bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Linear Behavior of Electrothermal Flows
Authors: Kauffmann Paul , Loire Sophie , Sigurdson Marin , Mezic´ Igor
Published: August 2012

Recently, electrokinetic flows have raised the interest of scientific community. Driving flow with an electric field leads to promising applications for mixing, concentration and pumping application in lab on chip. However, current models are still inaccurate and in many cases dont fit the measured data. The work presented here is mainly focused on AC electrothermal flows (ACET) carried out in microwells. An AC electric field is applied between 3 interdigitated gold electrodes. Using μPIV (μ Particle Image Velocity) vortex flows are characterized. The competition between light induced (LEF), AC induced electrothermal (ACET) and buoyancy flows (BF) is discussed. Based on those experimental observations, a new theory is tackled. It takes into account the observed instability like behaviour and the discrepancy of the voltage influence on velocities at high conductivity.
Design of Urinary Biomarker Sensor for Early Ovarian Cancer Detection
Authors: Onen Onursal , Kruk Patricia , Guldiken Rasim
Published: August 2012

In this paper, our efforts on the design, surface functionalization and characterization of ultrasonic MEMS sensor for early ovarian cancer is presented. The sensor detects urinary anti-apoptotic protein Bcl-2 level that has been presented as being elevated for different stages of ovarian cancer. Our novel biosensor approach employs a pair of MEMS ultrasound transducers for generating and sensing surface acoustic waves and a delay path in-between with oriented Bcl-2 antibodies (C8C) attached. Piezoelectric surface acoustic wave devices are employed for sensor for their high coupling efficiency and ease of fabrication. The sensor quantifies the cancer progression by detecting mass loading change generated by adhesion of Bcl-2 molecules to antibodies on the sensor surface. The device is fabricated using common MEMS fabrication techniques and a multi-step surface functionalization is utilized for effective protein adhesion. As a result, our biosensor platform has various unique advantages such as: ultra-sensitive (sub pg/ml), low cost, and simple operation (reminiscent of a pregnancy test) not necessitating trained personnel.
Mechanical Properties of Jute/PLA Injection Molded Products-All Natural Composites
Authors: Murakami Masuo , Yang Yuqiu , Hamada Hiroyuki
Published: August 2012

Natural composites have been important materials system due to preservation of earth environments. Natural fibers such as jute, hemp, bagasse and so on are very good candidate of natural composites as reinforcements. On the other hand regarding matrix parts thermosetting polymer and thermoplastic polymer deriver form petrochemical products are not environmental friendly material, even if thermoplastic polymer can be recycled. In order to create fully environmental friendly material (FEFM) biodegradable polymer which can be deriver from natural resources is needed. Therefore poly(lactic acid) (PLA) polymer is very good material for the FEFM. However, PLA is very brittle polymer, so that polymer chemists have been made the efforts to make tough PLA. In this paper Jute/PLA composites was fabricated by injection moldings and mechanical properties were measured. It is believable that industries will have much attention to FEFM, so that injection molding was adopted to fabricate the composites. Long fiber pellet pultrusion technique was adopted to prepare jute fiber-PLA pellet (Jute/PLA). Because it is a new method which is able to fabricate composite pellets with relative long length fibers for injection molding process, where, jute yarns were continuously pulled and coated with PLA resin. Here two kinds of PLA materials were used including the one with mold releasing agent and the other is without it. After pass through a heated die whereby PLA resin impregnates into the jute yarns and sufficient cooling, the impregnated jute yarns were cut into pellets. Then Jute/PLA pellets were fed into injection machine to make dumbbell shape specimens. In current study, the effects of temperature of heat die i.e. impregnation temperature and the kind of PLA were focused to get optimum molding condition. The volume fractions of jute fiber in pellet were measured by several measuring method including image analyzing, density measurement and dissolution methods. And the mechanical property were investigated by tensile and Izod testing. It is found that 250 degree is much suitable for Jute/PLA long fiber pultrusion process. Additionally the jute fibers seem much effective to increase the tensile modulus and the Izod strength. That is to say, the addition of Jute fiber in PLA, the brittle property can be improved.
Effect of Hot Water Immersion on the Mechanical Properties of Jute and Jute Hybrid Reinforced Composites
Authors: Yu Ying , Kawabata Shinichiro , Yang Yuqiu , Hamada Hiroyuki
Published: August 2012

