bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Engineering Curriculum Improvement Using Product Lifecycle Management (PLM)
Authors: Vuksanovich Brian , Wallace Darrell , Costarell Michael
Published: July 2010

This paper discusses the alignment between industry needs and the content of a 4 year ME or MET curriculum by using Product Lifecycle Management (PLM) principles as a bridge. An initial concept for a device is used as an example throughout the 4 year curriculum, allowing the courses to progressively develop the design from concept through end-of-life by using PLM principles. The four-year curriculum discussed begins with an introduction to PLM, where the steps of a manufacturing process are described, from concept, to 3D design, to analysis, to final product to end of life. This provides the basis for a design concept that will be pursued throughout the curriculum. The four-year curriculum is then presented as a traditional engineering program with a superimposed design problem. The freshman curriculum includes the basic 3D modeling of the parts, while the sophomore classes generate the first prototype parts and beginning analyses. The junior classes progress into more involved stress and thermo/fluid analysis of the part, while the senior classes look into the mass manufacture of the part; it’s interaction with the rest of the system and the systems role in serving society. Students are well prepared for industry, with improved knowledge of design methods, manufacturing processes, life cycle issues and how these different areas can work together to make a successful design. The use of PLM as an over-arching theme brings it into the classroom in a practical hands-on way with minimal impact on the existing class content while improving the delivery by bringing continuity to the problems.
Interfacial Kinetics of High Temperature Oxidation in YSZ Thermal Barrier Coatings With Bond Coatings of NiCoCrAlY With 0.25% Hf
Authors: Soboyejo Winston , Mensah Patrick , Diwan Ravinder
Published: July 2010

This paper presents the results of an experimental study of the high-temperature isothermal oxidation behavior and micro-structural evolution in plasma sprayed thermal barrier coatings (TBCs) at temperatures between 900 and 1200 °C. Two types of specimens were produced for testing. These include a standard and vertically cracked (VC) APS. High temperature oxidation has been carried out at 900, 1000, 1100 and 1200 °C. The experiments have been performed in air under isothermal conditions. At each temperature, the specimens are exposed for 25, 50, 75 and 100 hours. The corresponding microstructures and microchemistries of the TBC layers are then examined using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy EDS. Changes in the dimensions of the thermally grown oxide (TGO) layer are determined as functions of time and temperature. The evolution of bond coat microstructures/interdiffusion zones and thermally grown oxide (TGO) layers are compared in TBCs with standard (STD) and vertically cracked (VC) microstructures.
Improved Lawnmower Blade Design and Optimization
Authors: White Robert , Seaman Jackie , Fan Xuejun , Corder Paul R.
Published: July 2010

With an estimated three billion man-hours of use each year, improvements to the mechanical efficiency of lawnmower systems may yield significant reductions in emissions. Modifications to either the blade geometry or material have been considered in order to achieve the desired gains in efficiency. Specifically, focus is placed upon identification of a more efficient edge shape, reduction of required power input to the blade, and extending the life of the blade sharpness. Using software packages such as Parametric Technology Corporation’s (PTC’s) Pro/Engineer the students were able to increase the quality of design via finite element analysis (FEA) programs such as MSC. Nastran or PTC’s Mechanica. AISI 440C stainless steel was selected as a possible candidate based upon several appealing properties such as high strength, hardness, and resistance to corrosion. It does however have a lower fracture toughness and therefore presents a higher susceptibility to brittle fracture. When both the traditional stress analysis and fracture analysis were considered, opposing results were found. Due to this, other criteria such as cost of material, machining costs, and carbon footprint were considered before making a final design decision. Enhancing education in engineering by diversifying design criteria and encouraging students to address contemporary, real-world design problems was a primary goal of this project. The traditional mechanical design approach relies on stress-strain analysis in order to predict potential failure scenarios, and is the primary technique presented in most undergraduate engineering curricula. Despite its significance, the fracture mechanics approach is not often presented in great detail at the undergraduate level. The academic benefits of including these more universal considerations in the undergraduate engineering curriculum are illustrated in this paper.
Buckling Analysis of Frames With Imperfections and Uncertain Parameters
Authors: Alibrandi U. , Impollonia N. , Ricciardi G.
Published: July 2010

The paper describes a procedure for the reliability analysis of frame structures with respect to the buckling limit state under the assumption that the elastic parameters are uncertain and modeled as random variables. The procedure relies on a Response Surface Method adopting simple ratio of polynomials without cross-terms as performance function. Such a relationship approximates analytically the dependence between the buckling load and the basic variables furnishing a limit state function which is very close to the exact one when a proper experimental design is adopted. In this way a Monte Carlo Simulation applied to the response surface leads to a good approximation with low computational effort. Some numerical examples show the accuracy and effectiveness of the method, for different values of probability failure.
Experimental Measurements and Computational Predictions for an Internally Cooled Simulated Turbine Vane
Authors: Dees Jason E. , Bogard David G. , Ledezma Gustavo A. , Laskowski Gregory M. , Tolpadi Anil K.
Published: July 2010

