The behaviors of a single droplet and bubble in dielectric liquid on which the dielectrophoretic (DEP) force was imposed, were studied. It is possible to apply the DEP force to the bubble elimination device under the reduced gravity condition because the bubbles could be moved without contact or disturbance by the DEP force. It was shown that the A. C. (alternating current) electrical field is more preferable than the D. C. (direct current) one because the effect of the electrophoretic (EP) force, whose strength is not definite, is often considerable under the D. C. electrical field. Furthermore, it was observed that the droplets and bubbles in the dielectric liquid moved along a straight path under the nonhomogeneous A. C. field. One-dimensional motion of a single bubble was analytically investigated by solving equation of the motion for the bubble. It was shown that the experimental results were consistent with analytical ones in the region where the electric field was strong.

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One of the next-generation reactors, SBWR (simplified boiling water reactor), is currently under development. It has a large upper plenum surrounded by the so-called "chimney" to keep a driving force of natural circulation. An accurate method for predicting bubble-induced natural circulation is therefore indispensable for the rational design of SBWR. In the present study, the applicability of the multidimensional two-fluid model to bubble-induced transient natural circulation was examined by comparing measured transient flow patterns with calculated ones. The calculation was conducted by coupling a two-dimensional incompressible two-fluid model with available constitutive equations for interfacial drag force, lift force, virtual mass force and viscous force. The 3rd-order new-class TVD scheme was adopted for the convection term of the mass equations to reduce the numerical diffusion of volumetric fractions. As the result, we could obtain good predictions for transient flow patterns. It was also confirmed that the large-scale turbulent flow field induced by the bubble plume can be predicted well without any turbulence model.

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Homogeneous shear flow and forward-facing step flow are studied numerically using the k-ε model based on a statistically derived nonequilibrium eddy- viscosity representation. In this model, the usual k-ε model is extended to include the nonequilibrium effect through the Lagrange derivative of the eddy viscosity. Various computed turbulence quantities are compared with the direct numerical simulation data and the numerical results from the conventional k-ε model. The comparison shows that the present model gives reasonable results for the major characteristic properties of the homogeneous shear and forward-facing step flows.

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The Reynolds stress model and the standard k-ε eddy viscosity model were applied to highly swirl-confined flows in six types of cyclones, which are widely used as centrifugal separators in industrial applications, in order to numerically predict the collection efficiency of dust particles and the pressure loss across the cyclone. The Reynolds stress model can capture the feature of the highly swirling turbulence field accurately, while the standard k-ε model misrepresents the flow characteristics due to the error in its eddy viscosity hypothesis. Prediction of the collection efficiency is, therefore, improved by the Reynolds stress model over the standard k -ε model. In addition, the pressure losses obtained by the Reynolds stress model calculation are in good agreement with experimental data.

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In order to perform a reasonable numerical prediction of two -phase flow based on a multi-fluid model, it is necessary for us to understand whether the model constitutes a well-posed or ill-posed initial-value problem. Otherwise, we cannot take appropriate measures for numerical instability caused by ill-posedness. Hence, mathematical characteristics of several multiphase models such as a one-dimensional three-fluid model, a two-dimensional two-fluid model and a dispersed flow model were examined in the present study. For this purpose, the existing mathematical method for evaluating the well-posedness was reviewed in detail. It was pointed out by this review that the existing method is applicable to a model of incompressible multiphase flow as well as compressible multiphase flow even though the coefficient matrix of the incompressible model is singular. Then, the well-posedness of several multi-fluid models and dispersed flow models was clarified.

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Two-phase flow dynamics plays an important role in understanding the kinetics of nuclear reactors and boilers. Difficulty has been reported in obtaining the numerical solution of two-phase flow by a two-fluid model which was described as ill-posed. In the present paper, all analysis is performed for an ill-posed nonlinear partial differential equation which can be a reasonable simplified alternative to the two-fluid model. We attempt to gain a practical understanding of the ill posedness by numerical implementation of the present equation with the finite difference method.

