bluuebunny/crossref_metadata_2025 huggingface dataset:
A Spectroscopic Analysis of Combustion in Homogeneous Charge Compression Ignition Engine
Authors: Iijima Akira , Shoji Hideo
Published: April 2009

The principal issues of Homogeneous Charge Compression Ignition (HCCI) combustion that must be addressed include ignition timing control and expansion of the stable operation region. Detailed analyses of ignition and combustion mechanisms must be undertaken to resolve these issues. In this study, spectroscopic technique was used to investigate the effects of the air-fuel ratio (AFR) and residual gas state on ignition and combustion characteristics. Spectroscopic measurement was made of light emission spectra. The results revealed that the distribution profile of the light emission intensity of the hot flame differed substantially depending on the air-fuel ratio (AFR). In high AFR condition, a continuous spectrum attributed to carbon monoxide-oxygen (CO-O) glow is seen between 300–500 nm, but there is no strong light emission such as that from the OH radical. However, decreasing the AFR, a strong light emission is seen a little after the CO-O glow in a wavelength range from visible light to the near-infrared region (500–850 nm). It is also clear that increasing the internal EGR declined the cool flame magnitude, which substantially altered the ignition characteristics of HCCI combustion. Specifically, when a low-octane fuel was used, the heat release rate waveform for HCCI combustion showed two-stage ignition, which was clearly observed in the light emission spectra.
Heat Transportation by an Oscillatory Flow Through a Parallel-Plate Channel With an Inserted Slanting Plate
Authors: Ishii Yoshihisa , Zhang Xiaojin , Hishida Makoto
Published: April 2009

Heat transportation devices with small size and high transportation rate are highly required for achieving effective cooling of electronic devices and equipments. Heat transportation devices exploiting reciprocal flow are considered as one of important candidate technologies. Since a heat transportation pipe exploiting reciprocal flow was invented by Kurzweg and Zhao[1], many researchers have attempted to improve its performance. In the present paper we proposed a new concept of heat transportation channel which was a parallel-plate channel with a slanting plate inserted. The slanting plate separated the parallel-plate channel into two tapered channels. We analyzed numerically the heat transportation performance of the channel when a reciprocal flow was given at one end of the channel. Womersley number Wo was varied in a range of 7≤ Wo ≤40 and Remax in a range of 100≤ Remax ≤1300, by changing the tidal amplitude Am of the reciprocal flow from 0.005 to 0.102 m and reciprocal frequency from 0.07 to 2.56Hz. The present study was summarized in the followings: (1) In the present channel, oscillatory flow comprised of a reciprocal flow component superimposed on a one-directional flow component was induced. (2) u-velocity profiles in pushing phase and in pulling phase were not symmetrical when Wo was relatively small or Remax was large. They approached symmetrical profile in large Wo range and in small Remax range. (3) The time-averaged flow rate V remained almost constant in the Wo range from 7 to 20. They decreased with increasing Wo beyond 20. It also decreased with decreasing Remax. (4) Heat transportation rate Q and heat transportation efficiency η decreased with increasing Wo and decreasing Remax. (5) Work rate W increased with increasing Wo and Remax. (6) The present heat transportation channel was able to transport about 5 to 13 times the heat with 1.4 to 4 times the efficiency by only inserting a slanting plate in a hollow parallel-plate channel.
Research on Hard-Core of the Steamed Bread Caused by Microwave Heating
Authors: Wang Li , Wang Qiuying , Sun Shufeng , Tong Lige
Published: April 2009

Microwave heating has been extensively used in the area of food handling, and many investigators have been studying the effect of microwave heating on the quality of food. However, the phenomenon concerning on the hard-cores in steamed breads caused by microwave heating is poorly understood. A series of experiments are designed in this paper to investigate the impact of microwave heating on the quality of steamed breads under different heating conditions. The experiment results show that the hardness and cohesiveness can be used to measure the hard-core of steamed breads. The mechanism of hard-core caused by microwave heating is discussed. According to the results of experiments, the hardness of the steamed breads increases with the increment of the power, the duration and the times of microwave heating. The cohesiveness of the steamed breads shows a trend, which drops at first, then increases, and decreases finally with the duration of microwave heating. According to the experiment data, a hard-core in a steamed-bread appears under the following conditions: when it is heated for 50s with the power of 900W when the overheating time is 20s, for 65s with the power of 720W when the overheating time is 25s, or for 80s with the power of 540W when the overheating time is 30s. Heated twice with the same heating time, the steamed bread begins to appear hard-core phenomenon under the following conditions: when it is heated for 55s with the power of 540W, for 40s with the power of 720W, or for 30s with the power of 900W.
Heat Transfer Analysis for the Structural Integrity of EO Reactor
Authors: Park Sung Won , Nam Kwanwoo , Lim Young Soon , Park Jung Yean , Lee Choong Dong
Published: April 2009

