Flows around a circular cylinder in oscillatory flow were studied by a numerical simulation using a finite-volume method. The computations were carried out by assuming 3-dimensional (3-d), unsteady, incompressible and viscous flow through Keulegan-Carpenter number (KC) in the range 3≤KC≤25 at Stokes number (β) of 95. The predictions obtained by 3-d computations were compared with experimental results by using a U-tube water tank. As a result, typical flow-patterns induced by oscillatory flow, for example, "longitudinal vortices" at KC=3∼4, "transverse-vortex street" around KC=12, "double-pair pattern" around KC=16 and "wake vortex street" at KC≥20 were able to be successfully reproduced. The computed flow-patterns were in good agreement with experimental results. The collapse of 3-d vortical cell-structure at KC=5 causes a temporal change of the direction of vortex-shedding. Furthermore, it is found that the flow-patterns of transverse-vortex street, double-pair and wake vortex street have the 3-d vortical structures which changes complicatedly in the span-direction.

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This paper describes the generation and growth of isolated turbulent puff, which is produced by a ring-shaped roughness element at the entrance region of a pipe flow. Flow visualization and LDV measurement were carried out using a straight glass tube of diameter D=5.02 mm and total length L=2712 mm. The roughness elements were installed at a downstream location of 77D from the entrance of the tube. The feature of the origin of turbulence, which is due to the separated flow on the leading edge of the roughness element, was photographed. It was found that, even if the intense turbulence is produced by the roughness element at a Reynolds number of 2100, the puff generates at a far downstream location at which the relaminarization of flow has considerably proceeded. It was also found that the equilibrium puff is achieved at a downstream distance of about 100D from the origin of the puff.

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There are many numerical methods in the computational fluid dynamics. In these methods, FEM (Finite Element Method) is easy to handle the complicated boundary, and it is suited to the analysis of the practical problems. In general, bilinear element is used in FEM and the discretization by this method corresponds to the 2nd-order central difference. Therefore, we can't obtain adequate accuracy in the case of the analysis which the effect of the non-linearity remarkably appears in. In the previous works, we analyzed the natural convection in a cubic cavity at 10³≤Ra≤10⁸ using CIP (Cubic Interpolated Pseudo-particle)-FEM. We showed the effectiveness of CIP-FEM through the work. It is difficult to analyze this flow at higher Rayleigh numbers Ra≥10⁹ because numerical divergences and vibrations occur in the energy equation and quantity of the calculation becomes enormous. In this paper, we analyze the flow at Ra=10⁹ using CIP-FEM, and verify the validity of the results basing on the previous work.

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There are some formulations of the convection term in the Navier-Stokes equation, for example gradient form, divergence form, skew-symmetric form and rotational form. These formulations aren't equal to each other in our calculations because the continuity equation isn't completely satisfied. As a result, the numerical results by each formulation are different. In the present paper, we discuss the numerical accuracy of the different formulation of the convection term discretized by finite element method. The numerical models are the rid-driven flows in a square and a cubic cavity and the turbulent channel flow using Large Eddy Simulation. Turbulent model is the Smagorinsky model. Their results show that the divergence form is better one in terms of the numerical accuracy and the conservative property.

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Recently, High-porosity porous media with many small porous is used for chemical reactor and combustion reactor. Since high-porosity porous media is complex geometry, it is expected that the high-porosity porous medeia has high mixing and high reaction rates. In the future, it will be applied to various engineering device. For the practical use of the high-porosity porous media, it is necessary to investigate flow characteristics through the porous media. However, it is difficult to experimentally investigate flow characteristics. In the present study, three-dimensional immiscible lattice gas model (3-D ILG model) is used to simulate the formation of high-porosity porous media. By using the simulated porous media, flow through porous media is analytically investigated with three-dimensional fifteen-velocity lattice gas cellular automata (3-D 15-V model LGA). As the results, it is confirmed that the present technique is applicable to simulate formation of porous media and to simulate the flow through porous media.

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The PCC (Partial Cells in Cartesian coordinate) method CFD code featured with less pre-processing time was used in this study to calculate the flow field around a rectangular cube. The turbulence model was consisted using a low Reynolds number κ-ε model and log law. To test the case of existence of many partial cells, the rectangular cube was set with 10 degrees of offset angle to the flow direction, and calculation mesh does not correspond to the cube surface. The mean flow velocity and turbulence intensity were set to 4.0 m/s and 1.5%, respectively in both experiment and calculation. The experiments were carried out by using two-dimensional laser Doppler anemometry (LDA) and particle image velocimetry (PIV). The numerical results were compared with the experimental results. Both results show good agreement between calculation and experiment in the mean velocity, turbulence intensity and Reynolds stress.