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Experiments were conducted for two-phase flow (air-water) in a rotating pipe in order to investigate the flow behavior and characteristics. Pressure measurements together with flow visualization were carried out between the inlet and the outlet of the rotating pipe, where in upstream of the rotating section, the flow is fully developed in a stationary pipe. From flow visualization and experimental measurements, a bubble fusion model is proposed and an attempt is made to correlate the data. It is revealed that the correlation based on the model can approximate the experimental data of the friction multiplication factor φ²_L satisfactorily within the range in the present experiment.

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An experimental study has been presented which deals with the deflection and reattachment of a radial turbulent jet (main jet) discharged from a cylindrical nozzle onto an adjacent disk plate in the presence of a lateral controled flow from an annular nozzle, Static pressure distributions along the side wall and across the jet flow were measured using a disk-type pressure hole. The relation between the deflection of the main jet, the reattachment point on the side wall, the mean negative pressure in a recirculating flow region and the curvature of the jet center axis were obtained for various values of the control flow rate and the step height, which describe the length of and the pressure within the recirculating flow region.

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The paper describes flow behavior with an oscillating motion of an impinging jet upon a flame dome head and its reattachment to the casing wall, when a distorted flow is induced at the inlet of the dump diffuser combustor. A laser doppler velocimeter was used for measurement of the time-averaged flow within a sudden expansion region. Measurement of surface pressure fluctuation on the flame dome head and flow visualization by a smoke wire technique with a high-speed video camera were conducted. The jet near the dome head has favorable characteristics about the flow rate distribution into the branched channel. High Reynolds shear stress and turbulence energy are produced near the reattachment region. The jet undergoes an oscillating motion near the dome head with asymmetric vortex formation at the jet boundary.

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The Benard thermal convection field is known to have multiple solutions for a certain Rayleigh number condition. This means several convection flow patterns can be stably sustained without external control force. This study demonstrates that bimodal switching control is possible by means of estimating flow states. A neural network was used to recognize the transition state of the convection flow pattern. In order to change the flow pattern, an unstable feature of Benard convection was utilized. That is, the chaotic nature of wobbling around multiple solutions contributes to fast switching between stable modes. Numerical simulations were carried out to show the ability of the current controlling method.

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Nonlinear phenomena known as steady pressure distribution, steady streaming and steady heat flux induced by finite-amplitude oscillation of an air column in a closed tube are not only investigated from a standpoint of physical interest, but also for engineering applications. Steady pressure distribution provides a valveless standing-wave compressor. Steady streaming and heat flux, which are called acoustic streaming and thermoacoustic effects, respectively, are able to improve heat and mass transfer. These are estimated from the steady part of the second-order term of a perturbation expansion in which the first-order approximation is a sinusoidal oscillation of the air column. In engineering applications, however, nonlinear phenomena induced by finite- amplitude oscillation accompanying shock wave propagation become the subject of studies. The present study deals with numerical analysis of the nonlinear phenomena described above. In this case a numerical scheme with stability and high accuracy is required. In the first step of this study, in order to examine the numerical method, nonlinear deformation of pressure waves and steady pressure distribution produced in the closed tube are investigated by one-dimensional analysis. Calculated results agree well with experimental results.

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Steady streaming, known as acoustic streaming, is one of the nonlinear phenomena produced by strong sound waves. This type of streaming is driven by means of acoustic momentum flux in an attenuating sound field. When a strong standing wave is produced in a closed tube by finite-amplitude oscillation of the air column in the tube, the propagating wave is attenuated by friction at the tube wall. This type of oscillatory flow produces acoustic streaming. The velocity of streaming is estimated from the steady part of the second-order term of a perturbation expansion in which the first-order approximation is a sinusoidal oscillation of the air column. However, finite-amplitude oscillation of the air column gives rise to shock-wave propagation in the tube. In order to estimate acoustic streaming produced by finite-amplitude oscillation, it is necessary to analyze the response of the oscillatory boundary layer to shock waves in detail. The present paper deals with numerical analysis of the acoustic streaming described above. In the previous paper, the fourth-order spatial difference method was examined for analysis of finite-amplitude oscillation. This method is expanded for two-dimensional analysis of acoustic streaming in this paper. Calculated results show velocity distributions in the oscillatory boundary layer and structures of steady streaming for various amplitudes of oscillation.

