bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular Dynamics Problem Initialization and Statistics Collection for Arbitrary Geometries
Authors: Wemhoff Aaron P. , Haas Geoffrey
Published: June 2010

Molecular dynamics (MD) simulations have been extensively used for analysis of thermophysical properties of a variety of nanoscale systems. The majority of MD codes are developed for a specific system or application type, and thus their use in a wide variety of systems is limited. In addition, these codes can contain a steep learning curve for new users. Therefore, we have developed the Molecular Dynamics in Arbitrary Geometries (MDAG) code package for the explicit purposes of adaptability and ease of use. We describe various standard programming techniques we employed to allow for these goals to be achieved. We also discuss the approaches used for problem initialization based on arbitrary zone placement, and for statistics collection based on the mapping of Cartesian grid-based results onto arbitrary zones. We finally provide example applications of this code on nanoscale thermophysical systems.
Justification of Fire Field Models by Atrium Hot Smoke Tests
Authors: Chow W. K. , Li S. S. , Chow C. L.
Published: June 2010

Computer thermal fire models are used in hazard assessment for performance-based fire design. Fire field model using Computational Fluid Dynamics (CFD) is now a popular design tool. The thermal fire environment can be predicted in a ‘microscopic’ picture with air flow pattern, pressure and temperature contours. However, most of the field models are only validated by some experiments not specially designed for such purpose. Whether those models are suitable for use is queried, leading to challenges. In this paper, prediction on smoke filling in a big atrium by the CFD tool Fire Dynamics Simulator developed at the National Institute of Standards and Technology in USA was justified by field tests. Smoke layer interface height and air temperatures inside the atrium were taken as the parameters. CFD results predicted were compared with the field measurement results.
Dynamic Analysis of Heat Transfer Through a Fin of Constant Cross-Sectional Area: Specified Fin Tip Temperature
Authors: Carranza Richard G. , Ospina Giraldo Juan F.
Published: June 2010

A dynamic analysis is performed for heat transfer through a fin with constant cross-sectional area and with a specified fin tip temperature. The process starts with a dynamic energy balance around the fin. Laplace transforms and the Bromwich Integral are used to solve analytically the resulting partial differential equation. The final purely analytical solution is compared to the well known steady state solution. The two match exactly as time approaches infinity. Furthermore it is shown that the steady-state and dynamic characteristics of the fin are directly tied to the Biot number.
Effect of Pin Base-Fillet on Heat Transfer Enhancement of an Internal Blade Pin-Finned Tip-Wall
Authors: Xie G. N. , Sunde´n B. , Wang L. K. , Utriainen E.
Published: June 2010

A common way to cool the tip is to use serpentine passages with 180-deg turn under the blade tip-cap. Improving internal convective cooling is therefore required to increase the blade tip life. In this paper, augmented heat transfer of a blade tip has been investigated numerically. The computational models consist of a two-pass channel with 180-deg turn and pin-fins mounted on the tip-cap, and a smooth two-pass channel. On the other hand, In particular manufacture, the casting process does not make a perfect cylinder pin, a fillet needs to be placed at the endwall. In order to make the conditions of simulations as close to real practice as possible, it is desirable to examine the effect of fillet on the tip heat transfer. Therefore, in the present study, the effect of pin base-fillet on heat transfer enhancement of a blade pin-finned tip-wall is investigated numerically. Inlet Reynolds numbers are ranging from 100,000 to 600,000. The computations are 3D, steady, incompressible and stationary. It is found that the pin-fins make the counter-rotating vortices towards pin-fin surfaces, resulting in continuous turbulent mixing near the pin-finned tip. Due to the combination of turning, impingement and pin-fin crossflow, the heat transfer coefficient of the pin-finned tip is a factor of as much as 2.66 higher than that of a smooth tip. Besides, with base-fillets the heat transfer enhancement is increased by about 10% while almost no additional pressure loss is resulted. It is suggested that the pin-fins could be used to enhance blade tip heat transfer and cooling.
Numerical Simulation of Two-Phase Slug Flows in Microchannels
Authors: Mehdizadeh A. , Sherif S. A. , Lear W. E.
Published: June 2010

In this paper the Navier-stokes equations for a single liquid slug have been solved in order to predict the circulation patterns within the slug. Surface tension effects on the air-water interface have been investigated by solving the Young–Laplace equation. The calculated interface shape has been utilized to define the liquid slug geometry at the front and tail interfaces of the slug. Then the effects of the surface tension on the hydrodynamics of the two-phase slug flow have been compared to those where no surface tension forces exist. The importance of the complex flow field features in the vicinity of the two interfaces has been investigated by defining a non-dimensional form of the wall shear stress. The latter quantity has been formulated based on non-dimensional parameters in order to define a general Moody friction factor for typical two-phase slug flows in microchannels. Moreover, the hydrodynamics of slug flow formation has been examined using computational fluid dynamics (CFD). The volume-of-fluid (VOF) method has been applied to monitor the growth of the instability at the air-water interface. The lengths of the slugs have been correlated to the pressure fluctuations in the mixing region of the air and water streams at an axisymmetric T-junction. The main frequencies of the pressure fluctuations have been investigated using the Fast Fourier Transform (FFT) method.
Critically Assessing the Application of Quantum Corrections to Classical Thermal Conductivity Predictions
Authors: Turney J. E. , McGaughey A. J. H. , Amon C. H.
Published: June 2010