Thermal characteristics of an EO (Ethylene Oxide) reactor are analyzed to investigate its structural integrity against thermal loads. A two-dimensional axisymmetric simulation model of the whole reactor structure is developed. A porous media model for the long tube bundle packed with catalyst and a flow resistance model for the thin impingement baffle is proposed to simplify the reactor. Simultaneous simulation of fluid and solid zone for a part with many holes is applied to analyze heat transfer of tubesheet which is connected with the tube bundle and the outer shell. The EOC (End of Catalyst Cycle) condition is used for the normal operation condition because general temperature of the EOC condition is the highest during operation cycle. Transient heat transfer analysis is also conducted to simulate the abnormal ignition in the reactor. Two kinds of ignitions are investigated and thermal diffusion in the reactor during the expected shutting down time is simulated as well. Three-dimensional local heat transfer analysis based on the two-dimensional whole analysis is conducted for the local stress evaluation of the product nozzle elbow and the impingement baffle. Results of the heat transfer analysis have been utilized as a thermal boundary condition for the further structural analysis.
Understanding the Effect of Trenching on Film Cooling
Authors: Lu Yiping , Ekkad Srinath V.
Published: April 2009

Recently, there has been a strong focus on film cooling holes embedded in trenches. In this study, film cooling predictions are used to understand the mechanisms of the jets that exit these trenched holes. The present work employs RSM (Reynolds stress transport models) for simulation of turbulent flows in film cooling and the simulation was run using FLUENT computer code. Comparisons are made with experimental data for the film effectiveness distributions. Results show that the film cooling jet exiting the trenched hole shows more two-dimensional flow than the typical cylindrical holes. The jet appears to remain closer to the surface providing more coverage to the surface.
PIV Measurements of the Effects of Geometric Scale on Electronics Cooling Axial Fan Flow
Authors: Grimes Ronan , Quin David , Walsh Edmond , Punch Jeff
Published: April 2009

The emergence of highly functional portable electronic systems in recent times means that passive dissipation of heat in these devices may not be an option in the near future. Micro fan technology is currently being developed to address this emerging need. Past investigations by the current authors indicate that the reduction of scale of conventional electronics cooling fan design to the mini scale does not excessively impair the bulk pressure flow performance of the fan. However, the detailed velocity distribution at the outlet of mini scale axial flow fans is unknown, and so effective thermal design in systems which use mini scale fans may be difficult, as the designer does not know the path taken by the flow emerging from the fan. To address this issue, this paper presents PIV measurements performed at the outlet of a series of geometrically similar axial flow fans, whose diameters range from 120 to 6mm, and whose design is based on that of a commercially available macro scale electronics cooling fan. The measurements show that as fan scale is reduced, there is a significant change in the fan outlet velocity distribution, and a large increase in the outlet radial flow angle. As a result, a designer using a small scale axial flow fan must be aware that the region downstream of the fan, where one would normally expect high velocity flow, will in fact be uncooled. Therefore, components should be mounted radially downstream of the fan, where highest air velocities are shown to exist.
Parametric Study and Optimization of an Irreversible Closed Intercooled Regenerative Brayton Cycle
Authors: Wolf Brian , Revankar Shripad T.
Published: April 2009

In this paper, entropy generation minimization techniques are used in the analysis of an irreversible closed intercooled regenerative Brayton cycle coupled to variable temperature heat reservoirs. First, dimensionless power and efficiency equations are derived for a base case (single stage) which replicates those obtained in recent literature. Second, equations are derived for a multi-stage Brayton cycle. The dimensionless power and efficiency equations are used to analyze the effects of total pressure ratio, intercooling pressure ratio, thermal capacity rates of the working fluid and heat reservoirs, and the component (regenerator, intercooler, hot and cold side heat exchangers) effectiveness. Using detailed numerical examples, the optimal power and efficiency corresponding to variable component effectiveness, compressor and turbine efficiencies, intercooling pressure ratio, total pressure ratio, pressure recovery coefficients, heat reservoir inlet temperature ratio, and the cooling fluid in the intercooler and the cold side heat reservoir inlet temperature ratio are analyzed.
Study on Molecular Thermal Energy Transfer in a Lipid Bilayer
Authors: Nakano Takeo , Ohara Taku , Kikugawa Gota
Published: April 2009

In recent studies, lipid bilayers attract a great deal of interest as a material for nanoscale structure. Some devices utilizing lipid bilayers, which include various kinds of sensors and molecular sorting devices, have been proposed. Understanding of thermal energy transfer in the lipid bilayers plays an important role in developing such devices with nano structures. In this study, we have investigated the energy transfer along and across the bilayer membrane by molecular dynamics simulations of the lipid bilayer in liquid water. We found that along the bilayer, the thermal energy is transferred by the interaction principally between water molecules and barely between lipid molecules. On the other hand, in the latter case, total thermal resistance of the lipid bilayer structure is composed of the thermal resistance of the structure’s various parts, including water, head group of lipid, and tail hydrocarbon chain of lipid, which show different values. It is found that the tail hydrocarbon chains have the highest thermal resistance.
Experiment of Solidification With Thermocapillary Convection in a Liquid Layer
Authors: Watanabe Takamasa , Kawamura Hiroshi
Published: April 2009