In this study the conjugate heat transfer effects for an internally cooled vane were studied experimentally and computationally. Experimentally, a large scale model vane was used with an internal cooling configuration characteristic of real gas turbine airfoils. The cooling configuration employed consisted of a U-bend channel for cooling the leading edge region of the airfoil and a radial channel for cooling the middle third of the vane. The thermal conductivity of the solid was specially selected so that the Biot number for the model matched typical engine conditions. This ensured that scaled non-dimensional surface temperatures for the model were representative of those in the first stage of a HPT. The performance of the internal cooling circuit was quantified experimentally for internal flow Reynolds numbers ranging from 10,000 to 40,000. The external surface temperature distribution was mapped over the entire vane surface. Additional measurements, including internal surface temperature measurements as well as coolant inlet and exit temperatures were conducted. Comparisons between the experimental measurements and computational predictions of external heat transfer coefficient are presented.
Test Results From the Idaho National Laboratory of the NASA Bi-Supported Cell Design
Authors: Stoots C. , O’Brien J. , Cable T.
Published: July 2010

The Idaho National Laboratory has been researching the application of solid-oxide fuel cell technology for large-scale hydrogen production. As a result, the Idaho National Laboratory has been testing various cell designs to characterize electrolytic performance. NASA, in conjunction with the University of Toledo, has developed a new cell concept with the goals of reduced weight and high power density. This paper presents results of the INL’s testing of this new solid oxide cell design as an electrolyzer. Gas composition, operating voltage, and other parameters were varied during testing. Results to date show the NASA cell to be a promising design for both high power-to-weight fuel cell and electrolyzer applications.
Performance of Single Electrode-Supported Cells Operating in the Electrolysis Mode
Authors: O’Brien J. E. , Housley G. K. , Milobar D. G. , Petigny Nathalie
Published: July 2010

An experimental study is under way to assess the performance of electrode-supported solid-oxide cells operating in the steam electrolysis mode for hydrogen production over a temperature range of 800 to 900°C. Results presented in this paper were obtained from single cells, with an active area of 16 cm2 per cell. The electrolysis cells are electrode-supported, with yttria-stabilized zirconia (YSZ) electrolytes (∼10 μm thick), nickel-YSZ steam/hydrogen electrodes (∼1400 μm thick), and manganite (LSM) air-side electrodes. The experiments were performed over a range of steam inlet mole fractions (0.1–0.6), gas flow rates, and current densities (0 to 0.6 A/cm2). Steam consumption rates associated with electrolysis were measured directly using inlet and outlet dewpoint instrumentation. On a molar basis, the steam consumption rate is equal to the hydrogen production rate. Cell performance was evaluated by performing DC potential sweeps at 800, 850, and 900°C. The voltage-current characteristics are presented, along with values of area-specific resistance as a function of current density. Long-term cell performance is also assessed to evaluate cell degradation. Details of the custom single-cell test apparatus developed for these experiments are also presented.
Transient Heat Delivery and Storage Process in a Thermocline Heat Storage System
Authors: Van Lew Jon T. , Li Peiwen , Chan Cho Lik , Karaki Wafaa , Stephens Jake
Published: July 2010

Parabolic trough power systems utilizing concentrated solar energy have proven their worth as a means for generating electricity. However, one major aspect preventing the technologies widespread acceptance is the deliverability of energy beyond a narrow window during peak hours of the sun. Thermal storage is a viable option to enhance the dispatchability of the solar energy and an economically feasible option is a thermocline storage system with a low-cost filler material. Utilization of thermocline storage facilities have been studied in the past and this paper hopes to expand upon that knowledge. The current study aimed to effectively model the heat transfer of a working fluid interacting with filler material. An effective numerical method and efficient computation schemes were developed and verified. A thermocline storage system was modeled under specific conditions and results of great significance to heat storage design and operation were obtained.
Observations of Changes in Rate Dependent Flow of SnAgCu Solder Alloys Due to Aging
Authors: Chavali Sri Chaitra , Mysore Kaushik , Subbarayan Ganesh , Dutta Indranath
Published: July 2010

Aging affects both microstructure and behavior [1, 2]. Microstructural changes are driven by dislocation motion and diffusion processes. Together they affect the flow behavior in solder alloys. We address four aspects of solder microstructure and behavior as affected by aging (a) EDS studies on Ag dispersion in Sn matrix (b) a procedure for modeling intermetallic particle growth (c) a model for estimating effective viscosity of solder alloy (d) both primary and secondary creep models to predict aging effects on behavior. Solder samples were aged for different aging times (15, 30, 60, 90 days aging) and at different aging temperatures (25 C, 75 C, 125 C) prior to running creep tests. Another set of solder samples were similarly aged to characterize the microstructure. The creep data for the experiments are from a series of sixty four experiments performed using a micromechanical tester that is specially fitted with a sensitive capacitance gauge (with a resolution of 0.1 microns) to accurately measure viscoplastic responses of solder to applied loads.
Using Excel for the Thermodynamic Analysis of Air-Standard Cycles and Combustion Processes
Authors: Karimi Amir
Published: July 2010