Quantum corrections can be used to map the thermal conductivity predicted in a classical framework [e.g., a molecular dynamics (MD) simulation] to a corresponding value in a quantum system. This procedure is accomplished by equating the total energies and energy fluxes of the classical and quantum systems. The validity of these corrections is questionable because they are introduced in an ad hoc manner and are not derived from first principles. In this work, the validity of these quantum corrections is examined by comparing the thermal conductivity of Stillinger-Weber silicon calculated using a full quantum mechanical treatment to a quantum-corrected value predicted from a classical framework between temperatures of 10 K and 1000 K. The quantum and classical predictions are obtained using anharmonic lattice dynamics calculations. We find discrepancies between the quantum-corrected predictions and the quantum predictions obtained directly. We investigate the causes of these discrepancies and from our findings, conclude that quantum thermal conductivities cannot be predicted by applying simple corrections to the values obtained from a purely classical framework.
Sensitivity Analysis of Flow Conditions and Geometric Parameters on the Film Cooling Effectiveness for a Flat Test Plate—Part 1: Single Row of Cylindrical Hole Film Cooling
Authors: Nguyen Cuong , Rodriguez Sylvette , Zuniga Humberto , Ho Son , Kapat Jayanta
Published: June 2010

End-wall film cooling technique is an advanced technology which has been employed in modern gas turbines to protect the surface of the end-wall. The sophistication of this technique has allowed an increase in the combustor outlet temperature, resulting in higher engine overall efficiency. Several criteria are used to judge the performance of film cooling; one of them is film cooling effectiveness (ETA) which has been adopted in most of the literature nowadays. In part I of the investigation, we aim to withdraw an overall correlation between film cooling effectiveness and flow conditions and geometric parameters. A lot independent parameters, that could play a role in film cooling performance, are: blowing ratio, cooling mass flow rate, pitch distance, geometry of the hole, injection angle, and inlet to exit hole-area ratio to name a few. But we need to screen some factors out that seem to be more potentially affect the output based on previous experiences (or available literature), or by conducting pilot runs. Due to nature of preliminary investigation in this part I, the authors found that blowing ratio (BR), density ratio (DR), jet inclination angle (α) and hole length-to-diameter ratio (L/D) are more important and are selected as investigated factors. A full design of experiment is then performed and it is worth to note here that typical values are assigned for those less important factors and they are kept constant in the sensitivity analysis. Regression equation is also extracted to predict the spatial average film cooling effectiveness (ETAaa). This investigation is supported by numerical analysis where the solution of the computational domain is performed using FLUENT package [1]. Second order schemes are used to provide the highest accuracy available. The realizable k-ε model (RKE) is integrated in this work with enhanced wall treatment for all its runs. For the baseline case, computational fluid dynamic (CFD) result is compared against actual experimental data where the experimental baseline work was conducted for a row of cylindrical holes on a flat plate at the Center of Advanced Turbine and Energy Research (CATER). Temperature distribution is captured by using the temperature sensitive paint (TSP) technique and the output design parameter is then calculated.
Numerical Study of Flow and Heat Transfer in Novel Structure Packed Beds
Authors: Yang Jian , Wang Qiuwang , Zeng Min
Published: June 2010

A forced convection heat transfer inside micro pores of structure packed beds with spherical or ellipsoidal particles are numerically studied in this paper. Three-dimensional Navier-Stokes equations and RNG k-ε turbulence model with scalable wall function are adopted for present computations. The effects of packing form and particle shape are carefully studied and the flow and heat transfer performances in uniform and nonuniform packed beds are also compared in detail. The macroscopic hydrodynamic and heat transfer results are obtained from micro pore cells by using integrating method. The results show that, with the same physical parameters, the pressure drops in structure packed beds are much lower than those in randomly packed beds while the overall heat transfer efficiencies (except SC packing) are much higher. The traditional correlations of flow and heat transfer extracted from randomly packings are unavailable for structured packings, and some modified correlations are obtained. Furthermore, it finds that, with the same particle shape (sphere), the overall heat transfer performance of SC packing is better than that of BCC packing. With the same packing form (BCC), the overall heat transfer performance of spherical particle model is better than that of ellipsoidal particle model and with the same particle shape and packing form (BCC packing with sphere), the overall heat transfer performance of uniform packing is better than that of non-uniform packing.
Quantifying Energy Transfer From a Reacting Thermite to a Target Using Infrared Diagnostics
Authors: Crane Charles , Pantoya Michelle , Dunn Jerry
Published: June 2010