To produce high-quality materials, a large number of studies have been carried out for the solidification and melting process of metals and semiconductors in both terrestrial and space environments. The previous studies focused mainly upon the solidification and melting processes themselves. In the real system, however, one cannot neglect effects of convection in molten materials, such as natural and thermocapillary convections, upon the resultant quality of the materials. This study aims to investigate experimentally the effect of the thermocapillary convection upon the directional solidification in a liquid layer with the free surface. Especially, the solidification morphology is emphasized. Three types of interface morphology, planar, cellular and dendrite, can be seen during the growth of solid-liquid interface (SLI). These three types emerge depending upon the increasing interface instability in the order of the planar to the dendrite. The interface instability is a function of the growth rate and the temperature gradient. In case of no convection, it is already known which morphology among the three types emerges according to the balance between the growth rate and temperature gradient. In this experiment, succinonitrile-acetone (SCN-ACE) system was used as test fluid for a model of an alloy. This is often used for solidification experiments, because its coagulation form is similar to real metal and its main physical properties and phase diagram are known in detail. Basically experimental set-up was a typical Bridgman-type furnace. The temperature gradient and the growth rate were able to be controlled independently. Thermocapillary convection was induced over the molten material surface, because a temperature gradient was imposed in a liquid layer with the free surface. The growth of SLI was observed with a microscope. All of experimental apparatus were placed into a glove box filled with Ar gas because SCN-ACE oxidized easily. In case of the experiment without the free surface, a single type of morphology emerged depending upon the solidification condition. On the other hand, in case of “with” the free surface, two types of morphology co-existed across the thickness in a fairly large range of experimental condition. Even if the growth rate of the SLI at the free and bottom surfaces is equal, a distinct difference is observed in the solidification morphology between the both surfaces. That is, either planar or cellular morphology appears in the free surface while the dendrite in the bottom surface (see Fig. A).
Assumed Multivariate Beta-PDF Modeling for Turbulent Nonpremixed Flames
Authors: Noda Susumu , Yamamuro Kunihiko , Nada Yuzuru , Fujisaka Masato
Published: April 2009

Numerical simulation based on a moment method is conducted to investigate the feasibility of an assumed probability density function (PDF) approach in the configuration of a turbulent jet nonpremixed flame. In this study, a multivariate β-PDF is employed to account for turbulence-chemistry interaction. The multivariate β-PDF approach has an advantage that only one additional transport equation of sum of composition variances is solved to determine the shape of species PDF to transport equations of mean compositions. The numerical simulation is carried out for H3 flame. Reaction mechanism is a single-step irreversible reaction including H2, O2 and H2O species. The results are compared with those from measurements and a combined PDF/moment method that detailed reaction mechanism is applied. Velocity distributions obtained by the multivariate β-PDF approach show good agreement with measurements and combined PDF/moment results, which indicates that the present approach can predict the flow pattern of nonpremixed flames. The present approach also provides good predictions in terms of mean temperature and mass fraction. PDFs of mass fraction obtained by the present approach are similar to those by the combined PDF/moment method. On the other hand, the variance of temperature is underpredicted, which is attributed to an approximation of temperature variance. In order to achieve a good prediction of the reaction rate, a PDF approximation of enthalpy is proposed for the evaluation of mean reaction rate.
Temperature Control Inside Steel Cabinet in Open Air Using Underground Heat Source
Authors: Ohbayashi Hiroaki , Masada Yoichi , Takeuchi Masanori , Nagai Niro , Ando Kenji
Published: April 2009

This research aims to develop temperature control system for a cabinet which is set up in outfield and has heat source inside. Underground heat source was utilized for this system with steel pipes embedded into underground and water as working fluid. The cabinet was cooled the in summer season and warmed in winter season. The experimental results show that this system can favorably control the inside air temperature of the cabinet in summer and winter season with relatively high COP. The results of numerical simulation using only meteorological data show good agreements with experimental data in summer and winter season. The results of numerical simulation where some parameters such as pipe distance, diameter, and length were changed show the effect of these parameters on performance of the system.
Relaxation of Phonons in Classical MD Simulation
Authors: Matsumoto Mitsuhiro , Kunisawa Tomohisa , Xiao Peng
Published: April 2009

We propose a novel technique of molecular dynamics simulation to evaluate the relaxation time of phonons in solids for investigation of solid heat conductivity. The basic idea is to observe relaxation behavior of the power spectrum of atomic velocities after energetically stimulating modes in a specific frequency region. The transient entropy S(t) is defined with the power spectrum based on non-equilibrium statistical mechanics to quantitatively evaluate the relaxation speed. In this paper, two example systems are shown: a Lennard-Jones model crystal and a silicon crystal. For both systems, we found that the observed S(t) is well fitted to a single exponential function, from which we can obtain a frequency-dependent relaxation time.
Heat Transfer Enhancement of a Backward-Facing Step Flow in a Duct by Static and Dynamic Devices
Authors: Inaoka Kyoji , Kawakami Kouji , Nishii Yoshi , Senda Mamoru
Published: April 2009