As well known, the corrosion resistance and durability of the material are always considered in the safety design of the materials. In this study, the jute fabric from recycled coffee bags was used to fabricate ecologically friendly composites. Jute fabrics with two kinds of different moisture contents were used to fabricate the natural fiber reinforced composites, and the hot water immersion properties have been evaluated. Additionally, the effects of the hybridization with glass woven fabric laminated structures were also investigated. Jute/Jute laminated composite, Jute/Jute/Glass, and Glass/Jute/Glass laminated hybrid composites had been fabricated by hand lay up method. A preliminary investigation on the effect of moisture contents of the jute fabric on the mechanical properties of the jute and jute/glass hybrid composites was discussed based on the results of 3 point bending test. Moreover, the durability of the composites in the hot water immersion was also evaluated. The effects of hot water immersion on the mechanical properties were investigated by the way of 3 point bending test. The specimens were immersed in hot water maintained at 80°C with the immersion time of 24, 120 and 240 hours. Specimens were taken out from the hot water at the same time and repeated the 3 point bending test after each immersion time and the weight changes had been measured. Results showed that the Jute/Jute composite absorbed water easily, and it could be noted that all of the natural dried composites showed comparable higher water absorbed value to the deeply dried ones. The bending strength after aging decreased remarkably. In particularly, all of the natural dried composites showed higher bending strength than the deeply dried one before aging. However, after 120 hours aging, on the contrary, almost the deeply dried composites showed comparable higher value to the natural dried ones. That could be due to the better bonding between fiber and matrix for the deeply dried composites which decreased the water absorption of the composites. Additionally, the hybrid structure is effective in protecting the composites from water absorbing especially for the Glass/Jute/Glass hybrid one.
Electrical and Crack Responses of CNT-Based Polymer Composites Under Tension
Authors: Kuronuma Yu , Shindo Yasuhide , Takeda Tomo , Narita Fumio , Fu Shao-Yun
Published: August 2012

This paper studies the electrical and mechanical responses of cracked carbon nanotube (CNT)-based polymer composites. Tensile tests were conducted on single-edge cracked plate specimens at room temperature and liquid nitrogen temperature (77 K), and the electrical resistance change of the specimens was monitored. An analytical model was also developed to predict the resistance change resulted from crack propagation. In addition, the fracture properties of the nanocomposites were evaluated in terms of the J-integrals from an elastic-plastic finite element analysis.
Study on Burning Characteristics of Small-Scale Ethanol Pool Fire in Closed and Open Space Under Low Air Pressure
Authors: Zeng Yi , Fang Jun , Tu Ran , Wang Jinjun , Zhang Yongming
Published: August 2012

This paper presents results of different burning rates of small-scale ethanol pool fires at pressures of 0.6∼1.0 atm in closed and open space. Experiments were performed using a square burner of side length of 4 cm under two different conditions: one was taken in a closed low air pressure cabin (0.5 m3, the interior pressure ranges from 0.6–1.0 atm); another was taken in open space respectively in Hefei (air pressure: 1.0 atm) and Lhasa (air pressure: 0.66 atm). The pool fire characteristics including the burning rate, the axial temperature and pulsation frequency of flame were measured. In closed space, the burning rate, flame temperature, and pulsation frequency of small-scale ethanol pool fires decreased with the decreasing pressure, while in open space they increased when the air pressure reduced. As a result of different ambient conditions and oxygen depletion, the burning rate, flame temperature and pulsation frequency were lower at lower air pressure in closed space but were higher at higher air pressure in open space.
The Architecture of the Dragonfly Wing: A Study of the Structural and Fluid Dynamic Capabilities of the Anisoptera’s Forewing
Authors: Mingallon Maria , Ramaswamy Sakthivel
Published: August 2012

This paper studies the smart behaviour observed in the dragonfly wing combining advanced digital modelling techniques with non-linear structural analysis. The morphology of the dragonfly wing is an optimal natural construction built by a complex patterning process, developed through evolution as a response to force flows and material organisation. The seemingly random variations of quadrangular and polygonal patterns follow multi-hierarchical organizational logics enabling it to alter between rigid and flexible configurations. By means of digital experiments, this paper reveals how the geometrical complexity of the wing responds to function and efficiency, displaying emergent behaviour and being responsible for its performance capacity in passive flight.
Regulator and Tracking System Design for a Single-Rod Hydraulic Actuator via Pole-Placement Approach
Authors: Moradi Hamed , Hajikolaei Kambiz Haji , Bakhtiari-Nejad Firooz
Published: August 2012

Due to the nonlinear dynamics of hydraulic systems, applying high performance closed-loop controllers is complicated. In this paper, a single-rod hydraulic actuator is considered in which load displacement (for positioning purposes) is controlled via manipulation of the input voltage to the servo-valve. Dynamics of the servo-valve is described by first and second order transfer functions (named as Models 1 and 2). Through linearization of the system around its operating points, dynamics of the hydraulic actuator is represented in the state space. A full-order observer is designed for on-line states estimation. Then, feedback control system is designed for both regulation and tracking objectives through pole-placement approach based on general canonical control form (GCCF). For tracking of the desired commands, a modified integral control is required (since the plant has not integrator). Results show that the regulation, states estimation, desired tracking and final tracking accuracy are achieved after applying the controller. Required input voltage and load positioning are compared for the two distinct dynamics of the servo-valve (Model 1 and 2).
Analytical Approach to Vibration Analysis of a Pendulum Wrapping on a Cylinder
Authors: Mazaheri H. , Hosseinzadeh A. , Ahmadian M. T. , Barari Ahmad
Published: August 2012

