bluuebunny/crossref_metadata_2025 huggingface dataset:
Convection-Free Thermodiffusion in a Water-Ethanol Mixture Subject to Varying Thermal Boundary Conditions
Authors: Chacha M. , Saghir M. Z.
Published: April 2009

The paper presents a precise numerical simulation of the transport processes in a rectangular cavity saturated with a water-ethanol mixture. The full transient Navier-Stokes equations coupled with the heat and mass transfer equations are solved by the means of the finite volume method. The mixture properties are drawn from the recent work by Dutrieux et al. [1]. The density is assumed to vary linearly with temperature and concentration (Boussinesq approximation) in the working temperature range while other thermo physical properties are held constant. After validation the present code is used for a series of numerical experiments. Thermodiffusion in a liquid-mixture of Ethanol and Water is analyzed under zero gravity condition. Different thermal boundary conditions scenarios are considered to simulate possible thermal control system shortcomings. Results of investigations might help in the preparation and monitoring of the heat sources control systems during the direct Soret coefficient measurement experiments.
Surface Effects on Confinement-Driven Pool Boiling Enhancement in Vertical Parallel-Plate Channels
Authors: Geisler Karl J. L. , Bar-Cohen Avram
Published: April 2009

Evidence of confinement-driven boiling heat transfer enhancement in vertical channels is very well documented in the literature and much has been observed about its nature and behavior. However, the majority of the available correlations is empirically-based and they tend to be very restricted in their range of applicability and portability. In order to further elucidate the effect of this type of geometrical confinement on boiling heat transfer, an experimental study has been performed on vertical, rectangular parallel-plate channels immersed in the dielectric liquid FC-72. The enhancement of nucleate boiling performance with decreased channel spacing was found to depend on the type of heater employed but could not be explained by the surface roughness. On the other hand, degradation of the Critical Heat Flux (CHF) limit with decreasing channel spacing was found to be independent of the surface and to be well predicted by a correlation available in the literature.
PIV Measurements Within the Waves of Wavy and Wavy-Annular Horizontal Two-Phase Flow
Authors: Foster R. E. , Shedd T. A.
Published: April 2009

A novel technique of microscopic Particle Image Velocimetry (PIV) is presented for two-phase annular, wavy-annular and stratified flow. Seeding of opaque particles in a water/dye flow allows the acquisition of instantaneous film velocity data in the film cross-section at the center of the tube in the form of digital image pairs. An image processing algorithm is also described that allows numerical velocities to be distilled from particle images by commercial PIV software. The approach yields promising results for stratified and wavy-annular flows, however highly bubbly flows remain difficult to image and post-process. Initial data images are presented in raw and processed form.
A Theoretical Comparison of the Efficacy of Microwave and Ultrasound Applicators Used in Transurethral Thermal Therapy
Authors: Thamire Chandrasekhar , Divi Rao L. , Verma Mukesh
Published: April 2009

Microwave and ultrasound energy sources are commonly used in minimally invasive thermal therapy for benign prostatic hyperplasia. Successful management of the therapy using either of these methods requires an accurate estimation of the thermal dosage. The purpose of this study is to evaluate, theoretically, the thermal damage caused by typical transurethral microwave and ultrasound applicators for different thermal doses and compare the efficacy of the two methods. Using an Alternating-direction implicit method, the Pennes bio-heat transfer equation is solved for different levels of power and heating times. Internal and external cooling is applied to preserve the urethral and rectal lining and to control the temperatures within the tissue. The extent of thermal coagulation is determined from the resulting temperature histories, using the existing experimental thermal damage data for prostate tumor cells. The temperatures and damage contours calculated are validated using an Arrhenius analysis of the temperature and thermal-lesion data from the available experimental results. Results show that the calculated damage zones are in good agreement with those observed in the experiments. Results from calculations for different combinations of the parameters are presented in terms of the transient temperature histories and radial and axial extent of the lesion shapes. These results suggest that both methods can yield comparable thermal damage, though ultrasound appears to possess an improved control of directional heating.
Laser Surface Texturing: Applications and Research Opportunities
Authors: Willis David A.
Published: April 2009

Laser surface texturing refers to techniques for altering surface topography either by laser-induced material removal and/or displacement of material from the melt pool. A review of thermal transport issues involved in laser surface texturing is discussed, with an emphasis on texturing at low laser fluences. The paper will discuss new applications of laser surface texturing, particularly reduction of stiction in MEMS devices. Experiments with laser surface texturing of thin metal films and silicon wafers at low fluence are presented. The results show that texturing of a metal film is possible without opening a hole in the film. At higher laser fluences, a hole opens in the film and droplets are ejected from the molten pool. Texturing of silicon wafers also suffers from droplet ejection, with debris-free texturing possible at fluences only slightly above the melting threshold. Directions for future research are discussed, including understanding the effect of density variation during melting and solidification on the final surface topography.
Flow Field and Heat Transfer in a Cavity With Inlet and Outlet Ports Due to Incoming Flow Oscillation
Authors: Saeidi S. M. , Khodadadi J. M.
Published: April 2009