A study was conducted to examine the energy transfer from a reacted thermite placed on a steel target substrate. A high speed infrared camera captured a temporally evolving thermal distribution on the substrate, while the thermite, which was placed in a v-notch, self propagated. The thermite investigated for this experiment was Aluminum with Iron (III) Oxide (Al-Fe2O3). An energy balance model was developed to predict temperatures near the v-notch in order to quantify the amount of energy transferred into the steel. Results quantified the percent of energy available from the reaction that was conducted through the substrate and energy losses were estimated. The thermite reaction transferred 10% of the heat of reaction to the steel. The Al-Fe2O3 exhibited greater heat losses to convection and radiation upon propagation through the powder mixture. The Al-Fe2O3 reaction produced more gas by chemistry, 10% by mass, which contributed to transporting energy away from the v-notch. Much work had been performed that examined the combustion behaviors from a reacting thermite, but there are very few studies that quantify the energy transfer from a reacting thermite to a target. This diagnostic approach and numerical analysis were the first steps toward understanding energy transferred from a thermite into a target, and lost to the environment.
Design of Compact BIPV Fac¸ades for the Buildings at the University of Technology Sydney (UTS)
Authors: Madadnia Jafar , Park Myung Hun
Published: June 2010

Ecologically Sustainable buildings are being designed for the University of Technology, Sydney (UTS) where the building fac¸ade and equipment may serve as a project-based environment for engineering students learning about energy efficiency. Building Integrated Photovoltaic (BIPV) panels with poly-crystalline Photovoltaic (PV) module were designed and experimentally tested. The power input, and power output, surface temperatures, and channel spacing(s) between the PV module and glazed layer(s) were measured at cooling conditions with both fan-on and fan-off conditions. The electric energy conversion efficiency and the heat transfer ratios of conduction, natural convection, forced convection, and radiation reflection were determined for BIPV panels and optimized against the surface temperature and the channel spacing(s). An optimum BIPV with compact spacing for the single glazed (double-skinned) facade was suggested to be retrofitted to existing buildings, while an optimum BIPV with compact spacing for the double glazed (triple-skinned) fac¸ade was suggested for the building development at UTS. The project is ongoing and serves as a collaborative educational platform for students and staff.
Evaporators for High Temperature Lift Vapor Compression Loop for Space Applications
Authors: Semenic Tadej , Tang Xudong
Published: June 2010

An Advanced Vapor Compression Loop (AVCL) for high temperature lift for heat rejection to hot lunar surface during lunar daytime was developed. The loop consists of an evaporator, a compressor, a condenser, and an electronic expansion valve. Different types of evaporators were evaluated in this study: a circular tube evaporator, a circular tube evaporator with a twisted tape, a circular tube evaporator with a wick, and a circular tube evaporator with a wick and a twisted tape. The evaporators were tested with two different compressors. The first was a 0.5hp oil-less compressor and the second was a 5.3hp compressor that used oil as lubricant. A heat exchanger (recuperator) was used to subcool the high pressure liquid and to superheat the low pressure vapor. Tests were performed with and without the recuperator. Vapor superheat during the tests was controlled with an electronic expansion valve controller. The working fluid was R134a. The results show that the heat source-to-working fluid thermal resistance of the circular tube evaporator with the wick and the twisted tape was one-third of that of the circular tube evaporator. The recuperator was able to decrease the vapor quality at the evaporator inlet and increase the vapor superheat at the compressor inlet. The evaporators without wicks were able to operate at a heat flux of 5.7W/cm2 with the recuperator and vapor superheat set at 5°C. Evaporators with wicks reached dryout at lower heat fluxes when maintaining superheat at 5°C. However, the wicked evaporators reached a heat flux of 7.6W/cm2 when decreasing superheat below 5°C. A temperature lift of 70°C was achieved with the 5.3hp compressor.
Laminar Flow and Heat Transfer Characteristics of Colloid Suspensions in Water: A Numerical Study
Authors: Alammar Khalid N. , Hu Lin-wen
Published: June 2010

Numerical analysis is performed to examine axisymmetric laminar flow and heat transfer characteristics of colloidal dispersions of nanoparticles in water (nanofluids). Effect of volume fraction on flow and heat transfer characteristics is investigated. Four different materials, Alumina, Copper, Copper Oxide, and Graphite are considered. Heat transfer and property measurements were conducted previously for Alumina nanofluid. The measurements have shown that nanofluids can behave as homogeneous mixtures. It is found that oxide-based nanofluids offer the least heat transfer enhancement compared to elements-based nanofluids. When normalized by friction pressure drop, it is shown that graphite can have the highest effective heat transfer enhancement. For a given volume flow rate, all nanofluids exhibited linear increase in heat transfer enhancement with increasing colloids volume fraction, up to 0.05.
Characteristics of Nanopatterns and the Associated Thermal Mechanisms During Near Field Laser-Material Interaction of Nanosecond Laser on Different Targets
Authors: Sundaram Vijay M. , Wen Sy-Bor
Published: June 2010

