In the authors' previous study, using the Fire Dynamics Simulator (FDS), the tunnel fires were simulated, and these results mimic other research result. This article shows the effect of water droplet diameter of the sprinkler for controlling the thermal flow and smoke flow. The fires in small size tunnel with width 6m, height 3m and length 800m are simulated by FDS with the water screen, created by 6 sprinklers. Simulations are performed with various water droplet diameters and two kinds flow rate. These results show that the traveling distance of thermal and smoke flow is shortest when the water droplet diameter is smallest.

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We investigated the deterministic behavior of combustion instability in a lean premixed gas-turbine model combustor from the viewpoint of nonlinear forecasting. A genetic algorithm, which quantifies the predictability of time variation in pressure fluctuations, is applied as a nonlinear forecasting method in this work. The dynamic behavior in the combustion instability near lean blowout exhibits the fractional Brownian motion with anti-persistent, and intermittent oscillation represents chaos. This is clearly demonstrated by nonlinear forecasting based on genetic algorithm, which has not been addressed in the fields of combustion science and physics.

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A flame propagation in the vortex flow in a meso-scale, 10-mm tube has been experimentally investigated using N_2, Ar, He, and CO_2 as diluents. Methane was used as fuel. Results show that, the flame propagation range of Ar- and N_2-dilution is almost the same as their flammability range. However, the propagation range of He-dilution is considerably narrower, whereas the range of CO_2-dilution is wider than their flammability range. These results indicate that the flame can propagate beyond the flammability limits when Lewis number is less than unity, whereas the flame cannot propagate even in the flammability range when Lewis number is greater than unity.

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To clarify the stabilization mechanism of coaxial oxygen-jet diffusion flames, experiments on the measurement of flame base position and stream lines near the burner lip were performed. It was found that, at high pressure, flame base located in the recirculation zone near the lip, while, at atmospheric pressure, it located downstream of the recirculation zone. This means that the stabilization of the flame base at high pressure is dominated by the existence of the recirculation zone and that at atmospheric pressure is determined by the balance between the local gas velocity and burning velocity of the premixed gas formed by diffusion. Therefore, the stabilization mechanism changes depending on the ambient pressure.

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The present study performed spray combustion experiments of alcohol aqueous solution/heavy oil emulsified fuel to investigate the effects of alcohol concentration on the flame temperature and exhaust gas concentration. In the experiment, the emulsified fuel is produced by mixing heavy oil A and an ethanol aqueous solution by varying the ethanol concentration of the solution. The emulsified fuel flame shows the maximum temperature closer to the burner than the heavy oil flame, indicating that the combustion characteristics are improved in the emulsified fuel owing to the micro-explosion. In addition, a decrease in NOx concentration is observed in the emulsified fuel with increasing the ethanol concentration in the solution.

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Behaviors of flame propagation in a detonation tube were observed by a high-speed video camera in order to clarify the effects of rapid flame propagation in a vortex flow on DDT. The flame speeds near the wall of the detonation tube are faster than those at the central part of the tube. The flame is accelerated between the first half part and the latter half part of the observation windows due to a turbulence which is generated at the ramp between the first half part and the latter half part of the windows. The flame speeds show nearly constant value even when the rotating velocity is increased, thus the effects of rapid flame propagation in the vortex flow on DDT is not observed.

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The phenomenon of flame merging is observed when two burners on which diffusion microflames are established approach parallel to each other. On this phenomenon, the way to predict the distance between burner axes that makes the flame-tops merged at various burner diameters and flowrates are discussed. It is found that the maximum distance that makes the flame-tops merged agrees with the flame width (maximum horizontal diameter of flame) before interaction. In other words, the flame-tops are found to be merged when the distance between burner axes is less or equal to the flame width.

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In order to clarify the characteristics of the catalytic reaction under high concentration of CO_2, experimental investigation and two-dimensional numerical simulation were conducted in this research. As a result, the stability reduction of catalytic reaction was confirmed under CH_4/O_2/CO_2 mixture compared to CH_4/O_2/N_2 mixture in both of simulation and experiment. This is because the wall and gas phase temperature, exposure of Pt(s) and heat of reaction on catalyst wall surface were decreased in CH_4/O_2/CO_2 mixture.

