bluuebunny/crossref_metadata_2025 huggingface dataset:
Mathematical Model to Describe Thermal Behavior of Phase Change Materials Contained in a Cylindrical Enclosure
Authors: ElGafy Ahmed , Mesalhy Osama , Lafdi Khalid , Bowman K.
Published: December 2008

Heat transfer processes undergoing liquid-solid phase transformation have been of continuing interest for many researchers. Phase Change Materials, (PCMs); have received great consideration in electronic industry for cooling of electronics and in telecommunication equipment to control internal temperature under emergency operating conditions. High melting temperature materials have been proposed as thermal energy storage mediums in space applications because of their high melting temperatures and latent heat. In the present work, a numerical simulation is developed to predict the thermal performance of a phase change material of high melting point in a cylindrical enclosure. In this simulation the phases are assumed to be homogeneous and a source term, S, arises from melting and solidification processes is considered as a function of the latent heat of fusion and the liquid phase fraction. By introducing the thermo-physical properties of one of those materials, the thermal performance of it as a phase change material is predicted.
Heat Transfer and Drag Reduction in Flows Over Riblet Mounted Surfaces
Authors: aus der Wiesche Stefan
Published: December 2008

The heat transfer in a channel with its lower wall mounted with streamwise V-shaped riblets is investigated numerically using a LES approach. Both laminar and turbulent flows are considered. At the riblet wall the turbulent drag is reduced by 6% in comparison to the smooth wall, whereas for laminar flow the riblets lead to a significant drag increase. The effect of riblets on heat transfer is investigated explicitly for small Prandtl numbers Pr and an appropriate correlation is derived. This correlation indicates that the Reynolds analogy is not violated in case of Pr = 1 despite the extraordinary turbulent drag reducing mechanism. The numerical results for drag reduction are in good agreement with available experimental and numerical data, and the results are faced with corresponding heat transfer results found in the literature.
Droplet Impingement Cooling for Electronics Using Silicon Nozzles
Authors: Wu Chi-fu , Yao S. C.
Published: December 2008

This paper examines the performance of a silicon nozzle on the droplet impingement cooling of a simulated electronic chip with a dielectric coolant. A silicon nozzle plate with 49 orifices on a 1 inch square area is bonded with swirl chips. A compact test beds with embedded cartridge heaters and thermocouples at specified locations, is built and integrated with a condenser to test the cooling performance at a given heat flux. Through the system testing, the importance of vapor/excess-liquid exits, orientation due to gravity, and the temperature control of recirculating liquid are revealed. The use of Swiss-roll micronozzles have provided up to 45 W/cm2 uniform heat removal at 23 cc/min cm2 liquid flux.
Investigation on Thermal Loading of Disc Brakes: An Approach
Authors: Jancirani J. , Chandrasekaran S. , Tamilporai P.
Published: December 2008

In the wide range of braking speed, the disc brakes are subjected to temperature variation and thermal loading. Different modelling approaches ranging from a simple lumped parameter model to complex three-dimensional models are available for the thermal analysis of the disc brakes. Based on the review of the above models, a model has been developed and formulated for the analysis of thermal loading of disc brake. The developed model is proposed to couple with a model for the thermal distortion of disc brake. It is also proposed to conduct the necessary experiments and thermal analysis to validate the results obtained from the synthesized analysis.
Development of a Gravity-Assist Water Loop Heat Pipe With Flat Evaporator for Waste Heat Removal
Authors: Hoang Triem T. , O’Connell Tamara A. , Conroy C. Thomas , Mahorter Robert G. , Savchik John A. , Rosenfeld John
Published: December 2008

Use of capillary pumped heat transport devices such as heat pipes, Capillary Pumped Loops (CPLs), and Loop Heat Pipes (LHPs) are being considered for cooling of shipboard electronics. These capillary devices contain no mechanical moving parts to wear out, require no electrical power to operate, and demand virtually no maintenance. Heat pipes have been the mainstay of spacecraft thermal control systems over the past 30 years. However with limited pumping heads, heat pipes were utilized only in a few terrestrial applications. Successful demonstration of much higher pumping capability of CPLs and LHPs in recent years now makes them feasible for ground-based heat transport systems. Fluid management in a gravity environment is also much easier that the traditional design of a CPL/LHP does not really apply to terrestrial systems. In addition, a gravitational pressure head generated by a vertical distance between the condenser and evaporator can assist the capillary pumping to augment the overall pumping capability of the loop. Thus, when properly designed, a gravity-assist CPL/LHP can transport a large amount of waste heat over a long distance for dissipation.
Single Passive Condenser Failure During a Large-Break LOCA in the SBWR-1200 Reactor
Authors: Revankar S. T. , Ishii M. , Xu Y. , Yoon H. J. , Cheng L.
Published: December 2008

