bluuebunny/crossref_metadata_2025 huggingface dataset:
Innovative Devices That Enable Variable Flow Systems for Energy Savings
Authors: Miller A. Keith , Bode John R. , Sachs Robert , Jensen Kirt
Published: August 2012

Over the past decade numerous studies both conducted by and authorized by the US Department of Energy Office of Industrial Technology have identified significant energy savings potential by adjusting flow rates to meet process demands. As much as 40% energy savings have been achieved when variable flow pumping systems were implemented in some DOE demonstration projects. To date, only a small fraction of the identified companies in various industries which can benefit in energy savings resulting from adjustable pumping flow rates have installed the requisite capabilities. One reason for the slow rate of adoption of variable pumping is that there are few commercially available methods for adjusting pump rates. Electronic Variable Frequency Drives (VFDs) are the most commonly implemented method of varying pump speeds, usually resulting in reduced operating life of the electric drive motors and sometimes in significant costs of plant modifications. Veritran Inc. with the support of Team Technologies, Inc. is developing low-cost mechanical devices for varying electric motor speeds without the large initial investment associated with VFDs nor the other detracting features of the need to install larger electric motors and reduced motor life expectancy. Veritran’s Infinitely Variable Transmissions (IVTs), such as SM-15IVT (www.veritraninc.com) are installed between the motor and the load, which allows for soft starts, and precise output set speeds, all under programmable microprocessor control. The amount of power demanded from the motor varies as the output speed of the transmission is changed or the load torque is changed. This paper will describe the engineering development that Veritran has been pursuing over the past decade of their novel IVTs, and will present some of the test data collected to date. Results will also be presented of systems analyses where IVTs are inserted into various industrial operations and significant energy savings result.
Evaporation of Liquid Marbles on a Heated Surface: Coating-Assisted Leidenfrost Phenomenon
Authors: Aberle Cedric , Lewis Mark , Yu Gan , Lei Nan , Xu Jie
Published: August 2012

The Leidenfrost effect is a well-known heat transfer phenomenon, which predicts that liquid droplets will show prolonged evaporation time when they are placed on a hot surface with a temperature higher than a critical value. This effect is due to film boiling, where a vapor film helps insulate the drop from the hot surface. In this paper, we show that specially engineered droplets — liquid marbles — can exhibit Leifenfrost effect at any temperature above the boiling point without experiencing any transition. Liquid marbles are spheres with a liquid core that are coated with hydrophobic particles. When brought into contact with a solid surface, liquid marbles are completely nonwetting due to the fact that the hydrophobic powder is in between the liquid and solid surface. Liquid marbles may be used as excellent microreservoirs for biosample handling and chemical reagent manipulation. In our study, liquid marbles are synthesized by coating water droplets with graphite particles. We investigate the thermal evaporation of the fabricated graphite liquid marbles on a hot substrate at prescribed temperatures, and compare the results with pure water droplets. The evaporation time of both liquid marbles and water droplets are recorded at various temperatures. If the temperature is above the Leidenfrost point, the evaporation of both liquid marbles and water droplets are prolonged with similar amount of time (about 100s), which indicates that similar physics might at play in both cases: heat transfer is impeded by a thin layer of vapor. If the temperature is below the Leidenfrost point, water droplets evaporate a hundred times faster. This is because the vapor film cannot self-sustain and levitate the droplet anymore. On the other hand, liquid marbles still evaporate slowly with the same level of time as Leidenfrost evaporation times, which indicates that the Leidenfrost effect still takes effect for liquid marbles even below the critical temperature. This might be due to the fact that the coating of the liquid marble helps levitate the liquid core, maintaining a layer of insulating vapor. In the end, we report detailed deformation of liquid marbles during evaporation. This coating-assisted Leidenfrost phenomenon could be useful in many applications where film boiling is desired. The strong thermal robustness of graphite liquid marbles over a wide temperature range, together with the inert reactivity, electrical conductivity and superior lubrication properties of graphite, make graphite liquid marbles potentially useful in a wealth of applications in microfluidics and lab on a chip devices.
Experimental and Numerical Characterization of an Orifice Type Cryogenic Pulse Tube Refrigerator
Authors: Antao Dion Savio , Farouk Bakhtier
Published: August 2012

An orifice type pulse tube refrigerator (OPTR) was designed, built and operated to provide cryogenic cooling. The OTPR is a travelling wave thermoacoustic refrigerator that operates on a modified reverse Stirling cycle. We consider a system that is comprised of a pressure wave generator (a linear motor), an aftercooler heat-exchanger, a regenerator (comprising of a porous structure for energy separation), a pulse tube (in lieu of a displacer piston as found in Stirling refrigerators) with a cold and a warm heat-exchanger at its two ends, a needle-type orifice valve, an inertance tube and a buffer volume. The experimental characterization is done at various values of mean pressure of helium (∼ 0.35 MPa–2.2 MPa), amplitude of pressure oscillations, frequency of operation and size of orifice opening. A detailed time-dependent axisymmetric computational fluid dynamic (CFD) model of the OPTR is simulated to predict the performance of the OPTR. In the CFD model, the continuity, momentum and energy equations are solved for both the refrigerant gas (helium) and the porous media regions (the regenerator and the three heat-exchangers) in the OPTR. An accurate representation of heat transfer in the porous media is achieved by employing a thermal non-equilibrium model to couple the gas and solid (porous media) energy equations. In the future, a validated computational model can be used for system improvement and optimization.
The Mechanics of Fast-Start Performance of Pike Studied Using a Mechanical Fish
Authors: Feng Chengcheng , Bonafilia Brian R. , Modarres-Sadeghi Yahya , Triantafyllou Michael S.
Published: August 2012

