bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle Image Velocimetry and Heat Transfer Measurements of a Disk at High Rotational Speeds
Authors: Saniei N. , Olcay A. B. , Yan X.
Published: May 2008

Flow field and local heat transfer measurements were conducted on a rotating disk in an open environment for a variety of rotational speeds ranging from 1500 to 5500 rpm. Two-dimensional particle image velocimetry (PIV) measurements were conducted on the flow field above the surface of the rotating disk. Experiments were made on a rotating disk twice as large as a computer hard disk drive and therefore, the flow conditions may be comparable with a computer disk rotating with a speed up to 20,000 rpm. Velocity field, local heat transfer, and temperature distribution are presented as the result of this investigation. Transient liquid crystal technique was employed for heat transfer measurements, while a back calculation scheme was used to obtain the temperature distributions. Heat transfer measurements were made for r/R > 0.4 which excludes the central hub holding the disk assembly. Results reveals that heat transfer increases with a smaller slope near the corner of the hub, while it increases sharply near the outside edge of the disk.
A Numerical Study of Dynamic Meniscus
Authors: Liu C. S. L. , Lee S. H.-K.
Published: May 2008

Air entrainment is one of the bottlenecks during high speed coating process. Numerous studies concerned with the mechanics of air entrainment in coating process have been reported during the last four decades. The difficulty in visualization of three-phase contact point due to small dimension made it a hard task to unveil the mechanism of air entrainment experimentally. In most numerical studies on free surface flow, the effect of air upon dynamic meniscus was usually neglected, which induced the coarse accuracy in air entrainment study. In the present study, the numerical simulation of free surface coating flow as well as airflow upon dynamic meniscus was given. The effect of several parameters, such as coating material viscosity, and coating cup geometry, especially airflow upon free surface on the dynamic meniscus, was studied. The results showed that the dynamic effects of air in the vicinity of dynamic meniscus should not be disregarded. The pressure near the dynamic meniscus, especially at the dynamic contact point in the coating flow simulation, was much smaller than the atmosphere pressure, while in the gas phase calculation, the value was larger than the atmosphere one at the same position. These results indicated another explanation of the mechanics of air entrainment: the low pressure in the vicinity of dynamic contact point in the liquid makes the gas dissolve easily into the coating material, and the gas flow will even break the dynamic meniscus when the pressure difference between the gas and liquid phase is large enough. The effects of several factors on pressure distribution at the dynamic meniscus were also presented.
The Effects of Dimpled Surface Geometry on Heat Transfer in an Impinging Jet Flow
Authors: Anderson Ann M. , Chapin David M.
Published: May 2008

The objective of this study was to characterize the heat transfer performance of a dimpled surface in an impinging jet flow field. Using a statistical design of experiments approach we designed 8 (23) test plates to study the effects of dimple spacing, dimple depth and dimple diameter and compared them to smooth plate heat transfer. The plates were placed opposite a square jet and tests were run for Reynolds numbers based on jet hydraulic diameter of 10,000 to 30,000 at a range of jet to plate spacings. Plate averaged heat transfer coefficients, based on actual surface area (including dimple area) were measured under steady state conditions. The results show that the dimple spacing to diameter ratio has the most significant effect on heat transfer performance at high velocities, while the dimple depth to diameter ratio is more significant at lower velocities. The effect of dimple diameter was found to be significant only under poor heat transfer conditions. Particle Image Velocimetry images of the dimple surface flow field showed enhanced entrainment at high velocities which may explain why the dimple spacing to diameter effect is more significant at high velocities.
Numerical Investigation on the Effect of Marangoni Convection in an Industrial Czochralski Crucible
Authors: Kumar V. , Brenner G. , Durst F. , Biswas G.
Published: May 2008

The quasi direct numerical simulations (DNS) of the flow and the thermal fields in an industrial Czochralski crucible have been carried out in order to investigate the effect of thermocapillary or Marangoni convection employing an optimised parallel-vector block-structured Navier-Stokes equations solver. The simulations have been performed without and with the Marangoni effect at a specified rotation of the crucible during the synthesis of mono-crystalline Silicon (Pr=0.011). The time-averaged flow field reveals that the inward radial velocity at the free surface of the melt is quite high for the case with Marangoni convection. The flow is directed towards the solid crystal due to the presence of significant surface tension gradients at the free surface. A stronger downward flow has been observed at the center of the crucible owing to this strong radial velocity. Due to the superposition of the Marangoni convection, temperature fluctuations are reduced under the free surface and at the crystal interface. Thus the fluctuations in the growth rate are reduced. The turbulent kinetic energy, k is smaller below the crystal at different depths in the melt for the cases without any effect of the Marangoni convection as compared to the cases with Marangoni convection. The temperature along the free surface of the melt is increased when the thermocapillary effect is included.
An Experimental Study on Forced Convection From a Rectangular Heated Block by Acoustic Excitation in a Channel Flow
Authors: Moon J. W. , Kim S. Y. , Cho H. H.
Published: May 2008

