysis
Authors: Mazumder A. K. M. Monayem , Wang Ting , Khan Jobaidur R.
Published: August 2012

To help design a mild-gasifier, a reactive multiphase flow computational model has been developed in Part 1 using Eulerian-Eulerian method to investigate the thermal-flow and gasification process inside a conceptual, hybrid entrained-flow and fluidized-bed mild-gasifier. In Part 2, the results of the verifications and the progressive development from simple conditions without particles and reactions to complicated conditions with full reactive multiphase flow are presented. Development of the model starts from simulating single-phase turbulent flow and heat transfer in order to understand the thermal-flow behavior, followed by introducing seven global, homogeneous gasification reactions progressively added one equation at a time. Finally, the particles are introduced, and heterogeneous reactions are added in a granular flow field. The mass-weighted, adiabatic flame temperature is validated through theoretical calculation and the minimum fluidization velocity is found to be close to Ergun’s correlation. Furthermore, the predicted exit species composition is consistent with the equilibrium values.
Frequency-Weighted Variable-Length Controllers Using Anytime Control Strategies
Authors: Runge Gundula B. , Ferri Al , Ferri Bonnie
Published: August 2012

This paper considers an anytime strategy to implement controllers that react to changing computational resources. The anytime controllers developed in this paper are suitable for cases when the time scale of switching is in the order of the task execution time, that is, on the time scale found commonly with sporadically missed deadlines. This paper extends the prior work by developing frequency-weighted anytime controllers. The selection of the weighting function is driven by the expectation of the situations that would require anytime operation. For example, if the anytime operation is due to occasional and isolated missed deadlines, then the weighting on high frequencies should be larger than that for low frequencies. Low frequency components will have a smaller change over one sample time, so failing to update these components for one sample period will have less effect than with the high frequency components. An example will be included that applies the anytime control strategy to a model of a DC motor with deadzone and saturation nonlinearities.
Mass-Area Method to Measure the Contact Angle on Hydrophilic Surfaces
Authors: Kang Hie Chan , Jacobi Anthony M.
Published: August 2012

A mass-area method is proposed to overcome problems in the measurement of the equilibrium contact angles for rough and hydrophilic surfaces. A goniometer usually measures the contact angle at the top plane of a rough surface, not the contact line of the solid-liquid interface. The present method estimates the contact angle indirectly from the volume of the liquid and the size of the contact area, assuming a spherical cap and consistent with a minimization of the free energy. The present method shows a roughly linear relationship with measurements by a goniometer for smooth surfaces of various solid materials with various liquids, but the goniometer measurements are smaller. An example test and the error of the present measurement method are presented and discussed.
Numerical Simulation on Heat Transfer Characteristics of Turbulent Gas Flow in Micro-Tubes
Authors: Isobe Kyohei , Hong Chungpyo , Asako Yutaka , Ueno Ichiro
Published: August 2012

Numerical simulations were performed to obtain for heat transfer characteristics of turbulent gas flow in micro-tubes with constant wall temperature. The numerical methodology was based on Arbitrary-Lagrangian-Eulerinan (ALE) method to solve compressible momentum and energy equations. The Lam-Bremhorst Low-Reynolds number turbulence model was employed to evaluate eddy viscosity coefficient and turbulence energy. The tube diameter ranges from 100 μm to 400 μm and the aspect ratio of the tube diameter and the length is fixed at 200. The stagnation temperature is fixed at 300 K and the computations were done for wall temperature, which ranges from 305 K to 350 K. The stagnation pressure was chosen in such a way that the flow is in turbulent flow regime. The obtained Reynolds number ranges widely up to 10081 and the Mach number at the outlet ranges from 0.1 to 0.9. The heat transfer rates obtained by the present study are higher than those of the incompressible flow. This is due to the additional heat transfer near the micro-tube outlet caused by the energy conversion into kinetic energy.
Longitudinal Flight Control for a Novel Airborne Wind Energy System: Robust MIMO Control Design Techniques
Authors: Tierno Nicholas , White Nicholas , Garcia-Sanz Mario
Published: August 2012