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An oscillating heat pipe (OHP) is desired as an excellent heat transfer device for the thermal management system of a future spacecraft with larger heat dissipation, and a flat-plate heat pipe (FHP), a type of OHP, has been developed. Applying FHP to the spacecraft, the heat transfer characteristics of FHP under micro-gravity conditions should be examined. The on-orbit experiment of FHP is currently underway to conduct the performance evaluation of FHP under micro-gravity environment, as one of the Small Demonstration Satellite-4 (SDS-4) missions. The initial evaluation shows that the heat transfer characteristics under micro-gravity condition are the same as those under 1-g condition, and no degradation is seen after three months on orbit.

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Enhancement of natural-convection boiling heat transfer by electric field is investigated experimentally. Boiling of refrigerant water occurs on an aluminum rod and platinum sphere under the atmospheric pressure, and a D.C. voltage up to 660V is applied between the heat transfer surface and an electrode made of stainless-steel wire-mesh 10 mm apart. The whole boiling curve is measured under different applied voltages. The results of experiment indicate that boiling heat transfer is enhanced by electric field. An enhancement ratio of film boiling heat transfer as high as 9 times is obtained. As a result, confirmed the effect of EHD on boiling heat transfer.

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We carry out an experimental study with a special interest on growing and collapsing processes of vapor bubbles in subcooled pool. We examine the boiling phenomenon on copper block with using pure water. We especially focus on the microbubble emission boiling (MEB). The MEB is a phenomenon in which the heat flux exceeds the CHF accompanying with a formation of small bubbles of the order of 10^<-6> m and a radial emission of those bubbles from the heated surface. We propose a model that is named 'Core-periphery model.' This model shows a correlation between behaviors of the vapor bubbles and the characteristics of the heat transfer over the heated surface.

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A series of experiments on subcooled pool boiling on a thin wire are carried out. We focus on the condensation and collapse processes of vapor bubbles generated on the heated wire. We find two major patterns of the vapor bubble behaviors resulting in the emission of the microbubble around the thin wire by employing high-speed observation with frame rate up to 150,000 fps. Effect of the surface roughness of the wire on the vapor bubble behavior and heat transfer coefficient is discussed.

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Critical Heat Flux (CHF) is one of the most important factors in the designing of the water tube in boiling two-phase flow equipments, such as a conventional boiler, a nuclear power plant and so on. However, the CHF has quite different mechanism on each flow patterns, i.e. bubbly flow, slug flow and annular flow. In this investigation, in order to understand the influence of the flow pattern on CHF, the axial stepwise heating tube along the axial direction is used, which is so called hot patch test. As the experimental results, the obtained CHF was drastically changed with inlet flow pattern, and was evaluated by using a regime-based modeling.

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In this study, the effect of channel gap size for boiling heat transfer of the plate-type evaporator for small thermal energy conversion such as OTEC system was investigated. The heat transfer coefficient of ammonia was measured for three different gap sizes of 1, 2 and 5mm. The result shows that the heat transfer coefficient is increasing with a decreasing in gap size. On the other hand, the present data was compared with conventional correlation by Liu et al. The result of that the correlation indicate underprediction heat transfer coefficient. Therefore, Mortada's correlation which is made for mini-channels was adopted. The correlation for the case of δ=1mm is closer to present data than the former one.

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The thermal-hydraulic analysis of the coolant in the supercritical pressure water cooled reactor (SCWR) , which is an advanced nuclear reactor, is conducted by dividing into a number of subchannels in the fuel assembly. Turbulent mixing is a fluid mixing between subchannels by turbulence, and it affects the velocity and temperature distribution of the coolant in the core, so it is the important parameter required for the analysis. However, the characteristics of the supercritical pressure fluid have not been clarified yet. Therefore, in the present study, we carried out experiments in parallel circular channels with a mixing region, and obtained the basic data on the turbulent mixing of supercritical pressure fluid.

