Thermal free convection is simulated by the Lattice Boltzmann Method using two types of particles, that is red particles and blue ones. The gravitational force is introduced into the collision stage, at which the impulsive force is added by making the population of blue particles moving downward increase. The buoyancy force is taken into consideration in the translating stage of the particles. The velocity field and the density or the temperature field are obatained by averaging these calculated two stage fields. The results agree well with those obtained by the finite difference method.

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A grid-free particle method is developed for solving Navier-Stokes equations of one dimensional viscous compressible fluids in unsteady motion. The particles, representing fluid density, are moved at the acceleration derived from the motion equation, and the total energy of each moving particle is increased/decreased according to the energy equation. A shock wave and an expansion wave in a shock tube are simulated as numerical experiments to study the accuracy and the stability of the present method. The structures of a steady shock wave of Argon simulated by our method, the finite difference method and the direct-simulation Monte Carlo method were compared.

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With the recent advances in computers, large eddy simulation (LES) has become applicable to engineering prediction. However, most cases of the engineering applications need to use the nonorthgonal curvilimear coordinate systems. The staggered grids, usually used in LES in the orthgonal coordinates, don't keep conservative properties in the nonorthgonal curvilinear coordinates. On the other hand, the colocated grids can be applied in the nonorthgonal curvilinear coordinates without losing its conservative properties, although its prediction accuracy isn't so high as the staggered grid's in the orthgonal coordinates especially with the coarse grids. In this research, the discretization method of the colocated grids is modified to improve its prediction accuracy. Plane channel flows are simulated on four grids of different resolution using the modified colocated grids and the original colocated grids. The results show that the modified colocated grids have higher accuracy than the original colocated grids.

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Direct numerical simulation is used to investigate the identification of quasi-streamwise vortices and the mechanism of self-sustenance of them in near-wall region. A quasi-streamwise vortex is identified using an intesity of streamwise vorticity as indicator, that is confirmed statistically on the basics of attitude angle of vortex line, By analysing properties of vortices in near-wall region with respect to their tilting angle, it is found that vortices are categorized into two groups, i. e. strong and nearly streamwise oriented ones and weak and strongly spanwise oriented ones. New split of production rate term of the transport equation for streamwise vorticity which is more reasonable than conventional one is proposed. On the basis of new split, interpretation of the mechanism of enhancement and supply of streamwise vorticity is presented.

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An analysis of steady cavitation on flat plate cascade is performed by a singularity method based on closed cavity model. As a result, it is found that two kinds of the steady cavitation patterns exist. One is equal length cavitation in which the cavity lengths of all blades are the same. The other is alternate blade cavitation in which the cavity length changes alternately from blade to blade. Although the present model fails to predict the range of cavitation number where alternate blade cavitation occurs, it predicts alternate blade cavitation in terms of cavity length fairly well. The static pressure losses in both the equal length cavitation and the alternate blade cavitation are estimated. A parameter study is carried out to educe the general characteristics of alternate blade cavitation.

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This paper is concerned with cavitation and erosion in submerged water jet. Impulse forces generated by cavitation in the jet are measured by impulse force gauges. Accumulated count of impulse forces in unit time is shown against the force and the standoff distance from the nozzle exit. It is found that there are maxima in impulse forces at two different standoff distances at 30 and 80, which are respectively the values normalized by the nozzle diameter (=1.5mm) and that impulse forces mainly appear in frequencies of a few Hz. Laser-microscopic observations show that erosion patterns of material are classified into two ones.

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A theoretical model was developed to study the mechanism of free surface sloshing in a vessel induced by a steady vertical jet flow. In the model, jet deflection is calculated with eigen values of the generalized Orr-Sommerfeld equation which is applicable to slightly non-parallel jet. Instability criteria employed in the model are (1) resonace condition between sloshing and jet frequencies and (2) π phase relation between jet displacement at an inlet and global jet deflection. Numerical results of the mathematical model have shown good agreement with experimental ones, which justifies that the inherent instability of free jet itself and edge tone feedback are the main causes of the self-excited sloshing.