This paper deals with the longitudinal flight control for a novel Airborne Wind Energy (AWE) system: the EAGLE System. It is a tethered lighter-than-air flyer wind turbine composed of a blimp, several aerodynamic airfoils (wings) with specific aerodynamic control surfaces (ailerons, elevator, rudder), a counter-rotating aerodynamic rotor for the wind turbine (four identical sections, symmetrically arranged, with three blades each), an electrical synchronous generator attached to the counter-rotating rotors, and a tether to secure the airship and to transmit the generated power. Additional information can be found in US Patent, Provisional Application No. 61/387,432 developed by the authors. The designed system proposed here supports a 2.5 kW generator and flies at approximately 100 meters. The mathematical model developed for the AWE system incorporates a hybrid blimp-airfoil design, modeled using a hybrid Cartesian-polar coordinate system to capture the dynamics of both the airship and the tether, and includes the effect of the counter-rotating aerodynamic rotor of the wind turbine, as well as the aerodynamic control surfaces. This paper presents the design of a robust Multi-Input Multi-Output (MIMO) controller for the 3×3 longitudinal flight dynamics of the tethered airborne wind energy system. The control system is designed by applying sequential MIMO robust Quantitative Feedback Theory (QFT) techniques.
Modeling of Blood Flow in the Human Brain
Authors: Hossain Md. Shahadat , Pillapakkam Shriram B. , Dalal Bhavin , Fischer Ian S. , Aubry Nadine , Singh Pushpendra
Published: August 2012

Under normal conditions, Cerebral Blood Flow (CBF) is related to the metabolism of the cerebral tissue. Three factors that contribute significantly to the regulation of CBF include the carbon dioxide and hydrogen ion concentration, oxygen deficiency and the level of cerebral activity. These regulatory mechanisms ensure a constant CBF of 50 to 55 ml per 100g of brain per minute for mean arterial blood pressure between 60–180 mm Hg. Under severe conditions when the autoregulatory mechanism fails to compensate, sympathetic nervous system constricts the large and intermediate sized arteries and prevents very high pressure from ever reaching the smaller blood vessels, preventing the occurrence of vascular hemorrhage. Several invasive and non-invasive techniques such as pressure and thermoelectric effect sensors to Positron Emission Tomography (PET) and magnetic resonance imaging (MRI) based profusion techniques have been used to quantify CBF. However, the effects of the non-Newtonian properties of blood, i.e., shear thinning and viscoelasticity, can have a significant influence on the distribution of CBF in the human brain and are poorly understood. The aim of this work is to quantify the role played by the non-Newtonian nature of blood on CBF. We have developed mathematical models of CBF that use direct numerical simulations (DNS) for the individual capillaries along with the experimental data in a one-dimensional model to determine the flow rate and the methods for regulating CBF. The model also allows us to determine which regions of the brain would be affected more severely under these conditions.
A Computational Study of Active Heat Transfer Enhancement of Air-Cooled Heat Sinks by Actuated Plates
Authors: Yu Youmin , Simon Terrence , Agrawal Smita , North Mark , Cui Tianhong
Published: August 2012

Heat transfer performance of air-cooled heat sinks must be improved to meet thermal management requirements of microelectronic devices. The present paper addresses this need by putting actuated plates into channels of a heat sink so that heat transfer is enhanced by the agitation and unsteadiness they generate. A proof-of-concept exercise was computationally conducted in a single channel consisting of one base surface, two fin wall surfaces, and an adiabatic fourth wall, with an actuated plate within the channel. Air flows through the channel, and the actuated plate generates periodic motion in a transverse direction to the air flow and to the fin surface. Turbulence is generated along the tip of the actuated plate due to its periodical motion, resulting in substantial heat transfer enhancement in the channel. Heat transfer is enhanced by 61% by agitating operation for a representative situation. Translational operation of the plate induces 33% more heat transfer than a corresponding flapping operation. Heat transfer on the base surface increases sharply as the gap distance between it and the plate tip decreases, while heat transfer on the fin wall surface is insensitive to the tip gap. Heat transfer in the channel increases linearly with increases of amplitude or frequency. The primary operational parameter to the problem is the product of amplitude and frequency, with amplitude being slightly more influential than frequency. The analysis shows that the proposed method can be used for modern levels of chip heat flux in an air-cooled model forestalling transition to liquid or phase-change cooling.
Analysis of Hybrid Bus Powertrain With Different Transmissions
Authors: El-Sayed Mohamed E. M. , Barber Jeffrey
Published: August 2012

The main goals for developing hybrid power train system are reducing emissions and providing commercially viable low cost transportation solutions. To achieve these goals, a well defined set of targets and specifications are necessary for the hybrid system development. These targets and specifications are needed for design, analysis, and validation of the power train subsystems, components, and successful system integration. During hybrid system design and development, there are many alternatives and design configurations to choose from. To select the most efficient systems duty cycle data and profiles are needed to assist in defining the design targets and specifications. For buses, due to their well defined routes the duty cycles can be achieved through data acquisitions or by using the American Public Transit Association (APTA) standard duty cycle. In this paper, the APTA duty cycle profiles are used to evaluate two alternatives power train configurations for a bus series hybrid system. The first configuration consists of two electric motors and one speed transmission while the second configuration consists of one electric motor with two speed transmission. The simulation and analysis results of both configurations are presented.