A northern pike (Esox lucius) is capable of achieving a maximum instantaneous acceleration of 25g, far greater than that achieved by any manmade vehicle. In order to understand the physical mechanisms behind achieving such high accelerations, we have built a mechanical fish to emulate the motion of a pike, a fast-start specialist. A live pike bends its body into either a C-shaped or an S-shaped curve and then uncoils it very quickly to send a traveling wave along its body in order to achieve high acceleration. We have designed a mechanical fish whose motion is accurately controlled by servo motors, to emulate the fast-start by bending its body to a curve from its original straight position, and then back to its straight position. Furthermore, this mechanical fish is designed to be adjustable in swimming pattern, tail shape, tail rigidity, and body rigidity, making it possible to study the influence of all of these parameters on the fast-start performance. Peak accelerations of 2.0 m/s2 and peak velocities of 0.09 m/s are measured. Although the maximum accelerations and velocities observed in our mechanical fish are smaller than those of live fish, the form of the measured acceleration signal as function of time is quite similar to that of a live fish. The hydrodynamic efficiencies are observed to be around 12%, and it is shown that the majority of the thrust is produced at the rear part of the mechanical fish — similarly to the live fish.
Fabrication of Surface With Hydrophobicity Gradient Using ZnO Nanowires
Authors: Chakraborty Anirban , Wang Hui , Luo Cheng
Published: August 2012

Current techniques focus on generating ZnO nanowires with uniform density and length on a substrate. However, ZnO nanowires with gradients of density and length over a single substrate could make the corresponding devices have varied properties. Here, we have explored the possibility of fabricating nanowires with gradients in density and length using the vapor-solid method via tilting of the substrate using a mixture of ZnO and graphite powder. This setup creates a non-uniform boundary layer (δ) over the substrate which varies the concentration of reactants reaching the surface leading to the asymmetric growth of the nanowires. A 2-D model was developed in Fluent in order to determine the distribution of velocities around the substrate and calculate δ, with the following substrate tilt angles: 0°, 30°, 45°, 60° and 80°. From the simulation results, the variation of δ was maximum for the 80° tilted substrate. Hence, this angle of tilt was chosen for our experiment. The nanowires were sampled for their densities, lengths and diameters at four locations (L1–L4), spaced 5 mm apart. As an application, we have demonstrated the formation of a surface with continuously varying hydrophobicity. The water contact angles measured were as follows: L1: 105°; L2: 116.5°; L3: 129.5°; and L4: 171.0°. A water droplet (volume: 4 μL) was able to move a distance of 10 mm in 0.8 s, with a substrate tilt of ∼1°.
Closed-Loop Feedback Control Algorithms for Flow Control Over NACA 0015 Airfoil
Authors: Obeid Sohaib , Jha Rataheshwar , Ahmadi Goodarz
Published: August 2012

This study investigates control algorithm for closed-loop feedback control system design aimed at reduction of turbulent flow separation over a NACA 0015 airfoil equipped with leading-edge synthetic jet actuators (SJAs). The algorithm employs system identification technique based on Nonlinear Auto Regressive Moving Average with eXogenous inputs (NARMAX) method to model nonlinear dynamics of the flow and design controller for single-input singleoutput systems. The resulting closed loop response tracks the desired pressure value and significant improvement in the transient response over the open-loop system at high angles of attack is realized.
Thermal Conductivity Characterization of Nano-Enhanced Paraffin Wax
Authors: Sakalaukus Peter J. , Mosley Andrew , Farah Basil I. , Hsiao Kuang-Ting
Published: August 2012

Paraffin waxes are commonly used phase change materials for energy storage. However, the low thermal conductivity of the paraffin wax can limit the energy charging and discharging rate. In this research, a new nano-enhanced paraffin wax with dispersed conductive nanoparticles is tested for the thermal conductivity enhancement. A notable increase in the thermal conductivity has been measured from the carbon nanofiber enhanced paraffin wax.
Automatic Optimization of Casting Feeders Using Feed-Paths Generated by VEM
Authors: Sutaria M. , Joshi D. , Jagdishwar M. , Ravi B.
Published: August 2012