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Aerodynamic forces generated on a three-dimensional bluff-body with a slanted base, have been experimentally investigated in a low-speed wind tunnel. The Reynolds number based on the whole length of the model, ranged from 1 × 10⁶ up to 2.76 × 10⁶. In order to clarify the cross-wind effect, yaw-sweep operation was executed. As a result, nonlinear aerodynamic characteristics with hysteresis of drag and lift forces in the yaw-sweep, were found in the case of the slanted base angle θ of 30 degrees. Two different flow patterns appearing at θ = 30 degree were revealed by using flow visualization and pressure measurement. These results show that the hysteresis phenomenon is due to the change of the flow structure : from the closed-type flow separation to the open-type flow separation.

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An eccentric vortex plays an important role in cross-flow fans. Experiments were carried out to study the balance of vorticity supply and diffusion in the eccentric vortex. From the consideration of the measured distribution of vorticity, a diffusion model for the eccentric vortex is proposed. In this model, vorticity is supplied to the eccentric vortex region by the circumferential change of impeller blade circulation and it is diffused to the through flow region with an effective viscosity. The effective viscocity, which is 300 times as large as the molecular viscosity of the fluid, is almost independent of the flow rate. Quantitative discussions are presented as to the energy transfer from the impeller to the fluids in the recirculating and through, flow regions, and as to the work transfer between these regions owing to the shear stress. Numerical simulation with the effect of vorticity diffusion, the random walk model, were carried out by using a value close to that of the measured effective viscocity. Calculated flow fields are in good agreement with experimental results.

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In our country, some hypersonic wind tunnels for development of space planes and supersonic transports are now under construction and planned to construct. For designing these wind tunnels, it is indispensable to make use of CFD technology. This paper describes the results of a numerical simulation of the flow passage of a hypersonic wind tunnel. The flow from the hypersonic nozzle, which had exit Mach number of 7. 0, to the supersonic diffuser exit of the hypersonic wind tunnel in National Aerospace Laboratory (NAL) was calculated using 3D Navier-Stokes code with q-ω model of turbulence by T. J. Coakley. The calculated results were compared with the experimental data which had been obtained by NAL. Comparison between experiment and calculation showed a reasonable agreement. As for the nozzle, the effect of the wall temperature upon the nozzle exit Mach number distribution was investigated by analysis.

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An analysis is made on diffraction of plane waves by a corner. Basic equations of the analysis are linearized gasdynamic equations which are considered to be valid for flow fields induced by weak shock waves. Analytical expressions are obtained for velocity fields as well as density fields of diffraction of plane waves by a corner. Numerical examples of the analysis show that the velocity tends toward infinity at the apex of the corner although neither the density nor the pressure has singularity there. Numerical simulations are conducted for diffraction of weak shock waves on a corner at 270 degrees employing the explicit TVD finite difference method in conservation form. The analytical results are compared with computed results of simulations. Good agreement is obtained between them except in the neighborhood of the apex of the corner. In the computed flow fields, a vortex is observed to be generated and attached just behind the apex of the corner.

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In the preceding papers, we proposed an analytical method based on the two-dimensional discrete vortex method for a bending propulsion mechanism in water, such as fish or cetaceans, and investigated the characteristics of energy consumption and propulsive efficiency. In this paper, we extend the proposed method to three-dimensional flow based on the three-dimensional discrete vortex method in order to improve the precision of analysis. It is found that analytical values of the propulsive speed obtained from three-dimensional analysis show better agreement with the experimental values than those obtained from two-dimensional analysis. It is also found that the difference between values obtained using three-dimensional analysis and those obtained using two-dimensional analysis is not as great for propulsive efficiency as for propulsive speed.

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When plasma parameters are practically estimated from the detected current-voltage curve of a Langmuir probe, a significant measurement error is generated mainly due to the time dependent sheath characteristics. A new technique is proposed here to compensate the sheath time dependence by controlling the time rate of externally impressed probe voltage with sawtoothed waves. The obtained result shows that the present method allows acuurate mesurement of the plasma parameters in weakly ionized plasma fields, with high speed and reproducibility.