An experimental study on forced convection from a heated block in a pulsating channel flow has been carried out. This problem is of particular interest in various thermal applications such as electronics cooling and industrial heat exchangers. A pulsating flow is imposed by an acoustic excitation at the channel inlet and a constant heat flux is given along the surfaces of the block. The impact of the important governing parameters such as the Reynolds number, the Strouhal number, and the pulsation amplitude on the heat transfer rate from the heated block is investigated in detail. The vortex shedding frequencies generated from the block are measured and the flow around the block is visualized by means of the particle visualization technique. The experimental results show that the inlet flow pulsation and the Reynolds number substantially affect thermal transport from the heated block. The heat transfer is dramatically enhanced at the frequencies of fF=75Hz and fF=150Hz. It is found by the flow visualization that this phenomenon is related to the intensified fluid mixing at the frequencies. The increase of the pulsation amplitude also significantly amplifies the heat transfer rate from the heated block.
Preparation of Nanocrystalline Titanium Silicide Powder and Its Consolidation Using Sodium Silicate
Authors: Srinivasan M. N. , Keshoju K. , Aripaka S.
Published: May 2008

Statistical design of experiments was employed to assess the effect of mechanical alloying variables and the chemical binder (sodium silicate) percentage on the crystallite size of mechanical alloyed titanium silicide powder and the microhardness of samples consolidated by chemical bonding. The results indicate that mechanical alloying the powder with higher milling time, higher milling speed and lower ball-to-powder ratio and consolidating with 20% sodium silicate gives a combination of fine crystallite size and good microhardness in the compact.
Board-Side Boundary Condition for a Single Component on a PCB in Forced Convection
Authors: Neelakantan Sriram , Chiriac Victor Adrian
Published: May 2008

Computational Fluid Dynamics (CFD) tools are routinely used to get accurate predictions of junction temperatures of Integrated Circuit (IC) packages. However, it is desirable to obtain reasonably accurate junction temperature estimates as early as possible in the design process without having to model the board and flow in large detail. In order to accomplish this, a good estimate of the board side thermal resistance is required. The new method presented here estimates the board side resistance for a standard JEDEC high conductivity board in forced convection. The overall board resistance incorporates the spreading resistance of the board, taking into account the multiple layers of copper and dielectric, also the heat transfer coefficient from the board using established correlations. The results of the calculation method are further compared with a full CFD simulation of a simplified package on a board. Good agreement is obtained between the CFD simulation and the proposed method in predicting the junction and case temperatures. The numerical discrepancies are within 1.5% and 4.2% respectively, over a broad range of airflow speeds typical of forced convection cooled electronics systems. The accuracy of the proposed analytical calculation method recommends it as a potential method of replacement of a full CFD simulation of the board and component with a conduction only analysis. The board-side boundary condition for this analysis could be represented with an equivalent heat transfer coefficient.
ISO-Gradient Lines in a Differentially Heated Cylindrical Fluid Layer Using Coherent Gradient Sensing Interferometer
Authors: Mishra D. , Wong S. L. , Longtin J. P. , Singh R. P. , Prasad V.
Published: May 2008

Non-invasive flow visualization and measurement of temperature fields in convective fluid systems continues to be a challenging problem for researchers. Radiation based measurements such as laser interferometry are one of the few available tool for this purpose. Laser interferometry allows for an accurate and convenient full field visualization and measurement of fluid properties. In the present study a single-beam Coherent Gradient Sensing (CGS) interferometer is used to obtain line-of-sight projections of a three-dimensional temperature field in a convective fluid medium. Due to its inherent insensitivity to vibrations, simple and cost effective optical layout and, most importantly, the absence of a separate reference beam, this interferometer is an ideal choice for measurements in convective fluids. In the present study, line-of-sight interferometric projections of a differentially heated water medium in a cylindrical cavity are presented. The cavity employed has an aspect ratio (diameter/height) of 3.9. The interferograms represent contours of gradient in the temperature field. Each of the interferograms is evaluated to obtain the two-dimensional projection of the temperature field. The temperature field obtained shows the absence of a radial-symmetric pattern at a Rayleigh number of 1.6×105.
Electrical and Thermal Layout Design and Optimization Considerations for DPS Active IPEM
Authors: Pang Ying Feng , Chen Jonah Zhou , Scott Elaine P. , Thole Karen A.
Published: May 2008