A finite-volume-based computational study of transient laminar flow and heat transfer (neglecting natural convection) within a square cavity with inlet and outlet ports due to an oscillating velocity at the inlet port is presented. The inlet port is placed at the top of the left wall and the outlet port is positioned at the bottom of the right wall of the cavity. The inlet velocity varies sinusoidally with time for a range of dimensionless frequencies (St = 0.1, 0.5, 1, 2 and 10). The instantaneous Reynolds number also varies sinusoidally between 100 and 500 and Pr = 5. It takes more cycles for the temperature field to reach its periodic state in comparison to the corresponding flow field. For cases with greater Strouhal numbers, it takes more cycles to reach a periodic state. The throughflow stream undergoes cyclic growth and decay. The throughflow is in constant contact with the CW rotating primary vortex, which in turn interacts with two rotating vortices on the left wall. A CCW rotating vortex at the top right corner also experiences periodic growth and decay. Minimal heat transfer is consistently observed on the left wall. In contrast, certain segments of the other three walls and the boundary of the throughflow are zones of active heat exchange. For St = 0.1, the mean Nusselt numbers on the four walls clearly exhibit large amplitudes of oscillation and periodicity. With St = 10, the amplitudes of oscillation are degraded. These behaviors are directly linked to the relation between the period of oscillation and the convection time scale. Regardless of the Strouhal number, heat transfer enhancement in comparison to the steady state case is consistently observed. The best heat transfer rate is realized when the Strouhal number is close to unity. This is the case when the period of the incoming stream resonates with the convection time scale.
Thermal Characterization of Dielectric and Phase Change Materials for the Optical Recording Applications
Authors: Yang Y. , Li Chun-Teh , Sadeghipour S. M. , Asheghi M. , Dieker H. , Wuttig M.
Published: April 2009

Advances in the phase change optical recording technology strongly depend on the optical and thermal optimizations of the metal/ZnS-SiO2/phase change multilayer structure, which requires accurate modeling and thermal characterization of PC media structure. In the present work, the thermal conductivities of the amorphous and crystalline Ge4Sb1Te5 (GST) phase change; and ZnS-SiO2 dielectric layers of thickness in the range of 50 nm to 300 nm have been measured using the transient thermoreflectance technique. The data are between a factor of 2–4 different from the previously measured values for thin film and bulk samples. The thermal boundary resistance at metal/ZnS-SiO2 interface is found to be around 7×10−8 m2W−1. This might have serious implications for the future phase change recording application which attempts to achieve the high writing speeds by decreasing the thickness of ZnS-SiO2 dielectric layer.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
Modeling of Solidification and Filling of Thin-Section Castings
Authors: Felicelli Sergio D. , Poirier David R.
Published: April 2009

A finite element model for simulating dendritic solidification of multicomponent-alloy castings is used to study the filling and solidification of castings of thin cross section. The model solves the conservation equations of mass, momentum, energy, and alloy components and couples the solution with the thermodynamic of the multicomponent alloy through a phase diagram equation. The transport of mass and energy in the mushy zone is done considering the mushy zone as a porous medium of variable porosity. The same set of conservations equations are used for the liquid, solid and mushy zones, in which the volume fraction of liquid acts as the variable that makes the equations transition continuously from one zone to another (Felicelli et al. [1]). During filling, the model tracks the advancing front as the metal flows into the thin mold, and solidification is calculated as the metal loses energy by convection and radiation to the mold, including the dynamic calculation of view factors. The code supports two fluid models that emulate the flow behavior under equiaxed or columnar solidification. In the former case a slurry fluid model is used in which the viscosity is determined by the volume fraction of solid. In this slurry state, the solid and liquid move at the same velocity. For the case of columnar solidification, the solid is fixed and the liquid flows through a porous structure of dendrictic solid. The model development is based on the work by Felicelli et al. [2], to which several features were added, including a front-tracking technique (Gao [3]) and thermal radiation boundary conditions. Calculations for Ni and Al alloys were performed to illustrate the effect of several physical and operation parameters in the filling of a horizontal channel of thin thickness. A wide range of process parameters was tested in order to determine how much of the channel length could be filled before blockage of flow by solidification occurred. In a separate section, the effect of alloy concentration on the fluidity was studied using a Pb-Sn hypoeutectic system, and the importance that the dendrite breaking phenomenon can have on the results is shown. Conclusions about the parameters that most influence the filling process are presented, as well as recommendations on which experimental data are more critical in order to conduct a proper validation of this type of models.
Optimization of Multistage Vapor Compression Systems Employing Genetic Algorithms
Authors: West A. C. , Sherif S. A.
Published: April 2009