Nano-patterns are generated on semiconducting and metallic surfaces through coupling an apertured near field scanning optical microscope (NSOM) with a pulsed laser source in this study. To understand the dominant mechanisms for the generation of the nano-patterns, a series of experimental measurement of the size and shape of nano-patterns generated on targets under different experimental conditions with different targets is conducted. The characteristic dimensions of nano-patterns show dependence on optical properties of the target material. The qualitative trend of the variation of nano-patterns as a function of laser and material conditions indicates that the dominant mechanisms for the generation of nano-patterns through a combination of nanosecond laser and an apertured NSOM under different conditions studied is near field laser-material interaction.
Numerical Analysis of Flow Behavior Inside the Blast Furnace
Authors: Fu Dong , Tian Fengguo , Chen Guoheng , Huang D. Frank , Zhou Chenn Q.
Published: June 2010

Gas and burden distributions inside a blast furnace play an important role in optimizing gas utilization versus the furnace productivity and minimizing the CO2 emission in steel industries. In this paper, a mathematical model is presented to describe the burden descent in the blast furnace shaft and gas distribution, with the alternative structure of coke and ore layers being considered. Multi-dimensional Ergun’s equation is solved with considering the turbulent compressible gas flow through the burden column. The porosity of each material will be treated as a function of three dimensional functions which will be determined by the kinetics sub-models accordingly. A detailed investigation of gas flow through the blast furnace will be conducted with the given initial burden profiles along with the effects of redistribution during burden descending. Also, parametric studies will be carried out to analyze the gas distribution cross the blast furnace under different cohesive zone (CZ) shapes, charging rate, and furnace top pressure. A good agreement was obtained between the CFD simulation and published experimental data. Based on the results, the inverse V shape is proved to be the most desirable CZ profile.
Numerical Study of the Effects of Pressure and Gravitational Acceleration on Soot Formation in Laminar Axisymmetric Coflow Methane/Air Diffusion Flame
Authors: Liu Fengshan , Smallwood Gregory J. , Kong Wenjun
Published: June 2010

The structure and soot formation characteristics of a coflow laminar methane/air diffusion flame under conditions of constant p2g and mass flow rates of the air and fuel streams were numerically investigated in order to examine the validity of the p2g scaling relationship. The p2g scaling relationship has been used to experimentally investigate soot formation in weakly-buoyant laminar diffusion flames by conducting experiments at reduced pressures. Detailed numerical calculations were conducted by solving the elliptic conservation equations of mass, momentum, species, and energy in axisymmetric cylindrical coordinates using a standard control volume method. Detailed multi-component thermal and transport properties and detail combustion chemistry were employed in the modelling. Soot formation was modeled using a semi-empirical acetylene based model in which two transport equations for the soot mass fraction and soot number density per unit mass were solved. Thermal radiation was calculated using the discrete-ordinates method and a 9-band non-grey model for the radiative properties of the CO-CO2-H2O-soot mixture. The flame structure and soot formation characteristics exhibit strong dependence on the ambient pressure even though p2g and the mass flow rates are kept constant. Significantly more soot is produced with increasing the pressure and decreasing the gravity level. Numerical results clearly demonstrate that the p2g scaling relationship is invalid as far as soot formation is concerned.
Toward the Detailed Simulation of the Heat Transfer Processes in Unsaturated Porous Media
Authors: Jafar F. A. , Thorpe G. R. , Turan O¨. F.
Published: June 2010

Trickle bed chemical reactors and equipment used to cool horticultural produce usually involve three phase porous media. The fluid dynamics and heat transfer processes that occur in such equipment are generally quantified by means of empirical relationships between dimensionless groups. The research reported in this paper is motivated by the possibility of using detailed numerical simulations of the phenomena that occur in beds of irrigated porous media to obviate the need for empirical correlations. Numerical predictions are obtained using a CFD code (FLUENT) for 2-D configurations of three cylinders. Local and mean heat transfer coefficients around these non-contacting horizontal cylinders are calculated numerically. The present results compare well with those available in the literature. The numerical results provide an insight into the cooling mechanisms within beds of unsaturated porous media.
Mechanism on Mass Transfer in Micro-Scale During the Microwave Drying of Plant Porous Materials
Authors: Yang Junhong , Di Qianqian , Zhao Jun , Wang Liqiu
Published: June 2010

