bluuebunny/crossref_metadata_2025 huggingface dataset:
Self-Powered Interface External Circuit for Low-Frequency Acoustic Energy Harvester
Authors: Li Bin , You Jeong Ho , Kim Yong-Joe
Published: April 2014

We present a self-powered interface external circuit design for multiple piezoelectric oscillators used in our recently developed low-frequency acoustic energy harvester. A synchronized switch harvesting on inductor (SSHI) interface circuit has exhibited a significant improvement in the energy harvesting efficiency of piezoelectric oscillator, compared with a standard circuit in AC/DC conversion. A self-powered SSHI interface circuit was developed to overcome the difficulties of typical SSHI, such as the requirements for external power and displacement sensor. The previous studies on self-powered SSHI only considered a single piezoelectric oscillator. The electrical response and operation of multiple piezoelectric oscillators in self-powered SSHI interface circuit has not been reported. In our previous study, multiple piezoelectric cantilever plates were installed in a quarter-wavelength tube resonator to harvest acoustic energy. The interface circuit for our acoustic energy harvester was not further discussed. In this study, a self-powered series-SSHI circuit (self-powered S-SSHI) for multiple cantilever piezoelectric plates has been studied by circuit simulation software Multisim. The simulation results indicate the total powers increase linearly with the piezoelectric plate numbers for both standard and self-powered S-SSHI circuits. The harvesting efficiency for multiple piezoelectric plates of self-powered S-SSHI is obviously higher than the standard circuit. The total maximum output power of 5 piezoelectric plates reaches 8.417 mW with the areal power density 0.421 mW/cm2. This is 335.2% better than the standard circuit (1.934 mW with the areal power density 0.0967 mW/cm2). Compared with the standard circuit, self-powered S-SSHI circuit significantly enhances the conversion efficiency by increasing the piezoelectric voltages and reducing the phase shifts between piezoelectric sources currents and voltages.
Experimental Investigation of the Effect of Materials and Their Surface Colours on Nocturnal Cooling
Authors: Ogueke Nnamdi V. , Nwaigwe Kevin N. , Nwaiwu Chidiebere , Anyanwu Emmanuel E.
Published: April 2014

The experimental investigation of the effects of materials and their surface colours on nocturnal cooling is presented. Two materials, galvanized steel and aluminium, were considered. Three plates of each material were used. One was painted black, the other white, while the third was left unpainted. Each of the plates (0.5 × 0.5 m) was used to cover a wooden box of dimension 0.5 × 0.5 × 0.24 m, made of 0.02 m thick plywood, thus producing an air tight arrangement. Six of such boxes were formed in all; three from galvanized steel and three from aluminium. Ambient temperatures, temperatures of the air inside the box and on the outside surface of the plates were measured between 19:00 hours and 06:00 hours for 6 months. Also measured was the relative humidity. Results obtained reveal that the plates’ performances greatly depended on how clear the night was. For very clear night, the black painted aluminium gave the best result, maintaining a temperature difference of 3–8°C with the ambient. For a partly overcast night, the best result of 1–5°C difference between the inside air and the ambient was recorded by the unpainted galvanized steel while on heavily overcast night the best performance came from the unpainted aluminium with a temperature difference of 1–4°C. Thus unpainted galvanized steel and aluminium are considered best in region where the night sky is hardly clear.
A Study on the Performance and Emission Characteristics of a Diesel Engine Fuelled With Linseed Oil and Diesel Blends
Authors: Rai Ashutosh Kumar , Chauhan Bhupendra Singh , Cho Haeng Muk , Kumar Naveen
Published: April 2014

To meet the challenges of increased energy need and concerned about environmental friendly, renewable fuels are being explored in the current energy scenario. In the present study non edible Linseed oil was used as alternative source for diesel engine fuel. The physico-chemical properties were evaluated and compared with mineral Diesel and found in close resemblance. The fuel was tested by using performance and emission parameters on an unmodified single cylinder diesel engine. The study was done by using diesel & Diesel-linseed oil blends at various loads from no load to 100% loads with interval of 20%. The linseed fuel was blended into 5%, 10%, 15% and 20% v/v ratio with neat diesel and compared with baseline data of neat diesel operation. Performance parameters such as brake thermal efficiency and brake specific fuel consumptions were studied and emission parameters such as CO (carbon mono oxide), UBHC (unburned hydrocarbon), NOx (oxides of nitrogen), CO2 (carbon di oxide), exhaust temperature were measured. The thermal efficiency of the engine was lower and the brake specific energy consumption of the engine was higher when the engine was fueled with Linseed oil-Diesel blends compared to diesel fuel. Emission characteristics are better than diesel fuel. NOx formations, using various fuel blends during the whole range of experiment were lower than diesel fuel. The results from the experimental study suggest that the linseed oil could be a potential substitute for diesel engine in the near future as far as small and medium energy productions are concerned.
Modeling and Control of a Network of Cooperative Satellites Using Neural Networks
Authors: Einafshar Atefeh , Sassani Farrokh
Published: April 2014