A methodology was developed to optimize the 3D geometrical design layout of an active integrated power electronics module (IPEM) by considering both electrical and thermal performance. This paper is focused on the thermal analysis, which was performed using 3D finite element and computational fluid dynamic (CFD) analyses. A parametric study was conducted to determine the thermal performance of several different design layouts. A sensitivity analysis was performed to determine the overall uncertainty of the predicted simulations. The final design, Gen-II.C, provided a 70% reduction in the common mode current, a 4% reduction in the size of the geometric footprint, and a 3°C reduction in the maximum temperature over Gen-II.A, thus providing an increase in the overall performance.
Optimization of Pin-Fin Heat Sinks Using the Two Medium Anisotropic Porous Model
Authors: Kim Seo Young , Kuznetsov Andrey V.
Published: May 2008

A numerical study has been carried out to optimize the thermal performance of a pin-fin heat sink. A pin-fin heat sink placed horizontally in a channel is modeled as a hydraulically and thermally anisotropic porous medium. A uniform heat flux is prescribed at the bottom of the heat sink. Cold air is supplied from the top opening of the channel and exhausts to the channel outlet. Comprehensive numerical solutions are derived from the governing Navier-Stokes and energy equations, using the Brinkman-Forchheimer extended Darcy model and the local thermal non-equilibrium (LTNE) model for the region of heat sink. Results from this study indicate that the anisotropy in permeability and solid-phase effective thermal conductivity changes substantially with the variation of porosity. The pin-fin heat sinks considered in the present study show an optimum porosity of 0.75<εopt<0.95 for maximum thermal dissipation depending on the flow and geometric conditions. Generally, a thick pin-fin displays a lower optimum porosity.
Generation of Equivalent Circuit Models From Simulation Data of a Thermal System
Authors: Bikdash M. , Pang Y. P. , Scott E. P.
Published: May 2008

To enable the design and analysis of Integrated Power Electronics Models (IPEMs), a high level of software integration is needed. The solvers needed range form electrical circuit simulators, like Saber, to thermal analysis and CFD solvers like I-DEAS. As an electrical design parameter is changed, its effect will, in principle, be felt all the way to the temperature distribution in the cooling fluid, and hence a complete solution of the temperature field may have to be recomputed. This is of course computationally prohibitive. Hence a reduced-order model of the thermal behavior of the heat sink is of great interest. In this paper, we will present an algorithm that can automatically generate these reduced-order models from finite-element simulations.
An Enthalpy Approach for the Solidification of Metal Matrix Composites
Authors: Lee E. K. , Amano R. S. , Rohatgi P. K.
Published: May 2008

In this paper, a numerical simulation of the solidification of metal matrix composite (MMC) is presented. The metal alloy used in the MMC is Al-4.5%Cu. The simulation is based on an axisymmetric model with enthalpy formulation of the energy equation coupled with the momentum equations. The simulation will facilitate an approximation to the experimental result when the real setup is carried out in the laboratory. This paper focuses on the importance of the sink heat used at the end of the fibers to extract heat from the liquid metal.
A Thermal Model of the Friction Stir Welding Process
Authors: Khandkar Mir Zahedul H. , Khan Jamil A. , Reynolds Anthony P.
Published: May 2008

A novel finite element method based 3-dimensional thermal model has been developed to study the temperature distributions during the friction stir welding process. The moving heat source generated by the rotation and linear traverse of the pin-tool has been correlated to input torque data obtained from experimental investigation of butt-welding of AA6061-T651. The moving heat source includes heat generation due to torques at the interface between the tool shoulder and the workpiece, the horizontal interface between the pin bottom and the workpiece, and the vertical interface between the cylindrical pin surface and the workpiece. Temperature-dependent properties of the weld-material have been used for the numerical modeling. Excellent conformity between simulated temperature profiles and experimental data has been demonstrated. The effects of various heat transfer conditions at the bottom surface of the workpiece, different thermal contact conductances at the interface between the workpiece and the backing plate, and different backing plate materials on the thermal profile in the weld material have also been investigated.
Numerical Analysis of Heat Conduction in Cooling of Aluminum Extrusion
Authors: Bianco Nicola , Manca Oronzio
Published: May 2008

A thermal analysis of the cooling of an extruded aluminum alloy by means of water sprays is carried out. The heat conduction problem has been solved numerically by means of a finite volume method. The heat transfer coefficients used in the boundary conditions has been evaluated by means of spray heat transfer correlations, which relate these coefficients to the spray hydrodynamic parameters. The influence of the number of sprays and of the solid velocity has been investigated. Results show that the efficiency of the cooling system decreases as the number of jets increases. The efficiency of each spray increases with the velocity for the same number of sprays. As the workpiece velocity increases it needs to increase the number of sprays to obtain the same temperature difference between the entry and the exit of the cooling system. The greater the number of sprays related to the case with lower velocity, the smaller the increase of the number of sprays.
Natural Convection in Cylindrical Configuration: Effect of the Obstacle on the Unsteadiness
Authors: Choukairy K. , Bennacer R. , Matthey P. D. , Duval R.
Published: May 2008