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Flow visualizations using the two kinds of tracer methods and LDV measurements with shearthinning aqueous solutions of polyacrylamide through an axisymmetric contraction and two eccentric contractions have been carried out. In these experiments the effect of contraction eccentricity on flow patterns has been studied. In the steady regime the largest vortex length for the eccentric contractions is almost the same as that for the axisymmetric contraction ; on the other hand, within the vortex the streak line circulates in a radial plane for the axisymmetric contraction while it spirals from the minimum vortex region toward the maximum one for the eccentric contractions. Furthermore, a "small-scale instability" occurs near the boundary between main flow and upstream end of vortex. Finally the main flow spirals both for the axisymmetric and eccentric contractions in entirely unstable flow regime.

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The instability wave developing in the separated shear layer from a circular cylinder is investigated by using continuous wavelet transform with Gabor wavelet. The instability wave is recognized as short, intermittent wave packets. Each wave packet is successfully captured with a tuned Gabor function. Setting an appropriate threshold level for the amplitude of the wave packets gives interval, duration, intermittency and intensity information. The results reveal quantitatively that the instability wave develops along the separated shear layer and that its activity is strongly correlated to the intensity of the mean shear.

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The hydrodynamic forces generated by interaction between water and a rectangular cylinder have been investigated experimentally. Five rectangular cylinder models of 6, 12, 30, 60 and 120 mm width, 60 mm height and 200 mm span were used. A period parameter ranged from 0.2 to 3.2 in the investigation. The test frequency was 2 Hz. The characteristics of the hydrodynamic force acting on a circular cylinder, square cylinder, diagonal square cylinder and elliptic cylinder reported previously by the present authors depended on the period parameter but not on the Reynolds number and the test frequency less than 6 Hz. The results are as follows : the hydrodynamic force coefficient, the wave form and the phase difference to the period parameter are shown : the effects of the cross sectional width/height ratio to the force coefficient and the phase difference are explained.

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In this paper we describe the flow around two-dimensional circular cylinder bundles supported by wires. The experiment was carried out in an N.P.L. blow-down-type wind-tunnel with a working section of 500mm×500mm×2000mm, and with the Reynolds number of 9.4×10³. The displacement, time-mean pressure distributions, and fluctuating pressure distributions of the oscillating circular cylinder were measured. The excitation mechanism of fluid-elastic vibration was investigated with the existing research. Consequently it was found that (i) while the displacement amplitude in X direction becomes larger than in Y direction, the occurrence of the fluid-elastic vibration is due to the jet switch for single row, and (ii) the displacement amplitude in Y direction is predominant as compared with that in X direction for three rows, and the fluid-elastic vibration occurs in the wake switch phenomenon.

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There are many types of acoustic noise from flow fields, for example, jet noise, boundary layer noise, tone due to Karman vortex, singing flame, and Rijke tube. This paper proposes an equation of acoustic energy conservation in open systems, which explains various types of oscillating phenomena excited by fields. This equation is from perturbation of the Navier-Storkes' equation. From this analysis it became clear that the generation and dissipation of acoustic energy are caused by the following : work by pressure, viscous loss, interaction between pressure variation and heating rate variation, stable heating, and work by vortex. A simplified model is used to describe these unstable factors by wave equation. Also, a one-dimensional analysis for a duct with a large temperature gradient and a large sectional area gradient was done by the transfer matrix method. Those factors have an effect on the phase velocity.

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The objective of this investigation is to develop a method to detect the aerodynamic sound source in the wake of a circular cylinder at Reynolds number 4.0×10⁴. We estimate the intensity of surface pressure which is related to vortex shedding in the wake of circular cylinder by using the coherent output power (COP) in terms of static-pressure and surface pressure on the circular cylinder. Then, we obtain vortices distribution which contribute dipole sound source on the cylinder by measuring COP at various positions in the wake of the circular cylinder. Moreover, we can calculate aerodynamic sound by using the Curle's equation with this estimated surface pressure. We also define the spatial distribution of aerodynamic sound source by means of this method. The result shows the aerodynamic sound generate near the formation region of Karman vortices, that is, X/D=1.5 to 2.0, Y/D=±0.4. Therefore, separated shear flow contributes strongly to the aerodynamic sound generation.