The performance of the safety systems of a new design of the 1200-MWe simplified boiling water reactor during a large-break, loss-of-coolant accident transient was investigated when one of three passive condenser system failed. The accident considered was a break in the main steam line which is the major design basis accident. The integral test was performed to assess the safety systems and the response of the emergency core cooling systems to accident conditions in a scaled facility called PUMA. The loss of single condenser system did not affect the LOCA transient indicating that the existing safety system will adequately handle the large break LOCA with single condenser failure. The details of the safety system behavior are presented.
Thermal Performance of Triangular Folded Fin Heat Sinks in a Duct
Authors: Kim Seo Young , Ji Taeho , Choi Dong Gyu , Kang Byung Ha
Published: December 2008

Experiments have been carried out to investigate the convective heat transfer characteristics from triangular folded fin heat sinks in a suction-type fan duct. The dimension of the triangular folded fin heat sinks is 62 mm in height with a 12 mm thick base plate, 292 mm in width, and 447 mm in length. The inlet flow velocity is varied in the range of 0.6–5.3 m/s. Thermal performance of triangular folded fin heat sinks is evaluated in terms of thermal resistance of heat sinks according to flow velocity and fan power. The results obtained show that the present triangular folded-fin heat sink shows a higher thermal performance compared to a conventional extruded plate-fin heat sink. Especially, a perforated slit folded-fin heat sink displays a lower thermal resistance. As the number of slit fabricated on the perforated folded fins increases, thermal performance is more pronounced.
An Experimental Investigation of the Thermal Interaction of Electro-Optical Components on a Printed Circuit Board in Natural and Forced Convection
Authors: Fleischer Amy S. , Weinstein Randy D.
Published: December 2008

The thermal interaction of an electrical and an optical component located on the same vertical circuit board is studied experimentally. The effects of component proximity and convective flow rate on overall power dissipation from each component are analyzed. The components are represented by isothermal heat sources mounted to a standard 1.59mm (0.0625 in) thick FR4 circuit board. In natural convection situations, when the spacing between components is great enough that the component thermal footprints do not interfere, the power dissipation reaches a maximum “plateau” value that is independent of spacing. If the components are located close enough together that their thermal footprints interfere then the total power dissipation is highly dependent on component spacing (relative location of the electrical source and the geometric positioning of both sources). In forced convection, the total power dissipated increases with both Reynolds number and component spacing. As in natural convection, the relative location of the electrical sources and the positioning of the sources are found to have a strong influence on power dissipation.
A Study of Non-Equilibrium Heat Transfer in Microporous Media
Authors: Nnanna A. G. Agwu
Published: December 2008

A numerical study of the non-Fourier heat conduction in microporous media is presented. The governing energy equation is formulated based on the two-equation model and the non-Fourier heat conduction model. This formulation leads to the emergence of three thermal lag-times. These parameters account for the thermal interaction between the fluid and neighboring solid matrix as well as the delay time needed for both phases to approach thermal equilibrium. Numerical experiments were conducted for various microporous media to study the thermal non-equilibrium behavior. Results show that the thermal non-equilibrium phenomena have significant effect on the transient response of the porous media only during the early stage of the heating process and in the near-field region where the heat source is located. The thermal responses of the various microporous media were compared to gain understanding of the effect of thermal diffusivity on thermodynamic non-equilibrium phenomena. It was found that the influence of thermal diffusivity is small especially in the near-field (96–200μm). Also, results obtained using the non-Fourier heat conduction model deviates from the predictions based on the classical Fourier model only during the early stage of the heating process. At large time, results obtained from both models are in good agreement.
An On-Line Model to Calculate the Strip Temperature at Run-Out Table of Tisco’s Hot Strip Mill
Authors: Mukhopadhyay A. , Sikdar S. , Sen S.
Published: December 2008

A Mathematical model has been developed to predict the temperature profile of the strip during water-cooling on the Run-out Table (ROT) of the Hot Strip Mill (HSM). This work describes the development and implementation of the model at Tisco’s HSM. The model has been developed using Explicit Finite Difference technique to predict the coiling temperature (CT). The model has been implemented successfully after having been validated with the actual coiling temperature (CT) for several thousand coils. A number of grades of steel with various thicknesses have been tested with this on-line model and the agreement of actual CT with the predicted ones was found very good. The on-line model is used to calculate the cooling rates at different segments of the strip that are used to obtain microstructure and mechanical properties.
Comparison of Predictive and Experimental Data From Graphite Irradiations in the Advanced Test Reactor Irradiation Test Vehicle
Authors: Ambrosek Richard G. , Utterbeck Debbie J.
Published: December 2008