In this paper, nonlinear oscillation of a pendulum wrapping and unwrapping around two cylindrical bases is studied and an analytical solution is obtained using multiple scales method. Equations of motion are derived based on energy conservation technique. Applying perturbation method on the equations, nonlinear natural frequency of the system is calculated along with its time response. Analytical results are compared with numerical findings and good agreement is found. Effect of nonlinearity due to large amplitude and radius of cylinders on the system frequency is evaluated. Results indicate that as the radius of cylinder is increased, nonlinear frequency is enhanced. Initial amplitude plays a dual role on the frequency. As initial amplitude increases up to a certain point, frequency increases and decreases after wards.
Characteristics of Extended Evaporating Meniscus on Nanotextured Rough Solid Substrate for Wenzel States
Authors: Zhao J. J. , Duan Y. Y. , Wang X. D. , Wang B. X.
Published: August 2012

The surface nanostructure determines the system wettability and thus has significant effects on the thin liquid film spreading and phase change heat transfer. A model based on the augmented Young-Laplace equation and kinetic theory was developed to describe the nanoscale roughness effects on the extended evaporating meniscus in a microchannel. The roughness geometries in the model were theoretically related to the disjoining pressure and the thermal resistance across the roughness layer. The results show that the dispersion constant for the disjoining pressure increases with the nanopillar height when the solid-liquid-vapor system is in the Wenzel state. Thus, the spreading and wetting properties of the evaporating thin liquid film are enhanced due to the higher nanopillar height and larger disjoining pressure. Since the evaporating thin film length increases with the nanoscale roughness due to better surface wettability, the total liquid flow and heat transfer rate of the evaporating thin liquid films in a microchannel can be enhanced by increasing the nanopillar height. The effects of the nanopillar on the thin film evaporation are more significant for higher superheats. Hydrophilic nanotextured solid substrates can be fabricated to enhance the thin film evaporation and thus increase the maximum heat transport capability of the two-phase cooling devices.
Directed Assembly of Microstructures Using Bubble Latches
Authors: Jiang Li , Erickson David
Published: August 2012

We introduce a highly flexible method for the assembly of microscale components using laser-activated bubble latching. Arbitrary structures are created through combining directed fluidic assembly and surface tension-driven latching. The bubbles are generated through laser degradation of the SU-8 tile. This gives the user control over the time and location of latching, as opposed to predefined latching locations in other microscale assembly methods. Shear force experiments show that each bubble is able to support a tensile force of 0.33μN. By utilizing the compressibility of bubbles, assembled objects are switched between rigid and flexible states, facilitating motion through irregular channel geometries. Further, through the use of bubble hinging at component corners, reconfiguration is quickly and effectively achieved. This novel hybrid approach to the assembly of microscale components offers significant controllability to the user.
Process Design for the Controlability of Chemical Vapor Deposition Grown Vertically Aligned Single Walled Carbon Nanotubes
Authors: Abuhimd Hatem , Zeid Abe , Jung Yung Joon , Kamarthi Sagar
Published: August 2012

Carbon nanotubes (CNTs) have received much attention from both the scientific and industrial communities due to their structural properties and unique morphology. There has also been growing interest in vertically aligned single walled carbon nanotubes (VA-SWNTs) because of their suitability for building devices such as hydrogen storage and super capacitors. Various methods including chemical vapor deposition (CVD) have been developed for growing VA-SWNTs. Among them is alcohol catalytic CVD which is well known for its economic viability, comprehensive substrates selectivity and good yield of VA-SWNTs. In order to fully understand the growth mechanism of those CNTs, an examination of the role of inputs like hydrocarbon flow rate, reaction time, chamber temperature, and pressure is essential. This work studies the controllability of VA-SWNTs growth by a hybrid process model of an experimental design and an artificial neural network (ANN). Process analysis shows that CVD pressure and temperature are the most significant input factors. In addition, interactions and response surface plots confirm these results and add that higher temperature and pressure will yield VA-SWNTs with high probability.
Development of Mechanical Probe Station for Characterization of Micro-Flexure Mechanisms
Authors: Gandhi Prasanna S. , Prajapati Vishal , Shah Himani , Pai Ramanath
Published: August 2012

Similar to electrical probing of semiconductor chips, mechanical probing of MEMS chips (especially containing moving elements) is essential to verify their functionality before packaging. The functionality may include as simple as verification of release of the device from substrate or more sophisticated force vs displacement performance characterization. In this paper we develop a novel mechanical probing station based on the parallelogram flexure mechanism with a magnetic coil as an actuator for probing. We propose a design which allows application of forces in two directions. The proposed design is realized in practice using mechanical and electronic modifications in a standard CD ROM head. The mechanical probe station is calibrated for applied voltage vs force. Successful probing of micro-flexural NOT gate and pneumatic actuator, fabricated by SOIMUMPs process, is demonstrated.
Design, Fabrication, and Characterization of a Pneumatic Micro Actuator
Authors: Gandhi Prasanna S. , Savalia Anand , Shah Himani
Published: August 2012