An adaptable control system within and on-board a network of interacting satellites is an important module which is desired for unmanned space vehicles. However, such a control system is not easy to develop since it is the core of the network’s operation and all the earth-linked operational information is reviewed and analyzed through it. Due to multipurpose missions of satellites, several decisions are made simultaneously about necessary changes to the satellite’s operational parameters (i.e., orbit, inclination, etc.). In this paper, a neural network model-based control scheme is developed for a network of interacting satellites. The proposed neural control scheme refers to a methodology in which the controller is assumed as a neural network and the dynamical model of the system is identified through the training stages of the neural model. The simulation results show that the neural control method can be effectively applied in monitoring and controlling the satellite networks, without the necessity of determining the mathematical model of the system.
Counter-Rotating Type Tidal-Stream Power Unit Playing Favorable Features in Various Ocean Circumstances
Authors: Usui Yuta , Takaki Kohei , Kanemoto Toshiaki , Hiraki Koju
Published: April 2014

The authors have invented the unique counter-rotating type tidal-stream power unit, which is composed of the tandem propellers and the double rotational armature type peculiar generator without the traditional stator. In the unit of the downstream type, the front and the rear propellers counter-drive the outer and the inner armatures of the peculiar generator respectively, in keeping the rotational torque counter-balanced between both propellers/armatures.

This paper discusses and verifies experimentally the almighty features of the power unit. The axial force acting on the pillar increases naturally with the increase of not only the stream velocity but also the drag of the tandem propellers. Besides, the tandem propellers bring the symmetrical vertical force from side to side though the single propeller brings the force in one direction. The counter-balanced torque makes it possible to moor the power unit with only one cable/wire/rope, and the behavior of the submerged unit was confirmed experimentally.
An Analytical Model of Micromachined Electromagnetic Inductive Contactless Suspension
Authors: Poletkin Kirill V. , Chernomorsky Alexsandr I. , Shearwood Christopher , Wallrabe Ulrike
Published: April 2014

The paper presents an analytical model of a micromachined electromagnetic inductive contactless suspension, which describes the dynamics of a levitated disk shaped proof mass in space, near an equilibrium point. The proof mass is levitated in an electromagnetic field created by a ring shaped coil. The model derives from the analysis of the set of Lagrange-Maxwell equations obtained for the proof mass-coil system in a general form. Also the condition for the stable levitation of the proof mass in space is developed and expressed in terms of coefficients of the quadratic form of a function of mutual inductance between the disk shaped proof mass and ring shaped coil.
Experimental and Numerical Investigation of Plasticity-Induced Fatigue Crack Closure in Overmatched Welds
Authors: Sarzosa Diego F. B. , Ruggieri Claudio
Published: April 2014

This work provides a numerical and experimental investigation of fatigue crack growth behavior in steel weldments including crack closure effects and their coupled interaction with weld strength mismatch. A central objective of this study is to extend previously developed frameworks for evaluation of crack closure effects on fatigue crack growth rates (FCGR) to steel weldments while, at the same time, gaining additional understanding of commonly adopted criteria for crack closure loads. Very detailed non-linear finite element analyses using 3-D models of compact tension C(T) fracture specimens with square groove, weld centerline cracked welds provide the evolution of crack growth with cyclic stress intensity factor which is required for the estimation of the closure loads. Fatigue crack growth tests conducted on plane-sided, shallow-cracked C(T) specimens provide the necessary data against which crack closure effects on fatigue crack growth behavior can be assessed. Overall, the present investigation provides additional support for estimation procedures of plasticity-induced crack closure loads in fatigue analyses of structural steels and their weldments.
Partnering With Industry on Mechanical Engineering Capstone Projects
Authors: Saad Hani S. , Weiser Martin W. , Richter Donald C.
Published: April 2014

The purpose of a Capstone course is to present the students with an engineering problem that needs to be solved. The students work in teams and are expected to document and research each step of the process. The idea is to mimic, as much possible, the situation encountered by engineers in the field. While industry sponsored projects are preferred, suggestions from students are also welcomed. The Mechanical Engineering (ME) and Mechanical Engineering Technology (MET) Department at Eastern Washington University has traditionally pursued industry sponsored projects by reaching out to the local businesses and through the department Industrial Advisory Committee. While the ME degree is a relatively new addition, the MET degree has been offered for many years. With the addition of the ME program, change came to the Capstone course. Emphasis is placed more on research and not on production. The goal now is to create one prototype instead of fifteen while focusing heavily on the research part. This change has an effect on the dynamics of the course and presents additional challenges, especially with industry sponsored projects. These changes are relevant to both the MET and ME Capstone courses. This paper highlights these challenges for four projects done in the spring of 2012 and proposes efficient ways of addressing them. One of these projects was very successful, two were moderately successful, and one was not particularly so. Recommendations for teachers and students on the best ways to approach such a project are also highlighted.
Frequency Response of Ligament Deficient Knees in Anterior-Posterior Drawer Test
Authors: Caruntu Dumitru I. , Martinez Thania A. , Granados Eduardo
Published: April 2014