The heat transfer by natural convection are frequently used in the various processes and are also met in various situation in nature. In order to improve these kind of heat transfer, it’s possible to disturb the flow of origin by an obstacle along the way of the principal flow. This obstacle modifies on the one hand the structure of the flow and affects the local transfers. On the other hand, it allows the transition towards and obtaining a macroscopic contribution (eddy) in complement of the microscopic transfer (molecular diffusion). The effect of an obstacle on the thermal transfer, was previously studied and we purpose to complete such studies in transitional domain. The obtained non-stationary natural convection is analysed. A study is carried out by considering the transient resolution (DNS) of such problem in two-dimensional configuration. The density variation is taken into account by the boussinesq approximation. The control-volume approach is used for solving the governing equation. The temporal variation of Nusselt and energy is given with and without obstacle. We illustrate the necessary condition in order to improve the transfer in such configuration. The effect of height and width of the inserted body is systematically analysed.
Determination of Boundary Conditions During the Start-Up of DC Casting
Authors: Suyitno  , Katgerman L. , Burghardt A.
Published: May 2008

The start-up phase of DC (direct chill) casting of aluminium alloys is a critical stage during which unwanted phenomena can occur, for example: butt curl, ingot cracking, and re-melting. To avoid these problems, simulation of the DC casting process during this phase is very important. However, the simulation task is not an easy job, because the boundary conditions to be applied are not easily defined and established. To define the boundary condition inverse methods are used in combination with experimental data. The aim of the simulations is intended to predict butt curl and butt temperatures. By application of inversely determined boundary conditions, results can be obtained that correlate well to measured data, even for different casting practices.
Macroscopic Effects of Surface Roughness in Confined Air-Flow
Authors: Boutaous M’hamed , Bourgin Patrick
Published: May 2008

The general framework deals with the winding of thin plastic films. It is well known by the man-of-the art that the “windability” of plastic films is mainly governed by their surface topography. One key issue is then to optimize their surface topography so that to improve the quality of the wound roll. In a previous work, we proposed a simple model which considers the flow of an air layer squeezed between a solid smooth substrate and a plastic film sample : it was shown experimentally that the macroscopic characteristics of the flow are connected to the film roughness, but how? To answer this question, we assimilate the confined air flow to a flow through a periodic array of cylinders. A mathematical model based on homogenization techniques was proposed, where the heights of the cylinders, their diameter and their spatial distribution are the governing parameters. In the present paper, we propose pertinent parameters which describes the real surface roughness of plastic films fairly well. The measurements were carried out by using a 3D roughness measurement device. The first observation is that the films roughness distribution is not uniform, but forms “packages” (agglomerates) giving place to large packs of roughness. We made a sampling at different levels expressed by the percentage of peaks exceeding some given height. The heights of the peaks over a threshold value are averaged and the corresponding averaged value will be regarded as the initial gap in the squeeze flow model. Now, the networks of cylinders is built as follows : • The cylinder diameters is the averaged width of the large peaks, • The distance between the cylinder axes is the mean value of the spatial distribution of the peaks. Thus, for each type of film, the threshold value will be the only adjustable parameter. Introducing these parameters into the mathematical model which predicts the evolution of the squeezed air layer and comparing to the experimental data, the following results are obtained: (1) It is possible to adjust one single parameter so that to obtain a very good agreement between the experimental data and the theoretical results. (2) The smoother the film, the more important the highest peaks are in terms of air leakage.
A Study and Development of Fluid Cobot
Authors: Wannasuphoprasit Witaya , Chanphat Supaphon
Published: May 2008

Cobots are a class of passive robotic devices that utilize steering joints to impose nonholonomic constraints on their joints. These steering joints are a subclass of transmission called Continuous Variable Transmission, CVT. Here we purpose to develop a cobot that utilizes a CVT joint based on flow rate divider of pneumatic actuators. We studied characteristics of a valve and a cylinder. We designed and built a multi channel flow divider. Furthermore, to test our concept we constructed a simple x-y pneumatic cobot.
Modeling of a Radiative RTP-Type Furnace Through an Inverse Design: Mathematical Model and Experimental Results
Authors: Gamba Mirko , Ertu¨rk Hakan , Ezekoye Ofodike A. , Howell John R.
Published: May 2008

