bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Investigation of Oxygen-Enriched Pulverized Coal Combustion
Authors: Ghenai C. , Lin C. X. , Ebadian M. A.
Published: December 2008

This paper presents calculations of oxygen-enriched coal combustion. Enriching combustion air with oxygen is considered one of the most effective methods to improve thermal efficiency, reduce pollutant emissions such as NOx, and facilitate capture of CO2 pollutant from flue gas. In addition to solving transport equations for the continuous phase (gas), a discrete second phase (spherical particles) is simulated in the Lagrangian frame of reference. Reaction is modeled by a two-mixture fractions/PDF approach. Discrete phase modeling is used for the prediction of discrete phase trajectory and heat and mass transfer to and from particles. The coal used is a Canadian high sulfur bituminous coal. The mass fraction of oxygen in the combustion air was varied from 21% (air) to 100% (pure oxygen). The results show that the temperatures of the gas phase and coal particles increase, respectively, by 13% and 9% when the mass fraction of oxygen is increased from 21% to 100%. One important result is that the CO2 in the oxygen/coal exhaust stream is at a much higher concentration (50% higher) compared with the air and coal exhaust stream highly diluted by N2. This will help the capture of CO2 emissions from flue gas and consequently reduce the CO2 capture costs.
Soot Particle Measurements in Steady and Unsteady Laminar Diffusion Flames Using Laser-Induced Incandescence
Authors: Sapmaz H. , Lin C. X. , Ebadian M. A. , Ghenai C.
Published: December 2008

Laser-Induced Incandescence (LII) is used in this study to measure the soot volume fraction for steady and unsteady laminar ethylene diffusion flames. For the steady flame the soot profiles obtained in this study using LII showed good agreement with those obtained previously using scattering/extinction technique. For the unsteady or flickering flames, we generated very repeatable time-varying diffusion flames by forcing the fuel flow at frequencies between 1–10 Hz. Phase lock images of the soot volume fractions were obtained for different phases between 0° and 360°. The sequential images showed the dynamics of the interactions between the generated vortices in the fuel and the flame. The phase-locked soot images revealed the entire motion process of the soot field during each pulsation period. The results obtained in the course of this study show that the soot emission decreased by lowering the oscillation frequency of the flame.
Experimental Study of Microscale Bubble Growth and Departure Dynamic Over a Surface With Constant Heat Flux Boundary Condition
Authors: Moghaddam Saeed , Kiger Kenneth T.
Published: December 2008

Boiling heat transfer has been the subject of research for many years, with a substantial amount of effort devoted to understanding the microscale transport processes of nucleate boiling. This information is essential to determine appropriate expressions for the boiling heat transfer coefficient. As a result, several different competing models based on the bubbling dynamics and its associated heat transfer mechanisms have been hypothesized to account for the sensible and latent heat transport and liquid motion adjacent to the heat transfer surface. Many of the early models were based on the assumptions that growth, departure and the associated pumping action of the bubbles are responsible for heat transfer during nucleate boiling. Jakob [1] and Rohsenow [2] were apparently the first to postulate that the process of growth and departure of the bubble is responsible for the induced motion of the liquid adjacent to the heat transfer, as in any single-phase convection process. Rohsenow [2] modeled the heat transfer by using bubble diameter as a characteristic length to determine a Nusselt number based on a defined Reynolds and Prandtl number. Even with the same line of reasoning, Rohsenow’s analysis resulted in a different formulation compared to Froster and Zober [3], who implemented an alternate hypothesis for the velocity of the bubble interface used in defining the Reynolds number. Other models of this nature were also proposed by Forster and Greif [4] and Zuber [5].
Spot-Cooling by Confined, Impinging Synthetic Jet
Authors: Vukasinovic Jelena , Glezer Ari
Published: December 2008

Spot-cooling of discrete electronic packages mounted on a printed wiring board (PWB) is achieved by the impingement of an axisymmetric synthetic jet when the jet actuator is attached to one board and cools target integrated circuit (IC) on the opposite board. Present work demonstrates that even when the jet outflow is confined between two closely-spaced boards, the jet entrains ample volume flow rate of cooler ambient air, induces effective cooling by strong mixing near the heated surface, and ultimately dispenses the heated air to ambient. The cooling performance of the jet module is investigated experimentally in a scaled up model that enables high-resolution thermal and flow measurements. The test setup comprises of two circular parallel plates (D = 158.8mm) where one plate contains an integrated jet actuator and the opposite plate includes a target heater (dh = 86mm). The spacing between the plates is variable between D/12 and D/3. The flow within the gap is mapped using particle image velocimetry (PIV). It is found that confined jet impingement induces a countercurrent radial flow within the gap that includes a layer of cool ambient air entrained along the actuator plane and a layer of heated air that is dispensed along the target surface. Particle pathlines demonstrate significant mixing between the countercurrent streams and strong entrainment into the vortex rings that synthesize the jet. Heat transfer coefficient attains a local maximum away from the stagnation point that can be attributed to strong vorticity diffusion into the thermal boundary layer and enhanced mixing that accompanies the vortex ring impingement. Although the jet Reynolds number does not exceed 3300, the stagnation heat transfer coefficient is about 90 W/m2K for H/D = 0.32.
Turbulent Free Convection in a Composite Enclosure
Authors: de Lemos Marcelo J. S. , Magro Viviani T.
Published: December 2008