Astragalus slice is one species of stem and root medicinal herb with the widely curative effects, also a special and typical plant porous material, and the drying operation is one of important processing technologies in its storage and further practical application. This paper characterizes the microstructure of Astragalus slices dried by microwave technique at 200 W by using scanning electronic microscope (SEM). The study also compares Astragalus slices dried by microwave with those untreated and discusses the drying mechanism. Result shows that as compared to the untreated sample, the microwave dried sample behaves much shorter drying time with more and larger pore and open structure on the surface layer of matrix, but without significant change about the distribution status of cytoplasm inside parenchyma cells. Further analysis suggests that the vapor diffusion is the dominant mode of moisture transfer inside matrix during the microwave drying process of sample, resulting in the well-preserved structures of sample, including parenchyma cell and trachea. This is also helpful for maintaining the distribution status of cytoplasm, particularly avoiding the agglomeration of biological macro-molecular, which is benefit to improving the permeability of moisture transfer path, leading to the rapidly dehydration of moisture. This work seems to be helpful for developing the optimized drying technology of plant porous material focused on micro-mechanism and the quality of dried products.
Periodic Fluid Flow and Heat Transfer in a Square Cavity Due to an Insulated or Isothermal Rotating Rectangular Object
Authors: Shih Y.-C. , Khodadadi J. M. , Dai H.-W. , Fan Liwu
Published: June 2010

Computational analysis of transient phenomenon followed by the periodic state of laminar flow and heat transfer due to a rectangular rotating object in a square cavity is investigated. A finite-volume-based fixed-grid/sliding mesh computational methodology utilizing primitive variables is used. Rectangular rotating objects with different aspect ratios (AR = 1, 2, 3, 4) are placed in the middle of a square cavity. The motionless object is set in rotation at time t = 0 with a constant angular velocity. For the insulated and isothermal objects, the cavity is maintained as differentially-heated and isothermal enclosures, respectively. Natural convection heat transfer is neglected. For a given shape of the object and a constant angular velocity, a range of rotating Reynolds numbers are covered for a Pr = 5 fluid. The Reynolds numbers were selected so that the flow field is not affected by the Taylor instabilities (Ta < 1750). The periodic flow field, the interaction of the rotating objects with the recirculating vortices at the four corners and the periodic channelling effect of the traversing vertices are clearly elucidated. The corresponding thermal fields in relation to the evolving flow patterns and the skewness of the temperature contours in comparison to conduction-only case were discussed. The skewness is observed to become more marked as the Reynolds number is lowered. Transient variations of the average Nusselt numbers of the respective systems show that for high Re numbers, a quasi-periodic behavior due to the onset of the Taylor instabilities is dominant, whereas for low Re numbers, periodicity of the system is clearly observed. Time-integrated average Nusselt numbers of the insulated and isothermal object systems were correlated to the rotational Reynolds number and the aspect ratio of the rectangle. For high Re numbers, the performance of the system is independent of the aspect ratio. On the other hand, with lowering of the hydraulic diameter (i.e. bigger objects), objects with the highest and lowest aspect ratios exhibit the highest and lowest heat transfer, respectively. High intensity of the periodic channelling and not its frequency are identified as the cause of the observed enhancement.
Pressure Gradient Variations During Reflux Condensation in a Closed Thermosyphon
Authors: Moaveninejad Siamak , Heyhat Mohammad Mahdi
Published: June 2010

The heat and mass transfer in the condenser region of a variable conductance thermosyphon, consisting of two components (R11 + R113) has been studied and special attention has been devoted to pressure drop during reflux condensation. The mass, energy, and species conservation equations in conjunction with the overall mass conservation and continuity of momentum at liquid-vapor interface constraints and the thermodynamic equilibrium condition have been solved numerically by use of the integral method. In contrast to the flat-front model which assumes a sharp interface between the active and shut-off portions in a variable conductance thermosyphon, in this paper a continuous model has been used. In this model a continuous variation of physical properties with condensation of both components along condenser is assumed. The results of the present study have been compared with available numerical and experimental results of other investigators and pressure gradient profiles have been achieved. A calculation of the frictional, accelerational and gravitational components of the pressure drop shows that the gravitational component has the greatest magnitude due to the relatively high density of the vapor.
Impact and Fire Modeling Considerations Employing SPH Coupling to a Dilute Spray Fire Code
Authors: Brown Alexander L.
Published: June 2010

Transportation accidents and the subsequent fire present a concern. Particularly energetic accidents like an aircraft impact or a high speed highway accident can be quite violent. We would like to develop and maintain a capability at Sandia National Laboratories to model these very challenging events. We have identified Smoothed Particle Hydrodynamics (SPH) as a good method to employ for the impact dynamics of the fluid for severe impacts. SPH is capable of modeling viscous and inertial effects for these impacts for short times. We have also identified our fire code Lagrangian/Eulerian (L/E) particle capability as an adequate method for fuel transport and spray modeling. A fire code can also model the subsequent fire for a fuel impact. Surface deposition of the liquid may also be acceptably predicted with the same code. These two methods (SPH and L/E) typically employ complimentary length and timescales for the calculation, and are potentially suited for coupling given adequate attention to relevant details. Length and timescale interactions are important considerations when joining the two capabilities. Additionally, there are physical model inadequacy considerations that contribute to the accuracy of the methodology. These models and methods are presented and evaluated. Some of these concerns are detailed for a verification type scenario used to show the work in progress of this coupling capability. The importance of validation methods and their appropriate application to the genesis of this class of predictive tool are also discussed.
Condensation in a Vertical Tube Bundle Operating in Passive Condensation Mode
Authors: Henderson Gavin , Zhou Wenzhong , Revankar Shripad T.
Published: June 2010

