bluuebunny/crossref_metadata_2025 huggingface dataset:
Kratos: Automated Management of Cooling Capacity in Data Centers With Adaptive Vent Tiles
Authors: Wang Zhikui , McReynolds Alan , Felix Carlos , Bash Cullen , Hoover Christopher , Beitelmal Monem , Shih Rocky
Published: July 2010

In data centers with raised floor architecture, the floor tiles are typically perforated, delivering the cold air from the plenum to the inlets of equipment located in racks. The environment of these data centers is dynamic in that the workload and power dissipation fluctuate considerably over both short-term and long-term time scales. As such, airflow requirements vary continuously. However, due to labor costs and lack of expertise, the tiles are adjusted infrequently, and many data centers are grossly over provisioned for airflow in general and/or lack sufficient airflow delivery in certain local areas. This wastes energy and reduces data center thermal capacity. We have previously introduced Kratos, an Adaptive Vent Tile (AVT) technology that addresses this problem by automatically adjusting mechanical louvers mounted to the tiles in response to the needs of nearby IT equipment. Our initial results were limited to a 3-tile test bed that allowed us to prove concept but did not provide for scalability. This paper extends the previous work by expanding the size of the test bed to 28 tiles and 29 racks located in multiple thermal zones. We present experimental modeling results on the MIMO (Multi-Input Multi-Output) system and provide insights on the external behavior of the system through CFD (Computational Fluid Dynamic) analysis. We develop an MPC (Model-based Predictive Control) controller to maintain the temperatures of racks below the thresholds through vent tile tuning. Experimental results show that the controller can maintain the temperature below the thresholds while reducing overall cooling air requirements.
Reliable Power Electronics for Wind Turbines
Authors: DeVoto Douglas , McCluskey Patrick
Published: July 2010

Power electronics are used in wind turbines to convert variable voltages and frequencies produced by the generator to fixed voltages and frequencies compliant with an electrical grid with minimal losses. The power electronic system is based on a series of three-phase pulse width modulated (PWM) power modules consisting of insulated-gate bipolar transistor (IGBT) power switches and associated diodes that are soldered to a ceramic substrate and interconnected with wirebonds. Power electronics can generate thermal loads in the hundreds of watts/cm2, therefore the design of the packaging and cooling of the electronics is crucial for enhancing their energy efficiency and reliability. Without adequate heat removal, the increase in device temperature will reduce the efficiency of power electronic devices, leading to thermal runaway and eventual failure of the entire power electronic system. Furthermore, the increased temperatures can lead to failure of the packaging elements. Turbines utilizing these power electronics are often placed in harsh and inaccessible offshore environments; power electronic failures causing unscheduled maintenance lead to costly repairs. This paper will provide an overview of the fundamental package level mechanisms that can cause failures in the power electronic system. These include wirebond and lead fatigue, die attach fatigue, substrate cracking, and lead micro-voids. Attention will then be given to the reliability of a plastic-insert liquid cold plate used to manage the thermal loads from the power electronics.
Experimental Identification of Component Parameters for Multiple-Evaporator Vapor Compression Refrigeration Cycle
Authors: Catano Juan E. , Zhang Tiejun , Zhou Rongliang , Michna Gregory J. , Jensen Michael K. , Peles Yoav , Wen John T.
Published: July 2010

Vapor compression refrigeration cycles have become a promising alternative for high-heat-flux electronic cooling. Still, this area of research lacks the modeling and control design tools to facilitate its practical implementation. At Rensselaer simulation models for system level design and algorithms for temperature control are being developed to bridge that gap. However, these models need to be validated by experimental results. Since the models are not entirely based on first-principle equations, the empirical relations should be matched to the particular experimental setup used for validation. Therefore, the first step towards validation is the identification of empirical parameters that are intrinsic to the experimental apparatus and are required for the simulation. Consequently, this paper presents the experimental identification of the expansion valve coefficient, and the compressor’s volumetric efficiency used in the model. Experiments are performed at different expansion valve openings and different compressor speeds until steady-state is reached. The steady-state data is used to obtain the expansion valve coefficients, and the compressor’s volumetric efficiency. Finally, the data is used to obtain correlations, which are adequately accurate with reasonable computation cost, for each of the evaluated parameters to be incorporated into the simulation model.
Experimental Analysis of Poiseuille Number in Square Microchannels
Authors: John T. J. , Mathew B. , Hegab H.
Published: July 2010

