This paper describes the deformation, breakup, displacement, and acceleration of liquid bubbles due to air streams. Experiments are conducted using a horizontal air-suction wind tunnel. The shattering processes of liquid bubbles are observed using a stroboscope. The breakup pattern of a liquid bubble varies with air stream velocity. In this experiment several breakup patterns are observed. Dimensionless time variations of dimensionless displacement, and dimensionless accelerations of liquid bubbles are investigated in detail. The dimensionless displacements are approximately proportional to the square of dimensionless time. At the initial stage, liquid bubbles have unsteady acceleration which is greater than steady acceleration.

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Vortical structures in a rectangular jet were educed by measurements of phase-average fluctuating pressure, and the results were discussed in comparison with those by visualization experiments. The measurements were carried out for the air jet issuing from a sharp-edged rectangular orifice. The jet was excited at the interaction mode where the stable interaction of vortical structures was generated. In the phase-average measurements, reference signals were detected by an I-type hot-wire probe fixed near the jet center, and the phase-average fluctuating pressure was measured over the flow field with a pressure probe. The contours of phase-average fluctuating pressure provided us with more information on the details of vortical structures than visualization experiments. The results suggest that direct measurements of fluctuating pressure are very useful to detect the complicated vortical structures occurring in the rectangular jet.

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Flow fields around rotating Savonius rotors were simulated by solving 2-d incompressible Navier-Stokes equations. Results showed good agreement with experimental performance for the following points : torque grows weaker in inverse proportion to tip speed ratio ; gap of rotor buckets is effective in increasing maximum power. Simulated flows were visualized by relative velocity, vorticity, pressure, etc. The behavior of shed vortices were observed carefully, and it has been clarified that the shed vortices have a large effect on flow fields and the running performance.

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This numerical study focuses on the three-dimensional vortical structure of a flow field inside a side-ported rotary engine. Since both two-dimensional numerical simulation and experimental visualization methods may not be applicable to side-ported rotary engine where the flow field inside is essentially three-dimensional, the authors have developed a three-dimensional computer simulation code based on the compressible Navier-Stokes equations. A Chakraverthy third-order TVD scheme devised in the code successfully calculates a flow field in a light load region at 3000 rpm, since the macroscopic stroke characteristics show appropriate behaviors. The velocity vector fields alone do not seem to provide fundamental images of the flow fields, thus characteristic vortex tubes are sought. Although it is not easy to extract vortex tubes closely surrounded by the moving boundary walls, they are capable of providing useful information which otherwise may not be given. The shapes and their change in vortex tubes, in fact, refine perspectives on the flow fields, and hence the effects of the intake flow and the rotor motion on the flow structure are well understood.

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Homogeneous three dimensionally anisotropic turbulence with extremely large anisotropy was generated in a wind tunnel. Early in the return-to-isotropy process, pancake-shaped anisotropic turbulence evolved into a cigar-shaped axisymmetric one and then decayed into quasi-isotropic turbulence. The ratio of the rate of energy dissipation to that of return to isotropy, α, changed stepwise in each stage of the return-to-isotropy process. Such an aspect in the change of αwas related to the streamwise variations of the anisotropy tensor and turbulence intensity and to the restoration of energy defects in the one-dimensional spectra. The anisotropy invariant map showed that Sarkar's quadratic nonlinear model gave a better prediction for the return-to-isotropy process of turbulence with large anisotropy.

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The terms of the coherent energy equation were experimentally evaluated for a large-scale coherent vortex developed in a turbulent boundary Layer. X and Y components of the terms were chiefly concentrated around the symmetrical plane between the two legs of the coherent Vortex where the outflow occurred, whereas Z components were distributed along the central axes of the legs at about Z/δ=±0.3. The mean advection, the coherent production, the random production and the random diffusion were dominant in the energy equation. The dissipation was about two orders of magnitude smaller than the production, which suggested that most of the coherent energy was dissipated by the random production and the random diffusion.

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The interaction of weak normal shock wave with turbulent boundary layer in a supersonic nozzle was investigated experimentally by wall static pressure measurements and by schlieren optical observations. The time-mean flow in the interaction region was classified into four patterns according to the ratio of the pressure P_k at the first kink point in the pressure distribution of the interaction region to the pressure P₁ just upstream of the shock. It is shown for any flow pattern that the wall static pressure rise near the shock foot can be described by the "free interaction" which is defined by Chapman et al. The ratio of the triple point height h_t of the bifurcated shock to the undisturbed boundary layer thickness δ₁ upstream of the interaction increases with the upstream Mach number M₁, and for a fixed M₁, the normalized triple point height h_t/δ₁ decreases with increasing δ₁/h, where h is the duct half-height.