Flow modification downstream of a backward-facing step has been tried in order to achieve heat transfer enhancement by introducing two kinds of devices, a triangle prism rib and electromagnetic actuators, on the step edge. The triangle rib attached to the side-wall corner makes the downward flow inclined and generates a circulation-like fluid motion behind it. Because both flows work effective in reducing the flow re-circulation caused behind the step, large heat transfer recovery is obtained near the side-wall. This advantage of the triangle rib remains effective when the flap actuations are imposed. Thus, the large-scale unsteady vortex intensively reduces the flow recirculation, the triangle rib with flap actuations attains the largest heat transfer recovery behind the step.
Molecular Dynamics Study on Phonon Dynamics in Single-Crystal Silicon and Argon
Authors: Xiao Peng , Matsumoto Mitsuhiro , Kunisawa Tomohisa
Published: April 2009

Modern semiconductor industry and nanotechnology have profoundly impacted the study on thermal transport in dielectric solids such as single-crystal silicon. For these heat conduction phenomena whose characteristic length and time shrink into nano scale, it is efficient to utilize phonon dynamics as a promising approach to investigate the fundamental features of heat transfer at nano scale as well as the distinguished thermal properties of nano-materials. A new computational method is proposed to explore phonon dynamics in single-crystals on the basis of classical Molecular Dynamics technique. This method utilizes the Fourier-Laplace transformation of molecular trajectory, with anharmonicity of molecular vibrations accounted in the investigation on phonon dynamics. Instantaneous mode-dependent energy of phonons and density of vibration state is obtained at each simulated time step. Mode-dependent phonon relaxation is simulated and verified with perturbation method, which gives a way to measure relaxation time of single-mode phonon. The feasibility of the proposed scheme is confirmed by a series of simulations which are carried out in this paper on 1) monatomic crystal of argon with FCC structure and 2) diatomic crystal of silicon with diamond structure, under Lennard-Jones 6-12 potential and Tersoff-1989 model, respectively.
Flow Around a Rising Clean Microbubble in a Vertical Square Tube
Authors: Lee Shong-Leih , Chang Yuang-Jung
Published: April 2009

Flow structure around a rising clean microbubble in a vertical square tube is investigated on a fixed nonstaggered Cartesian grid system. A single set of three dimensional governing equations over the entire physical domain including the liquid, the air, and the bubble surface (the liquid-air interface) is formulated without smearing the bubble surface. There are three step functions in the problem, namely, the density jump, the viscosity jump, and the pressure jump across the bubble surface. A modified NAPPLE algorithm is proposed to handle the pressure jump on a fixed nonstaggered Cartesian grid system, while the density and viscosity jumps appearing in the momentum equations are solved with the extended weighting function scheme. This strategy prevents the occurrence of “parasitic current” on the bubble surface. Solutions of flow structure (velocity and pressure) are obtained for bubble diameters of less than 500 micrometers rising in quiescent pure water. The numerical result evidences that the distorted microbubble under study is of the oblate spheroid type. The distortion parameter is only 1.0006 when the bubble diameter is 250 micrometers. However, the surface tension force due to bubble distortion generates a large pressure jump across the bubble surface that dominates the flow around the bubble. It plays a role similar to the non-transpiration condition on a solid surface. The resulting terminal velocity of the bubble agrees excellently with the existing analytical solutions and numerical results.
Performance Evaluation and Optimization of a Refrigerant Distributor for Air Conditioner
Authors: Yoshioka Shun , Kim Hyunyoung , Kasai Kazushige
Published: April 2009

Refrigerant mal-distribution in a distributor located at the inlet of the heat exchanger used for air conditioning systems plays an important role in the heat exchanger performance. The distribution performance at the distributor is greatly affected by flow conditions as well as geometrical parameters of the distributor. To clarify the distribution characteristics, it is essential to know flow rates of both liquid and vapor state at every branch tube after distribution. In other word, the information of the quality and the flow rate at the every branch tube are required. Acquiring this information, however, requires quite complicate experimental setup so far. This paper proposes a quite simple test method, however, allowing to obtain the value of quality and the flow rate of the refrigerant at the every branch tube of the distributor by measuring pressure drop and heat transfer rate of the branch tubes after distribution. By using the proposed evaluation method, the optimization for the geometrical parameters of the distributor was conducted to reduce the refrigerant mal-distribution and an optimized distributor is suggested. It is confirmed that the optimized distributor greatly reduces the mal-distribution of the refrigerant over the every branch tube regardless of the flow conditions. Meanwhile, by the flow visualization in the distributor, it is observed that certain amount of liquid refrigerant is stayed and swaying unstably at the bottom of the distributor. It is supposed that the liquid refrigerant behavior in the distributor great affects the distribution performance.
Experimental Study on Flow Visualizing and Heat Transfer Characteristic of Pulsating Heat Pipe
Authors: Jia Li , Yin Dayan
Published: April 2009