The applications involving fluid flow through microchannels in industry and research have increased significantly with the evolution of microfluidic devices such as lab-on-chip systems. Most of the previous studies concerning fluid flow were done using circular microchannels. However, there is an increased usage of noncircular microchannels, especially square microchannels, in microfluidic devices. Thus there is need for experimental studies on the behavior of fluid flow in square microchannels, and the comparison of the results with the results obtained from the conventional fluid flow equations is relevant. In this study the authors are focusing on the analysis of the friction factor associated with square microchannels of rounded edges under laminar flow conditions. Microchannels with hydraulic diameters of 200, 300, 400 and 500 micrometers and length of 10 cm and 5 cm are used in the analysis. DI-water and ethylene glycol at room temperature is used as the liquid for experiments. A constant liquid flow rate is achieved in the channels using a syringe pump that can pump from 50 μl/hr to 7,500 ml/hr using a 60 ml syringe, and a high precision pressure gauge is used to measure the pressure drop across the channel. The Reynolds number of the liquid flow in all the channels is kept constant between 20 and 120 by varying the flow rate. The friction factor at each Reynolds number is calculated and the results are compared with the friction factor of conventional channels. Experiments are conducted to measure the pressure drop across the channels. The pressure drop obtained across the 5 cm channel is subtracted from the pressure drop obtained across the 10 cm channel so that the effect of entrance effect can be eliminated from the results. The fiction factor obtained from the experiments is used to calculate the Poiseuille number. The experimental values of Poiseuille number are showing a median deviation of around 9% from the conventional values for all the different channels. The uncertainty is observed to be ca.9% for all the channels at all values of Reynolds numbers. The major factor contributing towards the total uncertainty is the uncertainty in the measurement of liquid flow rate.
Multi-Packaging-Level Thermal Modeling Technique for Silicon Chip Transistors
Authors: Suwa Tohru , Hadim Hamid
Published: July 2010

Although thermal performance is always a critical issue in electronic packaging design at every packaging level, there is a significant lack of reliable and efficient thermal modeling and analysis techniques at the silicon chip level. With millions of transistor gates acting as heat sources, accurate thermal modeling and analysis at micrometer level has not been possible using conventional techniques. For the present study, an efficient and accurate multi-level thermal modeling and analysis technique integrating transistor level into silicon chip level has been developed. The technique combines finite element analysis sub-modeling and superposition methods for more efficient modeling and simulation. Detailed temperature distribution caused by a single heat source is obtained using the finite element sub-modeling technique, while the temperature rise distribution caused by multiple heat sources is obtained using the superposition method. Using the proposed thermal modeling methodology, one case of finite element analysis with a single heat source is sufficient for modeling a silicon chip with millions of transistors acting as heat sources. When the whole package is modeled in the finite element analysis, the effect of the package is also included in the superposition results, which makes possible to model over one million transistors in a silicon chip. No present methodologies for existing silicon chip thermal modeling techniques have been able to model such a large number of transistors. The capabilities of the proposed methodology are demonstrated through a case study involving thermal modeling and analysis of a microprocessor chip.
Improving Turret Control on Military Vehicles
Authors: Anderson Thomas W. , Clark Nathaniel A. , Kotz Wesley E. , Stremick Briana D. , Arnas O¨zer , Tamm Gunnar , Ingold Kirk , Kiel Thomas
Published: July 2010

Recent additions of armor have made light tactical vehicle turrets heavy enough that mechanical assistance is required for them to rotate. The Army’s solution is the Battery Powered Motorized Traversing Unit (BPMTU) which uses a joystick to traverse the turret. Use of the joystick distracts the gunner and prevents the gunner from continuously engaging the target while rotating the turret. This paper presents a modification to the weapon mount that allows the turret to be controlled by the position of the weapon itself and emphasizes the design process used to develop the inovation. With this design, the gunner can now maintain contact with a target, while rotating the turret, without fiddling with the joystick. The Weapon Activated and Controlled Turret (WACT) consists of two primary components; the bottom component is stationary relative to the turret and contains a Hall effect sensor and the top component rotates with the weapon and holds a linear magnet. As the position of the sensor relative to the magnet changes, the corresponding strength of the magnetic field also varies. This change in magnetic force induces a similar response in the output voltage of the Hall effect sensor, effectively translating rotational motion into an electric signal able to control the turret motor.
Chaotic Vibrations of Circular Shells Conveying Flowing Fluid
Authors: Amabili Marco , Karagiozis Kostas , Pai¨doussis Michael P.
Published: July 2010

Shells containing flowing fluids are widely used in engineering applications, and they are subject to manifold excitations of different kinds, including flow excitations. Usually these shells are made as thin as possible for weight and cost economy; therefore, they are quite fragile, and their response to such excitations is of great interest. The response of a shell conveying fluid to harmonic excitation, in the spectral neighbourhood of one of the lowest natural frequencies, is investigated for different flow velocities. The theoretical model has been developed using the Donnell theory retaining in-plane inertia. Linear potential flow theory is applied to describe the fluid-structure interaction, and the steady viscous effects are added to take into account flow viscosity. For different amplitudes and frequencies of the excitation and for different flow velocities, the following are investigated numerically: (i) periodic response of the system; (ii) unsteady and stochastic motion; (iii) loss of stability by jumps to bifurcated branches. The effect of the flow velocity on the nonlinear periodic response of the system has also been investigated. Poincare´ maps, bifurcation diagrams and Lyapunov exponents have been used to study the unsteady and stochastic dynamics of the system.
Experimental Investigation of Flow and Heat Transfer Characteristics of Latent Functionally Thermal Fluid in Mini-Tube
Authors: Lu Jinli , Hao Yingli
Published: July 2010