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Supercritical pressure water cooled reactor (SCWR), which is operated at supercritical pressure, is one of the next generation reactors for the purpose of improving economic efficiency and safety. In the SCWR, water pressure passes the critical pressure during startup, shutdown or in case of loss of coolant accident (LOCA). In the near-critical pressure region which the pressure slightly below the critical pressure, critical heat flux (CHF) condition tends to occur at relatively low heat flux and then there is a risk of serious damage of fuel rod due to abrupt rise of surface temperature. In this study, experiments on CHF at near-critical pressure in vertical upward flow inside a tube were conducted to clarify characteristics of CHF at near-critical pressure.

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Spray cooling has been used as a technique of heat treatment of metals in the metallurgical industry. The advent of the Thermo-Mechanical Control Process (TMCP) in the steel industry brings about a need for precise control of cooling rate. In this study, droplets that impact onto hot plate were investigated. A high-speed camera was used to observe the impact behavior of water droplets. The effects of droplet impact velocity and droplet diameter were predicted by the model. Correlating equations of the impact behavior of water droplets were proposed and compared with experimental data.

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Effect of surface wettability on boiling heat transfer was studied by applying radiation induced surface activation. Oxidized metal surfaces were irradiated by ultraviolet light, gamma ray, and proton beam, to investigate the radiation effect on the surface wettability. Proton irradiation experiments were performed at the FFAG accelerator complex of Kyoto University with 100MeV proton energy. Wettability enhancement on the oxidized metal surface was observed in each radiation method, where the radiation conditions were 20 minutes exposure with 5mW/cm^2 for ultraviolet, 97kGy for gamma ray, and 50 hours irradiation with 4.7nA for 100MeV proton beam, respectively. In addition, boiling heat transfer experiment was also performed with and without gamma ray irradiation. Experimental results show that the critical heat flux increases with the gamma-ray irradiated copper surface, however the heat transfer enhancement was not obvious at present experimental conditions.

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Boiling heat transfer from a hydrophilic/hydrophobic combined surface is studied to examine effects of the size of PTFE (hydrophobic) circle dots on subcool boiling. In comparison with among different degree of subcooling, the degree of subcooling become smaller , the heat transfer enhanced and bubble nucleation starts earlier. Under the subcooled condition, as the size of PTFE dots become smaller, the heat transfer improved more after bubble nucleation starts. And, the domain of PTFE acts as nucleation sites. The bubbles stay on the dots area of PTFE coating without departing and the bubbles keep the hemispherical shape with oscillating up and down.

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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 copper surface and some mirror-finished copper surfaces with very thin metal films by using spattering. The copper surfaces with the thin metal films were created by the MEMS technology. The film-condensation and also the drop-wise condensation were observed on the copper surface. The film-wise condensation heat transfer coefficient was higher values than the Nusselt's equation. It was approximately of the drop-wise condensation heat flux. The condensation on the mirror-finished copper surface was the drop-wise condensation. The heat flux was approximately the drop-wise condensation heat flux on the copper surface. The condensation on copper surfaces with thin Copper(Cu), Chromium(Cr) and Lead(Pb) films were drop-wise condensation. The condensation on copper surfaces with thin Titanium(Ti) film was film-wise condensation.

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At present, a microchannel heat exchanger is requested to achieve miniaturization and high efficiency in a small size energy equipment. In order to clarify the heat transfer mechanism in a microchannel heat exchanger, knowledge on thermal hydraulic characteristics in a microchannel is essential. The objective of the present study is to clarify the thermal hydraulic characteristics of phase change flow in a capillary tube through the observation of phase change behavior. From observation results, it is confirmed that the flow pattern is transformed from bubbly flow to annular flow through injection flow in a single capillary glass tube as simulated unit microtube

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In this study, numerical analysis using VOF(Volume of Fluid) method on gas-liquid two phase flow accompanied with phase change has been conducted. The thermal-recovery method is used for estimating mass transfer by phase change. Film boiling problem and Nusselt's film theory was selected and calculated as verification problem. As a result, it is found that the numerical results are good agreement with theory or empirical equation in terms of film growth rate or heat transfer coefficient. Finally, the developed method is applied to the condensation heat transfer between cooled tube and saturated vapor.

