bluuebunny/crossref_metadata_2025 huggingface dataset:
A High Performance Semi-Passive Cooling System: The Pulse Thermal Loop
Authors: Weislogel Mark M. , Bacich Michael A.
Published: March 2009

Over the past decade, the search for and development of high performance thermal transport systems for a variety of cooling and thermal control applications have intensified. One approach employs a new semi-passive oscillatory heat transport system called the Pulse Thermal Loop (PTL). The PTL, which has only recently begun to be characterized, exploits large pressure differentials from coupled evaporators to force (pulse) fluid through the system. Driving pressures of over 1.8MPa (260psid) have been demonstrated. Other passive cooling systems, such as heat pipes and Loop Heat Pipes, are limited by capillary driving forces, typically less than 70kPa (10psid). Large driving forces can be achieved by a mechanically pumped loop, however, at the expense of increased power consumption, increased total mass, and increased system cost and complexity. The PTL can be configured in either active or semi-passive modes, it can be readily designed for large ∼ O(100kW) or small ∼ O(10W) heat loads, and it has a variety of unique performance characteristics. For low surface tension dielectric fluids such as R-134a, the PTL system has over a 10-fold heat carrying capacity in comparison to high performance heat pipes. Data accumulated thus far demonstrate that the PTL can meet many of the requirements of advanced terrestrial and spacecraft cooling systems: a system that is robust, ‘semi-passive,’ high flux, and offers high heat transport thermal control while remaining flexible in design, potentially lightweight, and cost competitive.
Thermal Conductivity Prediction of Periodic Nanocomposites Using Phonon Boltzmann Equation
Authors: Yang Ronggui , Chen Gang
Published: March 2009

In this paper, we study theoretically the phonon thermal conductivity of nanocomposites with nanowires embedded in a host semiconductor material using the phonon Boltzmann equation. Special attention is paid for using periodic boundary conditions. The simulation shows that the temperature profiles in nanocomposites are very different from those in regular composites, due to ballistic phonon transport at nanoscale. Such temperature profiles cannot be captured by exiting models in literature. We predict the thermal conductivity dependence on the size of the nanowires, the volume fraction, and the bulk properties of the constituent materials. Comparison is also made with the thermal conductivity of superlattices. Results of this study can be used to direct the development of high efficiency thermoelectric materials.
Microscale Ion-Driven Air Flow Over a Flat Plate
Authors: Schlitz Daniel J. , Garimella Suresh V. , Fisher T. S.
Published: March 2009

A microscale air pump concept that uses ionized air molecules under the influence of an electric field is studied. The method employed is an extension of the corona wind concept and is referred to here as microscale ion-driven air flow. The two major differences are that the ions are created in a distinct generation region, and are then put in motion by a traveling electric field in the pumping region. The ions create bulk motion of the air because of ion drag. One application of this technology involves generation of air flow through microchannels or other micro-featured surfaces to create compact, high flux heat sinks for electronics cooling. This work focuses on the ion pumping aspect of the technology. A device was constructed and tested with an array of micro-fabricated electrodes that generate strong electric fields in the air. The electrode potentials were cycled to impart a unidirectional force to the ions over meso-scale distances. The microscale ion-driven air flow concept was demonstrated by electrical means, through the measurement of the ion current produced. A set of designed experiments were conducted that showed the electrode potential to be the most significant factor for sustaining an ion current. A two-dimensional numerical model of the ion motion has been developed and validated against the experimental results. The model describes the time-dependent ion flow induced over an array of evenly spaced microscale electrodes that are used to generate a translating electric field.
Numerical Study of Swirling Impinging Jets With Heat Transfer
Authors: Ha¨llqvist Thomas , Fuchs Laszlo
Published: March 2009

This paper deals with numerical simulations of circular impinging jets with heat transfer, by means of Large Eddy Simulation (LES). The LES code uses higher order finite-differences on staggered Cartesian non-uniform grids. The current LES have the potential of dealing with transition as well as providing data on details of larger scale structures, statistical correlations and turbulent spectral content. The impinging circular jet has a nozzle-to-plate spacing ranging from 0.5 to 2 nozzle diameters and the Reynolds number is 20000. Three different swirl numbers have been considered, ranging from non-swirling to strongly swirling flow. From the LES results the transition process in the jet is clearly detected. Swirling flow strongly influences the development of the jet. The wall heat transfer rates become obstructed, even though the turbulence level increases.
A Calculation Method for Analysis Condensation of a Pure Vapor in the Presence of a Noncondensable Gas on a Shell and Tube Condenser
Authors: Haseli Yousef , Roudaki S. Javad M.
Published: March 2009

Based on film theory model, an approach is developed to analyze the condensation of a binary mixture, while one is non-condensable component, on a baffled shell and one path tube condenser. Using of this approach leads to have the condensation rate and both mixture and coolant temperatures at the end of each baffle spacing, which is considered as a control volume in this research. This method is checked for a set of steam-air mixture and water as coolant on a counter and a parallel current condenser. The results show that the condensation rate and temperature profiles in each condenser have consistence trend. Also comparisons of output values of both types of the condenser for different air mass fraction indicate an overall superior operation of counter type than the parallel type.
A New Conduction Heat Transfer Technology
Authors: Dilloway Victor J. N.
Published: March 2009