An experimental research using the latent functionally thermal fluid of n-hexadecane microcapsules in deionized water was conducted in order to investigate the flow and heat transfer characteristics of microencapsulated phase change material (MEPCM) slurry. Experimental measurements were done for a large region of Reynolds number in the mini-tube with a constant wall heat flux. Experimental measurements were also conducted using deionized water as the working fluid under the same conditions. Some important parameters such as pressure, temperatures of wall and fluid were obtained experimentally. The relationships between pressure drop and mass flow rate, dimensionless outlet temperature of working fluid and Reynolds number, mean convective heat transfer coefficient and Nusselt number and Reynolds number were obtained. Results show that the using of MEPCM particle increases the pressure drop and then close to that of single phase water with increasing mass flow rate. The outlet and wall temperatures decrease 50% comparing with single phase water under the same conditions. The Nusselt number of slurry containing small concentration MEPCM particle is about 2.0–2.3 times greater than that of single phase water in the minitube. The experimental data might be helpful in the design of thermal-energy transportation systems in small scale using MEPCM slurry.
Comparison of Cyclic Oxidation Performance of APS and EBPVD Processed TBCs on In738 With a Bond Coat of NiCoCrAlY Powder With 0.25% Hf
Authors: Akwaboa Stephen , Silva Monica B. , Mensah Patrick , Diwan Ravinder , Wolfe Douglas E. , Guo Shengmin
Published: July 2010

Thermal barrier coatings (TBCs) are used in gas turbine engines to achieve higher turbine inlet temperatures (TITs), improve turbine operating temperatures, reduce fuel consumption, increase components lives and thus lead to better turbine efficiency. Yttria-stabilized zirconia (YSZ), is an ideal candidate for TBCs as it has good thermal shock resistance, high thermal stability, low density, and low thermal conductivity. Traditionally, there are two main methods of fabricating TBCs: air plasma spray (APS) TBCs and electron beam physical vapor deposition (EBPVD) TBCs. It is the objective of this paper to study the effects of APS TBC microstructures in comparison with EBPVD TBCs deposited on NiCoCrAlYHf bond coated In738 substrate material for applications in advanced gas turbines. The bond coat NiCoCrAlY contains 0.25w% Hf which is expected to improve the reliability of standard (STD) and vertically cracked (VC) APS TBC material. TBC top coatings of 300 μm and 600 μm thickness for both standard and VC APS TBC and 300 μm EBPVD TBC were further investigated to determine the effect of coating thickness of TBC performance. Selected test specimens were evaluated for dry and wet thermal cyclic oxidation performance. Thermal property determination of select samples was achieved using a laser flash system that measures the thermal diffusivity and specific heat capacity from which the thermal conductivity is calculated. Lastly, select YSZ-Al2O3 composite structures were analyzed in addition to APS and EBPVD TBC microstructure, porosity, and thermal conductivity determination using a variety of analytical techniques. A laser flash system was used to measure the thermal diffusivity for all the samples. A POREMASTER 33 system was used to measure the porosity of the APS and EBPVD samples.
Characterization of Contact Damping in Elastic-Plastic Contact of Two Nominally Flat Rough Surfaces
Authors: Sepehri Ali , Farhang Kambiz
Published: July 2010

Elastic-plastic interaction of a block of rough surface with a rough plane is considered in this paper. The nonlinear normal vibration response of the block is examined when subject to an external compressive load. Free vibration response of the block is studied. The vibration response corresponds to the application of a constant compressive external load and the study yields closed-form equations for the contact damping rate and contact natural frequency. It is shown that vibration decay rate is constant as opposed to the exponential decay rate for the linear vibrating systems. Closed form equations relating contact damping rate and contact natural frequency to the surface parameters are given.
Stresses in Area Array Assemblies Subjected to Thermal Cycling
Authors: Roberts Jordan , Rahim M. Kaysar , Hussain Safina , Suhling Jeffrey C. , Jaeger Richard C. , Lall Pradeep
Published: July 2010