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Flow header for small multiple pipes is commonly used in boilers and heat exchangers. The system contributes to raise the heat transfer efficiency in the components. The flow distribution mechanism of the header for a water has been studied and the method for the design has been recommended. It is also recommended to avoid the bubbles in the header to obtain a uniform water flow rate to each small pipe. But in some cases, the header is used to distribute a flow containing bubbles. Distribution behavior of a water with or without bubbles was studied experimentally in a horizontal header with four vertical pipes. The prediction method developed for a single-phase fluid was extrapolated to the flow containing bubbles. The prediction agreed well with the experimental results.

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When mist flow is injected from a pipe between horizontal parallel disks, a thin liquid film and liquid droplets are left on the lower disk. The behavior of residual liquid on the disk is studied experimentally. The distance between the disks is equal to the inner diameter dn of the pipe joining to the upper disk. The behavior of residual liquid is greatly concerned with the flow near the lower disk. On the lower disk where the ratio of the distance from the center of the disk to dn is 4.3-4.5, the condition of the flow near the lower disk changes. When the velocity of the mist flow in the pipe is high, the residual liquid droplets coalesce at this position. The deformation of the shape of the droplet exposed to air flow depends on the initial shape and the modified Weber Number.

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When mist flow is injected from a jointed pipe vertically between horizontal parallel disks, a liquid film is standing at the specific position on the lower disk. The position of standing liquid film is concerned with the flow between disks. The numerical calculation is performed on the flow using low-Reynolds-number k-ε model. As a result, in the direction of downstream from the position of maximum of pressure gradient on the lower disk, the condition of the flow near the disk changes and intensity of turbulence begins to increase. Comparing with the position of standing liquid film, it is greatly concerned with the condition of the flow near the lower disk.

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The local refinement technique is very useful method to get high-precision solution with lower efforts in the structural grid system and has been applied to many cases. In using this method, some methods are needed to specify the regions on which the mesh should be fined on the calculation domain and a method based on the truncation error estimation theory was proposed. This method makes it possible to determine the regions with only one, non-iterative calculation and is useful for implicit method. A local mesh refinement method with SIMPLE algorithm was applied to the abovementioned region. This method basically satisfies the conservation law on the fine/coarse cell boundaries. As a result, high-precision solution was got with shorter time and smaller memory in comparison with the usual method.

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A direct numerical simulation (DNS) of a turbulent flow in a wavy channel was carried out with consistent finite-difference method of high-order accuracy. The application of the database generated by the DNS is suited not only for study of the structure of turbulent flow but also for the design and testing of turbulence models in more practical fields. The wavy channel causes periodic pressure gradient, successively acceleration and deceleration of streamwise velocity, and separating region. The scale of separating region depends on the amplitude of wavy wall. Some characteristics of the flow are shown, for example the momentum distribution. It is also demonstrated that the flow is characterized by the simple linear approximation

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The pump is often the major source of loss in a three-element automotive torque converter in the higher speed ratio range where vehicles are most frequently operated in everyday driving. The complex flow fields in the pump were analyzed using a three-dimensional CFD code in order to identify the loss generation mechanism in this speed ratio range. The results show that a low kinetic energy region is found in the corner where the suction and the core surfaces intersect, which qualitatively but essentially coincides well with flow visualization results obtained with the resin-film method. A reduction of the flow rate and an increase in the nonuniformity of the inlet circulatory velocity distribution increase the pump loss. A relatively greater loss is generated near the leading edge section and in a reverse flow region the area of which increases as the speed ratio increases. The secondary flows near passage walls and the change in the loss distribution between passage crosssections can be explained by the pressure field formed by the main stream.

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Passenger car torque converters have been designed with an increasingly flatter profile in recent years for the purpose of achieving a weight saving and more compact size. However, a flatter design has tended to result in reduced hydrodynamic performance and the basic mechanism involved is still not fully understood. In this study, four torque converters with different flatness ratios were manufactured and tested in order to evaluate the effect of the flatness ratio on overall performance. The internal flow characteristics of the torque converters were numerically investigated using a CFD code. It was found that performance deteriorated when the flatness was less than about 0.2. The main cause of this performance deterioration can be attributed to nonuniformity of the velocity fields of the pump. Such nonuniformity occurs not only from the inlet to the exit, but also from the shell to the core in the flow passage.