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A numerical analysis has been performed on developing turbulent flow in a square-sectioned 180 deg bend. The ratio of bend mean radius of curvature to hydraulic diameter is 3.35 and straight ducts of 31 hydraulic diameter long are attached to the inlet and outlet planes of the bend. In calculation, an algebraic stress model was adopted in order to predict Reynolds stresses precisely, and a boundary fitted coordinate system was introduced to briefly set boundary conditions. Calculated results were compared with the experimental data available. Moreover, the transition from the secondary flow of the second kind to that of the first kind and vice versa are examined. It was found that the present method predicted the mean flow velocity with a minimum at 90 deg of bend without much discrepancy. In a straight duct of a bend inlet, the secondary flow of the second kind transforms into that of the first kind at 1.0∼1.6 hydraulic diameter upstream from the bend inlet. In contrast, in a straight duct of a bend outlet, the secondary flow of the first kind is accelerated downstream from bend outlet by increasing the pressure gradient of the square cross section. After this acceleration, the secondary flow of the first kind decays and gradually transforms into the secondary flow of the second kind.

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We proposed a theory for estimating the spectral density distribution and the overall sound pressure level of the turbulent noise radiated from a multiple-disk fan. In the theory, experimental data of correlations of the longitudinal and the lateral correlation length as well as the pressure spectral densities were used. The effects of the casing on the radiated noise were clarified by experiments by comparing the spectral density distributions with and without casing. The validity of theoretically obtained formula was examined with respect to the effects of parameters such as the gap between two disks, the rotational speed, the number of disks, the thickness of disks, the radius of an impeller and the flow rate. The agreement between the theoretical and the experimental results was generally satisfactory.

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An organized structure in a fully developed turbulent channel flow with uniform injection is investigated using conditional sampling techniques. Mean frequency and duration time of bursting are obtained using the VITA method. The contributions to uv in the four quadrants of the u-v plane are examined by means of the quadrant analysis technique. The frequency and duration time of bursting increase with increasing injection rate. The contribution of the sweep to Reynolds shear stress increases near the wall region. In the core region of the channel, the contribution of the ejection increases. These results are consistent with the finding that the Reynolds shear stress increases due to injection.

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The paper describes the experiments on the swept shock/boundary layer interactions with and without boundary layer bleed, as the fundamental research issue in the development of a supersonic air intake. The experiments were conducted in a supersonic wind tunnel with a cross section of 1 m by 1 m of the National Aerospace Laboratory. The emphasis was placed on understanding the flow structures of the interaction, using a shock generator with a 15 deg. wedge at Mach numbers of 3.25, 3.11 and 2.63. Attention was also focused on suppression of the interaction by a bleed system of hole arrangement. Three cases of the bleed system, where the bleed portions were located upstream, downstream, and in both regions of the swept shock wave, were employed. It was found by both Pitot-pressure rake and surface pressure survey methods, in addition to the vapor screen visualization technique, that the interaction becomes stronger with increasing Mach number. The arrangement of the bleed portion covering both upstream and downstream of the shock position is effective to suppress swept shock wave/boundary layer interactions.

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The tunnel theory was presented in the previous paper in order to analyze aggregation phenomena in magnetic fluids under an applied magnetic field. The cluster-cluster interaction is taken into account in this model. The present study applies this tunnel theory to stronger particle-particle interactions to clarify the dependencies of mean particle number per cluster on the strength of particle-particle interactions. Furthermore, Monte Carlo simulations are carried out to clarify the aggregate structures of ferromagnetic particles, in which our cluster-moving Monte Carlo algorithm is used. The main results obtained here are as follows : the number densities of particles have an influence on the size of clusters : the larger the number densities are, the bigger the clusters will be ; the size of clusters increases exponentially with magnetic interactions between particles beyond certain values ; the number densities of large clusters relatively increase as particle-particle interactions become large ; the results of the tunnel theory are in qualitative agreement with those of Monte Carlo simulations.

