bluuebunny/crossref_metadata_2025 huggingface dataset:
Tracking of Capillary Interface in Microfluidic Channels
Authors: Waghmare Prashant R. , Ahmad Farhan , Nobes David S. , Mitra Sushanta K.
Published: August 2012

Capillarity is commonly used for fluid transport in microfluidic devices. The capillary flow can be divided into three different flow regimes: entry regime, Poiseuille regime, and surface tension regime as shown in Fig. 1[1]. Generally, it is anticipated that at the entrance of any narrow confinement, the flow goes through entrance flow regime. For capillary flow, this entrance regime has generally been neglected in the literature. Beyond this entrance regime, the flow attains the fully developed velocity profile across the channel, which is termed as a Poiseuille flow. Moreover, in the capillary flow, the interface is always under traction — due to the capillary forces and hence, a third flow regime needs to be considered behind the interface which is referred as the surface tension regime. These regimes are yet to be experimentally explored and analyzed. An “in-house” developed μ-PIV system is used to quantify the flow field at the liquid/air interface (surface tension regime) in a rectangular glass microchannel of dimension 1.5 mm (width) × 500 μm (depth). The magnitude of velocity and the flow front evolution along the microchannel is calculated utilizing commercially available image processing software. Figure 2 shows the μ-PIV experimental setup used here. The main components of the experimental setup include an imaging device, magnification optics, and a continuous laser source (473 nm) in back illumination mode. The fluorescent particle of 1.9 m in diameter with DI water is used as a working fluid. The concentration of the microparticles is very less which is approximately 1%, therefore the effect of microbead concentration on the wetting properties is considered to be negligible for the present study. Moreover, it is assumed that the surface properties of the particles also do not affect the fluid flow. The capillary flow interface is captured and the corresponding processed images are presented to depict the velocity field at the liquid/air interface. The enlarged view of the microchannel cross section is shown in Fig. 2. The section A-A is the location at which the images are captured for the analysis.
Effects of Augmented Air Pressure on the Nasal Erectile Tissue and Blood Flow During Breathing Therapies
Authors: White David E. , Al-Jumaily Ahmed M. , Bartley James , Lu Jun
Published: August 2012

During breathing therapies, air delivered under augmented pressure normally requires external humidification in order to avoid upper airways dryness and discomfort. Heat and water transfer between the air and nasal mucosa is dynamically regulated through changes in the nasal erectile tissue volume. This investigation uses magnetic resonance imaging (MRI) to investigate the effects of augmented pressure on nasal erectile tissue size and blood inflow. Eight healthy participants undertook head MRI scans during breathing of ambient and pressurized air. Results demonstrate that the congested airway volume increases in response to augmented air pressure at a level consistent with previous observations. The patent airway; however, demonstrates no significant change. Using arterial spin labeling (ASL) techniques, this research has also qualitatively determined that blood inflow to the patent airway inferior turbinate varies in response to pressure. This new finding is attributed to changes in nasal erectile tissue blood inflow occurring during breathing augmented pressure air.
Cost/Performance Comparisons of Water Conserving Power Plant Cooling Systems
Authors: Maulbetsch John S.
Published: August 2012

This paper documents the results of a study of alternative cooling systems for electric power generating plants to understand the tradeoffs between wet, dry and hybrid cooling technologies. Results are presented through case studies of a 500 MW coal plant, a 600 MW nuclear plant and a 500 MW gas-fired combined-cycle plant, each at five different sites. Alternative cooling systems are configured and optimized for each site. For optimized designs under nearly all conditions, wet cooling systems are not only the least expensive but result in the highest plant output and efficiency. For both all-dry and hybrid systems, the system using indirect dry cooling has higher capital and operating costs than one using the direct system. The use of either dry or hybrid cooling can result in a large reduction in the amount of water used by a plant. The savings cost approximately $7 to $10 million per year for plants of the specified size, depending on the plant and site implying a breakeven water cost of $3 to $6 per thousand gallons.
Characterization of a Ferritic Stainless Sheet Steel in Simple Shear and Uniaxial Tension at Different Strain Rates
Authors: Isakov Matti , Seidt Jeremy , O¨stman Kauko , Gilat Amos , Kuokkala Veli-Tapani
Published: August 2012

In this study the mechanical properties of ferritic stainless steel EN 1.4521 (AISI 444) were characterized in uniaxial tension and simple shear. The specimen geometries were designed so that tests could be carried out both with a conventional uniaxial materials testing machine and at high strain rates with the Tensile Hopkinson Split Bar method. During the tests, specimen surface deformation was measured using a three dimensional digital image correlation technique based on a two-camera stereovision setup. This technique allowed direct measurement of the specimen gauge section deformation during the test. Test results indicate that the selected approach is suitable for large strain plastic deformation characterization of ductile metals. The stress-strain data obtained from the simple shear tests shows a correlation with the tensile test results according to the von Mises effective stress-strain criterion. Since necking is absent in shear, test data can be obtained at considerably higher plastic strains than in tension. However, the final fracture occurs under a complex loading mode due to the distortion of the specimen geometry and multiaxial loading introduced by the simple shear arrangement. Test results also show that reliable material data can be obtained at high strain rates.
Effect of Mechanical Length Oscillations on Airways Smooth Muscle Reactivity and Crossbridge Cycling
Authors: Mbikou P. , Al-Jumaily A. M.
Published: August 2012