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A new erosion model was proposed due to a theoretical approach. Using of the erosion model, a new evaluation technique to estimate the erosion magnitude on a pipe surface was developed. The flow field was estimated by the k-ε turbulent model. And, particle motions were estimated by Stokes equation and bouncing coefficient by Tabakoff et al. Further, a numerical simulation for a elementary experiment was carried out. The main results are as follows : (1) The erosion rate depends on the particle size strongly. The result is in good agreement with the experimental result. (2) The effect of particle size for the erosion rate depends on flow field and experimental apparatus.

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The purpose of this study is to reveal (1) the energy dependence of albumin uptake into endothelial cells, and (2) the effect of shear stress on the albumin uptake area and the its content per unit area. The uptake of the fluorescent labeled albumin (tetramethylrhodamine isothiocyanate conjugated albumin, TRITC-albumin) was visualized with a confocal laser scanning microscope. The uptake into the endothelial cells is inhibited completely at 4°C or by 1 μM FCCP, that is a potent energy metabolism inhibitor. This result indicates that the albumin uptake is an energy-dependent, active transport. After 48 hour exposure to shear stress to the endothelial cells, the albumin uptake area and the albumin content per unit area were changed. At 10 dyn/cm², at 5 μm the uptake area increases by 363% and the albumin content per unit area increases by 192%. At 60 dyn/cm², at 3μm the uptake area decreases by 21% and the albumin content per unit area decreases by 54%. It is, therefore, considered that the effect of shear stress on the uptake area is more influential than that on the albumin content per unit area. We conclude that endothelial cells affected by sher stress change the albumin uptake function and especially the cells change the uptake area.

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A measuring method based on the exciplex fluorescence technique has been developed for planar measurements of the liquid phase temperature distribution in fuel sprays. The liquid fuel (n-hexadecane or squalane) was doped with pyrene (C₁₆H₁₀). The fluorescence intensity ratios of the pyrene monomer and excimer emissions has temperature dependence, and were used to determine the liquid phase temperatures in the fuel sprays. The spray was excited by laser radiation at 266 nm, and the resulting fluorescence was imaged by an intensified CCD camera. The cross-sectional distribution of the liquid phase temperature was estimated from the fluorescence image by the temperature dependence of the intensity ratio. The results demonstrate that this laser-based thermometry technique is available for 2-D measurements of the liquid phase temperature in fuel sprays.

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The two-dimensional distributions of the liquid phase temperatures in diesel sprays injected into high-pressure and high-temperature environments were measured using the laser-induced fluorescence technique. The liquid fuel (n-hexadecane) was doped with pyrene (C₁₆H₁₀). The fuel spray doped with pyrene was injected under a high-pressure of 3.1 MPa and a high-temperature of 773K. The evaporating diesel spray was excited by laser radiation at 266 nm, and the resulting fluorescence was imaged by an intensified CCD camera. The fluorescence intensity ratios of the pyrene monomer and excimer emissions have temperature dependence, and were used to determine the liquid phase temperatures in the diesel sprays. The cross-sectional distribution of the liquid phase temperature was estimated from the fluorescence images by the temperature dependence of the intensity ratio. The results demonstrate that the laser-based thermometry technique is available for planar measurements of the liquid phase temperature in evaporating diesel sprays under high-pressure and hightemperature environments.

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A model for examining ignition of a single fuel droplet passing through a propagating flame was presented, and the effect of the initial droplet diameter and the equivalence ratio of the mixture on ignition time of a droplet was investigated numerically. The results showed that each equivalence ratio had a minimum ignition time against the initial droplet diameter because of the competition between the evaporation time and the reaction time, and that each initial droplet diameter had a minimum ignition time against the equivalence ratio of the mixture because of the competition between the effect of the flame temperature and that of the oxidizer concentration. The results also showed that the burning velocity of propagating flame increased as the flame front approached the droplet surface. This increase of the burning velocity may result in a local disturbance on the planar propagating flame through flame-droplet interaction and thus suggests the occurrence of the thermal-diffusion instability in spray combustion.