In an undergraduate course or a course-sequence in thermodynamics mechanical engineering students are introduced to air-standard power cycles, refrigeration cycles, and the fundamentals of combustion processes. The analysis of air-standard thermodynamic cycles or solving problems involving combustion processes requires the evaluation of thermodynamic properties either from ideal gas tables or equations developed based on the assumption of constant specific heats. Many students have a difficult time to distinguish the differences between the two property evaluation methods. Also, solving problems involving power and refrigeration cycles or parametric studies of combustion processes involve several steps of property evaluation and some steps require interpolation of data listed in the thermodynamic property tables. Also solution to problems requiring trial and error iterative procedure makes the solution process tedious and time consuming, if it is done manually. This paper provides several examples to demonstrate the effectiveness of Excel in solving problems involving air-standard cycles and combustion processes.
Hydrodynamics and Heat Transfer of Liquid Nitrogen Laminar Falling Films in Cryogenic Heat Exchanger
Authors: Xie Ying-Bai , Zhao Cheng , Tang Jian-Cheng , Mai Ying-Cheng
Published: July 2010

As an efficiency heat and mass transfer method, thin liquid film has been widely used in industry. This paper studies on liquid nitrogen laminar film flows in the brazed cryogenic heat exchanger with 2.3mm distance between plates. Simplified theoretical models are established based on the characteristics of both the dynamic and heat and mass transfer of nitrogen film. Relationship between the dimensionless thickness and the coefficient of heat convection of liquid nitrogen film is derived. And the impact of rate of vapor content, intensity of interfacial convection heat transfer and Reynolds numbers are calculated and analyzed.
Investigation of Board-Level and Package-Level Drop Reliability of RF MEMS Packages
Authors: Sun Li , DeReus Dana , Cunningham Shawn , Morris Arthur
Published: July 2010

Board-level and package-level drop reliability is of critical importance for RF MEMS packages. In this paper, we present a numerical study of reliability of RF MEMS packages during board-level and package-level drop testing. The RF MEMS package consists of a 3.8 mm × 2.5 mm × 0.5 mm RF MEMS die flip-chip assembled on a 5.2 mm × 5.2 mm × 0.4 mm LTCC substrate using lead-free solder balls and a metal lid soldered down on the LTCC substrate to cover the RF MEMS die. The board-level and package-level drop modeling were conducted in accordance with JEDEC standards JESD22-B111 and JESD22-B110A, respectively. The support excitation method was employed to investigate the transient response of the packages. With board-level drop modeling, it was found that the maximum peeling stress in the land grid array (LGA) on the test board side was approximately 170 MPa when the package was mounted on the test board center, and LGA stress reduced to approximately 80 MPa when the package was mounted on the test board edge. As high peeling stress may cause fracture of the intermetallic compound in the solder, the modeling result suggests that the RF MEMS package be placed near the board edge or pins in handheld electronic products. A parametric study of the impact, peak acceleration and pulse duration, was also conducted. It was observed that the maximum stress increased with higher peak acceleration. The maximum stress, however, did not vary monotonically with pulse duration. Package-level drop modeling revealed that the failure of the RF MEMS package would be primarily driven by the inertial force. The transient response of the package synchronized with the drop impact. The maximum stress in the package did not appear in the solder balls but in the seal ring that connects the metal lid to the LTCC substrate. The modeling result indicates that it is important to carry out hermeticity tests before and after package-level drop tests to ensure the package integrity.
Development of Plate-Type Heat Exchanger That Significantly Reduces Indoor Pollutants With a Minimum Loss of Energy
Authors: Lee Dae Hee , Bae Jong Ryeol , Kim Young Saeng
Published: July 2010

We have developed a new innovative plate-type heat exchanger using thin aluminum foil sheet that significantly reduces the indoor pollutants with a minimum loss of energy. The thin aluminum foil sheet has a thickness of 17μm, and having a width of 330 mm and a length of 1,510 mm. The heat exchanger consists of 45 layers of aluminum foil sheets which are placed on top of each other with a spacing of 7 mm. The exchanger is structured such that air dust and pollutants can be effectively filtered as the air stream passes through the heat exchanger. The experimental results show that the concentration of carbon dioxide inside the office room is reduced to as low as 650 ppm, while maintaining the room temperature difference to within ± 1 degree Celsius before and after operating the present heat exchanger. This device can be installed in any indoor places that need the good air quality control with a little sacrifice of energy consumption.
System-Level Reliability Qualification of Complex Electronic Systems
Authors: Farley D. , Dasgupta A. , Al-Bassyiouni M. , de Vries J. W. C.
Published: July 2010