Superimposition of length fluctuations on contracted ASM have shown to reduce active force and stiffness. This effect is usually attributed to disruption of the actomyosin crossbridge cycle; however no direct experimental data is available to support this hypothesis. This in vitro study investigated the effect of the mechanical strains on 1) the ASM reactivity and 2) on the actin-myosin crossbridges. Experiments were carried out on maximally contracted bovine ASM subjected to length strains at various frequency in the range from 10 to 100Hz, superimposed on normal tidal stretches (frequency 0.33Hz, amplitude 4%). An organ bath system was used to apply strains and measure the force; immunofluorescence technique was performed to assess the crossbridges. The results show that superimposed length strains increase breathing relaxation effect with an optimal effect obtained at 50Hz. The cholinergic stimulation promotes actin-myosin connection, and length stretches promote the detachment of those crossbridges.
Effect of Nanosized Filler on Matrix Dominated Properties of Fiber Reinforced Epoxy
Authors: Zhou Yuanxin , Jeelani Shaik
Published: August 2012

In this study, a high-intensity ultrasonic liquid processor was used to obtain a homogeneous molecular mixture of epoxy resin and carbon nano fiber. The carbon nano fibers were infused into the part A of SC-15 (diglycidylether of Bisphenol A) through sonic cavitations and then mixed with part B of SC-15 (cycloaliphatic amine hardener) using a high-speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using high vacuum. Nanophased epoxy with 2 wt.% CNF was then utilized in a vacuum assisted resin transfer molding (VARTM) set up with carbon fabric to fabricate laminated composites. The effectiveness of CNF addition on matrix dominated properties of composites has been evaluated by compression, open hole compression and inter-laminar shear. The compression strength, open hole compression strength and ILS were improved by 21%, 23% and 15%, respectively as compared to the neat composite.
Role of Edge Chirality and Isotope Doping in Thermal Transport and Thermal Rectification in Graphene Nanoribbons
Authors: Wang Yan , Ruan Xiulin
Published: August 2012

Thermal transport processes in graphene nanoribbons (GNRs) within and beyond the linear response regime has been studied using classical molecular dynamics simulations. Zigzag-edged GNRs have higher thermal conductivities than armchair-edged ones, and the difference diminishes with increasing width. Analysis on the cross-sectional distribution of heat flux reveals that edge atoms cannot transport thermal energy as efficiently as interior ones. Edge localization of phonon modes reduces thermal transport through edge carbon atoms, especially on armchair edges, which results in a lower thermal conductivity. Isotope (13C) doping can reduce the thermal conductivity of GNRs by 30%–40% by an addition of only ∼20% isotope atoms. The significant reduction in thermal conductivity is partially attributed to phonon localization induced by isotope defects, which is confirmed by phonon mode participation ratio analysis. We also demonstrate that a GNR asymmetric in edge chirality or mass density can generate considerable thermal rectification, which is essential for developing GNR-based thermal management devices.
Investigation of the Potential for Reducing Energy Usage in Cam Follower Systems by Means of Variable Pitch Springs
Authors: Yau Henry , Longman Richard W.
Published: August 2012

Although the spring is an integral component of most any cam follower system, its design is often ignored in studies aimed at minimizing energy loss. This study makes an initial assessment of the possible energy savings that can be achieved by using a spring designed with a variable pitch. Using a simple spring model that accounts for coil contacts, the pitch is optimized in numerical experiments and the energy savings are calculated. The experiments show that savings in energy are promising enough to warrant further investigation.
Investigation on Blade Flutter in Transonic Compressor With a Coupled Numerical Approach
Authors: Zhang Mingming , Hou Anping , Zhou Sheng , Yang Xiaodong
Published: August 2012

A fluid-solid coupled approach for investigating blade flutter in a compressor under the parallel computation of aeroelasticity is presented. The unsteady flow field of rotor is studied by a CFD model of the entire compressor flowpath, coupled with a finite element model for the blades to identify modal shapes, natural frequencies, vibratory stress and the structural deformations. Interactions between fluid and structure are dealt with in a coupled manner, based on the interface exchange of information between the aerodynamic and structural model. The coupled computational results are presented and compared with experimental data. Blade variations and the way of these variations is related to vibratory stress amplitude are investigated. Transient responses of blade stress are provided to determine whether flutter occurs. This coupled method successfully predicts the flutter of a transonic rotor over range of operating conditions. The nonlinear behaviors of flow field, blade vibrations, and inter-blade phase angle are discussed.
Functional Testing for Industrial Control Systems
Authors: Martens John , Fecke Mark , Bishop Justin , Ogle Russ
Published: August 2012