The present study considers the inverse thermal design of an existing radiatively heated chamber for rapid thermal processing (RTP) of semiconductor wafers and compares the numerical results from the inverse mathematical model with experimental measurements directly taken on the physical system. The purpose of this study is to calculate with an inverse approach the power input of the chamber heating elements in order to achieve specific temperature and heat flux distributions on the design surface (wafer). Once a reasonable solution is found, the experimental confirmation takes place. The study starts with characterizing and modeling the system formed by an axisymmetric vacuum chamber designed to reproduce the major characteristics of a generic RTP process in the semiconductor industry, such as for rapid thermal annealing of wafers. A Monte Carlo model is employed for the radiative heat transmission using measured specular/diffuse reflectivities for the radiation shields, and diffuse emissivities for all other surfaces. The actual geometry of the chamber is modeled. The inverse problem is then solved by using the Conjugate Gradient Method. Using the calculated input powers of the heaters to maintain an isothermal wafer as the initial setting for the instrumented radiative chamber, experimental measurements of the steady temperature distributions on the elements of the chamber and on the wafer surface are taken. The study ends by comparing the experimental and numerical results to determine the necessary enhancement to apply to the system model with the final objective of developing an effective design tool using an inverse approach.
Optimal Design of Cooling Flow Path by Homogenization Design Method
Authors: Roh Wonjoo , Kikuchi Noboru
Published: May 2008

Topology optimization by homogenization design method has made successful results in the structural design. The idea can be extended to find an optimal structure which interacts with fluid flow, which is coupled to energy conservation. From the fact that an initial design domain is a type of black box composed of repetitions of unit microcells, analysis of a fluid flow through porous media is to be accomplished. Newly developed unit cell structure makes fluid run through a void area in the microcell. The fluid flow is governed by Darcy’s law which is theoretically derived by applying homogenization theory to momentum and continuity equation while assuming inertia-less viscous flow. A sequential linear programming is implemented to converge a final structure as an optimum.
Fin Analysis Under Transition Boiling Heat Transfer: Part II — Radial Fins
Authors: Krikkis Rizos N. , Sotirchos Stratis V. , Razelos Panagiotis
Published: May 2008

The thermal characteristics of six profiles of radial fins subject to transition boiling heat transfer are analyzed. The profiles considered are the rectangular the trapezoidal, the triangular, the convex parabolic, the parabolic and the hyperbolic. The model of the physical mechanism is based on one-dimensional heat conduction using certain simplifying assumptions while the heat transfer coefficient is modeled as a power-law function of the temperature difference between the fin and the saturated boiling liquid with a negative exponent. The problem is formulated by means of dimensionless variables and parameters such as the conduction-convection parameter, the radius ratio and the Biot number that characterize the problem. The multiplicity structure is obtained in order to determine the different types of bifurcation diagrams, which describe the dependence of a state variable of the system (for instance the fin temperature or the heat dissipation) on a design (CCP, radius ratio) or operation parameter (power-law exponent). Specifically the effects of the radius ratio, of the CCP and of the Biot number are analyzed and presented in several diagrams since it is important to know the behavioral features of the heat rejection mechanism such as the number of the possible steady states and the influence of a change in one or more operating variables to these states.
Thermal Design of Supercritical Water Oxidation Reactors
Authors: Rogak S. N. , Khan M. S. , Vera-Pe´rez I.
Published: May 2008

Waste destruction using supercritical water oxidation (SCWO) was demonstrated in laboratories in the early 1980’s and in full-size facilities by the early 1990’s. The process offers thorough destruction of toxins in a compact facility without supplementary energy. Early estimates that SCWO could auto-thermally treat wastewaters with as little as 2% weight organic ignored some practical factors, such as corrosion, fouling, heat transfer limitations. In this paper, a thermal model for a SCWO system based on pure water properties and heat transfer correlations is used to estimate heat exchanger size and frictional pressure losses. Information on real mixtures at SCWO conditions is not established to the point needed for rigorous thermal modeling, but the pure-water model can be interpreted using real-fluid properties and experience from operating SCWO systems. It is shown that the waste composition has a direct influence on the SCWO design. Auto-thermal treatment of dilute streams (2% organic) is economic only if inorganic compounds are absent from the waste stream or treated effluent, and the plant is of moderate size. For more corrosive wastes, or those with fouling agents, it becomes very expensive to preheat the feed beyond the critical temperature. Without preheating to supercritical temperatures, some back-mixing of hot products is needed to stabilize reaction, so that plug-flow reactor designs become inappropriate.
Governing Equations for Heat Conduction With Finite Speed of Heat Propagation
Authors: Shnaid Isaac
Published: May 2008

In heat conduction, two different analytical approaches exist. The classical approach is based on a parabolic type Fourier equation with infinite speed of heat propagation. The second approach employs the hyperbolic type governing equation assuming finite speed of heat propagation. This approach requires fundamental modifications of classical thermodynamics which are developed in the frame of extended thermodynamics. In this work, governing equations for heat conduction with finite speed of heat propagation are derived directly from classical thermodynamics. For a linear flow of heat, the developed governing equation is linear and of parabolic type. In a three dimensional case, the system of nonlinear equations is formulated. Analytical solutions of the equations for linear flow of heat are obtained, and their analysis shows characteristic features of heat propagation with finite speed, being fully consistent with classical thermodynamics.
The Formation Process of Nanoparticles in Laser Materials Interaction
Authors: Wang Xinwei , Xu Xianfan
Published: May 2008