Feeding or risering system of a casting significantly affects the internal quality as well as the yield of a casting. It is however, quite difficult to predict the effect of a particular set of feeder design parameters (such as location, shape and dimensions) on casting quality. Hence feeding system design is iterative in practice, involving tooling modification, foundry trials and inspection. Computer simulation can save material and production resources involved in foundry trials, but requires a higher level of human effort for preparing the inputs and interpreting the results properly. In this work, we have evolved a new approach to evaluate and optimize casting feeding system design using feed-paths. The feed-paths are computed by Vector Element Method (VEM). It is possible to automatically track the direction of the feed metal flow from a given point, and to check if a feeder is effective. The convergence of the feed-paths provides a clear indication of directional solidification and location of shrinkage defects. Further, this takes a fraction of the time taken by FEM-based simulation, making it more useful for practical application. The proposed approach is demonstrated by automatically optimizing the feeder size for a benchmark casting, and validated by pouring and sectioning Al-alloy castings made in sand molds.
Experimental Study of Transient Natural Convection in an Inclined Porous Enclosure With Time-Periodically-Varying Wall Temperature
Authors: Zeng M. , Wang G. , Ren Y. C. , Ozoe H. , Wang Q. W.
Published: August 2012

The transient natural convection in an inclined enclosure filled with porous media is studied experimentally and numerically for the time-periodically-varying wall temperature on one side wall and constant average temperature on the opposing side wall. This system has no temperature difference between the opposing two side walls in time-averaged sense. The porous media with three kinds of porosity consist of water and three kinds of glass ball with different diameter. The temperature and heat flux across the two above-mentioned walls are measured by a heat flux meter. The effects of inclined angles and porosity of the enclosure on heat transfer characteristics have also been studied. The experimental results show that, with the upper wall temperature oscillating, the heat flux across the enclosure is also periodically varied with time. However, the net heat flux is always from the lower wall to the upper wall and reaches maximum at a certain inclined angle. Numerical computations are also conducted and numerical results are qualitatively assured by the experimental measurements.
Numerical Analysis on Flow Characteristics of Anti-Gravity Flow
Authors: Li Yan , Zhang Shuchao , Mei Ning
Published: August 2012

Fluid flow phenomena in micro channels received wide attention due to its high heat transfer coefficient. As a new technique in the field of micro channel phase-change heat transfer, anti-gravity flow can drive fluid flow by capillary force and create enhanced evaporation heat transfer conditions by promoting the formation of an extended meniscus in the three-phase contact-line region. Resulting from the circumferential discrepancy of degree of superheat, the radius of curvature of intrinsic meniscus decreases rapidly as liquid rising up, leading to the formation of capillary pressure gradient. With the increase of heat flux, subcooled boiling occurs and micro-bubble appears at the bottom of the fluted tube. Under the action of buoyancy and drag force, the bubble rises along the channel and at the same time grows continually for the presence of superheat until its break. This paper focuses on the numerical study of flow characteristics of anti-gravity flow in the micro channel and the influence of bubble under the subcooled boiling circumstance. The results shows that bubble plays a positive role in the formation of anti-gravity flow and the analytical expressions are presented for the rising velocity of liquid, the contact angle and the curvature of the intrinsic meniscus, which are all influenced by heat flux, superheat temperature and the geometric parameters of the channel.
The Coupling Effect of Driving Forces to the Anti-Gravity Flow in the Spiral Micro-Channel
Authors: Li Yan , Zhang Shuchao , Mei Ning
Published: August 2012

In this paper, the anti-gravity flow in the spiral micro-channel on the surface of horizontal tube was visualized by the three-dimensional ultra-microscope system. The coupling relationship between the driving force and the flow was studied by Onsager reciprocal relations. The results show that the formation of the anti-gravity flow in the spiral micro-channel on the surface of horizontal tube is impacted by the combining effect of several factors, such as the capillary pressure, wettability, temperature, and bubbles.
Studies on Downstream Stator With Rotor Re-Staggering and Forward Sweeping in a Subsonic Axial Compressor Stage
Authors: Ramakrishna P. V. , Govardhan M.
Published: August 2012

The present numerical work studies the flow field in subsonic axial compressor stator passages for: (a) preceding rotor sweep (b) preceding rotor re-staggering (three stagger angle changes: 0°, +3° and +5°); and (c) stator sweeping (two 20° forward sweep schemes). The following are the motives for the study: at the off-design conditions, compressor rotors are re-staggered to alleviate the stage mismatching by adjusting the rows to the operating flow incidence. Fundamental to this is the understanding of the effects of rotor re-staggering on the downstream component. Secondly, sweeping the rotor stages alters the axial distance between the successive rotor-stator stages and necessitates that the stator vanes must also be swept. To the best of the author’s knowledge, stator sweeping to suit such scenarios has not been reported. The computational model for the study utilizes well resolved hexahedral grids. A commercial CFD package ANSYS® CFX 11.0 was used with standard k-ω turbulence model for the simulations. CFD results were well validated with experiments. The following observations were made: (1) When the rotor passage is closed by re-staggering, with the same mass flow rate and the same stator passage area, stators were subjected to negative incidences. (2) Effect of stator sweeping on the upstream rotor flow field is insignificant. Comparison of total pressure rise carried by the downstream stators suggests that an appropriate redesign of stator is essential to match with the swept rotors. (3) While sweeping the stator is not recommended, axial sweeping is preferable over true sweeping when it is necessary.
A Generalized Method for Weld Load Balancing in Multi Station Sheet Metal Assembly Lines
Authors: Segeborn Johan , Segerdahl Daniel , Ekstedt Fredrik , Carlson Johan S. , Carlsson Anders , So¨derberg Rikard
Published: August 2012