The flow of looped pulsating heat pipe was studied by a visualizing experiment, and the PHP is made of high quality glass capillary tube. Under different fill ratio, heat transfer rate and many other influence factors, the flow patterns were observed in the start-up, transition and stable stage. The experimental results indicate that bulk flow, transition flow and annular flow are the major flow patterns in PHP. Under different fill ratios and heat transfer rate, the flow pattern in PHP is transferred form bulk flow to semi-annual flow and annual flow, and the performance of heat transfer is improved. In the experiment, nuclear boiling, the convergence and break up of liquid-plug and vapor-slug were observed. The influence characterization has been done for the variation of fill ration, heat transfer rate, non-condensable gas and inclination angle. The experimental results indicate that the total heat resistant of PHP is increased with fill ratio, and heat transfer rate achieves optimum at filling rate 50%; the heat resistance is decreased with heat transfer rate, and non-condensable gas also has significant influence on it. The temperature of tubes in heating, condensing and observe sections were recorded, The fluctuation of heat pipe wall temperature was analysed, and the phenomena of suddently increase or decrease of temperature, the unregular fluctuation of temperature were analyzed. Otherwise the response time under different conditions was also analyzed.
Temporally- and Spatially-Periodic Laminar Flow and Heat Transfer in Staggered-Plate Arrays
Authors: Lamoureux Alexandre , Baliga B. Rabi
Published: April 2009

A computational investigation of temporally- and spatially-periodic laminar two-dimensional fluid flow and heat transfer in staggered-plate arrays is presented in this paper. The objective and the novel aspect of this study is the investigation of the influence (on the numerical solutions) of including single and multiple representative geometric modules in the calculation domain, with spatially-periodic boundary conditions imposed on the instantaneous velocity and temperature fields in both the streamwise and the lateral directions. The following geometrical parameters, normalized with respect to a representative module height, were studied: a dimensionless plate length equal to 1, and a dimensionless plate thickness of 0.250. This relatively high value of dimensionless plate thickness, compared to those commonly encountered in rectangular offset-fin cores of compact heat exchangers, was deliberately chosen to induce and enhance the unsteady features of the fluid flow and heat transfer phenomena. Different specified values of the time-mean modular streamwise gradient of the reduced pressure were investigated, yielding values of Reynolds number (Kays and London definition) in the range of 100 to 625. The Prandtl number was fixed at 0.7. In the multiple-module simulations, for Reynolds number values exceeding 400, it was found that multiple solutions are possible: the particular solution which is obtained in any one simulation depends on the specified initial conditions. The results presented include time-mean modular friction factors, modular Colburn factors, and Strouhal numbers.
Experimental Study of Heat Conduction in Aqueous Suspensions of Aluminum Oxide Nanoparticles
Authors: Ju Y. Sungtaek , Kim Jichul , Hung Ming-Tsung
Published: April 2009

We perform a systematic experimental study of heat conduction in aqueous suspensions of aluminum oxide nanoparticles at volume concentrations up to 10%. We develop a micro-hotwire device to reduce experimental errors resulting from spatial or temporal temperature inhomogeneity within a sample. The volume concentration dependence of the thermal conductivity can be explained using the effective medium model with a physically reasonable set of parameters. The average particle size as well as the thermal conductivity is measured as a function of sample sonication time and temperature. The size of particles/aggregates in our nanofluid samples is much greater than the nominal particle size reported by the manufacturers and does not change appreciably with sonication for up to 24 hours. Our data do not reveal any anomalous enhancement in the thermal conductivity or strong temperature dependence reported in other previous studies. The discrepancy may reflect subtle differences in nanopowders or nanofluid preparation procedures that result in drastic difference in the size or shape of suspended particles/aggregates.
Computational Fluid Dynamics Analysis on Underfloor Air Distribution (UFAD) System in BTLab
Authors: Chen Huajun , Chen Yitung , Hsieh Hsuan-Tsung , Tan Liangcai , Novosel Davor
Published: April 2009

As an alternative to Conventional Air Distribution (CAD) systems, underfloor air distribution (UFAD) systems have been widely used in different country. Although many advantages of a well-designed UFAD system can be found, there is still a higher risk to designers and building owners due to a lack of objective information and standardized design guidelines. UFAD systems design have been influenced by increasing emphasis on indoor air quality (IAQ), energy conservation, environmental effects, safety, and economics. To investigate the performance of the UFAD system, a detailed 3-D computational fluid dynamics (CFD) analysis on the turbulent buoyancy flow and heat transfer inside the BTLab, which locates at University of Nevada, Las Vegas, has been made in this paper. The particular interest has been concentrated on the flow distribution through underfloor swirl diffuser. By CFD analysis with unstructured meshes associated with using parallel processing, the impact of different operating parameters on the air flow and temperature distribution has been studied in detail. Usefully information has been provided on the development of high energy efficiency with human comfort of UFAD systems.
Effect of the Initial Solute Concentration on the Flow Pattern Inside an Evaporating Polymer Solution Droplet on a Substrate
Authors: Kaneda Masayuki , Hyakuta Kentarou , Ishizuka Hirotaka , Fukai Jun
Published: April 2009