Nanoparticles formed in short pulsed laser materials interaction have strong effects on laser micro-machining, material surface processing, and thin film deposition. In this work, Molecular Dynamics (MD) simulations are conducted to attain physical origins and the nature of nanoparticle formation in picosecond laser materials interaction. The MD simulation reveals that nanoparticles originate from an intense vapor phase explosion process occurring after laser heating. This phase explosion is driven by an accumulated high pressure of the order of 30 MPa in the near surface region. It is observed that nanoparticles start coming out after laser heating as a result of the after-heating intense phase explosion. Also observed is that the pressure in nanoparticles undergoes a reduction because of the temperature decrease and atom re-construction in space. In addition, saturation of the nanoparticle yield is observed when the laser fluence reaches a certain level, which is a result of limited heat penetration depth during laser heating.
Manufacturing of Electrically Conductive Microstructures by Dropwise Printing and Laser Curing of Nanoparticle-Suspensions
Authors: Bieri N. R. , Haferl S. E. , Poulikakos D. , Grigoropoulos C. P.
Published: May 2008

A novel method for the manufacturing of electric microconductors for semiconductor and other devices is presented. The method brings together three technologies: controlled (on demand) printing, laser curing, and the employment of nanoparticles of matter, possessing markedly different properties (here, melting point) than their bulk counterparts. A suspension of gold particles in toluene solvent is employed to print electrically conducting line patterns utilizing a modified on demand ink jet printing process. To this end, microdroplets of 80–100 μm diameters are deposited on a moving substrate such that the droplets form continuous lines. Focused laser irradiation is utilized in order to evaporate the solvent, melt the metal nanoparticles in the suspension, and sinter the suspended particles to form continuous, electrically conducting gold microlines on a substrate. The ultra fine particles in the suspension have a diameter size range of 2 – 5 nm. Due to curvature effects of such small particles, the melting point is markedly lower (400°C) than that of bulk gold (1063°C). Thermodynamic aspects of the effect of particle size on the melting and evaporation temperatures of gold and toluene, respectively, are discussed in the paper. The structure and line width of the cured line as a function of the laser irradiation power and stage velocity are reported in detail. Preliminary measurements of the electrical conductivity are represented.
A Numerical Study of the Effect of Contact Angle on the Dynamics of a Single Bubble During Pool Boiling
Authors: Abarajith H. S. , Dhir V. K.
Published: May 2008

The effect of contact angle on the growth and departure of a single bubble on a horizontal heated surface during pool boiling under normal gravity conditions has been investigated using numerical simulations. The contact angle is varied by changing the Hamaker constant that defines the long-range forces. A finite difference scheme is used to solve the equations governing mass, momentum and energy in the vapor and liquid phases. The vapor-liquid interface is captured by the Level Set method, which is modified to include the influence of phase change at the liquid-vapor interface. The contact angle is varied from 1° to 90° and its effect on the bubble departure diameter and the bubble growth period are studied. Both water and PF5060 are used as test liquids. The contact angle is kept constant throughout the bubble growth and departure process. The effect of contact angle on the parameters like thermal boundary layer thickness, wall heat flux and heat flux from the microlayer under various conditions of superheats and subcoolings is also studied.
Liquid-Liquid Mixing Due to G-Jitter in Microgravity
Authors: Benjapiyaporn C. , Timchenko V. , Leong S. S. , de Vahl Davis G. , Leonardi E.
Published: May 2008

This paper describes a study of double diffusive convection inside a rectangular cavity in low gravity; it arose out of a much broader study of solidification of a binary alloy in microgravity. The cavity initially contained two different but miscible liquids meeting at a sharp vertical interface at the middle of a cavity. One vertical wall was kept at a uniform low temperature, while the opposite wall was at a uniform higher temperature. The top and bottom walls were adiabatic. All walls were impermeable. A numerical simulation was made of the induced convection and mixing for a range of values of buoyancy ratio and gravity characteristics, including both steady g and g-jitter.
A Computational, Multi-Physical Assessment of Commercial Structures Subjected to Fire
Authors: Borowski G. E. , Furtaw C. E.
Published: May 2008

In commercial construction, where concrete masonry units have certain fire rating requirements, there are two methods that may be used. The first method (and least used) is to have the Underwriters Laboratories (UL) review in person the manufacture of the block, including the mixing of the aggregates. When the blocks are manufactured under the UL’s inspection, the block are then stamped and approved for specified fire rating. The next method (and most used) is to determine the equivalent thickness of the unit where the volume of the masonry unit is divided by the area of the exposed face. Depending on the type of aggregate used, a four hour fire rating may vary from an equivalent thickness of 6.7” for siliceous gravel to 4.7” for Pumice or expanded slag.
A Comparison of Computer Simulation Predictions to Experimental Data Taken From Side-by-Side Residential Homes Configured With a Radiant Barrier
Authors: Moujaes Samir F. , Brickman Richard
Published: May 2008

