bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Analysis of Direct Chill Casting
Authors: Nallathambi Ashok Kumar , Tyagi Mohit , Specht Eckehard , Bertram Albrecht
Published: March 2011

Direct Chill (DC) casting is a semi-continuous casting technique which is used to produce aluminum rolling ingots and extrusion billets. The knowledge of temperature field is highly essential for the prediction of displacement field and hot tears. Modeling the thermal field of DC casting is a challenging task due to the liquid-solid phase transition, time-dependent domain and boundary conditions, inverse nature of secondary boundary conditions, etc. Therefore, an attempt is made to model the thermal field of DC casting using a finite element method. A temperature-based finite element model is used to capture the effect of latent heat release. A temperature-dependent heat transfer coefficient is employed to incorporate the bottom block and mold boundaries. The influence of casting speed is studied in detail. Through the proper ramping procedures, it is proved that the start-up phase sump depth and mushy length can be lowered. However, it is found that the steady-state sump parameters are independent of ramping. Further, the influences of secondary cooling profile, and melt superheat are investigated. AA1201 alloy is considered for the study.
New Thermal Management Systems for Data Centers
Authors: Ouchi Mayumi , Abe Yoshiyuki , Fukagaya Masato , Kitagawa Takashi , Ohta Haruhiko , Shinmoto Yasuhisa , Sato Masahide , Iimura Ken-ichi
Published: March 2011

The almost half amount of power consumption in data centers which has been increasing drastically in late years is due to air conditioner for cooling down the data centers. The present authors proposed new thermal management systems for data centers aiming for the data centers without air conditioning, and R&D subjects have been conducted under the so called Green IT Project sponsored by NEDO (New Energy and Industrial Technology Development Organization). In this system, three liquid cooling methods for CPUs have been developed simultaneously, which are two types of direct liquid cooling with single-phase or two-phase heat exchanger and an indirect liquid cooling with high performance thin heat pipes. To establish this system, five R&D subjects have been conducted. In this paper, current progress of these subjects such as development of heat transfer components, verification test using real server racks, and nanofluids technology for heat transfer enhancement is reported.
Numerical Study on Subcooled Pool Boiling
Authors: Ose Yasuo , Kunugi Tomoaki
Published: March 2011

This study focuses on the clarification of the heat transfer characteristics of the subcooled pool boiling, the discussion on its mechanism, and finally the establishment of a boiling and condensation model for numerical simulation on the subcooled pool boiling phenomena. In this paper, the boiling and condensation model is improved by introducing the following models based on the quasi-thermal equilibrium hypothesis; (1) a modified phase-change model which consisted of the enthalpy method for the water-vapor system, (2) a relaxation time derived by considering unsteady heat conduction. Resulting from the numerical simulations on the subcooled pool boiling based on the MARS (Multi-interface Advection and Reconstruction Solver) with improved boiling and condensation model, the numerical results regarding the bubble growth process of the subcooled pool boiling show in good agreement with the experimental observation results and the existing analytical equations.
Measurement of Cellular Adhesion Ratios Under Shear Flow on Various Substrates
Authors: Shirakashi Ryo , Takano Kiyoshi , Provin Christophe , Sakai Yasuyuki , Fujii Teruo
Published: March 2011

Perfusion culture is an effective method to enhance the oxygen and nutrient mass transfer for the culture of highly metabolic cells and/or the culture at a high cell density. However, the flow rate of culture medium induces a shear stress that may lead to the death of cells if it is too high. In this study, we measured the cellular adhesion ratio on various materials coated with type-I collagen under Poiseuille flow with flow rates in the range 1–21 mL/min. Hepatoma cell line, HepG2 cells, attached better on a polystyrene plate for tissue culture coated with type-I collagen (with τ0.5, the shear stress required to detach 50% of cells, equal to 42.2 Pa) followed by a collagen coated glass plate (τ0.5 of 40.5Pa), then a polystyrene plate for tissue culture without collagen coating (τ0.5 of 33.8Pa), and finally on a PDMS (τ0.5 of 24.8Pa) plate coated with collagen. The fluorescence staining of the collagen suggests that clumps of cells and collagen were detached from the surface, which implies that the cell-collagen bonds are stronger than collagen-substrate bonds. Accounting these results, it can be concluded that by reinforcing the bonds between collagen and substrate, it might be possible for the cellular monolayer to stay attached on the substrate until τ0.5 reaches ∼40Pa. This conclusion suggests the importance of carefully choosing the cell substrate, which has a strong binding with the coated extracellular matrix, for the cell culture under a high shear stress.
Enhancement of Saturation Boiling of PF-5060 on Microporous Surface
Authors: Jeon Saeil , Jo Byeongnam , Banerjee Debjyoti
Published: March 2011