This paper deals with nonlinear dynamics of deficient knees. A two dimensional model of the human knee to include tibia and femur, and the ligamentous structure between the two bones has been developed. The aim of this paper is to use nonlinear dynamics to differentiate between normal and deficient knees. An exercise in which the femur is fixed in a sitting position, and tibia is actuated by an anterior-posterior soft harmonic force at various frequencies is proposed. The results clearly show a significant difference between the behavior of normal knees and Anterior Cruciate Ligament (ACL), and Posterior Cruciate Ligament (PCL) deficient knees.
Significance of Damping and its Simulation in Fatigue Damage
Authors: Rao J. S.
Published: April 2014

Aircraft engine fan blades and Steam turbine LP stage blades are the longest blades in a given turbomachine and are prone for fatigue failures. The alternating stresses induced are very high due to foreign objects ingestion in aircraft engines and off-design operations of steam turbines causing high stresses in the last stage blades. Damping is the main unknown factor in life estimation of such blades and this paper describes a procedure of analytical determination of damping due to hysteresis, macro and microslip damping mechanisms and determination of resonant stresses leading to accurate life estimation.
Dynamic Analysis of Piezoelectric Valveless Micropumps: Effects of Piezoelectric Transducer Material
Authors: Sayar Ersin , Farouk Bakhtier
Published: April 2014

Dynamic structural and fluid flow analysis of bulk acoustic wave piezoelectric valveless micropumps are carried out for the transport of water. The micropumps consist of trapezoidal prism inlet/outlet elements; the pump chamber, a thin structural layer (Pyrex glass) and a piezoelectric transducer element (PZT-5A, PZT-4, or BaTiO3), as the actuator. Flow contraction and expansion, through the trapezoidal prism inlet and outlet respectively, generates net fluid flow. Governing equations for the flow fields and the structural-piezoelectric bi-layer membrane motions are considered. For the compressible flow formulation, an isothermal equation of state for the working fluid is employed. Two-way dynamic coupling of forces and displacements between the solid and the liquid domains in the systems are considered where actuator deflection and motion causes fluid flow and vice-versa. The effects of the piezoelectric transducer material on the flow rate are investigated for several commonly used actuators: PZT-5A, PZT-4, and BaTiO3. The net flow rate developed by the pump varies with the piezoelectric material. PZT-5A actuator generates the largest pump net flow, and the BaTiO3 actuator results in the lowest pump flow.
Application of Artificial Neural Network for Single Horizontal Bare Tube and Bare Tube Bundles in Gas-Solid (Air-Solid) Fluidized Bed of Small and Large Particles: Heat Transfer Predictions
Authors: Govindaswamy Ravindranath , Srinivasan Savitha
Published: April 2014

This paper presents heat transfer analysis of single horizontal bare tube and in-line arrangement of bare tube bundles in gas-solid (air-solid) fluidized bed and predictions are done by using Artificial Neural Network (ANN) based on the experimental data. Measurement of average heat transfer coefficient was made by local thermal simulation technique in a cold square bubbling air-fluidized bed of size 0.305m × 0.305m. Studies were conducted for single bare tube and bare tube bundles of in–line arrangement using beds of small (average particle diameter less than 1mm) silica sand particles and of large (average particle diameter greater than 1mm) particle (raagi and mustard). Within the range of experimental conditions influence of bed particle diameter (Dp), fluidizing velocity (U) were studied, which are significant parameters affecting heat transfer.

Artificial neural networks (ANNs) have been receiving an increasing attention for simulating engineering systems due to some interesting characteristics such as learning capability, fault tolerance, and non-linearity.

Here, feed-forward architecture and trained by back-propagation technique is adopted to predict heat transfer analysis found from experimental results. The ANN is designed to suit the present system which has 3 inputs and 2 outputs. The network predictions are found to be in very good agreement with the experimental observed values of bare tube heat transfer coefficient (hb) and Nusselt number of bare tube (Nub).
Study the Geometrical Effects on the Unsteady Pulsatile Flow Through a Microchannel With a Sudden Step Shape
Authors: Nejat Amir , Kowsary Farshad , Ebrahimi Saman , Hasanzadeh Amin
Published: April 2014

