bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance of Gaseous Counter-Flow Micro Heat Exchangers
Authors: Miwa J. , Hong C. , Asako Y. , Faghri M.
Published: April 2009

Heat exchangers performance of two-stream counter-flow gas-gas type micro-heat exchangers is investigated numerically. The flow passages of the micro-heat exchangers are parallel-plate channels with heights in the range of 10 to 100 μm and selected lengths of 12.7 and 25.4 mm. The numerical methodology is based on the Arbitrary-Lagrangian-Eulerian method. The computations were performed to find the effects of capacity ratio, channel height and length on the heat exchange characteristics of micro heat exchangers. The results are presented in form of temperature contours, bulk temperatures, total temperatures and heat flux variation along the channel. Also, the correlation between the effectiveness and Ntu is discussed.
A Study on the Heat Transfer Enhancement in Magnetron Sputtering System
Authors: Baik Jae-Sang , Kim Youn-Jea
Published: April 2009

Magnetron sputtering systems have been widely used in the field of thin film technologies, such as making ultra-thin semiconductors, metal films, etc. The feature of magnetron sputtering system is used high voltage and electric current as the power of system. The energy is converted to heat which must be removed by the appropriate cooling system. Otherwise, it may damage the target, the magnets, and the substrate as well. Also, the current trend of magnetron sputtering is towards that with larger size of target, which can improve the efficiency. Consequently, heat transfer of magnetron sputtering system becomes complex and needs to develop more efficient cooling system. The main parameters affecting the cooling performance are the flow path of cooling water and flow rate. In this study, we investigated the characteristics of cooling effect with various flow paths of cooling water and flow rates. Using a commercial code, FLUENT, which uses FVM (Finite Volume Method) and SIMPLE algorithm, the governing equations have been solved for the pressure, mass flow rate, and temperature distributions in the magnetron sputtering system.
Optimal Package Design of Stacks of Convection-Cooled Printed Circuit Boards Using Entropy Generation Minimization Method
Authors: Yang Wen Jei , Furukawa Takahiro , Torii Shuichi
Published: April 2009

Thermal optimization of a stack of printed circuit boards using entropy generation minimization (EGM) method is presented. The study consists of two parts. One is focused on the entropy generation of a module in periodically fully-developed channel flow (PDF), while the other is the optimization applied to electronic packages composed of a stack of printed circuit boards. In the process of optimizing electronics packaging, consideration is given to two constraints which are the maximum junction temperature specified by a chip manufacturer and the allowable pressure difference across the channel maintained by cooling fans. The Reynolds number, block geometry and bypass flow area ratio are varied to search for an optimal channel spacing using the EGM method whose validity is borne out by comparing with those obtained by the conventional thermal optimization (or overall thermal conductance) method. A dimensionless optimal board spacing parameter C is derived which involves the relative migration speed (or time) of heat transfer and viscous friction over the PDF channel length. A correlation equation is derived which expresses C in terms of the Reynolds number and block geometry. This equation can be employed in the optimal design of electronic packages.
Direct Numerical Simulation of Turbulent Rayleigh-Be´nard Convection Using a Higher Order Scheme
Authors: De A. K. , Eswaran V.
Published: April 2009

In the present paper a Direct Numerical Simulation of turbulent Rayleigh-Be´nard convection of a Boussinesq fluid with Prandtl number 0.7 in a 6 : 6 : 1 aspect ratio box at Ra = 2.106 is attempted. The incompressible Navier-Stokes equations are solved on non-uniform cartesian grids using a finite difference method with a high resolution convective scheme and 2nd order Adams-Bashforth Crank-Nicolson (ABCN) time-stepping. The numerical simulation is conducted on a parallel computer. We observed that temperature and velocity variances lead to different length and temperature scales. Negative skewnesses of vertical velocity and its derivative are observed. A non-uniform distribution of temperature near the surface proceeds to an exponential like variation in the center via an intermediate region outside the surface layer. Instantaneous snapshots of the flow field reveal intense sheet-like structures near the surface layers becoming plumes in the middle region. In the vertical cross-sectional planes, strong shearing effect near the surfaces, horizontal spreading and induction of plumes are observed.
Optimization of a Dimpled Channel Using a Surrogate Model
Authors: Kim Kwang-Yong , Shin Dong-Yoon
Published: April 2009

A numerical procedure to optimize the shape of a staggered dimpled surface to enhance the turbulent heat transfer in a rectangular channel is presented in this work. A Kriging model-based optimization technique is used with Reynolds-averaged Navier-Stokes analysis of the fluid flow and heat transfer with Shear Stress Transport turbulence model. The dimple depth-to-dimple print diameter ratio, channel height-to-dimple print diameter ratio, and dimple print diameter-to-pitch ratio are chosen as design variables. The objective function is defined as a linear combination of terms related to heat transfer and friction loss with a weighting factor. Latin Hypercube Sampling is used to determine the training points as a mean of the Design of Experiment. Through a sensitivity analysis, it was found that the objective function is most sensitive to the ratio of the dimple depth to dimple print diameter. Optimal values of the design variables were obtained in a range of the weighting factor.
Analytical Methods for Transport Equations in Similarity Form
Authors: Tiwari Abhishek , Tagavi Kaveh A. , McDonough J. M.
Published: April 2009