Sheet metal assembly is investment intense. Therefore the equipment needs to be efficiently utilized. The balancing of welds has a significant influence on achievable production rate and equipment utilization. Robot line balancing is a complex problem, where each weld is to be assigned to a specific station and robot, such that line cycle time is minimized. Industrial robot line balancing has been manually conducted, based on experience and trial and error rather than mathematical methods. However, recently an automatic method for robot line balancing was proposed by the authors. To reduce robot coordination cycle time losses, this method requires identical reach ability of all line stations. This limits applicability considerably since in most industrial lines, reach ability differs over the stations to further line reach ability and flexibility. Therefore, in this work we propose a novel generalized simulation-based method for automatic robot line balancing that allows any robot positioning. It reduces the need for robot coordination significantly by spatially separating the robot weld work loads. This is furthermore achieved at a cost neglectable to line cycle time. The proposed method is furthermore successfully demonstrated on an automotive stud welding line. Moreover, algorithm CPU-times is a mere fraction of corresponding manual optimization times.
A Note on Inverse Kinematics of Hybrid Actuation Robots for Path Design Problems
Authors: He Dong , Sun Zhihong , Zhang W. J.
Published: August 2012

Hybrid actuation robotic systems are mechanical systems that contain both servomotors and constant-velocity (CV) motors. Due to this nature of hybrid actuation, design of hybrid actuation robots is governed by both mechanism and robot design theories and methodologies. For instance, the path generation problem in mechanism design may take advantage of the effect of the servomotor for its real-time adjusting function, for which inverse kinematics needs to be established on the servomotor. In this paper, we first generalize four types of path design problems. We then present a general formulation of inverse kinematics for a five-bar hybrid actuation robot and compare two specific approaches to inverse kinematics in the literature in terms of of their computation and suitability to the path design of hybrid actuation robots. Finally, we extend the result for the five-bar hybrid actuation robot to a general hybrid actuation robot.
Effect of Compression Ratio on the Performance Characteristics of a Palm Oil Methyl Ester Run Diesel Engine
Authors: Debnath Biplab K. , Saha Ujjwal K. , Sahoo Niranjan
Published: August 2012

Palm Oil Methyl Ester (POME) is a very promising alternative renewable biofuel. This is because it has a better cetane number and a comparable lower calorific value with respect to its competitors. However, due to difference in molecular composition and hence dissimilar properties, it does not perform proficiently in diesel engine with standard design and operating parameters. Therefore, a study is arranged to realize the effect of compression ratio variation on POME run in diesel engine. The load is varied from ‘no load’ to ‘full load’ with six equal intervals. During this study, standard diesel injection timing is maintained unaffected. The study conveys that at higher compression ratio, POME causes reduction in brake fuel consumption and thereby increases the engine efficiency. The increase in compression ratio also causes smoother combustion, lower ignition delay with early heat release than diesel operation. The detrimental emission quantities in the form of carbon monoxide, oxides of nitrogen and hydrocarbon emissions are also cut down with presence of POME in the diesel engine at high compression ratio. Thus, POME can be regarded as a good alternative fuel for diesel engine for locomotive applications.
Analysis of Multiphase Transport Phenomena in PEMFCS by Incorporating Microscopic Model for Catalyst Layer Structures
Authors: Khan Munir , Xiao Yexiang , Sunde´n Bengt , Yuan Jinliang
Published: August 2012

The catalyst layer (CL) in polymer electrolyte membrane (PEM) fuel cells is one of the key components regulating the overall performance of the cell. In PEM fuel cells, there are two CLs having identical composition for hydrogen oxidation (HO) and oxygen reduction (OR) reactions. There are four phases inside the CL, namely: carbon, Pt particles, ionomer and voids. In this work, a micro-model of the cathode CL has been developed mathematically using finite volume (FV) technique to investigate the transport phenomena of reactants and product species, ions and electrons by incorporating the above stated phases at the cathode side only, due to the fact that the OR reactions are the rate limiting as compared to HO reaction. The 3D CL has been reconstructed based on a regularly distributed sphere’s method with dimensions 4.1 × 4.1 × 4.1 μm3. Platinum particles combined with carbon spheres (C/Pt) are regularly placed in the domain, an ionomer layer of a given thickness is extruded from the sphere surfaces. The C/Pt, ionomer and void distribution, as well as the triple phase boundary (TPB) are analysed and discussed. A microscopic model has been developed for water generation and species transport via Knudsen diffusion through the voids and the proton transport in the ionomer has been included here to aim for the rigorousness of the work. In addition, the electrochemical reactions have been simulated on the surface of Pt particles fulfilling the TBP conditions.
Reduction of Drag Friction and Increase of Buoyant Force for a Microboat Using Micropillars
Authors: Qiao Lei , Luo Cheng
Published: August 2012