Passive condenser systems are used in a number of industrial heat transfer systems. Passive containment cooling system (PCCS) which is composed of a number of vertical heat exchanger serves as an engineered safety system in an advanced boiling water reactor. The PCCS condenser must be able to remove sufficient energy from the reactor containment to prevent containment from exceeding its design pressure. Experiments were designed to simulate the PCCS condensation with a tube bundle. Scaling analysis was performed to scale down the prototype PCCS with a tube bundle consisting of four tubes. The tubes in the bundle were of prototype height (1.8 m) and diameter (52.5 mm) and the operating conditions and boundary conditions such as the operating pressure, secondary cooling system were designed to represent prototype conditions. Steam condensation tests were carried out in complete condensation mode where all the steam entering the condenser bundle is completely condensed. Condensation heat transfer coefficients (HTC) were obtained for various steam flow rate. The condensation pressure depended on the inlet steam flow rate which happens to be the maximum condensation rate for the given test pressure. Data on condensation heat transfer were obtained for primary pressure raging from 110–270 kPa. The tube bundle condensation heat transfer rates were compared with single tube heat transfer rates from previous work. The results showed that the condensation heat transfer coefficient for the tube in bundle was comparable with single tube, however the secondary side heat transfer coefficients for the tubes in bundle was higher than for the single tube. Condensation heat transfer for tube in bundle ranged from 7500 W/ m2K to 20,000 W/ m2K for the range of pressure studied. A heat and mass analogy model was developed and the condensation heat transfer prediction from the model was compared with experimental data.
Investigation of Loop Heat Pipe Survival and Restart After Extreme Cold Environment Exposure
Authors: Golliher Eric , Ku Jentung , Licari Anthony , Sanzi James
Published: June 2010

NASA plans human exploration near the South Pole of the Moon, and other locations where the environment is extremely cold. This paper reports on the heat transfer performance of a loop heat pipe exposed to extreme cold under the simulated reduced gravitational environment of the Moon. A common method of spacecraft thermal control is to use a loop heat pipe with ammonia working fluid. Typically, a small amount of heat is provided either by electrical heaters or by environmental design, such that the loop heat pipe condenser temperature never drops below the freezing point of ammonia. The concern is that a liquid-filled, frozen condenser would not re-start, or that a thawing condenser would damage the tubing due to the expansion of ammonia upon thawing. This paper reports the results of an experimental investigation of a novel approach to avoid these problems. The loop heat pipe compensation chamber is conditioned such that all the ammonia liquid is removed from the condenser and the loop heat pipe is non-operating. The condenser temperature is then reduced to below that of the ammonia freezing point. The loop heat pipe is then successfully re-started.
Undergraduate Class Project: Design and Build a Helical Coil Heat Exchanger Experiment
Authors: Abdelmessih Amanie N. , Cummings Stanely G. , Jorgenson Mary , Parker Joel
Published: June 2010

At Saint Martin’s University, the Mechanical Engineering Department incorporates design throughout the curriculum, starting from the freshman course ‘Introduction to Engineering’ up through the senior capstone design. Undergraduate Mechanical Engineering students are required to take three Mechanical Engineering elective courses. Each of these elective courses is 3 credits; one of these credits must be design. For ME 436 Thermal Design of Heat Exchangers course, the students were assigned a project to meet the Accrediting Board of Engineering and Technology student outcome criteria a, b, c, d, e, g, and i. In addition to course work the students designed, market searched for parts, budgeted, manufactured and built, then tested a finned helical coil heat exchanger experiment. A limited budget was assigned for this project. Currently, the apparatus is being used as an additional experiment in the Thermal Engineering Laboratory. This article includes the preliminary design, final design, experimental results, and assessment by students and faculty.
Thermal Conductivity and Thermal Contact Resistance of Metal Foams
Authors: Sadeghi Ehsan , Djilali Nedjib , Bahrami Majid
Published: June 2010