Genetic algorithms involve the coding of a solution into a binary string in the same manner that DNA is a biological coding. A population of binary strings are randomly created, evaluated, allowed to mate, and mutated to form a new generation of strings. There is a mating preference given to those strings which rate the highest to simulate the survival of the fittest theory that exists in nature. This process of evaluation, mating, and mutation is repeated until some termination criteria are met. A computer code was written to simulate the vapor compression systems and perpetuate the genetic algorithm. The genetic algorithm functioned adequately enough to provide general trends but it did not find a universal optimum. After numerous runs, the code produced data that suggest that systems which employ intercooler/flash tanks and operate at lower evaporating temperatures have a higher multistage effectiveness. Multistage effectiveness is a novel term defined as the ratio of the overall coefficient of performance (COP) of the multistage system and the combined coefficient of performance of a group of basic vapor compression systems with cooling capacities and evaporating temperatures that parallel the evaporators in the multistage system.
Investigation of the Natural Convection Boundary Condition in Microfabricated Structures
Authors: Hu Xuejiao , Jain Ankur , Goodson Kenneth E.
Published: April 2009

Heat loss through surrounding air has important thermal effect on microfabricated structures. This effect is generally modeled as a natural convection boundary condition. However, how to determine the convective coefficient (h) at microscales is a debate. In this paper, a micro heater is fabricated on a suspended thin film membrane. The natural convection is investigated using the 3-omega measurements and complex analytical modeling. It is found that h seems larger than that at larger scales; however, it is also proved that the increased h is actually contributed by heat conduction instead of heat convection. A method of determining the phenomenal h that can be used for microfabricated structures is proposed by using the heat conduction shape factor.
Heat Transfer and Fluid Flow in Metal Foam Subjected to Oscillating Flow
Authors: Leong K. C. , Jin L. W.
Published: April 2009

The need for higher performance and an increased level of functional integration as well as die size optimization on the microprocessor leads to preferential clustering of higher power units on the processor. Conventional natural or forced convection cooling methods are not capable of removing such a high heat flux for maintaining a proper operational temperature. It is imperative to look for new methods of cooling the modern high-speed electronic components. The porous medium has emerged as an effective method of heat transfer enhancement due to its large surface area to volume ratio and intense mixing of fluid flow. Many researchers have studied heat transfer and fluid flow in a channel filled with metal particles or woven-screens. However, uni-directional flow through the porous channel yields a relatively high temperature difference along the flow direction on the substrate surface. For modern high-speed microprocessors, the reliability of transistors and operating speed are not only influenced by the average temperature but also by temperature uniformity on the substrate surface. Therefore, maintaining the uniformity of on-die temperature distribution below certain limits is imperative in thermal design. It is conceivable that oscillating flow through a porous channel will produce a more uniform temperature distribution, due to the presence of two thermal entrance regions for oscillating flow. In the present investigation, a novel porous material of open-cell metal foam was employed to study heat transfer and fluid flow of oscillating flow through a porous channel. The metal foam with fully inter-connected structure, large surface area to volume ratio and high permeability lends itself to applications in electronics cooling. This paper describes an experimental study on heat transfer and pressure drop behavior of oscillating flow through a channel filled with open-cell aluminum foam. Both cycle-averaged and length-averaged local Nusselt numbers were calculated to evaluate heat transfer rate of oscillating flow in metal foam channel. The effects of the dimensionless flow amplitude and frequency of oscillating flow on heat transfer were analyzed. A correlation equation of maximum friction factor of oscillating flow in metal foam was obtained and compared with the results for wire-screens obtained by other investigators under the oscillating flow condition. The results revealed that heat transfer performance can be enhanced substantially by oscillating flow through metal foam with moderate pressure drop.
Nucleation Kinetics for Boiling in Microstructures
Authors: Lu J. F. , Peng X. F. , Bourouga B.
Published: April 2009

Theoretical investigation is conducted to understand the bubble nucleation process in microstructures. The bubble evolution in microstructures is investigated for momentum conservation, and the evolution rate is deeply dependent on the structure. According to different dynamic characteristics in the region close to the critical radius, the nucleation process is divided into two stages. Based on the characteristics of these two stages, a nucleation kinetic equation is modified from classical theory and then is conducted to understand the special bubble nucleation process. The result concludes that the nucleation rate will be deduced if bubble evolution is restrained in microstructures.
Natural Convection Over Bodies in the Transition Zone Between Laminar Thin Boundary Layer Dominated and Conduction Dominated Natural Convection
Authors: Willockx Arnout , Tjoen Christophe , Steeman Hendrik-Jan , De Paepe Michel
Published: April 2009

Different Rayleigh (Ra)-Nusselt (Nu)-correlations exist for natural convection from bodies. Different characteristic lengths are used by different authors. This paper reports of an experiment in which Ra is varied in an intermediate range. It is an interesting range because the values lie in a transition zone between laminar thin boundary layer dominated and conduction dominated natural convection. The experimental data is compared with existing correlations to check the accuracy and validity of these correlations for this transitional range of Ra. A new correlation that is only valid in this transitional zone is also proposed.
Thermal Management of Electronic Equipment Using Closed and Open Loop Cooling Systems
Authors: Heydari Ali
Published: April 2009