In 2000, British Nuclear Fuels Limited (BNFL) commissioned an irradiation program at the United States Department of Energy’s Idaho National Engineering and Environmental Laboratory (INEEL) to assess the effects of extended operating scenarios upon the integrity of Magnox reactor cores. In this program, predictions of thermal and physical effects on these graphite cores were developed using analytical computer models. To benchmark results, experimental graphite assemblies representative of the Magnox graphite were irradiated in the Advanced Test Reactor (ATR). This paper analyzes and contrasts the thermal predictions with those experimental results. These investigations were conducted to extend existing graphite physical property databases for higher radiolytic weight loss (35–50% density reduction) than occur during the economic planning life of these reactors. These data then can be used to make extended life projections regarding the suitable function of the graphite in its various roles of providing the physical structure for the fuel, neutron moderator, medium for instrumentation, and coolant channels. Extended irradiation effects will be obtained with samples of archived, pre-characterized graphite used in the Magnox type reactors. The new Irradiation Test Vehicle (ITV) facility in the ATR contained the experiments and provided the desired irradiation conditions as well as on-line temperature control. The capability to provide both oxidizing and inert gas atmospheres for the graphite specimens was added to the ITV to enable assessment of the individual and combined effects of oxidation and neutron damage to the specimens. In this paper the thermal evaluations (performed to size the control gaps to obtain the desired thermal performance) are contrasted to actual experimental results.
Heat Transfer Model for an RF Cold Crucible Induction Heated Melter
Authors: Hawkes Grant , Richardson John , Gombert Dirk , Morrison John
Published: December 2008

A method to reduce radioactive waste volume that includes melting glass in a cold crucible radio frequency induction heated melter has been investigated numerically. The purpose of the study is to correlate the numerical investigation with an experimental apparatus that melts glass in the above mentioned melter. A model has been created that couples the magnetic vector potential (real and imaginary) to a transient startup of the melting process. This magnetic field is coupled to the mass, momentum, and energy equations that vary with time and position as the melt grows. The coupling occurs with the electrical conductivity of the glass as it rises above the melt temperature of the glass and heat is generated. Natural convection within the molten glass helps determine the shape of the melt as it progresses in time. An electromagnetic force is also implemented that is dependent on the electrical properties and frequency of the coil. This study shows the progression of the melt shape with time along with temperatures, power input, velocites, and magnetic vector potential. A power controller is implemented that controls the primary coil current so that the power induced in the melt does not exceed 60 kW. The coupling with the 60 kW generator occurs with the impedance of the melt as it progresses and changes with time. With a current source of 70 Amps (rms) in the primary coil and a frequency of 2.6 MHz, the time to melt the glass takes 0.8 hours for a crucible that is 10 inches in diameter and 10 inches high.
Mathematic and Statistic Method for Analysis of Heat Transfer in Regenerative Heat Exchanger of Packed Bed
Authors: Li Chaoxiang , Lu Zhongwu , Cai Jiuju
Published: December 2008

The partial differential equation of heat transfer of a packed bed was solved with Lapalace’s translation, and the Characteristic number of the temperature distribution function were obtained from the mathematic and statistic analysis. The temperature distributing function of the packed bed was derived from using the Hermite’s Polynomials, and characteristic number of the temperature distribution related to the thermal parameters were expressed by simple algebraic equations.
A Physical Model of the Molecular-Quantum Natural Convection Heat Transfer Mechanism
Authors: Soare G.
Published: December 2008

In this work a physical model of the natural convection heat transfer mechanism, molecular-quantum in nature, is proposed. On the surface of the solid there are a lot of chemical defects (atoms of different chemical elements) and geometrical ones (steps, kinks, terraces, dislocations) at microscopic and nanoscopic scale. All these defects make the surface of the wall to be not an equipotential surface. On the other hand, the existence of a gradient of temperature in a metal wall, which is involved in a heat transfer process, generates a gradient of conduction electrons. On the cool face of the wall there are more electrons as a result of Pe´ltier-Thomson effect. Because of surface’s defects the electrons are not uniformly distributed, on a high defect there are more electrons than on a depth defect and the electrical field is more intense on the high defect. The molecules of the fluid are adsorbed on the surface, and become polar molecules, as a result of the polarization by influence. The absorbed molecules form a multilayer in which take place more elementary processes, molecular-quantum in nature. These elementary processes are: the overlap between the electronic orbital of the solid and fluid, electron clouds perturbation, solid-fluid electron exchange by quantum tunneling effect, the motion under action of the Helmann-Feynman force between adsorbed molecules and a high defect of the wall, the absorption of the phonons from the surface’s atoms and rejection of the molecules from the surface. In this way natural convection is generated. The proposed model needs directly experimental confirmation.
An Integrated Model for Czochralski Melt Growth of Optical Crystals
Authors: Song S. P. , Li B. Q. , Lynn K. G.
Published: December 2008