Compact high force linear displacement pneumatic microactuators are useful in several applications including robotic systems, surgical micro-grippers, micro mechanisms, and so on. This paper presents development of a general purpose bellow type microactuator using silicon as structural material with a low stiffness double parallelogram flexure guides for a planar bellow piston. Double flexure mechanism achieves frictionless guiding in a perfect straight line of the actuator. The proposed design is different as compared to similar other designs in the literature in that the new design proposes a flexure guide for piston. Moreover, it is integrated with comb drive for servo actuation and is five times smaller. The actuators are fabricated using standard SOIMUMPs process and are further characterized. Actuation pressure, displacement and blocking force are measured which further demonstrates their performance in comparison with simulation results. Finally, as an application example micro-flexural logic device viz. NOT gate, actuated using the micro-pneumatic actuator is presented.
Capillary-Based Liquid Micro/Nano Deposition
Authors: Lutfurakhmanov Artur , Wang Yechun , Schulz Douglas L. , Akhatov Iskander S.
Published: August 2012

Micro/Nanolithography is a creation of micro/nano features on the substrate. Several lithography techniques have been recently developed, including dip-pen nanolithography, nano-imprint lithography, electron-beam lithography, and photolithography. However, all these techniques possess some limitations because of a direct contact with the substrate. This paper proposes a new method that is non-invasive both to the substrate and to the writing tip. The method is based on hollow capillary filled with liquid to be deposited. The application of pressure from one side of capillary causes the liquid meniscus to form at the capillary outlet. Touching the substrate with the meniscus only leads to the liquid bridge formation between the capillary and the substrate. Withdrawing the capillary away from the substrate causes deposition of liquid droplet on the substrate. Theoretical modeling reveals two possible regimes of the liquid bridge formation: stable — “good” bridge and unstable — “bad” bridge. Liquid bridge stability map was created based on two parameters: liquid pressure and the capillary-substrate distance. It was found that the main parameter responsible for the deposition process is the applied pressure. Three pressure ranges were identified with different deposition scenarios. The influence of liquid-capillary and liquid-substrate equilibrium contact angles along with the capillary wall thickness on the liquid bridge stability is discussed.
Investigation of the Fundamental Frequency of Double Walled Carbon Nanotubes Using Molecular Mechanics Approach by an Averaging Van Der Waals Forces Modeling
Authors: Asadi Ehsan , Karimzade Ali , Farid Mehrdad
Published: August 2012

Carbon nanotubes have received a lot of attention since their introduction in 1991 because of novel properties that show substantial promises for use in many applications. Their usage depends on the strength of our knowledge of their properties. In this work, molecular mechanics approach is used to study the mechanical properties of multi-wall carbon nanotubes. In particular this paper investigates fundamental frequency of double walled carbon nanotubes. Carbon nanotubes are big and long molecules that can be regarded as mechanical structures. In modeling of multi-walled carbon nanotubes, two distinct atomic bonds are required to be modeled, i.e. covalent bonds between the neighboring carbon atoms in the same layer and Van der Waals bonds between close atoms in neighboring layers. In this approach, for modeling of each wall; covalent bonds are modeled by beam joints such that atoms are considered to be concentrated masses at the ends. Interactions of neighboring walls that are mainly due to Van der Waals forces are treated to be truss rods in modeling. The most challenging aspect of modeling is to define truss rod properties as they are highly nonlinear. We utilized an averaging method for finding truss rod properties. Finite Element Method is employed to obtain Fundamental frequencies. Results are compared to available researches and a close agreement is observed. Results indicate that by increasing aspect ratio, fundamental frequency of double walled nanotubes decrease. In addition, double walled carbon nanotubes have higher fundamental frequencies at clamp-clamp in comparison to clamp-free condition; however, this difference becomes negligible as aspect ratio increases.
Phononic Crystals With Full Phase-Space Properties: Application to Boolean Logic Gates
Authors: Swinteck N. , Bringuier S. , Deymier P. A.
Published: August 2012

Based on a phononic crystal (PC) constituted of a square array of cylindrical Polyvinylchloride inclusions in air, a theoretical model is constructed that details three schemes for controlling the relative phase between propagating acoustic waves in this PC. In exploiting the spectral, wave vector and wave-phase properties of this PC, a series of acoustic based Boolean logic gates are constructed. Finite-difference time-domain simulations are employed to validate theoretical models and demonstrate the NAND, XOR and NOT Boolean logic gates.
An Experimental Study of Spent Fuel Transport for On-Board Hydrogen Storage
Authors: Li Long , Biggs Luke J. , Zheng Yuan
Published: August 2012