We present a novel approach for deriving analytical solutions to transport equations expressed in similarity variables. We apply a fixed-point iteration procedure to these transformed equations by formally solving for the highest derivative term and, from this (via requirements for convergence given by the contraction mapping principle), deduce a range of values for the outer limit of solution domain, for which the fixed-point iteration gives a converged solution.
CFD Model of a Planar Solid Oxide Electrolysis Cell: Base Case and Variations
Authors: Hawkes Grant , Jones Russell
Published: April 2009

A three-dimensional computational fluid dynamics (CFD) model has been created to model high-temperature steam electrolysis in a planar solid oxide electrolysis cell (SOEC). The model represents a single cell, as it would exist in an electrolysis stack. Details of the model geometry are specific to a stack that was fabricated by Ceramatec, Inc. and tested at the Idaho National Laboratory. Mass, momentum, energy, and species conservation and transport are provided via the core features of the commercial CFD code FLUENT. A solid-oxide fuel cell (SOFC) module adds the electrochemical reactions and loss mechanisms and computation of the electric field throughout the cell. The FLUENT SOFC user-defined subroutine was modified for this work to allow for operation in the SOEC mode. Model results provide detailed profiles of temperature, Nernst potential, operating potential, activation over-potential, anode-side gas composition, cathode-side gas composition, current density and hydrogen production over a range of stack operating conditions. Mean model results are shown to compare favorably with experimental results obtained from an actual ten-cell stack tested at INL. Mean per-cell area-specific-resistance (ASR) values decrease with increasing current density, consistent with experimental data. Predicted mean outlet hydrogen and steam concentrations vary linearly with current density, as expected. Effects of variations in operating temperature, gas flow rate, cathode and anode exchange current density, and contact resistance from the base case are presented. Discussion of thermal neutral voltage, enthalpy of reaction, hydrogen production, cell thermal efficiency, cell electrical efficiency, and Gibbs free energy are discussed and reported herein.
Large-Eddy Simulation of Turbulence / Radiation Interactions in a Reacting Turbulent Channel Flow
Authors: Gupta Ankur , Modest Michael F. , Haworth Daniel C.
Published: April 2009

Large-eddy simulation (LES) has been performed for a planar turbulent channel flow between two infinite, parallel, stationary plates. The capabilities and limitations of the LES code in predicting correct turbulent velocity and passive temperature field statistics have been established through comparisons to DNS data from the literature for nonreacting cases. Mixing and chemical reaction (infinitely fast) between a fuel stream and an oxidizer stream have been simulated to generate large composition and temperature fluctuations in the flow; here the composition and temperature do not affect the hydrodynamics (one-way coupling). The radiative transfer equation is solved using a spherical harmonics (P1) method, and radiation properties correspond to a fictitious gray gas with a composition- and temperature-dependent Planck-mean absorption coefficient that mimics that of typical hydrocarbon-air combustion products. Simulations have been performed for different optical thicknesses. In the absence of chemical reaction, temperature fluctuations and turbulence/radiation interactions (TRI) are small, consistent with earlier findings. Chemical reaction enhances the composition and temperature fluctuations, and hence the importance of TRI. Contributions to emission and absorption TRI have been isolated and quantified.
Optimum Fin Aspect Ratio of a Heat Sink for the Maximum Cooling Effectiveness Including Fin Tip Convection Effect
Authors: Kou Hong-Sen , Lee Ji-Jen , Chen Chih-Wei
Published: April 2009

The optimum approach of a heat sink with the least material cost for maximum heat dissipation is presented in this study. The longitudinal fin arrays of a heat sink can have either cylindrical, square, equilateral triangular and rectangular cross section in the theoretical analysis of the cooling effect. In addition, the convection effect due to the fin tip loss has been incorporated into the derivation. By input the Biot number, Bi*, heat transfer ratios Hb* and He*, the optimum heat transfer equation can be derived in transcendental form which can be solved by iterative method to calculate the optimum fin length and fin cross section. Meanwhile, the thermal resistance of a heat sink can be obtained to illustrate the cooling performance under various design conditions. Finally, examples are provided to show the results for practical purpose.
Modified Zonal Method for Thin Solid Semi-Transparent Media With Reflective Boundary
Authors: El-Hitti Georges M. , Nemer Maroun , El Khoury Khalil , Coldic Denis
Published: April 2009

In this paper a detailed description of a modified zonal method used for the prediction of transient operation in glass treatment furnaces is presented. This method calculates the radiative transfer factors for scenes containing both diffusive surfaces and absorbing-emitting/non-scattering media with high indices of refraction all embedded in a totally transparent atmosphere. The method used combines the flux plans approximation for calculation of the view factors, the plating algorithm originally developed by Edwards for calculation of the total heat transfer factors, and finally, Emery’s equations for deduction of the surface-volume and volume-volume heat transfer factors. The matrix of radiative transfer is then simplified by eliminating the low energy level factors, thus rendering the matrix hollow and thereafter decreasing the time required for calculation.
Molecular Scale Mechanism of Thermal Resistance at Solid-Liquid Interfaces (Influence of Interaction Parameters Between Solid and Liquid Molecules)
Authors: Torii Daichi , Ohara Taku , Ishida Kenji
Published: April 2009