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The accuracy of 3-D Kalman filter PIV in high-particle-concentration flow fields is quantitative-ly investigated. 3-D PIV measurements with many "ghosts" are numerically simulated for accuracy tests. The number of time steps considered in Kalman filter particle tracking is increased in order to exclude ghosts, which makes it difficult to improve spatial resolution of 3-D PIVs. It was confirmed that by increasing the number of time steps, the particle trackability of the 3-D Kalman filter PIV was maintained and the ghost exclusion rate was markedly improved, even when the particle concentration in a measuring region was dense. As a result, 3-D measurements with higher spatial resolution can be attained by means of Kalman filter particle tracking more than four time steps.

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Sonic booms which were generated by the entrance of a high-speed train into a tunnel were experimentally reproduced using a scaled tunnel sonic boom simulator, whose test section was a tube with diameter 40 mm and length 25 m. An 18-mm-diam., 200-mm-long cylindrical piston was launched into the test section, so that a shock wave was emitted from the exit of the test section. An impulsive pressure wave, that is, the source of the sonic boom, was experimentally reproduced. A hood installed at the entrance of the test section effectively delayed the formation of the shock wave, thereby reducing the sonic boom. This method was effective in the range of relatively low piston speeds. By installing a 0.5-m-long porous wall at the exit of the test section, the pressure gradient of the shock wave became finite and the peak overpressure was decreased. Even in the case that the wall was only partially covered with the porous material, the poromeric effect was significant, in particular, for high piston speeds. When the hood at the entrance and the partially installed porous material on the exit wall were combined, the reduction of the peak overpressure became 50 to 80% in the range of the piston speeds from 60 m/s to 100 m/s.

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We attempted to elucidate the mechanism of fan noise reduction at low frequencies below 1000 Hz through cavity and acoustic treatment. The experimental data showed that significant reductions were obtained at several frequencies while no reduction was obtained at others. By the numerical analysis conducted in this paper, it might be concluded that such phenomena were caused by the longitudinal mode of sound waves travelling in the cavity.

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A numerical method for simulation of unsteady flow in an air-lift pump, which is the main element of a deep-sea mining system, has been developed. The authors have proposed an iterative scheme for implicit time marching of density and pressure, and performed a numerical simulation of air-water two-phase flow using a drift -flux model. In the present paper, improvement of the scheme, especially for the convection term, is described. First, convective terms are discretized based on the velocity component of each phase. Second, the finite difference method, which has excellent energy conservation properties, is applied. Then, the upstream-shifted interpolation technique is introduced. Numerical results for both the unsteady features and the steady-state flow field show reasonable agreement with the experimental data obtained with the air-lift system of 200 m depth.

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In order to clarify the detailed behavior of the pulp fluidization in the operation of an MC pump, some effective factors (consistency, degassing pressure, rotational speed and diameter of the booster blade) were discussed. In the medium consistency field, a successful method for deciding the limited consistency as well as the maximum possible consistency was also found.

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The effect of the density inversion of water on the melting process of ice in porous media confined in a rectangular cavity was numerically examined. The cavity consisted of a hot vertical side -wall and three insulated walls. In the calculations, the temperature of the hot wall was changed from 40°C to 16°C, and the Darcy number from 4.01×10^-5 to 5.01×10^-6. The timewise variations of the velocity field, the temperature field, the melting fraction and the mean Nusselt number over the hot wall were compared. Complicated flow patterns appeared for the hot wall temperatures of 8°C and 12°C, and the mean Nusselt number over the hot wall became minimum for the hot wall temperature of 8°C. The change in the Darcy number largely affected the melting process for the hot wall temperature of 16°C ; however, the change was very slight in the case of the wall temperature of 8°C.

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Experimental study has been performed using two different types of multipass tubes, one with 4 vertical upward passes attached to a horizontal main pipe and the other with 5 horizontal passes placed to a vertically oriented main pipe. Passes had 6 [mm] I. D., and the I. D. of main pipes were 20 [mm] for the vertical type and 6 [mm] for the horizontal type. Multipass tubes simulated evaporators for air-conditioning systems, and the refrigerant R 11 was used as the working fluid. Vapor and liquid flow rates at each pass were measured under various conditions of two-phase mixture at main pipe inlet, i. e., inlet flow rate and quality. Results suggested that measured values of flow distribution ratio presented a marked distinction between the vertical and horizontal types. On the other hand, in spite of different pass orientations, the same data trend that the flow distribution is dominated by the main tube inlet flow condition, was observed, and the flow division ratio was estimated in terms of both phase flow rates before the junction. Based on these results, the flow split model was suggested and an attempt for the prediction of flow distribution was made.