Pool boiling experiments were conducted to investigate the saturation boiling of PF-5060 dielectric liquid on micro porous copper surface. The micro porous surface is deposited on a copper coated silicon wafer diced to a size of 40 mm × 68 mm. Reference experiments were performed using a bare silicon wafer of the same size. Experiments are also performed using deionized water that was degassed prior to the experiment. The experimental results show that there is ∼48% enhancement of heat flux in nucleate boiling regime on the micro porous copper surface, compared to that on a bare surface for pool boiling of PF-5060. The measurement uncertainty for heat flux in these experiments is estimated to be ∼15%. The enhanced surface area provided by the micro porous copper surface as well as the reduction in the magnitude of the Taylor instability wavelength on a copper surface, increase in the nucleation site density on the porous surface, capillary replenishment of the dry out regions and the increase in transient heat transfer from the porous surface — are postulated to be the enhancement mechanisms for the observed augmentation in heat flux values.
Transport Process by Natural Convection and Molecular Diffusion of Two Component Gases in a Stratified Fluid Layer
Authors: Takeda Tetsuaki , Isomi Hirotaka , Hanazawa Hiroki
Published: March 2011

This study is to investigate an effect of natural convection or natural circulation on a transport process by molecular diffusion in a stratified fluid layer consisting of two component gases. There are many experiments and analysis regarding natural convection in a vertical slot or natural circulation in a circular tube. However, there are few studies on natural convection or circulation with molecular diffusion in the stratified fluid layer consisting of two component gases. It is confirmed that these phenomena appear when the depressurization accident occurs in the very high temperature reactor (VHTR). Therefore it is important to evaluate the transport and mixing processes of two or more component gases during the depressurization accident of the VHTR. The experiment has been performed regarding the combined phenomena of molecular diffusion and natural convection or natural circulation in a parallel vertical slot filled with two component gases. The one vertical slot consists of the heated wall and the other side cooled wall. The other one consists of both the cooled wall. The dimension of heated wall is 500mm×200mm and thickness is 3mm. The width of the slot is 20mm and the aspect ratio of the slot is 25. Combination of nitrogen/argon is used as the two component gas system. The density change of the gas mixture and the gas temperature distribution in the slots were obtained. The mixing process of the heavier gas from the bottom side of the slot filled with the lighter gas was discussed in this paper.
Effect of Inner Pipe Rotation on Natural Convection Heat Transfer of Concentric Pipes
Authors: Hosseini R. , Gholaminejad A. , Alipour M.
Published: March 2011

In the present work, natural convection heat transfer is studied experimentally in a concentric annulus with constant heat flux and stationary outer pipe and rotating and insulated inner pipe. The experimental setup used consisted of an annulus with radius ratio of Ro/Ri = 0.253 and length of 2.2m. Heat fluxes of 58, 96.5, 145 and 193W/m2 were applied to the heater in the present study and surface temperature of the outer pipe is measured at 39 points along its length. Average Nusselt number was plotted versus Taylor number. It is observed that Nusselt number slightly decreases up to Taylor number of 4.5E+5.
Effects of Fuel Species on Soot Formation in Laminar Counterflow: Comparison Between Diesel Fuel and Palm Methyl Ester as an Alternative Fuel
Authors: Hayashi Jun , Akamatsu Fumiteru , Hashimoto Nozomu , Nishida Hiroyuki
Published: March 2011

Spray combustion of liquid fuel is utilized in many combustion systems. There are, however, still remained-problems. One of the most important problems is to clarify the combustion characteristics, especially soot formation process. At the same time, the liquid fuel of biomass is getting a lot of attention as an alternative fuel in recent years from the viewpoint of the environmental issues and the exhaustion of fossil fuels. In this study, we focused on the palm methyl ester (PME), which has a large production capacity and oxygen content in its molecular structure. The aim of this study is to clarify the combustion characteristics and soot formation characteristics of PME spray flame for the effective utilization to the conventional combustion systems as the alternative fuel. In order to clarify the soot formation characteristics of PME spray flame, measurements of Sauter mean diameter (SMD) and droplet size distribution by using phase Doppler anemometry (PDA) and measurement of two dimensional soot formation characteristics by using Laser Induced Incandescence technique (LII) are conducted in laminar counterflow field. In addition, since the PME has a normal chain structure and oxygen content in its molecular structure, it needs to clarify effect of the oxygen content and normal chain structure. The comparison with diesel fuel and n-dodecane are also conducted. Results of LII measurements show that the PME and the n-dodecane spray have similar spray flame structures, time-averaged soot volume fraction and instantaneous structure of soot formation while PME has the oxygen content in the molecular structure. On the other hand, the time-averaged soot volume fraction and soot formation area of PME are smaller than those of diesel fuel. It is because the diesel fuel has some components with the aromatic ring. These results indicate that it is not the oxygen content but the normal chain structure in the PME play an essential role in influencing soot formation characteristics.
Linear Stability Analysis for the Onset of Convection During Microwave Heating of Samples Confined Within Horizontal Plates
Authors: Bhattacharya Madhuchhanda , Basak Tanmay
Published: March 2011