This paper deals with the problem of heat transfer in square cavities partially filled with porous material. Local flow and energy equations are integrated in a representative elementary volume in order to obtain a set of equations valid in both the clear flow region and in the porous matrix. A unique set of equations is discretized with the control volume method and solved with the SIMPLE algorithm. Enhancement of convective currents within the porous substrate is detected as the Rayleigh number increases. Thin boundary layers along the cavity vertical walls and stratification of the thermal field are observed for Ra > 109.
A Validation Quality Heat Flux Dataset for Large Pool Fires
Authors: Brown Alexander L. , Blanchat Thomas K.
Published: December 2008

A series of experiments has been performed in the Sandia National Laboratories FLAME facility with a 2-meter diameter JP-8 fuel pool fire. Sandia heat flux gages were employed to measure the incident flux at 8 locations outside the flame. Experiments were repeated to generate sufficient data for accurate confidence interval analysis. Additional sources of error are quantified and presented together with the data. The goal of this paper is to present these results in a way that is useful for validation of computer models that are capable of predicting heat flux from large fires. We anticipate using these data for comparison to validate models within the Advanced Simulation and Computing (ASC, formerly ASCI) codes FUEGO and SYRINX that predict fire dynamics and radiative transport through participating media. We present preliminary comparisons between existing models and experimental results.
Mass Transport Modeling for Turbulent Flow in Saturated Porous Media
Authors: Mesquita Maximilian S. , de Lemos Marcelo J. S.
Published: December 2008

This paper presents derivations of mass transport equations for turbulent flow in permeable structures. Equations are developed following two distinct procedures. The first method considers time averaging of the local instantaneous mass transport equation before the volume average operator is applied. The second methodology employs both averaging operators but in a reverse order. This work is intended to demonstrate that both approaches lead to equivalent equations when one takes into account both time fluctuations and spatial deviations of velocity and mass fraction. A modeled form for the final transport equation is presented where turbulent transfer is based on a macroscopic version of the k-ε model.
Dynamic Behavior of Cryogen Spray Cooling: Effect of Spray Distance
Authors: Wang G.-X. , Aguilar G. , Nelson J. S.
Published: December 2008

Cryogen spray cooling (CSC) is used to minimize the risk of epidermal damage during laser dermatologic surgery. During CSC, skin surface is cooled by a short spurt of refrigerant R134a with boiling point of −26.2°C. Since R134a is volatile in open atmospheric conditions, the atomized liquid droplets undergo continuous evaporation as they fly in air, leading to a lost momentum and mass. Therefore, the cooling effect of CSC depends strongly on the spray distance between the nozzle and the skin surface (L). The objective of this study was, therefore, to investigate the effect of L on the dynamic heat transfer of CSC. A skin model system made of poly methyl-methacrylate resin (Plexiglass®) is used to simulate CSC during laser dermatologic surgery. A fast-response temperature measurement sensor is built using thin (20 μm) aluminum foil and placed on top of the plexiglass with a 50 μm bead diameter thermocouple positioned in between. Variation of the surface temperature is then measured under various spray distances. The surface heat flux (q) as well as the heat transfer coefficient (h) between the surface and the cryogen is estimated by solving an inverse heat conduction problem with the measured temperature data as input. The effect of L on surface cooling in CSC is then investigated systematically. Both the estimated q and h show strong dynamic characteristics and are strong functions of the L. Two distinct spray-surface interaction mechanisms are identified within the spray distances studied. For short L (< 30 mm), the spurt droplets impinge on the substrate violently, resulting in a fairly thin cryogen film deposited on the surface. Strong dynamics and high q result in this case, corresponding to a high h as well. Interestingly, h becomes strongly fluctuating and even larger after spurt termination for these cases. For long L (> 30 mm), q is lower and it steadily decreases after spurt termination. The dynamic variation of h in this case is similar to that of q. These results should help in the selection of optimal CSC parameters, which are needed to produce high heat fluxes at the skin surface and thus obtain maximal epidermal protection during various dermatologic laser therapies.
Optical Diagnostics of Nucleate Boiling From Transparent Heated Surfaces
Authors: Zimmermann Anton , Holland Adrian M. , Garner Colin P.
Published: December 2008