Nonequilibrium molecular dynamics simulations have been performed for systems of a liquid film confined between atomistic solid walls. The two solid walls have different temperatures to generate a steady thermal energy flux in the system, which is the element of macroscopic heat conduction flux. Three kinds of liquid molecules and three kinds of solid walls are examined, and the thermal energy flux is measured at control surfaces in the liquid film and at the solid-liquid interfaces. By analyzing the thermal energy flux in detail by decomposing it into several molecular-scale contributions, influence of interaction parameters between solid and liquid molecules and the spacing of molecular alignment on the surface of the solid wall are clarified, and the molecular-scale mechanisms that govern the thermal resistance at a solid-liquid interface are elucidated.
Unsteady Simulation of Film Cooling Flow From an Inclined Cylindrical Jet
Authors: Kim Sung In , Hassan Ibrahim G. , Zhang Xuezhi
Published: April 2009

Film cooling is extensively used to provide protection against the severe thermal environment in gas turbine engines. Most of the computational studies on film cooling flow have been done using steady Reynolds-Averaged Navier-Stokes (RANS) calculation procedures. However, the turbulent stress field is highly anisotropic in the wake region of the coolant jet, and the inherent unsteadiness of the coolant jet-crossflow interactions may have important implications in the cooling performance. In this paper, a computational investigation about the unsteady behavior of jet-in-crossflow applications is performed using DES. Detailed computation of a single row of 35 degree round holes on a flat plate has been obtained for a blowing ratio of 1.0 and a density ratio of 2.0. Firstly, time step size, grid resolution tests have been conducted. Comparison of the time-averaged DES prediction with the measured film cooling effectiveness shows that DES prediction is reasonable. From present simulations, the typical coherent vortical structures of the jet-in-crossflows can be seen. The unsteady physics of jet-in-crossflow interactions and a jet liftoff in film cooling flows have been explored.
Constant Wall Temperature Nusselt and Poiseuille Numbers in Rectangular Microchannels
Authors: van Rij Jennifer , Ameel Tim , Harman Todd
Published: April 2009

Slip flow convective heat transfer and friction loss characteristics are numerically evaluated for constant wall temperature rectangular microchannels. The effects of rarefaction, accommodation coefficients, aspect ratio, second-order slip boundary conditions, axial conduction, and viscous dissipation with flow work are each considered. Second-order slip boundary conditions, axial conduction, and viscous dissipation with flow work effects have not been studied previously for rectangular channel slip flows. The effects of each of these parameters on the numerically computed convective heat transfer rate and friction loss are evaluated through the Nusselt number and Poiseuille number respectively. The numerical results are obtained using a continuum-based computational fluid dynamics algorithm that includes second-order slip flow and temperature jump boundary conditions. Numerical results for the three-dimensional, fully developed Nusselt and Poiseuille numbers are presented as functions of Knudsen number, first- and second-order velocity slip and temperature jump coefficients, aspect ratio, Brinkman number, and Peclet number. Effects of rarefaction, accommodation coefficients, and aspect ratio are consistent with previously reported analytical results for rectangular channel constant wall temperature flows. The effects of second-order slip terms, axial conduction and viscous dissipation are also shown to significantly affect the Nusselt and Poiseuille numbers.
Effects of Hydrogen and Helium Addition to Fuel on Soot Formation in Axisymmetric Coflow Laminar Methane-Air Diffusion Flame
Authors: Liu Fengshan , Migliorini Francesca , Cignoli Francesco , De Iuliis Silvana , Zizak Giorgio
Published: April 2009

Numerical and experimental studies were conducted to investigate the effects of hydrogen and helium addition to fuel on soot formation in atmospheric axisymmetric coflow laminar methane-air diffusion flame. Soot temperature and volume fraction distributions were measured using a two-dimensional two-color technique. Numerically the conservation equations of mass, momentum, energy, and species in the limit of low-Mach number were solved. Detailed gas-phase chemistry and thermal and transport properties were accounted for. Radiative heat transfer by CO, CO2, H2O, and soot was calculated using the discrete-ordinates method with the radiative properties of the mixture obtained from a wide-band model. Soot was modeled using a two-equation semi-empirical model in which the mechanisms for inception and surface growth are assumed to be PAH coagulation and H-abstraction acetylene addition. Both experimental and numerical results show that helium addition is more efficient than hydrogen addition in reducing soot formation in the methane flame. These results are different from the previous investigations in ethylene flames where the hydrogen addition was found to be more effective in reducing soot formation than helium addition due to the additional chemical suppression of hydrogen on soot. It is suggested here that hydrogen chemically enhances soot formation when added to methane.
An Experimental Investigation on Thermal Analysis of Loop Heat Pipe
Authors: Bhullar Bhupinder Singh , Gangacharyulu D. , Tathgir Ram Gopal
Published: April 2009