Numerical results of a computer simulation using the RESHEAT code are made with experimental data obtained from side by side testing of a Radiant Barrier (RB) technology on a set of residential houses in the Southern MidWest. The code is a dynamic one dimensional heat transfer model which incorporates all the effects of heat through attics and building structures. The code also models the effect of radiant heat gain in supply air ducts placed in the attic. The code solves for temperature histories of over 90 nodal points around the structure and uses the hourly weather information already available in the open literature as its input. It was found that in a majority of cases where the experimental data was deemed reasonably accurate and without problem the code predicted the temperature profiles in the different attic layers reasonably well. In some of the experimental data, obtained by others, the validity of the data was somewhat in question.
Improving Radiator Design Through Shape Optimization
Authors: Guessous Laila , Maddipatla Sridhar
Published: May 2008

The current emphasis by auto manufacturers on improving the quality and fuel economy of their vehicles requires enhancements in the efficiency and operation of all engine components, including those in the engine cooling system. Improvements in the pressure drop and flow homogeneity in the water tank of a radiator are needed to reduce the power demands on the vehicle water pump and increase the lifetime of the radiator. The latter criterion is particularly important in the reduction of premature fouling and failure of heat exchangers. Rather than relying on ad hoc geometry changes with the goal of improving the performance of radiators, the coupling of CFD flow simulations with numerical shape optimization methods could assist in the design and testing of automotive heating and cooling components. This paper describes ongoing efforts to develop a fully automated suite of virtual tools to aid in the design and testing of automotive heating and cooling components. The development and validation of optimization criteria for pressure drop and mass flow rate distribution in a water-to-air automotive heat exchanger are discussed, as well as the methodology used to automate the mesh generation, CFD simulation, and shape optimization procedures using the GAMBIT® and FLUENT® software combined with an in-house code.
Range Door Design Through the Aid of Computational Heat Transfer
Authors: Tekriwal Prabhat
Published: May 2008

UL requires that cooking appliances meet temperature restriction requirements on the outside surfaces for consumer safety. Application of Computational Fluid Dynamics has revealed the relative importance of conduction, convection and radiation in the thermal management of a natural convection-cooled Range door design. After the initial verification of the door outer surface temperature predictions with experimental measurements, the computer model was used to evaluate design options. Results show that stuffing an air pocket with insulation in the upper part of the door will do very little to reduce the door outer surface temperature. Reducing emissivity of the door liner surface, baffle and trim inner surface reduces outer door temperature. Contrary to intuition, putting a thin trim insulation behind the outer door increases the door outer surface temperature. Opening up the convection channel, on the other hand, reduces the door surface temperature by a considerable amount. Use of numerical computations has also shown that a more economical fiberglass insulation is almost as good as an expensive micro-porous insulation in thermal management of the door design.
Geometric Optimization of Radiant Enclosures Containing Specular Surfaces, Through Non-Linear Programming
Authors: Daun K. J. , Morton D. P. , Howell J. R.
Published: May 2008

This paper presents an optimization methodology for designing radiant enclosures containing specularly-reflecting surfaces. The optimization process works by making intelligent perturbations to the enclosure geometry at each design iteration using specialized numerical algorithms. This requires far less time than the forward “trial-and-error” design methodology, and the final solution is near optimal. In this application, the radiant enclosure is analyzed using a Monte Carlo technique based on exchange factors, and the design is optimized using the Kiefer-Wolfowitz method. This design methodology is demonstrated by solving two industrially-relevant design problems involving two-dimensional enclosures that contain specular surfaces.
A Boundary Element Method for the Computation of Thermal Radiation Exchanges Between Gray and Spectral Surfaces
Authors: Cui X. , Song S. P. , Li B. Q.
Published: May 2008

A Galerkin boundary element computational methodology is developed to predict thermal radiation exchange between gray and/or spectral surfaces. The concept of computer graphics used for image clipping, and image object sorting, and an adaptive integration algorithm are incorporated to improve the accuracy and efficiency of the computation of the radiation exchange kernels with abrupt discontinuities due to blockages of various complexity. A parallel computing scheme is applied to further enhance the computational efficiency. Examples of 2-D, 3-D and axisymmetry of various complex geometries, as applied to combustion processes, materials processing and manufacturing processes, are presented. The parallel performance of the computational algorithm and the coupling of the surface radiation with conduction and other calculations are also discussed.
Field Validation of a Systematic Approach to Modeling of Glass Delivery Systems
Authors: Jian Christopher Q. , Muralidharan  , Dutta Abhijit
Published: May 2008