Indium Tin Oxide (ITO) coated glass was used to provide transparent heated surfaces with heat fluxes high enough to generate nucleate boiling in water. The technique enables extended horizontal surfaces exhibiting nucleate boiling to be analysed with novel optical diagnostic methods. A horizontal glass substrate coated with an ITO layer on its top surface was immersed in demineralised water of temperatures between 70 and 80°C. A direct electrical current was passed through the ITO to heat the water. A high-speed imaging system comprising an infrared laser and CCD camera was used to analyse the resulting nucleate pool boiling from the ITO surface. This system was operated at up to 1 kHz frame rate and the bubbles analysed in terms of size and shape. Statistical data regarding bubble size and nucleation site density were obtained for heat fluxes ranging from 63 to 105 kW.m−2. Nucleation site densities were found to be up to 35 000 sites.m−2. Furthermore, non-intrusive cross-sectional void fraction measurements were made, and ranged from zero to 14% of surface area. The increase in both site density and void fraction with increasing heat flux was found to be in good agreement with published literature.
Application of a Parabolic Wave Equation to Sub-Micron Thermal Radiation Analysis
Authors: Hammonds James S.
Published: December 2008

Coordinate transformation of the homogeneous Helmholtz equation is applied such that, upon invoking the paraxial wave approximation, a parabolic wave equation is derived that is independent of the propagation vector, in the limit of wave transmission over very short distances. Thus, similarity solutions applicable to wavelengths in the UV and IR range can be calculated using this approach. This work proposes that these solutions are appropriate for analysis of thermal radiation at sub-micron distances from a surface, as interference effects are captured by this method. Furthermore, by employing a source tensor as the boundary condition, surface wave effects can also be accounted for. In this paper, the method is applied to a case where surface wave propagation is limited to one direction. The solution of the normalized amplitude field is shown to be equivalent to the Green function for thermal emission.
Modeling of Temperature Rise in Giant Magnetoresistive (GMR) Sensor During an Electrostatic Discharge (ESD) Event
Authors: Yang Yizhang , Sadeghipour Sadegh M. , Asheghi Mehdi
Published: December 2008

With the further miniaturization of the GMR heads, the electrostatic discharge (ESD) failure has become the primary reliability issue in manufacturing of these sensors. The Joule heating effect during the ESD events result in both thermal and magnetic damages in GMR heads. In this paper, the thermal response of the GMR read head to the excessive current/voltage during an ESD event is investigated numerically using a 3-D finite element analysis. Unlike the previous studies, the thermal properties of the GMR and Al2O3 gap layers used in the simulation are the experimentally measured values. The temperature-rise in GMR heads under human-body-model (HBM) source current is obtained for a range of GMR dimensions and thermal properties of its constituent materials. The simulation results show that temperature in the GMR element sharply increases as the GMR dimensions are reduced, indicating the future GMR heads are more susceptible to the ESD damages. In addition, thermal properties of the GMR and gap materials play key roles in accurate prediction of the temperature field in GMR head during ESD events.
Thermal Characterization of the 144 nm GMR Layer Using Microfabricated Suspended Structures
Authors: Zhang Shu , Yang Yizhang , Sadeghipour Sadegh M. , Asheghi Mehdi
Published: December 2008

The performance and reliability of GMR heads are influenced by the level of temperature rise, which may occur in the device during the normal operation or during an electrostatic discharge (ESD) event. However, the reliable electro-thermal modeling of the GMR sensor to predict the temperature rise, demands an accurate knowledge of the thermal properties of its constituent materials such as Al2O3 passivation and GMR layers. The lateral thermal conductivity of the GMR layer, which has not been measured previously, can largely influence the maximum temperature rise in the GMR sensor. The present effort will be directed at thermal characterization of the CoFe/Cu multilayer structures made of extremely thin periodic layers, using steady-state and frequency domain heating and thermometry in suspended bridges. The measurements are performed on several suspended structures with the lengths and widths in the range of 250 to 500 μm and 16 to 20 μm, respectively.
Modeling of Localized Heating Effect in Sub-Micron Silicon Transistors
Authors: Etessam-Yazdani Keivan , Sadeghipour Sadegh M. , Asheghi Mehdi
Published: December 2008

The performance and reliability of sub-micron semiconductor transistors demands accurate modeling of electron and phonon transport at nanoscales. The continued downscaling of the critical dimensions, introduces hotspots, inside transistors, with dimensions much smaller than phonon mean free path. This phenomenon, known as localized heating effect, results in a relatively high temperature at the hotspot that cannot be predicted using heat diffusion equation. While the contribution of the localized heating effect to the total device thermal resistance is significant during the normal operation of transistors, it has even greater implications for the thermoelectrical behavior of the device during an electrostatic discharge (ESD) event. The Boltzmann transport equation (BTE) can be used to capture the ballistic phonon transport in the vicinity of a hot spot but many of the existing solutions are limited to the one-dimensional and simple geometry configurations. We report our initial progress in solving the two dimensional Boltzmann transport equation for a hot spot in an infinite media (silicon) with constant temperature boundary condition and uniform heat generation configuration.
Modeling of Carbon Nanotube Emission Using Airy Functions
Authors: Walker D. G. , Fisher T. S.
Published: December 2008