This paper describes a new conductive heat transfer technology that has been developed to the point of commercial application in China. Although the technology, QuTech™, was granted a U. S. Patent on October 17, 2000, only one North American commercial applications exist at this time. This technology imparts extremely high thermal conductivity to a tube or pipe. It functions similar to a heat pipe except that there is no internal liquid to vaporize and condense for transportation of thermal energy from one point to another along the pipe. The technology is typically used to transfer thermal energy from one side of a barrier to another. The barrier may be the wall of a pressure vessel or a “divider plate” between flowing media.
The Use of Solution Adaptive Grid for Modelling Small Scale Turbulent Structures
Authors: de With G. , Holdo̸ A. E.
Published: March 2009

The use of Large Eddy Simulation (LES) is computationally intensive and various studies demonstrated the considerable range of vortex scales to be resolved in an LES type of simulation. The purpose of this study is to investigate the use of a Dynamic Grid Adaptation (DGA) algorithm. Despite many developments related to adaptive methods and adaptive grid strategies, the use of DGA in the context of turbulence modelling is still not well understood, and various profound problems with DGA in relation to turbulence modelling are still present. The work presented in this paper focuses on the numerical modelling of flow around a circular cylinder in the sub-critical flow regime at a Reynolds number of 3.9·103. LES simulations with conventional mesh and DGA have been performed with various mesh sizes, refinement criteria and re-meshing frequency, to investigate the effects of re-meshing on the flow field prediction. The results indicate that the turbulent flow field is sensitive to modifications in the mesh and re-meshing frequency, and it is suggested that the remeshing in the unsteady flow region is affecting the onset of small scale flow motions in the free shear layer.
Interrelation Between Fluid Particles Rotational Motion in Rotating Flow Passage of Centrifugal Pump and Overall Efficiency
Authors: Tanaka Takaharu , Liu Chao
Published: March 2009

Main purpose of investigation has been put on the hydraulic energy losses caused in the rotating flow passage of centrifugal pump. Result of discussion shows that fundamental poor efficiency is brought by the fluid particles poor rotational motion at the trailing edge of impeller outlet, including the rotational motion caused in the flow passage between impeller blades rather than the hydraulic energy losses caused in the rotating flow passage. Therefore, our main purpose of investigation has to be put on the way rather to the fluid particles rotational motion caused at the trailing edge of impeller outlet and that caused between impeller blades.
Rheological Flows in Channels With Complex Geometry and Porous Medium
Authors: Gurbanov Ramiz S. , Abdinov Eldar T. , Bakhtiyarov Sayavur I.
Published: March 2009

The article describes a new method of rheological stationary fluids flow calculation in pipes and channels. By means of a complex variable method the universal formulae for velocities and flow rates distribution have been received. A technique called “linearization of single-bonded area” has been used in this research. The quasi Newtonian approach method has been suggested for the first time. To study of rheological stationary fluids flow in porous medium the model of “hypothetical canal” is assumed. This model allows predicting the rheological behavior of anomalous fluids flow through porous medium based on the results obtained on the capillary flowmeter. The “real” rheological equation of condition construction has been pointed out. The resistance laws generalized for the rheological stationary fluid have been received.
Uncertainty Analysis of Infrared Thermography in Convective Heat Transfer
Authors: Akafuah Nelson K. , Hall Carsie A. , Wang Ting
Published: March 2009

Infrared thermography is the preferred choice in many industrial processes for thermal diagnostics, condition monitoring, and non-destructive testing. However, the inherent uncertainty of surface emissivity affects the accuracy of temperature measurement by infrared thermography. In this paper a comprehensive experimental investigation was conducted to assess the uncertainty of infrared thermography in convective heat transfer. Four convective heat transfer conditions, including natural and forced convection on a flat plate, were studied. A composite test plate was constructed with an embedded heater and thermocouples. The thermocouples were used as references to compare with measurements by the infrared camera. The results indicate that the uncertainty of temperature measurement is about 4°F (2.7% of the wall-to-ambient temperature difference) with the largest uncertainty being contributed by calibration of the infrared camera. The uncertainty of the heat transfer coefficient is 4.2% which is largely contributed by wall temperature measurement.
High-Pass Filtered Eddy-Viscosity Models for Large-Eddy Simulations of Compressible Wall-Bounded Flows
Authors: Stolz Steffen
Published: March 2009

Eddy-viscosity models such as the Smagorinsky model [1] are the most often employed subgrid-scale (SGS) models for large-eddy simulations (LES). However, for a correct prediction of the viscous sublayer of wall-bounded turbulent flows van-Driest wall damping functions or a dynamic determination of the constant [2] have to be employed. Alternatively, high-pass filtered (HPF) quantities can be used instead of the full velocity field for the computation of the subgrid-scale model terms. This approach has been independently proposed by Vreman [3] and Stolz et al. [4]. In this contribution we consider LES of a spatially developing supersonic turbulent boundary layer at a Mach number of 2.5 and momentum-thickness Reynolds numbers at inflow of approximately 4500, using the HPF Smagorinsky model. The model is supplemented by a HPF eddy-diffusivity ansatz for the SGS heat flux in the energy equation. Turbulent inflow conditions are generated by a rescaling and recycling technique proposed by [5] where the mean and fluctuating part of the turbulent boundary layer at some distance downstream of inflow is rescaled and reintroduced at inflow.
Hydrodynamics of the Flow Around a Circular Cylinder Sheathed by a Porous Layer
Authors: Sobera M. P. , Kleijn C. R. , Brasser P. , van den Akker H. E. A.
Published: March 2009