With the incremental heat dissipation requirements of the CPU and intricate electronic circuits requiring flexible piping for the extraction of large amount of heat, a loop heat pipe [LHP] is studied and empirically designed. An experimental study of a LHP has been conducted under the natural convection conditions taking into consideration the variable heat inputs and the quantities of working fluid. The LHP made of copper tubing with horizontal evaporator having a brass mesh wick have been studied and presented for various heat inputs 25 W, 50 W, 75 W, 100 W, 125 W and 150 W. The heat was transferred to the evaporator by constructing a parallel flow heat exchanger. The study was conducted at a vertical orientation using distilled water as the working fluid. Exhaustive attempt has been done in analyzing the effect of various quantities of working fluid (120 gm, 125 gm, 130 gm, 135 gm and 140 gm) on heat transfer parameters. The results includes an achievement of an averaged value of LHP efficiency of 94%, irrespective of the power input in the range of 25 W to 150 W, when working fluid is filled at 40% (130 gm) of evaporator volume. Another credited feature is the attainment of a constant value of LHP efficiency within the range of 75 W to 150 W irrespective of the change in the mass of working fluid.
Spectral Control of Thermal Radiation Using Micro-Structured Emitter-Surface for Thermophotovoltaic Generation of Electricity
Authors: Hanamura Katsunori , Kameya Yuki
Published: April 2009

Spectral control of thermal radiation emitted from micro-cavities made on a mirror-like-polished Ni metal surface was investigated through numerical simulation and experiment. In simulation, thermal radiation from solid surface was dealt as hemispherical emission from point sources, and Maxwell’s equations were solved using CIP (Cubic Interpolated Propagation) method. It was demonstrated that the emittance could be increased around the wavelength corresponding to the standard mode of cavity resonance, while the emittance at wavelengths corresponding to the higher modes was much the same as that of smooth flat surface. Furthermore, in experiment using rectangular micro-cavities (0.5×0.5×0.5μm3) made periodically on Ni smooth surface, spectral emittance was measured in the near-infrared region. The experimental results disclosed that the emissive power only in the range of shorter wavelength than 1.2μm was increased by the micro-cavities that played a role of a wave guide to produce cutoff effect clearly.
Study on Guarded Hot Plate Apparatus for Measurement of Thermal Conductivity of Small Polymer Specimens
Authors: Fujino Junichi , Honda Tomohiro
Published: April 2009

The aim of this work is to develop a guarded hot plate test apparatus for measuring the thermal conductivity of polymer specimen, the size of which is smaller and thicker than that recommended by the ISO and JIS. The authors made three experimental apparatus suitable for the different sizes of specimen 50×50, 100×100 and 200×200 mm2 in area, measured the thermal conductivity of polymer as homogeneous materials, which ranged from 0.2 to 0.6 W·m−1·K−1, and carried out the numerical analysis. The uncertainty for the measurement of the thermal conductivity of the polymer specimens is estimated to be within ±4% using our test apparatus. For the test apparatus suitable for the specimen 50×50 mm2, the gap has an effect on the measurement of the thermal conductivity. In addition, the temperature difference ΔTg of the heat source has a direct influence on the deviation in the thermal conductivity data. The influence of the aspect ratio of the specimen and gap width on the measurement is estimated to be within 0.9% for the specimens 50×50 mm2 used in the present study.
Measurement of Oxygen Diffusion Characteristics of Porous Media Used for the Gas Diffusion Layer of Proton-Exchange Membrane Fuel Cells
Authors: Wang Shixue , Utaka Yoshio , Tasaki Yutaka
Published: April 2009

It is known that the mass transfer characteristics of the gas diffusion layer (GDL) are closely related to the performance of a proton-exchange membrane fuel cell. In this study, an experimental method was established for measuring the gas diffusion coefficient in porous media by using an oxygen concentration sensor based on a galvanic battery operating at normal temperature. The oxygen diffusion coefficient in air measured by this method corresponded with data in the literature within ±6% deviation. The oxygen diffusion coefficients of two kinds of porous media generally used for the GDL were measured by the experimental method for dry and wet samples. The results indicate that the gas diffusion coefficient in porous media not only depends on porosity but is also affected by other factors, for example, tortuosity. It was also found that the diffusion coefficient in different directions, for example, through-plane and in-plane, in porous media can be very different. The oxygen diffusion coefficient in the porous media containing liquid water varied nonlinearly with the saturation level and was strongly affected by other factors as well.
Investigation on the Interactions Among Light, Material and Temperature Field in Transient Lens Effect
Authors: Yamazaki Kimiharu , Tokushige Masaya , Fushinobu Kazuyoshi , Okazaki Ken
Published: April 2009

Recently, analysis and diagnosis based on laser technology is progressing rapidly by means of the advancement of the technology related to optics. It is remarkable that the technology using high intensisty laser pulses, e.g. nanosecond to femtosecond laser pulses, has advanced. Using intense laser pulses gives high industrial advantages. However, there are few reports to investigate the relation between laser pulses and liquid. In this research, we investigate the influence of the local temperature distribution generated in applications that utilized cw-laser. Furthermore, we discussed the transient lens effect that is based on the interaction between light, material and temperature field experimentally and theoretically.
Analytical Study of Thermal Control Method to Minimize Temperature Change of a Plate With Changing Heat Generation
Authors: Hirasawa Shigeki , Ito Shinya
Published: April 2009