This article presents the phenomena of melt flow, heat transfer, and solidification in Czochralski (CZ) melt growth processes of optical crystals, with emphasis on the effect of internal radiative heat transfer on the temperature distributions in oxide melt and crystal, melt convection, and melt-crystal interface shape. An integrated numerical model has been developed for simulating the physical phenomena in generic CZ furnaces, which includes the models for electromagnetic induction in crucible, surface exchange radiation in furnace, internal radiation in semi-transparent oxide melt and crystal, Marangoni convection in the melt, and solidification. Each developed model compares well with available analytical solutions. Numerical simulations were carried out for the prediction of fluid flow and heat transfer in furnaces. The simulation results show that the variation in optical properties of melt and crystal strongly impact their temperature distributions. It also affects the melt flow profile and intensity. The interface shape becomes more deeply convex toward the melt, as the optical thickness of the melt increases. However, the optical thickness of the crystal exhibits a minor impact on the interface shape. The results also show that the natural convection is dominated in the melt and the Marangoni flow enforces the natural convection.
A Universal Simulation Model of Air-Cooled Condenser Consisting of Plate-Fin-Tube
Authors: Shao Shuangquan , Li Xianting , Shi Wenxing , Yan Qisen
Published: December 2008

Air-cooled condenser used for refrigeration and heat pump applications generally consists of plate-fin-tubes. A universal simulation model has been developed for simulation of plate-fin-tube condenser with distributed-parameter method. The model discretizes coil into circuit to circuit, tube to tube and then node to node along the refrigerant path and carries out repetitive marches from the refrigerant inlet to its outlet while simultaneously updating the values of the air stream properties for obtaining quick convergence. Unlike previous models, this model is capable of analyzing complicated circuiting arrangements and can take into count the variation in heat transfer coefficient and pressure drop coefficient along the tube. Especially, the coefficient of heat transfer and pressure drop of two-phase refrigerant strongly influences each other, so the pressure balance among parallel refrigerant circuits is carried out by adjusting the mass flow rate of refrigerant in each circuit. The distinguishing feature of this model is that it performs a node-to-node discretized analysis of the condenser along each circuit, making fewer assumption about the nature of heat transfer and pressure drop than traditional models. The model has been validated against experimental data on such coils available in the literature. It is not only helpful for optimal design of air-cooled condenser with any kind of complex circuiting arrangement, but also can act as a main part of the simulation model of refrigeration and heat pump systems.
Nucleate Boiling From Micro-Machined Surfaces
Authors: Holland Adrian M. , Garner Colin P.
Published: December 2008

This paper discusses the production and use of laser-machined surfaces that provide enhanced nucleate boiling and heat transfer characteristics. The surface features of heated plates are known to have a significant effect on nucleate boiling heat transfer and bubble growth dynamics. Nucleate boiling starts from discrete bubbles that form on surface imperfections, such as cavities or scratches. The gas or vapours trapped in these imperfections serve as nuclei for the bubbles. After inception, the bubbles grow to a certain size and depart from the surface. In this work, special heated surfaces were manufactured by laser machining cavities into polished aluminium plates. This was accomplished with a Nd:YAG laser system, which allowed drilling of cavities of a known diameter. The size range of cavities was 20 to 250 micrometers. The resulting nucleate pool boiling was analysed using a novel high-speed imaging system comprising an infrared laser and high resolution CCD camera. This system was operated up to a 2 kHz frame rate and digital image processing allowed bubbles to be analysed statistically in terms of departure diameter, departure frequency, growth rate, shape and velocity. Data was obtained for heat fluxes up to 60 kW.m−2. Bubble measurements were obtained working with water at atmospheric pressure. The surface cavity diameters were selected to control the temperature at which vapour bubbles started to grow on the surface. The selected size and spacing of the cavities was also explored to provide optimal heat transfer.
Transient Pool Boiling Under Self Pressurized Systems
Authors: ElGafy Ahmed , Lafdi Khalid
Published: December 2008

An experimental investigation of the transient pool boiling under self-pressurized systems is presented in this work. A vertical cylindrical heating surface of known surface roughness is used. Test runs are carried out on a closed vessel to attain self-pressurized system while water is utilized as the working fluid. Two glass windows are opened in the test vessel to observe the phenomenon. The increasing pressure and the consequent variable difference between the mean heating surface temperature and the saturation temperature corresponding to the system pressure are measured during each of the test runs. The runs cover an input heat flux from (40 × 103 to 80 × 103 W/m2) over a pressure range from the atmospheric to 5.5 bars. For transient conditions, an empirical correlation to relate the heat transfer coefficient to both heat flux and pressure is obtained. Also, a comparative study is performed between the present work and a previous work under steady state atmospheric conditions.
Three-Dimensional Measurement of Aerosol Particle Clustering in Homogeneous Isotropic Turbulence
Authors: Cao Lujie , Pan Gang , Meng Hui
Published: December 2008

