The purpose of this study is to clarify the effectiveness of sintered metal in cavitation erosion. For measurement of cavitation erosion, a decrease in the test time is desirable because present methods are time-consuming. Accordingly, the use of a fragile material for cavitation erosion experiments is proposed in this study. Sintered metal was chosen as the fragile material and the cavitation erosion experiment was performed using the rotating disk method. It was confirmed that the erosion characteristics of our sintered metal were similar to those of other metals and that the erosion data could be obtained in only one or two hours. The sintered metal was also applied to a pipe wall exposed to cavitation due to a butterfly valve. From the measurement of erosion under the cavitation occurring at maximum noise, it was found that the volume loss was largest at a valve opening of 40∼45 degrees.

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In order to study the effect of cathodic protection on cavitation erosion, a series of experiments using 3 percent aqueous sodium sulfate solution is carried out by means of a vibratory erosion apparatus, and the erosion patterns on an eroded specimen surface are observed using a scanning electron microscope (SEM). The results show that the mass loss decreases markedly with increasing cathodic current. Although the process of cavitation erosion development shows a similar tendency whether cathodic current is applied or not, the erosion rate is markedly suppressed by hydrogen gas evolving from the cathodic specimen surface, resulting in a monotonic decrease in mass loss.

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Simultaneous measurements of a bubble collapsing behavior and a bubble impulsive force were conducted near a solid wall behind a circular cylinder. The appearance of a bubble was recorded using a high-speed video camera. The impulsive force was measured with a pressure sensor made of piezo-ceramics. As a result, it was found that the bubble collapsing behavior has three patterns. The first pattern is a quasi-spherical bubble collapse at a distance from the solid wall. The second one is a bubble collapse accompanied by a severe impinging motion toward the solid wall. The third one is a bubble collapse in which the bubble does not lose its long shape. According to some discussions, the second pattern has an intense impulsive force and provides experimental evidence of the existence of high speed flow toward the wall. Hence, this impinging collapse pattern of a cavitation bubble plays an important role in a highly impulsive force, as well as the first pattern of a quasi spherical collapse.

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The vortex method is powerful for analyzing high Reynolds number flows, and so it is applied to many fluid flow problems. Using this method, the velocity field is obtained from the calculated vorticity field using the Biot-Savart formula. However, the pressure field is not obtained directly. The pressure field has been calculated by (1) using the unsteady Bernoulli equation, (2) solving Poisson's equation using the finite difference method and (3) solving Poisson's equation using the boundary element method. In the present work we show that (1) the pressure field can be analytically obtained on the fluid flow around a two-dimensional circular cylinder, (2) this approach is easily applied to the flow past an arbitrary body, provided that the conformal mapping function is given, and (3) the mapping function is easily obtained when the vortex method is combined with the panel method. To confirm the validity of the present approach, numerical calculations are carried out for the flows around circular and elliptical cylinders using a classical vortex method and a high accurate vortex method. The numerical results show that the pressure distribution around a circular cylinder is in good agreement with that obtained using the unsteady Bernoulli equation.

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It is well known that the fluid dynamics of arterial blood flow play an important role in arterial disease. Periodic blood flow through a stenosed tube and a locally expanded tube was analyzed numerically. The fluid is assumed to be non-Newtonian, and the flow is assumed to be periodic, incorpressible and axisymmetric. It is found that the vortex downstream of stenosis or expansion is strongest at a certain frequency, which is called resonance of vortex. The flow pattern, sparated region and the distributions of pressure and shear stress at the wall are obtained. The results show that the resonance of vortex, which has great influence on the physical quantity of flow at the wall, occurs in both tubes. The mechanism of the resonance of vortex can be explained by a balance of forces between pressure and friction at the wall.

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One interesting phenomenon in a vertical bubbly flow is that bubbles sliding near a wall can exit under certain flow conditions. It has been reported that the lift force pushing the bubbles into the wall is generated by a bubble moving with slip velocity. We present an experimental study of bubble configuration in a gas-water bubbly flow under microgravity conditions carried out using on underground drop tower at the Japan Microgravity Center. The purpose of the experiment is to clarify the effect of reduced slip velocity between the gas and liquid phases on bubble configuration when the conditions vary from normal to microgravity. The bubble configuration, that is the diameter and position of the bubbles in the tube cross section, has been measured in detail using a stereo imageprocessing method (SIM). The results showed that the void fraction profile changes from a saddle shape that has a local void peak near the wall in sliding bubbly flow under normal gravity conditions before the drop, to a parabolic shape or a power-law shape that is approximated by a power-law function in core bubbly flow under microgravity conditions. The void fraction profile can be explained by simulation analysis.