Thermal cycling accelerated life testing is often used to qualify area array packages (e.g. Ball Grid Arrays and Flip Chip) for various applications. Finite element life predictions for thermal cycling configurations are challenging due to the complicated temperature/time dependent constitutive relations and failure criteria needed for solders and encapsulants and their interfaces, aging/evolving material behavior (e.g. solders), difficulties in modeling plating finishes, the complicated geometries of typical electronic assemblies, etc. In addition, in-situ measurements of stresses and strains in assemblies subjected to temperature cycling is difficult because of the extreme environmental conditions and the fact that the primary materials/interfaces of interest (e.g. solder joints, die device surface, wire bonds, etc.) are embedded within the assembly (not at the surface). For these reasons, we really know quite little about the evolution of the stresses, strains, and deformations occurring within sophisticated electronic packaging geometries during thermal cycling. In our research, we are using test chips containing piezoresistive stress sensors to continuously characterize the in-situ die surface stress during long-term thermal cycling of several different area array packaging technologies including plastic ball grid array (PBGA) components, ceramic ball grid array (CBGA) components, and flip chip on laminate assemblies. The utilized (111) silicon test chips are able to measure the complete three-dimensional stress state (all 6 stress components) at each sensor site being monitored by the data acquisition hardware. The die stresses are initially measured at room temperature after packaging. The assemblies are then subjected to thermal cycling over various temperature ranges including 0 to 100 °C, −40 to 125 °C, and −55 to 125 °C, for up to 3000 thermal cycles. During the thermal cycling, sensor resistances at critical locations on the die device surface (e.g. the die center and die corners) are recorded. From the resistance data, the stresses at each site can be calculated and plotted versus time. The experimental observations show significant cycle-to-cycle evolution in the stress magnitudes due to material aging effects, stress relaxation and creep phenomena, and development of interfacial damage. The observed stress variations as a function of thermal cycling duration are also being correlated with the observed delaminations at the die surface (as measured using scanning acoustic microscopy (C-SAM)) and finite element simulations that include material constitutive models that incorporate thermal aging effects.
Semi-Autonomous Control of a Multi-Arm Telemanipulator With Adaptive Impedance
Authors: Chung Jae H. , Coleman Norman P. , Cheung Yushing
Published: July 2010

This paper addresses problems to achieve transparency and contact stability for Single Master Multi-Slave telemanipulation that consists of unconstrained and constrained motions. The adaptive bilateral control with a local force compensator is developed based on adaptive impedance control and contact force driven compensation with auto-switching functions. With a limited amount of knowledge about robotic and environment dynamics and a time-varying communication delay, the developed method guarantees good adaptive tracking performance in unconstrained motion and reduction of oscillating contacts to keep a balance of the system in constrained motion. Based on an actual haptic device and virtual robots, haptic simulations are presented to demonstrate adaptive transparency and contact stability in the presence of communication delays.
A Developed Toolkit for Analysis of Large Deflections of Beams
Authors: Navaee Shahnam
Published: July 2010

In the presented paper, an interesting and unconventional approach for analysis of non-linear bending of a flexible cantilever beam subjected to an inclined end-load is explored utilizing LabVIEW. The numerical scheme employed in the LabVIEW Virtual Instrument (VI) developed in this study utilizes elliptic integrals to generate the theoretical solution. The procedure employed in the study is capable of determining not only the primary deflected shape, but also other possible stable configurations of the beam subjected to an end-load. In earlier research done by the author, it was proven that depending upon the specific beam and loading parameters, multiple deflected configurations are possible for flexible beams subjected to loads. Utilizing the front panel of the developed VI, the user can conveniently control the beam and load parameters and interactively generate the internal shear and moment reactions along the length of the beam and the deflected configurations. Provisions are included in the VI to ensure that the maximum normal and shearing stresses exerted on the beam do not exceed the beam’s allowable stresses. A visual indicator placed on the front panel of the created VI alerts the user if this occurs. Virtual Instrument developed in this study will be prepared in a form to allow the users to be able to run the toolkit remotely over the web for any desired input. A special executable version of this VI will also be created to further enhance the accessibility of the toolkit. This executable file can run on any computer with or without LabVIEW installed. The developed toolkit will allow the students, educators, and researchers to create a variety of “what if” scenarios and gain a better insight into predicting the behavior of beams undergoing large deflections. The sample solutions included in this paper will clearly demonstrate the utility and efficiency of the developed toolkit. The procedure developed in this study can further be extended to obtain the solutions for other cases, such as deflections of beams with initial curvature, and beam subjected to other static and dynamic loads.
Experimental Analysis of the Nusselt Number for Jet Impingement on a Flat Plate
Authors: Carbajal Gerardo , Peterson G. P. , Sobhan C. B.
Published: July 2010

An experimental analysis was performed to calculate the local Nusselt number associated with the impingement of a jet of hot gases on a steel flat plate. A plate was subjected to a constant-rate propane torch, with a measured average temperature of the hot gases at approximately 896 °C. The jet was applied to the flat plate at different angles of 45, 60, 75 and 90 degrees. The jet was horizontally located at 0.044m away from the flat plate and experiments were performed with two different vertical distances. The temperature distribution on the front and back sides of the plate were recorded by using 20 thermocouples. The plate reached steady-state conditions after 4100 seconds. The unheated side was cooled by combined natural convection and radiative effects. To perform the experiment, the steel plate was mounted on a tubular apparatus that holds the plate vertically, with a provision to change the angle of impingement. It was found that the combined effects of tilt angle and vertical switch reduce the local Nusselt number, by 51% for a tilt angle equal to 45 degrees. The maximum heat flux at the center of the plate was found to be 15.5 kW/m2.
Sensitivity of NL-RDM to Errors in Parameters Used From the Underlying Linear System
Authors: Sarmast Mehdi , Wright Jan R.
Published: July 2010