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The experimental study has been carried out to investigate the self-excited shock wave oscillation in a transonic wind tunnel using a circular arc airfoil (chord length of 120 mm, thickness of 15%). Shock wave position of each side and wake position were simultaneously measured by using two line scan cameras (line scan frequency of 32 kHz). Shock wave and wake fluctuations are analyzed by the wavelet transform with Gabor wavelet. The results show that the phase difference between shock wave fluctuations of each side are almost 180 degrees, and the phase difference between shock wave and wake fluctuations was fixed in spite of the change of the frequency.

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Rarefied supersonic free jets through an orifice are investigated by the DSMC method over a wide range of pressure ratio (ρ₀/ρ₁=15∼16000 for 1/Kn=500 and 2500, and ρ₀/ρ₁=∞ for 1/Kn =10∼2500). As the pressure ratio increases, the Mach disk and the barrel shock become thick and weak, then the background gas invades deeply into the jet cell. The density starts to deviate from the isentropic expansion far upstream from the expected location of the Mach disk. The parallel temperature also starts to deviate further upstream from the perpendicular temperature and does not reach the lowest value predicted by the sudden freezing model. The DSMC calculations are compared with the experimental results and the existing analytical result.

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A new method named full way coupling of large eddy simulation for particle-laden turbulent flows using two modified dynamic subgrid scale (SGS) models and considering particles collision based on a Eulerian-Lagrangian approach was presented. In order to simulate the interactions of SGS components, two new SGS models were introduced by report 1 and 2 previously : Dynamic random walk SGS model was used to calculate the particles diffusion by fluid SGS component, and the fluid turbulence modification of particle SGS component has been investigated using a proposed dynamic two way coupling SGS model. The advantage of these new SGS coupling models is that the dimensional analysis coefficient of proposed SGS model could be optimized by Germano's (1991) dynamic procedure. The effects of interparticle collision on particles motion were taken into accounts using direct numerical simulation. Using this full way coupling method, the numerical simulations were performed for downward channel flow at Reynolds numbers of 644 that was identical to the experiments done by Kulick et al. in 1994. The capability and limitation of the full way coupling LES method in predicting particles diffusion and fluid turbulence modification for particle-laden turbulent flows were investigated.

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Non-linear κ-ε models have been extensively used in engineering applications. The existing non-linear models, however, can not satisfy the wall limiting behaviour of Reynolds stress component, μ²₂^^^-, in the wall-normal direction, which is proportional to χ⁴₂ near the wall. Since the wall limiting behaviour of Reynolds stress diagonal components in the non-linear model is determined by the turbulence energy κ, which is the highest order term in the model, the Reynolds stress components, μ²₁^^^-, μ²₂^^^- and μ²₃^^^- are proportional to χ²₂. In this study, we propose a new non-linear κ-ε model which satisfies exactly the wall limiting behaviour of Reynolds stress components. The proposed model can also predict well the anisotropy in the normal stress components near the wall.

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2-D unsteady cavitating flows around hydrofoils are numerically calculated, and the performance characteristics of hydrofoils in cascade are investigated under several cavitating flow conditions. A locally homogeneous model of compressible gas-liquid two-phase media is applied to simulate above cavitating flows using TVD-MacCormack's numerical method. The present method permits us to treat the whole cavitating and noncavitating unsteady flows field and fluid transients without any remeshing procedures, though it gives somewhat diffusive cavity surface compared with two fluids cavity flow model. Some calculated results are obtained, and discussed on the validity of the present method and its applicability to wide range of cavitating cascade flows.

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This paper treats transient low Reynolds number flows around (1) an impulsively started rotating circular cylinder and (2) an impulsively started and rotated circular cylinder. The main purpose of this paper is to discuss the difference between the two initial cases for large enough time and to know the asymptotic behavior of the transient flow to the steady flow as time to infinity. In the two-dimensional flow, the transient flow is determined uniquely by the initial condition, however, there are several initial flows, which are considered to approach the same steady flow as time to infinity. Thus, it is an interesting problem to know the asymptotic behaviors of the above mentioned two initial cases as time to infinity. The present paper shows that the convergence to the steady flow in the case (2) is, at most, of order of T^-3/2 where T is the stretched time.