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Numerical calculation of behavior of a spherical ice particle (motion, melting and solidification) in flowing supercooled water inside a cooled circular tube was performed. By assuming that the single ice particle moved from its position on the upper or lower cooling surface in fully developed laminar flow, the variation of ice particle radius during the moving process could be calculated under various Reynolds numbers for water, initial ice particle radii and cooling conditions. For the particle motion in flowing water, the numerical results were in good agreement with the measurements obtained from visualization using paraffin particles (density : 926 kg/m³). It was found that the initial ice particle radius, Reynolds number of water and the cooling wall temperature exerted pronounced effects on the ice particle radius at the tube exit ; however the inlet temperature of the flowing water had little effect on the radius at the tube exit.

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Water flash evaporation in vaccum exhibits high performance of heat exchanger and is an important means especially for spacecraft. As the first report, this paper mainly describes the verification of the relation between the heat transfer coefficient and the saturation temperature in [Ref. (1) ] which is fundamental and essential for the phenomena mentioned above. The results show that flash evaporation has better capablities of cooling under low pressures, especially below the triple-point pressure of water than the mentioned in [Ref. (1) ], and that the phenomenon below the triple point pressure is so unstable that it may cause rapid icing ; hence, flash evaporation is unsuitable for use under such a condition and finally that the maximum heat flux exists above the triple-point pressure for the target cooling temperature, so the pressure control is necessary for the flash evaporation cooling with high efficiency.

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This paper investigates the solidified-shell formation process during the dipping process of a cooled solid surface into a melt pool. Since the shell formation process during this dipping process is related to the dynamic behavior of the meniscus contact line, the solidification process may be different from the usual solidification process on a stagnant cooled surface. The solidified shell obtained in this experiment has many surface defects on the surface. The results from visual observation of the shell formation process show that the shell does not grow continuously in the casting direction but is formed as a vertical pile of the horizontal shell units resulting from the following sequential process ; collapse of the meniscus, appearance of a locally solidified shell and propagation of the local shell along the contact line. Experimental results indicate that the formation of the surface defects is considered to relate to this dynamic process.

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The evolution of two- and three-dimensional vortical structures in an initially nonpremixed temporally developing reacting mixing layer is simulated by solving the time-dependent, compressible Navier-Stokes equations. The result of the numerical simulations shows that, as the evolution of hydrodynamic instability is suppressed, and the vorticity and the amount of chemical product are reduced by the baroclinic effect and volumetric expansion due to reaction heat release. In the case of temperature dependent diffusivities, the vorticity is reduced as well, in comparison with the temperature-independent case. Structures of the cores, ribs and legs are observed in the three dimensional mixing layer. Similarities between the distributions of spanwise vorticity and product mass fraction, and between those of streamwise vorticity and reaction rate, can be identified when the pairing process is saturated which may imply that the streamwise vortical dynamics plays an essential role in the progress of the chemical reaction.

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In order to clarify the behavior of falling films in the absorber of absorption chillers, numerical analysis of the falling films in the transition regions was performed. Since the treatment of the surface becomes difficult in x-y cooridinates, y coordinates are normalized by the film thickness to fix the surface. The fundamental equations are changed into conservative forms by the method of Shyy et al. before discretization. The critical wavelengths for an aqueous solution of lithium bromide and water were determined by the proposed method. The film Reynolds numbers were varied in the range of 10-200. For a few cases in the unstable region, the waveforms are calculated for the initial disturbance of 10% of average film thickness. As they grow, slopes of waves become steeper at the front, and for Ref =100, film is divided into a thin base film of uniform thickness and a liquid mass sliding on it.

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A method of particle sizing of irregularly shaped aerosols by dynamic light scattering was established. The feasibility of the method was tested with irregularly shaped aerosol particles modeled by diesel soot and mass-equivalent spherical particles. From the analysis on the effects of the scattering angle and the variation of particle shape factors, we proved the effectiveness of backward dynamic light scattering for the in situ measurement of diameter and mass concentration of irregular aerosol particles.