Functional testing is an essential part of the process of developing trust in safety-critical control systems. A typical life cycle for a control system begins with a functional specification, which defines the system functionality. An important step in the design-to-commissioning process is the on-line functional testing that typically precedes release for operation. The functional testing is usually the last step in verifying operation and validating the design of the control system with respect to the functional description. Functional testing can often be the last chance to catch costly mistakes that may result from a system performing in unexpected ways. Many aspects of functional testing need careful consideration, including identifying hazards that the system is to guard against, developing tests to validate the control system response to the potential hazards, and performing the functional tests. This paper includes several case studies that highlight incidents where the functional testing has caught flaws in the control system that could have lead to catastrophic failures. Additional case studies where functional tests were not completed and catastrophic failures did occur are discussed and the lack of functional testing in those cases is examined. A simple methodology for selecting control loops that may benefit from functional testing is presented and useful guidance documents are identified.
Methods for Supporting Bioinspired Design
Authors: Glier Michael W. , Tsenn Joanna , Linsey Julie S. , McAdams Daniel A.
Published: August 2012

Bioinspired design, the use of nature to inspire solutions to engineering problems, is a powerful approach for innovation but is generally practiced on an ad hoc basis. Only recently, however, have researchers sought to develop formal tools and principles to effectively tap the wealth of design solutions found within nature. Research efforts in applying design tools such as the Theory of Inventive Problem Solving (TRIZ), functional modeling, and keyword searches to bioinspired design are summarized in this paper. The efforts to develop effective tools to search biological information for design inspiration are also discussed. This paper presents a case study where BioTRIZ, functional modeling, and bio-keyword searches were taught in a weekend-long workshop to working professionals in the process of obtaining their graduate degrees. The students were then given a project to re-engineer a product using the bioinspired methods. An analysis of their reports is given that discusses student success in implementing bioinspired design methods and student feedback on the methods.
Characterization of a Condenser for a High Performance Multi-Condenser Loop Heat Pipe
Authors: Hanks Daniel F. , Peters Teresa B. , Brisson John G. , Wang Evelyn N.
Published: August 2012

We experimentally characterized a condenser design for a multi-condenser loop heat pipe (LHP) capable of dissipating 1000 W. The LHP is designed for integration into a high performance air-cooled heat sink to address thermal management challenges in advanced electronic systems. The multi-layer stack of condensers utilizes a sintered wick design to stabilize the liquid-vapor interface and prevent liquid flooding of the lower condenser layers in the presence of a gravitational head. In addition a liquid subcooler is incorporated to suppress vapor flashing in the liquid return line. We fabricated the condensers using photo-chemically etched Monel frames with Monel sintered wicks with particle sizes up to 44 μm. We characterized the performance of the condensers in a custom experimental flow rig that monitors the pressure and temperatures of the vapor and liquid. The condenser dissipated the required heat load with a subcooling of up to 18°C, while maintaining a stable liquid-vapor interface with a capillary pressure of 6.2 kPa. In the future, we will incorporate the condenser into a loop heat pipe for a high performance air-cooled heat sink.
Experimental Study on Shell Side Heat Transfer Performance of Circumferential Overlap Trisection Helical Baffle Heat Exchangers
Authors: Chen Yaping , Cao Ruibing , Wu Jiafeng , Dong Cong , Sheng Yanjun
Published: August 2012

A set of experiments were conducted on the circumferential overlap trisection helical baffle heat exchangers with inclined angles of 20°, 24°, 28° and 32° single-thread and inclined angle of 32° dual-thread one, and a segmental baffle heat exchanger as a contrast scheme. The cylinder case of the testing heat exchanger is a common shell, while the tube bundle core could be replaced. The shell side heat transfer coefficient ho is obtained by subtract tube-side convection thermal resistance and tube wall conduction resistance from the overall heat transfer coefficient K. The curves of shell side heat transfer coefficient ho, pressure drop Δpo, Nusselt number Nuo, and axial Euler number Euz,o are presented versus axial Reynolds number Rez,o. A comprehensive performance index Nuo/Euz,o is suggested to demonstrate the integral properties of both heat transfer and flow resistance of different schemes, and the curves of Nuo/Euz,o versus Rez,o of the different schemes are presented. The results show that the scheme with inclined angle 20° performs better than other schemes, and the scheme with inclined angle 24° ranks the second, however the segment scheme ranks the last. The curves of Nuo/Euz,o of both schemes with inclined angle 32° of single-thread and dual-thread are almost coincident, even though their heat transfer coefficient and pressure drop curves are quite different. The results indicate also that for the circumferential overlap trisection helical baffle schemes the optimal inclined angle is around 20° instead of around 40° as rated by many literatures for the quadrant helical baffle schemes.
Phase Change Materials as Thermal Storage for High Performance Homes
Authors: Campbell Kevin R. , Sailor David J.
Published: August 2012