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The etching process is investigated using the two-dimensional experiment and the Monte Carlo simulation. The quasi-two-dimensional etching of aluminum plate from NaCl aqueous solution is achieved through a Hele-Show cell under an applied electric field. The time evolution of etching surface on the aluminum plate is analyzed by the two-dimensional technique. The transport equation of anions governing the etching process is shown. The transport phenomena (diffusion and migration) and the surface reaction are taken into account as the multiparticle Brownian motion with drift and the reaction probability. The etching process is simulated by the multiparticle Monte Carlo method. It is shown that the simulation result is nearly consistent with the experimental result.

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This paper presents the experimental and simulation results for thin-layer electrochemical deposition around the circular plate. The effect of the ion drift on the electrochemical deposit is investigated by using the experimental method of electrodeless reduction of silver ions from a AgNO₃ aqueous solution. For comparing with the experiment, a Monte Carlo simulation is carried out for the two-dimensional thin-layer electrochemical deposit around the circular plate. The mass transfer (diffusion and electric migration) and the surface reaction are taken into account in this simulation. It is shown that the experimental growth process of the electrochemical deposit is consistent with the Monte Carlo simulation result.

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The gas dis solution process of a spherical rising carbon dioxide bubble in water was investigated experimentally and numerically. We developed an experimental system that use a CCD camera coupled with a microscope to follow the rising bubble. By measuring the bubble size and the rising speed from the bubble motion data captured by a personal computer, we could precis ely estimate the drag coefficients and the Sherwood number for the dis solution of gas bubbles at Reynolds numbers below 100. The experimental results show that the drag coefficients of the carbon dioxide bubble in water show the same value of solid particle even when we use relatively clean water. We also numerically estimated Sherwood number for dis solution of gas bubbles in an infinite liquid by directly solving the Navier-Stokes equation and diffusion equation. The experimental and numerical results are in good agreement. Moreover, we compared the experimental results with a proposed equation for estimating the drag coefficients and Sherwood number and clarified the applicable region of the equation.

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An experimental study was conducted in order to establish the thermal and fluid design criteria for a new steam reforming device, and a proposal was submitted to employ a flow laden with droplets (water and methanol mixture solution) directly impinging on a heated plate in the new reforming device. Experiments have been conducted by controlling spray impingement on a heated plate covered with a porous plate made by sintered metal. The new configuration of the reforming device is able to enhance the evaporation of liquid by using a low-level heat source held at lower than 600K. Droplets atomized by a spray nozzle instantaneously evaporate on the heating surface without bouncing, since the sintered metal surface provides a higher Leidenfrost temperature due to surface roughness. The characteristics of spray flow and evaporation efficiency have been measured by Phase Doppler Anemometer which permits local measurements of size and velocity of liquid droplets, size distribution and mass flux of droplet. Results have confirmed that superheated gas was directly generated from the spray liquid with high efficiency, and the locations of heating plates and spray nozzle were optimized. Finally the rate of evaporation was enhanced by pre-heating the liquid before atomization.

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Water molecule is dissociated at high temperatures. PVT properties of dissociated steam have been calculated with molecular simulation of general Monte Carlo method using 1 center Lennard Jones 12-6 potential model for temperatures from 1000K to 3000K at pressures from 0.1MPa to 300MPa. The uncertainty in density calculations with NPT ensemble is estimated to be±1%. Density values of dissociated steam become smaller than those of pure steam with increasing temperature and decreasing pressure. Percentage deviation of density for dissociated steam from density for pure steam at 3000K and 0.1MPa is calculated to be 17.1%. Comparison of density between the present calculations and values in thermophysical property tables by Vargaftik is reported.