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In this paper we describe the flow associated with two-dimensional surface-mounted rectangular cavities. The experiment was carried out in two types wind tunnel and water channel. A significant aspect of the study has been an examination of the effects of changing the ratio of width/depth in the sectional geometries of two-dimensional cavities from 1 to ∞ to be backward facing step. The time mean surface pressure distributions, mean velocity, fluctuating velocities, and Reynolds stresses inside cavities were measured as the ratio of width/depth was varied. The flow pattern inside cavities was observed by flow-visualization. Consequently it was found that (i) the transition from the open cavities to the closed cavities occurs at W/D=8.8∼9 in wind tunnel experiment, (ii) this is reflected in the mixing phenomenon associated with an increase in cavity drag, and (iii) the similarity is established in the velocity profiles of the shear layer around the cavity flow and the reverse flow in the recirculation region.

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The response of fully developed turbulent pipe flow, in which air was at a Reynolds number of 6.2×10⁴, to a pulsewise disturbance due to an attached ring-type manipulator with a rectangular cross section, was investigated by the measurement of triple velocity correlations. The results show that the tendency of the profiles of each triple velocity correlation can explain the reason for the changes in the turbulent flow field ; this is indicated by the differences in the response to turbulent diffusion between the turbulent flnw cnmponents. Subsequently, the production term and the diffusion term of both the turbulent kinetic energy transport equation and the Reynolds shear stress transport equation near the reattached point were evaluated and compared with those of other disturbance flows. The reasons, because the present flow's separated shear layer was determined by the intermediate characteristics (between the upstanding and downward disturbance), could be illustrated by the aforesaid results. Furthermore, streamwise change of the typical value and the typical positions, which were concerned with turbulent kinetic energy diffusion towards the pipe center, were examined to clarify characteristics of the separated shear layer behind the manipulator ring in the present flow.

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The effects of the different thermal wall boundary conditions on the mean velocity and temperature profiles in the compressible turbulent channel flows are investigated. Dimensional analysis says that the mean velocity and temperature profiles depend on the non-dimensional heat flux B_q and the friction Mach number M_τ, when the Prandtl number and the ratio of specific heats are constants. The effects of B_q and M_τ on the mean velocity and temperature profiles are examined using direct numerical simulation (DNS). Two cases of DNS are carried out. The first case is the compressible turbulent flow between isothermal walls, which is the same as that performed by Coleman et al. The second case is one between adiabatic and isothermal walls. In the DNS, the Mach number based on the bulk velocity and sound speed at the isothermal wall is 1.5 and the Reynolds number based on the bulk density, bulk velocity, channel half-width, and viscosity at the isothermal wall is 3000. The main results are as follows : (1) The mean velocity profile with Van Driest transformation is independent of B_q and M_τ, while the untransformed one increases with an increase of -B_q and decreases with an increase of M_τ. (2) The mean temperature increases with an increase of -B_q and decreases with an increase of M_τ. (3) The similarity law between the mean velocity and temperature is not satisfied when the effect of friction work is large. As a result, logarithmic law of the mean temperature is not obtained.

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The effects of the variable-property on the profiles of the turbulence statistics and the near-wall asymptotic behavior for the compressible turbulent channel flows are investigated using direct numerical simulation (DNS). Two cases of DNS are carried out. The first case is the compressible turbulent flow between isothermal walls, and the second case is one between adiabatic and isothermal walls. In the DNS, the Mach number based on the bulk velocity and sound speed at the isothermal wall is 1.5 and the Reynolds number based on the bulk density, bulk velocity, channel half-width, and viscosity at the isothermal wall is 3000. The main results are as follows : (1) When the velocity fluctuations, kinetic energy, and turbulent dissipation profiles are scaled by the wall variables, these profiles are larger near the isothermal wall and smaller near the adiabatic wall, comparing with those of the incompressible turbulent channel flow. On the other hand, these profiles agree well with the data of the incompressible turbulent channel flow, when these profiles are scaled by the local mean variables. It means Morkovin's hypothesis is applicable to these profiles. (2) The rms temperature fluctuation profile scaled by the mean temperature is almost the same as the rms density fluctuation profile scaled by the mean density, except that the rms temperature fluctuation on the isothermal wall is zero. (3) Differences between Favre and Reynolds averages on the Reynolds stresses are negligible in the wall bounded flow. (4) Morkovin's hypothesis is not applicable to the wall asymptotic behavior. (5) The rms temperature fluctuation profile scaled by the wall temperature varies linearly with the wall unit y⁺ near the isothermal wall and approaches a constant non-zero value with the decrease of y⁺ near the adiabatic wall.