There is a strong need to improve our current capabilities in thermal management and electronic cooling, since estimates indicate that IC power density level could reach 50 W/cm2 in near future. This paper presents several possible closed and open loop cooling schemes for thermal management of electronic equipment in data centers. Additionally, analytical modeling of two kinds of direct expansion refrigeration cooling evaporator and a secondary liquid cooling fan coil heat exchanger is incorporated with a computational fluid dynamics (CFD) model to analyze a refrigeration cooled high heat density electronic and computer data center installed on a raised floor. Both models incorporate an accurate tube-by-tube thermal hydraulic modeling of the heat exchanger. The refrigeration coil analysis incorporates a multi region heat exchanger analysis for a more precise modeling of two phase refrigerant flow in the evaporator. The single phase secondary loop fan coil heat exchanger modeling uses an effectiveness method for regional modeling of the spotcooling coil. Using an iterative method, results of the heat exchanger modeling is simultaneously incorporated in the CFD model and an optimal design of spot cooling heat exchanger is developed.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
Evaporative Heat Transfer in Microtubes With Diameters From 244 μm to 792 μm
Authors: Hwang Yun Wook , Kim Min Soo
Published: April 2009

The characteristics of the evaporative heat transfer in microtubes were investigated with three circular tubes with inner diameters of 244, 430, and 792 μm, respectively. The interrelation between the heat flux and the mass flux about the heat transfer coefficients was expressed by the boiling number, which was considered to be a very important parameter to predict the trend of the heat transfer coefficients in microtubes versus the quality. A new correlation for the evaporative heat transfer coefficients in microtubes was developed by considering the following factors; the laminar flow heat transfer coefficient of liquid-phase flow, the enhancement factor of the convective heat transfer, and the nucleate boiling correction factor. The correlation developed in this study predicts the experimental heat transfer coefficients within an absolute average deviation of 8.4%.
Role of Random Roughness on Thermal Performance of Micro-Fins
Authors: Bahrami M. , Yovanovich M. M. , Culham J. R.
Published: April 2009

Heat transfer in rough circular cylinder microfins is studied and a novel analytical model is developed. Surface roughness is assumed to posses a Gaussian isotropic distribution. It is shown that, as a result of roughness, both cross-sectional and surface areas are increased. As a result, an enhancement is observed in the heat transfer rate and thus the thermal performance of microfins. The present model can be implemented to analyze other geometries such as rectangular and tapered microfins.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
Numerical Computation of Fluid Flow and Heat Transfer in Microchannels
Authors: Liu Ningli , Chevray Rene , Domoto Gerald A. , Panides Elias
Published: April 2009

A finite difference numerical approach for solving slightly compressible, time-dependent, viscous laminar flow is presented in this study. Simplified system of Navier-Stokes equations and energy equation are employed in the study in order to perform more efficient numerical calculations. Fluid flow and heat transfer phenomena in two dimensional microchannels are illustrated numerically in this paper. This numerical approach provides a complete numerical simulation of the development of the fluid flow and the temperature profiles through multi-dimensional microchannels.
Laminar Fully-Developed Flow in a Microchannel With Patterned Ultrahydrophobic Walls
Authors: Woolford B. , Jeffs K. , Maynes D. , Webb B. W.
Published: April 2009

Microfluidic transport is finding increasing application in a number of emerging technologies. At these scales, classical analysis shows that the required fluid driving pressure is inversely proportional to the hydraulic diameter to the fourth power. Consequently, generating fluid motion at these physical scales is a challenge. There is thus considerable incentive for developing strategies to reduce the frictional resistance to fluid flow. A novel approach recently proposed is fabrication of micro-ribs and cavities in the channel walls which are treated with a hydrophobic coating. This reduces the surface contact area between the flowing liquid and the solid wall, yielding walls with no-slip and shear-free regions at the microscale. The shear-free regions consist of a liquid-vapor meniscus above the cavities between micro-ribs. Reductions in the flow resistance are thus possible. This paper reports results of an analytical and experimental investigation of the laminar, fully-developed flow in a parallel plate microchannel whose walls are microengineered in this fashion. The micro-ribs and cavities are oriented parallel to the flow direction. The channel walls are modeled in an idealized fashion, with the shape of liquid-vapor meniscus approximated as flat and characterized by vanishing shear stress. Predictions are presented for the friction factor-Reynolds number product as a function of relevant governing dimensionless parameters. Comparisons are made between the smooth-wall classical channel flow results and predictions for the microengineered channel walls. Results show that significant reductions in the frictional pressure drop are possible. Reductions in frictional resistance increase as the channel hydraulic diameter and/or micro-rib width are reduced. The frictional pressure drop predictions are in good agreement with experimental measurements made at dynamically similar conditions, with greater deviation observed with increasing relative size of the shear-free regions.
Thermal Conduction Phenomena in Advanced Interface Materials for Electronics Cooling
Authors: Hu Xuejiao , Prasher Ravi , Goodson Kenneth
Published: April 2009