Qualifying functional complex electronic systems and products for reliable performance under a given life cycle history is a difficult task, because of the complex competing aggregation of potential failure sites and failure modes. The current approach, driven by industry specifications and standards, is to conduct standardized tests that are intended to represent a compressed version of representative life cycles. The problem is that there is no clear articulation of what failure mechanisms are being targeted. Consequently, it is not clear what the acceleration factor is likely to be. Especially, as technologies and materials undergo changes, new failure mechanisms may emerge and acceleration factors for old obsolete test conditions may no longer be adequate for expected life cycle conditions. In this study, a systematic and system level approach is used to qualify the interconnects of a new electronic system by using a rapid-assessment method based on the physics of failure approach. The rapid-assessment approach is based on a combination of experimentation and simulation which is focused on identifying and ranking potential modes and mechanisms. The system analyzed in this case is an electronic control box used on a rotating non-stationary platform for a medical instrument. The box contains three PWBs stacked on top of each other and secured using stand-off fasteners and rotates in a gantry up to 220rpm. Dynamic mode shapes are found using finite element simulation, which informs ideal places for instrumentation during experiments to measure the life cycle stress conditions. Quasi-static bending, vibration, and thermal life-cycle conditions are collected with on-board strain gages, accelerometers and thermocouples. The results of these measurements are used as inputs for rapid-assessment simulations, to directly estimate durability and life. All PWAs are found to meet durability goals, although the smallest PWA on top of the stack is found to have the smallest durability margins, and further study is recommended. Tailored accelerated stress testing is recommended in future to verify the predicted durability margins for the entire product.
Modeling a Non-Adiabatic Counter Flow Microchannel Heat Exchanger With Axial Heat Conduction
Authors: Kunjumon A. , Mathew B. , John T. J. , Hegab H.
Published: July 2010

In this paper the effect of axial heat conduction in a non-adiabatic counter flow microchannel heat exchanger is analyzed. The non-adiabatic nature of the heat exchanger causes fluids to exchange heat with the ambient which is at a constant temperature. There are three governing energy equations, one for each fluid and one for the wall separating the fluids. Two of the boundary conditions are the inlet temperature of the fluids. Insulated boundary conditions are used for the wall separating the fluids. The temperature of the fluids and the wall at several points between the inlets and outlets of the MCHXCF are obtained by solving the governing equations using finite difference method. Second order difference schemes are used for discretizing the governing equations. The effectiveness of the fluids depends on the NTU, axial heat conduction parameter, the ambient temperature and the ratio of the thermal resistance between the fluids to that between the ambient and the individual fluids. There is a decrease in the effectiveness of the fluids due to axial heat conduction alone. In the presence of just external heat transfer, increase in ambient temperature reduces the effectiveness of the hot fluid while increasing that of the cold fluid and the opposite trends occur if the ambient temperature is decreased. The combined effect of these two phenomena on the effectiveness of the fluids will depend on the net heat gained/lost by them.
Effects of Waste Vegetable Oil/Water Emulsions on the Emissions of a Listeroid Diesel Engine
Authors: Reding Thomas J. , Naraghi Mohammad , Bosco Stephen , Rodriguez Sergio A. , Miranda Alexander W. , Basinger Matthew
Published: July 2010

This study presents the experimentally determined effects of filtered, heated, waste vegetable oil (WVO) and water emulsions on gaseous emissions, opacity, and fuel efficiency of a Listeroid diesel engine. Emissions studied are NOx, CO, CO2, SO2, O2, unburned hydrocarbons (UHCs), and opacity. WVO emulsions with water additions of 0%, 10%, 20%, 30%, and 40% by weight, heated to 95°C at injection are studied, and results are compared to diesel. The water addition limit was found to be between 41–49%, inclusive, at 50% load. Emulsions are maintained with a magnetic stirrer prior to entry into the fuel line. The WVO is preheated using heat from the exhaust gases. This reduces its viscosity prior to entering the fuel pump, reducing engine wear, pumping losses, and fuel starvation. The WVO is heated again to 95°C immediately before injection, using an externally powered heater to standardize test conditions. A new metric is introduced, namely, brake specific global warming potential (BSGWP). There is a significant reduction in BSGWP at 50% engine load and 30% water addition. Emissions from 40% water addition most closely resemble diesel engine emissions at all engine loads and are consistently lower than with pure WVO.
Optimal Placement of Heat Generating Components at Various Levels of Electronics Packaging
Authors: Suwa Tohru , Hadim Hamid
Published: July 2010