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A high-quality precision-controlled turntable apparatus was designed to study the dynamic behavior of viscous fluids contained in a cylindrical container. Vortex breakdown produced by a rotating endwall disk was visualized by using a fluorescent dye technique. This flow problem is governed by a combination of two non-dimensional physical parameters, i.e., the height-to-radius ratio H/R and a rotation Reynolds number ΩR²/ν. Limiting boundaries for first, second and third vortex breakdown bubble in a steady flow were reproduced to compare with the previous visualization studies of Escudier. The domains for the periodic axial oscillation and the precession were represented clearly in an unsteady flow. The experimental results in the steady flow were in excellent agreement with Escudier's results. The location and size of the vortex breakdown bubble were estimated quantitatively in the steady flow. The amplitude and time period of the periodic axial oscillation and the polar angle and time period of the precession in the unsteady flow were also estimated.

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A steady flow in collapsible tube as an in vitro model of the flow in the vein and the airway has been investigated. We think that the interaction between inner flow and largely deformation of collapsible tube cause it various problems. So when solving these problems, we must have simultaneous measurement to know interrelation between deformation of the tube and inner pressure which is influenced by the flow. When measuring the pressure, the sensor must be put in the collapsible tube. Because the sensor disturbs inner flow, it is difficult to know correct information. In this paper, we propose a computational method in which the measured area and shape of the tube cross-section is utilized in order to know undisturbed pressure. When largely deformed with contacting the tube wall and flow separation exists in the tube, it is found that we need to correct the method. As a result, the followings have been shown : The agreement of the experimental result with the computational one enables us to use this method for the prediction of pressure distribution along the tube.

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The present investigation describes a novel measurement technique to determine both velocity and diameter of transparent spherical particles. The system enhances the spatial resolution by compressing the out-of-focused image into linear interferogram while maintaining the information of the fringe spacing that is related to the particle diameter. The velocities of individual particles are obtained by capturing sequential images of interferograms with double-pulsed illumination and CCD camera. The technique was applied to the spray flow and the results of the simultaneous measurement of size and velocity demonstrated the difference of the particle behavior by their diameter.

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In order to evaluate the possibilities for realizing a new printing system, in this study, we have proposed a new numerical analysis method that forms a relationship between an electric field and a flow field that includes a free surface. This analysis method is applied to the flow field of a water-based ink layer that has a free surface, which is greatly deformed by electrostatic force. Fundamental experiment was also conducted to judge the validity of the numerical analysis method. The following conclusions can be drawn from the results of this study. (1) Ink was deformed and transported to the paper by electrostatic force both in the numerical analysis and the experiment. (2) The effects of the initial shape of the free surface on the characteristic of ink transportation can be predicted by the numerical analysis. (3) The effects of viscosity and surface tension of ink on the characteristic of ink transportation can be predicted. (4) These experiments indicated no clear effects of applied voltage on the ink transport time, but the numerical analysis indicated an effect that was considered pertinent. (5) It was clarified that it was possible to control ink transport time by adjusting ink viscosity, surface tension, externally applied voltage and the shape of the initial ink surface. (6) By a creativity of a bias voltage, a shape of projection tip and ink properties, it got obvious that it is possible to reduce a switching voltage.

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The vortex method was applied to the unsteady flow in a diffuser pump with 6 impeller blades and II diffuser vanes at various off-design operating points. The calculated unsteady total pressure rise showed a good agreement with the experimental data and the CFD calculated ones. The numerical results of unsteady flow at a partial discharge range (approximately 83 percent of the rated flow-rate) showed that the asymmetrical separation bubble appears near the pressure surface side of the impeller blade. It was concluded that the intermittence of the separation bubble is one of the main factors to cause the unstable characteristics of the test diffuser pump. The calculated unsteady flow at lower partial discharge range (50 percent of the rated flow-rate) presented the rotating stall in impeller passage as well as in diffuser passage.

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Students in mechanical courses at technical high school learn a hydraulic torque converter in the subjects of "motor" or "automobile engineering". Ordinarily, the hydraulic torque converters are covered with a metalic case and therefore, the impellers and the working fluid in it are invisible. Accordingly, we developed a teaching tool for visually learning the principle of a hydraulic torque converter and investigated its teaching effect by lesson practices. This tool is constructed as follows : two driving and driven impellers are set up in a transparent acryl spherical vessel and it is filled with a distilled water. Therefore, the state of transmissions of driving power by working fluids can be learned visually. As a result of experimental lessons, it was made clear that this teaching tool had the good effects for the students to understand the power transmission mechanism of hydraulic torque converter.

