bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural Performance Analysis of Hydroxyapatite Scaffolds for Tissue Engineering
Authors: Gallegos-Nieto Enrique , Medellín-Castillo Hugo I. , de Lange Dirk F. , Mejía-Rodríguez Gilberto
Published: April 2014

The development of hydroxyapatite (HA) scaffolds for tissue regeneration, particularly for bone regeneration, is an alternative to treat bone defects due to cancer, other diseases or trauma. Although the hydroxyapatite has been widely studied in the literature, there are still some disparities regarding its mechanical performance. This paper presents the analysis of the structural performance of hydroxyapatite scaffolds based on experimental tests and numerical simulations. HA scaffolds with variable porosity were fabricated by the water soluble polymer method, using the Poly Vinyl Alcohol (PVA) as pore former. These scaffolds were then characterized by scanning electronic microscopy (SEM), stereo microscope and X ray diffraction (XRD). Different porous structures models were considered and analyzed by the finite element method (FEM). Compressive tests were carried out and used to validate the proposed numerical models. Also a theoretical analysis based on the Gibson and Ashby [1] model was performed. Finally the experimental, numerical and theoretical results were compared and the results show that the proposed numerical and theoretical models can be used to predict, with adequate accuracy, the mechanical behavior of HA scaffolds for different porosity values.
Analyzing Steady-State Visual Evoked Potentials for Effective User Response Detection for Brain-Computer Interfaces
Authors: Riyahi Pouria , Eskandarian Azim
Published: April 2014

This article evaluates an M-order Adaptive Kalman filter analysis on Steady-State Visual Evoked Potentials (SSVEPs). This model is based on finding the original brain source signals from their combined observed EEG signals. At each time step, observed brain signals are filtered according to their ideal reference signals measured from 10, 11, 12 and 13 Hz LED stimuli. SSVEP response detection is based on maximum Signal to Noise Ratio (SNR) of the brain source signals. In each test, the average system accuracy is calculated with and without overlapped time-windows along with system Information Transfer Rate (ITR). The overall system accuracy and ITR are showing promising level of SSVEP detection for future online BCI systems.
Temperature Dependent Solid Fuel Combustion Characterization and Fuel Ranking
Authors: Agarwal Gaurav , Liu Gang , Lattimer Brian
Published: April 2014

Fuel combustion performance was quantified through measurement of the gravimetric response of the fuel as well as the energetic behavior. A Simultaneous Thermogravimetric Analyzer (STA) was used to measure the gravimetric, sensible energy, and latent heat energy (including heat of pyrolysis) for fuels. The heat release rate and heat of combustion of the fuels as a function of temperature released due to the combustion of the pyrolysis gases was measured using a Micro-Combustion Calorimeter (MCC). Fuels were tested at a heating rate of 20°C/min from room temperature to 800°C in inert (nitrogen) environment. Fuels considered in this study included US eastern coal, biomass (cornstover and switchgrass), polystyrene, glycerol and mixtures of some of these fuels. Biomass feedstocks were also evaluated for the effect of water leaching on fuel performance. A lumped model energy balance on a fuel particle revealed that fuel volatility can be ranked based on the net energy required to produce the volatile gas times the ratio of the heat of combustion to the heat of decomposition. This is different compared with previous research results in that it includes the temperature dependence of the fuel production in the volatility.
A Numerical Approach for the Simulation of Internal Nozzle Flow in a Pressure Swirl Atomizer Using Different Turbulent Models and Towards an Effective Inlet Weber Number
Authors: Abbasi Baharanchi Ahmadreza , Gokaltun Seckin , Eshraghi Shahla
Published: April 2014

VOF Multiphase model is used to simulate the flow inside a pressure-swirl-atomizer. The capability of the Reynolds Stress Model and variants of the K-ε and K-ω models in modeling of turbulence has been investigated in the commercial computational fluid dynamics (CFD) software FLUENT 6.3. The Implicit scheme available in the volume-of-fluid (VOF) model is used to calculate the interface representation between phases. The atomization characteristics have been investigated as well as the influence of the inlet swirl strength of the internal flow. The numerical results have been successfully validated against experimental data available for the computed parameters. The performance of the RNG K-ε model was found to be satisfactory in reducing the computational cost and introducing an effective Weber number for the flow simulated in this study.
Mechanical Characterization of the Decellularized Porcine Small Intestinal Submucosa Extracellular Matrix
Authors: Zhao Shijia , Gu Linxia , Hammel James M. , Lang Haili
Published: April 2014