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The motion of a liquid column in a circular tube, driven by the motion of a magnetic fluid under an oscillating magnetic field in the axial direction, is studied experimentally. Nondiluted hydrocarbon-based magnetic fluid and a kind of fluorocarbon are employed as working fluids. The displacement of the magnetic fluid column becomes larger than that reported in the previous work. However, the magnetic fluid column is separated. from the driven liquid at the interface in the frequency range where the displacement is expected to increase. For a U-tube of constant diameter, the time variation of displacement shows a distorted waveform in the lower frequency range due to smaller hydraulic loss, although the displacement is considerably large even in the case of rather weak input current to the solenoid. Numerical analyses are also carried out using conditions similar to those of the experiments. The predicted results agree well with experimental data in the case of no separation at the interface.

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Drag reduction of pipe flow using flexible tubes was experimentally examined with respect to the displacement fluctuation characteristics, by means of a noncontact-type measuring instrument. The results show that the thinner the flexible tube and the larger the Reynolds number, the larger is the energy of the power spectrum distribution of the fluctuating displacement. Therefore, these phenomena have negative correlations with those of the fluctuating pressure mentioned in the previous paper. In the case of the thinnest flexible tube measured newly in the present paper, this tendency, which is the reason for drag reduction, is the same for the higher frequency of the fluctuating pressure. On the other hand, the band energy having the lower frequency of fluctuating pressure is the reason for drag increase.

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The theoretical basis of three dimensional flow analysis is presented for the cavity of finite aspect ratio. When defining the flow discharge for each semi-closed cavity model on the span, then its spanwise variations are pointed out to induce a trailing source sheet downstream of the cavity end by law of mass conservation. Corresponding to this, the method of flow analysis based on the cavitating-line concept is developed for the cavity of finite aspect ratio within the framework of linearization. As the results, the three dimensionality of the cavity of finite aspect ratio is shown to result from the effective cavitation number induced by the trailing source sheet. Thus some notable effects of cavitation number, aspect ratio and cavity model on the three dimensional characteristics of the symmetrical cavity of elliptic plan form are clarified through numerical examples.

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We present a numerical analysis method for optimization problems of domains in which incompressible potential flow problems are defined. Our idea is to apply the traction method that was proposed as a solution to the domain optimization problems in which elliptic boundary value problems are defined. The traction method is implemented to analyze the speed field, which represents the domain variation, with regard to the deformation field of the linear elastic continuum formed in the objective domain applying the force in proportion to the shape gradient function. In the previous paper, we applied the numerical analysis method based on the traction method to the viscous flow problems in which we chose the total dissipation energy for the objective functional. In the case of potential flow problems, we select the velocity square error norm that is defined to a prescribed velocity in an indicated sub region of the design region, as the objective functional. Using the Lagrange multiplier method we obtain the shape gradient function for these problems. For the numerical analyses we employ the finite-element method. The successful results to two-dimensional problems of a straight channel and a nozzle show the validity of the presented method.

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An optical switching system that uses a robotic mechanism and an intersecting waveguide with grooves requires contact-free removal of the matching oil from the grooves. This suction phenomenon was studied by experimentally sucking liquid from a Hat plate by using a subsonic gas How through a microcapillary tube. The results show that the shape of the liquid during suction is constantly changing and the shape immediately before uptake depends little on the amount of liquid on the plate. They also show that the liquid is not sucked until it assumes a particular shape. Therefore, the liquid shape indicates the amount of remaining liquid that cannot be removed by suction. The tube shape that minimizes the amount of remaining liquid varies according to the distance between the tube and the plate, and the amount of remaining liquid depends little on the kinetic viscosity of the liquid.

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The interface oscillation of an encapsulated liquid drop, which comprises the outer liquid shell and the inner gas bubble, are studied experimentally and theoretically. Using a sequential production device of encapsulated drops in liquid-liquid-gas systems, the oscillating motions of encapsulated drop interfaces are observed in detail for various flow conditions. To investigate the dynamics of the interface, the oscillations of interfaces are theoretically analyzed using a model assuming small-amplitude oscillation of the interfaces based on the experimental observations. The oscillating mode, frequency and amplitude ratio between the inner and outer interfaces of the encapsulated drop are investigated quantitatively. Furthermore, the oscillation frequency of the liquid-liquid interface of the encapsulated drop in the immiscible liquid are experimentally obtained for various liquids. Comparing the theoretical results with the experimental ones, the validity of the theoretical analysis is confirmed.