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Direct numerical simulation of a mixing layer using a 4th order central difference scheme is conducted and a transport phenomenon of momentum is discussed by the database obtained from the simulation. Retardation of momentum transport in the initial region of the mixing layer is pointed out and its mechanism is discussed. Retardation of momentum transport originates in the feature that the effect of the velocity-pressure-gradient correlation term overcomes that of the production term in the (u'v')^^^- transport equation. This phenomenon is discussed in detail, where the secondary flow induced by the interaction between the vorticies is considered to have a large effect on the momentum transport.

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A method is proposed for analyzing the swimming motions of bacteria. It is assumed that bacteria consist of a spherical cell body and several rotating flagella. The forces and torques exerted on each flagellum are evaluated in a coordinate system fixed with respect to the flagellum using the resistive force theory. They are transformed into a coordinate system fixed with respect to the cell body. Then, the velocity and angular velocity of the cell body are determined by assuming the condition that the net force and torque on the bacterium are zero. This method is applicable to the motion of bacteria with rotating flagella in any form of curve and attached to any point on the cell body. A numerical example shows that the trajectory of bacteria with a flagellum slanting from the radial direction of the cell body is a double helix, and the mean velocity of the bacteria depends slightly on the slant angle. Another example shows that bacteria with two flagella attached symmetrically to the center of the cell body and rotating in opposite directions swim faster than single flagellate bacteria.

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The purpose of the present research was to establish (1) the levitation process of a nonconducting liquid in material processing and (2) the drug transportation technique in blood vessels in the field of medicine. In this study, the behavior of a diamagnetic liquid droplet in nonuniform magnetic field was observed experimentally using a simple model consisting of a silicone oil droplet and a magnetic fluid. The influences of magnetic field strength, magnetic field distribution, droplet volume, density and surface tension of magnetic fluid on the shape and position of nonmagnetic droplet levitation were examined. Then, numerical analysis was carried out under various conditions to clarify the dominant nondimensional parameters. The experimental results and the numerical ones showed in good agreement.

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The results of an experimental study of magnetic liquid surface responses in a container subject to magnetic field and vibrating field were presented and discussed in detail. Experiments were performed on a vibration-testing system which provided lateral and longitudinal excitation. The effect of the magnetic field gradient on liquid surface motion in an open circular cylindrical tank was noted. Data obtained for the cylindrical tank were also compared with numerical results based on the linearized theory. Nonlinear phenomena were found for the symmetric free surface mode (0, 1) in longitudinal liquid sloshing. Details of surface responses of a magnetic fluid in the cylindrical tank excited longitudinally under an applied magnetic field were revealed. Some similarities and differences between single spike oscillation and the symmetric free surface mode (0, 1) of magnetic liquid sloshing in the presence of a magnetic field were also investigated.

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We study numerically a model of fluid membrane with fixed triangulation, where the number of bonds per molecule is made as uniform as possible. The action of the model is dependent on the triangulation of surfaces. We pay special attention to whether or not the observables are dependent on the triangulation at the critical point of the second-order phase transition. By making use of different triangulated surfaces, we observe that the specific heat is divergent at the critical point and that the observables of the model seem to be independent of the triangulations. From the peak height of the specific heat, we obtain a critical exponent of the phase transition. We see that the critical exponents of the models of fixed triangulation and of the dynamical one are not identical.

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In this paper, we discuss the stability of the convergence of a nonlinear iteration procedure which may be affected by a large number of numerical factors in a complicated way. A numerical parallel channel flow problem is solved using the finite element method and the Newton-Raphson iteration procedure. The numerical factors, on which we focus attention in this study, are the aspect ratio of the channel and the number of divided meshes. We propose a nondimensional value, which is obtained from the Reynolds number, the aspect ratio and the number of meshes. The results of the numerical experiment show that the threshold of divergence in the iteration is indicated clearly by the present nondimensional value.