The Non-linear Resonant Decay method (NL-RDM) addresses the identification of multiple degree of freedom non-linear dynamic systems. This method offers a practical approach to the identification of lumped parameter and continuous systems by producing a non-linear extension of the classical linear modal model. The method is introduced, its potential as a practical identification approach explained and some basic examples presented for a two degree of freedom system with a cubic stiffness non-linearity. Since the method makes use of modal parameters obtained at a low level of excitation to provide an estimated underlying linear model, its sensitivity to inaccuracy in these parameters, namely imperfect mode shapes, force vectors and natural frequency is considered using simulations of a two degree of freedom system. For each type of imperfection, the possible reasons for such errors occurring are firstly considered and the potential impact of the errors discussed in conceptual terms. The impact of the imperfections is then explored using simulation. Before applying the NL-RDM method to assess the effect of errors, the relevant inaccuracies are generated and introduced into the system under consideration. The effects of these inaccuracies are then evaluated and compared with perfect simulation results. Knowing the errors present in the identified parameters will help in understanding the influence of these factors on the method. Thus, knowledge of this behaviour could allow better control of levels of inaccuracies in the identification approach. The simulation results are presented later in this paper.
Evaluating the Energy Requirements of Small-Scale Biodiesel Production From Raw Tallow of Tanning Industry
Authors: Rangel-Hernandez V. H. , Lara-Barron F. , Zaleta-Aguilar A. , Riesco-Avila J. M. , Gallegos-Mun˜oz A.
Published: July 2010

The study at hand provides an analysis of the energy input-yield ratios of a planned small-scale raw-tallow-fuelled biodiesel production plant. In the state of Guanajuato, the rendering activities generate roughly 150 tonnes of raw tallow that is refused into nearby pounds or rivers, a common practice that causes an irreversible environmental damage. So in order to make use of this residue, it is proposed here to use it as feedstock for a biodiesel production plant. The plant is assumed to be comprised of a separation process, an acid catalized pretreatment, a transesterification process, a steam generator and a storage zone. Hence a detailed energy analysis was carried out to evaluate the mass and energy transfer ratios of each subsystem as well as their energy efficiencies so as to decide whether the plant could be technical and economically feasible and competitive. The results of this former study must be seen as the base for an informed dialogue with important stakeholders and governmental organizations.
Environmental Impact Index Using Exergy Destruction Within an Ecosystem: Methodology
Authors: Diaz-Mendez Sosimo E. , Hernandez-Guerrero Abel , Rodriguez-Lelis Jose M. , Rubio-Arana Cuauhte´moc
Published: July 2010

Theoretical bases of the use of the irreversibilities concept in an ecosystem as an environment impact index are presented in this paper. Because an ecosystem is composed by different biotics and abiotics parts, each part has a specific function in the processes to transport energy inside the ecosystem, all these processes having a large dependence between them. When anthropogenic emissions is produced part of the useful energy of the process are used to assimilate or to absorb those emissions, and irreversibilities are produced in the processes of the ecosystem when emissions are made by the human beings. Thus, the work that an ecosystem can carry out varies as a function of the irreversibilities produced by anthropogenic sources; the permanency or loss of the ecosystem depends on how many irreversibilities it can support. The second law of thermodynamics through a systematic use of the exergy concept o lost work concept are the basis of this methodology. The ecosystem can be divided in subsystems, each subsystem interrelated with the other ones, and then an ideal work variation can be obtained from each variation in the ecosystem (being the subsystems the water, the soil, the atmosphere, the organisms and the society). Thus, a global index could be determined by adding the partial irreversibility of each subsystem, and could be used to determine the trend that an ecosystem will follow due to alterations of its pristine, original or environmental line base state. Applying the methodology presented here an index of environmental impact could be developed, not in a subjective or ambiguous way, but based on energy calculations. An index of environmental impact and its methodology, based on quantitative terms that enable to evaluate in a very clear way the harmful effects of industrial operations, such as the phenomenon of contamination of the environment, could be used as a tool in the analysis of sustainability, resource depletion or health effects.
Experimental Evaluation of a Control Strategy for Real-Time Optimization of Low Temperature PEM Fuel Cell Stack
Authors: Kolavennu Panini , Das Susanta K. , Berry K. Joel
Published: July 2010