A minimally invasive method of adding thermal mass to a building is to apply Phase Change Material (PCM) to the interior of the structure. This paper describes a simulation-based approach for informing the integration of PCM in high performance homes without mechanical cooling. The analysis considers phase change transition temperature, quantity, and location of PCM within the building. The effectiveness of each test case was determined based on the number of hours that the indoor conditions were outside the ASHRAE defined comfort zone. Results showed that for most climates a PCM melt temperature of 25°C yielded the largest increases in occupant comfort; however the magnitudes of increases in occupant comfort were highly climate dependant. Reductions of 93% of zone-hours and 98% of zone-degree-hours outside the thermal comfort were achieved for simulations in Portland, Oregon. However, reductions of only 6.4% of zone-hours and 7.3% of zone-degree-hours outside the thermal comfort zone were realized in Phoenix, Arizona.
Shear/Pressure Driven Internal Condensing Flows and Their Sensitivity to Inlet Pressure Fluctuations
Authors: Kivisalu M. , Gorgitrattanagul N. , Mitra S. , Naik R. , Narain A.
Published: August 2012

The reported experimental results are for annular zones of fully condensing flows of pure FC-72 vapor. The flow condenses on the bottom surface (316 Stainless Steel) of a horizontal, rectangular cross-section duct. The sides and top of the duct are made of clear plastic. The experimental system in which this condenser is used is able to control steady-in-the-mean (termed quasi-steady) values of mass flow rate, inlet (or exit) pressure, and wall cooling conditions. It has been reported elsewhere that, with the condenser mean (time averaged) inlet mass flow rate, mean inlet (or exit) pressure, and wall cooling condition held at quasi-steady values, there is a very strong sensitivity to certain impositions of pressure fluctuations and accompanying flow rate pulsations at the condenser inlet. For these impositions, it was found that the mean exit (or inlet) pressure changes to significantly affect mean test-section pressure difference, local heat-flux variations over the annular portion of the flow, and the nature of the annular flow regime. This paper experimentally investigates how the strength of this sensitivity varies with amplitude and frequency of pressure fluctuations imposed on the inlet of the condenser from the vapor line. It has been found that, for various frequencies of interest, there are typically two classes of responses to inlet pressure fluctuations. These are termed supercritical (for the larger amplitudes for which a strong sensitivity exists) and subcritical (for the smaller amplitudes for which a weak sensitivity exists).
Superhydrophobic Surfaces Properties for Anti-Icing
Authors: Sarshar Mohammad Amin , Swarctz Christopher , Hunter Scott , Simpson John , Choi Chang-Hwan
Published: August 2012

In this paper, the iceophobic properties of superhydrophobic surfaces are compared to those of uncoated aluminum and steel plate surfaces as investigated under dynamic flow conditions by using a closed loop low-temperature wind tunnel. Superhydrophobic surfaces were prepared at the Oak Ridge National Laboratory by coating aluminum and steel plates with nano-structured hydrophobic particles. The contact angle and contact angle hysteresis measured for these surfaces ranged from 165–170° and 1–8°, respectively. The superhydrophobic plates along with uncoated control ones were exposed to an air flow of 12 m/s and 20°F with micron-sized water droplets in the icing wind tunnel and the ice formation and accretion were probed by using high speed cameras for 90 seconds. Results show that the developed superhydrophobic coatings significantly delay the ice formation and accretion even with the impingement of accelerated super-cooled water droplets, but there is a time scale for this phenomenon which has a clear relation with contact angle hysteresis of the samples. Among the different superhydrophobic coating samples, the plate having the lowest contact angle hysteresis showed the most pronounced iceophobic effects, while the correlation between static contact angles and the iceophobic effects was not evident. The results suggest that the key parameter for designing iceophobic surfaces is to retain a low contact angle hysteresis, rather than to have only a low contact angle, which can result in more efficient anti-icing properties in dynamic flow conditions.
High Velocity Impact Properties Characterization of Nano-Phased Bi-Layered Body Armor
Authors: Salekeen Sirajus , Khan Mohammad G. Kibria , Jeelani Shaik
Published: August 2012