In this paper, pulsatile flow through a microchannel with step expansion shape and working as valveless microvalve is investigated. The design of the microchannel is such that it causes the production of different vortex structures in the flow field and near corners. Our primary objective is to investigate how geometrical parameters affect the performance of the microvalve under different flow conditions. Unsteady, two-dimensional axisymmetric flow of an incompressible Newtonian fluid with laminar regime was simulated numerically using finite element approach. In order to imitate the actuation mechanism of a micropump, a time-varying sinusoidal pressure was set at the inlet region of the microchannel. Two basic dimensions were found to have crucial effect on the flow field configuration and vortex generation: the expansion ratio of the channel and the distance of the obstacle from the expansion region. The frequency of the actuation mechanism was varied from 1Hz to 1000Hz to cover the working range for many micropump applications. As the pressure is a key factor and should be manipulated in the right way, the pressure contours were studied. Vortex growth was captured through a single cycle and their size and existence time was compared for different geometrical inputs. At last, Strouhal number which is a measure of unsteadiness of the flow was calculated. This way we can investigate the sensitivity of the flow to changes in block obstacle distance from the expansion section and the expansion ratio. The obtained results lead to better understanding of the physics of pulsatile flows through microchannels and help in improving the efficiency of the existing configuration in designing more efficient micropump systems.
Experimental Characterization of Thin-Film Thermoelectric Based Active Cooling Modules
Authors: Annapragada S. Ravi , Pearson Matthew R. , Rioux William A. , Lents Charles E.
Published: April 2014

Improvements in electronic devices have led to increased power densities and need for small scale miniature cooling solutions. To address this issue, Defense Advanced Research Projects Agency (DARPA), Microsystems Technology Office (MTO) created the Active Cooling Modules (ACM) effort to develop technology solutions able to provide small scale (4 cm2) active high heat flux cooling of a 100W device (25 W/cm2) at a 15 °C temperature lift with Coefficient Of Performance (COP) comparable to state of the art thermoelectric coolers. Thin-film thermoelectric cooling devices are well suited to provide high heat flux active cooling. In the present work, an experimental apparatus is developed to characterize the performance of a subscale thin-film thermoelectric cooling modules 1/144th, 1/36th and 1/9th the size of a full scale 4 cm2 device. An in-situ calibration methodology is proposed to characterize the performance of these thermoelectric microcoolers. In this early development work, vacuum conditions are maintained to minimize thermal losses between the thermoelectric module sink and source sides. The small size of the subscale devices and vacuum conditions introduce additional uncertainties into the system and could lead to errors in COP measurement (>0.5). The additional sources of errors as the device dimensions shrink are identified and minimized leading to energy balance in the system.
A Hierarchical Model for Kevlar Fiber Failure
Authors: Recchia Stephen S. , Pelegri Assimina , Clawson Jan K. , Sahin Korhan , Chasiotis Ioannis , Zheng James
Published: April 2014

Advances in materials characterization at the submicron and the nano-scales have progressed in the last decade. At the same time, computational capability for finite element analyses are also improving through technological developments in parallel computing. However, large computational models of nanostructured materials are currently limited by the lack of validation data. The work reported in this paper describes the formulation of a representative nanoscale model for Kevlar fibers based on failure section imaging that captures its fibril and microfibril structure. In this regard, a finite element model that captures the nanoscale structure of Kevlar fibers was developed to predict their macroscale response. Experimental derivation of geometrical parameters and physical properties of fibrils and microfibrils is challenging due to the sensitive nature of polymers. There are several microfibril parameters that reflect into effective fiber response, such as the microfibril constitutive behavior, length, diameter, shape, the inter-fibril shear and normal strength, and the inter-fibril normal and tangential force decay the after peak strength is achieved. This paper investigates the effect of each of the aforementioned parameters on the initial modulus, yield strength, ultimate strength, and strain rate dependence of Kevlar fibers with 10 μm average diameter. The sensitivity of the macroscale response to each microfibril parameter can be used to identify areas where experimental information can further enable the predictive capability of the computational model. A parametric study was performed to calculate the effective macroscale fiber response. Subsequently, a local gradient sensitivity method was employed to plot the sensitivity of the fiber response to each microfibril parameter.
Enhanced Carbon Capture in a Multiport Microscale Absorber
Authors: Ganapathy Harish , Steinmayer Sascha , Shooshtari Amir , Dessiatoun Serguei , Alshehhi Mohamed , Ohadi Michael M.
Published: April 2014

Increasing concerns on the effects of global warming leading to climate change has necessitated the development of efficient technologies to separate acid gas components, such as carbon dioxide and hydrogen sulfide, from gaseous mixtures. Microscale technologies have the potential to substantially enhance gas-liquid absorption processes on account of their inherent high surface area to volume ratio. The present work reports the mass transfer characteristics during gas-liquid absorption in a multiport microscale absorber. The reactor was designed to comprise of 15 straight, parallel channels having a hydraulic diameter of 456 micrometer and square cross-sectional geometry. The absorption of CO2 mixed with N2 into aqueous diethanolamine was investigated. The performance of the absorber was characterized with respect to the absorption efficiency and mass transfer coefficient. Parametric studies investigating the effects of the gas and liquid phase superficial velocity were performed and discussed. Additionally, the effect of varying the liquid reactant concentration was investigated and discussed.
Heuristic GP Finite Element Method for Structural Thickness Optimization
Authors: Saad Mahmoud R. , Metwalli Sayed M.
Published: April 2014