In this work, the decellularized porcine small intestinal submucosa extracellular matrix (SIS-ECM), obtained from the commercial product under the trade name of CorMatrix, were tested in uniaxial tension. Preconditioning under cyclic loading of 2 N was conducted to stabilize the mechanical response of the tissue. The influence of rehydration time on the mechanical properties of the tissue was evaluated. Results suggested that the stiffness of SIS-ECM decreased with longer rehydration time. Considering the application of CorMatrix in pericardial closure, the native pericardium samples were also tested. The comparison indicated that the native pericardium is softer than rehydrated CorMatrix. This work can facilitate the surgeons to better choose the appropriate rehydration time when conducting the extracardiac implantations, such as pericardial reconstruction, pericardial closure, etc.
3-D Characterization of Global and Local Microstructural Effects on Spall Damage in Shock Loaded FCC Metals: Experimental and Modeling
Authors: Brown A. , Krishnan K. , Wayne L. , Peralta P. , Luo S. N. , Byler D. , Patterson B.
Published: April 2014

Global and local microstructural weak links for spall damage were investigated using 3-D characterization in polycrystalline (PC) and multicrystalline (MC) copper samples, respectively. All samples were shocked via flyer-target plate experiments using a laser drive at low pressures (2–6 GPa). The flyer plates measured approximately 500 μm thick and 8 mm in diameter and the target plates measured approximately 1000 μm thick and 10 mm in diameter. Electron Backscattering Diffraction (EBSD) and optical microscopy were used to determine to presence of voids and relate them to the surrounding microstructure. Statistics on the strength of grain boundaries (GBs) was conducted by analyzing PC samples and collecting the misorientation across GBs with damage present, and it was found that a misorientation range of 25–50° is favorable for damage. Statistics were also taken of copper PC samples that had undergone different heat treatments and it was found that although the 25–50° range is less dominant, it is still favorable for damage nucleation. Removal of initial plastic strain via heat treatments and an increase in Σ3 CSL boundaries, indicative of strong annealing twins, also led to an increased amount of transgranular damage. 3-D X-ray tomography data were used to investigate the shape of the voids present in untreated, as received and heat treated samples. It was found that the as received sample contained a higher amount of “disk”, or, “sheet-like” voids indicative of intergranular damage, whereas the heat treated samples had a higher fraction of spherical shaped voids, indicative of transgranular damage. MC samples were used to study microstructural weak links for spall damage because the overall grain size is much larger than the average void size, making it possible to determine which GBs nucleated damage. Simulations and experimental analysis of damage sites with large volumes indicate that high Taylor factor mismatches with respect to the crystallographic grain GB normal is the primary cause for the nucleation of damage at a GB interface and a low Taylor factor along the shock direction in either grain drives void growth perpendicular to the GB. Cases where experimental results show damage and simulation results show no damage are attributed to the presence of an intrinsic microstructural weak link, such as an incoherent twin boundary.
Numeric Investigation of Fluid Solid Interaction on Wind Turbine Blade
Authors: Hossain Mohammad A. , Lee Kyoungsoo , Huque Ziaul , Kommalapati Raghava R.
Published: April 2014

The current work is focused on numeric investigation of aerodynamic load developed on a wind turbine blade and its effects on aeroelastic characteristics of a wind turbine blade. In order to do that proper turbulent model along with appropriate assumptions need to be determined. Geometry is modeled with actual blade data for both twist and tapper. Blade tip is not considered during the modeling. Validation is done by NREL phase VI wind turbine blade data as well as other published data. Finally the aerodynamic load obtained from the CFD simulation is transferred to perform the structural analysis. It has been found that the load distribution along the blade span is not linear. It varies with the span length and it also varies along the chord of the blade airfoil. Due to this varying load the stresses developed in the blade is dissimilar which dictates the skin thickness of the blade and the shape of the spur inside the blade. It has also been observed that the aerodynamic characteristics such as lift coefficient (CL) and pressure coefficient (CP) changes with the deflection of the blade which affects the power output of the wind turbine.
BCI-Touch Based System: A Multimodal CAD Interface for Object Manipulation
Authors: Bhat Rohit , Deshpande Akshay , Rai Rahul , Esfahani Ehsan Tarkesh
Published: April 2014

The aim of this paper is to explore a new multimodal Computer Aided Design (CAD) platform based on brain-computer interfaces and touch based systems. The paper describes experiments and algorithms for manipulating geometrical objects in CAD systems using touch-based gestures and movement imagery detected though brain waves. Gestures associated with touch based systems are subjected to ambiguity since they are two dimensional in nature. Brain signals are considered here as the main source to resolve these ambiguities. The brainwaves are recorded in terms of electroencephalogram (EEG) signals. Users wear a neuroheadset and try to move and rotate a target object on a touch screen. As they perform these actions, the EEG headset collects brain activity from 14 locations on the scalp. The data is analyzed in the time-frequency domain to detect the desynchronizations of certain frequency bands (3–7Hz, 8–13 Hz, 14–20Hz 21–29Hz and 30–50Hz) in the temporal cortex as an indication of motor imagery.
Oscillatory Flow Between Two Hemispheres for Shearing Protein Solution
Authors: Kong Dejuan , Penkova Anita , Sadhal Satwindar Singh
Published: April 2014