In semiconductor manufacturing process, very accurate temperature control is required. In this work we studied precise temperature control methods for a simple model by numerical simulation. To minimize temperature change at an object position of a vertical plate with varying a noise-heat-generation, we calculated unsteady temperature change of the plate under the effect of a feedback control and a feed-forward control of a control-heater. The temperature change at the object position can be decreased 1/10 times (0.7°C) using the feedback control of 2 s monitoring-time-step with the control-heater placed between the object position and the noise-heat-generation position. The temperature change at the object position can be decreased 1/1000 times (0.001°C) using the feed-forward control of 2 s monitoring-time-step and 5 s forecasting-time with the control-heater placed between the noise-heat-generation position and the object position.
Heat Transfer for Round Air Jets Flowing Along a Concave Surface
Authors: Ito Ryuta , Takeishi Kenichiro , Oda Yutaka , Yoshida Naoki
Published: April 2009

Local Nusselt number distributions for a square array of round air jets impinging on a flat surface and a concave surface were measured in high resolution by naphthalene sublimation techniques. Corresponding numerical simulations using a realizable k-ε model were also conducted to investigate the heat transfer characteristics of the multiple jets and to clarify the complex flow structure. The experiments were conducted for Re = 5000, 10000, and 15000 at the non-dimensional nozzle to plate distance of 3.75. The Nusselt number for both flat and concave surfaces increased as Reynolds number increased from 5000 to 10000. Unexpectedly, experimental results showed the tendency of Nu to be saturated for Re = 15000, while showing a monotonic increase in numerical simulations. Most amount of wall jets from a central impinging jet formed large-scale recirculating flows, which surrounded free jet region of each jet, while some other wall jet were entrained by a small vortical structure near the target wall and merged into large-scale recirculating flow of the neighboring jets.
Development of Precise Visualization System for Small Transient Diffusion Field of Protein Using Phase Shifting Interferometer
Authors: Komiya Atsuki , Maruyama Shigenao , Moriya Shuichi
Published: April 2009

This paper deals with a development of precise visualization system for mass diffusion field of micro quantity proteins by using phase shifting interferometer. The visualization system developed in this study could solve several measurement difficulties and accomplish quick and precise measurement of mass diffusion coefficient. For the observation of small transient diffusion field, Mach-Zehnder type phase shifting interferometer and small shearing cell were utilized. The designed small shearing cell requires only 10 micro liter solutions to form the transient diffusion field. As a target protein, lysozyme extracted from hen egg white was used. For the avoidance of protein denaturation, the lysozyme was dissolved in universal buffer solution over a wide pH range from pH 4.29 to 8.44. This range corresponds to that of digestive system in human body. Also, to investigate concentration dependency of mass diffusion coefficient, solutions over a wide range of concentration were prepared. The experimental results indicated that the concentration profile in a diffusion field could be detected clearly even though the field of view is smaller than 1.0mm square. The mass diffusion coefficient was derived by an analytical method proposed by authors. This method can derive mass diffusion coefficient as a function of concentration from one measurement datum. From the experimental data, the dependency of pH value of surrounding buffer and that of concentration on diffusion phenomena were discussed.
On Correlating Experimental Pressure Flow and Heat Transfer Measurements From Silicon Microchannels With Theoretical Calculations
Authors: Eason Cormac , O’Keeffe Niall , Enright Ryan , Dalton Tara
Published: April 2009

The bulk pressure flow and heat transfer characteristics of rectangular and trapezoidal microchannels etched in silicon were measured in the laminar regime. The channel hydraulic diameters were 305 μm for the Deep Reactive Ion Etched (DRIE) etched channel and 317 μm for the wet etched channel and there were 22 channels in each sample. The fluid used was purified degassed water. The inlet and outlet temperature and pressure of the fluid and the wall temperatures of the channels were measured at the inlet and outlet of the channels. Theoretical and experimental results were calculated using fluid properties at the mean fluid temperature for each data point. These were then collapsed to a single curve at constant temperature by multiplying the measured value by the ratio of the relevant fluid properties at the experimental and required temperatures. The cross section of each channel on each channel sample was measured along with the channel height and width to give an area ratio between the actual channel width and the width calculated assuming the channel was perfectly rectangular or trapezoidal. This ratio is used to compensate the theoretical results and improve their correlation with the experiment. The uncertainty in the experimental results was calculated by running the result processing calculations three times, once at nominal values and then shifting input values to their upper and lower limits based on a 95% confidence interval on the standard deviation for each inputted measurement. Theoretical calculations were run for each experimental mass flow rate in order to produce equivalent theoretical points to the experimental values. Uncertainty in the theory is also determined by running the theoretical calculations at upper, lower and nominal 95% confidence interval values for the channels being tested. It was found that while the pressure flow data from the channels matched theoretical trends and that the results for the rectangular DRIE channels showed no experimentally significant deviation from theory, the experimental data from the wet etched trapezoidal channels was lower than predictions. The heat transfer from the channels is strongly affected by the heat transferred to the coolant by the manifolds. When this effect is removed, the experimental Reynolds number Nusselt number plot becomes strongly linear. This does not agree with theoretical predictions.
Development of Pressure Sensitive Molecular Film Suitable for Measurement in High Knudsen Number Flows
Authors: Mori Hideo , Matsuda Yu , Yamaguchi Hiroki , Sakazaki Yoshiki , Uchida Toru , Niimi Tomohide
Published: April 2009