Thermal resistances at packaging interfaces are occupying a larger portion of the overall thermal resistance from a semiconductor die to ambient. Substantial improvement of the performance of thermal interface materials (TIMs) is required to achieve effective electronic cooling. This report is a brief review of the current status of TIM research. Particular focus is given to the fundamental understanding of heat conduction phenomena in polymer-based TIM composites at packaging interfaces in thin-film form. Promising nanostructured TIMs for future applications are also discussed.
Analysis of Convective Heat Transfer for Laminar Flow in a Pin Fins Array
Authors: Shokouhmand H. , Moghari M.
Published: April 2009

In this paper, convective heat transfer for fully developed laminar flow in a pin fins array using a two-dimensional periodic model of porous structure has been studied. A macroscopically uniform flow is assumed to pass through an array of circular pin fins placed regularly in an infinite space. Due to periodicity of the model, only one structural unit is taken for a calculation domain to resolve an entire domain of pin fins array. In the structural unit, pin fins surface are maintained at constant temperature, and Continuity, Navier-Stokes and energy equations are solved numerically to describe the microscopic velocity and temperature fields at a pore scale. The numerical results thus obtained are integrated over the structural unit to evaluate the dimensionless macroscopic pressure gradient and the thermal diffusivity tensors. Finally, the obtained results compared with available numerical and experimental data.
A Numerical Study of the Effect of Multi-Injection Strategy on NOx Reduction in DI Diesel Engines
Authors: Wang Yan , Zhang Chao , Jiang Jin
Published: April 2009

Diesel engines are becoming more and more popular as a power source for transportation and industry utility because of their better fuel efficiency over gasoline engines. At the same time, more and more stringent emission regulations on internal combustion engines have been used by governments all over the world. NOx emission control has become one of the biggest challenges in the design of Diesel engines. Previous experiments and simulations have shown that the multi-fuel-injection strategy can potentially reduce NOx emission in Diesel engines. In this study, more detailed numerical simulations have been conducted for up to 5 split fuel injections as compared to the conventional single fuel injection strategy to explore the effect of multi-fuel-injection on NOx reduction. KIVA-3V release 2, a multi-dimensional computational code employing combustion model, turbulence model, spray model and NOx production model, has been used in the numerical simulation. The combinations of multi-fuel-injection strategy with EGR (Exhaust Gas Recirculation) technique and multi-hole injectors are investigated as well. The results of this investigation have demonstrated that the use of the multi-fuel-injection strategy can effectively reduce the NOx emission in Diesel engines. Combined with other NOx reduction techniques, multi-fuel-injection strategy is a very promising way to make modern Diesel engines comply with the ever-stringent emission targets.
High Rayleigh Number Flows in a Cubical Enclosure
Authors: Vargas Lucas , Ahmed Ikram , Koert David N.
Published: April 2009

High Rayleigh number (Ra) natural convective flows in cubical enclosures were investigated using Direct Numerical Simulation (DNS). Here the bottom of the cavity was heated while the top was cooled, each maintained at a different constant temperature, with the sidewalls insulated. The Prandtl number was maintained at 2.5 and the Ra varied between 106 and 108. In order to observe the transition to turbulence with increasing Ra, power spectrum slopes were compared with Kolmogorov’s −5/3 rule for turbulent flows. At the higher Ra studied, the flows showed characteristics typically attributed to “chaotic” flows. However, the transition to full turbulence was not observed, which is expected around Ra ∼ 109 and may not be predicted using DNS with the state-of-the-art computing technology.
Transit Simulation Analysis for the Pressure Infiltration of Aluminum Melts Into Metal Matrix Composites
Authors: Xie J. , Amano R. S. , Mohan Das P. M. , Rohatgi P. K.
Published: April 2009

Metal matrix composites (MMCs) possess superior modulus and strength due to the presence of the reinforce phase in the matrix metal in the form of short or long fibers and particles. Pressure infiltration can produce metal matrix composites containing much high volume fractions of reinforcement in the matrix. This process was recognized as one of the competitive routes to produce near-net shape MMC structures and has achieved successful commercial applications. A transit numerical simulation study is presented for tracking interfaces of two phases for the analysis of pressure infiltrating high-conductivity reinforcement carbon fibers by a molten metal under high-applied pressure conditions. The interface tracking method uses piecewise linear (PLIC) volume-of-fluid (VOF) methods with two-dimensional mesh. The method is coupled with the continuum surface force (CSF) algorithm for surface force modeling, a multi-grid solver support the resolution of large density ratio between the fluid and air. A fine scale infiltration filling flow phenomena between the fibers was solved so that the process parameters can be optimized to cast fibrous MMC engineering structures with fine and pore-free microstructure as well as satisfaction mechanical properties.
Thermal Transport in Nanocrystalline Materials
Authors: Zhong Zhanrong , Wang Xinwei
Published: April 2009