It has been already established by different investigators that addition of nano-reinforcements to plastics and fibers further enhances the mechanical and thermal properties of these materials. In this investigation, we have tested a bi-layer composite armor made of a ceramic layer and a nano-reinforcement infused epoxy layer. Our objective is to determine whether the infusion of nano-reinforcements in an epoxy layer enhances the ballistic properties of this bi-layer armor system. This bi-layered armor which was made of an alumina layer and a nano-infused epoxy layer was tested by a Fragment Simulating Projectile (FSP) method. Silica nanoparticles and multi walled carbon nanotubes (MWCNT) with a loading range of 0–1wt% were used for this purpose. Armors having the same thickness but made of only a single pure ceramic layer and a bi-layer composite made of a ceramic layer and a neat epoxy layer were also tested for comparison purposes. A gas gun with high velocity projectile was used to perform the experiment. A striking velocity of about 400m/s was used to hit the target armor plate. The striking velocity of the projectile was obtained by maintaining a breach end pressure of helium gas in the gas gun at about 500 psi. The striking velocity was chosen at a level which was well above the ballistic limits of the armor materials. A finite element analysis was also performed to evaluate the ballistic properties of the composite armor and to compare those with the experimental data. Numerical and experimental results for the residual velocity of the piercing bullets were found to be in good agreement. Details of the experimental and numerical data are presented in this paper.
Simulation of Mixed Convection Air Cooling of Protruding Heat Sources Mounted on One Side of a Vertical Channel
Authors: Dhingra Rajat , Ghoshdastidar P. S.
Published: August 2012

A numerical study of steady, laminar, two-dimensional mixed convection air cooling of identical as well as non-identical rectangular protruding heat sources located on one side of a vertical channel is presented in this paper. The stream function-vorticity-temperature approach with the finite-difference-based methodology implementing higher order upwind scheme has been applied. Three cases have been considered, namely (i) when the number of identical chips is two; (ii) when the number varies from 3 to 10; and finally, (iii) when five chips of different heights but of same width are placed in various orders. For the case of two chips the effects of Re, Gr/Re2 (that is, Richardson number), dimensionless separation distance between the chips (d/H), dimensionless chip height (h/H) and width (w/H) on the average Nusselt number of each chip have been investigated. A correlation based on regression analysis is also presented for each parameter. With increase in Reynolds number the average Nusselt number of both chips increases. Similar trend is seen when the separation distance between two chips is raised. It is also observed that as the number of chips escalates from 2 to 10, the average Nusselt number of downstream chips becomes smaller than that of the upstream chips, the rate of drop being much sharper near the channel inlet. A regression-analysis based composite correlation each for average Nusselt number of Chip 1 (lower chip) and Chip 2 (upper chip) as a function of Reynolds number, Richardson number, separation distance between the chips, chip height and width has been obtained for the 2-chip case. The model also predicts maximum chip temperature in an array of ten chips. Finally, for five non-identical chips having same width but different heights the simulation reveals that the chips placed in increasing order of their heights in the direction of air flow are cooled better as compared to any other pattern of placement of the chips.
An Acoustic Metamaterial Bending Waveguide Design Using Transformation Acoustics
Authors: Wu Liang-Yu , Chiang Tzeh-Yi , Wu Mei-Ling , Chen Lien-Wen
Published: August 2012

An acoustic bending waveguide is designed by transformation acoustics. A two-dimensional square area with anisotropic and homogeneous material properties is transformed into a fan-shaped area with anisotropic and inhomogeneous material properties to rotate the direction of beam propagation. The transformation medium can be realized by alternating layered structure consisting of water and fluid with negative mass density. We propose that an acoustic metamaterial composed of three layers in water background can be designed to replace negative mass density fluid and achieve the acoustic bending waveguide.
Cathodic Disbondment of Rubber/Steel Adhesive Bonds Modeled as Liquid-Solid Reactions
Authors: Tarhini Ali A. , Hamade Ramsey F.
Published: August 2012

Under cathodic conditions, rubber/steel adhesive bonded joints have been documented to ‘weaken’ due to attack by the generated alkali. If this were to occur under the action of cleavage mechanical loads, the bonds are likely to completely ‘delaminate’ causing the bonded constituents to physically separate. These two modes of disbondment are referred to as ‘weakening’ and ‘delamination’, respectively. Previously, Hamade and coworkers have implemented empirical and semi-empirical approaches to modeling cathodic disbondment of adhesive joints. Here, a method is presented to simulate bond weakening progress via numerical solutions. Bond degradation is modeled as a liquid-solid chemical reactor due to the attack by the alkaline medium. Specifically, the diffusion and chemical reaction processes involved in weakening are mathematically represented via a simplified, 2 partial differential equations (p.d.e.) boundary value problem (BVP). This is a reduced version of the more complex electrochemical formulation needed to fully describe the chemistry at the bondline under cathodic conditions. The weakening model is capable of simulating weakened bond lengths vs. time as function of electrolyte type (artificial sweater, ASW, or 1N NaOH), cathodic potential, and temperature. Furthermore and to model bond delamination, a mechano-chemical failure criterion is incorporated into the weakening formulation effectively coupling fracture mechanics principles with those of cathodic degradation. A fracture mechanics parameter, applied strain energy release rate, G, is used to represent the effect of externally applied loads. The failure criterion stipulates that the bond will delaminate if the applied G exceeds that of the degraded bond’s residual resistance. Both, the weakening and delamination formulations are validated against experimental data of bond weakening and delamination under a variety of conditions. As such, the numerical simulations developed in this work may be used to provide first order estimates of the life of rubber/steel bonded joints (weakened or delaminated lengths vs. time) as function of cathodic parameters and applied G (if the joint is loaded in the case of delamination).
Feasibility Study of Using Simultaneous Motion of Two Rotary Axes to Evaluate Machining Center: Simulation
Authors: Dassanayake K. M. Muditha , Tsutsumi Masaomi , Katsunori Ohta
Published: August 2012