The internal flow of an evaporating polymer solution droplet on a substrate is experimentally studied. The flow visualization is carried out. The effect of the initial polymer concentration is further investigated. A polystyrene-acetophenone (PS-Ap) and a polystyrene-anisole (PS-Ani) solution are employed as the droplet. A nylon powder is mixed with the droplet for the visualization by a YAG-laser sheet light. The droplet evaporates after the settlement on the substrate. Without the polymer dissolved in the solvent, complicated flow is observed in both droplets. For the cases with dissolved polymer, the flow pattern is rectified. In the PS-Ap droplet, the source flow is observed for the initial solute mass fraction c0 = 0.005 – 0.20. This convection becomes strong as c0 increases. The mechanism of the flow inside the PS-Ap droplet can be understood by the combination of the natural convection and Marangoni convection due to the differences of the temperature and the solute concentration. As for the PS-Ani droplet, the evaporation process and the flow pattern are affected by c0. For the dilute solution (0 < c0 < 0.03), the contact angle decreases during the contact line receding. The observed flow pattern becomes similar to that in the PS-Ap droplet. At c0 = 0.08 – 0.2, the decline of the contact angle is remarkable and the direction of the internal flow becomes inverse. This flow mechanism cannot be clarified, but it may have the relations with the decreasing contact angle.
A Molecular Dynamics Study on the Local Structure of Liquid-Vapor Interface of Water and L-J Fluid
Authors: Kikugawa Gota , Takagi Shu , Matsumoto Yoichiro , Ohara Taku
Published: April 2009

Microscopic structures of the liquid-vapor interface are investigated by molecular dynamics simulations. In previous studies, we proposed the local and instantaneous definition of the interface at the molecular level, which can capture the thermal fluctuation of the interface. By using this definition, the layering structure of water molecules at the interface is found, in other words, the structurization phenomena of water at the molecular level are clearly seen as usually found at the liquid-solid interface. In this study, we also investigated the liquid-vapor interface of Lenard-Jones fluid. Well depth of L-J potential parameter was somewhat changed and the effect on the structure was studied. Although the structurization was also found at the L-J fluid as well as water, characteristic of this structure is clearly different from that of water. We consider that the difference is ascribed to the intrinsic structure of liquid and associative trend of molecules. We also discussed the anisotropic character of the molecular diffusion at the interface. The anisotropy of the translational diffusion at the interface of water is stronger than that of the L-J fluid.
Auto Ignition and Knocking Phenomena in Stratified Mixture of Lean Condition
Authors: Ihara Tadayoshi , Qin Xiaojian , Tanaka Takafumi , Wakai Kazunori
Published: April 2009

Experimental study has been conducted on auto ignition and knocking phenomena of stratified mixture using a rapid compression machine (RCM) in order to investigate the effects of fuel concentration gradient on the auto ignition and combustion characteristics in the condition that mean equivalence ratio is lean. N-heptane is used as a fuel and mean equivalence ratio is 0.6, 0.8 and 1.0 in the combustion chamber. In the chamber, the lower the vertical location is, the richer the concentration of the mixture is. The difference of the equivalence ratio from bottom to top in the chamber is varied from 0 to 1.4. Mixture has no gradient in horizontal direction. Initial temperature of the mixture is 290K and pressure is 0.1MPa before compression. The diameter of the combustion chamber is 65mm and the compression ratio is 10.5. High-speed video camera is set in front of chamber so that direct images of mixture from cylinder axis direction can be obtained. A pressure transducer is used to obtain pressure histories of chamber, from which ignition delay, pressure rising rate and knocking intensity are determined. The results show that: 1. Flame speed of stratified mixture obtained from direct flame images is much faster than that of calculated laminar burning velocity for corresponding mixture, thus, rapid spread of flame in the experiment is caused not by flame propagation but by consecutive auto ignition. 2. Ignition delays of stratified mixture, not depending on the gradient of mixture, are constant as far as mean equivalence ratio is same and decrease with the decrease of mean equivalence ratio. 3. Pressure rising rate of stratified mixture combustion increases with the decrease of the gradient of mixture at 0.4≤φ≤1.0. 4. In homogeneous condition, knocking intensity of smaller mean equivalence ratio is smaller. 5. With slight gradient, knocking intensities of same mean equivalence ratio are similar to that of homogeneous mixture. In excess of certain value of the gradient, knocking intensity is smaller as the gradient is larger.
Evaporation and Condensation Flows of a Vapor-Gas Mixture Within a Closed Rectangular Region: A Simulation Based on the System of Kinetic Equations
Authors: Onishi Yoshimoto
Published: April 2009