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Experiments have been conducted for turbulent channel flow obstructed with a square rod placed perpendicular to the flow. The streamwise distributions of the similarity parameter 2St/Cf were examined for four different space ratios between the square rod and the channel wall. The dissimilarity between momentum transfer and heat transfer was intensified in the case when the square rod was slightly detached from the channel wall. Simultaneous measurements of velocity and temperature were taken by making use of hot-wire and cold-wire probes in the case when the space ratio, y'=0.7. Wavelet analysis applied to the velocity and temperature signals was found effective for the extraction of periodically changing patterns of flow and thermal fields. Through the analysis, heat transfer enhancement was related to the intensification of cold and hot interactions toward the wall and away from the wall, respectively, which occurs depending on the existence of periodical change of flow structure.

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Functionally gradient materials (FGM) with distributed properties have attracted special interest as advanced heat-shielding/structural materials for space applications. The objective of the present study is to derive an analytical solution of the temperature response in a multilayer-type FGM, the front surface of which is subjected to partial, stepwise heating. Heat losses from the front, rear, and side surfaces are also considered. The Laplace transformation has been used to obtain the analytical solution. This solution is expected to elucidate the dependence of the temperature response on various parameters, such as thermophysical properties and heat losses. It is also expected to reduce the calculation time to obtain thermal stress and/or strain in large-scale numerical calculations. Appropriateness of this solution has also been demonstrated by comparing the present results and the experimental results obtained by the National Aerospace Laboratory, Japan.

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The effect of dimensions of a three-dimensional rectangular heated body on close-contact melting is studied numerically and analytically, taking into account the temperature distribution in the heated body in a constant temperature environment. The critical melting velocity, below which there exists a steady melting state, is found in an analytical form. The relationship between the melting velocity and the dimension of the heated body under influence of gravity is obtained using a finite difference method and scale analysis. The dependence of dimension on the melting velocity is distinguished into three cases. In the case where the width of the heated body is large compared with its height, the dimensionless melting velocity decreases slowly as the ratio of width to height increases. In the opposite case, the dimensionless melting velocity is constant. In the case where the height is slightly larger than the width, the melting velocity depends on the ratio of height to width in a complex manner. In the case where the width and the height are of the same order, the steady melting phenomenon occurs near the critical melting condition. Thus, this case yields an effective method for melting the phase-change material.

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Critical heat flux (CHF) under circumferentially nonuniform heating conditions was experimentally investigated using direct current heating of a stainless steel tube. CHF in a smooth tube without internal twisted tape under nonuniform heating conditions was slightly higher than that under uniform heating conditions because of the lower average qualities at the tube outlet under nonuniform heating conditions than those under uniform heating conditions. CHF in tubes with internal twisted tape under nonuniform heating conditions was much higher than that under uniform heating conditions, though the average qualities at the tube outlet were the same for both cases. The higher CHF under the nonuniform heating condition was explained by the alternating development and disruption of the bubble boundary layer. The circumferential location of burnout initiation was observed by video camera, and it was confirmed that CHF started at the point where the bubble boundary layer developed the most.

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A quantitative analysis of critical heat flux (CHF) under countercurrent flow limitation (CCFL) or flooding was successfully carried out using the existing experimental results for the vertical circular, rectangular and annular channels, applying the criteria, which was proposed by the author, that the CCFL condition could be determined by maximizing the water mass flux falling down in the vertical channels with respect to the water film thickness and the model of dryout of water film flow at the CHF point. It was clarified that the analytical results give good predictions of the existing experimental results of vertical channels, identifying the factors determining the CHF under the CCFL conditions.

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A quantitative analysis of critical heat flux (CHF) in upward saturated two-phase flow in vertical rectangular channels under atmospheric pressure was successfully carried out by applying the completely separated two-phase flow model to the existing model of vapor blanket over the thin liquid sublayer on the heated walls at the CHF point. The analytical results give good predictions of the existing experimental results in vertical rectangular channels with 1.03 to 5.0 mm channel gap, 40 to 51 mm channel width, 350 to 750 mm channel length and 20 to 88°C inlet subcooling, and identify the effects of predominant parameters on CHF in upward saturated two-phase flow in vertical rectangular channels.