Protein aggregation rate is known to be influenced by shear flow in protein solutions. This has important physiological implications as many of the body functions involve shear flow. Fluid mechanical shear can affect interactions between protein molecules, initiate protein aggregation, and further affect their biological activity. The shear rate is therefore an important parameter either to determine or to influence the properties of the protein solution when it forms a nucleus or aggregates. For experiments, the number density of nuclei can be controlled by using an optimal shear rate and protein concentration. However, this requires theoretical information on the shear rate for the experimental conditions. With this motivation, we have designed an experiment in which we can effectively apply shear with flow characteristics that can be calculated. Specifically, in a small hemispherically-shaped bowl, 4 mm in diameter we place the protein solution and insert a rounded rod that can be vibrated rotationally or laterally, maintaining spherical symmetry in the liquid region. This system is particularly useful when only small quantities of expensive protein solutions can be used for experimentation. We have carried out the mathematical analysis of the time-dependent flow field between two concentric hemispheres by the perturbation method using ε = U0/ωa ≪ 1 as a small parameter where U0 is a characteristic velocity, ω is the oscillation frequency and a is a length scale based on the vessel dimensions (bowl radius). We have obtained an analytical solution for the velocity field, and the shear rate in the liquid. In addition, with the nonlinear interaction of the oscillatory flow, there is a nonzero time-independent mean flow (known as streaming). With the integrated effect of shear in the liquid region, this result will be useful for conducting aggregation experiment in which the effective shear rate can be correlated to the aggregation rate.
Durability Study of Low Velocity Impact Responses of Conventional and Nanophased CFRP Composites Exposed to Seawater
Authors: Hossain Mohammad K. , Chowdhury Md. Mahmudur R. , Imran Kazi A. , Salam Mahmud B. , Hosur Mahesh , Jeelani Shaik
Published: April 2014

The effect of nanoclay on the degradation of low velocity impact responses of carbon fiber reinforced polymer (CFRP) composites manufactured by the vacuum assisted resin transfer molding (VARTM) process is experimentally investigated with and without exposure to seawater for marine applications. Nanoclay was dispersed into the matrix by using magnetic stirring. Samples (100 mm by 100 mm) exposed to seawater for 0, 6, and 12 months in laboratory conditions were impacted at 20, 30, and 40 J energy levels using a Dynatup8210. The damage sustained by the samples was evaluated by a thermographic imaging technique. Comparisons between conventional and nanophased CFRP composites both in conditioned and unconditioned cases were made in terms of peak force, absorbed energy, deflection, delamination area, and specific delamination energy. Water absorption was observed to be reduced due to nanoclay infusion. After 12 months of exposure to seawater 2% nanophased samples absorbed 0.39% moisture whereas control samples absorbed 0.67% moisture. Impact strength, toughness, and energy absorption decreased with increasing conditioning time by weakening the bond between the fiber and matrix and softening the matrix materials. However, reduction in properties is significantly extenuated by the incorporation of nanoclay in the matrix. Specific delamination energy (SDE) is observed to be higher in the nanophased CFRP compared to that of the conventional one at different aging periods indicating an enhanced toughness in the nanophased composites. The larger and stronger interfacial area produced by the nanoclay inclusion has been found to facilitate more energy absorption in the nanophased sample compared to the conventional one. Furthermore, nanoclay reduced the development of delamination by arresting the crack propagation path or by toughening the matrix. It is concluded that the excellent barrier capacity, higher surface area, and high aspect ratio of nanoclay are responsible for the superior performance of CFRP composites, which in turn, enhances the durability of composites.
Modeling Criteria for Extraction Regime Transitions for Microscale In-Situ Vapor Extraction Application
Authors: Salakij Saran , Pence Deborah V. , Liburdy James A.
Published: April 2014

A major detriment of two-phase microscale flow systems is a relatively high pressure drop, as well as the potential for flow instabilities. A possible mechanism to overcome these disadvantages is vapor extraction through a hydrophobic porous wall in the channel to reduce vapor content and suppress vapor expansion. The vapor extraction may occur either as evaporation, bubble extraction or a mix of both. For the design of vapor extraction systems, it is important to accurately predict extraction regimes, extraction rates and the effect of extraction on the heat transfer and flow conditions. This study focuses on two parts: the development of physic-based models for the transition criteria among (i) the extraction mechanism regimes, and (ii) the extraction flow regimes for microscale flow boiling. The identification and conditions for the various extraction regimes are discussed and criteria for transition are developed based on physical concepts. Six potential extraction mechanism regimes are identified: (a) no extraction, (b) pure evaporation, (c) pure bubble extraction, (d) bubble extraction with partial liquid blockage, (e) bubble extraction with evaporation, and (f) liquid breakthrough. Based on the criteria for the extraction mechanism regimes, the rate of vapor extraction is modeled and used to analyze the effects of vapor extraction on the dynamics of two-phase flow boiling. The results show six extraction flow regimes for two-phase flow boiling: (i) single-phase evaporation, (ii) two-phase evaporation – bubble collapse, (iii) full extraction – stable, (iv) full extraction – unstable, (v) partial extraction – stable and (iv) partial extraction – unstable.
Measurement and Process Control in Precision Hot Embossing
Authors: Bageant Maia R. , Hardt David E.
Published: April 2014

Microfluidic technologies hold a great deal of promise in advancing the medical field, but transitioning them from research to commercial production has proven problematic. We propose precision hot embossing as a process to produce high volumes of devices with low capital cost and a high degree of flexibility. Hot embossing has not been widely applied to precision forming of hard polymers at viable production rates. To this end we have developed experimental equipment capable of maintaining the necessary precision in forming parameters while minimizing cycle time. In addition, since equipment precision alone does not guarantee consistent product quality, our work also focuses on real-time sensing and diagnosis of the process.