Ammonia borane (AB), a solid chemical under room temperatures, is a promising candidate material for on-board hydrogen storage. One of the major drawbacks that limit the use of this kind of materials is the difficulty to remove (transport) the spent fuels (reaction byproducts) out of the system. In the present study, a piston cylinder device was designed and used to study the spent fuel transport process and to find effective ways to improve the transportability of spent fuels. The piston, which has an area of 5.07 cm2, is designed to push out the spent fuel through a clear acrylic die, which has a diameter of 3.175 millimeters. The pushing force on the top of the piston is provided by compressed nitrogen gas. The piston/cylinder assembly is able to operate under a pressure of 30 bars, which gives a theoretical force of 1,520 N. The assembly can be mounted either vertically or horizontally. Experiments were carried out with sand surrogates and spent fuel of BmimCl (20 wt%) aided AB (80 wt%) thermolysis, which was conducted within the temperature range of 80°C to 120°C. A series of experiments with sands were conducted with different sand to oil weight ratios from infinite, 10:1, 7:1, 5:1, to 4:1. Results of the experiments with sand showed that the sand/oil mixture was extruded out from the piston/cylinder assembly when the mixture ratios were 5:1 and 4:1. The transportability of the 4:1 mixture is better than that of 5:1 mixture, indicated by the piston travel distance. Experiment also showed that the powder-like spent fuel could be moved out from the piston/cylinder assembly smoothly without any oil added. This study demonstrated that effective removal of AB spent fuel in hydrogen storage systems is possible. Considering that only a small amount of spent fuel sample was used, tests with more spent fuel need to be carried out to further support the present observation.
Dry, Closed-Cycle Cooling for Thermoelectric Power Plants Employing Low Temperature Organic Rankine Cycle Waste Heat Recovery and Cool Thermal Energy Storage
Authors: Nguyen Jack T.
Published: August 2012

A patent pending concept is presented for a dry, closed-cycle power plant cooling system employing low temperature organic Rankine cycle waste heat recovery (ORC-WHR) in combination with cool thermal energy storage (TES). It offers a compelling way for power plants to operate like conventional once-through cooling (OTC) — i.e., without an efficiency penalty due to heat rate increase experienced by state-of-the-art dry, wet, and hybrid cooling systems — while eliminating water consumption and attached negative environmental impact. Further, cool TES provides power plants the desirable capability and benefits associated with grid-scale energy storage. Key components of the concept are comprised of developed technology and field-proven equipment. Performance estimates to convert from OTC for the Diablo Canyon nuclear-powered steam electric generating facility located in central California are presented to illustrate the real benefits gained verses closed-cycle wet cooling.
Analysis of Two-Dimensional Bending Vibration of an Internal Combustion Engine’s Shafting System Based on Wave Equation
Authors: Liang Xingyu , Yang Kang , Shu Gequn , Wang Yuesen , Tan Linlin , Wen Yonghui
Published: August 2012

Reciprocating machines are widely used in many mechanical industries. Bending vibration of spinning components, such as the shaft system of a high-speed power engine (vehicles, ships, helicopters, etc.), turbine engines and generators usually requires the integration of both design and analysis. The general method to analyze vibration is the discretization method. The bending/torsion/axial vibration of these systems is often solved using the lumped parameter method, in which small diameter long shafts are neglected by concentrated masses. Well known since the Holzer’s tabulating methods, many researchers proposed both transfer matrix and extended transfer matrix methods to solve free and/or forced vibration under dampened and/or undampened vibration based on discrete methods. In many situations, however, the results from a discrete method couldn’t exactly agree with actual results. In particular, in bending vibration analysis there is no correction and precision method to calculate bending vibration of multi-stepped spin shafts because the shafts are often treated as one dimensional vibration. We should therefore develop a new precision method to analyze two-dimensional bending vibration of shaft systems. In this paper, a new precise approach is proposed to study and calculate the bending vibration of multi-step systems with N-stepped changes of their property under rotary conditions, supported by N+1 springs and dampers governed by a two-dimensional wave equation. At first, the author analyzed the source of bending vibration. When a crankshaft is excited by external forces which can be divided into vertical and horizontal forces, the shaft will deform in two planes. Then strain and stress equations of the spin shaft are established, applied to the Hamilton Principle, and a two-dimensional wave equation is established. After that, to simplify, the author deduced the calculation formula of one dimensional bending vibration — a sine exciting force acted on arbitrary concentrated masses between point No.1 and No.N+1. By using this formula, the total dynamic response of additional force can be obtained through a general procedure of superposition. And then, the influence of the coupled product of inertia is discussed and the two-dimensional dynamic response is obtained. To demonstrate the theoretic analysis, we checked the prediction using the bending vibration of a highspeed diesel engine’s crankshaft. By using a newly-designed axial/ torsion/ bending vibration testing device, we measured the bending vibration at the front free-end of the crankshaft. When the calculated results were compared with measured results, they agreed with each other. This verified that the author’s proposed new method to study bending vibration is warranted and correct.
Neural Network Application for Structure Design Optimization of Thin-Wall Structures
Authors: Kamel Hesham
Published: August 2012