Pressure sensitive paint (PSP) technique is based on the interaction of oxygen molecules with luminescent molecules, and it seems suitable for analyses of high Knudsen number flows which require diagnostic tools in the molecular level. However, application of the PSP technique to micro-devices is still very difficult because of the thickness of PSP layers of the order of microns and the aggregation of luminescent molecules caused by the “painting” methods. To resolve the problems of ordinary PSPs mentioned above, we adopt the Langmuir-Blodgett (LB) method to fabricate pressure sensitive molecular films (PSMFs) having nanometer order thickness. The fundamental properties of the PSMFs such as the pressure sensitivity and the surface roughness are examined, to evaluate the feasibility of the PSMF technique for pressure measurement around micro-devices. A PSMF based on palladium (II) mesoporphyrin IX shows high pressure sensitivity in low pressure regime, while a PSMF based on platinum (II) mesoporphyrin IX is optimum for atmospheric pressure. It is also clarified that the PSMFs do not degrade the roughness of solid surfaces. The results indicate the feasibility of the PSMF technique for pressure measurement in high Knudsen number flows such as micro flows.
Numerical Simulation of Liquid Water and Air Flow in Separator-Channels in PEM Fuel Cell Using LBM
Authors: Tabe Yutaka , Kibo Kohsuke , Kikuta Kazushige , Chikahisa Takemi , Kozakai Masaya
Published: April 2009

In a polymer electrolyte membrane (PEM) fuel cell, the condensed water in the separator-channel prevents the supply of reactants to electrodes, which deteriorates the cell performance. The Lattice Boltzmann simulation has been developed to understand the behavior of condensed water in the separator-channels. The calculation process was improved, and the effect on the stability and reliability of simulation of two-phase flows with large density difference was confirmed. Further, the comparison with experiment of the falling water droplet by gravitation on the slope of micro porous layer was conducted to validate effectiveness of the improved simulation. It was shown that the simulation can express the increase in falling speed of water droplet and the effect of inclined angle of the slope, and our simulation is effective enough to estimate the liquid water and air flow in the separator-channel. Finally, the simulation of liquid water behaviors in separator-channels with various cross-sectional shapes was conducted, and the drain efficiency of water droplet of separator-channel was discussed.
Simple Measuring Method of Thermal Conductivity of Silicone Grease and Effect of Carbon Nanomaterials on Its Thermal Conductivity
Authors: Tomimura Toshio , Nomura Seiji , Okuyama Masaaki
Published: April 2009

In the electronic equipment like personal computers with high heat fluxes for instance, the thermal contact resistance plays an important role in its cooling system. To attain high cooling performance, some kind of grease is often introduced between a heat source and a heat sink. In the present study, a simple method for thermal conductivity measurement of grease has been proposed and confirmed its validity by using greases with known thermal conductivity. From a series of measurements, the validity of the present measuring method has been confirmed. Further, the effect of the addition of carbon nanomaterials on the thermal conductivity of silicone grease has been investigated, and its quantitative relation has been clarified.
Effects of a High Porous Material on Heat Transfer and Flow in a Circular Tube
Authors: Ichimiya Koichi , Takeda Tetsuaki , Uemura Takuya , Norikuni Tetsuya
Published: April 2009

This paper describes the heat transfer and flow characteristics of a heat exchanger tube filled with a high porous material. Fine copper wire (diamete: 0.5 mm) was inserted in a circular tube dominated by thermal conduction and forced convection. The porosity was from 0.98 to 1.0. Working fluid was air. Hydraulic equivalent diameter was cited as the characteristic length in Nusselt number and Reynolds number. Nusselt number and friction factor were expressed as functions of Reynolds number and porosity. Thermal performance was evaluated by the ratio of Nusselt number with and without a high porous material and the entropy generation. It was recognized that the high porous material was effective in low Reynolds number and the Reynolds number which minimized the entropy generation existed.
Precise Control of Frozen Region During Cryosurgery Utilizing Peltier Effect
Authors: Takeda Hiroki , Maruyama Shigenao , Aiba Setsuya , Komiya Atsuki
Published: April 2009

In cryosurgery, it is necessary to control heat transfer precisely and actively in order to necrotize diseased part effectively and to avoid freezing healthy tissues. In order to control heat transfer, the cryoprobe utilizing peltier module was developed. This cryoprobe makes it possible to control cooling and heating rate actively and precisely due to peltier effect. Therefore, it is convenient to control the size of cell-destroyed area. In order to confirm cooling performance of the cryoprobe, gelatin cooling experiment and animal experiment was conducted. From the results, it can be said that this cryoprobe has enough cooling performance to destroy undesirable cell and it can control cooling and heating rate actively. Numerical simulation which considers biological heat production, freezing of tissue and peltier effect at same time was developed in order to evaluate frozen region or necrotized area, which are difficult to be measured.
System Configuration and Performance Studies of Solid Oxide Fuel Cell -Gas Turbine Hybrid Cycle
Authors: Jiang Wei , Fang Ruxian , Khan Jamil A. , Dougal Roger A.
Published: April 2009