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In order to realize high heat flux cooling by evaporative heat transfer in a microchannel, the bubble dynamics and heat transfer was evaluated by numerical simulation. In this study, a simulation program is developed which combined SIMPLE (Semi-Implicit method for pressure linked equation) method and VOF (Volume of fluid) technique. The bubble shape was calculated and compared with experimental results for validation. Simplified phase-change model was introduced and heat transfer process was also simulated. The film thickness and heat flux on wall boundary was evaluated and as a result, film evaporation in a 200μm microchannel may remove heat flux up to 0.6MW/m^2 according to the simulation.

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Flow boiling and evaporation heat transfer in mini-channels was examined by using water. The cross-sections tested were in a range of 0.163 mm x 3mm-1.25 mm x 3 mm. The length of the flow channel was 260 mm. When the flow channel gap became smaller than 0.273 mm, the single-phase flow pressure drop coefficient maintained the characteristics of laminar flow in the turbulent flow region. The single-phase flow heat transfer coefficient was smaller than the value predicted with the correlation for the usual size and the trend itself was also different in the turbulent flow region. In forced flow boiling and evaporation, the evaporation was dominant. The flow channel was filled with a large-long bubble. The critical heat flux condition was triggered by the formation of dry areas in the film under the large-long bubble. When the channel gap became smaller than 0.327 mm, the evaporation heat transfer coefficient became smaller than the value predicted with the usual correlation. The provable reason was the use of the usual turbulent flow heat transfer correlation to correlate the results. The effect of narrowing the channel gap on the thermal-hydraulics seemed to appear as the channel gap became smaller than 0.35 mm.

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The major reason for the lack of data in the multiphase flow lies in the difficulties in measuring the flow quantities of the multiple phases simultaneously. The difference in the refractive indices makes the visualization almost impossible. Presently, the simultaneous visualization has been carried out about the both phases of the liquid-liquid two-phase flow by adjusting the refractive indices of both phases. The PIV measurement has been carried out for a falling water droplet near the wall in the stationary oil. The pressure field around the droplet has been calculated using PIV data under the assumption of 2-D now.

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This study deals with flow behavior and associated heat transfer in a pulsating duct flow. Among the several parameters that govern the transport phenomena of pulsating flow, the effects of pulsating frequency and amplitude on flow instabilities in the rectangular duct is mainly discussed in this paper. Mechanisms of the interaction between these two kinds of governing parameter's effects on flow behavior are not cleared yet. Hydrogen bubble method was employed for the qualitative understanding of the flow structure with periodical velocity fluctuation. Results showed that heat transfer enhancement in the central and downstream region was attributed to the restraint of the boundary-layer development induced by the periodical temporal velocity fluctuation not to the large-scale fluid mixing such as turbulence developed from small-scale flow instabilities occurred in the upstream region.

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The internal blood flow of an aneurysm changes temporally and spatially according to the heartbeat and has a complex form; accordingly, time series volumetric velocity measurements are required. In the present study, we have developed a shadow imaged streak PTV system which enables time series volumetric velocity measurement with only two cameras. Applying this system to two types of aneurysm models in a cube measurement area, we have obtained three dimensional velocity streak results. The measuring volume size was 7.0 mm × 6.9 mm × 6.8 mm and velocity fluctuation was from 0.5 mm/s to 20.0 mm/s. Moreover, this system could accurately measure the small and large eddy changing spatially and temporally. From these results, it is concluded that the shadow imaged streak stereo PTV is applicable to milli-scale flows like an aneurysm.