In this work, thermal transport in nanocrystalline materials is studied using large-scale equilibrium molecular dynamics (MD) simulation. Nanocrystalline materials with different grain sizes are studied to explore how and to what extent the size of nanograins affects the thermal conductivity and specific heat. Substantial thermal conductivity reduction is observed and the reduction is stronger for nanocrystalline materials with smaller grains. On the other hand, the specific heat of nanocrystalline materials shows little change with the grain size. The simulation results are compared with the thermal transport in individual nanograins based on MD simulation. Further discussions are provided to explain the fundamental physics behind the observed thermal phenomena in this work.
CFD Analyses of Heat Sinks for CPU Cooling With Fluent
Authors: O¨ztu¨rk Emre , Tarı I˙lker
Published: April 2009

In this study, forced cooling of heat sinks mounted on CPUs was investigated. Heat sink effectiveness, effect of turbulence models, effect of radiation heat transfer and different heat sink geometries were numerically analyzed by commercially available computational fluid dynamics softwares Icepak and Fluent. The numerical results were compared with the experimental data and they were in good agreement. Conjugate heat transfer is simulated for all the electronic cards and packages by solving Navier-Stokes equations. Grid independent, well converged and well posed models were run and the results were compared. The best heat sink geometry is selected and it is modified in order to have lower maximum temperature distribution in the heat sink.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
Thermal Conductivity and Specific Heat Measurements of Single Nanowires
Authors: Dames Chris , Chen Gang
Published: April 2009

For the effective use of nanowires and nanotubes in their many possible applications in sensing, computation and memory, optoelectronics, and energy conversion, it is important to understand their thermal properties, which may differ considerably from bulk [1]. For example, there is good agreement between theory and experiments on Si nanowires showing that the classical size effect of phonon boundary scattering may reduce the thermal conductivity by up to several orders of magnitude for diameters of 40 nm and up [2, 3, 12, 13]. However, more experiments are needed at 20 nm and smaller diameters. There is also a need for experiments on the specific heat of single nanowires, which is intimately related to thermal conductivity by kinetic theory, and may be altered by quantum confinement effects. We have previously measured the specific heat of a pellet of TiO2 nanotubes of ∼3 nm wall thickness and found it similar to the bulk material at temperatures above ∼80 K [4]; however, questions remain about the possible interactions between adjacent tubes, which single-tube studies would resolve.
Radiative Heat Transfer During Growth of Carbon Nanotubes by Vertical Electric-Arc Process
Authors: Ostrogorsky A. G. , Glicksman L. R.
Published: April 2009

A macroscopic finite elements model of heat transfer occurring during production of carbon nanotubes was developed. Radiation heat transfer was modeled using the Discrete Ordinates (DO) model and the Rosseland diffusion approximation. The arc is modeled as semitransparent, with the optical thickness ranging from zero to infinity. The results are compared to the limited data available. The optical thickens has a significant impact on the temperature field in (i) the arc and (ii) the anode surfaces exposed to the arc. The temperature of the cathode side-surface on which the small diameter carbon nanotube grew, is not sensitive to the optical thickness of the arc. The model indicates that the optical thickness of the arc should be high, aL ≥ 100.
Computational Modeling of Intravitrael Drug Delivery in the Vitreous Chamber With Vitreous Substitutes
Authors: Kathawate Jyoti , Acharya Sumanta
Published: April 2009

Effective treatment of posterior segment diseases depends on the ability to deliver appropriate doses of drugs to target tissues in the posterior chamber of the eye. Intravitreal injection of drug is commonly used to treat vitreoretinal diseases. In order to assess the effectiveness of the injected drug, it is critical to know the drug distribution within the eye following injection. This is particularly important when the vitreous has been replaced by substitutes since there is little understanding of the transport of drugs in vitreous substitutes. The main objective of this research is therefore to characterize the drug distribution following intravitreal injection in the vitreous chamber of the human eye with different vitreous substitutes. In the present study, different intravitreal substitutes like silicone oil, fluorosilicone oil and perfluorocarbon liquids are considered. Both direct injection of drugs and injection of a time released drug distribution are studied. The results show that the concentration distribution is highly dependent on the vitreous substitute and the diffusion coefficient of the drug. For drugs with high diffusion coefficients, convection plays a small role. For drugs with low diffusion coefficients and for vitreous fluids with low viscosity, convection is seen to play a more important role.
Bora Mikic and Pool Boiling
Authors: Bergles Arthur E.
Published: April 2009