This paper covers both the basic details for a novel embossing machine, and the utilization of the force and displacement data acquired during the embossing cycle to diagnose the state of the material and process. The precision necessary in both the forming machine and the instrumentation will be covered in detail. It will be shown that variation in the material properties (e.g. thickness, glass transition temperature) as well as the degree of bulk deformation of the substrate can be detected from these measurements. If these data are correlated with subsequent downstream functional tests, a total measure of quality may be determined and used to apply closed-loop cycle-to-cycle control to the entire process. By incorporating automation and specialized precision equipment into a tabletop “microfactory” setting, we aim to demonstrate a high degree of process control and disturbance rejection for the process of hot embossing as applied at the micron scale.
Ultrasonic-Assisted Cylindrical Grinding of Alumina-Zirconia Ceramics
Authors: Tawakoli Taghi , Akbari Javad , Zahedi Ali
Published: April 2014

Due to its vast applications and stochastic nature, grinding has been the subject of investigations and modifications for decades. Applying ultrasonic vibration in grinding has been a successful innovation introducing benefits such as reduced forces and temperature, improved surface quality, and making higher removal rates possible. In this work a set-up is developed for utilizing ultrasonic vibrations in cylindrical grinding. This is done by rotating and simultaneously vibrating the workpiece material. The set-up is used for cylindrical grinding of Alumina-zirconia ceramic as a difficult-to-grind and widely used industrial ceramic. Optimized parameters for efficient grinding and surface characteristics of the ground ceramic are investigated and the effects of ultrasonic vibration are declared.
Entrainment Into High Speed Air Jet Blowing Out From a Hole to Stagnant Water
Authors: Koizumi Yasuo , Nago Kohei , Uchibori Akihiro , Kamide Hideki , Ohshima Hiroyuku
Published: April 2014

Flow visualization experiments of an air jet in liquid were performed. The test vessel was 270 mm wide, 5 mm depth and 300 mm high. The air jet was blown vertically upward into stagnant liquid in the test vessel from a nozzle of 1 mm wide, 5 mm depth and 20 mm long which was located at the bottom of the test vessel. A flow state of the jet in the liquid was recorded with a high speed video camera at fastest 5×105 f/s. The test liquid was water and kerosene. Experiments were performed at atmospheric pressure and ambient temperature. Filament-like ears and wisps pulled out from the wavy interface were noticed on the interface between liquid and the air jet. The ears and wisps were broken off and entrained into the air jet. The droplets broke up to small entrainments. This process seemed quite similar to the entrainment process in the annular dispersed flow in a pipe. As the air jet velocity increased, the number of entrainments created by the air jet increased lineally and the smaller entrainments increased. The correlation for the entrainment diameter distribution which was developed for the annular dispersed two-phase flow in a pipe predicted well the present results. The correlations for the entrainment diameter developed for entrainments in the annular dispersed two-phase flow in a pipe and for droplets that were blown out into open space above a water pool by a nitrogen gas jet that blew into water vertically upwards considerably underpredicted the experimental results. Measured entrainment rates were considerably lower than the prediction of the correlation for the annular dispersed two-phase flow in a pipe.
Front Wave Prediction in Water Hammer Phenomena Involving Two-Phase Flows
Authors: Bogoi Alina , Seynhaeve Jean Marie , Rugescu Radu D. , Sugar Oliviu , Giot Michel
Published: April 2014

A genuine mathematical model for one dimensional, unsteady, two phase (liquid-gas) flows is presented that intends to solve the complex problem of two phase behavior of fluids. The mechanism of the model describes the fluid flow characteristics of the mixture, supposing that the conditions for homogeneous vaporization are fulfilled and the condensate fraction of the composite fluid keeps constant. In particular, the equation of momentum conservation for the gas phase is derived from the Voinov equation. For its domain of validity (bubbly flows), the model is of hyperbolic type and can be written in the conservative form. The numerical results obtained for the water hammer phenomena show that the present work is able to supply accurate results, at least of the same degree of confidence as the results provided by an ordinary, commercial CFD code, still with a considerable reduction in computational time.
Investigation of Mechanical Properties of Nanoclay Incorporated Room Temperature Vulcanized (RTV) Silicone Foams
Authors: Fuad Kaji , Barua Bipul , Saha Mrinal C. , Robison Thomas , Wells Sabrina
Published: April 2014