A multidisciplinary placement optimization methodology for heat generating electronics components is demonstrated at various levels of electronics packaging design. The proposed methodology is capable of handling a large number of conflicting multidisciplinary design requirements and complex trade-offs including thermal, mechanical, electrical, electromagnetic, cost among others, which are optimized simultaneously using a genetic algorithm. An effective thermal performance prediction methodology is developed to shorten the calculation time while retaining sufficient accuracy. For simpler thermal problems, a superposition method is used to predict the temperature distribution caused by arbitrarily placed multiple heat sources. For more complex problems (e.g. variable local heat transfer coefficient) artificial neural networks (ANNs) and the superposition method are combined for more efficient prediction of surface (case) and junction temperatures. The proposed methodology is designed to handle existing complex design trade-offs at the crucial early design stage. Capabilities of the present methodology are demonstrated by applying it to several standard benchmarks at the enclosure (PCB) and chip (logic block) levels.
Influence of Unsteady Parameters on the Aerodynamics of a Low Reynolds Number Pitching Airfoil
Authors: Amiralaei M. R. , Alighanbari H. , Hashemi S. M.
Published: July 2010

The objective of the present study is to investigate low Reynolds number aerodynamics of a harmonically pitching NACA0012 airfoil. To this mean, the influence of some unsteady parameters; amplitude of oscillation, d, reduced frequency, k, and Reynolds number, Re, on the aerodynamic performance of the airfoil is investigated. Computational Fluid Dynamics (CFD) is utilized to solve Navier-Stokes equations discretized based on Finite Volume Method (FVM). The instantaneous lift coefficients are obtained and compared with analytical data from Theodorsen’s equations. The simulation results reveal that d, k, and Re are of great importance in the aerodynamic performance. They affect the maximum lift coefficients, hysteresis loops, strength and number of generated vortices within the harmonic motion, and the extent of the figure-eight phenomenon region. Thus, the optimum aerodynamic performance demands a careful selection of these parameters.
Effect of Rib Width on the Heat Transfer Enhancement of a Rib-Turbulated Internal Cooling Channel
Authors: Le A. P. , Kapat J. S.
Published: July 2010

In the quest for enhancing heat-transfer for the internal cooling channels of advanced turbo-machines, many schemes have been used and developed over the years. One such scheme is the use of rib turbulators. There have been fundamental studies in the past to understand the heat transfer enhancement phenomena caused by flow separation due to the presence of ribs. Typical ribs investigated in laboratory type experiments are square in nature i.e. the height, e, of the rib and the width, w, is the same. Although the literature deals with the effects of various rib shapes, little is known about the effect of having e/w not equal to unity. In this paper we investigate the degree of heat transfer enhancement caused by ribs with e/w not equal to unity. Experiments are carried out in a straight duct with ribs oriented normal to the main flow. The P/e ratio, P being the pitch of the ribs, is kept at a constant value of 10 while the ratio w/P is varied systematically from 0.1 to 0.5. Results are reported for Reynolds numbers ranging from 20,000 to 40,000. The aspect ratio of the channel is varied from 1:4 to 1:8 (Height : Width) and their effect is also shown. For all the cases investigated, pressure drop penalty is also presented.
F-22 Subsystem Fleet Management Trend Analysis
Authors: Glista Stefan M. , Rushing David J. , Lide Charles R. , McPherson Patrick C.
Published: July 2010

Reliability growth curves are modeled using the results of Weibull distribution regression analysis. The Weibull Learning Curve (WLC) model is useful because it provides an early statistical indication of wear out issues. The vibration, thermal, humidity and corrosion environments of the F-22 are severe. It is prudent to be concerned about wearout problems in severe aircraft environments. The power of Weibull is the ability to predict the characteristic life and distribution shape with a small amount of data. The proposed model is compared to the traditional Duane Learning Curve approach. Statistical model validity is evaluated using numeric and graphical methods, including coefficients of determination (r2) and residuals. The WLC model provides insight into interdisciplinary issues, including supplier quality control, qualification testing, physics of failure, and reliability engineering. In addition, the WLC model quantifies the number of items with removal statistics consistent with wearout; therefore, this study helps to quantify successes and shortfalls of durability analysis and testing approaches.
Performance Prediction of Electroosmotic Dehumidification
Authors: Gerlach David W.
Published: July 2010

In electroosmotic dehumidification (EOD), a membrane composed of a desiccant material removes moisture from air to be conditioned. Then the water is pumped through pores in the membrane by the application of a voltage and rejected on the other side. This allows the sensible and latent loads in air conditioning to be handled separately and may lead to improvements in energy efficiency and comfort control. The performance of an air conditioning system using an electroosmotic dehumidification system in series with a conventional vapor compression cycle was modeled. The electroosmotic system handles the entire latent load and the vapor compression system handles the entire sensible cooling load. Performance of the system was compared to a conventional vapor compression air conditioner that handles both the latent and sensible loads with a single evaporator coil. Literature data for Nafion membranes was used in a simple electroosmotic drag model. Modeling indicates the feasibility of electroosmotic dehumidification for separating the control of latent and sensible load in air conditioning systems. The total COP of the system, neglecting fan power, can be 1–2 times higher (depending on airflow rate) than a system using an evaporator for latent and sensible load.
Redistribution and Removal of Particles From Drop Surfaces
Authors: Nudurupati S. , Janjua M. , Singh P. , Aubry N.
Published: July 2010