Due to the inertial mismatch between dense particles and lighter surrounding gas, aerosol particles in the size range 1 to 10 μm cluster in a flow field. This phenomenon, sometimes referred to as preferential concentration, can increase the particle coagulation rate by as much as two orders of magnitude. Many direct numerical simulation (DNS) studies have been conducted to study preferential concentration and various theoretical models have been proposed to predict the effect of clustering on particle collision rate. However, to date there is very little experimental data available to validate DNS results and theoretical models. In this study, we apply our state-of-the-art holographic imaging system to measure the 3D position of particles in a turbulence chamber. Nearly homogenous isotropic turbulence is generated in the center of the chamber by use of eight fans mounted in the corners. With our holographic imaging system, individual particles can be measured simultaneously and hence we are able to calculate particle radial distribution function (RDF), a statistical measure of particle clustering and a key variable in collision kernel. In this paper we report the first experimental 3D RDF to date. Comparison between our 3D RDF and 2D RDF results shows that significant bias exists in experimental results obtained using 2D experimental techniques.
Modeling and Preliminary Validation of a Regenerative Furnace Using the ANL Glass Furnace Model
Authors: Golchert Brian M. , Chang Shen-Lin , Olson Ed
Published: December 2008

The ANL Glass Furnace Model (GFM) was developed for steady state simulation of industrial glass furnaces. Unfortunately, a large fraction of the operating glass furnaces do not operate in a steady state mode and computational costs make it prohibitive to run the simulations in a transient mode. A solution methodology was developed to model these transient furnaces in steady state mode. This solution methodology was used to model a small, industrial furnace on which a relatively comprehensive set of data was taken. This paper presents the solution methodology in detail along with some of the qualitative validation results indicating the validity of the modeling approximation.
Laser-Induced Chemical Vapor Deposition on Moving Glass Rods
Authors: Kwok King Hong , Chiu Wilson K. S.
Published: December 2008

The feasibility of using pyrolytic Laser-Induced Chemical Vapor Deposition (LCVD) to deposit carbon coatings on moving fused quartz rods have been investigated in this study. This LCVD system uses a CO2 laser to locally heat substrates in open air to create a hot spot. Pyrolysis of hydrocarbon species occurs and subsequently deposits a layer of carbon film onto the substrate surface. The results of this study indicate that the deposition rate of carbon film increases exponentially within the range of laser power, while an increase in traverse velocity of the substrate will also increase the deposition rate until a maximum deposition rate is reached, and further increases in the traverse velocity will decrease the deposition rate. We suspect that this optimal deposition rate is caused by substrate motion, which affects the substrate surface temperature, and consequently the effective surface area available for film deposition.
A Fast Multi-Level Boundary Element Method for the Steady Heat Diffusion Equation
Authors: Grigoriev M. M. , Dargush G. F.
Published: December 2008

A fast, accurate and efficient multi-level boundary element method is developed to solve general boundary value problems. Here we concentrate on problems of two-dimensional steady potential flow and present a fast direct boundary element formulation. This novel method extends the pioneering work of Brandt and Lubrecht on multi-level multi-integration (MLMI) in several important ways to address problems with mixed boundary conditions. We utilize bi-conjugate gradient methods (BCGM) and implement the MLMI approach for fast matrix and matrix transpose multiplication for every iteration loop. Furthermore, by introducing a C-cycle multigrid algorithm, we find that the number of iterations for the bi-conjugate gradient methods is independent of the boundary element mesh discretization for problems of steady-state heat diffusion considered in this paper. As a result, the computational complexity of the proposed method is proportional to only N · log(N), where N is the number of degrees of freedom.
Liquid Entrainment at Tee Junction With Upward Oriented Vertical Branch
Authors: Wu Q. , Reyes J. N. , Welter K. B. , Bajorek S. M. , Han J.
Published: December 2008

Investigation on liquid entrainment in tee junctions with an upward oriented vertical branch was conducted. Existing correlations and test data were identified for evaluation and comparison. Theoretical analysis was carried out for the development of a new entrainment onset criterion and an entrainment rate model. Comparisons were performed with all available data with different test conditions, and the results indicated that the new correlations demonstrated a marked improvement.
Efficient Boundary Element Methods for the Time-Dependent Convective Diffusion Equation
Authors: Dargush G. F. , Grigoriev M. M.
Published: December 2008

Higher-order boundary element methods (BEM) are presented for time-dependent convective diffusion in two dimensions. The time-dependent convective diffusion free-space fundamental solutions originally proposed by Carslaw and Jaeger are used to obtain the boundary integral formulation. Boundary element method solutions up to the Peclet number 106 are obtained for an example problem of unsteady convection-diffusion that possesses an exact solution. We investigate the convergence rate and accuracy of the higher-order boundary element formulations. An extremely high accuracy of the BEM solutions for highly convective flows is demonstrated. Moreover, it is shown that the use of time-dependent convective kernels provides an automatic upwinding for the entire range of Peclet numbers and also leads to very efficient algorithms as the Peclet number increases.
Transient Radiative Transfer of Light Pulse Propagation in Three-Dimensional Scattering Media With Finite Volume Method and Integral Equation Model
Authors: Lu Xiaodong , Hsu Pei-Feng , Chai John C.
Published: December 2008

The transient radiative transfer process is studied with a finite volume method (FVM) and an integral equation (IE) model. Propagation of a short light pulse in the three-dimensional absorbing and isotropic scattering media is considered. Collimated irradiation enters at one side of the rectangular medium. The other five boundaries are cold and black, nonparticipating surfaces. The spatial and temporal distributions of the integrated intensity and radiative flux are obtained.
Three Boiling Instability Modes in Silicon Microchannels
Authors: Wu H. Y. , Cheng Ping
Published: December 2008