Room temperature vulcanized (RTV) silicone foams (SFs) have unique thermal and chemical properties due to the presence of inorganic Si-O backbones with organic methyl side groups. However, their low mechanical strength and low tear resistance are major drawbacks for many applications. We have incorporated Nanoclay as reinforcing filler to improve mechanical properties of silicone foams. A three step blending process was used to disperse Nanoclay in silicone elastomers. Initially, Nanoclay in the concentration range of 0.5%–1% by weight were mixed to silicone polymer using a mechanical mixer at 1200 rpm for 10 min followed by a tip sonication at 20% amplitude for 1 hr. Finally, a high speed mechanical mixer was used at 2000 rpm for 2 hours. Two different types of Nanoclays with different sizes were investigated. Both compression and tear properties were found to improve with addition of 0.5 wt% Nanoclay. It was found that the smaller Nanoclay particle size showed the best compressive property while the Nanoclay with larger particle size improved tear strength the greatest.
Two-Stage Lane Keeping Control Algorithm for Lane Sensing Inaccuracy Handling
Authors: Lee Jin-Woo , Litkouhi Bakhtiar B. , Huang Hsun-Hsuan
Published: April 2014

The Lane Keeping Assist (LKA) system is a safety feature that applies an automatic steering torque to the vehicle steering system to keep the subject vehicle in its lane. Like many other active safety systems, the LKA systems may often experience a performance issue in real road situations. The common LKA performance issues are mainly due to poor quality of the front camera’s curvature data and sudden drops of camera’s detection range. To overcome these issues, this paper proposes a two-stage lane keeping control. In this approach, the LKA has two independent algorithms running with a coordination. In the coordination layer, the secondary lane keeping (LK) control has the authority to override the primary LK control if the primary LK fails to maintain the subject vehicle in the current lane due to the above issues. The key aspect of this system is the accurate timing of the secondary LK’s override over the primary LK. The coordination logic between the primary and the secondary LK control, and smooth transition between the controls are also important performance measures. The determination algorithm of the LK initiation and termination plays a key role in achieving the objectives of LKA fail handling. This paper describes these algorithms as well as the path planning and the steering control algorithms. Several vehicle tests were carried out on curved roads. The results show successful and smooth transition from the primary to the secondary LK layer.
A 3D Wind Turbine Simulator for Aerodynamics Education
Authors: Moreland John , Dubec Steve , Okosun Tyamo , Wang Xiuling , Zhou Chenn
Published: April 2014

The energy production and performance of wind turbines is heavily impacted by the aerodynamic properties of the turbine blades. Designing a wind turbine blade to take full advantage of the available wind resource is a complex task, and teaching students the aerodynamic aspects of blade design can be challenging. To address this educational challenge, a 3D software package was developed as part of the Mixed Reality Simulators for Wind Energy Education project, sponsored through the U.S. Department of Education’s FIPSE program. The software is suited for introductory wind energy courses and covers topics including blade aerodynamics, wind turbine components, and energy transfer.

The simulator software combines a 3D model of a utility-scale Horizontal Axis Wind Turbine (HAWT) with animation, a set of interactive controls, and a series of computational fluid dynamics (CFD) simulations of an airfoil under a number of conditions. Students can fly around the wind turbine to view from any angle, adjust transparency layers to view components inside the nacelle, adjust a cross-section plane along the length of a blade to view the details of the blade design, and manipulate sliders to adjust variables such as angle of attack and Reynolds number and see contour plots in real-time. The application is available for download at www.windenergyeducation.org, and is planned for release as open source.
Condition Monitoring of a Single Cylinder Engine Running on Gasoline and Gasoline-Ethanol Blend Using Wear Particle Analysis Technique
Authors: Akl Sayed Y. , Abdel-Rehim Ahmed A.
Published: April 2014

Analytical techniques performed on oil samples for lubricated machines can be classified in two categories; used oil analysis and wear particle analysis. Used oil analysis determines the condition of the lubricant itself, determines the quality of the lubricant, and checks its suitability for continued use. Wear particle analysis determines the mechanical condition of machine components that are lubricated. Through wear particle analysis, you can identify the composition of the solid material present and evaluate particle type, size, concentration, distribution, and morphology, thus indicating the machine condition and its predictive maintenance.

The above mentioned techniques are suitable methods for the detection of abnormal wear occurring in internal combustion engines, especially for engines running on different fuels. These techniques provide cheap, fast and easy to use predictive maintenance methods which can replace other conventional methods.

The objective of the present study is to apply wear particle analysis technique as an engine monitoring technique to compare two new and identical engines running on gasoline (Engine 1) and gasoline-ethanol blend (Engine 2). The two engines were tested for a total running period of 850 hours. Spectrometric and ferrographic analysis were used for the comparison where quantitative and qualitative changes in the concentration and size distribution of different particles were analyzed and compared to baseline values.

Results showed an increase of wear rate for the engine running on gasoline-ethanol blend compared to the engine running on gasoline only. Two contents of ethanol were used where 10% content showed a moderate increase of wear rate; however 20% content showed a dramatic increase of wear rate.