Modeling of electron field emission has not advanced significantly since Fowler and Nordheim described the phenomenon eighty years ago. While their approach provides remarkable agreement with experiments for a large number of cases, the theory is strictly valid for planar geometries and low temperatures. Carbon nanotubes have been considered for field emission energy conversion devices. Under high-temperature conditions and significant field enhancement, the approximations used in the Fowler-Nordheim formalism become invalid. The present work predicts electron current densities emitted from carbon nanotubes using Airy functions to predict transmission and temperature dependent supply functions. Results indicate that Fowler-Nordheim compares favorably with the Airy function model for materials with large work function (φ ≈ 5eV, in the present study) at room temperatures. However, for materials with smaller work functions, the difference between the Airy function model and Fowler-Nordheim can be significant.
An Experimental Assessment of Computational Fluid Dynamics Predictive Accuracy for Electronic Component Operational Temperature
Authors: Eveloy Vale´rie , Rodgers Peter , Hashmi M. S. J.
Published: December 2008

The flow modeling approaches employed in Computational Fluid Dynamics (CFD) codes dedicated to the thermal analysis of electronic equipment are generally not specific for the analysis of forced airflows over populated Printed Circuit Boards. This limitation has been previously highlighted [1], with component junction temperature prediction errors of up to 35% reported. This study evaluates the predictive capability of candidate turbulence models more suited to the analysis of electronic component heat transfer. Significant improvements in component junction temperature prediction accuracy are obtained, relative to a standard high-Reynolds number k-e model, which are attributed to better prediction of both board leading edge heat transfer and component thermal interaction. Such improvements would enable parametric analysis of product thermal performance to be undertaken with greater confidence in the thermal design process, and the generation of more accurate temperature boundary conditions for use in Physics-of-Failure based reliability prediction methods. The case is made for vendors of CFD codes dedicated to the thermal analysis of electronics to consider the adoption of eddy viscosity turbulence models more suited to board-level analysis.
Coupled Heat and Mass Transfer by Mixed Convection From a Buried Pipe With Leakage
Authors: Ngo C. C. , Lai F. C.
Published: December 2008

Numerical solutions are presented for combined heat and mass transfer by mixed convection induced from a buried pipe with leakage. Two locations of leakage are considered in the present study: one is on top of the pipe and the other is at the bottom of the pipe. The governing equations formulated in the body-fitted coordinates are solved via the finite difference method. A parametric study has been performed to investigate the effects of Rayleigh number, Peclet number, Lewis number, and buoyancy ratio N on the heat and mass transfer results. It is found that both the Nusselt number and Sherwood number increase for the aiding flows (N > 0) and decrease for the opposing flows (N < 0). For aiding flows, Sherwood number increases with the Lewis number but Nusselt number decreases with the Lewis number.
Optimum Design of Heat Sinks Using Non-Isotropic Graphite Composites
Authors: Chen Gary , Capp Joe , Getz George , Flaherty David , Norley Julian
Published: December 2008

Recent developments in natural graphite composites by GrafTech International, Ltd. have led to novel highly conductive and lightweight materials with thermally non-isotropic structures [1]. The in-plane and out-of-plane thermal conductivities for such materials differ by a factor of up to 50. The non-isotropy in thermal conductivities is found to influence heat dissipation in different ways. This paper investigates the influence of thermal conductivity on the thermal performance of graphite heat sinks. In addition to addressing technology challenges encountered in design and optimization of heat sinks, this paper also discusses the efficient ways to utilize graphite composite materials, which can be expected to play an important role in future electronics cooling applications.
Mixed Convection in Rotating Concentric Annulus With a Porous Sleeve
Authors: Leong J. C. , Lai F. C.
Published: December 2008

Numerical solutions are presented for mixed convection in rotating concentric cylinders with a porous sleeve. The porous sleeve is press-fitted to the inner surface of the outer cylinder. While the inner cylinder is rotating at a constant speed, the outer cylinder remains stationary. The main objective of the present study is to numerically investigate the flow pattern and temperature distribution as affected by the presence of the porous layer, the centrifugal force, and thermal buoyancy. A parametric study has been performed to investigate the effects of Peclet number, Rayleigh number, and Darcy number on the heat transfer results.
Analysis of Melting in a Mixed Metal Powder Bed With Finite Thickness Subjected to Constant Heat Flux Heating
Authors: Chen Tiebing , Zhang Yuwen
Published: December 2008

Melting of a subcooled powder bed with the finite thickness that contains a mixture of two metal powders with significantly different melting points is investigated analytically. Shrinkage induced by melting is taken into account in the physical model. The temperature distributions in the liquid and solid phases were obtained using an exact solution and an integral approximate solution, respectively. The effects of porosity, Stefan number, and subcooling on the surface temperature and solid-liquid interface are also investigated. The present work built solid foundation to investigate the complex three-dimensional selective laser sintering (SLS) process.
Experimental Investigation of Heat Transfer in Microchannels
Authors: Lee Poh-Seng , Garimella Suresh V.
Published: December 2008