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Flow and solidification characteristics of tetradecane droplets [melting point of 5.8°C, latent heat of 229.1 kJ/kg, density of 770 kg/m³ (at 6°C) ] ascending in ethlene glycol water solution of 30 weight percent at low temperature were investigated experimentally in order to examine the possibility of a liquid-liquid or liquid-solid direct-contact-type latent cold heat storage system. A new type of solidification rate meter is proposed in the present study. As a result, some interesting freezing behaviors of droplets were observed by the visualization technique. From the measurements of solidification rate of tetradecane droplets, the relationships between the solidification rate and some experimental parameters were clarified.

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A numerical analysis has been made on a reflux condensation of binary vapor (R 113+R 11) in a two-phase closed thermosyphon in order to predict its variable conductance behavior and to clarify the detailed mechanism. The flow, and heat-and-mass transfer in the vapor phase and the condensate liquid film were solved simultaneously for the axisymmetric two-dimensional field in a circular pipe. It was shown that, in the case of smaller heat load, non-condensing region is formed in the upper part of the condensing section due to the accumulation of more volatile component of vapor (R 11), and the length of the non-condensing region increases with the decrease of heat load. As the result, the temperature difference between the inlet vapor and the condensing wall is kept nearly constant for varying heat load. The calculated temperature difference and system pressure were compared with experimental data, and reasonable agreements were obtained.

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The resonance tube refrigerator developed by Wheatley et al. has given rise to great interest in the field of refrigeration technology. Fundamental investigation has been conducted on the resonance tube refrigerator using a simplified model. The temperature response of the stack in the tube has been visualized by using a thermosensitive liquid-crystal sheet. The visualized image has demonstrated the heat-transfer mechanism based on the thermoacoustic theory. The temperature distribution in the tube has been discussed with reference to the resonance tube configuration, the mode of resonance and the working fluid property.

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In the analysis of water wall temperature in a thermal electric power plant, we must grasp many thermophysical properties correctly, such as wall emissivity and absorption coefficient of gas. However, their measurement during operation of the plant is very difficult and we cannot grasp them accurately. For this reason, we estimate the effect of thermophysical properties on the temperature of the water wall and thermal efficiency.

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The present work is a continuation of our previous study to obtain a fundamental understanding of instabilities of a flame front propagating in a constant-volume combustion chamber. In this report, attention was focused on effects of dilute gases on this phenomenon. Experiments were conducted in a disk-shaped constant-volume chamber of 100 mm diameter and 30 mm height with a window. The flames were visualized by instantaneous schlieren photography. It was found that the instabilities arise for lean hydrogen/oxygen mixtures diluted with argon as well as helium, wich can be explained as thermodiffusive effects. For methane or propane/oxygen mixtures, the diluent plays an important role. Using argon as a diluent renders the flame unstable in accord with the thermodiffusive theory, while using helium renders it stable which cannot be explained by this theory. For these mixtures diluted by helium, initial disturbances might be suppressed by viscosity.

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The effects of the temperature of the stagnation surface (surface temperature), the Lewis number of the deficient reactant and preheating of the unburned gas on the characteristics of premixed flat flames with heat loss stabilized in the stagnation flow were numerically examined in order to utilize the heat from the flame effectively and to develop new types of domestic burners and heaters. Then, the characteristics of convective heat transfer to the stagnation surface from the flame were discussed. (1) With an increase in the surface temperature T_w and in the preheat temperature of the unburned gas T_e, and with a decrease in the Lewis number Le, the flame temperatures at the same value of the first Damkohler number D_I are increased. (2) With an increase in T_e, and with a decrease in Le and T_w, the heat flux utilized from the flame at near-limit of the extinction is increased. (3) The characteristics of heat transfer to the stagnation surface in the case in which the premixed flat flame is stabilized in the stagnation flow are superior to those in the stagnation flow in which only the burned gas flows. (4) In order to increase the heat flux utilized from the premixed flat flame stabilized in the stagnation flow, it is necessary to maintain higher flame temperature and to stabilize the flame near the stagnation surface. Therefore, preheating of the unburned gas and use of the premixed gas with Le < 1.0 are effectual in improving characteristics of heat transfer to the stagnation surface.