It was recently shown by us that particles distributed on the surface of a drop can be concentrated at the poles or equator of the drop by subjecting the latter to a uniform electric field. In this paper, we present experimental results for the dependence of the dielectrophoretic force on the parameters of the system such as the particles’ and drop’s radii and the dielectric properties of the fluids and particles, and define a dimensionless parameter regime for which the technique can work. Specifically, we show that if the drop radius is larger than a critical value, that depends on the physical properties of the drop and ambient fluids and the particles, it is not possible to concentrate particles and thus clean the drop of the particles it carries at its surface because the drop breaks or tip-streams at an electric field intensity smaller than that needed for concentrating particles. However, since the dielectrophoretic force varies inversely with the drop radius, the effectiveness of the concentration mechanism increases with decreasing drop size, and therefore the technique is guaranteed to work provided the drop radius is sufficiently small.
Supersonic Flow Visualization Over Patented Rotors for a Novel Crypto-Steady Pressure Exchange Ejector Using Schlieren Photography
Authors: Bulusu Kartik V. , Garris Charles A.
Published: July 2010

The process of pressure exchange occurs where flows exchange mechanical energy through work of mutually exerted pressure forces at their interfaces. A novel ejector based on the concept of supersonic crypto-steady pressure exchange rather than the more energy dissipative turbulent entrainment phenomenon is being developed. To better understand the flow structures in context of the novel ejector, schlieren photography is being used as a flow visualizaton tool. The crypto-steady mode of pressure exchange can be achieved with rotors that enable the creating of psuedoblades and entrainment gullies by a primary supersonic fluid. The primary fluid can perform work on an entrained subsonic secondary fluid in a non-steady mode of fluid-fluid interaction. The primary fluid jets emanating from the rotor form a helical pattern whereby the secondary fluid becomes entrapped in the interstices of the helices. In the non-rotating case of the rotors, the voids between psuedoblades that create helical structure end up, providing entrainment gullies for the secondary fluid. In the rotating case, work is done by the expanding primary fluid on the secondary fluid by the pressure forces acting across the helical boundary between the two fluids. Crypto-steady pressure-exchange has the potential of providing society with a highly efficient means of compressing a low energy fluid through direct contact with a relatively high energy fluid, thereby circumventing the complexity and the energy dissipation associated with intervening machinery inherent in conventional compressors and turbulent mixing in ejectors. Global entropy can be calculated using steady inviscid two dimensional equations. The paper will report progress made by using schlieren photography on three patented rotors.
Bubble Injection to Enhance Heat Transfer in Microchannel Heat Sinks
Authors: Betz Amy Rachel , Attinger Daniel
Published: July 2010

Liquid cooling is an efficient way to remove heat fluxes with magnitude of 1 to 10,000 W/cm2. One limitation of current single-phase microchannel heat sinks is the relatively low Nusselt number, because of laminar flow. In this work, we experimentally investigate how to enhance the Nusselt number in the laminar regime with the periodic injection of non-condensable bubbles in a water-filled array of microchannels in a segmented flow pattern. We designed a polycarbonate heat sink consisting of an array of parallel microchannels with a low ratio of heat to convective resistance, to facilitate the measurement of the Nusselt Number. Our heat transfer and pressure drop measurements are in good agreement with existing correlations, and show that the Nusselt number of a segmented flow is increased by more than a hundred percent over single-phase flow provided the mass velocity is within a given range.
Environmental Impact Indicator Using Exergy Destruction Within an Ecosystem: Example of a Specific Case
Authors: Diaz-Mendez Sosimo E. , Hernandez-Guerrero Abel , Rodriguez-Lelis Jose M. , Botello-Arredondo Israel
Published: July 2010

Environmental impact index estimation for a specific ecosystem is presented. The strategy is based on techniques that incorporate assumptions of the methodology of irreversibilities within an ecosystem, setting the basis for an environmental impact index. The results obtained by the application of this method to a specific ecosystem provide valuable information about the quantity of exergy that an ecosystem could contain, gain or loss. Because most of the time emissions do not play an important role in the ecosystem in which emissions are released, consequently the useful energy for maintaining the processes in the different parts of an ecosystem is wasted (being the parts of the ecosystem the water, the soil, the atmosphere, the organisms and the society). The depletion of useful energy depends on the number of times that the emission pollution happens and on the ecosystem capability to transform contaminants, since exergy is consumed and entropy is produced by the emissions. This application leads to indicate that the concept of irreversibilities may be used as a measure of the reduction and excessive use of resources.
Natural Patterns Applied to the Design of Microchannel Heat Sinks
Authors: Rubio-Jimenez Carlos Alberto , Hernandez-Guerrero Abel , Rubio-Arana Jose Cuauhtemoc , Kandlikar Satish
Published: July 2010