Neural networks are trained to predict the response of a thin wall tube under dynamic impact loading then they are integrated with an optimization algorithm to improve the crashworthiness design of the thin wall tube. LS-DYNA is used to simulate the tube’s response under dynamic impact while MATLAB is used to train the neural networks and the optimization algorithm. The results show that the suggested approach succeeded in improving the thin wall tube design at an affordable computational cost. It is suggested that the approach can be expanded for the design improvement of more complex structures.
Two-Dimensional FEM Stress Analysis of Adhesive Butt Joints Filled With Nano-Composite in Adhesive Subjected to Static Tensile Loading
Authors: Sawa Toshiyuki , Tanabe Shougo , Kobayashi Takashi , Kotajima Kazunari , Sekiguchi Yasuhisa
Published: August 2012

The interface stress distributions and the stress distributions around fillers in adhesive butt joints including fillers under static tensile loading are analyzed using Finite Element Method (FEM). The effects of stiffness, size and filling rate of fillers on the interfaces stress distributions and the stress distribution around the fillers are examined in the FEM calculations. It is seen that the maximum value of the stress around the edge of the adhesive interface decreases as the filling rate increases, while the stress around the fillers increases. The result shows that the joint strength increases more than that of the joints without fillers when the filling rate is lower (around 10 weight %). In addition, it is observed that the joint strength decreases at high filling rate. For verification of the FEM calculations, experiments were carried out to measure the joint strength. The analytical results are in a fairly good agreement with the experimental results.
Numerical Simulation of GaN Growth in a MOCVD Process
Authors: Meng Jiandong , Jaluria Yogesh
Published: August 2012

This paper describes a model for the growth of gallium nitride in a vertical impinging metalorganic chemical vapor deposition (MOCVD) reactor. With trimethylgallium (TMGa) and ammonia (NH3) carried by hydrogen (H2) as precursors, the flow, temperature and concentration profiles are predicted by numerical modeling, which is performed using a commercial CFD software package CFD-ACE+. The growth rate is predicted based on detailed reaction mechanisms given in the literature, and related studies are carried out to verify the reliability and adaptability of the chosen chemical kinetics. A detailed mathematical model is developed first, and the complete chemical mechanisms are introduced. Then, the dependence of the growth rate and uniformity of the deposited layers on operating conditions, such as reactor operating pressure, susceptor temperature, inlet velocity and concentration of the precursors, is investigated to gain greater insight into the reactor performance and characteristics. Based on the simulation results, discussion is presented in this paper to offer the possibility of better control of the GaN film growth process, and to ultimately lead to an optimization of the process, with respect to production rate and film quality.
Viscoelastic Abrasive Waterjet
Authors: Ashrafi Nariman
Published: August 2012

Effect of addition of viscoelastic additive on the stability and precision enhancement of the abrasive waterjet is studied. Cornstarch is chosen to be added to the mixture of water and abrasive for it is readily available in large quantities at low cost. Yet it shows major nonlinear properties valuable for waterjet machining. It is shown that the normal stresses developed in the nonlinear viscoelastic cornstarch remains substantially unchanged throughout effective jet length resulting in an almost completely prismatic jet, most desirable for precision and straight machining. Furthermore, the jet becomes more stable upon increasing the cornstarch percentage. The additive also causes the jet to produce less friction with the surrounding air avoiding possible jet disintegration. Clearly, due to the increase of elastic as well as viscous effects, there is restriction to the pump delivery upon adding the dilatant cornstarch. Different percentages of the additive are therefore examined. It is found that, a 22% additive results in the best performance based on the precision, available pump power and stability of the jet. The experiment was carried out on three products; marble, aluminum and glass. In all cases, kerf angle was reduced significantly. Simulation of the problem is in good agreement with the experimental observations.
Tailoring Thermal Properties of Hybrid Glass Fibers/Carbon Fibers Reinforced Polymeric Composites
Authors: Luca-Motoc Dana , Pop Petru A. , Bou Santiago Ferrandiz , Da˘diˆrlat Nicolae
Published: August 2012

The herein paper tackles the issue of dimensional stability of composite materials from the perspective of characterization the overall linear coefficient of thermal expansion (CTE) for different hybrid polymeric composite architectures tailored with the aim of lowering the manufacturing costs and fulfilling few design requirements in several engineering applications. The hybrid configurations are made of unidirectional carbon fibers (max. 1 or 2) embedded along with different combinations of E-glass woven roving or chopped E-glass strand mat as wear/chemical resistant, outside reinforcement layers. A polyester resin type was used as binder. The thermal properties were measured using a differential dilatometer DIL 402 PC/1 from NETZSCH GmbH (Germany) imposing a linear, monotonic temperature rise with 1 K/min from 20°C up to 250°C. Thermal cycling behavior was underlined by imposing two successive heating cycles upon each hybrid composite samples. Thermal strains temperature/time evolution and peak values are further analyzed to size the thermal aging effects. The experimental retrieved data will be further compared with the values obtained by running a micromechanical based approach simulation on the DIGIMAT software (from X-stream Engineering Inc., Luxembourg).
Doing BiE: Lessons Learned From Teaching Bio-Inspired Engineering
Authors: Jenkins Christopher H.
Published: August 2012