Heat transport in microchannels is experimentally investigated to explore the validity of classical correlations for conventional-sized rectangular channels in predicting the thermal behavior and the onset of transition in microchannels. The microchannels considered range in width from 194 μm to 534 μm, with the channel depth being nominally five times the width in each case. Ten microchannels were machined into a 2.54 cm by 2.54 cm copper substrate for each test piece. The experiments were conducted with deionized water, with the Reynolds number ranging from approximately 300 to 3500. The results show that the heat transfer in microchannels is satisfactorily predicted with a classical, continuum approach. However, the applicable classical correlations need to be chosen carefully to match the boundary and entrance length conditions imposed in the experiment.
Two Dimensional Modeling of Laser Cladding With Droplet Injection
Authors: Han L. , Choi J.
Published: December 2008

Directed Metal/Material Deposition (DMD) process is one of additive manufacturing processes based on laser cladding process. A full understanding of laser cladding process is a must to make the DMD process consistent and robust. A two dimensional mathematical model of laser cladding was developed to understand the influence of fluid flow to the mixing, dilution, and deposition dimension, incorporating melting, solidification, and evaporation phenomena. The fluid flow in the melt pool driven by thermal capillary convection and energy balance at liquid-vapor and solid-liquid interface was investigated and the impact of the droplets on the melt pool shape and ripple was studied. Dynamic motion, development of melt pool and the formation of cladding layer were simulated.
A Xenon Flashlamp Induced Fluorescence Method to Measure Flowfield Temperature and Pressure
Authors: Catton Ivan , Mendoza John , Azzazy M.
Published: December 2008

A nonintrusive method to measure temperature and pressure utilizing broadband excitation with broadband detection (BE-BD) of oxygen fluorescence was investigated. The required finely-tuned laser excitation source for laser-induced fluorescence was replaced by a more rugged and less expensive xenon flashlamp where more lines are excited and more lines need to be monitored. A numerical model simulating photon absorption and emission of oxygen was developed to determine temperature and pressure sensitive fluorescence spectral regions. The spectral regions were located within a segment (200–300 nm) of the Schumann-Runge band. The two spectral bands selected were 5-nm wide and centered at 227.5 nm and 297.5 nm. These bins were monitored in a laboratory experiment and used to form a ratio to determine temperature. The resulting fluorescence ratio followed numerical predictions for temperatures between 80–170°C and pressures between 1 and 2 atm.
Inverse Determination of Eroded Smelter Wall Thickness Variation Using an Elastic Membrane Concept
Authors: Baker Daniel P. , Dulikravich George S. , Dennis Brian H. , Martin Thomas J.
Published: December 2008

A novel algorithm has been developed for the non-destructive determination of the shape of the interface between a melt and a refractory material wall in smelter furnaces. This method uses measurements of temperature and heat flux at a number of points on the outer surface of the furnace and assumes that the inner (guessed) surface of the furnace wall is isothermal. The temperature field is then predicted in the entire furnace wall material by numerically solving a steady state heat conduction equation subject to the measured temperature values on the external surface and the isothermal melt material solidus temperature on the inner surface of the wall. The byproduct of this analysis is the computed heat flux on the external surface. The shape determination method then uses the difference between the measured and the computed heat fluxes on the outer surface of the furnace as a forcing function in an elastic membrane motion concept for the determination of the inner (melt-refractory) surface motion. The inverse determination of the melt-refractory interface shape can be achieved by utilizing this algorithm and any available analysis software for temperature field in the refractory wall. The initial guess of the wall inner shape can be significantly different from the final (unknown) wall shape. The entire wall shape determination procedure requires typically 5–15 temperature field analysis in the furnace wall material.
Natural Smoldering of Cigarettes
Authors: Costa Fernando de Souza
Published: December 2008

The smoldering of cigarettes without drawing is described by a simple analytical model. A burning cigarette is assumed to be divided in 4 zones: unburned tobacco, dry tobacco, char and ash, separated by infinitesimally thin fronts of drying, pyrolysis and char oxidation. Circumferential heat losses and the convective-diffusive processes in the boundary layer are considered. A set of non-linear algebraic equations is solved to determine smoldering rates, drying lengths and pyrolysis lengths and to obtain the profiles of temperature. The influence coefficients of several parameters on smolder characteristics are calculated. Theoretical burn rates have shown a good agreement to experiments.
A Sensitivity Study of NOx Emission to the Change in the Input Variables of a FGR Industrial Furnace
Authors: Jiang Q. , Zhang C. , Jiang J.
Published: December 2008