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An experimental study has been performed on the three-dimensional mixing process in a circular jet which was injected into each wake of a two-dimensional symmetrical airfoil that was fitted with attack angles of 0° and 5° in a uniform flow. The results were compared with the that in the case of injection into the wake of the circular cylinder which has been examined by us previously. The profile of mean velocity relative to the wakes in the cases of the airfoil with the attack angles of 0° and 5° is axisymmetric, which agrees almost with the Gaussian profile. The decay of the relative maximum velocity takes place with the difference owing to the variation of the surrounding wake field. In all cases, the half width which was determined from the relative velocity distribution obeys the power law. In the case of the attack angle of 0°, the length scale shows symmetry, but in the case of the attack angle of 5°, the length scale shows asymmetry. It confirmed that this phenomenon is produced by the secondary flow.

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A numerical study based on the thin-layer Navier-Stokes equations was carried out on the pitch-oscillating two-dimensional transonic cascade around the midchord. A Baldwin-Lomax turbulence model was used to simulate the effects of turbulence. The unsteady aerodynamic characteristics and the role of shock wave behavior were investigated. The numerical results indicate that the shock wave movement acts as an aerodynamically unstable factor at high reduced frequency and in a range of interblade phase angle, but the pitch-oscillating transonic cascade remains aerodynamically stable in the range of calculations. However it becomes unstable if the pitching axis is located in front of X=0. 37.

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Flow visualization based on unsteady velocity information is utilized to understand directly and physically the flow structure. In this problem, the phase-average method is widely used which adjusts the fluctuating velocities in order to express them simultaneously. Prior to this, each of the velocities has been measured at their measuring points with hot-wire anemometry or laser Doppler velocimetry (LDV). However, the method has the disadvantage that velocities other than the fluctuating velocities that are being sought produce wave distortions such as FM-AM modulations. We propose a new method which uses 2 LDVs and the FFT analysis which determines the frequency, amplitude and phase of each fluctuating velocity. This method clarifies the time histories of the velocity, vorticity and velocity-energy distributions around a pitching aerofoil either with nonseparation or separation.

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Direct numerical simulations of spatially developing mixing layer were conducted by a higher-order accurate hybrid scheme with newly developed inflow and outflow boundary conditions. The boundary conditions consists of convection-viscous conditions for the velocity field and an approximate transport equation for the pressure. The applicability of these boundary conditions was verified by comparing the solutions of two simulations with two different computational domains. The vorticity, pressure and velocity fields with the shorter domain exactly agree with those with the longer domain. Correlation coefficients for higher-order statistical properties are also very high because the influence of the boundary conditions is very slight. From these results, we can conclude that the proposed boundary conditions are appropriate for direct numerical simulations of spatially developing mixing layers.

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From the point of view of molten carbonate fuel cell efficiency and cooling, the gas flow rate in the manifold should be divided equally among the monocells. In this paper, the gas flow in the fuel cell was replaced by steady incompressible air-flow through a reverse-flow-type rectangular multiple passage similar to a fuel cell at low Reynolds number Re(100≤Re≤800), and the air-flow velocities in each passage were measured using a hot wire anemometer. In this experimental study, deviations from mean flow rate at branch ducts increased with increasing Reynolds number. The flow rate at each branch duct was affected mainly by the pressure distribution in the region where the branch duct joined the main duct.

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Effects of magnetic field on the characteristics of boiling two-phase pipe flow of temperature-sensitive magnetic fluid are clarified in detail both theoretically and experimentally. Firstly, governing equations of two-phase magnetic fluid flow based on the thermal nonequilibrium two-fluid model are presented and numerically solved considering evaporation and condensation between gas- and liquid-phases. Next, behaviour of vapor bubbles is visualized with ultrasonic echo in the region of nonuniform magnetic field. This is recorded and processed with an image processor. As a result, the distributions of void fraction in the two-phase flow are obtained. Furthermore, detailed characteristics of the two-phase magnetic fluid flow are investigated using a small test loop of the new energy conversion system. From the numerical and experimental results, it is known that the precise control of the boiling two-phase flow and bubble generation is possible by using the nonuniform magnetic field effectively. These fundamental studies on the characteristics of two-phase magnetic fluid flow will contribute to the development of the new energy conversion system using a gas-liquid boiling two-phase flow of magnetic fluid.