Two dimensional transient motions of a vapor-gas mixture due to evaporation and condensation processes within a rectangular region have been considered with a view to grasping the effects of the presence of a noncondensable (inert) gas on the flow fields and their transition processes. Owing to the sudden change in temperatures of the condensed phases which are embedded in the solid boundary walls of the region, a flow takes place, and the development of this transient flow has been studied numerically based on the Boltzmann equation of BGK type for gas mixtures subject to the boundary condition of diffusive type appropriate for evaporation and condensation. The present results confirm those of the numerical analyses which have already been carried out based on the fluid dynamic formulation for binary gas mixtures established earlier in our laboratory.
Steady Measurement of Glucose Metabolism of Hepatocyte
Authors: Shirakashi Ryo , Yoshida Tomomi , Provin Christophe , Takano Kiyoshi , Sakai Yasuyuki , Fujii Teruo
Published: April 2009

Production of hybrid artificial organs for implantation is one of the main topics of tissue engineering. A large organ consisting of soft tissues requires a high cell density, c.a. 108 cells/mL, to satisfy the same physiological metabolic rate per organ-volume as an organ in vivo. Therefore, the supply of oxygen and nutrition to all the cells composing the soft tissue is always critical problem for the in vitro artificial organ production. Energy metabolic rates, such as oxygen and glucose metabolism rate, of single cell at various temperatures are the basic data for designing the oxygen and nutrition transport in an artificial organ. It is reported that several conditions including pH, temperature, oxygen or glucose concentration have effects on energy metabolism, although these interactions are not clearly quantitatively measured mainly because of the problems of measuring systems. In this study, convenient method to measure glucose consumption rate of hepatocyte (HepG2 cell line) at different temperature and glucose concentration is proposed. A device for the measurement was developed which consists of a small closed chamber with an inlet and an outlet of culture medium at the both ends of the chamber. On the one side of the walls in the chamber, confluent HepG2 on a coverslip was installed. Culture medium supplemented with various concentration of glucose was supplied to the open flow chamber in a constant flow rate. The whole chamber was in a thermostatic bath to keep the temperature in the chamber constant. Glucose consumption rate can be calculated by measuring the difference between glucose concentration of inlet culture medium and outlet culture medium, the flow rate and the number of cells in the chamber. Enzymatic analysis using D-Glucose-HK allows quantification of the sample glucose concentration. The advantages of the proposed method include; 1) small number of cells is required for the measurement, c. a. 105cells, 2) the flow pattern and the glucose supply are in steady state. Especially the latter advantage made it possible to evaluate the effects of different conditions on the glucose consumption rate. Since the most of the metabolic rate were measured under unsteady state, conditions, such as pH, oxygen concentration and glucose concentration, were changed sometime drastically during the measurement. The results provided the several parameters of Michaelis-Menten kinetics at various temperatures.
Effects of Atomization Condition on Flame Structure and Emission Characteristics of Burning Rich-Premixed Spray Jets
Authors: Nakachi Nobutoshi , Mikami Masato , Kojima Naoya
Published: April 2009

Flame structure and emission characteristics of burning premixed spray were experimentally studied for different atomization conditions. Two combustion modes with and without an internal flame were observed. As Sauter mean droplet diameter became larger than a specific value, the internal flame appeared inside the external group flame. The existence of the internal flame was affected by the equivalence ratio of premixed spray jet, too. As Sauter mean droplet diameter was increased, the average flame height increased but the average blue-flame height decreased. These tendencies were same for different equivalence ratios of premixed spray jet. As the equivalence ratio of premixed spray jet was increased, the average flame height increased but the average blue-flame height did not vary very much. Exhaust emission characteristics were also affected both by Sauter mean droplet diameter and the equivalence ratio of premixed spray jet. As Sauter mean droplet diameter was increased, the emission index of CO (EICO) increased. EINO took maximum at Sauter mean droplet diameter of about 60 μm ∼ 80 μm. These tendencies in terms of Sauter mean droplet diameter were same for different equivalence ratios of premixed spray jet. EICO concentration showed low values without the internal flame.
Numerical Analysis of Heat and Mass Transfer on Collision Dominated Particles Flow in a Vessel
Authors: Yamaguchi T. , Kanemaru K. , Momoki S. , Shigechi T. , Yamada T.
Published: April 2009