In the fiberglass production process, glass is produced from various batch ingredients in a glass furnace. The molten glass is then delivered, through a delivery system that is often called the front-end system, to the various downstream forming operations. Front-end systems consist of various covered channels and forehearths. One of the major tasks of a front-end system is to insure that the glass is conditioned to the stringent specifications required by the forming operations. Improperly designed and/or operated front-end delivery systems can cause a number of problems to the forming operations, ranging from poor conversion efficiency (resulting in waste generation) due to glass defects to shortened service life. In today’s business environment, improvement in productivity, reduction in energy consumption, and minimization or elimination of waste generation have become priorities in managing and optimizing manufacturing operations. CFD has become an increasingly important tool for glass manufacturers to guide and optimize such system designs and operations. The current front-end model is developed to simultaneously simulate the chemically reacting turbulent flows in the superstructure and the laminar glass flow with strong buoyancy effects. Radiation from the superstructure wall surfaces and burner flames and internal radiation within the glass is modeled with the discrete ordinates (DO) radiation model in FLUENT. The turbulent reacting flow in the combustion space is calculated to obtain the flame shapes and lengths to accurately determine the heat transfer rate to the molten glass. The laminar glass flow, which is strongly influenced by natural convection, is calculated with temperature dependent physical properties. Simulations of the two radically different flow regimes are coupled through the interface boundary conditions in terms of temperature and heat flux continuity. Significant efforts were made to validate this approach with field measurements. Vertical temperature profiles were obtained in the glass melt as well as the combustion space at several strategically selected locations. The measurements were performed using two 6-element thermocouples housed in a platinum sheath. This coupled approach is expected to provide an effective tool that can be used to guide field operations as well as future system designs.
Characterization of Industrial Foams
Authors: Solovjov Vladimir P. , Jones Matthew R. , Fackrell Kurt E. , Webb Brent W.
Published: May 2008

Applications involving foams in industrial processes are widespread. Often the development of foam is a desired outcome. Foams are used in enhanced oil recovery and drilling operations, in the production of cosmetics, and in the development of new insulation and construction materials. However, in applications such as glass melting and fining or fermentation processes, foam layers act as barriers to heat and mass transfer, and the presence of foam is undesirable. Due to their widespread use and importance, techniques for characterizing foams are of interest. Previously, diffusing-wave spectroscopy has been used to investigate the time evolution and the rheological properties of foams. This paper will describe the use of diffusing-wave spectroscopy to characterize the layer thickness, scattering coefficient, and asymmetry parameter of a foam layer. A model of the propagation of radiation from a steady source and from a sinusoidally modulated source through a non-absorbing foam layer is developed. Relationships between layer thickness, scattering coefficient, asymmetry parameter and the phase shift of the reflected radiative flux are derived based on this model. Model predictions reveal an experimentally viable technique for characterizing industrial foams. To the best of the authors’ knowledge, the determination these properties has been heretofore elusive, and the results presented here describe for the first time a non-intrusive method for determining foam properties.
A Global Heat Transfer Model for a New Silicon Crystal Growth System
Authors: Wang C. , Zhang H. , Wang T. H. , Ciszek T. F.
Published: May 2008

To suppress turbulent flow in a large silicon melt, Drs. Ciszek and Wang at NREL have proposed and patented a new Czochralski (CZ) growth furnace that has a shallow melt. To supply silicon to a shallow melt for long ingot growth, a crucible with partitions has been designed which allows continuous growth of a crystal by feeding silicon pellets into a dedicated compartment of the crucible. In this paper, temperature distributions in the entire furnace are simulated for the new system in a simplified manner as the first step to compare with those more sophisticated simulation results on a conventional CZ growth system. The effects of power level of individual heaters on temperature distribution in the melt are discussed. The simulation results show that a favorable temperature distribution can be obtained in the new furnace through changing the power ratio of the side and bottom heaters.
The Influence to Thermal Resistance to Conduction in Rotary Regenerators
Authors: No´brega Carlos E. L. , Brum Ni´sio C. L. , Worek William
Published: May 2008

The present work is devoted to the modeling of rotary regenerators. A mathematical model is proposed based on a number of simplifying assumptions, the validity of which is discussed in light of actual regenerator design figures. The results are presented in ε-NTU analysis. It is shown that the often neglected thermal resistance offered by the storage material might imply in substantial reduction on the regenerator effectiveness.
Monte Carlo Sensitivity Calculations Applied to Radiative Transfer-Combustion Coupling
Authors: El Hafi M. , de Lataillade A. , Fournier R.
Published: May 2008

In several applications such as meteorology or combustion, it is difficult to consider detailed radiative transfer modeling because of the high computing cost due to the numerous coupled physical phenomena such as fluid mechanics, heat transfer and chemistry. The aim of this work is to present an attempt to couple a highly accurate radiative transfer model to an advanced combustion code. This approach is based on a recently identified specific feature of Monte Carlo Methods. They provide not only the radiative source field but also its sensitivities to temperatures and concentrations with no additional random procedure. To illustrate this approach, a coupled simulation applied to a 1-D counterflow flame is presented.