This work performs linear stability analysis to investigate the onset of convection due to microwave incidences in water and oil confined between two semiinfinite horizontal plates. The onset has been characterized in terms of critical Rayleigh (Rac) and wave (kc) numbers, which are determined for the entire spectrum sample thickness varying from thin to thick samples exposed to various microwave source configurations including one sided to distributed incidences. The main finding of this work is the oscillatory variations of Rac and kc with sample thickness in sinusoidal regime of microwave heating, which indicates preferential onset for specific sample thicknesses. It has also been shown that materials as well as microwave source configuration play important roles in the onset of convection in this regime. The variation patterns of Rac and kc have been correlated to the spatial patterns of absorbed microwave power within the sample. These results are useful not only for forecasting the onset but also for controlling onset of convection by selecting suitable experimental parameters.
Computational Test Design for High-Speed Liquid Impact and Dispersal
Authors: Brown Alexander L. , Metzinger Kurt E.
Published: March 2011

Transportation accidents frequently involve liquids dispersing in the atmosphere. An example is that of aircraft impacts, which often result in spreading fuel and a subsequent fire. Predicting the resulting environment is of interest for design, safety, and forensic applications. This environment is challenging for many reasons, one among them being the disparate time and length scales that must be resolved for an accurate physical representation of the problem. A recent computational method appropriate for this class of problems has been developed for modeling the impact and subsequent liquid spread. This involves coupling a structural dynamics code to a turbulent computational fluid mechanics reacting flow code. Because the environment intended to be simulated with this capability is difficult to instrument and costly to test, the existing validation data are of limited scope, relevance, and quality. A rocket sled test is being performed where a scoop moving through a water channel is being used to brake a pusher sled. We plan to instrument this test to provide appropriate scale data for validating the new modeling capability. The intent is to get high fidelity data on the break-up and evaporation of the water that is ejected from the channel as the sled is braking. These two elements are critical to fireball formation for this type of event involving fuel in the place of water. We demonstrate our capability in this paper by describing the pre-test predictions which are used to locate instrumentation for the actual test. We also present a sensitivity analysis to understand the implications of length scale assumptions on the prediction results.
Local Quenching Recovery Processes of Premixed and Diffusion Interacting Flames in a Turbulent Opposite Flow
Authors: Makino I. , Kawanami T. , Yahagi Y.
Published: March 2011

A lean premixed CH4 air flame (LPF) impinges with a CH4 diluted with N2 diffusion flame (DF) having different turbulence conditions to create a lean heterogeneous combustion model such as a stratified combustion. The local quenching recovery processes of LPF and DF interacting with the turbulence in an opposed flow have been investigated experimentally using a Particle Image Velocimetry movie. The local quenching phenomena can be observed frequently with approaching the global extinction condition. The local quenching may trigger to global extinction. However, in many cases, the flame can recover from the local quenching phenomena and create the stable flame. There are three distinct local quenching recovery mechanisms namely a passive mode, an active mode, and an eddy transportation mode. These three modes depend on the local flame propagation mechanism, the bulk flow motion, and the eddy motion by turbulence. In the passive mode, the bulk flow plays an important role on the recovery process. The local quenching area is drifting outward from the stabilization point by the bulk flow and then, it is displaced by the stable flamelets. In the active mode, the local quenching area is recovered by the self-propagating wrinkled LPF from somewhere in the active zone. The active mode is observed only when the turbulence is added to the premixed flame side. In the eddy motion mode, the local quenching area is recovered by the eddy transportation. That is, the flamelet is transport by the eddy motion and the local quenching area is replaced. The wrinkled flamelet having self-propagation plays a very important role for the local quenching recovery mechanism. The turbulence on the premixed flame not only induces high possibility for the local quenching but also helps to recover from the local quenching.
Heat Transfer Characteristics of Baffled Channel Flow
Authors: Kang Changwoo , Yang Kyung-Soo
Published: March 2011

Heat transfer characteristics of baffled channel flow, where thin baffles are mounted on both channel walls periodically in the direction of the main flow, have been numerically investigated in a laminar range. In baffled channel flow, heat transfer characteristics are significantly affected by large-scale vortices generated due to flow separation at the tips of the baffles. In this investigation, a parametric study has been carried out to identify the optimal configuration of the baffles to achieve the most efficient heat removal from the channel walls. Two key parameters are considered, namely baffle interval (L) and Reynolds number (Re). We elucidate the role of the primary instability, a Hopf bifurcation from steady to a time-periodic flow, in the convective heat transfer in baffled channel flow. We also propose a contour diagram (“map”) of averaged Nusselt number on the channel walls as a function of the two parameters. The results shed light on understanding and controlling heat transfer mechanism in a finned heat exchanger, being quite beneficial to its design.
Evaluation of Gas Permeability in Microfluidic Device by Confocal Micro-PIV Combined With LIF Technique
Authors: Ichiyanagi Mitsuhisa , Sakai Keita , Kidani Shinya , Kakinuma Yasuhiro , Sato Yohei , Hishida Koichi
Published: March 2011