A detailed study of the turbulent flow at Re = 3900 around a circular cylinder, sheathed at some small distance by a porous layer, has been performed by means of Direct Numerical Simulation with a commercial unstructured finite volume based Computational Fluid Dynamics solver. First, to benchmark the performance of this code and the validity of the applied local grid refinement, simulations of the flow around a bare circular cylinder at the same Re were performed. Results were compared to that of an academic CFD solver and to numerical and experimental data from literature and good agreement was found. Subsequently, a detailed study of the flow around a porous layer sheathed cylinder at the same Re, was performed. The flow in the space between the outer porous and the inner solid cylinder was found to be laminar and periodic, with a frequency locked to that of the vortex shedding in the wake behind the cylinder. A good agreement was found to experimental data from literature.
Transient Discrete Ordinate Method and Experiments of Pulsed Radiative Transfer Through Scattering Absorbing Media
Authors: Trivedi Ashish , Basu Soumyadipta , Mitra Kunal
Published: March 2009

The objective of this paper is to validate the solution of transient radiation transfer equation with experimental measurements using short pulse laser source having a Gaussian distribution. The transient radiative transfer equation for the case of short pulse laser propagation through scattering absorbing media such as tissue is an integrodifferential equation and is therefore complicated to solve. The time-dependent discrete ordinates method in conjunction with high order upwind piecewise parabolic interpolation scheme is used to solve the transient radiative transfer equation for the case of anisotropically scattering absorbing medium having a rectangular geometry in which an inhomogeneity is embedded. A parametric study involving different scattering and absorption coefficients of the medium, inhomogeneity and inhomogeneity size as well as the detector position is performed. The numerical modeling results and experimental measurements are in excellent agreement for various parameters studied in this paper.
Measurement of Thermal Properties of Composite Panels
Authors: Druma A. M. , Alam M. K. , Kistner M. , Watts Roland
Published: March 2009

Thermal panels are used in spacecrafts and planned for thermal management in aircraft electronics and power systems. The requirements are light-weight, highly conductive emerging carbon materials that can withstand the stresses in the specific applications. A number of carbon fiber reinforced carbon-carbon and organic matrix composite panels were fabricated and tested by using a cryogenic Flash Diffusivity instrument and Differential Scanning Calorimeter (DSC). The properties were measured at cryogenic and above ambient temperatures.
Thermo-Hydrodynamic of the Evaporation of Refrigerant R134A in Brazed Plate Heat Exchangers
Authors: Jokar Amir , Eckels Steven J. , Hosni Mohammad H.
Published: March 2009

The evaporation of refrigerant R134a in three different sizes of Brazed Plate Heat Exchangers (BPHE) is analyzed in this article. The BPHEs are a type of compact plate heat exchanger with parallel corrugated plates which are brazed together in series. In this study, these heat exchangers are utilized as the evaporator of an automotive refrigeration system, and their heat transfer coefficients and pressure drops are obtained experimentally. The refrigerant flows on one side and a 50% glycol-water mixture on the other side of the BPHEs, in a counter flow configuration. The heat transfer coefficient for the single-phase glycol-water mixture flow through the BPHEs is obtained using the Wilson plot technique. The single-phase Fanning friction factor correlation is also obtained using experimental results from the hydrodynamic parameters of glycol-water mixture. The results from the single-phase flow analysis are then extended to the two-phase flow analysis to correlate the evaporation heat transfer and pressure drop for the refrigerant R134a in the BPHEs. In summary, the thermo-hydrodynamic behavior of the evaporation of R143a in brazed plate heat exchangers is analyzed and compared with previous studies.
The Effect of Thermo-Solutal Capillary Transport on the Dynamics of Liquid Bridge
Authors: Joly Fre´de´ric , Shyy Wei , Labrosse Ge´rard
Published: March 2009

The transport dynamics and stability limit of the axisymmetric steady flow driven by a surface tension variation in a liquid bridge configuration is studied numerically. The surface tension variation results from both thermal and solutal gradients, and varies linearly with both temperature and solute concentration. The pseudo-spectral method is employed to investigate the solutions under different combinations of Marangoni, Prandtl and Lewis numbers, and separation ratio. Steady bifurcations for low Prandtl numbers are observed. The Soret effect has important influence on the stability of the basic flow, as it can change the symmetry of the most destabilizing perturbations and affect the threshold for 3D convection. It is also shown that for large Prandtl number, the Hopf bifurcation observed for pure fluid is replaced by a steady one for negative separation ratio.
Numerical Simulation of Heat Transfer in Simultaneously Developing Flows in Parallel Rectangular Ducts
Authors: Al-Bakhit Hussien , Fakheri Ahmad
Published: March 2009