Even though Bora Mikic did his doctoral thesis on contact conductance, it was natural that he became involved immediately thereafter with the boiling group in the MIT Heat Transfer Laboratory. After all, contact conductance depends on randomly spaced points of contact between two surfaces, while nucleate pool boiling depends on randomly spaced cavities on a surface covered by liquid. Bora worked actively in boiling in the 1960s and 1970s. Collaborating with Warren Rohsenow, he developed what still is one of the most fundamental models for saturated pool boiling.
Computation of Velocity Profiles and Pressure Coefficients for a Laminar Flow of Air Over Staggered Array of Tubes
Authors: Rahmani Ramin , Ramezanpour Ahad , Mirzaee Iraj , Shirvani Hassan
Published: April 2009

In this study a two dimensional, steady state and incompressible laminar flow for staggered tube arrays in crossflow is investigated numerically. A finite-volume method is used to discretize and solve the governing Navier-Stokes equations for the geometries expressed by a boundary-fitted coordinate system. Solutions for Reynolds numbers of 100, 300, and 500 are obtained for a tube bundle with 10 longitudinal rows. Local velocity profiles on top of each tube and corresponding pressure coefficient are presented at nominal pitch-to-diameter ratios of 1.33, 1.60, and 2.00 for ES, ET, and RS arrangements. Differences in location of separation points are compared for three different arrangements. The predicted results on flow field for pressure coefficient showed a good agreement with available experimental measurements.
Transition Layer Effect on Thermal Radiative Near Field Mode Emission
Authors: Ghassemi S. , Hammonds J. S.
Published: April 2009

A spectrally selective thermally emitting device is proposed which takes advantage of near-field surface phonon polariton modes. Surface phonon polariton modes are usually restricted to the emitter surface and do not participate in energy exchange. In this work, the possibility of obtaining desirable spectral properties by using a thin-film surface active material, layered between dielectrics, is explored. This same multilayered structure is proposed to couple the surface modes into radiative modes that can participate in energy transport. This multilayer device is studied in this paper by developing the surface phonon mode dispersion relation to identify the spectral location of the surface modes. The fluctuation-dissipation theorem and impedance boundary condition is used to theoretically describe the near-field spectral radiative properties of the multilayer geometry. The near-field radiative properties show near monochromatic spectral characteristics due to the domination of surface phonon polariton modes.
Heat Transfer and Computational Simulations on the Drying Process of a Kiln
Authors: Chai Almon , Rigit Andrew , Ung Ha How
Published: April 2009

In this paper, the analytical and computational results are presented for a large-scale ceramic-tiles drying kiln. A lumped-parameter model was initially derived for the drying process of the kiln. This has led to the development of mathematical models for the energy conservation and convective heat and mass transfer drying process. Diffusion on the boundary layers of the tiles was also derived based on the basis of moisture isotherm, drying curve and different temperature profiles. This also takes into consideration the internal moisture transportation. The developed partial differential equations were discretized using the central-difference approximation method, which were further verified by a computational fluid-dynamics solver and the Gauss-Siedel iterative method. The modelling and simulations performed on the partial differential equations give possible auxiliary energy conservation and improvement on the drying process of the kiln.
Coupled Heat Transfer Phenomena in Cavitating Bubble Dynamics
Authors: Hauke Guillermo , Fuster Daniel , Dopazo Cesar
Published: April 2009

Cavitation is an incipient technique that finds application in advanced medicine, engineering and chemistry, where the high temperature and pressure of the cavitating bubbles are used as micro-reactors. However, present models to study the dynamics of cavitating bubbles have ignored important aspects of the transport phenomena, such as the actual gas and liquid thermal boundary layers across the bubble interphase. This leads to gross inaccuracies in estimating the heat transfer between the liquid and the gas, and to wrong interphase temperatures. In order to depth the understanding of this complex phenomena, a more realistic model has been developed, which includes the radial variation of the flow variables. In this model, the heat transfer across the bubble interphase is given directly by the coupled gas and liquid boundary layers. Other physical phenomena, such as, mass transfer and chemical reactions, have also been accounted for. The new model is able to predict the dynamics and internal state of the bubble with more accuracy than existing methods, allowing a more comprehensive knowledge of the bubble physics. In particular, it has been shown that the bubble dynamics depends heavily on the pressure difference across the bubble interphase. The predicted maximum temperature at the center of the bubble is slightly larger than that given by uniform models, whereas the calculated interphase temperature has been reduced to experimental values. Finally, the radial dependence of the temperature, pressure and chemical concentrations allows a more detailed analysis of the reaction processes occurring inside the bubble.
Cooling of the Heavy-Oil Trapped in the Reservoirs of the Sunk Oil Tanker Prestige
Authors: Garci´a-Ybarra Pedro , Dopazo Ce´sar
Published: April 2009

The cooling down of hot heavy-oil trapped within the reservoirs of a sunk tanker has been theoretically analysed and numerically simulated. Using the best available oil properties, and approximating the initial and boundary conditions in a rational way, a two-dimensional case-study has been investigated by several research groups. The volume average temperature within the lateral tank reaches 10°C after three months, while it takes five months for the central reservoir. Grid refinement tests have been conducted. The pressure dependence of the oil viscosity might have an important effect on the cooling time.
Diesel Spray Analysis
Authors: Jawad Badih A. , Riedel Chris H. , Bazzari Ahmad
Published: April 2009