Preliminary study has shown that the flue gas recirculation (FGR) is one of the effective ways to reduce the Nitric Oxides (NOx) emission in industrial furnaces. The research reported in this paper concentrates mainly on the development of dynamic models suitable for on-line and real-time feedback control to reduce the NOx emission in industrial furnaces with FGR. To construct an appropriate dynamic model, the relationship between the NOx emission and the furnace input variables, such as the inlet combustion air mass flow rate, inlet combustion air temperature, and the pressure head of the FGR fan, has been investigated. A moment closure method with the assumed β probability density function (PDF) for the mixture fraction is used to model the turbulent non-premixed combustion process in the furnace. The combustion model is derived based on the assumption of instantaneous full chemical equilibrium. The discrete transfer radiation model is chosen as the radiation heat transfer model, and the weighted-sum-of-gray-gases model is used to calculate the absorption coefficient.
Nanowire Arrays for Thermoelectric Devices
Authors: Kim Woo C. , Abramson Alexis R. , Huxtable Scott T. , Majumdar Arun , Wu Yiying , Trahey Lynn , Yang Peidong , Stacy Angelica , Sanda Timothy D. , Gronsky Ronald
Published: December 2008

This study reports on the fabrication and characterization of two prototype thermoelectric devices constructed of either silicon (Si) or bismuth telluride (Bi2Te3) nanowire arrays. The growth mechanisms and fabrication procedures of the Si and Bi2Te3 devices are different as described in this paper. To characterize the thermoelectric device components, current-voltage (I-V) characteristics were first used to estimate their performance. For the Si device, the I-V characteristics suggest ohmic contacts at the metal-semiconductor junction. For the Bi2Te3 device, the I-V characteristics curve showed a rectifying contact. Either low doping of the Bi2Te3 or surface contamination, i.e. native oxide, may cause the rectifying contact. The reversible Peltier effects occurring within the Si device were analyzed using a micro-thermocouple. Results indicated possible limitations of using Si nanowire arrays for the thermoelectric device.
Investigating the Integration of a Solid Oxide Fuel Cell and a Gas Turbine System With Coal Gasification Technologies
Authors: Plummer Dawson A. , Haynes Comas , Wepfer William
Published: December 2008

Solid oxide fuel cell (SOFC) technology incorporates electrochemical reactions that generate electricity and high quality heat. The coupling of this technology with gas turbine bottoming cycles, to form hybrid power systems, leads to high efficiency levels. The purpose of this study is to conceptually integrate the hybrid power system with existing and imminent coal gasification technologies through computer simulation. The gasification technologies considered for integration include the Kellogg Brown Root (KBR) Transport Reactor and Entrained Coal Gasification. Parametric studies were performed to assess the effect of changes in pertinent fuel cell stack process settings such as operating voltage, inverse equivalence ratio and fuel utilization will be varied. Power output, system efficiency and costs are the chosen dependent variables of interest. Coal gasification data and a proven SOFC model program are used to test the theoretical integration. Feasibility and economic comparisons between the new integrated system and existing conventional systems are also made.
Effect Analysis of Micro Mass Transfer on Steel Casting Solidification Process
Authors: Feng Yanhui , Zhang Xinxin , Wu Wenfei
Published: December 2008

Existing models for the solute redistribution during solidification have been reviewed. The typical models are applied for the numerical simulation of heat and mass transfer with phase change for the new inverse casting technology and the traditional CSP technology. The results show that the effect of micro mass transfer models on the perfection of continuous solidification processes for Fe-C alloy cannot be omitted for coupled heat and mass transfer phenomenon.
Numerical Simulation for Microconvection Around Nano-Particle With Brownian Motion in Liquid
Authors: Wang B. X. , Li H. , Peng X. F. , Yang L. X.
Published: December 2008

The development of a numerical model for analyzing the effect of the nano-particles’ Brownian motion on the heat transfer is described. By using the Maxwell velocity distribution relations to calculate the most possible velocity of fluid molecules at certain temperature gradient location around the nano-particle, the interaction between fluid molecules and one single nano-particle is analyzed and calculated. Based on this, a syntonic system is proposed and the coupled effect that Brownian motion of nano-particles has on fluid molecules is simulated. This is used to formulate a reasonable analytic method, facilitating laboratory study. The results provide the essential features of the heat transfer process, contributed by micro-convection to be considered.
Numerical Simulations of Industrial Melting Furnaces
Authors: Chang S. L. , Zhou C. Q. , Scheeringa K.
Published: December 2008

A computational fluid dynamics code developed at Argonne National Laboratory was used to simulate turbulent mixing, combustion reaction, radiation heat transfer, and pollutant kinetics of the combustion flow in industrial melting furnaces. The code employs an integral approach to incorporate a lumped combustion reaction model in the flow calculation and a separate hybrid technique to perform pollutant kinetics calculations for NOx and soot. The code validated with experimental data collected from industrial furnaces, was used to evaluate the impacts of burner operation conditions on the energy efficiency of furnaces. The results indicate that the furnace configuration has a significant effect on the combustion efficiency; the burner injection velocity affects the flow penetration and the species mixing; and the burner injection angle has a significant impact on the flow patterns and heat transfer. The study demonstrates that CFD can be a useful tool for analyzing the combustion flow of an industrial furnace.
Influence of Contact Mechanics in the Prediction of the Effective Thermal Conductivity of Spheroid Packed Beds
Authors: Buonanno G. , Carotenuto A. , Giovinco G. , Vanoli L.
Published: December 2008