Though the solid-gas multiphase flow has been studied experimentally and numerically, the transport phenomena have not been cleared due to its complexity, computational time required and economical costs for hardwares. In this study the heat and mass transfer of solid-gas collision dominated flow in a rectangular vessel is analyzed by the Discrete Particle Simulation (DPS), a kind of the Dispersed Element Methods (DEM)[1]. This method describes the discrete phase and continuous phase by the Lagrange and the Euler methods respectively, and has been used to simulate the multiphase flows of various geometrical systems. In order to analyze the thermal field we took account of the energy equation and heat conduction between colliding particles. We treated the continuous phase as a pseudo two dimensional flow, and the interaction between continuous and discrete phases as two way coupling. The positions, the momenta and the temperature information of particles and velocity and temperature distribution of fluid were obtained as functions of time from results of these numerical simulations. When the hot air flowed from bottom to top in the vessel of packed bed, we traced the particles and got the temperature distribution of fluid. The particles at the surface of the packed bed jumped first and made the void areas at the middle of vessel. We found the void areas that rise in the dispersed particles.
Experimental Investigation of Phase Change Phenomena in Nanofluids
Authors: Madhusoodanan M. R. , Sajith V. , Sobhan C. B.
Published: April 2009

Thermophysical properties of water like the thermal conductivity, viscosity and the surface tension are observed to change by the addition of nanoparticles. The nature of the variation of these properties with the addition of nanoparticles is a topic of increasing research interest. Rate of evaporation at a liquid surface is affected by various factors, among which the surface tension is the most predominant, and inversely affects the rate of evaporation. The introduction of nano particles into a base fluid obviously makes changes in surface geometry, which in turns alters the surface tension and hence the rate of evaporation. The present experimental study deals with the evaporation of nanofluids, obtained by suspending metal oxide nanoparticles in water. The rate of evaporation was determined by precise measurement of the rate of loss of weight of the nanofluid upon heating, keeping other parameters constant. Experiments with pure water and suspension of aluminum oxide nanoparticles showed that the rate of evaporation of the nanofluid is less compared to that of water, though a definite trend in the variation of the rate of evaporation with respect to the dosing level of nanoparticles was not found to exist. The surface tension is measured using the capillary rise method, which was observed to increase with nanoparticle addition without showing any clear functional relation with the nanoparticle dosing level. Distillation of nanofluids using standard apparatus also indicated a decrease in the evaporation rate with the addition of nanoparticles to the base fluid.
Effect of Acoustic Excitation on the Heat Transfer to an Impinging Air Jet
Authors: O’Donovan Tadhg S. , Murray Darina B.
Published: April 2009

Impinging air jets are known as a method of achieving particularly high heat transfer coefficients and are employed in many applications including the cooling of electronics, manufacturing processes such as grinding, etc. The current investigation is concerned with acoustically exciting an impinging air jet to enhance its overall cooling capacity. Distributions of the heat transfer to an axially impinging air jet for a range of Reynolds numbers (Re) from 10000 to 30000, non-dimensional nozzle to impingement surface heights (H/D) from 0.5 to 2 and excitation frequencies (f) that range from 0.5 to 1 times the natural frequency of the jet are presented. For this low range of nozzle to impingement surface spacings it has been shown that the heat transfer distribution exhibits a peak at the stagnation point and secondary peaks at a radial location that is both excitation frequency and Reynolds number dependent. Distributions of the fluctuating component of the heat transfer coefficient are also presented for the range of parameters tested. These have been used, along with spectral analysis of the heat flux signal, to discern whether local variations in heat transfer are due to changes in the local vortex flow or to changes in the mean flow structure of the impinging jet.
Heat Transfer Characteristics and Enhancement in Symmetric Wavy Channels in a Frequency-Doubling Transition Scenario
Authors: Guzman Amador M. , Aracena Tania A. , Cardenas M. J. , Escobar Rodrigo A.
Published: April 2009

We investigate the heat transfer enhancement due to flow mixing enhancement in a frequency-doubling transition scenario in symmetric wavy channels by direct numerical simulations of the mass, momentum and energy equations. The governing equations are solved for laminar and transitional flow regimes by the spectral element method, using a periodic computational domain, and with a high aspect ratio of r = a/(2L) = 0.375, where L is the periodic length, and a, the wavy wall amplitude. The frequency-doubling transition scenario is characterized by one flow bifurcation that develops to a critical Reynolds numbers Rec, leading to a periodic flow. Further increases in the Reynolds number leads to successive periodic flows where the fundamental frequency ω1, increases continuously. This scenario is different to the Ruelle-Takens-Newhouse transition scenario obtained for a symmetric wavy channel with an aspect ratio of 0.125, where periodic and quasi periodic flow regimes develop as the Reynolds number increases. Heat Transfer simulations are carried out assuming a constant heat flux on one wall and an adiabatic condition on the other wall. Numerical results demonstrate that the time-average mean Nusselt number increases significantly as the flow passes from a laminar to a periodic flow regime. As the flow becomes periodic and for increasing Reynolds numbers, the Nusselt number increases with respect to the laminar flow Nusselt number, up to a factor of 4, depending on the Reynolds number, which represents a significant heat transfer enhancement due to a better flow mixing. This increase is accompanied by a reasonable increase in both the friction factor and the pumping power. The obtained qualitative and quantitative features are compared to other channel geometries, such as grooved and asymmetric wavy channels, which also develop different transition scenarios.