Depending on the heat flux, mass flux, and subcooling of inlet water, three boiling instability modes in silicon microchannels are possible. These are: the LTAF (Liquid/Two-phase Alternating Flow) mode, the CTF (Continuous Two-phase Flow) mode, and the LTVAF (Liquid/Two-phase/Vapor Alternating Flow) mode. It is found that the LTAF mode occurs at low heat flux and high mass flux, and has medium-amplitude temperature and pressure oscillations. The CTF mode appears at the medium heat flux and medium mass flux, and has small-amplitude temperature and pressure oscillations. The LTVAF mode appears at high heat flux and low mass flux, and has large-amplitude temperature and pressure oscillations. During the two-phase period of the LTAF mode, bubbly flow is found to be the dominant flow pattern. Some peculiar flow patterns are observed during the two-phase period of CTF and LTVAF modes under the experimental conditions.
A Numerical Simulation of Pool Boiling Using CAS Model
Authors: Yang Jing , Guo Liejin , Zhang Ximin
Published: December 2008

This paper presents a new numerical model, called the CAS model, for boiling heat transfer. The CAS model is based on the cellular automata technique that is integrated into the popular—SIMPLER algorithm for CFD problems. In the model, the cellular automata technique deals with the microscopic non-linear dynamic interactions of bubbles while the traditional CFD algorithm is used to determine macroscopic system parameters such as pressure and temperature. The popular SIMPLER algorithm is employed for the CFD treatment. The model is then employed to simulate a pool boiling process. The computational results show that the CAS model can reproduce most of the basic features of boiling and capture the fundamental characteristics of boiling phenomena. The heat transfer coefficient predicted by the CAS model is in excellent agreement with the experimental data and existing empirical correlations.
Computations of Sub-Micron Heat Transport in Silicon Accounting for Phonon Dispersion
Authors: Narumanchi Sreekant V. J. , Murthy Jayathi Y. , Amon Cristina H.
Published: December 2008

In recent years, the Boltzmann transport equation (BTE) has begun to be used for predicting thermal transport in dielectrics and semiconductors at the sub-micron scale. However, most published studies make a gray assumption and do not account for either dispersion or polarization. In this study, we propose a model based on the BTE, accounting for transverse acoustic (TA) and longitudinal acoustic (LA) phonons as well as optical phonons. This model incorporates realistic phonon dispersion curves for silicon. The interactions among the different phonon branches and different phonon frequencies are considered, and the proposed model satisfies energy conservation. Frequency-dependent relaxation times, obtained from perturbation theory, and accounting for phonon interaction rules, are used. In the present study, the BTE is numerically solved using a structured finite volume approach. For a problem involving a film with two boundaries at different temperatures, the numerical results match the analogous exact solutions from radiative transport literature for various acoustic thicknesses. For the same problem, the transient thermal response in the acoustically thick limit matches results from the solution to the parabolic Fourier diffusion equation. Also, in the acoustically thick limit, the bulk experimental value of thermal conductivity of silicon at different temperatures is recovered from the model even at coarse phonon frequency band discretization.
Time-Resolved Thermal Surface Flow Structures in Impinging Slot Jet Flows
Authors: Narayanan V.
Published: December 2008

This paper presents low-frequency time-resolved measurements of impingement surface temperature in a turbulent submerged impinging slot jet flow at an exit Reynolds number of 22,500 using infrared (IR) thermography. The nozzle-to-surface spacing was varied from 0.5 to 5 nozzle hydraulic diameters. Time-traces of temperature at specific locations of interest, identified from mean temperature maps, are presented. At a nozzle spacing of 5 hydraulic diameters corresponding to transitional jet impingement, the time traces of surface temperature show mild, but periodically repeating hot and cold streaks, suggesting the presence of near-wall streamwise counter-rotating vortex pairs along the impingement line. At a closer nozzle spacing of 0.5 hydraulic diameter corresponding to impingement of the jet potential core, the temperature streaks at the impingement line could not be detected. Previously unreported distinct thermal streaks are observed at locations corresponding to the local minimum and secondary maximum in heat transfer. Data of rms-averaged temperature fluctuations for the two spacings corroborate well with time trace observations.
Determination of Surface Heating Condition for a Desired Thermal Growth Environment in an Industry-Size Hydrothermal Autoclave
Authors: Li Hongmin , Evans Edward A. , Wang G.-X.
Published: December 2008