Thermal contact conductance is an important parameter in a wide range of thermal phenomena, and consequently a large number of experimental, numerical and statistical investigations have been carried out in literature. In the present paper an analysis of thermal contact resistance is carried out to predict heat transfer between spherical rough surfaces in contact, by means of a statistical approach. The micro-geometry of the surface is described through a probabilistic model based on the peak height variability and invariant asperity curvature radius. The numerical model has been applied to evaluate the effective thermal conductivity of packed beds of steel spheroids and validated through the comparison with the experimental data obtained by means of an apparatus designed and build up for this purpose.
Thermal Diffusivity Micro-Measurement Using Photo-Thermal Technique
Authors: Lafdi Khalid , Teo Kia-Moh , ElGafy Ahmed
Published: December 2008

In this paper, both theory and experimental setup of the Transmission photo-thermal technique are presented. Based on this technique, two measurement methodologies are available: phase shift method and temperature change method. However, only the experimental results from the phase shift method are presented in this paper. The measurements can be performed at any radial direction on a sample’s surface. This technique appears to be a successful method for measuring the variation of surface thermal diffusivity of various materials. An automated platform has also been developed and integrated into the technique to measure and map the variation of surface thermal diffusivity of a material. This technique can be used to detect any surface’s thermal defects of a material. It is also useful in studying the surface temperature distribution of a heat application material.
An Analysis to Predict Forest Fire Danger and Fire Spread
Authors: Satoh Kohyu , Kitamura Shiro , Kuwahara Kunio , Yang K. T.
Published: December 2008

Forest fires are of common occurrence all over the world, causing severe damages to valuable natural environment and loss of human lives. In order to reduce the damages by forest fires, it is useful to utilize a system, which can predict the occurrence of forest fires and the spread of fires. Well known is a system in USA, called NFDRS to predict forest fire occurrence and FARSITE to predict fire growth, based on the fire weather information taken from a network, combined with forest fuel conditions and land topography data, and processed by an algorithm to generate the various fire danger indices. In Japan the number of forest fires is roughly 3,000 per year, which is 1/30 times compared with USA, and there are very few fires exceeding 1000 ha burnt area, hence there has existed scant demand for this type of intelligent system. Although recently there is an increasing demand for such a system in Japan, the US system for forest-fire prediction is however not applicable to Japan, since the forest topology and weather conditions between Japan and USA are far different. Moreover, many fire weather stations have been installed in the US forests, but in Japan no such fire weather stations are installed in forests. Thus, as a first step to develop an intelligent system for Japan, we have analyzed the fundamentals of forest fire danger rating and the fire spread, based on the weather data and other information on forest fires. The objective of this study is to examine how the fundamentals, based on analyzing the past fire occurrences and CFD simulations particularly on “Katunuma Fire”, can predict the occurrence of forest fires and the spread of forest fires.
An Analytical Evaluation of the Optimal Thermal Dose Delivery Parameters for Thermal Therapies
Authors: Cheng Kung-Shan , Roemer Robert B.
Published: December 2008

This study derives the first analytic solution for evaluating the optimal treatment parameters needed for delivering a desired thermal dose during thermal therapies consisting of a single heating pulse. Each treatment is divided into four time periods (two power-on and two power-off), and the thermal dose delivered during each of those periods is evaluated using the non-linear Sapareto and Dewey equation relating thermal dose to temperature and time. The results reveal that the thermal dose delivered during the second power-on period when T>43C (TD2) and the initial power-off period when T>43C (TD3) contribute the major portions of the total thermal dose needed for a successful treatment (taken as 240 CEM43°C), and that TD3 dominates for treatments with higher peak temperatures. For a fixed perfusion value, the analytical results show that once the maximum treatment temperature and the total thermal dose (e.g., 240 CEM43°C) are specified, then the required heating time and the applied power magnitude are uniquely determined. These are the optimal heating parameters since lower/higher values result in under-dosing/over-dosing of the treated region. It is also shown that higher maximum treatment temperatures result in shorter treatment times, and for each patient blood flow there is a maximum allowable temperature that can be used to reach the desired thermal dose. In addition, since TD2 and TD3 contribute most of the total thermal dose, and they are both significantly affected by the blood flow present for high treatment temperatures, these results show that perfusion effects must be considered when attempting to optimize high temperature thermal therapy treatments (no excess thermal dose delivered, minimum power applied and shortest treatment time attained).
Design and Heat Transfer Analysis of Automotive Disc Brakes
Authors: Jancirani J. , Chandrasekaran S. , Tamilporai P.
Published: December 2008