Fuel Cell is widely regarded as a potential alternative in the electric utility due to its distinct advantages of high energy conversion efficiency, low environmental impact and flexible uses of fuel types. In this paper we demonstrate the enhancement of thermal efficiency and power density of the power plant system by incorporating a hybrid cycle of Solid Oxide Fuel Cell (SOFC) and gas turbine with appropriate configurations. In this paper, a hybrid system composed of SOFC, gas turbine, compressor and high temperature heat exchanger is developed and simulated in the Virtual Test Bed (VTB) computational environment. The one-dimensional tubular SOFC model is based on the electrochemical and thermal modeling, accounting for the voltage losses and temperature dynamics. The single cell is discretized using a finite volume method where all the governing equations are solved for each finite volume. Simulation results show that the SOFC-GT hybrid system could achieve a 70% total electrical efficiency (LHV) and an electrical power output of 853KW, around 30% of which is produced by the power turbine. Two conventional power plant systems, i.e. gas turbine recuperative cycle and pure Fuel Cell power cycle, are also simulated for the performance comparison to validate the improved performance of Fuel Cell/Gas Turbine hybrid system. Finally, the dynamic behavior of the hybrid system is presented and analyzed based on the system simulation.
Investigation of Transport Phenomena in Three-Dimensional Gas Metal Arc Welding of Thick Metals
Authors: Zhou Jun , Davoud Mohammad S. , Tsai Hai-Lung
Published: April 2009

Arc welding is generally used to join thick metals in many engineering applications. However, poor penetration often occurs due to arc heat diffusion into the base metal. Hence, arc welding of thick metals normally requires grooving and/or preheating of the base metal and sometimes requires multiple passes for very thick metals or metals with high conductivity, such as aluminum alloys. In gas metal arc welding of thick metals with grooves and preheating, complicated melt flow and heat transfer are caused by the combined effect of droplet impingement, gravity, electromagnetic force, surface tension, and plasma arc pressure. Understanding these complicated transport phenomena involved in the welding process is critical in improving the penetration depth and weld quality. In this study, mathematical models and associated numerical techniques have been developed to study the effects of grooves and preheating on melt flow, diffusion of species, and weld penetration in gas metal arc welding of thick metals. Complex melt flow, transient weld pool shape and distributions of temperature and species in the weld pool are calculated. The continuum formation is adopted to handle liquid region, mushy zone and solid region. VOF technique is used to handle transient deformed shape of weld pool surface. The preliminary results show both grooves and preheating have important effects on the melt flow in weld pool and the weld penetration. Computer animations showing the evolutions of temperature; melt flow; and the interaction between droplets and weld pool will be presented.
Numerical Simulation of Thermocapillary Convection in an Annular Pool of Silicone Oil Heated From Inner Wall
Authors: Shi Wanyuan , Oshima Nobuyuki , Imaishi Nobuyuki
Published: April 2009

Thermocapillary convection in a shallow annular pool (depth d = 1 mm) of silicone oil (0.65 cSt, Pr = 6.7), heated from the inner wall, is investigated by numerical simulations. Under a fixed value of temperature difference between the outer and inner walls, surface temperature gradient in the inner heated pool is about 10% higher than that in the outer heated pool. Accordingly, the critical temperature difference for the incipience of HTW (ΔTc = 4.58K) is smaller than that (ΔTc = 5.0K) in the outer heated pool. Numerical simulations indicate that two groups of HTW, propagating in opposite azimuthal directions to each other, coexist and produce interference patterns in the inner heated pool. Rotation of the pool around its axis gives no significant influence on the behavior of HTW in the inner heated pool. The characteristics of HTW are discussed in contrast with those in the outer heated pool.
Effects of Clearance Between Heating Walls on Natural Cooling in a Channel Model of Electronic Equipment
Authors: Nishino Yasushi , Imai Ryoji , Nakagawa Shinji , Ishizuka Masaru
Published: April 2009