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To separate solid and water in alcoholic waste water, water used instead of the waste water was suctioned and atomized by sonic air jet exhausting from a nozzle with constant cross-sectional inner area. The outer configuration of the nozzle was shaped into conical forms to increase suction performance of water by the jet. As the results, it was clarified that water suction depends on the distance between the nozzle exit and the water surface, exhausting pressure, conical angles and the inner cross-sectional area of the nozzle. Also, the suction of the water is clarified into three regions, successive, intermittent suctions and no suction. Anymore, it was identified that the exhausting pressure with maximum efficiency exists for suction flow rate.

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This paper reports how heat transfer can be augmented by inserting a micelle squeezer at the inlet of the turbulent pipe flow drag-reduced by surfactant additives. The micelle squeezer gives very high shear to the flow and the rod-like micelles formed with surfactant molecules, which remarkably reduce both drag force of the flow and heat transfer, are broken by the high flow shear at the flow inlet. From this, the drag force is recovered in the very limited region below the micelle squeezer, but also heat transfer is recovered in the enough regions required for exchanging heat. This strategy can be applied for heat exchangers, which occupy the small part of district cooling flow system.

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An analytical method has been developed for inverse problem of two-dimensional heat conduction by using Laplace transform technique. The inverse problem is solved only for simple boundary cases ; the first one is one unknown surface condition and the second is two unknown surface condition and the other surfaces are insulated in a finite rectangular body. The method first approximates the temperature changes obtained in a solid with a half polynomial power series of time and the Fourier series of eigen function. The expression for the surface temperature is explicitly obtained in the form of the power series of time and the Fourier series. The results calculated for some representative cases show that the temperature can be predicted at good agreement compared with the given surface condition while the estimate of surface heat flux becomes slightly worse than the surface temperature.

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This paper has dealt with the heat transfer enhancement of flowing water with flow drag reduction additive into a heat transfer tube by inserting wire coils. The non-ion type surfactant was used as the additive to decrease the pipe flow resistance for the heat energy transport system. However, the decrease in the flow resistance was allowed to reduce the heat transfer coefficient in the heat transfer tube. Some kinds of wire coils having different diameters were tried to enhance the heat transfer in the heat transfer tube. The effects of wire coils on the pipe friction and the heat transfer coefficients were elucidated under various experimental parameters of flow velocity, wire coil diameter, pitch and length.

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A new plate-type heat exchanger for a water-refrigerant system such as chillers was developed, and its evaporation performance was exaluated. The main part of this heat exchanger consists of plates packed together in a casing, and winding tubes are connected to both sides of the plates. Refrigerant flows inside of the tubes, and water flows in the space between the plates, where a herringborn-like pattern is formed by the cross sections of the winding tubes. This heat exchanger can transfer an equivalent amount of heat by evaporation compared to commercially used herring-born-type plate heat exchanger. Furthermore, it has a measured pressure drop on the water side that is less than 1/10 of that of other heat exchanger.

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This paper presents discussions on predicting turbulence and heat transfer in square sectioned 180° U-bend ducts whose curvature ratios are Rc/D=0.65 and 3.357. The low-Reynolds-number cubic nonlinear κ-ε and κ-ε-A₂ turbulence models are applied for the flow field computation. In the thermal field computations, the higher order gradient diffusion heat flux model is applied in comparison with the standard models. The results suggest that the cubic nonlinear eddy viscosity and the higher order gradient diffusion heat flux models are very successful for predicting such three dimensional turbulence and heat transfer fields while some more modification in the models may be needed to capture heat transfer in the strongly curved case.

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For severe accident assessment in a light water reactor (LWR), heat transfer models in a narrow annular gap between the overheated core debris and the reactor pressure vessel (RPV) are important to evaluate the integrity of the RPV and emergency procedures. This paper discusses the boiling heat transfer and the average critical heat flux (CHF) restricted by countercurrent flow limiting (CCFL) based on existing data. At the cooling-down process, the heat flux in a narrow gap is similar to the pool boiling curve but the superheat at corresponding heat fluxes is higher than in pool boiling except in the case of film boiling, which can be expressed by the Bromley's pool film boiling correlation. However, experiments should be required to derive a heat flux correlation in the case of nucleate boiling. We derived an average CHF correlation using the Kutateladze-type CCFL correlation, with its empirical constant C_κ as a function of the dimensionless superheat. Average CHF at the cooling-down process was 3-4 times larger than CHF at the heat-up process and the CHF difference was well predicted by different flow patterns in the gap and the momentum balance between gas and liquid phases.