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Turbulence structures in a natural-convection boundary layer in air above an isothermally heated round plate is experimentally investigated by using two-dimensional velocity vector measurements with PIV, the accuracy of which is verified through the comparison with a hot-wire measurement. Special attention is paid to the developing process of the boundary layer with flow convergence along a heated surface. The development of boundary layer causes the velocity gradients in the horizontal direction, and increases in upward velocity and the velocity fluctuations in the vicinity of the surface. This leads to the multi-layer structures of the boundary layer: the turbulence structures in the lower layer significantly differ from those in the upper layer; in the upper layer, thermal plume becomes dominant.

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An experimental study was made on the promotion of turbulent mixing of hot and cold airflows in a T-junction that simulated an HVAC unit for automobile A/C system. Delta wings were used as a mixing promoter, and the influence of its angle of attack on the thermal mixing and flow field were examined. In particular, production terms of the fluctuating velocity component in the vertical direction, which dominates the turbulent thermal mixing of two flows, were evaluated, and the influence of the angle of attack of wings on the turbulence promotion was examined in detail.

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In the separated and reattachment flow, unsteady heat transfer, which is relative to the flow behavior, is observed near the reattachment point. To clarify the thermal fluctuation, it is necessary to measure simultaneously thermal and flow fields using measurement techniques of the high sensitive and fast response. The aim of this paper is to construct the simultaneous measurement system, which is able to measure unsteady heat transfer and flow behavior using PIV and high-speed infrared thermograph, and to discuss the corresponding to fluctuations of thermal and flow behavior in the separated and reattachment flow over the backward facing step.

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In order to acquire the basic data for the thermal conjugation problems between fluid and solid, we are planning to measure spatio-temporal heat transfer from a solid wall to a liquid flow using a high-speed infrared thermograph. The purpose of this work is to verify the feasibility of this measurement to a turbulent water flow in a circular tube. The test surface was fabricated from a 22μm thick titanium foil coated with black paint. As a result, the time-averaged heat transfer coefficient measured here agreed well to the conventional empirical correlation. Also, statistic values of the time-spatial distribution, such as the rms value of the fluctuating heat transfer coefficient and the mean spanwise wavelength of the thermal streaks were reasonably agreed to those reported in previously published literature.

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In this study, turbulent heat transfer in thermally-stratified turbulent boundary layers over a 2-dimensional hill (2DH) is investigated by means of direct numerical simulation (DNS). Since 2DH often yields a flow separation and reattachment and has the effect of curvature wall, both velocity and thermal fields are affected by these, and thermal stratification also influences these fields, where the thermal stratifications are set to stable, neutral and unstable conditions in the DNS. The results of DNS show the effects of the wall shape and the thermal stratifications to the turbulent boundary layer, and indicate the fundamental and detailed characteristics and structures of turbulent heat transfer in various thermally-stratified turbulent boundary layers over a 2DH.

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Exhaust gas temperature is an important factor in NO_x, THC and PM emissions of engines. Especially 2D temperature and concentration distribution plays an important role for the engine efficiency. A thermocouple is intrinsically a point temperature measurement method and noncontact 2D temperature distribution cannot be attained by thermocouples. In this study, the experimental research has been conducted in order to develop the noncontact and fast response 2D temperature and concentration distribution measurement method. The method is based on a computed tomography(CT) method using absorption spectra of water vapor at 1388nm. It has been demonstrated that the method has been successfully applied to engine exhausts to measure 2D temperature distributions using the 12-path measurement cell.

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2D temperature and concentration distribution plays an important role for the various types of combustor efficiency. A thermocouple is intrinsically a point temperature measurement method and noncontact 2D temperature distribution cannot be attained by thermocouples. Recently, as a measurement technique with high sensitivity and high response, laser diagnostics has been developed and applied to the actual combustion fields. In this study, the theoretical research has been conducted in order to develop the noncontact and fast response 2D temperature and concentration distribution measurement method. The method is based on a computed tomography(CT) method using absorption spectra of water vapor at 1388nm. It has been shown that the interpolation method along the laser path has been successfully applied to improve the special resolution and accuracy of 2D temperature distribution measurements.