In the recent scenario of braking system for automobiles, disc brake takes up a wide range of applications, because of its simplicity in construction, operation and not self energizing as in the case of drum brakes. Since the disc brakes takes up a wide range of application, it is essential to ensure the reliable function of the braking system under varied operating conditions. The reliable function of the disc brake system is purely depends on the system based design. In this work, a linear regression technique is used for the optimal design of the disc brake rotor for varied operating conditions. Various forces involved during braking, energy generated during braking and the corresponding effective stopping distances were also calculated using appropriate governing relations and equations. In the varied operating conditions, the heat energy generated during braking should be driven away form the working surfaces of the components. To analyze this thermal loading and cooling phenomenon, a conventional convective heat transfer approach was also formulated and developed in this work. The analytical findings of the above approaches are demonstrated at the end and it is found to be quite satisfactory.
Heat and Mass Transfer in Loop Heat Pipes
Authors: Hoang Triem T. , Ku Jentung
Published: December 2008

Loop Heat Pipes (LHPs) have gained acceptance among spacecraft engineers in recent years as high performance heat transport devices for thermal control systems (TCS). However, the most common criticism from people who use LHPs is that their behavior is difficult to predict. Complex interaction of thermodynamics and fluid flow dynamics inside a LHP poses a challenge for the analytical modeling of its performance. The need for a complete understanding of mechanisms involving the heat and mass transfer in a LHP cannot be overstated. During the initial spacecraft TCS design phase, trade studies are usually carried out to select an appropriate thermal control concept for the design. The inability to accurately predict the LHP response in the actual operating environment often leads to the dismissal of LHPs for lack of certainty. This paper attempts to present a simplistic explanation of LHP operation in terms of heat and mass transfer processes, in hope that it will help the potential end-users to understand the technology better. Most of the observed phenomena described herein are based on available test data of various LHP systems. Nevertheless, a few anomalies especially during operational transients are still not well understood. For that, research ideas will also be proposed.
Theoretical Analysis of Oscillating and Streaming Fields Between Two Parallel Beams and Numerical Investigation of the Cooling Efficiency
Authors: Wan Qun , Kuznetsov A. V.
Published: December 2008

The main purpose of this paper is to investigate the oscillating and streaming flow fields and the heat transfer efficiency across a channel between two long parallel beams, one of which is stationary and the other oscillating in standing wave form. The oscillating amplitude is assumed much smaller than the channel height. When the Reynolds number, which is defined by the oscillating frequency and the standing wave number, is much greater than unity, boundary layer structures are found near both beams, which are separated by a core region in the center of the channel. The oscillating fields within the core region and both boundary layers are obtained analytically. Based on the oscillating fields, the streaming fields within both boundary layers are also analytically obtained. Further investigation of boundary layer streaming fields shows that the streaming velocities approach constant values at the edges of the boundary layers and provide slip velocities for the streaming field in the core region. The core region streaming velocity field is numerically obtained by solving the mass and momentum conservation equations in their stream function–vorticity form. The temperature field is also computed for two cases: both beams are kept at constant but different temperatures (case A) or the oscillating beam is kept at a constant temperature and the stationary beam is prescribed a constant heat flux (case B). Cases of different channel heights are computed and a critical height is found. When the channel height is smaller than the critical value, for each half standing wavelength distance along the beams, two symmetric eddies are observed, which occupy the whole channel. In this case, the Nusselt number increases with the increase of the channel height. After the critical value, two layers of asymmetric eddies are observed near the oscillating beam and the Nusselt number decreases and approaches unity with the increase of the gap size. The abrupt change of the streaming field and the Nusselt number as the channel height goes through its critical value may be due to the bifurcation caused by instability of the vortex structure in the fluid layer.
Existence of an Optimum Spacing Between Horizontal Cylinders in a Horizontal Row Cooled by Natural Convection
Authors: Fakheri Ahmad , Gaganjit Sahota S.
Published: December 2008

The results of this research show that as the horizontal spacing between the cylinders in a single horizontal row is reduced; the natural convection heat transfer coefficient and thus the rate of heat transfer from each cylinder could increase substantially beyond those for natural convection from a single cylinder before rapidly decreasing. The rate of heat transfer from the array can therefore be significantly increased because of two factors; the enhanced heat transfer coefficient and the ability to add more cylinders in a given volume. The rapid reduction in heat transfer at very small spacing also points to the existence of an optimum tube spacing. This phenomenon does not appear to have been reported before and may lead to significant reductions in the size of many heat exchangers and may prove useful in cooling of electronic components.
Algorithm Dependence of the Weak Turbulent Solution in Porous Media Convection
Authors: Vadasz Peter
Published: December 2008

The details of multiple solutions for porous media convection within the weak turbulent regimes are being investigated. The sensitivity of the results to very small changes in an algorithm using the same method of solution is particularly sought. Analytical as well as computational results identifying the reason behind this sensitivity beyond the obvious known fact of diverging near-by trajectories, are presented. The issue of lack of predictability of the results obtained in the weak turbulent regime is dealt with as well. The latter indicates a way to use the results in all practical engineering applications despite this lack of predictability of detail.