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Thermo-hydraulic instabilities of a boiling natural circulation loop with a chimney under high pressure were investigated using linear stability analysis. Drift-flux model was used for two-phase flow model. The instability regions as well as the thermo-hydraulic characteristics in the chimney such as wavy feature were examined, which were compared with the characteristics in low pressure. Instability could occur when exit quality was relatively low, which was the same manner as the characteristics in low pressure. In high-pressure, void was generated near channel exit, and void wave propagated in the chimney. In low pressure, steam was generated only near the chimney exit due to gravity induced flashing, and single-phase enthalpy wave, that is, temperature wave propagated in single-phase flow region. Though flow could be very stable in the high pressure and high power condition, the decay ratio of higher mode could be larger than that of lower mode.

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Experiments were conducted to study the effects of micro-pin-fins and submicron-scale roughness on the boiling heat transfer from a silicon chip immersed in a pool of degassed and gas-dissolved FC-72. Square pin-fins with fin dimensions of 50×50×60μm³ (width×thickness×height) and submicron-scale roughness (RMS roughness of 25 to 32 nm) were fabricated on the surface of a square silicon chip (10×10×0.5 mm³) by use of microeletronic fabrication techniques. Experiments were conducted at the liquid subcoolings of 0, 3, 25 and 45 K. Both the micro-pin-finned chip and the chip with submicron-scale roughness showed a considerable heat transfer enhancement as compared to a smooth chip in the nucleate boiling region. The chip with submicron-scale roughness showed a higher heat transfer performance than the micro-pin-finned chip in the low-heat-flux region. The micro-pin-finned chip showed a steep increase in the heat flux with increasing wall superheat. This chip showed a higher heat transfer performance than the chip with submicron-scale roughness in the high-heat-flux region. The micro-pin-finned chip with submicron-scale roughness on it showed the highest heat transfer performance in the high-heat-flux region. While the wall superheat at boiling incipience was strongly dependent on the dissolved gas content, it was little affected by the liquid subcooling.

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If a flow obstruction such as a spacer is set in a boiling two-phase flow within an annular channel, the inner tube of which is used as a heater, the temperature on the surface of the heater tube is severely affected by the existence of the spacer. In some case the spacer has a cooling effect, and in the other case it causes the dryout of the cooling liquid film on the heating surface resulting in the burnout of the tube. But the burnout mechanism near the spacer is not still clear. In the present paper we discuss temperature fluctuation characteristics in relation to the change of the flow configuration near the spacer in boiling two-phase flow when burnout occurs.

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Zeolite is one of the functional materials controling air qualities, such as humidity or environmental particles. To predict and control adsorption or diffusion process precisely, it is important to clarify the structural and dynemical properties of adsorbed substances in zeolite on a molecular level. In the present work, powders of zeolite 4 A with various concentrations of water were prepared and x-ray diffraction data were collected. The populations and positions of water in zeolite-A were analyzed using Rietveld method. In addition, the same systems were simulated using molecular dynamics calculation. The both results show that water molecules tend to be near the eight-rings and then spread into α-cages or β-cages as the concentration of water increases. The Na⁺ ions near the eight rings strongly affects the distributions of water.

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The performance of electrochemical cells, such as fuel cells, which use solid polymer membranes as electrolytes, is strongly dependent on the water molecule concentration in the membrane. Hence, it is important to understand the transport mechanism and concentration distribution of water molecules in the solid polymer electrolyte (SPE) membrane. In this study, the concentration distribution of water molecules and its time evolution in the SPE membrane were measured by magnetic resonance imaging with 100μm space and 15s time resolutions. In the experiment in which the moistened membrane was taken to be the initial state. the diffusion coefficient of water molecules in the SPE membrane was entimated to be 0.8× 10^-10 m²/s. In the experiment in which the dried membrane was taken to be the initial state, the fast transport of water molecules, which seems to be caused by the advection effect, was observed, and its equivalent diffusion coefficient was estimated to be 5×10^-10 m²/s.

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The mutual diffusion coefficients of SF₆ into air and its component gases (N₂ and O₂) and those of CFC12 and HCFC22 into N₂ and O₂ have been measured in the temperature range 30∼180°C and at atmospheric pressure by the use of the Taylor dispersion method (The experimental data on the CFC 12-air and HCFC22-air systems have already been given in our 3rd and 4th Reports). For SF₆, CFC12 and HCFC22, the mutual diffusion coefficients do not vary in practice on substituting pure N₂ or O₂ for air.