A finite element procedure created based on the linear strain triangle method is developed for structural thickness optimization. A new stiffness matrix is developed after assuming a linear relation between the triangle corner nodes. Nodes thicknesses are optimized using the developed Heuristic Gradient Projection (HGP) method to reach uniform stress among the structure to satisfy the constrained allowable stress designated by the designer. The advantage of the proposed method is that structural optimization can be carried out easily. Furthermore, this method gives more stable converging results and reduced the number of iterations and number of elements needed compared to the constant strain triangle with variable thicknesses which produced oscillating results before settling. This facilitates combination with other finite element software for structural thickness optimization.
Effect of Sizing Removal Method and POSS Coating on Flexural Properties of Carbon Fiber Epoxy Composites
Authors: Ibn Afzal Fariz , Saha Mrinal C. , Altan M. Cengiz
Published: April 2014

Effects of sizing and surface modification on flexural properties of carbon fiber reinforced epoxy composites have been investigated. Carbon fiber was desized using three types of treatments, namely heat, acetone, and acetone-acid. In addition, these fibers were coated with three different types of Polyhedral Oligomeric Silsesquioxane (POSS) molecule. Composite panels were fabricated using the vacuum assisted resin transfer molding and samples were tested in flexure. Scanning electron microscopy analysis was performed to investigate the surface morphology and failure mechanisms. It was found that removal of sizing significantly reduced the flexural strength. About 19% and 29% reduction of flexural strength was reported for acetone treatment and heat treatment, respectively. Composites with POSS coated fibers showed improved properties, except for the heat treated fibers. Among POSS molecules investigated, the S10455 was found to be the best for improving the flexural properties of carbon fiber composites.
A Coupled Electromagnetic and Thermal Model for Picosecond and Nanometer Scale Plasmonic Lithography Process
Authors: Chao Ion-Hong , Pan Liang , Sun Cheng , Zhang Xiang , Lavine Adrienne S.
Published: April 2014

Plasmonic lithography may become a mainstream nano-fabrication technique in the future. Experimental results show that feature size with 22 nm resolution can be achieved by plasmonic lithography. In the experiment, a plasmonic lens is used to focus the laser energy with resolution much higher than the diffraction limit and features are created in the thermally sensitive phase change material layer. The energy transport mechanisms are still not fully understood in the lithography process. In order to predict the lithography resolution and explore the energy transport mechanisms involved in the process, customized electromagnetic wave and heat transfer models are developed in COMSOL. Parametric studies on both operating parameters and material properties are performed for optimizing the lithography process. Parametric studies show that the lithography process can be improved by either reducing the thickness of the phase change material layer or using a material with smaller real refractive index for that layer.
Analysis of a Feedback Assessment Loop in Engineering Sciences Core Curriculum
Authors: Ghosh Amitabha
Published: April 2014

A formal two-loop learning outcomes assessment process has been evaluated in the mechanical engineering department at Rochester Institute of Technology. This initiative, originally called the Engineering Sciences Core Curriculum (ESCC), provided systematic course learning outcomes and assessment data of student performance in Statics, Mechanics, Dynamics, Thermodynamics, Fluid Mechanics and Heat Transfer. This paper reports detailed analyses with some important observations in the Statics-Dynamics sequence to determine obstacles in student performance. New data shows that students’ mastery of Dynamics is affected largely by incorrect interpretations and weak retention of fundamentals in Statics. Further evidence of students’ behavioral influences are discussed requiring a future focus in this area. This report completes the 5 year feedback loop designed to achieve the ESCC goals on the Statics-Dynamics sequence.
Thermal Conductivity Measurements of Ultra-Thin Amorphous Poly(Methyl Methacrylate) (PMMA) Films
Authors: Kim Ickchan , Burzo Mihai G. , Komarov Pavel L. , Raad Peter E.
Published: April 2014

As technology progresses towards smaller and higher density microelectronic devices, we are faced with working with atomic-scale dimensions that present us with challenges but also opportunities. Since mechanical and chemical properties of ultra-thin polymeric films can vary dramatically from their bulk, the thermophysical properties of thin films are also expected to vary. Ultra-thin poly(methyl methacrylate) (PMMA) films have been the focus of numerous investigations in recent years as a data storage medium. Employing Atomic Force Microscopy (AFM) technology, it is possible to store data bits by heating a target zone until it melts, which leaves a nano-dimple indentation in the PMMA polymer film. The AFM technology has great potential because it possesses considerable data density when compared to conventional magnetic data storage. Since the amount of heat that needs to be used to melt the nanoscale region of the polymer needs to be precisely controlled, knowing the thermophysical properties of such films is a critical factor in advancing this technology. It is known that heat carriers such as electrons and phonons in metallic and dielectric materials, respectively, are influenced by the “size effect” in the micro and nano-scale dimensions. Therefore, a goal for this investigation is to determine whether any dependence exists between the PMMA’s film thickness and its thermal conductivity.