Microfluidic devices with the gas permeability through polymer membranes were developed for further high-efficiency of gas-liquid chemical reactions and high-accuracy of environmental diagnosis. The devices were composed of a cover glass and a polydimethylsiloxane (PDMS) chip which has the ability to permeate various gases, because PDMS is made of the elastomeric material. In the chip, microchannels with a width ranging from a few micrometers to a few hundred micrometers were manufactured by using the cryogenic micro machining. The gas permeation phenomena in microchannels are dominated by several factors, such as the gas and liquid flow rates, the membrane thickness between gas and liquid flow, and the surface area of membranes. The advantage of the present work is to realize the simple control of the gas permeability by changing the surface roughness of PDMS, because the cryogenic micro machining enables to control the surface roughness of microchannels and the increase in its roughness yields that in the surface area of membranes. For the evaluation of the gas permeability, the velocity and dissolved gas concentration distribution in the liquid flow field were measured by utilizing micron-resolution particle image velocimetry combined with laser induced fluorescence, and the measurement system was based on the confocal microscope to improve the depth resolution drastically. The experiments were performed under the several conditions with a change in the gas flow rate, the PDMS membrane thickness and the surface roughness, which affect the gas permeation phenomena. The results indicate that the velocity-vector distributions in the liquid flow have a similar pattern and the magnitudes of the velocity are approximately the same values under all conditions, while the dissolved gas concentration distributions have different patterns. It was quantitatively clear that the gas permeability through PDMS membranes was increased with an increase in the surface roughness and has the linearity to the surface area of membranes. The important conclusion is that the proposed device achieves to control the gas permeability by using the elastomeric material and changing the surface roughness.
Laser Direct Joining Between Stainless Steel and Amorphous Polyamide Plastic
Authors: Kawahito Yousuke , Katayama Seiji , Nishimoto Koji
Published: March 2011

Joining of the dissimilar materials is necessary and important from a manufacturing viewpoint. Therefore, the authors have developed a new laser direct joining method between metals and plastics. In this research, such joining was applied to join Si3N4 ceramic and PET engineering plastic, although the metal was replaced by the ceramic. The shear strength of the joints was 3100 N, which was strong enough to elongate PET plates of 2 mm thickness and 30 mm width. It was confirmed that this laser joining process was effective to directly produce a strong dissimilar material joint of a ceramic and an engineering plastic.
Multicanonical Molecular Dynamics Simulation Study of the Liquid-Solid and Solid-Solid Transitions in Lennard-Jones Clusters
Authors: Kaneko Toshihiro , Yasuoka Kenji , Mitsutake Ayori , Zeng Xiao Cheng
Published: March 2011

Multicanonical molecular dynamics simulations are applied, for the first time, to study the liquid-solid and solid-solid transitions in Lennard-Jones (LJ) clusters. The transition temperatures are estimated based on the peak position in the heat capacity versus temperature curve. For LJ31, LJ58 and LJ98, our results on the solid-solid transition temperature are in good agreement with previous ones. For LJ309, the predicted liquid-solid transition temperature is also in agreement with previous result.
Study on Simple and High-Speed Diesel Combustion Model for Driving Mode Simulator Available for Premixed and Diffusion Combustion of Sprays
Authors: Chikahisa Takemi , Tabe Yutaka , Kikuta Kazushige , Sayem A. S. M.
Published: March 2011

To design a diesel engine adapting to future exhaust gas regulation, it is important to develop a driving mode simulator which can simulate vehicle performance and exhaust emissions including after-treatment system. The combustion model for this objective must be able to simulate heat release rate, variety of emissions necessary for after-treatment simulation, and exhaust gas temperature in very short computational time. The authors have developed a diesel combustion model based on the Hiroyasu model by adding variety of modifications to minimize optimization process of the empirical constants. It was shown that the simulation results with the improvement model were in good agreement with the experimental results. By adding Tsurushima model consisting of nine reaction steps with several intermediate species, the model became available for the both combustions of spray diffusion flame and of homogeneous charge compression ignition.
Simultaneous PIV and PLIF Measurement on the Drag Reducing Channel Flow of the Homogeneous Surfactant Solution
Authors: Watanabe Takahiro , Tanaka Kohei , Motozawa Masaaki , Kawaguchi Yasuo
Published: March 2011

Simultaneous Particle Image Velocimetry (PIV) measurement and Planar Laser Induced Fluorescence (PLIF) measurement at the same position were performed to clarify the relationship between spatial structure and mass transfer in the drag reducing surfactant flow. In the drag reducing flow, mass flux is largely suppressed in the near-wall region with increasing drag reduction rate. To discuss the relationship between coherent motion and drag reduction more detail, weighted probability density function was also calculated. As a result of simultaneous measurement, diffusion of wall-normal direction is largely suppressed and this indicated that turbulent coherent structure changes and sweep and ejection which produce the skin frictional drag are suppressed.
Molecular Analysis on the Dynamic Properties of Water Droplet at Solid-Liquid Interface Based on MD Simulations
Authors: Yamaguchi Yasutaka , Surblys Donatas , Nakaoka Satoshi , Kuroda Koji , Nakajima Tadashi , Fujimura Hideo
Published: March 2011