Hydrothermal growth is the most common technique to grow piezoelectric single crystals such as quartz. Due to a high-temperature and high-pressure growth condition, hydrothermal autoclaves are designed to operate as a closed system. During operation, the only control mechanism that crystal growers have is adjusting the power input of the heaters, based on the temperature readings obtained by the thermocouples along the centerline inside the autoclaves. The power adjusting process, however, is purely experience dependent, and, normally, uniform heating conditions from electric heaters are employed along the autoclave wall. This study develops an inverse algorithm, with which the required heat flux distributions from the heaters can be obtained for a desired growth environment inside an autoclave. The algorithm involves solving three sub-models step by step. The first step is to solve a two-dimensional axisymmetric model of solution in the autoclave to obtain the temperature and heat flux on the solution/wall interface. Using these temperature and heat flux conditions as thermal boundary conditions, the second step solves an inverse heat conduction problem in the metal wall. The solution provides the heat flux and temperature on the outer surface of the metal wall. The final step is to solve a heat conduction problem in the insulation layer to obtain the heat flux on the inner surface of the insulation layer. The heat flux distributions for heaters are then determined by the heat flux on the outer surface of the metal wall and heat flux on the inner surface of the insulation layer. The paper describes the details of each model. As an example, the method is used to find the required heat flux distributions of heaters for the growth environment predicted by a 2-D isothermal wall model. The result is then used to develop a two-patch heater for industry autoclaves.
Thermomechanical Model of Spot Welding for Calculating Residual Stresses
Authors: Xu Lijun , Khan Jamil A.
Published: December 2008

A comprehensive axisymmetric model of the coupled thermal-electrical-mechanical analysis predicting weld nugget development and residual stresses for the resistance spot welding process of Al-alloys is developed. The model estimates the heat generation at the faying surface, the workpiece-electrode interface, and the Joule heating of the workpiece and electrode. The phase change due to melting in the weld pool is considered. The contact area and its pressure distribution at both the faying surface and the electrode-workpiece interface are determined from a coupled thermal-mechanical model using a finite element method. The knowledge of the interface pressure provides accurate prediction of the interfacial heat generation. For the numerical model, temperature dependent thermal, electrical and mechanical properties are used. The proposed model can successfidly calculate the nugget diameter and thickness, and predict the residual stresses and the elastic-plastic deformation history. The calculated nugget shape and the deformation of sheets based on the model are compared with the experimental data. The computed residual stresses approach the distribution of experimental measurement of the residual stress.
Combustion Using High Temperature and Low Oxygen Content Air and Technique Renovation of Traditional Gas-Fired Radiant Heating Tube
Authors: Peng Hao-Yi , Zhou Jie-Min , Jiang Shao-Jian
Published: December 2008

Combustion using high temperature and low oxygen content air is a new technique with many advantages such as larger energy saving and lower NOx pollution. In this new technique, air is preheated over the self-ignition point of the fuel and the volumetric oxygen content in combustion chamber is less than 15%. It can be implemented by utilizing high efficient regenerative heat exchanger and recycling exhaust gas in furnace. In this research, experiments were conducted to investigate the flame characteristics using nitrogen as diluting gas and adopting electric heating element to preheat air. The results show that on the condition of high temperature and low oxygen content air, the volume, the brightness, and the color of flame change significantly, the maximum temperature of flame decreases obviously, and the temperature distribution in furnace becomes uniform. A technique renovation is proposed for traditional radiant heating tube based on this new combustion scheme, and the advantages obtained by this renovation are evaluated. It is found that higher heat efficiency, uniform surface temperature, longer life expectancy, and lower NOx emission and combustion noise can be achieved. The calculation results show that the heat efficiency of radiant-tube can reach 85.3% and save energy up to 21.55% after the renovation. At the same time, the non-uniform coefficient of surface temperature is decreased to 0.02 or less. A small-scale test facility is being built to validate these results.
Atmospheric Pressure DC Plasma Microdischarges: A Characterization Study
Authors: Yi Jeong W. , Yan Fang , Farouk Bakhtier
Published: December 2008

Atmospheric pressure dc plasma microdischarges were generated between a thin cylindrical electrode and a flat surface. The glow discharges were characterized both experimentally and numerically. As the applied voltage is increased, the plasma potential in the plasma microdischarge remains constant while the plasma current increases proportionally. For the types of electrode materials and the range of the electrode diameters considered, the current-voltage characteristics of the plasma microdischarge are almost independent of the electrode material and the diameter of the electrodes. Predictions from a numerical model of the argon microdischarge compare favorably with the experimental measurements and the visualization studies. The atmospheric pressure plasma microdischarge can be used for deposition of thin films and for microfabrication.
CFD Calculation of Internal Natural Convection in the Annulus Between Horizontal Concentric Cylinders
Authors: Webb Stephen W. , Francis Nicholas D. , Itamura Michael T. , James Darryl L.
Published: December 2008

Thermally-induced natural convection heat transfer in the annulus between horizontal concentric cylinders has been studied using the commercial code Fluent. The boundary layers are meshed all the way to the wall because forced convection wall functions are not appropriate. Various oneand two-equation turbulence models have been considered. Overall and local heat transfer rates are compared with existing experimental data.
Numerical Modeling of the Oxidation of Aluminum Alloy
Authors: De Anindya Kanti , Mukhopadhyay Achintya , Sen Swarnendu , Puri Ishwar K.
Published: December 2008