The present work shows a study developed of the thermal and hydrodynamic behaviors present in microchannel heat sinks formed by non-conventional arrangements. These arrangements are based on patterns that nature presents. There are two postulates that model natural forms in a mathematical way: the Allometric Law and the Biomimetic Tendency. Both theories have been applied in the last few years in different fields of science and technology. Using both theories, six models were analyzed (there are three cases proposed and both theories are applied to each case). Microchannel heat sinks with split channels are obtained as a result of applying these theories. Water is the cooling fluid of the system. The inlet hydraulic diameter is kept in each model in order to have a reference for comparison. The Reynolds number inside the heat sink remains below the transition Reynolds number value published by several researchers for this channel dimensions. The inlet Reynolds number of the fluid at the channel inlet is the same for each model. A heat flux is supplied to the bottom wall of the heat sink. The magnitude of this heat flux is 150 W/cm2. The temperature fields and velocity profiles are obtained for each case and compared.
Effect of Vibration on the Liquid Water Transport of PEM Fuel Cells
Authors: Breziner Luis , Strahs Peter , Hutapea Parsaoran
Published: July 2010

The objective of this research is to analyze the effects of vibration on the performance of hydrogen PEM fuel cells. It has been reported that if the liquid water transport across the gas diffusion layer (GDL) changes, so does the overall cell performance. Since many fuel cells operate under a vibrating environment –as in the case of automotive applications, this may influence the liquid water concentration across the GDL at different current densities, affecting the overall fuel cell performance. The problem was developed in two main steps. First, the basis for an analytical model was established using current models for water transport in porous media. Then, a series of experiments were carried, monitoring the performance of the fuel cell for different parameters of oscillation. For sinusoidal vibration at 10, 20 and 50Hz (2 g of magnitude), a decrease in the fuel cell performance by 2.2%, 1.1% and 1.3% was recorded when compared to operation at no vibration respectively. For 5 g of magnitude, the fuel cell reported a drop of 5.8% at 50 Hz, whereas at 20 Hz the performance increased by 1.3%. Although more extensive experimentation is needed to identify a relationship between magnitude and frequency of vibration affecting the performance of the fuel cell as well as a throughout examination of the liquid water formation in the cathode, this study shows that sinusoidal vibration, overall, affects the performance of PEM fuel cells.
Development of an R245fa for Electronics Cooling System for High Heat Flux Applications
Authors: Saffaraval Farhad , Jokar Amir
Published: July 2010

The objective of this study is to experimentally explore thermodynamic performance of R245fa, as a low-pressure and environmentally-friendly refrigerant, in a microchannel heat exchanger. This heat exchanger is used in an electronics cooling application with high-power density. Due to the large amount of latent heat that is released during evaporation process, the two-phase microchannel coolers are able to remove much more energy compared to single-phase cooling systems. In this study, R245fa is used as the working fluid in a refrigeration pump loop that mainly includes an evaporator, a condenser, a refrigerant pump, and a pressure regulator valve. The goal is to obtain optimal mass flow rates and system pressures while the temperatures in evaporator and condenser are kept constant for specific conditions. The results obtained from this study are then compared to the results previously obtained for water as the working fluid in a similar cooling system. It is expected the evaporative cooling through the microchannel heat exchanger be a viable and effective solution, especially for higher heat flux applications.
The Inverse Least-Squares Finite Element Method Applied to the Convection-Diffusion Equation
Authors: Dennis Brian H.
Published: July 2010

A Least Squares Finite Element Method (LSFEM) formulation for the detection of unknown boundary conditions in problems governed by the steady convection-diffusion equation will be presented. The method is capable of determining temperatures, and heat fluxes in location where such quantities are unknown provided such quantities are sufficiently over-specified in other locations. For the current formulation it is assumed the velocity field is known. The current formulation is unique in that it results in a sparse square system of equations even for partial differential equations that are not self-adjoint. Since this formulation always results in a symmetric positive-definite matrix, the solution can be found with standard sparse matrix solvers such as preconditioned conjugate gradient method. In addition, the formulation allows for equal order approximation of temperature and heat fluxes as it is not subject to the inf-sup condition. The formulation allow for a treatment of over-specified boundary conditions. Also, various forms of regularization can be naturally introduced within the formulation. Details of the discretization and sample results will be presented.
Design and Characterization of an Electromagnetic Energy Harvester for Vehicle Suspensions
Authors: Scully Brian , Zuo Lei , Shestani Jurgen , Zhou Yu
Published: July 2010