Light scattering based particle sizing techniques have the advantage of nonintrusively measuring sizes of emulsions and dispersions. Depending on the parameters involved, there are several techniques that can be used and a choice of the most convenient method can be made. When the particles are large, Fraunhofer Diffraction Pattern Analysis (FDPA) can be employed in measuring particle-sizing distributions. The design of a high quality diesel engine would involve an understanding of the disintegration mechanism, spray penetration, and spray motion. It is the objective of this paper to implement the FDPA laser diffraction method to determine spray penetration and droplet mean diameters, for single injection of diesel fuel with synchronized time that will allow time dependent studies.
Comparison of Simulation and Experiment for Soot Concentration in a 2m Diameter JP-8 Fire
Authors: Tieszen Sheldon R.
Published: April 2009

A comparison is made between numerical simulations and experimental data for soot and water vapor concentration in a JP-8 fire. Soot concentration depends on soot generated/destroyed per unit flame area (subgrid soot model) and the overall flame area per unit volume (turbulence treatment). Two different turbulence treatments, a steady RANS variant and an unsteady LES variant, are used to determine the effect of overall flame area per unit volume. The results indicate that the difference in the two turbulence treatments is greater than the difference between the data and either approach.
Integrated Thermal Deformation Modeling and Measurement of Space Optical Systems
Authors: Sexton Mitra N. , Scott Mark I. , Stubbs David M. , Hashemi Ab
Published: April 2009

A computational and experimental study of the thermal, response and thermally induced deformation of a circular plano mirror (101.6 mm in diameter) undergoing mW heat loading was performed to verify the capability to model the response of a representative imaging optic on the Space Interferometry Mission (SIM) spacecraft. Novel state of the art experimental and computational techniques provided milliKelvin and picometer precision in temperature and deformation prediction and experimental measurement. Mirrors of two different substrates, initially at ambient temperature, were subjected to nominal thermal loading profiles of three 5 hour steps of 12 mW, 54 mW, and 295 mW respectively, representing flight-like and overdrive thermal disturbance conditions. The experimental setup measured milliKelvin level temperature changes using the mKTMS (milliKelvin Temperature Measurement System) instrument and picometer level deformation responses using the CoPHI (Common Path Heterodyne Interferometer) instrument. I-deas/TMG was used to generate an integrated model to predict milliKelvin level temperature changes of the mirror and picometer level deformation responses of the mirror surface. This paper focuses on the thermal modeling and correlation to thermal experimental data of the optical system. Comparison between experimental results and computational models for the thermal aspects of the test show good agreement for the two test mirror materials, fused silica and Zerodur. In particular for the flight-like regime of primary interest, agreement between the experimental temperatures and computational thermal results was within 14%.
Similarity Solution of Free Convection in a Stratified Porous Medium With Variable Permeability
Authors: Kalantarian A. , Khodabakhsh M. , Saidi M. H.
Published: April 2009

In this paper, similarity solution of free convection from inclined permeable wall embedded in a stratified porous medium is investigated. It is assumed that the heated wall has constant temperature and permeability along the wall is variable. Energy equation and Darcy’s law as momentum have been used. Due to similarity solution we consider only large wall inclination angle. Effects of mass flux, permeability variation function, and wall inclination angle on thermal and velocity boundary layer thickness and heat transfer at the wall are investigated.
A Novel Mechanism for Heat Transfer Enhancement Through Microchannels Using Electrokinetic Effect
Authors: Qazi Zade Azad , Monazami Reza , Manzari Mehrdad T. , Bazargan Vahid
Published: April 2009

In this paper a three-dimensional numerical model is developed in order to study the heat transfer enhancement in rectangular microchannels due to electrokinetic effect. The electrokinetic body force on fluid elements gives some superior convective transport properties to the flow relative to pure pressure driven flow in microchannels. Unlike the conventional parabolic velocity profile of pressure driven laminar flow, the electrokinetic body force transforms the velocity profile to a slug-like flow. Due to sharp velocity gradient near the wall, the convective heat transfer properties of the flow are improved dramatically. Net charge distribution across the channel is obtained by solving the 2D Poisson-Boltzmann equation. The incompressible laminar Navier-Stokes equations are then solved numerically by considering the presence of electrokinetic body force using the finite element method. Finally to obtain the temperature field through the channel, three-dimensional energy equation is solved for constant wall temperature condition. The analysis provides a unique fundamental insight into the complex flow and heat transfer pattern established in the channel due to combined pressure driven-electroosmotic pumping mechanism. The results are compared with the pressure driven flow in same channel. The comparison reveals significant change in flow pattern and heat transfer characteristics of single phase flow through microchannel by adding electroosmotic pumping mechanism to pressure driven flow.