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The pressure responses of an electrorheological (ER) fluid, containing ion exchange resin particles in silicone oil, in a piston cylinder-ER valve system which is modeled after an ER damper have been measured to investigate the steady ER effects and the transient pressure responses of the ER fluid against the application of electric field to the ER valve. The ER valve has a channel of 0.6 mm height between two fixed parallel electrodes, where the flow establishes the Poiseuille-flow geometry. During testing, the piston is moved at a given constant speed to maintain the mean flow rate through the ER valve constant. The pressure drop across the ER valve, caused by ER effects, increases in proportion to the square of electric field strength E², but decreases exponentially with increasing flow velocity U and then converges to a certain value of the pressure drop at sufficiently high flow velocity, and is characterized by an approximate function of E and U. These characteristics of ER effects are compared with the theoretical results based on the Bingham plastic model. The measured step response of the pressure can be approximated by a first-order response. The rising time constants are much higer than the usual response time constants of ER fluid. The above observations are discussed from the viewpoint of the damping performance and the system characteristics.

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Typical periodic velocity fluctuation in a near-wake flow of a flat-plate blade is caused by the Karman vortex shedding from its trailing edge. The Karman vortex shows a cellular structure in the spanwise direction in a rotating flow field. The Karman vortex street produces discrete frequency noise. A theory to estimate the sound pressure level (SPL) due to Karman vortex shedding is proposed. The spectral distribution of SPL is predicted by superposing SPLs due to each vortex shedding with different frequency in the near-wake flow along the blade span. SPL strongly depends on the intensity of velocity fluctuation and the spanwise scale of a vortex cell, which is experimentally determined by measuring the cross correlation along the blade span of the near-wake flow. The calculated spectral distribution agrees well with the experimental data.

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It was found, from fundamental investigations, that a proposed sand collecting system with an injection port at the collecting mouth can transport granular materials more effectively than other conventional systems, by means of fluidization of the settled bed before collecting the solid particles. In this work, a performance test of this system was carried out. The collecting efficiency is formulated using the total pressure loss not only of the vertical pipe but of the collecting system. It is verified that the efficiency in the case of injection flow is higher than that in the case of no injection flow. In this experiment, the highest efficiency is achieved at the inner diameter ratio of 0.17.

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The objectives of the present research are (1) the establishment of the levitation process of a non conducting droplet due to the action of a static magnetic field, and (2) the development of a technique to transport and fix a capsule of medicine in the affected part of the body. A numerical simulation using the SOLA-VOF method and an experiment using a magnetic fluid are conducted to demonstrate the possibility of magnetic levitation of an insulating droplet. While measuring the position of the magnetic droplet, PID control is performed on the coil current and stable levitation is realized. The shapes of the levitated droplets are examined while changing the concentration and the volume of the magnetic fluid. The effects of the control constants on the process of the droplet approaching a given position are elucidated.

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In this study, a high-speed servo valve with no outer leakage is developed, which is used to drive flexible hydraulic actuators (FHA) in extreme environments. In the valve, multilayered PZT devices are used to drive a spool directly and quickly, and are connected to lever mechanisms to magnify the device motion. A bellows is also used to prevent outer leakage from the space between the spool and the sleeve. Employing a disturbance observer, the lack of system damping of the valve is improved by feeding back the estimated velocity of the spool ; the estimated disturbance is also fed back to eliminate effectively the hysteresis between input voltage and output displacement of the PZT devices. The sampling frequency of the observer is 10 kHz. As a result, excellent response of the servo valve is obtained, with the maximum spool displacement of 100μm and the frequency band width of about 300 Hz. It is ascertained that the control method is suitable for this type of servo valve.

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This study investigates a bubble which is placed such that it bridges a cross section of a horizontal narrow divergent passage under the Earth gravity condition (1-G). In a narrow passage, inertia forces are known to be small compared with viscous forces. Also, gravity force is not dominant for bubble behavior in a horizontal narrow passage under the 1-G condition. In this sense, the bubble behavior in the passage is similar to that under a low-gravity condition. It is important to understand the bubble behavior in relation to separating gas from a gas-liquid two-phase flow and controlling a gas-liquid interface under a low-gravity condition. A single bubble was placed such that it bridged the cross section of a horizontal narrow passage under the 1-G condition. The bubble geometry and its behavior were studied experimentally for gap sizes ranging from 0.5 mm to 2 mm, divergent angles of 1 to 5 degrees, and using ethyl alcohol as a working fluid. The following results were obtained : (1) bubble was found to move to greater cross sectional area, (2) the gas-liquid interface geometry from the top view could be expressed as a "contact circle model" which takes the maximum radius in the passage, and (3) effects of the gap size and the bubble projected area on the bubble behavior were clarified.