Molecular dynamics simulations of single water or water-IPA (Isopropyl-alcohol) mixture droplets on a solid surface were performed. The interaction for solid-water molecules was modeled as the combination of L-J and Coulomb potentials, and the effects of Coulomb interaction were independently investigated by appending arbitrary electric charge as a parameter on the solid surface. The water droplet became more wettable both with positive and negative surface charges as the absolute value of the electric charge increased, and the cosine of the contact angle was roughly a linear function of the absolute value of the electric charge although the correlation was obviously different between positive and negative charge values. Multiple molecular orientations seemed possible as local equilibrium states near the adsorption layer on negatively charged surface, and the mean rotational diffusion was higher there. On the other hand, mean rotational diffusion was reduced in the vicinity of the positively charged surface.
Measurement of Optical Properties of Human Skin
Authors: Hattori Kazuhisa , Kuwahara Tomohiro , Ohmi Masato , Haruna Masamitsu , Okawa Shinpei , Masamoto Kazuto , Yamada Yukio
Published: March 2011

In order to predict the skin colors, we need to analyze the reflection spectra of the skins. For the diffuse reflection, it is essential to know the skin optical properties that describe the propagation of light in the skin. We measure the absorption coefficient μa, scattering coefficient μs, scattering phase function p(θ) and refractive index n of human skins in this study. We attempt to build a measurement system which can accurately measure the optical properties of the skin samples with a size of as small as 5 mm and a thickness of as thin as 50 micrometer in the visible wavelength range with the wavelength step of 50 nm. Then we measured the optical properties of stratum corneum obtained from a cultured model of human epidermis and those of epidermis obtained from human skin. The effect of the exposure of epidermis to sunlight on the optical properties is discussed.
DNS on Autoignition and Flame Propagation of Inhomogeneous Methane–Air Mixtures in a Closed Vessel
Authors: Katayama Makito , Fukushima Naoya , Shimura Masayasu , Tanahashi Mamoru , Miyauchi Toshio
Published: March 2011

Direct numerical simulations (DNSs) on autoignition and flame propagation of inhomogeneous methane–air mixtures in a closed vessel are conducted with considering detailed kinetic mechanism and temperature dependence of transport and thermal properties. The mixtures with spatial inhomogeneity of temperature or equivalence ratio are investigated. Periodic condition for non-heatloss cases or isothermal wall condition for heatloss cases is imposed on the boundaries. From the DNS results without heatloss, effects of spatial inhomogeneity of temperature and equivalence ratio on mean heat release rate are clarified. Increase of spatial variations of temperature or equivalence ratio suppresses drastic rise of mean heat release rate and reduces its maximum value. Autoignition process is affected by temperature more strongly than equivalence ratio. In the cases with heatloss, ignition delay increases and the maximum mean heat release rate decreases. After autoignition process, propagating flame is formed along walls. Heat transfer characteristics in a closed vessel are also discussed with combustion mechanisms.
A Molecular Dynamics Study on Heat Transfer Characteristics Over the Interface of Self-Assembled Monolayer and Water Solvent
Authors: Kikugawa Gota , Ohara Taku , Kawaguchi Toru , Kinefuchi Ikuya , Matsumoto Yoichiro
Published: March 2011

We performed molecular dynamics simulations of the interface which is comprised of self-assembled monolayer (SAM) and water solvent to investigate heat transfer characteristics. In particular, local thermal boundary conductance (TBC), which is an inverse of so-called Kapitza resistance, at the SAM–solvent interface was evaluated by using the nonequilibrium MD (NEMD) technique in which the one-dimensional thermal energy flux was imposed across the interface. By using two kinds of SAM terminal with hydrophobic and hydrophilic properties, the local TBCs of these interfaces with water solvent were evaluated, and the result showed a critical difference due to an affinity between SAM and solvent. In order to elucidate the reason for this difference, microscopic components contributing to thermal energy flux across the interface were evaluated in detail, i.e., the total thermal energy flux is decomposed into the contribution of molecular transport and that of energy exchange by molecular interactions.
Measurements of Fuel Concentration and Temperature Distributions in Lean Premixed Flame With Swirling Flow
Authors: Komiyama Masaharu , Takeishi Kenichiro , Araki Kazumi
Published: March 2011

Premixed combustion is one of the most efficient techniques to reduce NOx emission in industrial combustors. But it is necessary to mix gaseous fuel with air sufficiently before the mixture gas burns. In this study, we present an instantaneous and simultaneous measurement of 2-D mixing behavior and temperature distributions by combining acetone LIF and Rayleigh scattering methods. We examined air-fuel mixing characteristics in an unburned region where is adjacent to a reaction zone by laser induced fluorescence. Acetone vapor, which fluoresces by UV laser light, was used as a tracer. The CH4 concentration was estimated from the acetone concentration, which was obtained by acetone LIF intensity. The mixing behavior has been evaluated by measuring CH4 concentration distributions. Simultaneously, we measured instantaneous flame temperature distributions by Rayleigh scattering method and investigated the correlation between mixing characteristics in an unburned region and temperature distributions in a burned region.
Investigation of Liquid Water Behaviors in Carbon Paper GDL for PEMFCs by Soft X-Ray Radiography
Authors: Tsushima Shohji , Sasabe Takashi , Hirai Shuichiro
Published: March 2011