Examples of bio-inspired engineering (BiE) abound: from Da Vinci to Velcro to robotics. Showing students the excitement and utility of BiE is easy — teaching them how to “do” BiE is much more difficult. In teaching ME 455 Bio-Inspired Engineering at Montana State University. A fundamental challenge is to teach engineers BiE without the need for them to be biologists. The nature of design itself is another challenge. The value of BiE is in expanding the engineering design solution space. Today, the usual forward approach and the one most typical for design — an engineering problem in search of a biological solution paradigm — is essentially unavailable. In this paper, we provide rationale for some of the challenges in teaching BiE to engineering students. We then share lessons learned in addressing these challenges from direct experience in the classroom.
Inner Phase Change Behavior of Small Liquid Droplet on Heated Solid Surface
Authors: Lu Gui , Duan Yuan-Yuan , Wang Xiao-Dong
Published: August 2012

An experimental investigation was conducted to visually observe the transient boiling in an individual water droplet on different heated solid surfaces, covering the free surface evaporation, nucleate, transition and spheroidal boiling regime. Diversified bubble dynamics, phase change and heat transfer behaviors for different boiling regimes of droplet were discussed in present work. In nucleate boiling regime, plenty nucleate bubbles with uniform diameters were confined within the bottom of the droplet, enhancing the heat transfer and cooling performance. The surface properties had great effects on the bubble dynamics in this regime. In the transition boiling regime, the phase change behaviors of a droplet displayed a cyclical process, restricted, sole-bubble and metastable cyclical styles were observed in the experiments. A vapor film between the droplet and surface exists in the spheroidal boiling regime, leading to the random movement of droplet above the heated surface and prolonging the lifetime of droplet significantly.
A Novel Device to Investigate the Effect of Residual Tension in Natural Tissue Implants
Authors: Berg Robert J. , Saigal Anil , James Thomas P.
Published: August 2012

Natural collagen tissue implants derived from fetal bovine dermis are an attractive alternative to polymers for use in soft tissue repair. Constitutive relationships for this material are typically determined in vitro on a universal testing machine. However, upon implementation, tissue remodeling may cause the material properties to change rapidly. The literature indicates that the level of in vivo strain and the corresponding stress field may promote either tissue adaptation or undesirable resorption. The present work investigates a novel device for eventual use as an implantable tensometer. The device is not intended to be a substitute for material characterization on a universal testing machine, but rather a new device, representing a basic mechanical system that would facilitate the development of an even smaller instrument on the scale to be implanted in laboratory animals. An instrument of this type would enable the in vivo characterization of biomaterials under a prescribed load. The new device uses springs to generate a force on the biomaterial sample. Results show that the device creates a diminishing force that reaches quasi-static equilibrium displacement with acellular collagen implants (n = 11) of varying cross sectional areas under different loads. Reaching an equilibrium displacement is an essential starting point for an implantable instrument. Changes from the equilibrium position may forecast a threshold stress to initiate resorption. In addition, knowledge on resorption rate may be obtained.
Short-Term Generation Schedule Optimisation for Combined Heat and Power
Authors: Gomes E. E. B. , Pilidis P. , Polyzakis A. L.
Published: August 2012

In the last decades one of the most difficult problems in the electricity market has been how to dispatch and manage the electricity in power generation plants. Despite of all the benefits of distributed poly-generation and combined heat and power systems, their penetration in the power market worldwide is quite modest and one of the barriers against their increasing participation is the high fees for back-up supplies, which is one of the problems addressed in this investigation. This paper introduces a pool of distributed generation units (named nerve-centre) able to economically optimise the generation schedule of gas turbine power plants and end-users interconnected through a mini-grid. A hybrid genetic algorithm adapted priority list was developed to solve the multi unit generation schedule optimisation problem. The algorithm developed in this study leads the optimisation mechanism to a faster convergence and a very low risk of non-convergence to the optimal result. Despite the power generation optimisation studies reported in the technical literature, none of them has been modelled for such a pool of distributed generators trading electricity in the competitive market. This investigation shows that the proposed nerve-centre concept can result in significant savings to generators/end-users.
Falling-Film Absorption Around Microchannel Tube Banks
Authors: Nagavarapu Ananda Krishna , Garimella Srinivas
Published: August 2012

