Emulsified fuel combustion is supposed to be effective for the reduction of thermal NO_x and particulate matter. In our previous study, concentration of CO and HC in the exhaust gas decreased as the diameter of the waterdrops in emulsion droplets increased, when we used W/O emulsified fuels for a single cylinder 4-cycle diesel engine. So we examined the effect of waterdrop diameter on exhaust emissions of the diesel engine and microexplosin occurrence. Consequently, concentration of HC and CO decreased for larger waterdrop diameter, and the waterdrop diameter did not influence on the frequency of microexplosion but the special scale of the microexplosions.

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Regeneration process in a DPF was clarified through a visualization experiment, using a high-speed microscope camera and a half-cylindrical wall-flow DPF covered by a quartz glass plate. From the micro-scale visualization experiment, it is disclosed that the regeneration and the trapping phenomena in the millimeter-size channels were not uniform in the cross-sectional direction due to the velocity distribution of the wall-flow.

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This study focuses on the fundamental characteristics of DME (Dimethyl Ether) combustion, aiming at the development of the new low-NOx combustion technologies suitable to DME. Combustion experiments using a diffusion burner of 11.6kW were conducted for characterizing DME through the comparison with the results of LPG and 13A-city gas. Experimental results demonstrate a high potential of DME as a boiler and a gas-turbine fuel. In this study, the concept of the low-NOx combustion, referred to as the tube-nested combustion, is applied to DME combustion. NOx emission of the DME combustion is extremely reduced by applying this combustion system.

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In this article, we discuss microscopic particle deposition behaviors in a Diesel Particulate Filter (DPF). We measured a particle deposition process in a porous side wall in the DPF by using a long range microscope connected to a CCD camera. We also monitored variation of pressure drop due to particle deposition. We confirmed that the pressure drop curve had two different modes, i.e., a rapid increase of pressure drop observed in the initial stage and a moderate increase in the later. The microscopic observations show that in the initial stage, particles are trapped inside the porous wall and that thereafter particles accumulates on its surface of the porous wall. We also conducted a lattice Boltzmann Simulation of a particle depositon process in a porous system.

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A combustion phenomenon produces heat. General combustion phenomenon is the reaction of forming water. The combustion gas contains lots of water. Heat recovery drops the combustion gas temperature. A drop of the combustion gas temperature causes the formation of the condensation water. The condensation water causes the damage of heat exchanger. In this research, it pays attention to the condensation water formed with the high efficiency water heater of heat exchanger. In this paper, it is reported about the quantitative evaluation of condensation water's formation mechanism in the high efficiency water heater.

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As CO poisoning of platinum is one of the most important problems in PEFC, many studies are conducted to find alternative catalysis but replacing Platinum with alternative materials seems to be still difficult. In this study, another approach to find a scavenger that enhances CO removal is proposed. To this objective, behaviors of adsorbed CO on Pt surface are studied using Density Functional Theory (DFT). The results show that effect of a surrounding H_2O molecule on CO-Pt adsorption energy is small and the energy barrier of the reaction of ad-CO and O is about 0.4 eV and CO_2 produced can easily leave Pt surface.

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The dissociative chemisorption of SiH_4 on Si surface plays important roles for the epitaxial thin film growth. To investigate the dynamics of the dissociative chemisorption for this gas-surface system, we use molecular dynamics simulation. As the first step of the simulation, the activation energies are calculated from the lowest energy path and compared with DFT results to confirm the validity of the potential model. Then we analyze the relationship between the reaction probabilities and the effect of the internal energy. It is confirmed that the reaction probability of SiH_4 on Si (100)2×1 surface increases along with the incident translational energy. In addition, the excitation of stretching vibration mode enhances reaction probability efficiently.

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We found that Pt-based alloys had high reactivity for the oxygen reduction reaction. Using the computational method (ab initio analysis) and experimental method (EXAFS, XANES), we clarified the reason why alloying of Pt causes the reactivity enhancement of oxygen reduction reaction. Based on the results, we concluded that the increase of the Pt d-band vacancies, which causes the weakening of H_2O-Pt interaction, is the significant guiding principle for desiging of cathode catalysts.