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The finite-element method is one of the widely used numerical methods for complex geometries. However, no research on the accuracy of various kinds of deformed elements used in the finiteelement analysis has been made thus far. In this study, the error analysis technique initially proposed by one of the authors is applied for three-dimensional convection-diffusion problems. Firstly, the Galerkin formulation and the modified Galerkin formulation are investigated. Then, the numerical accuracy of various kinds of deformed elements is evaluated theoretically. A regular tetrahedral element and nonuniform tetrahedral and hexahedral elements are investigated and we find that a regular tetrahedral element gives the highest accuracy. Finally, we show the general agreement between the error analyses and the numerical simulation results.

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In a compact heat exchanger, a gas-liquid two phase mixture flows in a noncircular channel with a narrow cross sectional area. Therefore it is necessary to clarify the flow phenomena and the pressure drop in such a small channel. In the present experiment, we used capillary vertical rectangular channels. The shorter side length is constant at 1 mm, and the longer side length of each duct is 1.0, 2.0 or 5.0 mm. The effects of the aspect ratio of the channel on the velocity characteristics, flow patterns and two-phase frictional pressure drop are discussed. The modified correlations for the estimation of frictional pressure drop were obtained by taking the effect of aspect ratio into account. These formulae agree well with the experimental data.

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A stereoimaging technique was applied to the measurement of size and velocity of nonspherical fine particles. This technique was previously developed by us and verified by the measurement of transparent glass beads falling in a pipe. In the present study, several transparent/opaque and spherical/nonspherical particles, each approximately 100 μm in mean diameter, were measured to demonstrate the applicability of this technique to a wide range of particle shapes and particle materials. The measured size distributions were in reasonable agreement with those measured separately by a microscopy. The three-dimensional velocity measurement was also shown to give reasonably good results. Furthermore, the measured characteristics of the particle shape such as the maximum length, the width and the aspect ratio were compared with those obtained by the microscopy. Some statistical features of the attitude of falling particles were also discussed.

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The study of flow around a circular cylinder is one of the most important problems in not only basic research but also analysis of a complexity object. No numerical simulation of shock wave diffraction around circular cylinder has been carried out thus far. Under supersonic flow in particular, the numerical result is insufficient for the lack of resolution in the complicated flow around passing through circular cylinder. Therefore, we used unstructured adaptive meshes which can automatically divide elements only in the region of large variation. In the present paper, unstructured adaptive meshes were applied to MUSCL (monotone upstream centered scheme for conservation laws). Shocked flows around circular cylinder were investigated using the scheme. The reflection process was analyzed from the numerical results. The effects of limiter function were examined.

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The effects of base suction on the near wake of a flat plate with a blunt trailing edge were examined by the discrete vortex method. The Strouhal number of vortex shedding was independent of the suction slit height in the range of suction flow rate below a certain critical value. Above the critical value, the Strouhal number progressively decreased with the suction flow rate, and the decreasing rate was dependent on the suction slit height. In this flow regime, two separating shear layers were alternately sucked into the slit. The Strouhal-number halving phenomenon which had been observed experimentally in the case of a circular cylinder was not found in the thick flat-plate wake.

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The mechanism of three-dimensional rotational flow in a curved duct caused by distorted inflow is investigated numerically. The steady, laminar flow of viscous, incompressible fluid in a 90-deg. curved duct with a square cross section is simulated by the pseudo-compressibility method. A uniform velocity gradient is assumed at the entrance of the computational domain. The formulation of swirling motion is elucidated as follows ; in the curved portion, the secondary flow induced by the centrifugal force develops asymmetrically due to the angular momentum of the inflow ; downstream of the bend, the enhanced vortex dominates the entire cross section. The latter process is evaluated by an increase in the helicity factor.

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The flow field in a cavity that is attached to a supersonic duct at M=1.83 is computationally simulated. The basic characteristics of the cavity flow field and the effect of cavity dimensions (the length to depth ratio) are discussed. The computational results show good agreement with the experimental ones. From the numerical and the experimental results, time-averaged characteristics of the cavity flow fields are clarified. In the case of a longer cavity, the flow field is highly three-dimensional due to the effect of sidewalls. In the case of a shorter cavity, the flow field is essentially two-dimensional. The flow-in and flow-out mechanisms of the cavity are also clarified.