The F correction factor charts, or the ε-NTU relations all assume that the overall heat transfer coefficient is constant across the heat exchanger. The short lengths and the comparatively thick walls through which heat is conducted in microchannel heat exchangers preclude the existence of thermally fully developed flow over a large portion of the heat exchanger. In this study, a parallel flow heat exchanger is simulated numerically to determine the impact of different parameters on the performance and the accuracy of constant heat transfer coefficient assumption. It is shown that there is significant change in the overall heat transfer coefficient in the developing region and that the three-dimensional heat transfer in the heat exchanger wall must be included in the analysis.
Analysis of Intercooler in PEM Fuel Cell Systems
Authors: Ito Takamasa , Yuan Jinliang , Sunde´n Bengt
Published: March 2009

Heat exchangers are used in proton exchange membrane fuel cell systems (PEMFCs) for stack cooling, intercooling, water condensation and fuel reforming. Especially, the heat exchanger for the intercooling before the humidifier is investigated in this paper. It is found that, at high pressure or high mass flow rate, the need to cool the air (oxidant) is large. The heat exchanger uses coolant water from the stack cooling system or ambient air as the cold stream. With water-cooling, the volume of the heat exchanger will be small. However, difficulties exist because the small available temperature difference. Air-cooling can be used over a wide operating range but the heat exchanger volume will be large.
Multiphase Particle-in-Cell Simulations of Flow in a Gas-Solid Riser
Authors: Williams K. A. , Snider D. M. , Torczynski J. R. , Trujillo S. M. , O’Hern T. J.
Published: March 2009

The commercial computational fluid dynamics (CFD) code Arena-flow is used to simulate the transient, three-dimensional flow in a gas-solid riser at Sandia National Laboratories. Arena-flow uses a multiphase particle-in-cell (MP-PIC) numerical method. The gas flow is treated in an Eulerian manner, and the particle flow is represented in a Lagrangian manner by large numbers of discrete particle clouds with distributions of particle properties. Simulations are performed using the experimental values of the gas superficial velocity and the solids mass flux in the riser. Fluid catalytic cracking (FCC) particles are investigated. The experimental and computed pressure and solid-volume-fraction distributions are compared and found to be in reasonable agreement although the experimental results exhibit more variation along the height of the riser than the computational results do. An extensive study is performed to assess the sensitivity of the computational results to a wide range of physical and numerical parameters. The computational results are seen to be robust. Thus, the uncertainties in these parameters cannot account for the differences between the experimental and computational results.
The Dynamic Pressure Response of Phase Eruption in Micro Channels
Authors: Haendler Brenda E. , Liepmann Dorian , Pisano Albert P.
Published: March 2009

New results are presented in this paper quantifying the dynamic pressure response that is produced as a result of the phase eruption phenomenon in micro channels at a flow rate of 0.5 ml/min. The experimentally measured time-varying pressure change from phase eruption is profiled for water and conclusions are drawn which will help guide the design and operation of an intake manifold for a micro engine. Employing the method of discrete Fourier transform, the amplitude and frequency of the pressure response is characterized for a variety of flow conditions detailing the sensitivity of the system to external changes. Relationships are established between the temperature and Reynolds number of the flow and the pressure in the channel for non-boiling flows. The governing equations for flow in micro channels are presented and conclusions on modeling phase change are discussed. The single-phase relationships discussed are deviated from once phase eruption begins and future modeling directions are proposed.
Experimental Investigations Concerning Erosive Aggressiveness of Cavitation at Different Test Configurations
Authors: Bachert B. , Dular M. , Baumgarten S. , Ludwig G. , Stoffel B.
Published: March 2009

The experimental results, which will be presented in this paper, demonstrate the significant influence of the flow velocity, respectively the rotational speed, on the erosive aggressiveness of cavitating flows. On two of the three investigated test objects, cavitation erosion can only be observed in the initial stage by the so-called pit-count evaluation method. Developed erosion with mass loss is impossible to measure because of the very long duration until mass loss appears. The third test rig generates a very aggressive type of cavitation, so that mass loss, depending on the tested material, will appear after relatively short durations. In addition, the initial stage of cavitation erosion can be observed. Three different techniques were applied to investigate cavitation erosion in the initial and developed stage. Thereby, the capability of methods to quantify erosive effects in dependence of influencing operating parameters has been proven.
Development of an Electronic Speckle Pattern Interferometer for Measurement of Concentration Gradients in a Binary Mixture
Authors: McGuire David , Garvey Julie , Dalton Tara M. , Davies Mark R.
Published: March 2009

This paper describes the construction and performance of an Electronic Speckle Pattern Interferometer (ESPI) developed for measurements of concentration gradients in a binary mixture. The system uses a Mach-Zehnder interferometer with a commercially available CCD camera for image acquisition. A phase-shifting algorithm is employed to give full field measurements. The theoretical background to the optical process involved in these methods is also presented, with emphasis on using the system for analysing concentration gradients. Problems pertaining to the unknown Gladstone-Dale constants of a binary mixture are also discussed.
Experimental Study of Local Mass Transfer From a Flat Plate in Uniform Flow Using Electronic Speckle Pattern Interferometry
Authors: Dalton Tara M. , McGuire David , Davies Mark R.
Published: March 2009