A robust control strategy which ensures optimum performance is crucial to proton exchange membrane (PEM) fuel cell development. In a PEM fuel cell stack, the primary control variables are the reactant’s stochiometric ratio, membrane’s relative humidity and operating pressure of the anode and cathode. In this study, a 5 kW (25-cell) PEM fuel cell stack is experimentally evaluated under various operating conditions. Using the extensive experimental data of voltage-current characteristics, a feed forward control strategy based on a 3D surface map of cathode pressure, current density and membrane humidity at different operating voltages is developed. The effectiveness of the feed forward control strategy is tested on the Green-light testing facility. To reduce the dependence on predetermined system parameters, real-time optimization based on extremum seeking algorithm is proposed to control the air flow rate into the cathode of the PEM fuel cell stack. The quantitative results obtained from the experiments show good potential towards achieving effective control of PEM fuel cell stack.
Numerical Simulation of Vapor-Liquid Two-Phase Flow in a Closed Loop Oscillating Heat Pipe
Authors: Liu Xiangdong , Hao Yingli
Published: July 2010

A comprehensive mathematical model including the effects of vapor-liquid interface and surface tension was proposed to describe the vapor-liquid two-phase flow, heat and mass transfer and the phase change process in a closed loop oscillating heat pipe (CLOHP). The vapor-liquid two-phase flow in a typical CLOHP was numerically investigated using the proposed mathematical model and the VOF method. The comparisons between the computational and experimental results indicated that the proposed model could successfully simulate the initial distribution of working fluid, the complex flow patterns during different operation conditions, such as bubbly flow, slug flow, semi-annular/annular flow, back flow, and the flow pattern transitions in the CLOHP. The phenomenon that semi-annular/annular flow and slug flow formed in alternating vertical tubes at the initial stage of working fluid circulation was also simulated successfully. Those results were in good agreement with the experimental observations. The flow and heat transfer of a working fluid in two transition sections, and the effects of heating power on the interval flow patterns, were analyzed based on the numerical simulation. The results showed that the changes of temperature, pressure and flow pattern were obvious in the transition section between adiabatic section and condenser section, where the transition of heat transfer condition occurred. The violent boiling might occur in the evaporator section under the high heating power of 100 W and 120 W. The preliminary results indicated that the mathematical model proposed in present paper could effectively reveal the complex vapor-liquid two-phase flow in CLOHP, which established a basis for the further study of complex working mechanisms of CLOHP and effects of operation parameters.
Energy Analysis of Single Effect Thermal Vapor Compression Desalination Process Based on Pressure Exchange Phenomenon
Authors: Chabukswar Kaustubh A. , Garris Charles A.
Published: July 2010

A closed loop single effect thermal vapor compression desalination process is simulated based on pressure exchange phenomenon. Here the conventional ejector is replaced by a compressor-turbine device, where the high energy primary fluid expands over the turbine that drives the compressor through an ideal drive shaft. The compressor in turn compresses the low energy secondary fluid. Both the fluids are discharged at a constant pressure in a common mixing chamber where they undergo adiabatic mixing and then are discharged at an intermediate energy level. The functionality of the compressor-turbine device is similar to that of an ejector, hence this is also known as the turbomachinery analog of an ejector. The medium of energy transfer between the two fluids in case of compressor-expander device is pressure exchange. Energy analysis of the model is performed under various operating conditions. Key functional parameter like the boiling temperature, compression ratio, compressor-expander efficiencies and primary pressure are varied and its effect on the energy consumption per unit of distillate produced is examined. The system performance is evaluated based on the standard factors that affect the cost of the distillate like, thermal performance ratio, energy performance ratio and specific flow rate of cooling water. The model takes into consideration the inlet seawater conditions and its fouling effects as well as the use of superheated primary steam and its effects on performance of the system. With increase in the analog efficiency the energy consumption and thermal performance ratio improves steadily, where as it is observed that the flow rate of the distillate produced decreases. Initial results have shown performance ratios as high as 5.5 for ideal conditions at low primary pressures and low boiling temperature.
Entropy Generation Analysis for a PEM Fuel-Cell With a Biomimetic Flow Field
Authors: Dami´an-Ascencio Cesar , Hernandez-Guerrero Abel , Ascencio-Cendejas Fernando , Juarez-Robles Daniel
Published: July 2010

The present paper shows an entropy generation analysis for a PEM fuel cell. The numerical model takes into account the complete solution of Navier-Stokes, energy conservation, species conservation and two potential fields for the transport of electrons and protons in the collectors and membrane respectively. The entropy generation equation is added to the governing equations using the solutions provided from the energy, momentum, species and potential flow equations. The entropy generation analysis reveals the locations where the main losses (irreversibilities) are produced. This in consequence shows the best flow field to minimize the entropy production. A new parameter is proposed in this work that will compare the entropy production due to the mass flow to the total entropy production.
H2S and CO2 Filtration of Biogas Used in Internal Combustion Engines for Power Generation
Authors: Huertas Cardozo Jose Ignacio , Izquierdo Cifuentes Sebastia´n
Published: July 2010