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Experiments were performed to clarify the effects of the number and angle of flaps on the flow resistance of parallel dampers in a rectangular duct. The number N of flaps ranged from 4 to 10 and the angle θ ranged from 10 to 75°. The resistance coefficient ζ of the damper increases in proportion to (1-β) /β² for θ=10∼40°, [(1-β)/β²]^0.5 for θ=45∼60° and [(1-β)/β²]^0.45 for θ=70∼75°, where β is the opening ratio of the duct. ζ is independent of the number N for θ&InE;20°, and decreases with an increase in N as N^-0.2 for θ>20°. A large separated region exists behind the lowest flap on the lower wall of the duct. The height of the separated shear layer increases with the angle θ. This is closely related to the flow resistance of the damper.

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An experimental study was carried out for weakly swirling flows through a circular-sectioned 90° bend with a curvature radius ratio of 4.0. Three components of mean and fluctuating velocities were measured by the technique of rotating a probe with an inclined hot wire at a Reynolds number of 60000. Flow patterns of main and secondary streams, and turbulence energy distributions in pipe sections are shown, and explanations are offered for phenomena observed in the streamwise direction. Results are compared with those for nonswirling flow and the influence of swirl on the flow is clarified, especially in terms of intensities of secondary flow and turbulence.

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Fully developed laminar flow in a curved square duct rotating about a center of curvature is investigated by similarity arguments, computational studies and use of experimental data. Similarity arguments suggest that the flow characteristics are governed by four parameters : the Dean number K_LC, the body force ratio F, the curvature parameter λ and the Rossby number Ro. By using the computed flow patterns, the flow structure is elucidated for a wide range of these parameters. The computational results for the friction factor are compared with the practical formula for circular pipes and with various experimental data. It is proven that the formula for circular pipes can be applied to flow in square pipes.

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The numerical study has been performed on turbulent flow developing in a 90 degree curved duct of rectangular crosssection and an aspect ratio of 6. The ratio of bend mean radius of curvature to hydraulic diameter is 2.04 and straight ducts of 7.5 and 25.5 width are attached to the inlet and outlet of the bend, respectively. In addition to this straight duct, two-dimensional lateral contraction of the wind tunnel with an area ratio of 6 is considered as the numerical domain as well as the experimental apparatus. Calculated results were compared in detai with the experimental data measured for meanvelocity and Reynolds stress components. In this calculation, an algebraic Reynolds stress model was adopted in order to predict anisotropic turbulence precisely, and a boundary-fitted coordinate system was introduced as the method of coordinate transformation. As a result of the comparison with experimental data, it was found that calculated results showed good agreement with the experimental data of streamwise and transverse velocites except for that of the inner wall region of the outlet straight duct and suggested the existence of the Taylor-Gortler-type vortices on the outer wall by the distributions of secondary flow and wall shear stress.

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A reliable subgrid-scale (SGS) model and a higher order accurate discrete method are required for the large eddy simulation (LES) of practical problems. At least fourth-order accuracy is needed for the LES using a finite difference method, because SGS stress seems to be a second-order product of filter width. However, the LES using a fourth-order accurate finite difference method and a dynamic Smagorinsky model (DSM) does not give proper solutions in cases of poor resolution. This indicates that the reliability of the DSM is insufficient for the LES of practical problems. In this paper, a dynamic two-coefficient mixed SGS model (DTMM) and a revised model (DTMMR) of the DTMM are constructed. The DTMMR is proposed as a better SGS model than the DSM and DTMM through the LES of plane channel turbulence at Reynolds numbers (based on the channel half-width and friction velocity) 180 and 650.

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Turbulent flows have been investigated experimentally and analytically in a straight pipe with rough surfaces. Three-dimensional measurements are made using a rotating probe with an inclined hot-wire, to show the effects of a rough wall on turbulence properties such as turbulence energy and Reynolds stress and so on. Also, trubulence dissipation is estimated by balancing the turbulence energy transport equation. These experimental results are refered to computationally predict turbulent flows in straight rough pipes based on the turbulence viscosity model. Predicted results agree with measured ones practically under a wide range of wall surface roughness conditions.