In this work, we explored the possibility to reduce the friction drag and increase buoyant force of a SU-8 microboat by incorporation of micropillars. We considered mechanism, design, and fabrication, followed by experimental tests. Through two sets of tests, we demonstrated that the incorporation of the micropillars reduced the friction drag and increase buoyant force as expected.
Linear Sawing Apparatus and its Evaluation for Research Into High Speed Bone Sawing
Authors: Pearlman John J. , Saigal Anil , James Thomas P.
Published: August 2012

Previous research into the cutting mechanics of bone sawing has been primarily approached from the perspective of orthogonal metal machining with a single edge cutting tool. This was a natural progression from the larger body of knowledge on the mechanics of metal cutting. However, there are significant differences between typical orthogonal metal cutting parameters and those encountered in bone sawing, such as anisotropic material behavior, depth of cut on the order of cutting edge radius, chip formation mechanism in the context of a saw blade kerf, non-orthogonal considerations of set saw blade teeth, and cutting speed to name a few. In the present study, an attempt is made to overcome these shortcomings by employing a unique sawing fixture, developed to establish cutting speeds equivalent to those of typical sagittal saws used in orthopaedic procedures. The apparatus was developed for research into bone sawing mechanics and is not intended to be a commercial sawing machine. The sawing fixture incorporates the cutting speed possible with lathe operations, as well as the linear cutting capabilities of a milling machine. Depths of cut are on the same order of magnitude as the cutting edge radius typical to saw blade teeth. Initial measurements of cutting and thrust force, obtained with this new experimental equipment, are compared to previous work.
Transition From Cassie-Baxter to Wenzel States on Micropillar-Formed Surfaces Induced by Evaporation
Authors: Xiang Mingming , Wilhelm Anderson , Luo Cheng
Published: August 2012

As a liquid droplet is placed on a rough surface, the wetting may be either in Wenzel state [1] or in Cassie-Baxter state [2]. In the Wenzel state, the droplet completely penetrates between microstructures (e.g., lines and pillars), while in the Cassie-Baxter state air is trapped between these microstructures and the droplet stays on top of the microstructures and trapped air. The Cassie-Baxter state may be transited to the Wenzel State when Laplace pressure reaches a certain value [3]. To date, three pressure criteria have been reported in the literature to predict when the transition may occur from the Cassie-Baxter state to the Wenzel State. The first criterion is [4] Pl−Pg>−4γlgcosθe2b(1+b2a),(1) where Pl is the pressure in liquid, Pg is the pressure in gas, (Pl − Pg) is so-called Laplace pressure, γlg is surface tension between liquid and gas, θe is the equilibrium contact angle on the flat surface and b is the space between two adjacent pillars. The second criterion has the form Pl−Pg>−4γlgcosθe2b.(2) The third criterion is given by [5] Pl−Pg>−4γlgcosθe2b.(3) Although these pressure criteria have similar forms, there still exist differences in their denominators. It is not clear which criterion gives the best prediction of the transition during the evaporation of a water droplet. Therefore, in this work, we examined these three criteria based on the experimental data obtained through in-situ observation of the transition of a droplet.
Applying Advanced FMEA Methods to Vehicle Fire Cause Determinations
Authors: Parrott Kerry D. , Mattes Pat J. , Stahl Douglas R.
Published: August 2012

This paper proposes that the advanced Failure Modes and Effects Analysis (FMEA) techniques and methodology currently used by the automotive industry for product and process design can be reversed and used as an effective failure/root cause analysis tool. This paper will review FMEA methodologies, explain the newest advanced FMEA methodologies that are now being used in the automotive industry, and will then explain how this methodology can be effectively reversed and used as a failure analysis and fire cause determination tool referred to as a “reverse FMEA” (rFMEA). This paper will address the application of these techniques and methodology to vehicle fire cause determination. This methodology is particularly suited to situations where multiple potential fire causes are contained within an established area of origin. NFPA 921 Guide for Fire & Explosion Investigations [1] and NFPA 1033 Standard for Professional Qualifications for Fire Investigator [2], often referenced by the fire investigation community, prescribe following a systematic approach utilizing the scientific method for fire origin and cause determinations. The rFMEA methodology is proposed as a fire investigation tool that assists in that process. This “reverse FMEA” methodology will then be applied to a hypothetical, illustrative case study to demonstrate its application.
Sputtering Power on Electrical Characteristics of Er,Ti Co-Doped HfO2 Films
Authors: Pei Yili , Wu Ping , Li Xianfei , Khaskheli Murad A. , Chen Sen , Zhang Shiping
Published: August 2012