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In order to predict effects of additional gas concentration on carburization of metallic surface, numerical analysis of chemical kinetics and ab initio calculation were conducted in the present study. Time history of mole fraction of chemical species in reaction gas were calculated by CHEMKIN II and GRI-Mech3.0 with changing additional gas conditions. Reactivity of CO_3 CH_4,C_2H_2 C_2H_4 and C_2H_6 in reaction gas was estimated qualitatively by GAUSSIAN98 in a simple model system of two Fe atoms. Effects of gas addition on carburization were estimated simply by putting calculation results together.

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The computational research has given a great contribution to the various materical processes. However, the approaches generally have been limited to the fixed resolution of time and spaces. Recently we have developed the new method based on the multi-scale analysis that connects the thermofluid phenomena from the electron energy distribution to the macroscopic properties such as temperature and density. This multi-scale modeling is extended to the gas-phase reaction here and the collision induced dissociation of SiH_4 is analyzed in this study. As the first step of the research, the existent classical Si-H potential model is employed. The potential model proposed by M. V. Murty reproduces all the vibrational mode of SiH_4. The result of the classical molecular dynamics calculation shows that the initial internal energy plays an important role on SiH_4 dissociation.

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We have proposed the new catalytic CVD generation technique of SWNTs from alcohol. By using alcohol as a carbon source, high-purity SWNTs were produced at relatively low temperature (550∿900℃). Here, using ferrocene as a precursor of floated iron catalyst clusters, high-purity SWNTs were generated from alcohol. Vapor of ferrocene ethanol solution was injected into a quartz tube, which was heated by an electronic furnace. Keeping the pressure of quartz tube at about 200-400 Torr, black soot was collected at a trap located at downstream of quartz tube. Raman scattering, TEM, SEM and TGA showed the generation of high-quality SWNTs, at low gas flow velocity (about 1 cm/s) and with Ar gas buffer. This simple technique is expected to be an efficient low-cost generation technique of bulk SWNTs.

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A spectroscopy measurement of local chemiluminescence of a micro flame was conducted in the present study in order to know effects of atmosphere temperature and wall temperature on radical distribution in the vicinity of surface. Local chemiluminescence of a micro flame was measured by Cassegrain optical system and ICCD spectroscope system with changing burner diameters and flow rate. Intensity of chemiluminescence of OH radical was relatively stronger in the vicinity of a small scale burner outlet in the cases of premixed supply of oxygen and methane.

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Extinction and stability of micro-scale diffusion flames (we call 'microflame') established over a circular jet burner in atmospheric air is studied numerically. By imposing adiabatic condition for burner surfaces, artificial heat loss in the system is excluded. Flame extinction focused in the present study is lead by size effect. Numerical model considered in the present study includes the convective-diffusive heat and mass transport as well as one-step finite rate chemical reaction. Our numerical results show that extinction is finally achieved in the order of tens micron of burner port, and hundreds micron of flame size (∿ typical reaction layer thickness of hydrocarbon flames). As the size gets extensively smaller, diffusive transport rate becomes very fast while the reaction rate is kept constant irrespective of the size. This discrepancy must be a reason for extinction in the small size limit.

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Microscopic diffusion flame mechanism is important when understand mutual connection of a combustion condition and a condition in molecule diffusion of a flow that a molecule to maintain routine diffusion combustion has quantitatively. Micro-jet diffusion flames, formed by a minute burner of a few hundreds of a few tens μm inner diameter, should be interesting and useful, partly because they resemble micro-gravity flames and partly because they provide some insight into the mixing and chemical kinetics process occurring in turbulent diffusion flames. This flexible double micro burner can begin to make non-symmetric combustion region by free movement of inner burner in the outer flame region. This study observed the time-dependent combustion state by direct photography method with highspeed CCD camera.

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Turbulent premixed combustion is supposed to be effective for the control of soot alnd thermal NOx, but the flame structures formed in intence turbulant flowfields are not elucidated. So we examine the premixed flames formed on microburners which have small diameters from a microscopic point of view for claribying the combustion characteristics of small flamelets. First of all, we examine the flammable limit and the extinction characteristics of the flame formed on simple microburners.