Liquid water behaviors in the porous gas diffusion layer used for PEMFCs were investigated by high-resolution soft X-ray radiography. We observed water evaporation process from the soaked carbon paper GDL and showed the gradual disappearance of liquid water with spatial inhomogeneity. The visualization of liquid water revealed that thin water film was retained in the GDL. This was also observed in the operating fuel cell. Our soft X-ray observation suggests that this thin water film formed in the carbon paper GDL possibly caused increase in the toutuosity of the GDL, resulting in deterioration of cell performance due to less mass transport in fuel cells.
NEGF Quantum Simulation of Field Emission Devices
Authors: Musho T. D. , Claiborne S. M. , Walker D. G.
Published: March 2011

Recent studies of wide band-gap diamond field emission devices have realized superior performance and lifetime. However, theoretical studies using standard Fowler-Nordheim (FN) theory do not fully capture the physics of diamond semiconductor emitters as a result of the fitting parameters inherent to the FN approximation. The following research computationally models wide band-gap field emission devices from a quantum point of view, using a novel non-equilibrium Green’s function (NEGF) approach previously applied to modeling solid-state electronic devices. Findings from this research confirm non-linearities in the FN curve and provide alternative explanations to discrepancies between standard FN theory.
A Platform for Thermal Property Measurements and Transmission Electron Microscopy of Nanostructures
Authors: Harris Tom , Martinez Julio , Shaner Eric , Swartzentruber Brian S. , Huang Jianyu , Sullivan John , Chen Gang
Published: March 2011

Measurements of the electrical and thermal transport properties of one-dimensional nanostructures (e.g., nanotubes and nanowires) typically are obtained without detailed knowledge of the specimens atomic-scale structure or defects. To address this deficiency, we have developed a microfabricated, chip-based characterization platform that enables both transmission electron microscopy (TEM) of atomic structure and defects as well as measurement of the thermal transport properties of individual nanostructures. The platform features a suspended heater line that contacts a suspended nanostructure/nanowire at its midpoint, which is placed on the platform using in-situ scanning electron microscope nanomanipulators. Because the nanostructure is suspended across a through-hole, we have used TEM to characterize the atomic and defect structure (dislocations, stacking faults, etc.) of the test sample. As a model study, we report the use of this platform to measure the thermal conductivity and defect structure of GaN nanowires. The utilization of this platform for the measurements of other nanostructures will also be discussed.
Analysis of Mass Transport Loss in PEMFC Induced by Rib/Channel Geometry
Authors: Tabuchi Yuichiro , Shiomi Takeshi , Fukuyama Yosuke , Aoki Osamu , Kubo Norio , Shinohara Kazuhiko
Published: March 2011

Key challenges to the acceptance of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) for automobiles are the cost reduction and its improvement in power density for compactness. In order to get the solutions for these issues, further improvement in the cell performance is required with high current density operation. In this study, the impacts of heat and water transport on the cell performance under high current density were investigated by experimental evaluation of liquid water distribution and numerical validation. Liquid water distribution in-plane direction was evaluated by neutron radiography. Furthermore, electrochemical reaction distribution was also evaluated by using inserted metal wires at anode, and then the experimental results were qualitatively validated by the numerical model. The experimental and numerical validation results revealed that significant increase in mass and ohmic loss was induced by temperature, liquid water, and electrochemical reaction distribution in-plane direction.
Study on Cooling of Hot Water by Air Flow With Evaporation
Authors: Koizumi Yasuo , Ebihara Yutaka , Murase Michio
Published: March 2011

Evaporation heat transfer from the hot water flow to the cold air flow in a horizontal and rectangular flow channel was examined. The water temperature was 35°C ∼ 65°C. The air velocity was 0.02 m/s ∼2.57 m/s. The heat transfer rate from the water flow to the air flow became large with an increase in the air velocity and the water temperature. The evaporation heat transfer was much larger than the convection heat transfer and dominant in the heat transfer. The ratio of the evaporation heat transfer rate to the total heat transfer rate was approximately 0.9 ∼ 0.7 in the present experimental conditions. It showed the slightly decreasing tendency for the air velocity. The evaporation heat transfer coefficient showed strong dependency on the air velocity in both the laminar and the turbulent flow region of the air flow. The convection heat transfer coefficient showed the same tendency for the Reynolds number of the air flow as that for the air single-phase flow in the turbulent flow region although the value was much larger than that of the single-phase flow. In the laminar flow region, the convection heat transfer coefficient was constant as in the single-phase flow when the water temperature was low, although the value itself was much larger than that of the single-phase flow. As the water temperature became high, the convection heat transfer coefficient became large and showing dependency on the Reynolds number of the air flow. As the Reynolds number of the air flow became further small, the convection heart transfer coefficient greatly decreased irrespective of the water temperature.
Study on Condensation Heat Transfer of Micro Structured Surfaces (Effect on Condensation Heat Transfer of Metal-Spattering Surfaces)
Authors: Komatsu Takeru , Ohtake Hiroyasu , Koizumi Yasuo
Published: March 2011