During the everyday usage of an automobile, only 10–16% of the fuel energy is used to drive the car — to overcome the resistance from road friction and air drag. One important loss is the dissipation of vibration energy by shock absorbers in the vehicle suspension under the excitation of road irregularity and vehicle acceleration or deceleration. In this paper we design, characterize, and test a retrofit regenerative shock absorber which can efficiently recover the vibration energy in a compact space. Rare-earth permanent magnets and high permeable magnetic loop are used to configure a four-phase linear generator with increased efficiency and reduced weight. Finite element method is used to analyze the magnetic field and guide the design optimization. A theoretical model is created to analyze the waveforms and regenerated energy of the harvester at various vibration amplitudes, frequencies, equilibrium positions, and design parameters. Experimental studies of a 1:2-scale prototype are conducted and the results agree very well with the theoretical predictions.
A Study on Developing Intelligent Control System for Charging/Discharging Lithium Secondary Battery Cells With Numerical Impedence Predictions
Authors: Lee Jung-Su , Kim Kwang-Sun , Kim Jun-young , Lim Geun-Wook , Cho Hyun-Chan
Published: July 2010

The Lithium secondary battery system needs very high capacity with high effectiveness because the industrial applications have been increased to include a hybrid car, airplanes, and the other aerospace fields, etc. Battery control system will switch off the charging current if one cell has reached full charge for stabilization; this happens due to serial connection and old status of battery cells in order to prevent being over charged and to increase the efficiency of them by keeping the rest of cells from being fully charged. It is a quite important to estimate impedance for state of charge in characteristics of battery cells to set the time to charge the each cell of the battery pack. This paper suggests the method of predicting battery impedance because of aging effects by using numerical simulations, which are verified with the experimental laboratory works. This paper also develops an Intelligent fuzzy control algorithm to maximize the efficiency of the battery cells by keeping the time to charge or discharge each cell of battery pack be more uniform.
Dynamics of Shallow Cables With General Initial Shape Due to Mean-Flow Loads
Authors: Impollonia N. , Ricciardi G. , Saitta F.
Published: July 2010

In the classic cable theory, vibration of cables is usually analysed by writing the equations of motion in the nearness of the initial equilibrium configuration. Thus, a fundamental difference exists between out-of-plane motion, which substantially corresponds to the linear behaviour of a taut string, and in-plane motion, where self weight determines a sagged initial profile. This work defines a continuous approach in order to establish the initial shape when the cable is subjected to wind or fluid flow arbitrarily directed and a finite element approach in order to investigate the dynamic around the initial equilibrium shape of the cable. In particular, the equations of motion for a three dimensional case are written fully accounting for initial shape. This means that in the additional deformation also in the out-of-plane and along cable directions there is a term linked with the initial position. Stochastic solutions in the frequency domain are derived for a wind-exposed cable after linearization of the problem and by applying the Proper Orthogonal Decomposition Technique (POD) with the aim of reducing computational effort. Differences are shown with respect to the case in which out-of-plane initial displacement is neglected. In addition, a POD based approach to simulate modal wind forces is proposed and applied to the fully nonlinear equations of motion.
An Investigation of Capped Glass Frit Sealed MEMS Devices in Contemporary Accelerometers
Authors: Burke Cillian , Punch Jeff
Published: July 2010

Hermetic sealing is a stringent design constraint for contemporary MEMS devices such as accelerometers, gyroscopes, resonators, IR bolometers and RF devices. MEMS capping using glass frit seals is the most commonly used technique in practice. In this paper an investigation of glass frit sealed MEMS capping techniques in commercially-available inertial accelerometer sensors is reported. Destructive testing was the primary methodology used to characterize the accelerometer parts. X-ray analysis was used to identify the internal structure of the accelerometers. Microscopy and SEM analysis were then used to accurately measure the seal dimensions and the proportionate relationship with overall dimensions. EDX analysis of the glass frit was conducted to establish its composition. As a further investigative step, test samples were chemically decapped and analyzed. It was observed that four of the five samples maximized cap footprint area over the base silicon of the part. All samples featured glass frit voiding, and examples of both insufficient and excessive glass frit coverage were identified. The results of the investigation were compared for common themes: cap structure, glass frit seal, glass frit voiding and cap singulation techniques. This identified points of similarity in the industrial assembly processes. A clearer understanding of industry practice in accelerometer packaging was obtained particularly in cap structure; glass frit defects and glass frit composition.
Control of Thermo Magnetic Heat Transfer in Porous Cavity With Baffle(s)
Authors: Heidary H. , Davoudi M. , Pirmohammadi M.
Published: July 2010

Steady, laminar, natural-convection flow in the presence of a magnetic field in a porous cavity heated from left wall sinusoidally and cooled from right wall is considered. It is well known that unavoidable hydrodynamic movements can be damped with the help of a magnetic field. The Finite Volume method and SIMPLE algorithm for discretizing is used to solve the non-dimensional governing equations. The Convection and Diffusion term of the equations are discretized by Central Difference Scheme (CDS). The numerical procedure has been done over a range of Rayleigh number, Ra, and value of Hartmann number (Ha), 0 ≤ Ha ≤ 150 and effect of them is investigated on average and local Nusselt number. Effect of position and length of baffle in cavity in different models is studied in this paper. It is shown that as the value of Hartmann number (Ha) increases and with growth of baffle length, the convection heat transfer reduces. Also position and numbers of baffle play an important role in control of heat transfer.