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In this article, application of magnetic resonance (MR) imaging to pressurized gas is described. A specially-designed non-magnetic test vessel offers cylindrical sample chamber with 12mm i.d. and 114 mm in length, in which methane gas was supplied up to 10.0 MPa in order to investigate its feasibility of gas MR imaging. Experiments with glass beads were also conducted and it is shown that MR imaging technique successfully produces methane images with glass beads owing to high proton density at pressurized fields. Futhermore, hydrogen gas was used instead of methane in an effort to examine influence of gaseous properties on gas MR imaging. It is shown that signal intensity on MR images of hydrogen was much less than that of methane due to high diffusivity of hydrogen molecules, which was also confirmed by numerical calculation.

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The paper presents a method to reduce the energy consumption rates in civil utility, focusing on the new idea of bathing. The fundamental idea is based on the soft-flexible porous materials, such as the toweling clothes, through which the falling hot water flows from the top to the bottom, as the Darcy flow and heats the human body. The analytical results are illustrated to show the transient heat transfer characteristics to warm up the body and to maintain pseudo-steady state for a certain period of time. The overall energy saving rates for the present conditions have been demonstrated to be very high compared with the energy consumption rates of existing bathing scheme.

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The objective of this work is to provide information about the details of the gas phase reaction on solids material ignition. An experiment of radiative ignition has been performed in microgravity to determine the events occurring in ignition processes in a quiescent field. Filter papers were irradiated by Diode laser (800.1 nm), which is little absorbed in gas phase, in various oxygen concentrations (0-50%). Using this laser makes it possible to observe the radiative ignition without the effect of gas phase absorption. The ignition delay was measured for various experimental conditions. The density change of gas phase before ignition were observed by a Mach-Zehnder interferometer. The results showed that heat conduction from the sample surface induced weak chemical reaction in the vicinity of the sample surface, which propagated outward to reach strong combustion. Ignition delay time decreased with increase in O₂ concentration because mixture near the sample surface might contain more oxygen with higher oxygen atmosphere to cause immediate transition from the weak chemical reaction to the strong combustion.

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The present investigation describes an application of a novel measurement technique for determining both velocity vector field and spatial distribution of the particle size. The technique enables us to get a high-resolution spatial information of the particle characteristics by compressing the out-of-focused image into linear interferogram so as to maintain the information of the fringe spacing which is related to the particle diameter. The velocity of individual particles are obtained by capturing sequential images of interferogram with double pulsed laser illumination. The system consists of a high resolution CCD camera, large amount of data storage, high power pulsed laser source, high speed computer which are basically the same equipment as PIV system but with a fully automated image processing software. The technique was applied to the transient spray flow and the results of the simultaneous measurement of size and velocity fields demonstrated on the difference of the particle behavior by their individual diameter.

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Temperature and concentration measurement of water vapor based on infrared absorption spectroscopy was conducted by a diode laser of 1392.1 nm. The measured water vapor absorption spectra agreed better with the calculated absorption spectra based on Toth's database than those based on HITRAN 96 in the wavelengths of this study. Relation between temperature and intensity ratio measured by the proposed pair of absorption spectra agreed well with those calculated by the Toth's database. The water vapor concentration measured by the absorption spectroscopy using the Toth's database agreed with those measured by a probe hydrometer.

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A series of our counter-flow premixed spary flame experiments were reviewed, ranging from flames dominated by a rather intense turbulence to sufficiently laminar ones. It was found that highly turbulent flames were dominated by a number of large-scaled droplet clusters burning in the droplet group combustion mode, whereas sufficiently laminar flames hardly showed the group combustion characteristics. Then the detailed structure of a laminar spray flame was observed in two-dimensional counter-flow configuration, where a spray flame having a flame front stable enough except of dynamic irregularities of 1 mm or so peculiar to two-phase flames. The velocity was determined for various sizes of droplets across the flame front by phase-Doppler anemometry (PDA), and the laminar burning velocity was estimated, from the minimum value in velocity of minute droplets around the flame front, to be ca. 0.34 m/s. The Lagrangian histories of evaporating or burning droplets were tracked by the particle-tracking velocimetry (PTV) across the flame front.