In this paper, a new motion: the two rotary axes simultaneous motion was proposed and the mathematical model which was used to carryout simulations was described. The effect of each deviation on the proposed motion was identified and described one by one. A methodology to estimate all the eight deviations which inherent to tilting rotary table type machining centers was described step by step. This methodology consists of two motions: the proposed motion and C axis radial direction motion. Both the two motions used only the rotary axes. All the motions can be run on one setup. The simulations were carried out by considering that the double ball bar as the measuring device. Furthermore, number of settings which can be used for the new motion were discussed. From this study, it was confirmed that this method can be used for estimate all the eight deviations, accurately.
Developing the Modular Background-Oriented Full-Scale Schlieren Technique
Authors: Hung Yu-Cheng , Chen Chien-Chih , Wang Shun-Chih , Ting Chen-Ching
Published: August 2012

This article mainly presents the full-scale schlieren technique using modular background-oriented light source instead of the retroreflective method. Moveover, this article is also focused on investigating sensitivity influence of the cutoff light percentage by the cutoff grid. An unit background-oriented light source is composed of the fluorescent lamps of Philips-865, the atomizing film, and the linear grating mask in this work. The applied cutoff grids are with 50, 60, 70, 80, and 90% of the cutoff light percentage respectively. The results show that a cutoff grid with 90% cutoff light for the conventional Z-arrangement schlieren technique and a cutoff grid with 60% cutoff light for the full-scale schlieren technique receives the best visualization.
Two-Port Network Model of Fluid-Loaded SAW Delay-Line Sensors
Authors: Kim Jaegeun , Ohm Won-Suk , Park No-cheol
Published: August 2012

Surface acoustic wave (SAW) devices usually come in the form of inter digital transducers (IDTs) deposited on a substrate. In addition to being used as filters and delay lines in communication systems, their use nowadays expands to various sensor and actuator applications [1,2]. There are two different ways to employ a SAW device as a sensor. The first is the propagative signal type and the second is the reflective signal type. The output response of a propagative signal type can be predicted by an electro-acoustical equivalent circuit, which is comprised of input/output IDT admittances and the substrate delay line admittance. In a propagative signal type, the main objective is to sense the change in load impedance that is attached to the output IDT [3]. The reflective type is mainly used in bio/chemical applications, and measures the reflected signal due to the electrical impedance or admittance change by fluid loading at the delay line of the substrate [4,5]. Up to now, studies on reflective signal types have heavily focused on the experimental side, and little theoretical work has been done. In this paper, we consider a delay-line type SAW sensor used in fluid loading conditions, and propose an equivalent circuit model that can predict the overall response of the SAW sensor.
Comprehensive Quantification of Sorption Characteristics in Polymer Material of Thin Film Form
Authors: Park Heejin , Lim Ji-Hyuk , Ham Suk-Jin , Han Bongtae
Published: August 2012

In this paper, the standard procedures for measuring moisture sorption properties of thin film form of polymer materials such as polyethylene terephthalate (PET) using thermo-gravimetry method and permeation method to characterize the moisture diffusion in polymer is presented. Analytical solution of moisture diffusion and FEA implementation using thermal-moisture analogy for comparison with measurements are presented, in which temperature dependent material properties are characterized. The measurement of permeability is used for validation of moisture diffusion characteristics. Nonlinear behavior of moisture diffusion dependent on concentration is investigated using a specimen having diffusion on half side and diffusivity constants are obtained by solving non-Fickian model and minimizing errors of least square with measurement. Application of characterizing moisture sorption properties to moisture effect on the interfacial layer in multi-layered printed circuit board (PCB) and estimation of relative humidity (RH) through permeation of moisture in hermetic sealing of crystal resonator are presented in this paper: i) The discrepancy of moisture concentration at the interlayer in multi-layered PCB was estimated as loading condition varies. ii) Moisture content through sealant based on temperature dependent permeability was estimated using mixture of ideal gases and vapor pressure.
Structural Response of Thin-Walled Austenitic Pipes to Internal Gaseous Detonation Loading
Authors: Offermanns Stefan , Roos Eberhard , Stadtmu¨ller Werner
Published: August 2012