The present study was intended to examine how the condensation heat transfer, especially the drop-wise condensation, was affected by modifying the surface nature. In the present study, condensation heat transfer experiments for steam were performed by using mirror-finished copper surface, mirror-finished silicon surface and some mirror-finished silicon surfaces with very thin metal films by using spattering. The silicon surfaces with the thin metal films were created by the MEMS technology. The film- and also the drop-wise condensation were observed on the copper surface. The filmwise condensation heat flux was in good agreement with the values of the Nusselt’s equation. It was approximately one-tenth of the drop-wise condensation heat flux. The condensation on the mirror-finished silicon surface was the drop-wise condensation. The heat flux was approximately one-tenth of the drop-wise condensation heat flux on the copper surface. The condensation on silicon surfaces with thin Copper (Cu), Chromium (Cr), Lead (Pb) and Gold (Au) films were drop-wise. The condensation on silicon surfaces with thin Nickel (Ni), Titanium (Ti) and Aluminum (Al) films were filmwise.
Thermal Transport in Few-Quintuple Bi2Te3 Thin Films and Nanoribbons
Authors: Qiu Bo , Ruan Xiulin
Published: March 2011

In this work, thermal conductivity of perfect and nanoporous few-quintuple Bi2Te3 thin films as well as nanoribbons with perfect and zig-zag edges is investigated using molecular dynamics (MD) simulations with Green-Kubo method. We find minimum thermal conductivity of perfect Bi2Te3 thin films with three quintuple layers (QLs) at room temperature, and we believe it originates from the interplay between inter-quintuple coupling and phonon boundary scattering. Nanoporous films and nanoribbons are studied for additional phonon scattering channels in suppressing thermal conductivity. With 5% porosity in Bi2Te3 thin films, the thermal conductivity is found to decrease by a factor of 4–6, depending on temperature, comparing to perfect single QL. For nanoribbons, width and edge shape are found to strongly affect the temperature dependence as well as values of thermal conductivity.
Film Cooling Effectiveness Distributions on a Flat Plate With a Double Hole Geometry Using PSP
Authors: Wright Lesley M. , Martin Evan L.
Published: March 2011

Detailed film cooling effectiveness distributions are obtained on a flat plate using the pressure sensitive paint (PSP) technique. The effects of average blowing ratio (M = 0.25–1.0) and coolant – to – mainstream density ratio (DR = 1.0–1.4) are evaluated in a low speed wind tunnel with a freestream velocity of 8.5 m/s and a freestream turbulence intensity of 6.8%. The coolant – to – mainstream density ratio is varied by using either nitrogen (DR = 1.0) or argon (DR = 1.4) as the coolant gases. The double hole geometry consists of a row of simple angle (θ = 35°), cylindrical holes coupled with one row of compound angle holes (θ = 45°, β = 50°). With the selected geometry, the compound holes effectively weaken the counter rotating vortex pair formed within the traditional simple angle hole. Therefore, the surface film cooling effectiveness is increased compared to a single row of simple angle film cooling holes. While increasing the blowing ratio decreases the film cooling effectiveness, the severity of the film cooling effectiveness reduction is less than with the single row of holes.
Heat Transfer and Pressure Drop During Condensation of R-134a Inside Parallel Microchannels
Authors: Goss Ju´nior Gil , Macarini Stefano Frasson , Passos Ju´lio Ce´sar
Published: March 2011

In this study the pressure drop and local heat transfer coefficient were investigated experimentally during the convective condensation of R-134a inside eight round (D = 0.8 mm) horizontal and parallel microchannels. The test conditions included mass velocity and pressure ranges of 57 to 125 kg.m−2s−1 and 6.8 to 11.2 bar, respectively. The experimental results are compared with correlations and semi-empirical models described in the literature.
Fabrication of Thermoelectric La0.95Sr0.05CoO3 Thin Film and Seebeck Coefficient Measurement
Authors: Xu Weihe , Chen Qi , Shi Yong , Hadim Hamid
Published: March 2011

The P-type perovskite oxides La1-xSrxCoO3 are a promising group of complex oxide thermoelectric (TE) materials because of its a higher Seebeck coefficient. In this paper, the La0.95Sr0.05CoO3 thin film was prepared by spin coating. A custom-made MEMS (micro-electromechanical system) based device was used to measure the voltage output and Seebeck coefficient of the thin film. The measured Seebeck coefficient of the thin film was 350 μV/K.
Thermal Contact Resistance at a Metal Foam-Solid Surface Interface
Authors: Sadeghi Ehsan , Hsieh Scott , Bahrami Majid
Published: March 2011

Accurate information on heat transfer and temperature distribution in metal foams is necessary for design and modeling of thermal-hydraulic systems incorporating metal foams. The analysis of this process requires determination of the effective thermal conductivity as well as the thermal contact resistance (TCR) associated with the interface between the metal foams and adjacent surfaces/layers. In the present study, a test bed that allows the separation of effective thermal conductivity and thermal contact resistance in metal foams is described. Measurements are performed in a vacuum under varying compressive loads using ERG Duocel aluminum foam samples with different porosities and pore densities. Also, a graphical method associated with a computer code is developed to demonstrate the distribution of contact spots and estimate the real contact area at the interface. Our results show that the porosity and the effective thermal conductivity remain unchanged with the variation of compression in the range of 0 to 2 MPa; but TCR decreases significantly with pressure due to an increase in the real contact area at the interface. Moreover, the ratio of real to nominal contact area varies between 0 to 0.013, depending upon the compressive force, porosity, and surface characteristics.
Numerical Simulation of Heat and Mass Transfer of Limestone Decomposition in Normal Shaft Kiln
Authors: Do Duc Hai , Specht Eckehard
Published: March 2011