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The flame stability limits essentially define the fundamental operation of the combustion system. The critical conditions at the stability limits are highly dependent on flow configurations and some species of fuels. For various species of fuels (Methane, Propane and Hydrogen), the flame-base stability mechanism for flame holding has been studied. In this study, the transition behavior from the stable flame attached to nozzle rim to lifting and blow off is observed experimentally in unconfined, quiescent atmosphere air. Experiments were conducted to investigate the stability minimum limits and flame behaviors for various nozzle diameters from 0.14 to 8.1mm. The results obtained are as follows. It turns out that the minimum limit of a stable flame does not depends on the average jet velocity, but it depends on the fuel flow rate. Regarding to the micro scale nozzle, the flame length of the laminar flow is decided by fuel flow rate.

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It is of interest for designing micro combustors to know the minimum size of chamber in which flammable gases can be ignited. The minimum diameter of a ignitable bubble of the mixture of hydrogen and air in water is then measured in the present study, where a bubble in water is used as a spherical combustion chamber. The results obtained at the equivalence ratios 0.3,0.4,0.5,2.0,4.0 show the minimum diameter of the ignitable bubble decreases (increases) when the equivalence ratio increase 0.3 to 0.5 (2.0 to 4.0), which is consistent with the trend of quenching distance.

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Characteristics of combustion in micro-channel heated by external heat source were examined. We chose quartz channel of inner diameter 2mm, being smaller than the quenching distance of Methane-air mixture. The effects of equivalence ratio and averaged mixture flow velocity on the stability were examined. In addition to the conventional flame, repetition of extinction and auto-ignition which we all "oscillatory combustion" was observed in wide equivalence ratio and smaller mixture velocity conditions. Mechanism of the phenomena was discussed by simple analysis.

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Quick mixing of fuel and air is one of the most essential factors to improve combustion and emissions in diesel engines. This paper investigates diffusion structure of sprays injected in engines using entropy analysis. The method allows the analysis of heterogeneity degree and diffusion intensity in pictures. Introducing laser sheet in an engine, cross-sectional images of the spray were obtained, and diffusion structures were compared for the swirl ratios. The result of the analysis shows that the swirl has an effect of changing fuel distribution but it does not have effect of increasing local diffusion coefficients, rather the medium scale diffusion intensity decreases by the swirl.

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The method to apply chaos mixing into micro liquid-liquid reactor, and more specifically, the way of stretching and folding of fluid elements without any rotors has been sought in the present study. The ferric nitrate solution is injected into the potassium thiocyanate solution bath from the bottom. Both solvents are mixtures of water and glycerin with high viscosity. The effect of the ratio of glycerin and water on the profile of interface between two solutions is tested as well as the difference of profile between continuous injection and intermittent injection. Injection of lower density solution intermittently into higher density solution in the bath shows a potential to be one of the ways to achieve the stretching and folding of fluid elements without any rotors.

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Eddy correlation method is one of the useful methods to measure latent heat flux and sensible heat flux in the atmospheric surface layer. The necessary performances of the measurement system are 10Hz changes of specific humidity, vertical wind speed and air temperature, respectively. In order to measure specific humidity, a near infrared hygrometer using 1.37μm absorption band of water vapor was newly developed and evaluated in the grass field with a commercial near infrared hygrometer and an ultrasonic anemometer. We also discussed on frequency dependence of heat flux.

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The concentration fluctuation of tracer gas emitted from an elevated point source within the atmospheric turbulent boundary layer was simulated and measured in a wind-tunnel experiment, and the concentration fluctuation of tracer gas was measured using a fast-response flame ionization detector. The effects caused by the averaging time to concentration fluctuation characteristics were analyzed in this study. The variations with the averaging time for the ratios of peak concentration to mean values showed almost similar profiles as those obtained in atmosphere. Furthermore, the relations between the skewness and flatness factors of were also observed for concentration fluctuation measured in wind tunnel.

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The convective boundary layers (CBL) have a very complex structure by an effect of buoyancy from heated ground and a strong temperature inversion aloft. We simulate (DNS). Both results show a good agreement and simulate the field studies successfully. Furthermore, DNS results show the detailed flow structure dependent on the CBL stability.

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Collisions of monodispersed particles in turbulent flows are important both in the mechanical engineering and in the cloud microphysics. A number of studies investigated the phenomenon but they neglected the gravity acting on the particles in order to assume the isotropy of particle motions. In this study, therefore, we investigated the effect of the gravity on the collision frequency by using a direct numerical simulation. The results show that if we neglect the particle weight, i.e. the gravity, is neglected the collision frequency becomes higher. It is also found that when the particle terminal velocity is comparable to or greater than the root mean square value of the fluid velocity the particle weight cannot be neglected.