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The velocity and size of coal particles in a laboratory-scale pulverized coal combustion flame were simultaneously measured by Shadow Doppler Velocimetry (SDV) which has the advantage over other Laser-based sizing methods for arbitrary shaped particles. The Laser Doppler Velocimetry (LDV) was also used to measure the airflow velocity and particle velocity. The results show that mean velocity of large particles is larger than mean airflow velocity due to the inertia force of particles in the case of noncombustion condition. The particle rms velocity in the combustion condition is smaller than that in the noncombustion condition. The particle size in the combustion condition gradually increases with an increase of the distance from the burner. The circurarity of the particles in the combustion condition is slightly lower than that of particles in the noncombustion condition. The mean velocity and rms particle velocity don't change with the particle size in the case of combustion condition.

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Premixed flames in highly turbulent flow have been investigated by a cyclone-jet combustor. The velocity field has been measured using LDV (laser-doppler velocimeter) to analyze the experimental conditions on the combustion diagram. Especially, the requirement for determination of turbulence scale has been examined. In conventional data-sampling, the interpolated velocity data does include errors so that the auto-correlation coefficient is higher, resulting in the larger integral time scale of turbulence. Slot-Correlation method is useful to examine the velocity fluctuation based on randomly sampled data by LDV. For determining integral time scale, the data number of the order of 10⁵ is needed within 10% error. The flow field is changed by combustion and the turbulence is reduced, with the turbulence scale smaller. On the combustion diagram, the condition of U_m<15 m/s belongs to the flamelet regime, and that of U_m>20 m/s belongs to the distributed reaction zone regime.

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The relation between blowoff characteristics of the edge flame in a methane-air diffusion flame and its flame structure has been investigated by using our original burner. The burner can form an edge flame without premixed flame, as a hole, in the stagnation region of an axisymmetric impinging jet. Varying the hole diameter, blowoff limits and maximum flame temperature were measured for an edge flame's blowoff character, and also, for an edge flame's structure, temperature profile and flame location were measured and a thermal boundary layer around the edge flame was visualized with laser tomographic technique. It is found that all the edge flames in the stagnation flow have a critical stagnation velocity gradient, beyond which the flame can never be existed. The critical stagnation velocity gradient that represents the overall reaction rate in the edge flame zone decreases as the hole diameter is increased. The increase in a hole diameter leads to change of the edge flame's structure and to addition of two heat loss factors to the edge flame. One heat loss factor is the edge flame-wall interaction, which occurs due to decrease in the edge flame's location. Another is penetration of cold flow into a hole in the flame, which occurs due to decrease in the overlapping range of thermal boundary layer of the edge flame in the hole. These additional heat losses occur at lower stagnation velocity gradient and have stronger influence on the edge flame as a hole diameter becomes larger. Consequently the overall reaction rate in the edge flame zone is reduced by the increase in a hole diameter. Finally it is clarified that the edge flame shows qualitatively same extinction as a pure diffusion flame, when the flame zone of the edge flame lies spatially as the boundary that divides between oxidizer side and fuel side in spite of existence of a partially premixture of fuel and oxidizer ahead of the reaction zone in the edge flame region.

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A theoretical approach was carried out for thermal gravimetric analysis (TG) and differential thermal analysis (DTA) of Asphalt/Water (As/W) emulsified fuels. It was observed in the experiments of Ref. (1) for the single droplet combustion of As/W emulsified fuels that some fuels had puffing phenomena and the others had various intensity of microexplosion phenomena. The phenomena may be caused by an internal pressure rise in the combustion process. In this paper, the experiments of thermal analysis (TG/DTA) were carried out for making clear the phenomena and an attempt was tried to predict both heating process and occurrence of the microexplosion of the fuels in terms of the pressure rise. The prediction gave a good agreement with the experimental results, and made clear theoretically the mechanism of the microexplosion.

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Small distributed generation systems are currently attracting much attention because of their high energy utilization efficiency. Among them, a hybrid system based on micro gas turbine (μGT) and solid oxide fuel cell (SOFC) is expected to achieve a much higher efficiency than traditional μGT. In this paper, we investigate the effects of cycle design parameters on the performance and feasibility of a μGT-SOFC hybrid system for small apartments and businesses. As a result, a general design strategy is found that less direct fuel input to combustor as well as higher recuperator efficiency lead to higher generation efficiency, while higher steam-carbon ratio moderates requirements for the material strength. It is also confirmed that the hybrid system is much superior to the recuperated gas turbine in terms of its power efficiency and aptitude for small distributed generation. The conceptual design of a 30 kW μGT-SOFC hybrid system, of which diameter and height are 750 mm and 1500 mm, respectively, is shown to give a power efficiency over 65% (LHV) in the best possible case.

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