In this work we investigated whether a “scale effect” on intrinsic thermal conductivity actually exists for amorphous PMMA films with thicknesses ranging from 40 nm to 2 μm. The approach is based on the transient thermoreflectance (TTR) method, where the change in the surface temperature is measured by detecting the change in the reflectivity of the sample. The sample is heated by laser irradiation and probed using a continuous-wave laser that detects changes in the reflectivity of the heated material surface. The experimentally obtained transient temperature signature is then used to extract unknown values of thermal properties. Based on our previous experience with measuring a wide range of thin-film materials and the data available in the literature, we expected a lower thin-film thermal conductivity as compared to the bulk value. Surprisingly, the results show that the intrinsic thermal conductivity of layers thinner than 40 nm PMMA film deposited on native silicon oxide is about three times higher than the bulk PMMA value. A similar trend was observed for all ultra-thin (sub 100 nm) films.
Application of Phase Change Material in Sustainable Cooling of Data Centers
Authors: Dhiman Nikhil , Shah Jeet , Agonafer Dereje , Kannan Naveen , Hoverson James , Kaler Mike
Published: April 2014

The ever increasing information technology heat load and data center cooling energy are the main reasons to investigate the performance of microencapsulated phase change slurry over other heat transfer fluids.

Microencapsulated phase change slurry is dispersion where the phase change material, microencapsulated by a polymeric capsule, is dispersed in water. Compared to water, these new fluids have a higher heat capacity during phase change and a possible enhancement, as a result of this phase change, in the heat transfer phenomenon. The composition of phase change material used in slurry greatly affects its efficiency, If not selected properly it can cause serious damage, e.g. agglomeration and clogging of pipes.

The main objective of this work is to develop standalone pumpable microencapsulated phase change slurry that is able to withstand shear stresses of the pump and other course surfaces of pipe and pipe joints. In this study, experiments were performed, to determine performance of microencapsulated phase change slurry over conventional heat transfer fluids. After certain pumping cycles, scanning electron microscopy (SEM) has been done to analyze the conditions of shell material of polymeric capsule. Results obtained from SEM show that centrifugal pump is compatible with mPCM particle size upto 3 μm.

It is true that selected mPCS have shown better performance over water in hot water bath in case of thermal storage. Also, closed loop final testing has shown that heat flux is about 2–3 times higher with mPCS than water.
Stochastic Multiscale Modeling and Damage Progression for Composite Materials
Authors: Johnston Joel , Chattopadhyay Aditi
Published: April 2014

Modeling and characterization of complex composite structures is challenging due to uncertainties inherent in these materials. Uncertainty is present at each length scale in composites and must be quantified in order to accurately model the mechanical response and damage progression of this material. The ability to pass information between length scales permits multiscale models to transport uncertainties from one scale to the next. Limitations in the physics and errors in numerical methods pose additional challenges for composite models. By replacing deterministic inputs with random inputs, stochastic methods can be implemented within these multiscale models making them more robust.

This work focuses on understanding the sensitivity of multiscale models and damage progression variations to stochastic input parameters as well as quantifying these uncertainties within a modeling framework. A multiscale, sectional model is used due to its efficiency and capacity to incorporate stochastic methods with little difficulty. The sectional micromechanics in this model are similar to that of the Generalized Method of Cells with the difference being the discretization techniques of the unit cell and the continuity conditions. A Latin Hypercube sampling technique is used due to its reported computational savings over other methods such as a fully random Monte Carlo simulation. Specifically in the sectional model, the Latin Hypercube sampling method provides an approximate 35 % reduction in computations compared to the fully random Monte Carlo method. The Latin Hypercube sampling is a stratified technique which discretizes the distribution function and randomizes the input parameters within those discretized fields. Within this multiscale modeling framework, a progressive failure theory is implemented using these stochastic methods and a modified Hashin failure theory. With a combined stochastic method and progressive failure theory, this multiscale model is capable of modeling the uncertainty and material property variations for composite materials.
Local Axial Relative Velocity Measurements in Bubbly, Cap-Bubbly, and Slug Flows
Authors: Doup Benjamin , Zhou Xinquan , Sun Xiaodong
Published: April 2014