In this paper an investigative study of the relationship between mass and momentum transport, which have a mutual dependence, is presented. Mass transfer is an important design consideration in engineering processes such as evaporation, chemical reactions, corrosion and mixing. The effect that Reynolds number and distance from the leading edge has on mass transport from fluid to fluid interface on flat plate geometry is examined. A concentration profile is developed above a surface by passing airflow across the plate containing a well of ethanol. The rate of mass transfer is obtained from the concentration profile produced as the ethanol vapour diffuses in the airflow. Measurements are taken using the non-intrusive optical technique of Electronic Speckle Pattern Interferometry (ESPI), which has not been applied in this manner before. This novel approach offers the ability to measure in real time the mass transfer rate. A phase-shifting algorithm is also employed to give whole field measurements. The experimental results compare well to the theoretical prediction, showing that as expected the Sherwood number increases with increasing Reynolds number.
Thermal Optimization of a Composite Heat Spreader
Authors: Jones G. F. , Ghassemi S.
Published: March 2009

A theoretical study is undertaken to determine the optimal geometry of a composite heat spreader subjected to cooling by a single phase fluid. Optimal geometry is obtained when heat transfer from the spreader is maximized. Constructal theory is employed, where the fundamental construct for the composite consists of a thin high-thermal conductivity blade in contact with a matrix of lesser conductivity. Following a systematic procedure, a tree-like geometry is built up from this fundamental unit, which increases in surface area with each successive construct and possesses optimal geometry at each construct level. Numerical results are calculated for a carbon-fiber composite in an epoxy matrix. We find the optimal aspect ratio for all constructs to be of the order of 1 for a wide range of prescribed surface area for the fundamental unit.
Calculation of Post-Closure Natural Convection Heat and Mass Transfer in Yucca Mountain Drifts
Authors: Webb Stephen W. , Itamura Michael T.
Published: March 2009

Natural convection heat and mass transfer under post-closure conditions has been calculated for Yucca Mountain drifts using the computational fluid dynamics (CFD) code FLUENT. Calculations have been performed for 300, 1000, 3000, and 10,000 years after repository closure. Effective dispersion coefficients that can be used to calculate mass transfer in the drift have been evaluated as a function of time and boundary temperature tilt.
Heat Transfer Measurements and Correlations for Air-Water Two-Phase Slug Flow in a Horizontal Pipe
Authors: Ghajar Afshin J. , Malhotra Kapil , Kim Jae-Yong , Trimble Steve A.
Published: March 2009

Local heat transfer coefficients and flow parameters were measured for air-water slug flow in a horizontal 25.4 mm stainless steel schedule 10S pipe with a length to diameter ratio of 100. For this systematic study, a total of 83 data points were taken by carefully coordinating the liquid and gas superficial Reynolds number combinations. The heat transfer data were measured under a uniform wall heat flux boundary condition ranging from about 3800 to 16000 W/m2. The superficial Reynolds numbers ranged from about 3160 to 30290 for water and from about 1480 to 5840 for air. Comparison of heat transfer data for slug flow revealed that the heat transfer results were significantly dependent on the liquid and gas superficial Reynolds numbers. Overall, the experimental heat transfer data showed that the liquid phase dominated the heat transfer. However, it was found that the heat transfer data having a fixed liquid superficial Reynolds number showed that the heat transfer coefficients decreased as the gas superficial Reynolds number increased. A general heat transfer correlation for two-phase gas-liquid flow was fitted to our experimental horizontal slug flow heat transfer data with a mean deviation of −2.77% and an RMS deviation of 9.92%. Furthermore, a simplified heat transfer correlation for slug flow was developed based on the trends of heat transfer coefficient over the superficial liquid and gas Reynolds numbers. The proposed correlation predicted the experimental data with a mean deviation of −1.44% and an RMS deviation of 5.15%.
High-Fidelity Computational Simulation of Nonlinear Fluid-Structure Interactions
Authors: Gordnier Raymond E. , Visbal Miguel R.
Published: March 2009

This paper reviews recent efforts to demonstrate a flexible computational framework for developing a high-fidelity, non-linear aeroelastic solver. A subiteration strategy is adopted to achieve implicit coupling between the computational fluid dynamics and the structural codes. The specific solver presented couples a well-validated, full Navier-Stokes code with a nonlinear finite element plate model. The versatility of the approach is shown by applications to several types of fluid-structure interaction problems including: panel flutter, delta wing LCO and delta wing buffet. The computational results are analyzed to elucidate the relevant physical phenomena involved in these complicated nonlinear fluid-structure interactions. This framework is extendible to other multidisciplinary problems where two or more disciplines may need to be coupled.
Simulation of Ventilation Efficiency, and Pre-Closure Temperatures in Emplacement Drifts at Yucca Mountain, Nevada, Using Monte Carlo and Composite Thermal-Pulse Methods
Authors: Case John B. , Buesch David C.
Published: March 2009