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Internal gravity waves with fundamental frequency components of 1.2,1.8,3.0Hz were spontaneously generated in a strongly stably-stratified mixing layer. The spatial structure of internal gravity waves was experimentally examined to clarify the mechanism of occurrence of counter-gradient heat flux. Multi-point simultaneous measurement was conducted on the spatial structure by using a multi-channel high precision thermo-anemometer system. Transverse spatial correlation between temperature fluctuations was enhanced, as the internal gravity waves grew downstream, which characterizes the development of vertical structure of the wave motion. Counter-gradient heat flux was confirmed to occur at the break down of the wave front of the internal gravity waves.

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Passive and active scalar fluxes in unsteady stratified turbulence are analyzed using the rapid distortion theory (RDT) with the diffusion effects of density and passive scalar. Analytical solutions of the RDT equations show that the passive scalar gives a stronger counter gradient flux than the density flux. The difference in these fluxes appear mainly appear at high wave number spectrum. However, longer time development than the previous experiments shows that the difference might be a transient one and may diminish at large times. Anyway tese all results show the importance of 'unsteady' analysis of the initial value problem in the diffusion problems in stratified turbulence.

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The direct numerical simulations (DNSs) of the turbulent Ekman layer over a smooth flat surface are performed. The Reynolds numbers are set to be Re_f=400 and 600,where Re_f is defined by Re_f=G/√<vf/2> with use of the geostrophic wind velocity G, kinematic viscosity v and Coriolis parameter f. The turbulent structure in Ekman layer shows the three-dimensional nature. A large-scale structure appears in the high upper region where the geostrophic balance is observed. In this region, the inertial oscillation can be obtained even in the turbulent field. In addition, the effect of Reynolds number onto the three-dimensional characteristics of the turbulent structure is examined. The effect of the large-scale structure onto the passive scalar transport is also discussed.

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The direct numerical simulation (DNS) is performed on the Ekman turbulent boundary layer around an isolated hill. Turbulence statistics such as the mean velocity profile are obtained. The streamline of the mean flow indicates that two mean vortices appear behind the hill and that they are asymmetric with respect to the vertical central plane along the mean flow direction. The reason of the asymmetry is discussed in conjunction with the system rotation and the pressure gradient force. The instantaneous vortex structures are visualized using the second invariant of the deformation tensor. Many small vortices are observed in the low pressure region behind the hill.

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Direct numerical simulations of a turbulent channel flow are performed to investigate the transition period of turbulence near the free-slip wall just after the boundary condition is changed from the non-slip to the free-slip one. In the side of a free-slip wall, the mean shear is attenuated with time development; the dissipation rate of the turbulent kinetic energy surpasses the production rate, and hence turbulence decays. It is found that turbulence becomes vertically homogeneous over the long distance away from the free-slip wall; the turbulence kinetic energy, the dissipation rate and the pressure-strain rate show the plateau over almost entire vicinity of the free-slip side. The horizontal energy spectrum show the definite k_H^<-3> slope as predicted by turbulence theory in decaying two-dimensional turbulence, and it decays in the self-similar form. The effect of the bottom wall, which makes turbulence three-dimensional, does not appear until the mean velocity profile becomes even in the free-slip side.

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In order to grasp and understand the carbon dioxide gas transferred into the sea, a direct numerical simulation (DNS) of turbulent atmospheric gas flows interacted with the sea surface has been carried out and the computational results and the satellite measurement data can be simultaneously visualized by a Web based network collaboration system developed here. The results from this DNS can be applied to the gas transfer modeling at the sea surface of the global climate modeling and the anti-environmental material transport modeling on the earth. Moreover many researchers can conduct the DNS and access the satellite database of the wind velocity and the wave height on the sea surface, and also handle the scientific visualization software through this Web based mutual research collaboration system. This system can provide a real-time steering and tracking simulation/visualization platform for mutual scientific research collaboration not only for the environmental science but also other many scientific and engineering fields.