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Universal equilibrium theory was experimentally verified in a turbulence field of R_λ=80∼393. The inertial subrange defined as l_i(≒32η)∼l_G extended over more than one order of magnitude in wavenumber for R_λ=393, where η is the Kolmogorov scale and l_G is the scale of the largest locally-isotropic eddy. Structure functions up to the 30th order moments were calculated to derive the relationship between their order and the power law exponents of the inertial subrange. The 3D binomial Cantor set model assuming the intermittency of the fine-scale structure gave the best approximation to the present experimental results. The Kolmogorov constant, α₁, was almost independent of R_λ for R_λ≳150 and its value of about 0.55 was close to the constants given by numerical simulations and field measurements. But α₂ increased with R_λ. Such R_λ dependence of the Kolmogorov constants suggests that the universal equilibrium theory holds for R_λ≳10³.

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In the present study, numerical simulations of the three-dimensional axisymmetric flow in a poppet valve for oil hydraulics are conducted using the vortex method. The fluids are assumed to be inviscid and incompressible. The vibration of the poppet occurs in the axial direction because the poppet is supported by a spring and a dashpot. Pulsating flow rates from a swash plate piston pump are employed as a boundary condition for comparison with experimental results and sinusoidal flow rates are also used as a boundary condition to investigate the effects of the frequency and the amplitude of the flow rate on the valve lift and flow in the valve. The process of jet flow development, the fluctuations of the valve lift and the velocity distributions in the valve are investigated for the vibrating poppet.

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Shell-type long-span gates in which the upstream gate face consists of vertical and inclined skin plates (also referred to as weir plates) possess two degrees of freedom, one each in the streamwise (horizontal) and vertical directions, due to the gate's bending flexibility in these two directions. The streamwise and vertical directions can become closely which one another through hydrodynamic forces acting on the weir plates, resulting in sever eself-excited vibrations. Here, a two-dimensional model study of a shell-type long-span gate with small gate opening was performed to examine the validity of an asumption of a hydrodynamic pressure acting on the inclined weir plate. In addition, the hydrodynamic pressure acting on the upstream gate face and the exact equation of motion of the flow-induced vibration of shell-type long-span gates were described.

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The purpose of this study is to investigate the effects of the length and the arrangement of a sound-absorbing duct on the aerodynamic characteristics and the turbulent noise of a counterrotating fan. Moreover, we performed a theoretical investigation of the turbulent noise reduction in relation to the thickness of sound-absorbing materials and the length of a sound-absorbing duct. The results are summarized as follows. The sound absorbing duct reduces a considerable amount of noise generated from the counter-rotating fan without degrading the aerodynamic characteristics. The sound-absorbing duct set upstream of the fan only reduces the noise radiated to the upstream and has no effect on that radiated to the downstream. The duct set downstream of the fan has an opposite effect. The agreement between predicted and measured values for the noise reduction is satisfactory.

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In order to improve the performance of a Wells turbine, the effects of the gap between rotor and guide vane and solidity of the guide vane have been investigated by model testing. The results have been compared with those of the case without guide vanes. It is found that the overall characteristics of the turbine are considerably improved by the guide vanes. Furthermore, a suitable choice of design parameters such as the gap and the solidity of the guide vane has been suggested.

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Since the configuration and variable flow rate characteristics of a cross-flow fan can be improved by changing the rotor length, they are increasingly used in the rear cooling units of mini vans, in wcich compact design and low noise characteristics are required. Although many studies have been carried out the flow and performance and it has been shown that the internal flow, depending on the configuration of the casing, has a large effect on the performance, the methods for predicting the performance and designing an efficient fan have not yet been established. In this work the internal flows analyzed by numerical simulation and measured by LDA (Laser Doppler Anemometer) are compared, and the results are found to agree with each other. Thus, information on improving the performance of the fan can be obtained using the numerical method presented in this work.

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Flow around a Darrieus wind turbine operating at low tip-speed ratios is studied by flow visualization using the dye injection technique and also by measuring the velocity field using a particle imaging and conditional sampling technique. The instantaneous flow patterns observed upon the visualization pictures correspond well to the measured velocity distributions, vorticity contours and velocity magnitude maps. It is found that two pairs of mushroom-type vortices are shed from the blade during a rotation of the rotor, which is due to the dynamic stall phenomenon. These stall vortices are produced by the flow separation over the suction side of the blade and the formation of roll-up vortices from the pressure side. The stall vortices at small incidence angles advance to the returning blade side, while those at large incidence angles grow along the moving blade and interact with flow near the blade. The effect of tip-speed ratios on the growth of stall vortices is also examined.