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Solid/liquid phase change heat transfer around cylinders occurs in many systems including latent heat thermal energy storage systems. In such systems, interaction of the heat transfer around the cylinders is often observed. Although several studies have reported on the heat transfer around a single cylinder, two or several cylinders, there have been no systematic studies to examine the effect of the initial superheat of water for solidification and the effect of the surface temperature of the cylinders for melting on the heat transfer. The purpose of the present study is to examine systematically the effects of the parameters mentioned above and the density inversion of water on the solid/liquid phase change heat transfer using two horizontal, vertically spaced cylinders.

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This paper is concerned with shock-tube experiments of the phase transition from vapor to liquid and its molecular dynamics computer simulation. The growth of a liquid film formed on the endwall surface of a shock tube in a shock wave reflection region is measured by an optical interferometer using laser beams with two different wavelengths. The condensation coefficient of methanol vapor is obtained from the conformity between the experiment on the liquid film growth and the gasdynamics theory with kinetic boundary conditions. The condensation coefficient of methanol vapor is found to be between 0.15 and 0.18. This value is in good agreement with a theoretical condensation coefficient (0.1∼0.3) which is obtained on the basis of molecular dynamics computer simulation. The simulation suggests that vapor molecules colliding with the liquid surface apparently drive other molecules out of liquid ; i.e., the fluxes of condensation and evaporation have a strong correlation.

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Solidification and flow characteristics of molten high-density polyethylene flowing in a rectangular cavity having a cooling wall are investigated experimentally. Experiments are carried out under various parameters of molten polyethylene temperature, flow velocity of the polyethylene, cooling wall temperature and the thickness of the cavity. The obtained results reveal that the solidification layer formation of the polyethylene is affected by flow behavior, polyethylene temperature and cooling wall temperature. The useful non-dimensional equations, which predict the amount of polyethylene and the time required for injecting the polyethylene into the cavity, are derived as a function of Reynolds number, cooling temperature ratio and Stefan number.

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The heat tranfer characteristics of free-convection condensation of ammonia/water vapour mixtures on a horizontal tube are investigated. The heat transfer coefficients of ammonia/water vapour mixture are predicted by solving the algebraic equations, and the results show that the heat transfer coefficients of the mixtures are lower than those of the pure components, ammonia and water. Experiments are also performed to investigate the condensation behaviour of the vapour mixture on a horizontal smooth tube over a wide range of mass fraction of each component. The results indicate that the experimental heat transfer coefficients agree well with the theoretically predicted values. Observation of the condensate film reveals the appearance of three types of film, namely, smooth film, stationary ringwise film, and turbulent ringwise film.

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Numerical and experimental studies are carried out on natural convection heat transfer to air from an array of vertical parallel plates with protruding and discrete heat sources such as IC packages. Two-dimensional Navier-Stokes and energy equations including heat conduction through the plates and heat sources are numerically solved under the conditions of modified Grashof number Gr=2.3×10³∼8.8×10⁵ and aspect ratio L=l/h=8∼30. The numerical solution agree well with the experimental values except for the large aspect ratio L=30 where the three-dimensional effects become significant. A correlation expression for the local Nusselt number is proposed which can predict the protrusion surface temperature within 20% error. The estimation of the protrusion center temperature is also discussed.

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An enhancement technique was developed for natural convection heat transfer from a vertical finned plate. The horizontal plates attached on the finned plate at equal spacing were utilized to promote heat transfer. These horizontal plates redirect the high-temperature fluid flow from the vicinity of the base plate to the outside of the boundary layer, and promote the low-temperature, incoming flow from the far wall region toward the base plate. The overall and local heat-transfer coefficients of thus-treated plates were measured and compared to those of the non-treated, finned plate. It is found that the overall and local heat-transfer coefficients were increased by 20% and 40%, respectively, when the horizontal plates with appropriate height and pitch were used.

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A grating composed of elliptical cylinders (GEC), specially designed, is applicable to control of radiation heat transfer from a heated surface, as reported in our previous work. In this study, an analysis of radiation heat transfer is performed for a physical model in which the GEC is placed in front of a heated black-base surface and the major axes of the elliptical cylinders are inclined at a certain angle from the normal to the row of elliptical cylinders. Numerical solutions are obtained. Variations of the direction and the radiative energy concentration with the slant angle of the major axis are shown for some parameters. It is verified that the GEC is able to widely change the direction of radiation heat transfer from the heated surface. An analysis taking account of radiative energy inward from the environment is also made, and the numerical results are discussed.