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Dissolution of liquid CO₂ accompanied by CO₂ clathrate-hydrate film into sea water is observed at CO₂ sequestration in ocean, which is considered to be an effective strategy of CO₂ mitigation. The dissolution mechanism was experimentally investigated by considering the relation between measured CO₂ surface concentration of hydrate-covered CO₂ droplets and CO₂ solubility. It was made clear that, in the temperature range of hydrate formation, the measured surface concentration decreases with the decrease of temperature and it exactly corresponds to CO₂ solubility. This fact indicates that the dissolution rate of a CO₂ droplet with hydrate film is controlled by the mass transfer rate of dissolved CO₂ at the droplet surface into water and the decrease of dissolution rate is caused by the decrease of CO₂ solubility in the hydrate formation region. Further, in order to clarify the decreasing mechanism of CO₂ solubility, a thermodynamic method was employed. CO₂ solubility was estimated from the relationship between the molar Gibbs free energy of water-liquid CO₂ mixture and that of hydrate and it has shown that the present method could predict the decrease of CO₂ solubility in hydrate formation region fairly well.

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Heat transfer in a rotating square duct was numerically simulated by using the fourth order finite difference method. In order to investigate the effect of the Coriolis force on the turbulence, the large eddy simulation was adopted with a dynamic subgrid scale model. The present results clearly showed the peripheral variation of the wall friction and the heat transfer coefficient : the increased and decreased values on pressure and suction surfaces, respectively. For higher rotation number cases, decay of the turbulence intensity near the leading wall (suction side) was observed. The friction coefficient, C_f and the Colburn's j factor were increased by the effect of the Coriolis force and the increased amount was larger for C_f than for j.

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The effects of angled rib turbulators on the heat transfer of an orthogonally rotating square straight duct were experimentally investigated. The Reynolds number based on mean velocity and hydraulic diameter was varied from 10000 to 20000 and the Rotation number from 0 to 0.08. The leading and trailing walls were rib-roughened with angle-of-attack of 90 or 60 degree. The rib height-to-hydraulic diameter ratio was 0.1 and the rib pitch-to-hydraulic diameter ratio was 1. The results showed that the angled rib case gave higher heat transfer than the results of a 90 deg rib duct and a smooth duct. Judging from the local heat transfer variation, the skewed secondary flow induced by the angled rib seemed to give additional contribution to the heat transfer enhancement. The rotation made the heat transfer of the pressure side higher and that of the suction side lower, although the overall Nusselt number stayed almost constant within the present experimental range.

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In order to derive a possible direction for improvements of an algebraic heat flux model, a priori explorations were attempted by processing the LES data presently performed under various flow and heat transfer conditions including shear-free boundaries. The present calibration has elucidated that the turbulent heat flux vectors obtainable from the simple GGDH hardly align with the simulation results in wall-shear flows with a wall normal temperature gradient of fluids at Pr≥0.71. However, the GGDH returns a quite reasonable approximation for heat flux vectors in shear-free flow regions and/or lower Pr fluid cases. In the former flow cases, it has been found that a further introduction of a tensor expression, consisting of quadratic products of the Reynolds stress tensor, into the gradient diffusion model may improve the predictive performance.

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Heat transfer and fluid flow in smooth and rib-roughened two-pass channels with a 180°sharp bend are investigated experimentally. Ribs are attached on two opposite walls of the straight passages with angles 90°and 60°to the flow. For 60°ribs, four different combinations of rib patterns in both the 1st and 2nd passes are studied. More than 450 thermocouples are utilized to record detailed distributions of local heat transfer coefficients over the four side walls of the entire channel. Flow visualization tests are also conducted. Based on the measured results, the effects of interaction on the heat transfer characteristics between the rib and the bend-induced secondary flows are disclosed. The rib-arrangement which gives the highest heat transfer performance is identified.

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Systematic experiments were conducted on the temperature distribution along the stack in a simulated acoustic-resonance tube refrigerator under various system parameters, as a step of research works to construct fundamental basis for the reliable theory of thermoacoustic refrigerators. The measured temperature distributions were classified into five patterns for reference and were compared with the existing linearized theory. Both measured distribution pattern and discrepancy between the theory and experiments were closely related to Strouhal and Peclet numbers, which have close relationship to forced convection heat transfer. In particular, Strouhal number had a dominant influence on the temperature distribution, and small strouhal number gave good agreement between the theory and experiments. Thus these dimentionless numbers had a high potential for the improvement of the existing theory.