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The cooling rate in actual roll casting systems is markedly decreased by contact resistance between the chilled roll and melt (or solidified shell). In this study, focusing on the dynamic behavior of a contact line, the mechanism generating the contact resistance is experimentally investigated using liquid paraffin as a melt and flat plates as chilled surfaces. The experimental results obtained show that the smoothness of the solidified shell is closely related to the stability of the contact line. The contact line is destabilized at both low and high immersion velocities of the plate, and stable contact lines appear only at middle immersion velocities. The range of immersion velocity in which stable contact lines appear becomes narrower with increasing undercooling degree of the plate. The unstable contact line appearing at high immersion velocities results from the dynamic nonwetting condition at the contact line. The unstable contact line at low immersion velocities is closely related to the formation of a solidified shell in the vicinity of the contact line and also to the interface temperature upon contact between the melt and the chilled surface.

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In this study, observation of boiling phenomena in a quasi-two-dimensional space is attempted to attain a good understanding of the bubble structure in high-heat-flux nucleate boiling. A horizontal ribbon heater is sandwiched by two vertical glass plates to realize the two-dimensional boiling space, and the boiling phenomena are observed through the glass plate. The experimental parameters are the ribbon width and glass plate height. First, it is concluded that the boiling phenomena observed in this experiment are similar to those in conventional three-dimensional space, because both the nucleate boiling curve and the critical heat flux are in good agreement with the respective conventional correlations. Experimental results indicate that filmwise coalescent bubbles appear in high-heat-flux nucleate boiling and a liquid subfilm with vapor domes exists between the boiling surface and the filmwise coalescent bubble. Interfacial waves, whose wavelengths are nearly equal to the most dangerous wavelength of the Rayleigh-Taylor instability, are observed at the upper interfaces of filmwise coalescent bubbles, and this result indicates that the bubble departure process in high-heat-flux nucleate boiling is dominated by the interfacial instability.

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A nonequilibrium condition is often used in plasma processing. A silent discharge is one of simplest methods for realizing this condition. In the case that a square pulsed voltage has been applied, this method enables high-energy input into a reaction field. However, the mechanism for this has never been clarified. In this study, an experiment on pulsed silent discharge has been carried out by use of a discharge tube with a corona electrode system and oxygen gas. Then the characteristics of this discharge were investigated, and its mechanism was estimated. As a result, it was clarified that the pulsed silent discharge, especially in the case of a developing positive streamer has highly nonequilibrium characteristics.

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Using R 113 vapor and liquid, behavior of the two-phase mixture level was examined in both cases of bubbling a stagnant liquid column in vertical pipes and bubbling a liquid column to which liquid was supplied as a falling film. The pipe diameters used were 10.0, 14.8, 20.2 and 26.0 mm. The initiation condition of flooding in the latter case was also examined. Observed phenomena were quite similar to those in previous air-water experiments. However, the level fluctuation amplitude and the mixture level swell height in the experiments with the falling film were smaller than those in the air-water experiments. Physical models devised to predict the mixture level height and the flooding velocity under a slug flow condition, which were developed in previous work, were found to reproduce the experimental results well.

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A three-dimensional analysis is carried out to study the effect of the fin-pitch irregularity on the heat transfer and the flow characteristics of offset fins for Reynolds number as low as 100 based on the hydraulic diameter. The results obtained are as follows. (1) The Nusselt number of the fin surface is maximum when the width r/s of the facing flow passage is increased by about 1.1 times the standard width, and is minimum when the width is decreased to as narrow as about 0.4 times. (2) The Nusselt number based on the base heating area decreases when the fin shifts from its standard position. The reduction decreases when the thermal conductivity ratio of the fluid to the fin increases. (3) The reduction rate of the friction factor increases as the aspect ratio h/s of the cross-sectional flow passage increases or the fin shifts markedly from its standard position.