Er,Ti co-doped HfO2 films, as candidate of the gate dielectric material for CMOS technology, were deposited on n-Si (100) by radio frequency magnetron sputtering. The dielectric characteristics of the films were compared with different sputtering powers. The surface morphology of HfTiErO was observed by atomic force microscopy (AFM). The thickness of the films was determined by SGC-10 film calibrator. The results show that the growth rate nearly has a linear increase with the sputtering power rising, the film with sputtering power 40W, 100W or 120W has better surface topography, the sputtering power of 60W and 80W leads to better interfacial and electrical properties. The results of the present work indicate that 60W is the optimal condition for preparing the HfTiErO film.
Microstructured Surfaces for Enhanced Pool Boiling Heat Transfer
Authors: Chu Kuang-Han , Enright Ryan , Wang Evelyn N.
Published: August 2012

We experimentally investigated pool boiling on microstructured surfaces which demonstrate high critical heat flux (CHF) by enhancing wettability. The microstructures were designed to provide a wide range of well-defined surface roughness to study roughness-augmented wettability on CHF. A maximum CHF of 196 W/cm2 and heat transfer coefficient (h) greater than 80 kW/m2K were achieved. To explain the experimental results, a model extended from a correlation developed by Kandlikar was developed, which well predicts CHF in the complete wetting regime where the apparent liquid contact angle is zero. The model offers a first step towards understanding complex pool boiling processes and developing models to accurately predict CHF on structured surfaces. The insights gained from this work provide design guidelines for new surface technologies with higher heat removal capability that can be effectively used by industry.
A Coupled Model Between Torsion and Bending in Nano/Micromirrors Under the Combined Effect of Van Der Waals Force and Capillary Force
Authors: Moeenfard Hamid , Darvishian Ali , Ahmadian Mohammad Taghi
Published: August 2012

The coupling effect between torsion and bending in nano/micromirrors under the combined effect of capillary force and van der Waals (vdW) force is presented in this paper. At the first, the dimensionless equations governing the statical behavior of the nano/micromirror are obtained using the minimum total potential energy principle. Then the equations governing the pull-in state of the mirror are obtained using the implicit function theorem. The related results show that neglecting bending effect can lead to considerable overestimation in predicting the pull-in limits of the nano/micromirror under combined vdW and capillary forces. It is observed that vdW force reduces the pull-in angle and pull-in deflection of the supporting torsion beams of the mirror. The static behavior of the nano/micromirror under capillary and vdW loading is also studied and the results reveal that the static behavior of the nano/micromirror under capillary and vdW forces highly depends on the bending of the torsion beams. The results of this paper can be used for a safe and stable design and fabrication of mirrors using the wet etching process, where the gap between the mirror and the underneath substrate is sufficiently small and as a results both capillary and vdW forces have significant role in the stability of the system.
The Trolley Problem and the Type IV Safety Device
Authors: Schmid Steven R. , Mason James J.
Published: August 2012

The Trolley Problem is a common problem considered by philosophers, because of the many variations that exist and the subtle differences in solutions that can be generated. Recent research has coupled the Trolley Problem with neuroimaging techniques (fMRI), and demonstrates a complex interaction between cognitive and emotional responses depending on the problem variant. This paper poses the Engineer’s variant of the Trolley problem, namely whether or not an engineer should incorporate safety devices in design if the safety devices have a downside with respect to safety. The authors provide a design paradigm that incorporates the Dangerous Safeguard Consensus, the Intrinsic Classification of Safeguard Devices, and the Safeguard Evaluation Protocol. This paradigm is consistent with the admonitions in the safety literature, industry standards, and governmental codes, the incommensurability of human lives and a utilitarian world view.
A Mesoscopic Friction Model Based on Surface Roughness and its Statistical Description
Authors: Stingl Bernhard , Hoffmann Norbert P.
Published: August 2012

In engineering practice frictional resistance is considered on a macroscopic scale: All the physical processes resulting in resistance against sliding are subsumed under a single friction coefficient, though there is no real evidence for this separation of scales. A feasible way to bring multiscale modelling to frictional problems can be the consideration of friction on a mesoscale on which the roughness of apparently smooth surfaces appears. Although surface roughness has always been connected with friction, recently experiments and models revealed that dynamic processes in the rough interface determine the frictional behaviour.
Teaching of Beam Deflection Analysis Through Laboratory Experiments
Authors: Eveloy Valerie , Bojanampati Shrinivas , Rodgers Peter
Published: August 2012

Hands-on laboratory skills play a vital role in providing students with a sound understanding of the scientific fundamentals and their application in solving real-life engineering problems. This paper describes a hands-on laboratory project focused on solid mechanics, which is taught as part of a one-semester, junior-level mechanical engineering course titled Core Measurements Laboratory. The project requires students to design, construct and commission an experimental test facility for the characterization of cantilever beam deflection and stress due to pure bending using concomitant methods, consisting of three experimental techniques and analytical predictions. Beam deflection is measured using both a linear displacement transducer (LDT) and digital camera, with corresponding stress measurements derived from strain gage measurements. These measurements are compared with analytical predictions. The project is undertaken over a five-week period by a team of four students. A written project report and oral presentation are conducted on project completion. Emphasis is placed on elaboration of a test plan, sensor installation, data acquisition and LabVIEW programming, as well as analysis of discrepancies between measurements and predictions. The teaching strategy employed to integrate fundamental theory with hands-on experiences is described, with a sample of the measurement results presented. The effectiveness of the laboratory project in enhancing student fundamental and applied knowledge in the subject area, and project management skills, is assessed by monitoring student performance improvements over the duration of the project, as well as through student surveys. On a scale of 1 (deficient) to 4 (exemplary), overall class scores of 2.92, 3.25 and 3.4 were obtained for ABET Criterion 3 Outcomes (b), (d) and (g), respectively, which were assessed using the hands-on project final report and oral presentation. The student survey indicates that student knowledge in fundamentals, sensors, data acquisition and LabVIEW programming improved by 16%, 23%, 30% and 48%, respectively, with the hands on project.
Optimization of Skin Cooling for Thermographic Imaging of Near-Surface Lesions
Authors: Cheng Tze-Yuan , Herman Cila
Published: August 2012