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This paper describes an experimental and theoretical study on the heat transport limits of an osmotic heat pipe operated under the atmospheric pressure, using aqueous polyethylene glycol 600 solution (0.1∼1.0kmol/m³) as the working fluid and 18 tubular-type acetyl cellulose osmotic membranes. As a result, the correlation between the heat transport rate and the osmotic area was revealed, and the effects of the physical properties of the solution and the geometry (i.e. inside diameters of the flow lines, etc.) of the osmotic heat pipe on the heat transport rate were theoretically investigated. Also, the heat transport rate of the present osmotic heat pipe is about 85% compared with that under such an ideal condition that the solution of the average concentration is assumed to be filled in the solution loop.

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We have been developping the more compact cooling unit compared with the conventional cooling aluminum fin and the heat pipe type cooling unit. The aim of this paper is to examine the cooling performance of the cooling unit using multi-stacked radiator cores and a new flow controller which forms refrigerant circulation. We proposed the new simple structure for the refrigerant circulation flow using multi-stacked radiator cores with the holes at the both ends. Further we clarified that the cooling performance greatly improved by the new refrigerant flow controller, compared that the cooling unit is inclined.

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We have developed a new closed two-phase loop thermosyphon with multi-stacked radiator cores and a new flow controller which forms refrigerant circulation. The features are ; (1) more compact and lighter weight than heat pipe cooling units. (2) cooling performance can be easily adjusted by the number of radiator cores according to heat dissipation quantity.

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Linear stability analysis is applied to the lithium bromide aqueous solution flowing down on an inclined flat plate and surface tension-driven instability is investigated. The analytical model includes effects of surface deformation on the long wave instability. The analysis gives neutral instability curves in the long wave region and shows that the thermal boundary condition applied to the bottom wall takes a significant role in the occurrence of the long wave instability. When the bottom wall is isothermal, the long wave instability occurs for a positive Marangoni number. To the contrary, when the bottom wall is insulated, the instability occurs for a negative Marangoni number. This behavior is very important and responsible for the wetness of the plate.

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A method for predicting the local heat transfer coefficient is presented for film condensation of vapor in a spirally grooved horizontal microfin-tube. Based on the flow observation study performed by the present authors, film flow model between fins in the annular flow regime is proposed. For the fin surface, laminar condensate film controlled by the combined effects of vapor shear and surface tension forces is analyzed. While, in the groove, thick condensate film driven by the vapor shear force is taken into consideration. A parameter which accounts for the transition from annular-to stratified flow regimes is also derived. The present and previous local heat transfer data for fluorocarbon refrigerants in the annular flow regime are found by the present numerical analysis to have a mean absolute deviation of 15.1 percent.

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An external pressure wave generated by a magnetic hammer is applied as an explosion trigger to a single or multiple hot LiNO₃ drops which have been in stable film boiling in subcooled ethanol and the process of vapor film collapse is studied by photographic observation and pressure history measurement. The vapor film begins to destabilize within about 0.1ms after the pressure wave arrival to the drop position. At about 1.0-1.5ms later, the vapor film begins to collapse from the lower part. The vapor film initiates to collapse at a portion around the drop after a complex destabilization process. The ripple waves generated near the central part of the drop at the initial stage are supposed to be due to the Rayleigh-Taylor instability because of the wave length. Generation of interface disturbance and that of tiny bubbles or hot liquid fragments are observed, though no penatration of cold liquid jets can not be observed in this experimental condition.

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Experimental study has been conducted on air-water two-phase flows in the evaporator flat channels with a sharp 180-degree turn. In order to achieve high ability of liquid film formation and low flow resistance, the triangular cross-sectioned microgrooves with 0.5mm depth and 0.98mm pitch have been engraved over the channel walls. The local void fractions and pressure drops have been measured in two channels with different groove-inclination angles, 45°and 90°to the channel axis, under four channel attitudes. The microgrooves, in particular 45° microgrooves, are very effective to make uniform distributions of the local void fraction and to suppress the liquid films deficit in the channel. The pressure drops of the micro-grooved channels are only 1.2-1.5 times those of the smooth channel, and they can be well correlated by modified Chisholm's equation irrespective of the channel attitudes.