The local axial relative velocity between the gas and liquid phases in vertical air-water two-phase bubbly, cap-bubbly, and slug flows is investigated at axial measurement locations of z/D = 10 and 32. These measurements are performed in an acrylic vertical pipe with an inner diameter of 50 mm and a height of 3.2 m. The local gas-phase velocity and void fraction measurements are performed using a four-sensor conductivity probe at 14 radial locations. The void fraction profiles are presented to show the flow structure and are used along with visual observation to classify the flow regimes. The liquid-phase velocity measurements are performed using a particle image velocimetry (PIV) system. To separate the liquid-phase information from that of the gas phase an optical phase separation method that uses fluorescent particles and an optical filtration technique is adopted. To remove other noises, such as bubble residuals, background noise, and optically distorted particles from the images that are not removed using the optical phase separation method, an image pre-processing scheme is applied to the raw PIV images. The local axial relative velocity obtained from these local gas- and liquid-phase measurements are important for modeling the momentum transfer between the two phases.
A Regional University Perspective on Engineering Education of Multi-Cultural Freshman Students From South Pacific Countries
Authors: Ram Krishnil R. , Sharan Roneel V. , Ahmed Mohammed Rafiuddin
Published: April 2014

Of late, there is a growing need for quality engineers who have the ability to solve complex engineering problems with reasonable knowledge of ethics and economics. This has led many universities to pursue accreditation by professional engineering bodies. While the accreditation process installs a standardized system of quality teaching, it is important that the engineering entrants have a degree of understanding that allows implementation of quality teaching methods. This study looks at the performance of first year engineering students in a bid to identify major issues that students face in a Bachelor of Engineering program. The learning of students in the School of Engineering and Physics at the University of the South Pacific is influenced by interactions of at least 12 different cultures from the 12 member countries of the university. The study looks at how students perform across cultures in the first year mechanical engineering courses, mainly engineering mechanics and engineering graphics & design. The general trend over the last five years shows that while the student numbers in the program have been increasing, student performance in one course seems to be improving but declining in the other; the two courses differ considerable in contents, required skill sets, and assessment methodologies. The study also presents possible reasons for the varied performance by considering issues such as cultural and academic backgrounds, use of teaching tools and resources, and revisions to the course and program and looks at how multi-cultural engineering education can be improved. The number of female students taking up engineering as their major is also looked at and positive trends are seen with female participation increasing from 7.6% in 2008 to 13.9% in 2013.
Sound Propagation Around Arrays of Cylinders
Authors: Zheng Zhongquan C. , Ke Guoyi
Published: April 2014

Sound propagation through sonic crystals has been widely studied through predictions and laboratory experiments, because of its potential applications in many areas such as environmental noise barriers and sound cloaking. In this paper, a finite-difference time-domain (FDTD) numerical simulation coupled with the immersed boundary method is used to investigate the transmission properties of sonic crystals. The sonic crystals in this study are modeled as arrays of cylinders with their axes parallel to a ground boundary. Compared with semi-analytical solutions, the numerical scheme is validated with cases of simple arrays of rigid cylinders. The locations of cylinders, different porous materials for cylinders, and the ground effect are taken into account in our simulation. The results are presented with discussions on achieving optimized sonic crystals.
What Fraction of the Fuel Consumed by a Heat-and-Power Cogeneration Facility Should Be Allocated to the Heat Produced? Old Problem, Novel Approach
Authors: Iora Paolo , Ghoniem Ahmed F. , Beretta Gian Paolo
Published: April 2014

The question of what fraction of the fuel consumed by a cogeneration plant is to be allocated to either the heat or the electricity is still open, leading to some arbitrariness in the quantification of the economic value of the different cogenerated goods and of the subsidies often granted to such facilities. In this work, we first evidence the drawbacks of the conventional allocation methods such as Incremental Electricity-Centered Reference (IECR), Incremental Heat-Centered Reference (IHCR) and Separate-Productions Reference (SPR), in that they use fixed partial primary energy factors chosen by some authority to represent the reference efficiencies of heat and /or electricity production technologies that can be different from the local energy portfolio. Here we propose a slightly more elaborate, but self-consistent method whereby the allocation is adaptive and self-tuned to the local energy scenario by sharing the fuel savings on the basis of the average primary energy factors for electricity and heat in the given local area including the cogeneration facility of interest. We call it the Self-Tuned Average-Local-Productions Reference (STALPR) method. We finally show by means of a representative case study that the classical methods might provides unfair, distorted figures that become increasingly important as cogeneration gains higher fractions of the energy market in a given local area.
Plate Vibration and Geometry Study of Impact-Control ABS
Authors: Dundar Mehmet Akif , Ayorinde Emmanuel
Published: April 2014

Acrylonitrile-Butadine-Styrene (ABS) has been receiving much attention as a cushion against impact and vibration, on account of its very favorable mechanical properties, including elevated impact strength, stiffness and tensile strength, as well as outstanding formability. The geometry of deployed samples does influence dynamic performance. In this work, the methods of analysis, experiment and numerical computation have been applied to explore different modal parameters of rectangular ABS specimens with completely free boundary conditions. Experimentally, Pulse 15.1 software was used to investigate the modal parameters while the specimens were numerically modeled in Abaqus/Standard 3D using C3D20R (second order 20-node quadratic brick) element types with the Lancsoz Eigensolver method. Parametric explorations over the geometry space enabled useful trends to be identified with respect to vibration and impact applications. Experimental and numerical results were found to compare very favorably.
Towards a Universal Scaling for Broadband Turbulent Noise in Internal Flow Devices
Authors: de Jong Arjen , Golliard Joachim
Published: April 2014