With the dramatic advances in IR imaging technology, the IR imaging technique has the potential to become a promising non-contact in-vivo diagnostic tool for the early detection of melanoma [1] as well as other conditions in which the temperature of the body deviates from normal temperature. Active or dynamic IR (thermal) imaging, which involves introducing external cooling, can induce or enhance relevant thermal contrast observed on the skin surface, leading to temperature differences that can be accurately measured with a properly designed IR imaging system. When the skin surface is cooled down in active IR imaging, the variation in the thermal properties of the lesion located underneath the surface result in identifiable temperature differences from the surrounding healthy tissue in the recovery phase, and therefore the dynamic thermal response of the structure acquired using active imaging provides critical information to distinguish the diseased and healthy tissues. Regarding the effectiveness of the active IR imaging, in this study, the performance of varied cooling parameters, including cooling method, cooling temperature, cooling duration, and cooling depth are discussed. Toward the objective of minimizing the discomfort of patient, by evaluating the transient temperature difference in the recovery phase for varied cooling conditions, our goal is to find out the optimized cooling conditions, which can provide effective thermal response contrast in the recovery phase, while applying appropriate cooling temperature and duration to facilitate the clinical feasibility of this technique. The optimized cooling condition concluded from the simulation will be verified by the in-vivo dynamic thermal imaging experiments.
Investigation of the Impact of Sintering on SOFC Charge Transfer
Authors: Nelson George J. , Cassenti Brice N. , Peracchio Aldo A. , Chiu Wilson K. S.
Published: August 2012

Solid oxide fuel cell electrodes are porous composites commonly produced by the sintering of powder compacts. Particle contact geometry within the electrode microstructure has been noted to impact electrode performance, particularly with respect to charge transfer. An analytical modeling concept has been applied to charge transport within the SOFC electrode microstructure using an approach similar to thermal fin analysis. This approach has the ability to account for variable cross-section solid geometry and replicates experimentally observed behavior related to SOFC electrode sintering quality. Microstructural geometries simulated by periodic structures composed of iterated base units with variable cross-section are investigated using two approaches: an axisymmetric one-dimensional analytical solution and an axisymmetric two-dimensional finite element solution. Results are cast in terms of dimensionless parameters and performance metrics that have been developed to assess the quality of SOFC electrode microstructures. Comparison of the one-dimensional and two-dimensional results demonstrates the predictive capabilities of the simplified approach.
The Effects of Operating Conditions on the Design of Radial Spiral Mandrel Dies
Authors: Nart Cagri , Yilmaz Oktay , Kirkkopru Kadir
Published: August 2012

Coextrusion heads are widely used to produce multi-layered products such as pipes and vessels in plastics industry. Spiral mandrel dies which are used in coextrusion heads provide good thickness uniformity with a broad range of processing parameters (raw material, throughput, temperature), short residence times (material or colour changes), low pressure drop and good thermal control. In the present study, the effects of operating conditions such as production rate and temperature on the pressure drop through the spiral mandrel die and the occurence of melt fracture are investigated by Computational Fluid Dynamics (CFD) simulations. The temperature dependent viscosity versus shear rate data for grade QB79P (CarmelTech) polypropylene (PP) melt under study are measured by use of an Anton-Paar Physica MCR 301 model rotational rheometer with a 25 mm diameter parallel plate geometry and a capillary rheometer using capillary dies of various lengths with 1 mm diameter hole [11]. The numerical simulations are performed by use of Ansys Fluent, a commercial software [12]. Stress terms in the momentum equations are modeled by Generalized Newtonian Fluid (GNF) Model. For this, Bird-Carreau Model employed as the viscosity model for the polymer melt. In order to avoid exceeding the critical shear stress which causes melt fracture and the value of which is dependent on the processing material, the operating temperature may need to be increased to reduce the viscosity or the flow rate to be decreased. In this case, operating cost increases as a result of energy consumption for heating and the production rate decreases, respectively. Hence, designing of flow channels of the spiral mandrel die by taking into consideration of material property (melt fracture) and extruder limitation (maximum pressure to be supplied) is of critical importance for extrusion with desired production rate at a specific processing temperature.
Noise Reduction by Perfect Absorbers Based on Acoustic Metamaterials
Authors: Climente Alfonso , Torrent Daniel , Sa´nchez-Dehesa Jose´
Published: August 2012