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Combinations of swirl flow and tumble flow generated by 13 types of Swirl Control Valves were tested using both an impulse swirl meter and LDV. The LDV used in this study was developed especially for engine research to realize stable beam crossing at very narrow beam waists to achieve high spatial resolution measurement. It is shown that tumble flow generates turbulence in the combustion chamber more effectively than swirl flow, and that swirl reduces the cycle variation of mean velocity in the combustion chamber. Performance tests are also carried out to determine the combustion characteristics under the condition of homogeneous charge. Tumble flow promotes combustion to a greater extent than expected from its turbulence intensity. It is also shown that the lean-limit air/fuel ratio is not strongly related to cycle variation of mean velocity but to turbulence intensity.

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An advanced method of flame stabilization by combining a recessed burner with a circular combustion chamber, is proposed. This type of combustor is expected to be effective for improving flame stabilization, if it is set in a part of turbulence region in a large-scale combustor. Nozzle diameter is kept constant, while inner diameters of combustion chambers are varied. Three kinds of combustors having area ratios of 3.2, 9.0 and 26.0 are used, where the area ratio is defined by d²₂/d²₁ (d₁ ; the nozzle diameter, d₂ ; the inner diameters of combustion chamber) . States of combustion are examined according to time-averaged combustion temperature profiles. As a result, it is found that the proposed combustor has an optimum area ratio of 9.0 among these scale of combustor.

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Noise analyses using sound intensity and other parameters were carried out for the purpose of reducing the noise which increases with the high-intensity combustion of domestic water heaters, and the quantification of sound sources and the propagation path of noise was carried out. Furthermore, based on the results of these analyses combustion noise, which is the main part of low frequency was, examined, and it was clarified that the compatibility of load increase and noise reduction can be attained by properly combining the primary air ratio and secondary air ratio, where in the case of the primary air ratio being constant, the secondary air ratio exerts am influence on the intensity of noise by the second to the fourth power. Additionally, it was shown that the dominant sound emitted during combustion is the pipe resonance where one end is closed and the other end is open, and the effective method of reducing dominant sound was shown.

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To reduce the dominant noise which is generated in small combustors of domestic water heaters, the phenomenological analyses of dominant sound were conducted, and the factors which exert an influence on the dominant sound were clarrified. In the loudspeaker experiment, it was clarified that the frequency of dominant sound coincides with the resonance frequency determined from the system of combustion chambers, and the oscillation of combustion chambers themselves increases the level of dominant sound. Moreover, the relationship of the input of fuel gas and air ratio with the frequency and level of dominant sound was determined, and the behavior of the transient dominant sound wihch arose at the time of ignition was clarified. Furthermore, based on the results of these analyses, the structure and the dimensions of various parts which are effective for the reduction of dominant sound were shown.

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A numerical model has been presented to analyze unsteady thermal boundary layers with exothermic reaction in spark ignition engine combustion chambers. The numerical technique features an additional computational grid system in the cells adjacent to the wall which allows us to perform the computations in a practical length of time with boundary layer resolution. The combustion model employs a three-zone concept for a temperature field in each cell and has a two-stage process. The model describes not only the combined turbulence-reaction-controlled combustion in the near-wall region, but also the turbulence-controlled-combustion in the core region. The present model reproduces the experimental evidence that local wall heat flux peaks intensify as the wall temperature increases, while the law of the wall does not describe this fact.

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A transparent collimating cylinder (TCC) which is capable of schlieren observation through its cylindrical inner surface is reported. The outer surface was designed in such a way that it does not disperse parallel light rays both inside and outside the cylinder. Numerical simulation of light rays passing through the TCC revealed the required fabricating precision to obtain a viewing field of 95% of the cylinder diameter. Based on this simulation, a quartz TCC was fabricated and used for an engine cylinder to confirm its schlieren potential. High-speed schlieren images of the early stage of flame propagation and unburned gas motion were obtained with good clarity. Consequently, TCC proved to be a new effective tool for visualization studies of the internal combustion engine.

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