Making electronic products smaller in size requires air passages in the products to be narrow. For effective thermal management with natural convection, the relationship between cooling performance and a space for the air passages must be clarified. In this study, the natural cooling capacity and flow field in relatively small electronic equipment have been investigated. A channel model was used as an experimental model of electronic equipments. The channel model has two vertical copper walls modeling the printed circuit boards and two transparent walls modeling the casing walls. The walls constitute a vertical channel with the height of 120mm, the depth of 56mm, and the variable width. The width of the channel is called “a wall clearance” here and it is varied from 5mm to 15mm. The copper walls were heated using electric heaters. Temperatures in the model were measured with thermo-couples. In addition, velocity distributions in the channel were quantitatively measured using a particle image velocimetry (PIV). The natural cooling capacity was obtained as functions of the wall clearance and heating power. Temperature rise of the heated wall showed small differences with the clearances of 10 mm and 15mm. However, when the clearance was decreased to 5mm, temperature rise increased. The relationship between Nusselt number and Rayleigh number obtained in this study agrees with those obtained for the parallel plates without side walls. The results of the velocity measurement revealed that the velocity showed a 33% decrease when the wall clearance decreased from 10mm to 5mm. On the other hand, the maximum velocity in the channel showed a 10% increase when the clearance decreased from 15mm to 10mm. The changes in the velocity profiles depending on the heating conditions are clarified.
Heat Transport Characteristics of a Pulsating Heat Pipe
Authors: Nagasaki Takao , Hokazono Toshiyuki , Ito Yutaka
Published: April 2009

Heat transport characteristics of a closed loop pulsating heat pipe (PHP) have been investigated experimentally. The heat pipe consists of 12 turn copper pipes with 2mm inner diameter. The lengths of heating, adiabatic and cooling sections are 53mm, 100mm and 51mm, respectively. The heat load was varied up to nearly 1000W for water and R141b as the working fluid. Three kinds of orientation, bottom heat vertical, horizontal, and top heat vertical, were tested. Detailed measurements of wall temperature fluctuations for water revealed several characteristic operating behaviors, such as intermittent oscillation and thermosyphon-like behavior. The performance of PHP with R141b is better than that with water in small heat load range due to its independence of orientation, conversely, PHP with water was more efficient than R141b in large heat load range. In order to improve the performance of PHP with R141b, diamond particles were added, resulting in better performance than water in the whole range of heat load.
Effect of Cooling Surface Temperature on Frosting Phenomena Under Natural Convection
Authors: Ohkubo Hidetoshi , Matsumura Masahiro , Ueno Masayuki , Yamashita Koji
Published: April 2009

Frosting is a phenomenon that takes place on a surface that has been cooled to a temperature below solidification temperature of water vapor in air. Frosting occurs by either sublimation or by solidification of condensate on the surface, and frost layer is a porous layer of ice and air. Advances in air-conditioning and refrigeration technology have brought about frosting issues in several fields as well as a broadening of the temperature range in which frosting occurs. In the present work, we investigated mass transfer characteristics in frosting phenomenon under natural convection condition in order to establish mass transfer in the process of frosting; the parameter of study was the cooling surface temperature, which was changed between −10 to −114°C. The effects of the cooling surface temperature and absolute humidity on the mass transfer characteristics in the frosting process were clarified.
Confinement Effects in Heat Transfer to a Miniature Compressible Impinging Air Jet
Authors: Lupton Thomas L. , Murray Darina B. , Robinson Anthony J.
Published: April 2009

The decreasing physical size of microchips accompanied by the increasing heat flux to be dissipated has led to the study of possible new innovative electronic cooling methods. Jet cooling has been successfully implemented in a variety of industrial applications and its capacity to maintain high heat transfer rates demonstrates its vast potential for incorporation into future cooling applications. The reduction in size of electronic components leads to the inevitability of jets used in this area being subjected to a degree of jet confinement. In this study the effects of confinement on the local heat transfer characteristics were experimentally investigated for a turbulent, fully developed, axisymmetric, compressible and submerged miniature air jet impinging normally onto an ohmically heated flat plate. The resulting surface temperature distribution was recorded via infrared thermography. Two 1mm diameter nozzles were examined, one confined and one unconfined. Tests were conducted for nozzle exit to impingement surface spacings of 1, 2, 4 and 6 jet diameters and for Reynolds numbers of 7,000 and 12,000 which corresponded to Mach numbers of 0.3 and 0.5. The heat transfer analysis accounts for compressibility effects by using the adiabatic wall temperature as the reference temperature in calculation of the heat transfer coefficients. Local heat transfer distributions are presented as a function of radial distance from the stagnation point. The results obtained indicate that confinement contributes to a flatter distribution of heat transfer over the impingement surface.
Notch Arrangement Effects on Heat Transfer in a Channel With Cut-Fins
Authors: Tatsumi Kazuya , Matsuzaki Shintaro , Nakabe Kazuyoshi
Published: April 2009

The effects of the attack-angle of the fin notch array against the main flow and size of the clearance at the fin-tip on the heat transfer and pressure loss performances of a channel with cut-fins (parallel fins with square notches) mounted on the bottom wall were evaluated in the present article. Three-dimensional numerical simulations, PIV measurements and heat transfer experiments employing a modified single-blow method were conducted to discuss these characteristics. Larger pressure loss reduction was obtained by the cut-fins case compared with the plain-fins case (parallel fins without notches) under smaller clearance conditions, while smaller thermal resistance was achieved with larger clearance. A maximum peak, therefore, appeared in the overall performance in relation with the clearance size. Larger heat transfer coefficients were obtained with smaller attack-angles of the notch array in both experimental and numerical results, particularly under larger Reynolds number conditions. This was due to the spanwise flow generated in the area adjacent to the notch, by which renewal of the thermal boundary layer was effectively produced at the trailing edge of the notch.