Unique specifications of metal foams such as relatively low cost, ultra-low density, high surface-area-to-volume ratio, and most importantly, the ability to mix the passing fluid provide them a great potential for a variety of thermal-fluidics applications. In the present study, a compact analytical model for evaluating the effective thermal conductivity of metal foams is developed. The medium structure is represented as orthogonal cylindrical ligaments that are equally spaced and sized. A unit cell is taken to represent the metal foam. The model accounts for varying cross-sectional ligaments which is consistent with microscopic images. A numerical analysis is performed to verify the proposed analytical models. The model predictions are in good agreement with existing experimental data and the present numerical results. A parametric study is then performed to investigate the effects of variation in ligament cross-section geometry, uniformity, and aspect ratio over a wide range of porosities. Moreover, Thermal contact resistance phenomenon is included in the analysis.
Harvesting Nanoscale Radiation Heat Transfer With Pyroelectric Materials
Authors: Fang Jin , Frederich Hugo , Pilon Laurent
Published: June 2010

Pyroelectric energy conversion offers a novel, direct energy-conversion technology by transforming time-dependent temperature directly into electricity. It makes use of the pyroelectric effect to create a flow of charge to or from the surface of a material as a result of heating or cooling. However, existing pyroelectric energy converter can only operate at low frequency due to relatively low heat transfer rate between the pyroelectric materials and the working fluid subjected to oscillatory fluid flow between hot and cold sources. On the other hand, energy transfer by thermal radiation between two semi-infinite solids can be enhanced by several orders of magnitude as the gap separating them reduces to subwavelength size thanks to interference and tunneling of electromagnetic waves across the gap. This paper proposes a novel way to harvest nanoscale radiation heat transfer for direct pyroelectric energy conversion of waste heat into electricity. A new device is investigated numerically by accurately modeling nanoscale radiation heat transfer between the pyroelectric materials and hot and cold surfaces. Performance of the pyroelectric converter is predicted at various frequencies. The result shows that rapid energy transfer and higher operating frequency can be achieved to increase efficiency and power density.
Solution of a Non-Linear Heat Conduction Problem in Automotive Clutch and Brake Systems
Authors: Al-Shabibi Abdullah M.
Published: June 2010

This paper investigates the transient solution for a non-linear heat conduction problem in automotive clutch system. The frictional heat generated during clutch disks engagement is known to cause thermoelastic distortion which in turn modifies the contact pressure distribution. The contact boundary condition that defines the area over which the heat is to be generated is also known to change and shift if the engagement process is run long enough. The thermal boundary in this case is time dependent and the problem becomes nonlinear. To account for such boundary condition, a solution methodology is proposed in this paper and tested in the context of a clutch disk sliding between two rigid bodies.
Multiscale Simulation of Nanoparticle Transport and Deposition in Fiber Matrix During a Nanofluid Filtration Process
Authors: Su Di , Ma Ronghui , Zhu Liang
Published: June 2010

A multiscale model is developed to simulate filtration process for the fabrication of composite material with nanoparticle additives. The model consists of two components. One is a particle trajectory tracking model (PTTM) which can predict the deposition rate of nanoparticle on the fiber matrix in a single pore structure, and the other one is a macroscale transport model of fluid flow in porous fiber structures. The flow of the fluid in the porous media with a free moving surface is solved by using the meshless SPH method. The integrated model is used to predict the local deposition rate coefficient and the distribution of the nanoparticle concentration in the carrier fluid and on the fiber surface. We envision this as the first step of a systematic study towards to an advanced understanding of the process as well as the optimization of the operational parameters for achieving homogeneous material properties of the materials.
Heat and Mass Transport Analysis of Polymer Electrolyte Membrane Fuel Cell With Bipolar Plates
Authors: Konnepati Pavan Kumar , Majumdar Pradip
Published: June 2010

Fuel cells convert chemical energy of fuels into electricity directly. Their higher efficiency and low emissions made them prime candidates for next generation power requirements. The Polymer Electrolyte Membrane (PEM) fuel cell has gained attention of both transportation and stationary power generation industries. In this study a three-dimensional computational model for the simulation of Polymer Electrolyte Membrane (PEM) fuel cell unit cell is developed to understand the complex internal mechanisms, and evaluate the effects of bipolar plate designs on the cell performance. The model includes combined heat and mass transfer processes due to convection and diffusion in the gas flow channels of bi-polar plates as well in the gas diffusion layers of the electrodes, and associated electrochemical reactions in a tri-layer PEM fuel cell. Simulation is carried out with straight parallel channels for operating current density in the range from 0.5–1.5 A/cm2 showed significant insight details of PEM fuel cell in terms of distribution of reactant gases, and heat and water transport across the cell. A significantly high variation in gas concentration across the electrode–membrane interfaces and along the channel length is noticed, requiring higher stoichiometric ratios to increase the limiting current density.
Review of the management of sudden cardiac arrest on the football field: Figure 1
Authors: Kramer Efraim , Dvorak Jiri , Kloeck Walter
Published: June 2010