An experimental investigation of heat and mass transfer in a falling-film absorber with microchannel tube arrays was conducted. Liquid ammonia-water solution flows in a falling-film mode around an array of small diameter coolant tubes, while vapor flows upward through the tube array counter-current to the falling film. This absorber was installed in a test facility consisting of all components of a functional single-effect absorption chiller, including a desorber, rectifier, condenser, evaporator, solution heat exchanger, and refrigerant pre-cooler, to obtain realistic operating conditions at the absorber and to account for the influence of the other components in the system. Unlike studies in the literature on bench-top, single-component, single-pressure test stands, here the experiments were conducted on the absorber at vapor, solution, and coupling fluid conditions representative of space-conditioning systems in the heating and cooling modes. Absorption measurements were taken over a wide range of solution flow rates, concentrations, and coupling fluid temperatures, which simulated operation of thermally activated absorption systems at different cooling capacities and ambient conditions. These measurements are used to interpret the effects of solution and vapor flow rates, concentrations, and coupling fluid conditions on the respective heat and mass transfer coefficients.
Graphical Interpretation of Exergy
Authors: Boettner Daisie D. , Bluman James , Rowland Matthew , Bodenhamer Jonathan , Arnas A. O˝zer
Published: August 2012

Exergy is a system thermodynamic property defined only with respect to the system’s surroundings. For a specified system state, exergy is the maximum potential useful work available from the system as it achieves equilibrium with the surroundings. For students exergy can be a very abstract concept. This paper presents a graphical means to clarify the concept of exergy for a closed system, demonstrating exergy at any state i corresponds to the sum of the net work of a power cycle that incorporates a process from system state i to the dead state and the net work of a refrigeration/heat pump cycle required to move the system from the dead state to state i.
Impact of an Anisotropic Fin Surface Design on the Thermal-Hydraulic Performance of a Plain-Fin-and-Tube Heat Exchanger
Authors: Yu Rong , Sommers Andrew D. , Okamoto Nicole C. , Upadhyayula Koushik
Published: August 2012

In this study, we have explored the effectiveness of heat exchangers constructed using anisotropic, micro-patterned aluminum fins to more completely drain the condensate that forms on the heat transfer surface during normal operation with the aim of improving the thermal-hydraulic performance of the heat exchanger. This study presents and critically evaluates the efficacy of full-scale heat exchangers constructed from these micro-grooved surfaces by measuring dry/wet air-side pressure drop and dry/wet air-side heat transfer data. The new fin surface design was shown to decrease the core pressure drop of the heat exchanger during wet operation from 9.3% to 52.7%. Furthermore, these prototype fin surfaces were shown to have a negligible effect on the heat transfer coefficient under both dry and wet conditions while at the same time reducing the wet airside pressure drop thereby decreasing fan power consumption. That is to say, this novel fin surface design has shown the ability, through improved condensate management, to enhance the thermal-hydraulic performance of plain-fin-and-tube heat exchangers used in air-conditioning applications. This paper also presents data pertaining to the durability of the alkyl silane coating.
Analytical Solutions for the Static Instability of Micro/Nano Mirrors Under the Combined Effect of Capillary Force and Casimir Force
Authors: Moeenfard Hamid , Darvishian Ali , Ahmadian Mohammad Taghi
Published: August 2012

This paper deals with the problem of static instability of Micro/Nano mirrors under the combined effect of capillary force and Casimir force. At the First the governing equations of the statical behavior of Micro/Nano mirrors under the combined effect of capillary force and casimir force is obtained. The dependency of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that existence of casimir force can considerably reduce the stability limits of nano/micromirror. It is also found that rotation angle of the mirror due to capillary force highly depends on the casimir force applied to the mirror. Finally analytical tool Homotopy Perturbation Method (HPM) is utilized for prediction of the mirror’s behaviour under combined capillary and casimir forces. It is observed that a sixth order perturbation approximation accurately predicts the rotation angle and stability limits of the mirror. Results of this paper can be used for successful fabrication of nano/micromirrors using wet etching process where capillary force plays a major role in the system.
Closed Form Solutions for the Problem of Statical Behavior of Nano/Micromirrors Under the Effect of Capillary Force and Van Der Waals Force
Authors: Darvishian Ali , Moeenfard Hamid , Zohoor Hasan , Ahmadian Mohammad Taghi
Published: August 2012

The current paper deals with the problem of static instability of Micro/Nano mirrors under the combined effect of capillary force and van der Waals force. First the governing equations of the statical behavior of Micro/Nano mirrors under the combined effect of capillary force and casimir force is obtained using the newtons first law of motion. The dependence of the critical tilting angle on the physical and geometrical parameters of the nano/micromirror and its supporting torsional beams is investigated. It is found that existence of vdW torque can considerably reduce the stability limits of the nano/micromirror. It is also found that rotation angle of the mirror due to capillary force highly depends on the vdW toque applied to the mirror. Finally analytical tool Homotopy Perturbation Mehtod (HPM) is utilized for prediction of the nano/micromirror behaviour under combined capillary and vdW force. It is observed that a sixth order perturbation approximation accurately predicts the rotation angle and stability limits of the mirror. Results of this paper can be used for successful fabrication of nano/micromirrors using wet etching process where capillary force plays a major role in the system.