Predictions of waste canister and repository driftwall temperatures as functions of space and time are important to evaluate pre-closure performance of the proposed repository for spent nuclear fuel and high-level radioactive waste at Yucca Mountain, Nevada. Variations in the lithostratigraphic features in densely welded and crystallized rocks of the 12.8-million-year-old Topopah Spring Tuff, especially the porosity resulting from lithophysal cavities, affect thermal properties. A simulated emplacement drift is based on projecting lithophysal cavity porosity values 50 to 800 m from the Enhanced Characterization of the Repository Block cross drift. Lithophysal cavity porosity varies from 0.00 to 0.05 cm3/cm3 in the middle nonlithophysal zone and from 0.03 to 0.28 cm3/cm3 in the lower lithophysal zone. A ventilation model and computer program titled “Monte Carlo Simulation of Ventilation” (MCSIMVENT), which is based on a composite thermal-pulse calculation, simulates statistical variability and uncertainty of rock-mass thermal properties and ventilation performance along a simulated emplacement drift for a preclosure period of 50 years. Although ventilation efficiency is relatively insensitive to thermal properties, variations in lithophysal porosity along the drift can result in a range of peak driftwall temperatures can range from 40 to 85 °C for the preclosure period.
Heat-Transfer Study of Aluminum-Foam Heat Sink for Electronic Cooling
Authors: Hsieh W. H. , Wu J. Y. , Shih W. H. , Chiu W. C.
Published: March 2009

The demand of high speed and miniaturization of electronic components results in increased power dissipation requirement for thermal management. In this work, the effects of porosity (ε), pore density (PPI) and air velocity on the heat-transfer characteristics of aluminum-foam heat sinks are investigated experimentally. The phenomenon of non-local thermal equilibrium (NLTE) is also observed and reported. Results show that the Nu increases as the pore density increases, due to the fact that aluminum foam with a larger pore density has a larger heat-transfer area. The Nusselt number also increases with the increase of porosity due to the same reason. It is noted that temperatures of the solid and gas phases of the aluminum foam decrease as Reynolds number increases, caused by the increased convective heat-transfer rate at higher Reynolds number. The deduced temperature difference between solid and gas phases clearly indicates the existence of non-local thermal equilibrium condition within the aluminum-foam heat sink. The increase of the porosity and the pore density enhances the phenomenon of non-local thermal equilibrium. The temperature difference increases with the decrease of Reynolds number and the distance away from the heat source.
Numerical Study on Substrate Remelting, Flow, and Resolidification in Microcasting
Authors: Hong F. J. , Qiu H.-H.
Published: March 2009

A large and highly superheated molten droplet impacting onto the substrate during the microcasting was studied numerically. In this study, same material for both the droplet and the substrate was considered. Numerical model including the complex fluid dynamics of droplet, interfacial thermal contact resistance, and substrate remelting, as well as the flow in the substrate has been developed. Numerical simulations of a microcasting experiment were conducted with the different thermal contact resistances. The results of simulations show that the spreading factor and substrate remelting agreed well with the experimental data under the assumption of an appropriate thermal contact resistance. It is also found that the thermal contact resistance plays an important role not only in droplet spreading arrest but also in the determination of substrate remelting volume and remelting front shape. The effects of droplet impacting velocity, superheat and substrate temperature were also investigated.
Detailed Performance Analysis of a Solid Oxide Fuel Cell: Micro Gas Turbine Hybrid Power System
Authors: Song Tae Won , Sohn Jeong L. , Kim Jae Hwan , Kim Tong Seop , Ro Sung Tack , Suzuki Kenjiro
Published: March 2009

Performance of a solid oxide fuel cell (SOFC) can be enhanced by converting thermal energy of its high temperature exhaust gas to mechanical power using a micro gas turbine (MGT). A MGT plays also an important role to pressurize and warm up inlet gas streams of the SOFC. Performance behavior of the SOFC is sensitively influenced by internal constructions of the SOFC and related to design and operating parameters. In case of the SOFC/MGT hybrid power system, internal constructions of the SOFC influence not only on the performance of the SOFC but also on the whole hybrid system. In this study, influence of performance characteristics of the tubular SOFC and its internal reformer on the hybrid power system is discussed. For this purpose, detailed heat and mass transfer with reforming and electrochemical reactions in the SOFC are mathematically modeled and their results are reflected to the performance analysis. Effects of different internal constructions of the SOFC system and design parameters such as current density, recirculation ratio, fuel utilization factor, and catalyst density in internal reformer on the system performance are investigated and, as a result, some guidelines for the choice of those parameters for optimum operations of the SOFC/MGT hybrid power system are discussed.
Separation of Natural Convection and Radiation by Changing Rotational Acceleration
Authors: Willockx Arnout , De Mey Gilbert , De Paepe Michel , Wiecek Boguslaw , Felczak Mariusz , De Craemer Mario , Stouff Arnaud , Van Rumst C.
Published: March 2009