Football is the most popular sport on earth. When a young, fit popular player suddenly collapses and dies during play, the tragic event is frequently screened and publicised worldwide. The reported incidence of sudden cardiac arrest (SCA) varies from 1:65 000 to 1:200 000 athletes. A broad spectrum of cardiac and non-cardiac causes have been implicated, and regular precompetition medical assessments are recommended as a preventive measure. Immediate cardiopulmonary resuscitation and early defibrillation is the treatment for SCA. High success rates can be achieved if this is initiated promptly, preferably within seconds of the arrest. Trained medical responders must be allowed to respond, ideally with a defibrillator (manual or automated) in hand, to a player who suddenly and unexpectedly collapses and remains unresponsive on the field. Immediate defibrillation of a pulseless ventricular tachycardia or ventricular fibrillation, within 1 to 2 min of onset, has a successful cardioversion rate exceeding 90%. Medical responders should be well trained and rehearsed in the recognition of SCA, including distractors such as seizures, myoclonic jerks and agonal (gasping) breathing. Prompt initiation of chest compressions on the field, together with early defibrillation, will result in many athletes' lives being saved by immediate implementation of these simple recommendations.
Melting of the continental crust during orogenesis: the thermal, rheological, and compositional consequences of melt transport from lower to upper continental crustThis article is one of a selection of papers published in this Special Issue on the the themeLithoprobe—parameters, processes, and the evolution of a continent.
Authors: Brown Michael
Published: June 2010

The formation and differentiation of the continental crust occurs at convergent plate margins in accretionary and collisional orogenic belts where sufficient heat is generated to achieve high-grade metamorphism and anatexis. Volumetrically significant H2O-present melting requires an influx of aqueous fluid along zones of high-strain deformation or via fracture networks, or recycling of the fluid dissolved in melt via melt migration and fluid exsolution during crystallization. In contrast, in “dry” crust, melting occurs via hydrate-breakdown melting reactions at higher temperatures than H2O-present melting; volumetrically significant melt production requires temperatures above ∼800 °C. Melting wets residual grains, and anatectic crust becomes porous at a few vol.% melt. Feedback between deformation and melting creates a dynamic rheological environment; as melt volume increases to the melt connectivity transition, which varies but is around 7 vol.% (see discussion later in the text), melt may escape from the source in the first of several melt-loss events with increasing temperature. Major and accessory phase controls on melt production and melt composition for different pressure–temperature–time paths are evaluated using calculated phase equilibria for average pelite. The pristine to slightly retrogressed condition of peritectic minerals in residual crust requires significant loss of melt from the system. The consequences of melt loss are evaluated here. In residual crust, evidence of melt at the grain scale may be preserved in microstructures, whereas evidence of melt extraction pathways at outcrop scale is recorded by leucosome networks. Strain and anisotropy of permeability control the form of mesoscale melt channels with strong anisotropy promoting high-melt focusing. The sequence of structures observed in nature records a transition from storage to drainage; focused melt flow occurs by dilatant shear failure of low-melt-fraction rocks, leading to the formation of networks of channels that allow accumulation and storage of melt and that form the link for melt flow from grain boundaries to ascent conduits. Melt ascent is via ductile-to-brittle fracture; ductile fractures may propagate along foliation as sills or from dilation or shear bands as dikes. Emplacement of horizontal tabular and wedge-shaped plutons occurs around the brittle–ductile transition zone, whereas vertical lozenge-shaped plutons represent crystallization of magma in the ascent conduit. Blobby plutons form by lateral expansion in the ascent conduit localized by thermal or mechanical instabilities.
Great earthquakes on Canada’s west coast: a review This article is one of a series of papers published in this Special Issue on the themeLithoprobe — parameters, processes, and the evolution of a continent. Geological Survey of Canada Contribution 20090196.
Authors: Hyndman Roy D. , Rogers Garry C.
Published: June 2010

The first Lithoprobe transect in 1984 across Vancouver Island had primary objectives to define the structure associated with subduction and constraints on the potential for great thrust earthquakes. The Lithoprobe results and the comprehensive multidisciplinary data collection and analyses that followed provide compelling evidence for past great earthquakes along the Cascadia subduction zone from Vancouver Island to northernmost California, and for present elastic strain build up toward future great events. There is evidence of sudden coastal subsidence up to 2 m and of deep-sea turbidite deposits indicating strong shaking from huge earthquakes at irregular intervals averaging about 500 years, the last in 1700. Precision geodetic measurements define the present buckling of the coastal region, diagnostic of elastic strain accumulation on a locked thrust fault. The landward extent of rupture and, therefore, shaking at coastal cities is constrained by (i) the pattern of elastic strain buildup, (ii) the estimated temperatures on the fault, (iii) the updip limit of episodic tremor and slip (ETS), (iv) the downdip change in reflection character of the thrust, and (v) the magnitude of coastal subsidence in the most recent, 1700, and previous great events. The major earthquakes are very large, M9, rupturing most of the Cascadia margin, but mainly offshore, limiting somewhat the shaking at inland cities but producing large tsunamis. The ETS that occurs at intervals of just over a year appears to involve slow slip on the subduction thrust downdip of the rupture zone that increases stress on the locked zone and may indicate time varying potential for great events.