Currently, there is an increasing interest in connecting thousands of small electrical plants powered by renewable energy sources to national electrical grids. The use of biogas as fuel for internal combustion engines connected to an electric generator is emerging as one of the most attractive alternatives because of its very low cost benefit ratio and very high positive impact on the environment. However, the use of biogas to generate electricity has been limited by its high content of H2S (1800–3500 ppm) and CO2 (∼40%). CO2 presence reduces the energetic density of the fuel and therefore the power output of the system. The high content of H2S corrodes important components of the engine like the combustion chamber, bronze gears and the exhaust system. This work aims to design and manufacture a low-cost industrial filter for this application. Among the different available methodologies, CaO, NaOH and amines where selected as the most appropriate for a typical farm application of 100 kW electric generations. Since there is not reported data for the H2S absorbing capacity of these substances, it was proposed to measure it by means of a bubbler. It is an experimental set up where the gas stream passes through a fixed amount of the absorbing substance until it becomes saturated. The absorbing capacity is determined as the amount of substance being trapped divided by the mass of the absorbing substance being used. Results showed an absorbing capacity of 2.8, 41.4 and 124.8 g of H2S per Kg of NaOH, CaO and monoethanolamine respectively. A gas absorbing system of amines was designed and manufactured for H2S and CO2 biogas filtration. Three different types of amines were evaluated: Monoethanolamine, Diethanolamine, and methyldiethanolamine. Results show that all the amines require a ratio of amines to biogas flow of 0.7 to obtain a 95% of H2S filtering efficiency. This data represent only a 30% of H2S mass transfer efficiency of the filter when it is compared against the mass transfer expected under quasi equilibrium conditions. Work is under way to design a high efficiency amine column for biogas treatment.
Development and Testing of a Prototype Heat Sink Within a Wind Tunnel for Use in an Engineering Course
Authors: Cortez Margarita L. , Jokar Amir
Published: July 2010

The purpose of this undergraduate research project was to develop a test section and prototype heat sinks that will be used in an existing electronics cooling wind tunnel for a project in a future Advanced Thermal Systems course. During the course, students will design and manufacture their own prototype heat sinks. Heat sinks are made of highly conductive materials with various geometries and are attached to computer chips to dissipate heat from them to the surroundings. The prototype heat sinks will be manufactured in the school’s facilities which will limit the complexity of the geometry. The purpose is not to design a commercial heat sink. The students will experimentally analyze and simulate the heat transfer that takes place between a computer chip and a heat sink. During the course project the students will also analyze the heat sinks using CFD and compare the results to the experimental data. In this study, an electronics cooling wind tunnel was used to simulate the flow conditions that normally exist in a personal computer. A test section was designed and built in order to measure temperatures at different locations on a prototype heat sink using 18 type-T thermocouples. A data acquisition unit was set up and a Labview program was developed to collect the temperature data as well as the air velocity of the wind tunnel. The recorded data were then transferred to an excel file for further analysis. The objectives of this summer internship project were achieved through testing and analyzing different prototype heat sinks.
An Introduction to Self-Excited Oscillations
Authors: Panciroli Riccardo , Abrate Serge
Published: July 2010

This paper describes an approach used to introduce a type of nonlinear problems in an undergraduate class on mechanical vibrations. Self-excited oscillations are encountered in a number of practical applications including brakes, clutches, belts, tires, and violins. To go beyond the derivation of the equations of motion for simplified models and examine the effect of various parameters requires the ability to find numerical solutions. It was found that developing numerical solutions using a simple integration technique such as Euler’s method with a spreadsheet program like Excel was most effective because: (1) Euler’s method is easy to implement; (2) Excel is widely available; (3) students are able to develop the solution themselves; (4) it can be done quickly. In this case students were able to explore problems with one or more degrees of freedom and compare their results with those found in recent publications which presents several advantages: students develop confidence in their ability to explore different models and examine the effects of different complicating factors, they develop their own solutions and are able to focus on understanding the physics of the problem, and they develop a sense that they are working on problems of current interest instead of some overly simplified textbook problem. Examples dealing with brake squeal problem were used and the effects of mass, stiffness, damping and friction were studied. Many different friction models are available and several of them were used to determine the effect of friction on the appearance of self-excited vibrations. The appearance of a limit cycle in the phase portrait is discussed along with the dynamics of the system. It is also shown that a short high frequency excitation can be used to squelch those self-excited oscillations.
Boundary Control of Temperature Distribution in a Thick Rectangular FGM Plate (Cubic Block)
Authors: Rastgoftar Hossein , Eghtesad Mohammad
Published: July 2010

In this paper an analytical method and a PDE-based solution to control temperature distribution in FGM thick plates is introduced. For the rectangular FGM thick plate under consideration, it is assumed that material properties such as thermal conductivity, density, and specific heat capacity are constant in length and width (x, y direction) but they vary in thickness direction of the plate; and the governing heat conduction equation of the thick plate is a second-order partial differential equation. Since there has been little control synthesis work for PDE-based systems as compared to the abundance of control design techniques available for ordinary differential equations (ODEs), most of the proposed control approaches for continuous domain rely on discretizing the PDE model into a set of ODEs. Using Lyapunov’s theorem, it will be shown how to obtain boundary heat flux required for producing a desired distribution of Td(x, y, z).
Theoretical Optimization of Cascading Magnets’ Structure for Oxygen Enrichment by Gradient Magnetic Fields
Authors: Li Fengchao , Wang Li , Wu Ping , Zhang Shiping
Published: July 2010