The objective is to separate natural convection and radiation experimentally. Therefore a heat source is placed inside a closed cavity and the acceleration inside the cavity can be changed. A centrifuge is used to change the acceleration. A flat resistor etched on a printed circuit board of 10mm × 48mm, is placed in a hermetically sealed cylinder, which hangs under the arm of the centrifuge. The resistor is powered by a battery, dissipates 0,35W and has a surface temperature of 60°C at 1g. Natural convection is maintained inside the cylinder. Conduction is reduced to a negligible amount by construction of the experiment, thus convection and radiation are the main modes of heat transfer. The rotational speed of the centrifuge determines the centrifugal force in the cylinder. When the centripetal force increases, the temperature of the resistor decreases due to the increase of natural convection. The amount of radiation and total heat transfer can be determined from the experiment, so the amount of natural convection can also be determined. The experimental results are compared with the governing equations to validate the experiment. The reproducibility of the experiment is also checked.
Experimental Investigation of the Tip Clearance Flow for an Axial Flow Fan Rotor Using a PIV System
Authors: Zhu Xiaocheng , Lin Wanlai , Du Zhaohui
Published: March 2009

The flow field in the tip region of an axial ventilation fan is investigated with a PIV (Particle Image Velocimeter) system at the design condition. Characteristics of a ventilation fan are an extreme low-pressure difference and a large tip clearance with a low rotating speed. Flow fields with three different tip clearances are surveyed on three different circumferential planes, respectively. The phase-locked average method is used to investigate the generation and the development of a tip leakage vortex. The result from PIV system is compared with that from a PDA (Particle Dynamics Anemometer) system. Both data are in good agreement. The structure of the tip leakage vortex for the rotor is illustrated. The characteristic of a leakage vortex is described in both velocity vectors and vortical contours. It is found that the tip leakage flow for a low speed and a low pressure ventilation fan also has a chance to roll up into a discrete vortex at three different tip clearances, which is similar to high speed and high-pressure compressors and turbines. When the tip clearance increases, the scope and the location variation for the tip leakage vortex increase. Finally, the trajectories of the tip leakage vortex by the experimental measurement are compared with predictions from the existing models for high speed and high-pressure compressors and turbines. A good agreement is obtained.
Performance Studies on a Compressor Stage With Uncambered Constant Thickness Low Solidity Diffuser Vanes
Authors: Ramana Murty G. V. , Siva Reddy T. Ch. , Prasad M. V. S. S. S. M. , Rama Raju G.
Published: March 2009

The results of experimental studies on a centrifugal compressor stage using uncambered constant thickness low solidity diffuser vanes (LSD) are reported in this paper. In the present work, efforts are concentrated for study of stage performance with LSD vanes for a typical compressor stage at a tip mach number of 0.35. The effect of solidity and setting angle on overall stage performance is evaluated in terms of flow coefficient, head coefficient and efficiency. The results were normalised with the data available at design flow using vaneless diffuser. Improvement in performance as well as static pressure recovery was observed with LSD vanes of the chosen configuration as compared to vaneless diffuser configuration. Variation of blade loading is studied from the measurements of static pressure on pressure and suction surfaces of LSD vane.
Local Thermal Non-Equilibrium Effect in Forced Convection of Non-Newtonian Fluids Through Porous Media
Authors: Khashan S. A.
Published: March 2009

In this paper, we examine the effect of local thermal non-equilibrium LTNE condition on the non-Newtonian forced convection flow through channels filled with porous media. Four representative dimensionless parameters are used in formulating the problem. Numerical solutions obtained over broad ranges of these parameters are utilized to map conditions at which local thermal non-equilibrium condition is important, occurrence of LTNE is found to be driven by higher modified Peclet number, lower modified Biot number, lower fluid-to-solid thermal conductivity ratio, lower power-law fluid index, and lower microscopic and macroscopic frictional flow resistance coefficients. The proportional effect of each parameter as related to others is investigated.
Computational Fluid Dynamics Simulation of Fire-Induced Air Flow in a Large Space Building: Key Points to Note
Authors: Li Y. F. , Chow W. K.
Published: March 2009

Fire-induced air flow in a large span building by computational fluid dynamics (CFD) will be discussed in this paper. The CFD model is based on Reynolds Averaging Navier-Stokes (RANS) equations with k-ε based turbulence model for predicting velocity, pressure and temperature distribution. This technique is commonly used in practical design for smoke management system. The fire is taken as a volumetric heat source and buoyancy effects are included in equations for the vertical momentum and turbulent parameters. Several key points to note in the simulation will be discussed. These are: • Relaxation factor and convergence criteria. • False diffusion. • Sudden changes in flow parameters across the heat source. A large terminal hall with 1 MW fire is taken as an example to discuss the above points. The fire scenarios in a region of interest will be assessed by CFD.
Automated Geometric Optimization of Turbulent Airflow in Ducts Using Genetic Algorithms
Authors: Sinclair Jarrod , Seeling Christoph , Kajtaz Mladenko , Dibb Stephen
Published: March 2009