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Experiments of two-phase flow instability in parallel multi-channels (of up to seven channels) using an apparatus with long or short riser pipes were performed. In both cases, the Type I density-wave instability was observed. In the experiments with shorter riser pipes the flow, as expected, was more stabilized with smaller oscillation amplitudes than that with the long riser pipes. Oscillation modes were classified in to the following : a mode (n-1) channels in-phase with one channel out-of-phase, a mode (n-2) channels in-phase with two channels out-of-phase and a mode with channels having phase differences of 360/n deg with each other. The results agreed with the authors' previous predictions.

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Detailed measurements are performed for time-averaged heat-transfer distributions around the leading edge of a blunt body that is subjected to periodically incoming wakes under the influence of mainstream turbulence. The blunt body is a test model of a front portion of a turbine blade in gas turbines and consists of a semicircular cylindrical leading edge and a flat-plate afterbody. Measurements for a wide range of steady and unsteady flow conditions, i.e., Reynolds number, wake-generating bar passing frequency and main stream turbulence intensity, are conducted. The wake-affected heat-transfer distributions indicate that the wake passage over the leading edge causes a significant increase in heat transfer there, but such a wake effect becomes less prominent for the case of higher mainstream turbulence. Maxmum heat trasnfer at the reattachment point decreases due to the wake passage. After the reattachment point, the heat-transfer distribution tends to follow the correlation for a turbulent boundary layer as the maintream turbulence increases. A comparison is made between the measured heat transfer, in particular the heat-transfer enhancement around the leading edge, and the calculations using a simple prediction method developed, which verifies the usefulness of the prediction method despite its simplicity.

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A double-pipe heat exchange model is proposed to describe the axial heat-transfer rate and to predict the effective thermal diffusivity of oscillating fluid in a thin tube (the so-called dream pipe). Since the profile of bulk temperature in the axial direction is very similar to that of the counter flow in a double-pipe heat exchanger, we can obtain the heat-transfer rate by using the expression of log-mean temperature difference and thermal resistance network for the overall heat-transfer coefficient. The experimental results utilizing three kinds of tube materials ; Pyrex glass, Teflon and aluminum, are also presented to reveal the contribution of the tube wall to axial heat transfer. Using the result of numerical analysis of the unsteady-state temperature profile in the tube, the local Nusselt number is calculated for some oscillating frequencies and compared with the expression given in terms of boundary layer thickness. The prediction of the effective thermal diffusivity based on this model is confirmed by the previous results as well as by these experimental ones.

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A novel concept of liquid-fluidized-bed heat cxchangers is proposed for severely fouling fluids such as sewage. Principal features are that the heat exchanger involves no element which causes clogging, and can be cleaned during heat exchange operation. Results from a fundamental experiment using a horizontal single tube are presented and compared with existing correlations. Further-more, a new correlation is proposed for the heat transfer coefficient.

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A printing characteristics estimation method for a thermal head has been developed. The optical density of thermal paper in arbitrary transient temperature response was formulated based on first-order reaction of the chemical agents of thermal paper. The temperature response of the thermal head and the contact pressure were obtained by FEM (finite-element method). Optical density of thermal paper heated by the thermal head was estimated by the formulation and the temperature response with contact heat resistance. The estimated result is found to be in good agreement with the experiment.

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Modern trains, such as the Shinkansen, pass through long tunnels at such a high speed that a pressure wave or weak shock wave generated at the nose of the train causes a large booming sound at the outlet of the tunnel. The authors have proposed the creation of a density gradient in the air in a tunnel at the exit for an interval of several times the tunnel height. In this report, more realistic patterns of the density distribution than previous one are discussed. Wedge shaped low density regions are created at the exit of the tunnel. The effects are discussed by both computer simulations and model experiments. They predict that the proposed density distributions can reduce the pressure gradients of the shock waves lower than previous pattern and they can also give preferable effect on the reduction of booming sound.