The predominant wear particles were the ferrous particles and aluminum particles indicating the wear of piston elements and piston rings. Corrosive wear was also highly remarked which indicates a chemical reaction in the presence of ethanol.
A Numerical Investigation on Nanofluid Laminar Mixed Convection in Confined Impinging Jets
Authors: Manca O. , Nardini S. , Ricci D. , Tamburrino S.
Published: April 2014

In this paper a numerical investigation on confined impinging slot jets working with a mixture of water and Al2O3 nanoparticles is described. The flow is laminar and a constant temperature is applied on the target surface. A single-phase model approach has been adopted because the particle concentrations are low. Different geometric ratios and nanoparticle volume concentrations have been considered at different Richardson numbers in order to take into account also the buoyancy effects.

The aim consists into study the behaviour of the system by means of average and local Nusselt number, convective heat transfer coefficient and required pumping power profiles, temperature fields and stream function contours. The dimensionless stream function contours showed that the intensity and size of the vortex structures depend on the confining effects, given by H/W ratio, Richardson number and particle concentrations. Furthermore, for increasing concentrations, nanofluids realize increasing fluid bulk temperature, as a result of the elevated thermal conductivity of mixtures. The local Nusselt number profiles show the highest values at the stagnation point and they depend on Richardson number and particle concentrations.
The Passive Control of Unsteady Flow Structure Downstream of a Circular Cylinder in Shallow Water
Authors: Durhasan Tahir , Pınar Engin , Aksoy Muhammed M. , Özkan Göktürk M. , Akıllı Hüseyin , Şahin Beşir
Published: April 2014

In the present study, it was aimed to suppress the vortex shedding occurred in the near wake of a circular cylinder (inner cylinder) by perforated cylinder (outer cylinder) in shallow water flow. The inner cylinder (Di) and outer cylinder (Do) have fixed diameters, such as Di = 50 mm and Do = 100 mm, respectively. The effect of porosity, β, was examined using four different porosity ratios, 0.3, 0.5, 0.6 and 0.8. In order to investigate the effect of arc angle of outer cylinder, α, four different arc angles, α = 360°, 180°, 150° and 120° were used. The experiments were implemented in a recirculating water channel using the particle image velocimetry, PIV technique. The depth-averaged free-stream velocity was kept constant as U∞ = 100 mm/s which corresponded to a Reynolds number of Re = 5000 based on the inner cylinder diameter. The results demonstrated that the suppression of vortex shedding is substantially achieved by perforated outer cylinder for arc angle of α = 360° at β = 0.6. Turbulence Kinetic Energy statistics show that porosity, β, is highly effective on the flow structure. In comparison with the values obtained from the case of the bare cylinder, at porosity β = 0.6, turbulence characteristics are reduced by %80. Also, the point, which the values of maximum TKE, shift to a farther downstream compared to the case of bare cylinder.
Fundamental Considerations for Designing Compact Solar Thermal Power and Ejector Cooling Systems in Hot Climates
Authors: Zhang TieJun , Mohamed Saleh , Li Guanqiu
Published: April 2014

A combined thermal power and ejector refrigeration cooling cycle is proposed in this paper to harness low-grade solar energy. It utilizes abundant and low-cost hydrocarbon as the working fluid. Hydrocarbon has been identified as a promising alternative to existing high global-warming-potential refrigerants (i.e., HFC refrigerant R134a) in next-generation refrigeration systems. Several typical alternative refrigerants are evaluated by considering their fundamental thermophysical properties: absolute pressure level, volumetric cooling capacity, surface tension, saturated liquid/vapor density ratio and kinematic viscosity. Comparing with R1234yf, R1234ze and R744 (CO2), hydrocarbon refrigerants, such as R290 (propane) and R601 (pentane), do have inherent advantages for either cooling or power generation purposes in hot climates: lower flow resistance and better heat transfer at higher temperature. Fundamental phase stability and transition issues have been considered in designing pentane vapor ejectors for combined power and cooling cycles operating at high ambient temperature. Thermodynamic analysis has indicated that the proposed solar thermal system can provide an effective way to sustainable energy production in hot and dry climates.
Optimization of a Thermoelectric Cooler for Time-Varying Heat Load and Sink Temperature
Authors: Pearson Matthew R. , Lents Charles E.
Published: April 2014

Thermoelectric coolers (TECs) are solid-state cooling devices that operate on the Seebeck effect. They can be used in electronics cooling applications as well as other refrigeration systems. Among the various factors that affect TEC performance within a system, it has been shown that the thermal conductance is an important parameter which can also be easily altered during the design of a TEC to deliver optimal TEC performance for a given application. However, these studies have considered only a fixed heat load and heat sink temperature, whereas in many realistic applications these quantities can vary. A procedure has been developed for optimizing the thermal conductance of a TEC based on a typical operating cycle of time-varying heat load and sink temperature, while permitting constraints that ensure that one or more worst-case operating conditions can also be met. This procedure is valid for any arbitrary heat load and sink temperature functions; however, for illustrative purposes, a simple heat load function at fixed sink temperature (and a sink temperature function at fixed heat load) are used. The results show that the optimal conductance can strongly depend on the operating cycle, and the corresponding reduction in electrical input work (and corresponding increase in net COP) can be significant.
Nonlinear Longitudinal Vibration Solutions of an Elastic Rod
Authors: Askari Hassan , Esmailzadeh Ebrahim , Younesian Davood
Published: April 2014