We have designed a cylindrical perfect absorber based on acoustic metamaterials. The absorber consists of a metamaterial shell that surrounds a center that dissipates the acoustic energy. The metamaterial shell is designed so that perfectly matches the acoustic impedance of the air background and guides the sound to the center. Numerical simulations are reported about the efficiency of the absorber as a function of the absorbing material employed at the center.
Aerodynamic Influence of Endwall Fences Located in the Vicinity of the Leading Edge-Endwall Junction of Nozzle Guide Vanes
Authors: Gokce Zeki Ozgur , Camci Cengiz
Published: August 2012

Secondary flow characteristics like horseshoe vortices and related total pressure losses decrease turbine efficiency. Computerized simulations of potentially favorable modifications in turbine systems could provide a fast, numerical and inexpensive method of evaluating their effects on flow properties: This paper consists of a comparative numerical study of the flow characteristics of a domain containing a vertical cylinder subjected to cross flow and upstream endwall modifications. Analyzing the flow around a turbine nozzle guide vane (NGV) could be simplified by modeling it as a vertical cylinder with a diameter proportional to the leading edge diameter of the blade, and adding upstream endwall fences of varying dimensions and alignments could attenuate the development of a horseshoe vortex. A commercial computational fluid dynamics (CFD) software package, Fluent, was used for the numerical analysis. To validate the modeling strategy, experimental data previously reported in the literature for conventional cylinders in cross flow were compared to the current predictions. A grid independence study was also performed. The lateral distance between the two legs of the horseshoe vortex downstream of the cylinder was decreased by 7% to 14%. All fence types effectively changed the location of the main horseshoe vortex roll-up. The height of the fence was more influential than the length of the fence in modifying flow characteristics. The existence of the fences slightly increased the mass-averaged total pressure loss far downstream of the cylinder; however, beneficial near-fence flow characteristics were observed in all cases. Also, it was noted that an endwall fence could possibly result in decreased interaction between the horseshoe vortices created by consecutive blades in a row of NGV blades, which would be expected to result in improved flow conditions within actual turbine passages.
Flow Visualization in Artificial Porous Media From Microfluidic PMMA Devices
Authors: Park D. S. , King S. , Thompson K. E. , Willson C. S. , Nikitopoulos D. E.
Published: August 2012

Microfluidic polymethylmethacrylate (PMMA) devices for study of particle transport in artificial porous media were designed and microfabricated using hot embossing with a brass mold insert containing a microchannel network with eight layers. After thermal bonding to enclose the microchannel network, a process protocol was applied to successfully remove bubbles in the PMMA device. Characterization protocols were developed for study of fluorescent particle tracking, accumulation, and retention in these microfluidic chip artificial porous media. Particle accumulation and retention was observed throughout the microfluidic network domain and predominantly at the inlet section of the PMMA device due to entrance effects. Particle Image Velocimetry of the PMMA device allowed for generating velocity profiles in the chip microchannel networks.
Numerical Investigation of Slider Bearings With Limited Corrugation and Power-Law Lubricant
Authors: Huynh B. P.
Published: August 2012

Performance of slider bearings of infinite width but having corrugation of limited extent is investigated numerically, using a commercial Computational Fluid Dynamics (CFD) software package. Lubricant is assumed to be a fluid of power-law type. Over a range of the power-law index, effects of the corrugated section’s location on pressure distribution in the bearing’s fluid film and its load supporting capacity is considered. Load-supporting capacity increases with power-law index n, but saturates when n reaches about 1.7. Ratio of load-supporting capacities between corrugated bearing and smooth-surface bearing varies significantly with respect to n when n < [about 0.8], but stays nearly constant at higher n value. Larger corrugation-wave amplitude enhances the difference in load-supporting capacity between corrugated bearings and the smooth-surface one.
Validation and Optimization of Heat Transfer in the Electrical Submersible Pump Motor by CFD
Authors: O’Bryan Roshani , Rutter Risa , Sheth Ketan
Published: August 2012

In oilfield applications, an electrical submersible pumping (ESP) system is placed inside the wellbore to provide the necessary energy to lift the fluids to the surface when the reservoir pressure is not sufficient. The ESP system consists of an electric motor, seal section, rotary gas separator (optional), multistage centrifugal pump, electric power cable, motor controller and transformers. The electric motor is placed on the bottom of the unit, and the production fluids are allowed to pass around the motor in order to cool it. The motor generates heat while operating. Study on the temperature rise inside the motor is important to prevent components from failing due to overheating. The temperature rise inside a motor has not been studied extensively. In this work, the temperature of components inside an electric motor was measured under different loading conditions, fluid viscosity and temperature. After testing, the computational fluid dynamic (CFD) was used to model the temperature heat rise in the same motor under the same conditions. The CFD models were validated by the test data within ± 5% error. Furthermore, the validated CFD model was used to calculate the heat rise for different insulation and bedding materials. These computational results from CFD are used to optimize the design of the electrical motor.