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Direct numerical simulation of turbulent mass transfer across a contaminated air-water interface is carried out. With increasing the Marangoni number, the thickness of the viscous sublayer in liquid is increased and the mean velocity profile converges to that near a solid wall. The tangential velocity fluctuations at the interface, however, have nonzero values even in a highly contaminated case, indicating that the velocity field near the interface is essentially different from wall turbulence. By decomposing the interfacial velocity vector into two components, i. e., irrotatioanl and solenoidal vectors, it is found that the irrotational motion is dumped significantly due to the surfactant, while the solenoidal motion kept almost unchanged. Since the irrotational motion at the interface plays a crucial role in the interfacial mass transfer, 40% decrease of the gas transfer rate is observed even in a slightly contaminated case.

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It is of great importance to investigate the mass transfer mechanism across the air-sea interface in order to improve the reliability of predictions for global warming. However, previous sub-models used in general circulation model for predicting mass transfer velocity across the air-sea interface have been based on the simple assumption that the transfer velocity is proportional to wind velocity over the ocean surface. This rough assumption reduces the reliability of the sub-models. To develop a reliable model for the mass transfer velocity, some factors that truly reflect the physical processes involved should be investigated. We experimentally investigated the effects of ocean surface physical processes on the mass transfer between the atmosphere and the ocean, including phenomena such as wave breaking, swells, density stratifications, surface contamination and rain. The results show that the conventional model of the mass transfer velocity has a lot of shortcomings.

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We have been developing GLAD ( Gas Lift Advanced Dissolution) System for the purpose of CO_2 sequestration at the deep sea. In the present paper, large-scale structure of turbulent bubbly flows in a large-diameter pipe (149mm in diameter and 11m in height), that is the key phenomena in the system, is experimentally considered using Four-Tip Optical-fiber Probe (F-TOP) and Laser Doppler Anemometer (LDA). Furthermore, characteristics of large-scale gas-lift pump (151mm in diameter and 212.6m in height) are discussed experimentally.

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Liquid phase motion in the vicinity of a zigzag-rising single bubble has been investigated. Interfacial motion and motion of the center of gravity of the bubble were measured by high-speed video camera. On the basis of the results, the liquid phase motion at some inflection points of the zigzag trajectory was measured via LDA and PIV system. Different patterns of the liquid phase motion have been found at each point of inflection. Further, it is confirmed that the liquid motion affected by a rising bubble is restricted just near a bubble.

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A numerical analysis has been developed to give a prediction for the induced flow and heat transfer in upwelling deep seawater using the perpetual salt fountain. The seawater is drawn up by the buoyancy force driven by simultaneous temperature and salinity differences. The upwelling behaviour is predicted by both laminar and turbulent flow models. A comparison of numerical prediction and experimental data obtained in Mariana Trench (Pacific Ocean) is presented to have a better understanding of the physical mechanism for the flow and heat transfer in upwelling deep seawater using the perpetual salt fountain.

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Turbulence modification in the presence of bubbles was investigated by time-series measurements using a high-time resolution PIV. The experiments were carried out in a fully-developed vertical pipe with upflow of water at the Reynolds number of 9700 and the void fraction of 0.5%. The two-dimensional flow structure in the vicinity of bubbles was measured by a high-time resolution PIV with fluorescent tracer particles and bubbles shapes and positions were obtained by using a shadow imaging technique. It is observed that turbulence production was rapidly decreased and dissipation rate was enhanced in a whole region. A strong vorticity region was generated in front of bubbles, on the other hand, vorticities behind bubbles show larger values and exist longer in center of pipe than near the wall.

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The dynamics of a single, rising air bubble in a linear shear flow was investigated by high speed and high spatial resolution CCD cameras in a vertical water channel. The present study focused on the influence of forces acting on the bubble and its lateral motion induced by the surrounding flow field. The flow structure in the vicinity of the bubble of 2 to 6mm in diameter was obtained by a PIV/LIF technique, and deformation of the bubble's interface was measured by a shadow imaging technique. It is found that the bubble trajectory was mainly affected by the three-dimensional vortex shedding in the wake. Experimental data of the averaged vorticity at the edge of bubble, the bubble aspect ratio and the curvature of bubble edge showed that the magnitude of vorticity correlates with the bubble shape.