An investigation is performed on the scalability of broadband noise sources from separated flows in internal pipe systems. Broadband sources from for example wellhead chokes, bends and valves can potentially excite subsea manifolds through fluid acoustic coupling and fluid structural coupling. The focus of the current work is evaluation and improvement of scaling laws for collapse of sound power spectra. The approach proposed here is to use steady-state Computational Fluid Dynamics [CFD] to better estimate the properties of the flow in order to improve the scaling law and obtain a universal broadband spectrum. Steady Reynolds Averaged Navier-Stokes [RANS] simulations of several bend and orifice geometries have been performed. A surface acoustic power model based on modeled turbulent quantities is implemented. Based on the RANS data, more advanced models for scaling have been developed. Experimental sound power spectra from literature of the simulated geometries are scaled using different methodologies in both amplitude and frequency. When a new scaling based on CFD modeled surface acoustic power was used, a universal collapse among geometries occurred. Using CFD, the velocity in the high-speed sound-producing region is obtained, as well as a more accurate length scaling in order to improve the frequency scaling. A vast improvement in collapse over different geometries is achieved. The current work indicates that a universal collapse might indeed be present. The methodology does not require high fidelity calculations and is thus easy to implement. By comparing original and new scaling laws, it turns out that the ratio of fluctuating drag over steady drag can vary among geometries.
Two Equation Two-Fluid Model Analysis for Stratified Flow Under Kinematic and Dynamic Instabilities
Authors: Lopez de Bertodano Martin A. , Fullmer William D.
Published: April 2014

The unstable one-dimensional incompressible two-fluid model including a hydrostatic force is reduced to a two equation model in terms of the liquid volume fraction and the liquid velocity. For small density ratios the model may be simplified to a formulation that is equivalent tothe Shallow Water Theory (SWT) equations [Whitham, 1975] with a source term corresponding to the two-fluid model constitutive relations for wall and interfacial shear and to a void gradient term that contains the Kelvin-Helmholtz mechanism.

Linear stability of the SWT equations shows that the model is made well-posed stable by the hydrostatic force. However, unlike the SWT equations, the two equation two-fluid model is only conditionally stable. As the gas velocity increases the model becomes unstable once the kinematic instability occurs, i.e., the Viscous Kelvin-Helmholtz (VKH) instability. When the gas velocity is increased further the model becomes dynamically unstable, i.e., it reaches the Inviscid Kelvin-Helmholtz (IKH) instability limit. Beyond the IKH limit the model becomes ill-posed and requires higher order modelling, e.g. surface tension. Simple analytic expressions for the two instabilities are obtained because of the simplified mathematics of the two equation model. Furthermore, the wave “sheltering” effect, which allows more accurate predictions of the flow regime transition, may be easily incorporated into the analysis. The theory is validated with the new HAWAC flow regime map [Vallee et al., 2010].

The two equation two-fluid model is consistent with all previous results of two-fluid model linear stability for stratified flow and, since it is a special case of SWT, it is amenable to non-linear stability analysis and a very broad body of mathematics literature on non-linear kinematic waves, e.g., Whitham (1974) is now directly applicable when the model is not IKH unstable.
Natural Convection Through an Open Cavity Heated From the Side and Filled With Fluid and Discrete Solid Blocks
Authors: Franco A. T. , Loyola L. T. , De Lai F. C. , Junqueira S. L. M. , Ganzarolli M. M. , Lage J. L.
Published: April 2014

In this study, natural convection inside a square open cavity containing several solid obstructions is modeled and numerically simulated. The horizontal surfaces of the cavity are adiabatic, while the vertical left wall is isothermally heated. The cavity, opened on the right side to a fluid reservoir, is filled with equally spaced, disconnected, square conducting blocks. The total amount of solid constituent within the enclosure is kept constant by fixing the cavity solid volume-ratio at 36% (equivalent to porosity equal to 64%). The effects of varying the number of solid blocks used and the Rayleigh number on the Nusselt number (based on the surface-averaged heat transfer coefficient along the heated wall of the enclosure) and on the volumetric flow rate entering the cavity induced by the natural convection are considered in detail. The results show the Nusselt number to be affected by the phenomenon of interference caused by the blocks, which increases in predominance as Ra increases. The volumetric flow rate, on the other hand, shows less of an effect by the interference of the blocks to the boundary layer, and more the flow hindrance effect of the blocks within the entire cavity. This effect is shown, nevertheless, to predominate when Ra is small — similarly to the interference effect.