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Behaviour of particle mixtures was investigated in a liquid-fluidized bed experimentally. In the experiment, two kinds of particles of different diameter, and of the same or different materials, were charged in a fluidization column and fluidized by water. Based on the observation of fluidization, a flow pattern map was proposed using the Archimedes number ratio and the terminal velocity ratio, which classifies the two patterns, i.e. separation and homogeneous mix. Measured mean void fractions of particle mixtures were agreed well with the values calculated from those for each particle independently.

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Characteristics of heat transfer in the rivulet-like liquid film region of an air-water dispersed flow in a heated vertical pipe have been studied. Simultaneous multi-point measurements show that wall-temperature fluctuations in this region are quite large and of low frequency, being compared with those reported previously for single-component two-phase flows, and that such fluctuations are caused by the meandering motion of rivulets. A model for predicting heat transfer mechanism is constructed by introducing the critical liquid-film thickness and the wetting fraction, with which the breakdown of annular liquid film and the subsequent appearance of wet and dry surfaces in the rivulet-like liquid film are handled. It is demonstrated that the numerical analysis based on the present model can predict well the wall-temperature characteristics observed experimentally. It is also shown that there is a clear correlation between the critical liquid-film thickness determined in the analysis and the friction velocity estimated at a liquid-gas interface in the annular liquid film region.

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The present study describes an experiment on natural convective heat transfer from horizontal cylinders to silicone oil or water in a rectangular enclosure. By means of the visualization of temperature distributions by a liquid-crystal suspension method and the measurements of temperature by thermo-couples, obvious thermal stratification and circulating flow were observed. The heat transfer coefficient for the cylinders with thermal stratification and circular flow are estimated. In case of those are weak, as fluid temperature which was located appropriately is assigned to reference, relationship between Rayleigh number and Nusselt number agree with the relation of previous works on natural convection. If those are effective, it is difficult to put in order by former equations.

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The effects of agglomerating particle on the fluidization and heat transfer characteristics around horizontal tube in the gas-solid fluidized bed were experimentally investigated. The inter-particle forces due to the liquid bridges between particles were controlled by change of bed relative humidity. The local particle behavior and instantaneous heat transfer coefficient around tube surface were simultaneously measured. It was revealed that an increase of inter-particle forces results in an increase of void fraction and a decrease of particle velocity and consequently the heat transfer coeficient decreases.

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The cause and effect of fluid type on thermo-fluid pattern of the suppression of the isothermal Karman vortex street to a modified vortex street and a plume-like flow due to positive buoyancy in a circular cylinder wake with an upward freestream of mercury, air and water are made clear by solving numerically of the two-dimensional, laminar, time-dependent continuity equation, Navier-Stokes equations with the buoyancy term, and energy equation. For any type of fluid, the cause of the suppression is an extinction of wake vorticity ; shear layers increases and the wake vorticity decreases due to positive buoyancy. Behavior of the suppression is different each other in mercury, air and water, beacuse an increase of the wall vorticity and a decrease of the wake vorticity are different in those fluid.

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The present study was carried out to reveal the possibility of controlling the ignition delay of hydrogen-air mixtures by applying electric fields. A quiescent stoichiometric hydrogen-air mixture was ignited by a suddenly heated thin wire of nickel or tungsten. DC electric fields were applied between the wire and outer electrode plates parallel with the wire. The mean ignition delay was calculated stochastically from the measured ignition delays which scattered considerably. Both with the nickel wire and with the tungsten wire, positive voltages applied to the outer electrode plates resulted in almost the same change of the mean ignition delay ; The mean ignition delay showed a slight increase at the lower applied voltages, while it became very short at the highest applied voltages. When the nickel wire was used and negative voltages were applied, the mean ignition delay decreased even at the lower voltages. However, it showed little change with the tungsten wire and the negative applied voltages.

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