Oxygen molecules are paramagnetic while nitrogen molecules are diamagnetic. In the same gradient magnetic field, the magnetizing forces on oxygen molecules are stronger than those on nitrogen molecules, which in opposite directions. The intercepting effect on oxygen molecules by gradient magnetic field can be used for oxygen enrichment from air. The structure, which is called multi-channel cascading magnets array frame in the paper, are optimized by additional yokes. By comparison of distributions of magnetic field in multi-channel array without yokes and that with yokes, the additional yokes can eliminate the differences among different magnetic spaces in multi-channel cascading magnets’ arrays and enhances the magnetic flux densities in spaces. Joining magnets together in the length direction can make the air stay longer in the ‘magnetic sieve’ and raise the oxygen concentration of air flowing out from the optimized multi-channel cascading magnets’ arrays. The inside additional yoke can used to avoid the gradient magnetic field at the joints of the magnets and get near uniform magnetic field along length direction. The optimized multi-channel cascading magnets’ array frames can effectively promote the development of oxygen enrichment from air by “magnetic sieve”.
Dynamics of Evaporation and Cooling of a Water Droplet During the Early Stage of Depressurization
Authors: Liu L. , Bi Q. C. , Wang G. X.
Published: July 2010

This paper reports an experimental and numerical study of evaporation and cooling of a water droplet during the early stage of depressurization in a test vessel. During the experiment, a distilled water droplet was suspended on a thermocouple, which was also used to measure the droplet center temperature, and the droplet surface temperature was captured by an infrared thermograph. Experimental data indicated a large temperature difference within the droplet during the early stage of depressurization. A thermodynamic analysis of the experimental data found that the pressure reduction was not fast enough to induce liquid superheating and thus equilibrium evaporation was expected. A mathematical model was then constructed to simulate the droplet evaporation process. The model solves one-dimensional heat conduction equation for the temperature distribution inside the water droplet, with the convective heat transfer inside the droplet simplified through an effective conductivity factor. A simplified treatment was introduced to quantify the convective evaporation due to air movement and droplet swing induced by sudden opening of the electro-magnetic valve and the following air exiting. The model-predictions agree well with the measured temperature data, demonstrating the soundness of the present model.
Flow of Electrolyte With a Surface-Charged Particle in a Nano-Channel: Quasi-Steady Modeling
Authors: Qin Z.-P. , Wang Y.-S. , Wang G.-X.
Published: July 2010

A Resistive Pulse Sensor (RPS) is a device for counting and characterizing small particles by recording the electrical current change (negative pulse) during the translocation of the particle through a small pore. RPS is now widely used to characterize various micro/nano size particles, including bio-particles, proteins, and DNA. This paper presents a comprehensive multi-physical model of RPS. The model involves a coupled system of the Navier-Stokes equation for flow field, the Nernst-Planck equation for electrolyte ion concentrations, and the Poisson equation for electrical field. The model is used to simulate the quasi-steady flow of electrolyte with a fixed surface charged particle in a micro/nano-channel connecting two reservoirs. The channel and reservoir are assumed to be cylindrical and a 2-D axial-symmetry system is used. The model predicts the flow and electric fields as well as the distribution of the ion concentrations in the channel. The effects of Electrical Double Layer (EDL) on the electric current change through the channel are then investigated. Conditions for the electric current change (positive and negative pulses) are then identified.
Physics of Failure Based Virtual Testing of Communications Hardware
Authors: George Elviz , Das Diganta , Osterman Michael , Pecht Michael , Otte Christopher
Published: July 2010

Communications hardware for high reliability systems are starting to include modern low profile parts such as Quad Flat Pack No-lead (QFN) and Land Grid Array (LGA) packages to take advantage of their size and weight. In these parts, heat sinks often provide a conductive thermal dissipation path. Printed circuit assemblies with these parts will still need to meet the industry specific qualification requirements for thermal and vibration testing. It is beneficial to identify if the equipment will be able to meet the qualification test requirements during the design phase particularly when new technology insertions are being made. In this design, various surface mount packages like LGAs, QFNs and so on were used in a printed circuit board which included two stiffening layers with non-standard laminates. calcePWA is a simulation software which estimates the cycles to failure of components under various loading conditions using Physics of Failure (PoF). The cycles to failure simulation of this design using calcePWA software identified the critical interconnects that are at risk for failure under non-operational test conditions. The design was also evaluated under a long haul aircraft profile, with the assembly in operational state. In operational state simulation, the effectiveness of thermal shunts in reducing board to component thermal differentials was evaluated. Effects of degradations of the thermal shunts with time were used in the evaluation. Results showed that the vibration and shock reliability were less of a concern than thermal cycling for this board layout. Risk mitigation methods for thermal cycling durability were identified and recommended to be used in the system redesign.