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A method to estimate the primary spherical particle number (PSPN) distribution pattern and average volume-equivalent diameter of soot aggregates suspended in a rich ethylene-air premixed flame was developed, where TEM data such as the primary spherical particle diameter, the fractal dimension and PSPN distribution pattern of soot aggregate specimens collected on a sheetmesh were combined with optical data such as the dissymmetry ratio in differential scattering intensity. The growth of soot particles along the central stream line was observed, and the effects of the complex refractive index were examined. The growth of soot particles mainly occurred through the aggregation of primary spherical particles, whereas the growth of the primary particles themselves was very slow. The fractal dimension and the PSPN distribution pattern of aggregates were kept almost constant during the growth process. The complex refractive index had only the secondary effects as compared with the effects of the fractal shape and PSPN distribution pattern of soot aggregates.

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Combustion of flying CWM droplets in an electric furnace was investigated to obtain basic data on the mass changes of CWM spray. The calculation model for the mass reduction of a single CWM droplet was made based on the experimental results on mass changes and combustion periods in the combustion of a suspended droplet. Using this model with the residence times of droplets calculated from flying velocities, mass changes of droplets for their flying distance were calculated. With these mass changes and size distribution of flying droplets in the furnace, their total mass changes were calculated and compared with the experimental data. The calculated values approximately agree with the experimental values except the furnace inlet where calculated mass reductions are less than experimental data.

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A circular rod was inserted in a spray flame stabilized by an annular hydrogen diffusion pilot flame to investigate the detailed structure of spray flames under the influence of the wake flow behind the rod. The light emissions in OH- and CH-bands, and the laser light scattered by droplets were monitored simultaneously and analyzed spectrally in the flame with and without a rod. The droplet velocity was also monitored using a laser Doppler velocimenter (LDV). It was experimentally confirmed that the inserted rod promoted the reduction of the length scale of droplet clusters and the flame propagation into the clusters associated with solid-body light emission. This result suggests that the combustion behavior of droplet clusters is influenced by the turbulent mixing and slip velocity between gas and droplets due to the wake flow behind the rod.

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Concerning the stretched cylindrical premixed flames formed in a radial-flow nozzle burner, effects of fuel mixing between methane and propane were examined on the extinction characteristics, such as the velocity gradient (stretch rate) and flame diameter at the state of extinction and flame temperature variations with the velocity gradient. These fuels were used because they have been known to show different behavior to the extinction due to flame stretch. The results showed that the characteristics were not linearly related with the volume fraction of each component fuel, but inclined to be weighted with propane and that at the stoichiometric condition some mixed fuels had a stronger resistibility to flame extinction than the pure component fuel. To explain the results, theoretical analysis based on the flame sheet model was carried out for the investigation of the effects of stretch, fuel mixing, Lewis number and preferential diffusion on the flame temperature which is closely related to the extinction phenomena.

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The flow velocity measurements and flux measurements of gas species of O₂, CO₂ and NO in an oil furnace were carried out. The velocity profiles in combustion and noncombustion were measured by the developed LDV, and the results show that the reversing flow regions for both cases were located at the same place and their volumes were almost equal. The comparisons of measured concentration and flux obtained using velocity and temperature were performed in spray combustion. The results show that there is little difference in the flame region but a large discrepancy outside of the flame region. The generated gas species in the flame and its convection outside of the flame were discretized, and the application of flux in spray combustion research was found to be very useful and effective.

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Reproducible vegetable oils have many advantages as alternative fuels for supplementing diesel fuels. Compared with common diesel fuel, however, vegetable oils result in higher exhaust emissions and carbon deposits because of high viscosity and low volatility. The work presented here describes results of experiments with stable water-emulsified rapeseed oils in a small direct-injection diesel engine. The purpose of this paper is to investigate the improvement of engine performance and the reduction of exhaust emissions upon changing the injection nozzle diameter and the valve opening pressure. The results show that BSFC, HC, CO, and smoke emissions decrease simultaneously with decreased injection nozzle diameter as compared to gas oil. In the present experiment, the optimum nozzle diameter is 0.22 mm with regard to engine performance and exhaust emissions.

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The processes of combustion and the soot formation in a direct-injection diesel engine were studied experimentally at a low engine speed. Injection was performed by a specially designed injection system relying on the principle of fast hydraulic acceleration of a spool. High-speed photographs at an injection pressure up to 120 MPa show that luminosity fluctuations of flames become less over the combustion space as the injection pressure increases, due partly to the fact that combustion becomes rapid and partly to the leaner mixture formed. Soot clouds taken by using a laser-light sheet method at similar rates of heat release but different injection pressures show that soot clouds do not exist in the later part of combustion processes at a pressurized injection and a smaller nozzle diameter.

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