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Laser interferometry system was developed to measure unsteady gas temperature. A 16-element photo-diode array was used as the system to detect moving direction of interference fringe more sensitively. Laser interferometry has advantage of nonintrusiveness and high-response. These advantages can improve weak point of general method such as thermistor and thermocouple. In this study, unsteady air temperature was measured by using developed system. Compared with K-type thermocouple of which wire diameter is 0.014mm, this system showed a good response. Because of high response, this system is expected to measure unsteady gas temperature in industrial field.

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In temperature measurement of fluid flows, heat conduction along the temperature-sensor body and/or its supports may cause large measurement errors. In the present study, a new theoretical analysis scheme for the heat-conduction error has been proposed to obtain accurate measurements in fluctuating temperature fields with mean-temperature gradients. The validity of the scheme has been verified experimentally to appraise the reliability and applicability of the present physical model for analyzing the heat-conduction error. The results show that the proposed scheme provides a useful guideline for selecting appropriate temperature sensors and enables us to evaluate accurately the heat-conduction errors in mean and r.m.s. temperature measurements.

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Cooling at trailing edge of gas turbine airfoil is one of the most difficult problems because of its thin shape: high thermal load from both surfaces, hard-to-cool geometry of narrow passages, and at the same time demand for structural strength. In this study, heat transfer experiments by using transient technique were performed for cutback surfaces with three types of dimples (spherical, teardrop, and 45deg angled teardrop). The present results clearly showed the precise distribution of local film cooling effectiveness and Nusselt number. Although overall film cooling effectiveness was almost same among three dimpled surfaces, overall Nusselt number of teardrop and 45deg angled teardrop cases were larger than those of spherical dimple. As a result, film cooling performance of teardrop case was the highest of all.

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This paper describes an experimental study on film cooling effectiveness of a circular and a fan-shaped film cooling holes with a swirling film coolant injected through the endwall of a high-loaded 1st nozzle. The film cooling effectiveness on the endwall of the enlarged 1st nozzle of E^3 turbine was measured by using PSP techniques. It appeared from the experimental results that the film cooling effectiveness of a circular hole was improved by increasing the angle θ of two impingement jets inside the cavity, which is used both to cool internal wall and to produce a swirling motion of film coolant. On the other hand, it was found that there exists an optimal jet angle between θ=5 to 10 degrees in the case of a fan shaped film cooling hole. Thus the new film cooling method with swirling cooling air has been demonstrated to maintain its high from cooling effectiveness even under such a complicated flow field.

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The guarded hot plate (GHP) method is the most popular way of measuring thermal conductivity of thermal insulations. However, there are large differences among the thermal conductivities measured by different GHP apparatuses in the temperature range above 100℃. In the previous study, the estimation method for thermal conductivity was proposed by making use of heat losses from side surfaces of the specimen. However, the evaluation of measurement error for this method was not shown satisfactorily. In this study, the measurement error was evaluated by dividing the specimen into extremely thin boards. It was assumed that the heat, which was flowing into the thin board, separated into two heats in the directions of thickness and plane of the thin board. It was derived that the main causes for the error of this method were the following three assumptions. Namely, the temperature gradients were uniform in the direction of thickness of specimen, and the heat conductances and temperature gradients were constant in the plane direction of any thin boards in the specimen. Furthermore, these causes of the error were evaluated experimentally.

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Polymer Electrolyte Fuel Cell (PEFC) is a very promising power source for automotive use. For the commercialization of fuel cell vehicles, cost reduction and improvement of power density are very important issues. It is well known that the oxygen transport incathode often limits the performance. Possibility has been shown from our previous investigation thatthe equivalent weight (EW) of ionomermay affect the oxygen transportresistance (OTR) in the catalyst layer (CL). The mechanism, however, has not been thoroughly studied. In this report we investigated theeffect, by using thein-situ measurement technique, and numerically analyzed the phenomena with a simple transportmodel in the CL.