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In order to predict various phenomena related to flow and heat transfer in space, it is necessary to carry out experiments under microgravity. The present work is concerned with the characteristics of gas-liquid two-phase annular flow under microgravity condition utilizing a drop tower. The experiments were carried out in a vertical transparent acrylic tube of 10.5 mm I.D. and 200 mm length, using a mixture of gaseous nitrogen (GN₂) and water as the working fluid, in an annular flow region. The mean void fraction, pressure drop and liquid film thickness under microgravity were obtained and compared with the results of a ground test. It was found that the roughness of the liquid film surface was less and the mean liquid film thickness became greater under microgravity than under normal gravity.

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A study on coaxial double pipe jets at different temperatures has been carried out with mean velocity ratios of inner pipe jet to annulus jet from 1.0 to 3.0. The radial distributions of the local mean velocities and the fluctuating intensities of velocity (axial turbulence intensities) in isothermal air jets (Pr≈0.7) were measured at various axial distances of up to twenty times the pipe diameter downstream. Measurements were also made of the radial distributions of the local mean temperature and the fluctuating intensities of temperature in nonisothermal jets. The profiles of velocity in relation to those of temperature are described in detail in the developing region of coaxial jets. Moreover, the fluctuating intensities of velocity are compared with those of temperature.

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To enhance and suppress ice formation around isothermally cooled cylinders in convective water flow, circular fins and heat conductor plates are used, respectively. The heat conductor plates are positioned around each cylinder with some clearance. In the present experiment, the cooled cylinders exhibit a staggered alignment. The experimental results show that the present analytical method for cooled cylinders with fins and heat conductor plates is useful for predicting ice volume under the conditions in which the cooled cylinders are not completely linked by ice in a steady-state condition. It is found that ice accumulation with fins is significantly enhanced as compared to that without fins. It is also shown that use of cylinders with the heat conductor plates is effective for suppression of ice formation.

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In this paper, we discuss the solidification of carbon dioxide in the flue gas from thermal energy power plants. In this case, the content of carbon dioxide in the flue gas is approximately 3∼5 volume percent. The freezing temperature of the carbon dioxide was measured using liquid nitrogen as a coolant in a transparent quartz glass tube. The results indicate that the carbon dioxide precipitates at a temperature below -135°C, approximately.

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A simulation has been developed for low-pressure chemical vapor deposition (LPCVD) of polysilicon thin film using a vertical multiwafer reactor. The model takes into account the empty inlet section and the spacing region between inner and outer tubes, for the purpose of determining the appropriate inlet and outlet boundary conditions. Several chemical reaction models have been proposed. The validity of these conventional chemical reaction models was verified and results were compared with out experimental data. Consequently, kinetic chemical reaction parameters were optimized for our equipment. Moreover, when the function of the optimization of injector flow rates and the locations for improving the uniformity of film growth rate was added to the simulation, its validity was shown.

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Numerical simulations were conducted for a liquid fuel droplet gasifying in an otherwise quiescent gas with temperature and pressure exceeding the critical point of the fuel. The pressure dependencies of gasification lifetime were examined in terms of the ambient gas temperature and the initial droplet temperature as parameters. Three gasification regimes are identified on the plots of pressure and ambient gas temperature, which show the ambient condition in which the transition to continuous phase change takes place. For a fixed gas temperature, the gasification lifetime takes a minimum value at a pressure such that the droplet surface becomes critical immediately after its exposure to the hot gas. The transitional regime shrinks as the initial droplet temperature increases. The underlying physics is also explored.

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A numerical analysis on the internal condition of a MCFC stack is necessary to estimate the performance and to control the maximum temperature of the stack. In this report, a numerical model is developed which can analyze temperature, current and cell voltage profile in the stack. The model calculates the heat generation distribution using the formulation for MCFC performance, as well as the cell voltage profile using the electric circuit model. The results of the temperature profile and each cell voltage determined by numerical analysis show good agreement with the experimental results of the stack ; thus, the model is an effective stack analysis method. Using this model, we show the cooling gas flow rate in the high output power density condition. Furthermore the results of the cell voltage profile analysis using the electric circuit model shows that the nonuniformity of internal resistance could be one of the reasons for cell voltage deviation.