Many industrial, automotive and aerospace systems generate power from fluid flows. A common challenge in designing such components is the routing of flow within a duct or pipe geometry. However, routing is often considered secondary to the design of main components and therefore subject to compromises. Further, optimal routing designs are difficult to achieve within these constraints using current engineering tools, and are often a manual process involving computer aided design (CAD) and computer aided engineering (CAE) packages. An automated tool is therefore required for the design and optimization of flow ducts and pipes in both the conceptual design and engineering phases. In this work, a fully automated tool chain is developed for the design and optimization of fluid routing based on minimal pressure drop. The tool, built in C++, utilizes the ACIS geometry modeling engine and interfaces with Gambit for unstructured grid generation. A steady-state flow analysis is performed using incompressible turbulent flow via the Fluent computational fluid dynamics (CFD) package. Optimization is controlled by the GAlib library of genetic algorithms (GA) which have been adapted to interface with the numerical description of the geometry. This paper outlines the process undertaken by the tool chain to reach an optimal pipe design, given the boundary sizes and positions in space, as well as constraints on the system. Specific case studies are presented for smooth pipe turbulent airflow. The case studies focus on using splines to define and parameterize the geometry. The resulting optimal duct geometries are verified with structured and grid independence analysis methods. Finally, the paper discusses wider applications of the developed tool chain to more complex routing fluid flow problems, and non-routing based applications.
Convection in a Porous Circular Cavity
Authors: Mansour Kamyar
Published: March 2009

This investigation in a porous circular cavity driven by heating in the horizontal direction is analyzed by a self-consistence boundary layer theory. We use Darcy’s law for this cavity filled with porous material. The solution is governed by dimensionless parameter Darcy-Rayleigh number. There are a lot of ways to approach boundary layer limit see Mansour [1]. Our model is based on the fact that the convective flow of fluid driven by buoyancy is carried entirely by the cross-flow in the core. In other words, we assume a thermally stratified core. This model is based on analyses of a rectangular cavity containing a viscous fluid (Gill [2]) carried over to porous material (Weber [3], Walker et al [4]). The global heat flux, the Nusselt number, is found asymptotically as the 1/2 power of Darcy-Rayleigh number, which is in consistence with other Results.
Numerical Simulation of Iridectomy for Surgical Treatment of Glaucoma
Authors: Kumar Satish , Acharya Sumanta
Published: March 2009

Pupillary block can lead to a convex bowing of the iris surface due to the increased posterior chamber pressures, and this, in turn, can partially block the outflow pathway through the Trabecular Meshwork (TM). This condition leads to Angle-closure glaucoma by elevating the Intraocular Pressure (IOP) of the eye to very high levels. To alleviate this condition, a surgical process called iridectomy can be performed to create an opening on the iris surface that enables an alternate route for the flow from the posterior chamber to the anterior chamber. This, in turn, reduces the elevated pressure in the eye. In the present work, flow simulations are performed in a three-dimensional model of the human eye, with reduced irido-lenticular gap and partial-blockage of the TM, to model the flow and pressure distribution associated with pupillary block and angle-closure glaucoma. Iridectomy is simulated by creating holes on the iris surface at different locations. The effect of angular locations of the iridectomy holes on the pressure and flow distributions are analyzed.
Nutrient Transport Within a Tissue Engineered Liver System
Authors: Coger Robin N. , Gudi Sravan , Niu Mei
Published: March 2009

For bioartificial organ devices containing cells packed at high density, establishing suitable nutrient transport pathways is an important engineering challenge. In the case of a tissue engineered liver densely packed with entrapped hepatocytes, the limited transport distance of the nutrient oxygen, restricts the dimensions of the device’s cellular space. This study focuses on improving the functional performance of such devices by enabling enhanced oxygen transport. This enhanced O2 transport is achieved using a technique we developed for increasing the porosity of extracellular matrix (ECM) [1–3]. By combining computational and experimental approaches, the results predict and test the effectiveness of our technique in improving nutrient (e.g., oxygen) flow and cell performance within densely packed liver tissue engineering systems.
Thermal Convection and Dispersion in Folded Gaps Embedded in Impervious Rocks
Authors: Sa´nchez F. , Medina A. , Montan˜es J. L.
Published: March 2009

It is presented a numerical and experimental study related to thermal convection and Taylor dispersion in a symmetrical folded gap of small aspect ratio. The gap is surrounded by an impervious rock which is affected by a constant vertical temperature gradient. Two cases were analyzed, the fluid-filled gap and the fluid-saturated porous layer. Their corresponding convective flows were calculated for small Rayleigh number regimes. Taylor dispersion of a passive contaminant, in both cases, was studied. It was found that dispersion is strongly limited by the convective flows. Indeed, the Peclet number and the gap aspect ratio seem to be tight related to an eventually limited dispersive transport rate.
Thermal Convection in Tilted Cylindrical Cavities Embedded in Rocks
Authors: Sa´nchez F. , Medina A. , Higuera F. J.
Published: March 2009

We present a theoretical and experimental study of the thermal convection in a fluid-filled, tilted cylindrical cavity and in a fluid-saturated porous medium filling a cylindrical cavity embedded in a solid slab (solid rock) which has a constant vertical temperature gradient far from the cavity. Closed-form, analytical solutions are obtained for the temperature field in the solid and for the velocity, temperature and pressure within the cavity.