One of the main risks with the occurrence or by the use of hydrogen in oxygen-containing environment is the easy ignitability of the gas-mixture. An example of unwanted aggregations of such a gas-mixture is the generation of gaseous hydrogen and oxygen in safety-relevant piping of nuclear power plants due to radiolysis. Radiolysis is the dissociation of water under the influence of gamma and neutron radiation. Within the scope of a research project funded by the German Federal Ministry of Economics and Technology (BMWi), the assessment of incident situations with appearance and ignition of different amounts of radiolysis gas should be provided. Of central importance for the pipe behavior under detonative loading is the knowledge about the pressure-profile of the deflagration (subsonic combustion before entry of detonation) as well as the mechanisms of an acceleration of the deflagration up to the detonation, which starts as a so-called overdriven detonation in a volume of pre-compressed gas and then decays to the stable detonation. Furthermore pressure-profile and speed of the detonation wave are elementary pipe load parameters. Detonation tests and numerical evaluations were performed to simulate detonations of radiolysis gas in pipes with O.D. × t (outer diameter × wall thickness) = (114 × 6) mm made of austenitic steel under operating pressure of p0 = 7 MPa. For the consideration of mixtures of radiolysis gas and steam inside a piping the volume proportion in percent of oxyhydrogen (H2+ 1/2 O2) to nitrogen (N2) was varied. The influence of the overdriven detonation is essential for the deformation and rupture behavior of the pipe and depends strongly on the ratio of oxyhydrogen to nitrogen. Due to the high-rate response of the pipes to the detonation, multiple longitudinal cracks and fragmentation occurred in certain cases. For the evaluation of the fracture mechanisms accompanying metallographic investigations were performed. For the numerical investigations an appropriate material constitutive law was chosen in order to describe the material behavior including strain rate sensitivity and thermal softening at high deformations. Material parameters are obtained from small-size specimen tests. The material model includes necking and was validated by numerical simulations of tensile and compression tests. For the numerical simulation of gas detonations in pipes the full pressure profile including deflagration and overdriven detonation is of a central importance. In this publication pressure profiles were obtained by tests and calculations. The numerical simulations of detonations inside the pipes were verified by the detonation tests using results of optical deformation measurement.
FE Analysis of Structures With Uncertain Model-Free Material Descriptions
Authors: Freitag Steffen , Graf Wolfgang
Published: August 2012

An artificial neural network concept is presented, which can be used to identify uncertain time-dependent material behavior. Dependencies between strain and stress processes obtained from uncertain results of experimental investigations are described by recurrent neural networks for fuzzy data. Direct and indirect approaches are presented for the computation of fuzzy stress and strain processes from experimental results. The identification of uncertain stress-strain-time dependencies with recurrent neural networks for fuzzy data is realized by a network training utilizing α-cuts and an α-level-optimization. After identification, the network can be applied instead of material models within the finite element method. An incremental finite element formulation is developed under consideration of different time scales for the material level and for the structural level. This enables the finite element analysis of structures with an uncertain model-free material description. An example is presented to demonstrated the applicability of the new approach.
Long-Term Operation Strategies Case Studies for Combined Heat and Power
Authors: Gomes E. E. B. , Olmos C. , Polyzakis A. L. , Pilidis P.
Published: August 2012

In the next years Distributed Poly-generation Systems are expected to play an increasingly important role in the electricity infrastructure and market. The successful spread of small-scale generation either connected to the distribution network or on the customer side of the meter depends on diverse issues, such as the possibilities of technical implementation, resource availability, environmental aspects, and regulation and market conditions. The aim of this study is to develop an economical and parametric analysis of a Distributed Generation System based on gas turbines able to satisfy the energy demand of a typical Hotel complex. Here we show the economic performance of six cases combining different designs and regimes of operation. The software Turbomatch, the gas turbine performance code of Cranfield University, was used to simulate the off-design performance of the engines in different ambient and load conditions. A clear distinction between cases running at full load and following the load could be observed in the results. Full load regime can give a shorter return on the investment than following the load. Despite of CHP systems currently are not economically attractive, in the future this scenario may change due to the environmental regulations and unavailability of low price fuel for large centralised power stations. CHP has a significant potential but requires favourable legislative and fair energy market conditions to successfully increase its share in the power generation market.
Position Control of PWM-Actuated Pneumatic Muscle Actuator System
Authors: Jouppila Ville , Ellman Asko
Published: August 2012