Nonlinear longitudinal vibration of an elastic rod is studied. The motion of a uniform elastic rod is described by a nonlinear partial differential equation, which has a cubic nonlinear term and a Winkler elastic force that acts along the longitudinal axis of the rod. Galerkin method is used to develop the nonlinear differential equation of elastic rod, which resembles similarity with the Duffing equation. Three different types of robust analytical methods are chosen to solve the nonlinear differential equation and obtain the natural frequency of the system. These are the Homotopy analysis method (HAM), Energy balance method (EBM) and Hamiltonian approach (HA). Subsequently, the analytical results are compared with the numerical solution of the exact equation in order to evaluate the correctness of the applied approaches. Moreover, the effects of the constant coefficients of the elastic force on the ratio of the nonlinear to the linear frequencies are studied. The singular points of the nonlinear differential equation of the elastic rod are extracted and the Jacobian matrix is constructed to recognize their types. Finally, phase-plane trajectories of the system are constructed in order to verify the results obtained from the Jacobian matrix.
Counter-Rotating Type Pump-Turbine Unit Stabilizing Momentarily Fluctuating Power From Renewable Energy Resources
Authors: Kanemoto Toshiaki , Kasahara Risa , Honda Hirotaka , Miyaji Toru , Kim Jin-Hyuk
Published: April 2014

It is difficult, for renewable energy resources, to provide constant power with excellent quality for the grid system. This serial research proposes a power stabilization system with a pumped storage to guarantee the power quality and capacity, while the energy resources are at unstable and/or fluctuating conditions. The power stabilization system with the counter-rotating type pump-turbine unit was prepared and operated at the pumping and the turbine modes. The experiments have verified that this type pump-turbine unit is reasonably effective to stabilize momentarily/instantaneously the fluctuating power from the renewable energy resources.
Computational Investigation of Vortex Structure in the Corrugated Channel
Authors: Unal Efe , Sorguven Esra , Ahn Hojin
Published: April 2014

Characteristics of the flow on a corrugated wall are investigated using computational fluid dynamics. Steady and unsteady k-w simulations and large eddy simulations (LES) are performed. Results are compared with the experimental data obtained via particle image velocimetry (PIV). RANS simulations predict a coherent vortex motion, which is contained within the cavity and has little effect on the outer flow. RANS results demonstrate a mainly 2-dimensional flow and underestimate the pressure loss and friction coefficient by about 25%, compared to LES results. LES results show that the flow is highly turbulent, 3-dimensional, unsteady, and there is a strong interaction between the flow inside the corrugations and the bulk flow. Both LES and PIV represent that the separation and reattachment points vary spatially and temporally, resulting in a thick boundary layer and high friction coefficient. Sudden ejection of the flow from the cavity to the outer flow is also observed in the instantaneous snapshots taken from LES and PIV. These flow ejections prevail in the time-averaged PIV results, indicating a mean inflow towards the cavity near the side walls and a mean outflow from the cavity at the channel center. Even though instantaneous LES results show similar flow bursts, time-averaged LES results even out the inflow and outflow from the cavities, yielding no net flow in and out of the cavities.
Two-Phase Flows in Mini-/Micro-Gas Flow Channels of PEM Fuel Cells
Authors: Cho Sung Chan , Wang Yun
Published: April 2014

In this paper, two-phase flow dynamics in a micro channel with various wall conditions are both experimentally and theoretically investigated. Annulus, wavy and slug flow patterns are observed and location of liquid phase on different wall condition is visualized. The impact of flow structure on two-phase pressure drop is explained. Two-phase pressure drop is compared to a two-fluid model with relative permeability correlation. Optimization of correlation is conducted for each experimental case and theoretical solution for the flows in a circular channel is developed for annulus flow pattern showing a good match with experimental data in homogeneous channel case.
Determination of the Slip-Up Time for Slip Form System Using Surface Wave Velocity
Authors: Kim H. S. , Kim Y. J. , Chin W. J. , Yoon H.
Published: April 2014