A mathematical model of lime calcination process in normal shafts kiln has been developed to determine the heat and mass transfer between the gas and the solid. The model is one-dimensional and steady state. The transport of mass and energy of the gas and the solid is modeled by a system of ordinary differential equations. A shrinking core approach is employed for the mechanics and chemical reactions of the solid material. The model can be used to predict the temperature profiles of the particle bed, the gas phase along the length of kiln axis. The calcination behavior of the particle bed can be also investigated. The influences of operational parameters such as: energy input, the origin of feed limestone and the lime throughput on the kiln performance including pressure drop are considered. Additionally, the local heat loss through the kiln wall is studied. The results of this study are direct utility for optimization and design of large-scale technical shaft kilns.
Examples of Solar Thermal Fuel Production
Authors: Sattler Christian , Mu¨ller-Steinhagen Hans , Roeb Martin , Thomey Dennis , Neises Martina
Published: March 2011

The conversion of renewable energy especially solar energy into versatile fuels is a key technology for an innovative and sustainable energy economy. To finally benefit from solar fuels they have to be produced with high efficiencies and low to no greenhouse gas emissions in large quantities. The final goal will most probably be the carbon free fuel hydrogen. But the main challenge is its market introduction. Therefore a strategy incorporating transition steps has to be developed. Solar thermal processes have the potential to be amongst the most efficient alternatives for large scale solar fuel production in the future. Therefore high temperature solar technologies are under development for the different development steps up to the final goal of carbon free hydrogen. This paper discusses the strategy based on the efficiencies of the chosen solar processes incorporating carbonaceous materials for a fast market introduction and processes based on water splitting for long term solar hydrogen generation. A comparison with the most common industrial processes shall demonstrate which endeavors have to be done to establish solar fuels.
Heat Transfer Effects on Dynamic Pressure Response of Pneumatic Vacuum Circuit
Authors: Guo Zhonghua , Li Xiaoning , Kagawa Toshiharu
Published: March 2011

In the industrial conveying systems powered by pneumatic ejector, the dynamic pressure response of vacuum circuit is critical to systematic strategic planning. This paper analyzes heat transfer effects on dynamic pressure response. Experiments are carried out in temperature measurement with the stop method. The heat transfer ratio is obtained when the air is entrained from the acrylic chamber under the vacuum condition. The decreasing value of the air temperature inside the vacuum chamber is concerned with ejector flow rate characteristics, the material of the vacuum chamber and heat transfer area. The heat transfer area could be enlarged with copper wires stuffed in the chamber and the isothermal condition is realized. The suction process in such isothermal chamber is then compared with that in the acrylic chamber. The pressure response is faster in the acrylic chamber at the beginning of the suction process but a long time to reach final vacuum degree for temperature recovery.
Heat Conduction Effect on Oscillating Heat Pipe Operation
Authors: Smoot C. D. , Ma H. B. , Wilson C. , Greenberg L.
Published: March 2011

The effect of heat conduction through the adiabatic section on the oscillating motion and heat transfer performance in an oscillating heat pipe (OHP) was investigated experimentally. Two, closed loop, 6-turn OHPs were constructed; one with a separate copper block for the evaporator and condenser sections (split block design) and one using a single continuous copper block for the evaporator, adiabatic, and condenser sections (continuous block design). The results show that the presence of heat conduction directly from the evaporator wall to the adiabatic section and from the adiabatic section to the condenser of a heat pipe will reduce the oscillating amplitude of the evaporator, adiabatic, and condenser temperatures. It was also found that in addition to a higher level of temperature uniformity, the continuous block design results in better heat transfer performance than a heat pipe without conduction through the adiabatic section.
Parametric Studies on PCI Performances
Authors: Fu Dong , Zheng Dezhi , Zhou Chenn Q. , D’Alessio John , Ferron Kyle J. , Zhao Yongfu
Published: March 2011

The pulverized coal injection (PCI) is widely utilized in the iron-making blast furnaces for its economic and environmental advantages. However, due its complexity, flow dynamics and chemical kinetics of PCI inside the raceway has not been well understood. Combustions of PCI and coke inside the raceway can be influenced by tuyere operation parameters. In this paper, a comprehensive three dimensional (3-D) multiphase flow computational fluid dynamics (CFD) model was utilized to investigate the PCI and coke combustion in the lower part of a blast furnace. Systematic parametric studies were conducted to analyze the effects of the natural gas injection, coal injection, PCI rate, and oxygen enrichment on the combustion performance, which include coal burnt-out rate, coke consumption rate, raceway shape, raceway temperature and etc.