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Some temperature-sensitive liquid crystals exhibit cyclic changes in color with an increase in temperature, and can be used in wider temperature ranges than conventional noncyclic liquid crystals. This cyclic liquid crystal, however, shows so complex correlation between color and temperature that it is difficult to calibrate using methods previously developed for noncyclic liquid crystals. In this study, two calibration methods based on the neural network and on nonlinear multiple regression are proposed for this cyclic liquid crystal. The results show that the neural network approach is applicable for the calibration of cyclic liquid crystal as well as for that of noncyclic liquid crystal, and that the third-order multiple regression method is also sufficient and useful for cyclic liquid crystal calibration from the engineering point of view.

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We describe the measurements of spectral transmittance and the calculations of the total transmittance for sodium chloride and potassium chloride water solutions. The spectral transmittance of NaCl and KCl water solutions over the infrared and nearby regions increases with increasing salinity. In the visible region, the spectral transmittance of NaCl w-s increases slightly, while that of KCl w-s decreases with increasing salinity. The total transmittance of the two salt water solutions can also be calculated by means of an integral method and a simple 5-partition method over 0∼3 m water depth. The simple method is of practical use to calculate the total transmittance for a conventional solar pond, because the rate of error between the two methods is about 10% at shallow depth and 0% at 3 m depth.

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We report measurements of the spectral transmittance and calculations of the total transmittance of magnesium chloride-water solution to be used as the working fluid for a solar pond. The spectral transmittance of MgCl₂-water solution in the visible, infrared and nearby regions decreases with increasing salt concentration. The total transmittance of MgCl₂-water solution can be calculated using an exact integration method and a simple 5-band partition method over a 3 m depth of pond water. The simple method is useful in practice to calculate the total transmittance for a conventional solar pond, because the rate of difference between the results calculated by the two methods is less than 10% at shallow depths and then it decreases rapidly being followed by 0% at a depth of 3 m. Furthermore, the absorption coefficient calculated from the spectral transmittance of the present work is compared with that from Usmanov's data as shown in references (6) and (7).

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A numerical study of low stretched premixed methane-air flame in a counterflow configuration is conducted. The present simulation includes detailed transport properties and chemical kinetics. It is found that near the flammability limit, there is a radiation extinction branch in addition to the normal stretch extinction branch, which has been extensively studied at a large stretch rate. Furthermore, far from the flammability limit, it is found that there are two stable flames, a normal flame and a weak flame which are the results of interaction between the stretch effect and the radiation effect, at a certain extent of stretch rate. In addition, the present results show that the flammability limit obtained in counterflow configuration cannot be extended directly to the flammability limit of its corresponding one-dimensional free propagating premixed flame.

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A study was carried out to determine the relationship between the sound pressure generated by open premixed flames and the velocity and fuel concentration fluctuations in unburned mixture flow at a cylindrical single-port burner. The sound pressure from the turbulent flames was measured for various velocity and gas concentration fluctuations in the mixture flow. To evaluate the velocity and concentration fluctuations, the radial profiles of the fluctuations were measured. The volocity fluctuation and concentration fluctuation averaged by the flow rate were used as indexes respectively. It was found that a strong relationship existed between the velocity fluctuations and sound pressure generated by the turbulent premixed flames on the burner. The maximum sound pressure was generated by turbulent flames having an air ratio between 0.8 and 1.0 when there was no concentration fluctuation. In the presence of gas concentration fluctuations, the level of sound pressure was increased for the same velocity fluctuation. It was found that the leaner the mixture, the stronger the effect of the concentration fluctuation on the sound pressure generation.

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The near-field structure of the jet diffusion flame is important for the mixing process of fuel and air, and for flame stability. The interaction between coherent vortices involved in the near field and the flame has been studied using the laser sheet method. The acoustic forced jet diffusion flames are also studied in order to investigate the possibility of the control of flame stability. We have developed a new seeding method of scattering particles for the laser sheet method. This method utilizes the combustion of magnesium ribbon and can produce smoky magnesium oxide particles of a mean size of 0.6 μm. Seeded particles distribute densely and uniformly. This method is applicable not only to laser sheet visualization but also to laser Doppler velocimeter and concentration measurement. Experiments of fuel jet revealed that coherent vortices enhance the mixing of fuel and surrounding air under the process of linear and nonlinear growths. Acoustic forcing of fuel flow can control the mixing process through coherent vortices of the flame base and flame stability.

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