Pneumatic servo positioning systems have been in use for long time and subject to wide spectrum of studies due to their numerous advantages: inexpensive, clean, safe and high ratio of power to weight. However, the compressibility of air and the inherent non-linearity of these systems continue to make achieving accurate position control a real challenge. Conventional pneumatic servo systems are based on cylinder actuators that are difficult to control precisely due to the aforementioned nonlinearities as well as the nonlinear behavior of the air flow through the valve, the friction between the cylinder and the piston, and the stick slip effect at the low velocity of the system. In this paper, a position servo control system using a pneumatic muscle actuator is studied. Pneumatic muscle actuator is a novel type of actuator which has even higher force to weight ratio than the cylinder. In addition, muscle actuator introduces a stick slip free operation giving an interesting option for positioning systems. However, significant hysteresis and position dependant force result in a highly nonlinear system, a real challenge for good control performance. In this paper, pneumatic muscle actuator is controlled by a low-cost on/off valve with PWM-strategy instead of costly servo or proportional valve. The main processes of the system, including flow dynamics, pressure dynamics, force dynamics and load dynamics are derived to provide a full nonlinear model that captures all the major nonlinearities of the system. This model is used for analyzing and tuning the controller performances by simulations before implementing in the real system. In addition, a recently introduced method of using bipolynomial functions to model the valve flow rate is utilized to provide a continuous and invertible description of flow for controller designs. A proportional plus velocity plus acceleration controller with feed-forward component (PVA+FF) is designed based on the linearized system model. For a comparison, a sliding mode controller (SMC) based on linear as well as non-linear system model are designed. The performance of the designed controllers is studied by simulations. The stability and performance analysis includes the effects of friction modeling error and valve modeling error. The robustness of the controllers is tested by varying the payload mass of the system.
The Direct Numerical Simulation of the Rising Gas Bubble With the Volume of Fluid (VOF) Method
Authors: Hironaka Shuji , Manabe Saki , Fujisawa Yuki , Inoue Gen , Matsukuma Yosuke , Minemoto Masaki
Published: August 2012

A gas-liquid two phase flow is complicated and it has not been understood well thus far, in spite of extensive investigation. Numerical simulation is a potential approach to understand this phenomenon. Although a number of studies have been conducted to understand the behavior of bubbles on the basis of computational fluid dynamics (CFD), it is difficult to completely simulate a complicated three-phase flow, including coalescence and breakup of bubbles. Although the two-fluid model based on the semi-empirical model can well estimate the actual behavior of the system in which the equations are derived, the estimation over the applicable region of equations does not always agree with the actual result. Since the 1960s, various procedures have been proposed to directly track the free surface between two phases, for example, the adaptive mesh method and the particle method. Although each of these methods has certain advantages and disadvantages, the volume of fluid (VOF) method is the most acceptable method for capturing the free surface accurately and clearly. However, a concern related to this method is the maintenance of a constant volume of the fluid. In this study, a simulation code using the VOF method is developed in order to estimate the behavior of bubbles in a vertical pipe. Further, an offset of the volume fraction is introduced to stably calculate and minimize the volume fluctuation. The effect of the surface tension is also built into the program in order to estimate the behavior of the bubbles rising through the liquid medium. The simulations of the collapsed water column and a single rising bubble are conducted with the proposed simulation code. Consequently, we confirm that these results fairly agree with the experimental ones.
Thermal and Fluid-Dynamic Behaviour of Confined Slot Impinging Jets With Nanofluids
Authors: Manca O. , Mesolella P. , Nardini S. , Ricci D.
Published: August 2012

Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications in the fields of automotive, aerospace, electronic and process industry. A possible solution to obtain efficient cooling systems is represented by the use of confined or unconfined impinging jets. Moreover, the introduction of nanoparticles in the working fluids can be considered in order to improve the thermal performances of the base fluids. In this paper a numerical investigation on confined impinging slot jets working with water or water/Al2O3 nanofluid is described. The flow is turbulent and a constant temperature is applied on the impinging surface. A single-phase model approach has been adopted. Different geometric ratios and nanoparticle volume concentrations have been considered at Reynolds numbers ranging from 5000 to 20000. The aim consists into study the thermal and fluid-dynamic behaviour of the system. The stream function contours showed that the intensity and size of the vortex structures depend on the confining effects, Reynolds number and particle concentrations. The local Nusselt number profiles show the highest values at the stagnation point and the average Nusselt number increases for increasing particle concentrations and Reynolds numbers and the highest values are observed for H/W = 10 The required pumping power increases as particle concentration as well as Reynolds number grow and it is at most 4 times greater than the values calculated in the case of base fluid.
A Semi–Computational Method to Predict Body Temperatures in an Automotive Paint Bake Oven
Authors: Rao Preetham , Teeparthi Sreekanth
Published: August 2012

The skeleton of a vehicle, known as a Body in White (BiW), with hundreds of sheet metal components is painted in an automotive assembly paint shop. Multiple ovens are used to bake and cure the layers of paint put on the BiW in a paint shop. These ovens are hundreds of feet long and impart heat to a BiW using radiation and convection modes. Prediction of temperature–time history at different locations of a BiW as it passes through a paint bake oven is important to understand the quality of the cured paint. This paper describes a method to predict the same using Computational Fluid Dynamics (CFD) and numerical heat transfer methods, combined with a single generic measurement from the oven. The flow field and the convection parameters around the BiW are obtained from a few quasi-steady CFD simulations of the BiW in the oven. A detailed temperature map on a BiW is then obtained by coupling the CFD results to a transient heat transfer analysis with a moving model of the BiW inside the oven in a thermal nodal network solver. Comparison of the results from the simulation of an actual vehicle and proposed improvements are discussed. The coupled simulation approach is shown to result in a reasonable level of accuracy within acceptable timelines for such a multi-scale physical problem with a highly complicated geometry.