When applying the slip form system, the early setting time of concrete corresponds to the hardening time of early-age concrete indicating that cast-in-place concrete has developed sufficient strength to be safely stripped off the form. This hardening time is thus an important indicator for the determination of the slip-up velocity of the slip form system. Therefore, need is for a technique enabling to evaluate the early hardening time of concrete in order to secure the safety of the slip form system and the quality of the constructed concrete. Among the methods using ultrasonic waves, this paper applies the surface wave velocity to evaluate the degree of hardening of concrete so as to estimate the early setting time and decide the slip-up time of the slip form system. To that goal, penetration resistance test, compressive strength test and surface wave velocity measurement test are performed concurrently with respect to the mix materials and curing temperature of concrete. The test results are used to derive the relationship between the compressive strength and surface wave velocity according to the early hardening time of concrete. Continuous wavelet transform is applied for the measurement of the surface wave velocity. The validity of the application of the continuous wavelet transform is verified through numerical analysis. Finally, the surface wave velocity required for the slip-up of the slip form system is proposed and the applicability of the proposed surface wave velocity for the determination of the climbing time of the slip form system is verified by means of tests on a reduced-scale slip form system prototype.
Metadamping in Dissipative Metamaterials
Authors: Hussein Mahmoud I. , Frazier Michael J.
Published: April 2014

Using a generalized form of Bloch’s theorem, we derive the dispersion relation of a viscously damped locally resonant metamaterial modeled as an infinite mass-in-mass lumped parameter chain. For comparison, we obtain the dispersion relation for a statically equivalent Bragg-scattering mass-spring chain that is also viscously damped. For the two chains, we prescribe identical damping levels in the dashpots and compare the damping ratio associated with all propagating Bloch modes. We find that the locally resonant metamaterial exhibits higher dissipation throughout the spectrum which indicates a damping emergence phenomena due to the presence of local resonance. This phenomenon, which we define as metadamping, provides a new paradigm for the design of material systems that display both high damping and high stiffness. We conclude our investigation by quantifying the degree of metadamping as a function of the long-wave speed of sound in the medium or the static stiffness.
Heat Recovery With Oscillating Heat Pipes
Authors: McCullough Charles R. , Thompson Scott M. , Cho Heejin
Published: April 2014

Waste-heat recovery applied in HVAC air systems is of interest to increase the energy efficiency of residential, commercial and industrial buildings. In this study, the feasibility of using tubular-shaped oscillating heat pipes (OHPs), which are two-phase heat transfer devices with ultra-high thermal conductivity, for heat exchange between counter-flowing air streams (i.e., outdoor and exhaust air flows) was investigated. For a prescribed volumetric flow rate of air and duct geometry, four different OHP Heat Exchangers (OHP-HEs) were sized via the ε-NTU method for the task of sub-cooling intake air 5.5 °C (10 °F). The OHP-HE tubes were assumed to have a static thermal conductivity of 50,000 W/m·K and only operate upon a minimum temperature difference in order to simulate their inherent heat transport capability and start-up behavior. Using acetone as the working fluid, it was found that for a maximum temperature difference of 7°C or more, the OHP-HE can operate and provide for an effectiveness of 0.36. Pressure drop analysis indicates the presented OHP-HE design configurations provide for a minimum of 5 kPa. The current work provides a necessary step for quantifying and designing the OHP for waste heat recovery in AC systems.
Ejection of Flammable Liquids During Loading and Unloading: A Preliminary Experimental Investigation
Authors: Hetrick Todd M. , Morrison Delmar (Trey) , Ramirez Juan C.
Published: April 2014

Flammable liquids in industrial settings, e.g., the shop floor or laboratory, may sometimes be transferred or handled in small containers. Pouring a flammable liquid from one container into another presents a hazard potential for static electric discharge and subsequent ignition of the flammable liquid vapors. This phenomenon is well-known and industry guidance documents are available. This risk is usually mitigated with appropriate safeguards against the generation of static electricity or other potential ignition sources.

In the instances where an ignition source is present, ignition of the flammable vapors accompanying the liquid pour or in the headspace of the container may occur. If the flammable vapor space above the liquid surface is ignited, the ensuing overpressure and fluid conditions may be sufficient to eject some of the liquid from the container. Flammable liquid ejection can potentially result in the projection or transport of fire over large distances with severe consequences.

In this study, we perform a series of bench scale experiments. We aim to determine and investigate the factors influencing the ejection of flammable liquids during loading and unloading of small containers. Developing a better understanding of the parameters governing this phenomenon may allow for the design of engineering safeguards to assist in the prevention of flammable liquid ejection.
Investigation of Enhancement in Pool Boiling Heat Transfer of a Binary Temperature Sensitive Magnetic Fluid
Authors: Karimi-Moghaddam Giti , Gould Richard D. , Bhattacharya Subhashish
Published: April 2014

In this paper, the performance of pool boiling heat transfer using a binary temperature sensitive magnetic fluid in the presence of a non-uniform magnetic field is investigated numerically. By using a binary magnetic fluid, enhanced boiling heat transfer is obtained by thermomagnetic convection without deterioration of properties of the fluid. This work is aimed at gaining a qualitative understanding the magnetic field effects on boiling heat transfer enhancement of magnetic fluids. In order to accomplish this, the boiling process and the effects of position of the external magnetic field on flow pattern and heat transfer are investigated in a 2D rectangular domain using COMSOL Multiphysics simulation software. Finally, the boiling curves for a binary temperature sensitive magnetic fluid and its base fluid (without magnetic particles) are compared for various applied heat flux magnitudes.