A significant amount of aluminum is processed by melting secondary aluminum that contains small amounts of magnesium. A major drawback of aluminum production in secondary melt furnaces is the formation of dross or aluminum oxide by the oxidation of the molten metal. Since aluminum scrap forms a major source of the metal in secondary aluminum processing, the presence of alloying elements plays a key role in the oxidation process. Here, we consider the early stage during the oxidation of Al-Mg alloys during which the primary oxidation is that of magnesium to magnesium oxide occurs. We have simulated the processes in an aluminum melting furnace and considered the metal oxidation to be limited by one–dimensional diffusion. Our results predict the temporal variation of the oxygen distribution and the rate of metal evaporation and formation of the metal oxide. The effects of melt composition, gas temperature and oxygen concentration in the gas are discussed.
A Multidisciplinary Design and Optimization Methodology in Electronics Packaging: Application to BGA Design
Authors: Hadim Hamid , Suwa Tohru
Published: December 2008

In this manuscript a systematic multidisciplinary electronic packaging design and optimization methodology based on the artificial neural networks technique is presented. This method is applied to a Ball Grid Array (BGA) package design as an example. Multidisciplinary criteria including thermal, structural (thermal strain), electromagnetic leakage, and cost are optimized simultaneously. A simplified routability criterion is also considered as a constraint. The artificial neural networks technique is used for thermal and structural performance predictions. Large calculation time reduction is achieved using the artificial neural networks, which also provide enough information to specify the individual weights for each design discipline within the objective function used for optimization. This methodology is able to provide the designers a clear view of the design trade-offs, which are represented in the objective function using various design parameters. This methodology can be applied to any electronic product design at any packaging level.
Effects of the Dimension of a Localized Heat Source on the Natural Convection in Square Enclosures: Comparison Between Numerical and Experimental Investigation
Authors: Paroncini Massimo , Calcagni Barbara , Marsili Federico
Published: December 2008

The present study investigates experimentally and numerically the natural convection of air in square enclosures with a localized heat source from below and symmetrical cooling from the sides. The heat source was centered on the bottom wall and the study analysed the effect of the variation in the heat source length on the natural convection inside the square cavity; the length of the heat source investigated are 1/5 and 2/5 of the wall The cooling was achieved by the two vertical walls and all the other zones were adiabatic; the symmetrical cooling from the sides is expected to be an efficient cooling option while the partial heating at the lower surface simulates the electronic components such as a chip. The experimental data are obtained by measuring the temperature distribution in the air layer by the real-time and double-exposure holographic interferometry and the numerical investigation was conducted using the commercial finite volumes code Fluent 6.0. Convection was studied for Rayleigh number from 103 to 106. Different convection forms were obtained depending on Ra and on the heat source length. The Nusselt number was evaluated on the heat source surface and it showed a symmetrical form raising near the heat source borders. Graphs with relations between average Nu, Ra and the heat source length are finally presented.
Convective Boundary Condition in the Mould Heat Transfer Simulation
Authors: Eliseu M. L. M. , Rouboa A. I.
Published: December 2008

In order to reduce the production cost of the shape in the foundry industries, we have to test and choose one of several mould materials. This way is not easily or impossible, in some cases, applicable. In fact, the high temperature and complex geometry of each mould make difficult to obtain the real property values of the material during the solidification process. The best way, in our point of view, is to simulate the heat transfer in the solidification process. For this, we propose to solve appropriate governing heat transfer equation with a curvilinear formulation using a convective heat transfer between the mould and the shape. The main objective of this paper is to develop a finite volumes method with the curvilinear formulation in order to discretizate the space (x,y,z). The time dependency will be linearised by the semi-implicit scheme. The boundary conditions used in this approach is the convective term in the solidification phase. We divide this paper in five parts. The first part, the mathematical model that describes a heat transfer between the mould and the piece is exposed. Then we expose the used boundary conditions. The second one, the finite volume method to solve such equation is detailed. After this, we present the test case, in the third part; then we expose the numerical results comparing with other boundary conditions. We conclude this paper with some critics and perspectives of this research work.
Evaluation of the Relative Time Scales of Mechanisms Controlling Fuel Droplet Behavior in Diesel Engines
Authors: Delplanque J.-P. , Labs J. , Lengsfeld C. S. , Parker T. E.
Published: December 2008

Prior studies have shown the importance of interfacial behavior on droplet secondary breakup and fuel distribution in diesel engines. These investigations have focused on the accurate evaluation of high-pressure phase equilibrium and surface tension coefficient at thermodynamic conditions relevant to diesel engine operation. This approach is extended here to account for droplet heat transfer, mass transfer, and dynamic behavior in order to adequately account for the relative magnitude of the droplet heating and species diffusion times (which control surface tension) as compared to the droplet dynamics characteristic time (over which the slip velocity vanishes) and the time required to reach interfacial equilibrium.