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Frictional pressure drops of horizontal adiabatic air-water two-phase flow in Pyrex grass tubes with inside diameters of around 1,2,4 mm, respectively, were measured. The experimental results are compared with the author's previous experiment on heated air-water vertical flow with stainless steel tube of 2 mm I.D., and good agreement is obtained between the present and previous experimental results. Two-phase multiplier Ф_l^2 is correlated very well by Chisholm-Laird's equation at relatively large liquid and gas superficial velocities, whereas Mishima-Hibiki's modified correlation for small diameter tube is valid for the case where the liquid superficial velocity is low. This depends on Reynolds number of liquid phase. Transition from laminar to turbulent flow is considered to occur at liquid phase Reynolds number of around 1000.

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A gas atomization method is successfully applied for fiber and powder production from a highly viscous slag. The slag suction pressure becomes higher, when a flow guide was inserted at the exit of the gas nozzle. When the molten coal gasification slag temperature was 1500℃, a smooth continuous fiber measuring approximately 9μm in diameter was produced, which could be used as a heat insulating media and a buffer material. Powders having a diameters of approximately 9μm were produced at 1600℃, which could be used as raw material for cement.

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The trend of the processor performance and heat dissipation has been significatly increased every year. In the year 2000,the clock speed of processor used in notebook was marginal 1GHz and heat dissipation marginal 20 W, but in the current year 2003 the processor's clock speed in higher than 3 GHz and heat dissipation higher than 50 W and approaching 100 W by year 2004 at maximum. Heat dissipation increased but in contrary the size of the processor reduced and thus the heat flux is critically high. The heat flux was about 10-15 W/cm^2 in the year 2000 and could reach over 100 W/cm^2 by year 2004. The purpose of this paper is to provide overview of various cooling solutions using heat pipe and vapor chamber for cooling high power processors in a confined space of the personal computer.

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In this paper is presented the results on performance of the cooling model used in the back area of the display using water-cooled system. In recent years, ever ending demand of high performance CPU led to a rapid increase in the amount heat dissipation. Consequently, thermal designing of electronic devices need to consider some suitable approach to achieve high cooling performance in limited space with low noise level. Under the present experimental condition, when the flow rate is 50 l/min, about half of the amount of heat dissipated was cooled by natural convection and radiation, and the rest was cooled by forced convection. A possible way to increase the cooling efficiency by forced convection is to install fins on the heat-dissipating panel.

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Critical heat fluxes are obtained in subcooled pool boiling of mixtures with alcohol and water by burning out stainless steel plate heater. The critical heat fluxes change with mass concentration of alcohol. For the mixtures of polyhydric alcohols, 1-butanol and 2-propanol, the maximum critical heat fluxes are about 200 percent higher than that of water. In subcooled flow boiling of ethanol-water and 1-butanol-water mixtures in a horizontal rectangular channel, microbubble emission boiling occurs in transition boiling and the heat fluxes are about 50 percent higher than water at same superheat of heating surface. The maximum heat fluxes of the mixtures reach 8 MW/m^2 at 40K of liquid subcooling and 0.5m/s of liquid velocity.

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Although most of liquids show a decrease in the surface tension with increasing temperature, dilute aqueous solutions of higher alcohols with more than four carbon atoms are known to exceptionally show the opposite behavior; the surface tension increases with the increase in temperature. In nucleate boiling, possible dry patches developed under the bubbles are expected to be wetted by a liquid supply due to the Marangoni effects induced by both temperature and concentration gradients at the bubble interface, provided a good wettability is maintained. This particular characteristics, the so-called "self-wetting" characteristics, may allow an outstanding cooling performance not only in microgravity environment but also the terrestrial condition. A series of performance evaluation experiments have been conducted for conventional heat pipes with self-wetting fluids as a working fluid, and some results are promising.

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To develop compact space heat exchangers, experiments on the increase of CHF for narrow heated ducts between parallel plates are conducted. Fine grooves are machined on the surface of heat transfer side, and liquid is supplied underneath flattened bubbles by capillary pressure from auxiliary liquid channels separated from the main channel by porous metal plates. With this structure, values of CHF for the heating surface are increased up to twice as much as those without the structure. Effect of inlet liquid velocity on CHF values is also investigated. At an optimum flow rate, values of CHF take the maximum for a given liquid subcooling. Teh increase in CHF values is expected to become much higher when the duct is elongated and/or gravity level is reduced.

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