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Microprobe measurement technique has been demonstrated to measure the diffusion constant of gaseous species in the electrolyte membrane of PEFCs (polymer electrolyte fuel cells.) Thin platinum wires are inserted between the electrolyte membranes to measure the diffusion-limited current density to obtain the value of diffusion coefficient of either hydrogen or oxygen. The results show Arthenius type of temperature dependence of the diffusion coefficient for both species. Increasing relative humidity of the supplied gas increases the diffusion coefficients, and the ratio of the hydrogen to oxygen diffusion coefficient decreases understanding the mechanism of the gas transport in the membrane.

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To reduce PEFC accessories, especially for water management, that account for 50% of FC system cost, it is effective to simplify the accessories with understanding water behavior in cell. In this study, we developed a new method of measuring temperature in cell with the array of thin thermocouples (φ 50 μm) to comprehend the water behavior based on the correlation between the water behavior and temperature. We fabricated an in-line thin thermocouple, which is adequate to this measurement. Here, butt-welding of the thin thermocouples was executed with a capillary tube in inner diameter φ 60 μm, whose ends were opened widely. In addition, polyimide coated the thermocouples with careful speed control of dipping. Though the butt-welding and coating of 2 μm thickness were done, the strenghts of butt-welding and electric insulation have not been enough to measure the temperature in cell.

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To alleviate membrane dryout in PEFCs under low-humidity operation, it is essential to understand and control water crossover through electrolyte membrane. This paper presented a novel method for quantitatively measuring the water vapor distribution in the gas channel of a low-humidity PEFC using humidity test paper (HTP), and investigated the effects of stoichiometry and gas humidification on the water transport in the anode. Furthermore, the flow distributions of hydrogen and water vapor on the anode side were estimated based on current distribution measurement, and the local water transport coefficient through the membrane was numerically predicted. It was found that the low stoichimetric cathode flow enhances the back-diffusion of product water across the membrane, and suppresses the membrane dehydration.

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In order to alleviate liquid water flooding in polymer electrolyte fuel cells (PEFCs), it is essential to design the optimum electrode structure on cathode side. In this study, the liquid water behavior in the cathode flow field of an operating PEFC was directly visualized using a high-resolution digital CCD camera, and the effect of perforation structure of cathode gas diffusion layer (GDL) on the liquid water transport and cell performance was investigated. The perforation holes were cut in the porous GDL by electric discharge machining or micro-driling technique. It was noted that the hydrophobic perforation holes machined by the micro-driling technique are effective in removing liquid water in the cathode GDL.

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We performed in situ through-plane visualization of liquid water distribution in a polymer electrolyte fuel cell operating at 30℃, 50℃, and 70℃ by using high-resolution soft X-ray radiography. Less liquid water accumulation in the membrane electrode assembly was observed in the elevated operating temperature. These observations indicated that water generated in the electrode is mainly transported as vapor phase at higher temperature conditions. It was also confirmed that liquid water accumulation was less significant in the micro porous layer than those in the gas diffusion layer.

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To optimize shape of reformer in case of the effect of heat conduction of catalyst on characteristics of methanol steam reforning (STR) using Cu-based catalyst is discussed numerically. The cylindrical tube reformer is considered amount of catalyst, mass flow rate, wall temperature were kept. The results are arranged by packing ratio and aspect ratio that means the thickness of catalyst bed while focusing temperature profile in the reformer and reformed gas component nearby output. As a result, if the catalyst bed is heated constantly, the packing ratio does not affect the reforming. When the aspect ratio is increased, H_2 moler fraction in reformed gas decreases while methanol moler fraction increases. Larger Aspect ratio causes lesser reactivity by increasing low temperature around the center of catalyst bed and increasing amount of non-reactant that does not touch the catalyst.

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Steam methane reforming is one of the most popular methods for fuel hydrogen production. Although the commercial steam reforming usually operates under high pressure conditions, experiments for research are mainly under atmospheric. In this study, we evaluated the pressure effect of surface steam reforming reaction by experiments operated with an annular (concentric double circular) channel tube reactor. This flow channel can avoid the effects of side walls in contrast with the experiment with different pressure, the rate equation was evaluated. Finally, the obtained reaction rate was applied for numerical simulation to confirm the validation.

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