It has been well known that flow separation pattern from a circular cylinder varies qualitatively near the critical Reynolds number. The interaction of separated flow with cavitation bubbles is very important for predicting cavitation characteristics. In the present investigation, the interaction between cavitation bubbles and separated flow is examined near the critical regime of a circular cylinder in the double-peak cavitation process. The changes in flow characteristics accompanying cavitation occurrence and development are compared with basic flow characteristics such as base pressure coefficient, shoulder pressure coefficient and Strouhal number obtained in noncavitating states. Further experiments were made using a circular cylinder with a trip wire. These results experimentally confirm that the occurrence of cavitation bobbles can induce the transition of critical Reynolds number region and a double-peak-type cavitation process.

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An experimental study was carried out on the transient behavior of a cavitating centrifugal pump during sudden opening or closure of the discharge valve. The experimental results indicate that the transient performance of the pump with cavitation shows a rather different change from the quasi-steady one. Moreover, it was established that a rapid change in boundary condition results in low-cycle pressure oscillation, the ocurrence of which depends on the speed of valve opening/closure and suction pressure, and is nearly independent of pipe length. The frequency of pressure oscilation was found to be related to the pipe length only for valve closure.

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In the unsteady incompressible flow simulation using the Navier-Stokes equations expressed by the vorticity and the streamfunction, a Sommerfeld radiation condition is adopted for the open boundary condition, i.e., the outflow condition. Two types of determination of the phase velocity are presented, that is, the phase velocity is calculated numerically and fixed by the uniform velocity. In the simulation of the flow past a cylinder, two Sommerfeld radiation conditions are compared with the usual one-side finite difference condition, i.e., the extrapolation. When the computational region is sufficiently long in the wake direction, the results obtained by the above three conditions are in good agreement with each other. When the region is short, the Sommerfeld condition with the calculated phase velocity is the most suitable condition among them.

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Two-dimensional flow of an incompressible viscous fluid past a rotating circular cylinder placed symmetrically in a uniform flow is considered theoretically using Oseen's approximation for small values of Reynolds numbers. The expansion formulae for the stream function and the vorticity are obtained up to the fourth power, O(Re⁴), of the Reynolds number and it is shown that the flow patterns calculated by these expansion formulae agree even in the neighborhood of an object with those as predicted by the numerical solutions to the Navier-Stokes equations in the range of the small Reynolds numbers. Furthermore, flow near a circular cylinder is investigated in detail. The expansion formulae for the lift, the moment and the pressure distributions on a circular cylinder are obtained up to O(Re²), O(Re³) and O(Re²), and it is confirmed that the results of these expansion formulae agree with those of the numerical solutions to the Navier-Stokes equations.

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The measurement of the drag of a circular cylinder at low Reynolds numbers with two-dimensional flow while the circular cylinder is being moved slowly between two parallel side planes in a viscous liquid is a popular subject. However, in almost all experimental cases up to now, it has been done with a finite circular cylinder. For the our experiment, the method of measuring the total drag of an infinite circular cylinder has been developed, as well as the measurement equipment using a link mechanism to obtain the dribblet drag smaller than a few grams because of the very slow moving speed of the circular cylinder. The measured results generally agree with results calculated using Tachibana's and Faxen's formulas. It has been proven that Tachibana's and Faxen's formulas can almost cover the range of 10^-4 of Reynolds number, by the our experiment. This paper provides a summary of the measuring method, the measured results and a comparison with the calculated results of Tachibana and Faxen.

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In a continuum, the resistance force of a spherical particle moving towards another particle increases with decreasing separation distance between particles and finally becomes infinite just before touching. However, there has been no investigation on the effect of discontinuity. The air in the minimum separation of two particles whose diameters are less than several tens of microns creates the discontinuum, and without it, a fine particle would collide with another particle more easily. In this study, we measured the resistance force of a 6.3 mm foam styrene ball under reduced pressure by using a high-speed camera. At 10 Pa, the mean free path of air is 670μm and the Knudsen number of a 6.3 mm foam styrene ball is equivalent to that of a 0.6μm particle in air. The experimental data show that the increment of the resistance force acting on a 6.3 mm foam styrene ball near the spherical particle under reduced pressure decreases with decreasing air pressure. Hence, it is concluded that the resistance force of a fine particle moving towards another particle in the air is much less than that acting in a continuum.

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Experiments were performed with two circular cylinders whose walls were porous and permeable in order to investigate the effects of flow of water through the wall. Each cylinder was made of bronze sintered compact, available as a sintered metallic filter. It had an outside diameter of 30 mm, wall thickness of 2 mm and nominal filter size of 2μm and 20μm, respectively. Force coefficients and pressure distributions of the test cylinders were measured over the Reynolds number 1.1×10⁵∼4.4×10⁵ and were compared with those of the same porous cylinders into which another circular cylinder, an "inner cylinder" with a solid wall, was inserted to obstruct such a through-flow. The measured results showed that the drag coefficients and the root-mean-square values of the fluctuating lift coefficients of the test cylinder equipped with the inner cylinder were smaller than those with the through-flow. This was caused by the increase in the effective surface roughness and the altered pressure distribution because of the permeability of the cylinder wall. The increase in the drag coefficient was accompanied by the decrease in the Strouhal number of the fluctuating lift, and vice versa.

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Two-phase critical flow with phase change through a converging nozzle is investigated and discussed in terms of the applications of three-layer model analysis, which was already reported for a case of two-component two-phase flow by Ochi & Ayukawa. In the theoretical analysis of single-component two-phase flow in rapid phase change, there are some difficulties arising from the modeling of a complicated flow pattern at the interface. The calculated results using our proposed model are in good agreement with some experimental data of the flow rate and the pressure of carbon dioxide or steam-water mixture flows. The flow properties in each layer through the channel are discussed in comparison with the completely separated flow or the homogeneous flow model. It is found that the three layer model is a considerably useful method for single-component two-phase flow with papid change of state in variable-area channels.

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Presently, in our quest to develop low-noise air conditioning equipment, it is important to reduce the refrigerant flow noise. To date, this problem has been investigated on the basis of trial and error. Fundamental cause and mechanism of the flow noise must be analyzed before a drastic reduction of noise can be achieved. In this study, air-water two-phase flow was used to create a slug flow with single large gas bubble for the purpose of modeling the problem. We investigated the relations among gas bubble state, static pressure pulsation and flow noise caused by single gas bubble passing through the orifice, In the results, it is shown that the noise level increases twice while the gas bubble passes through the orifice and that there exist correlations among flow state, static pressure pulsation and flow noise.

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An unexpected velocity distribution was found in the downstream field of a thin plate set upright on a flat wall. A steep velocity peak was detected behind the thin plate in the boundary layer of the flat wall with I-type hot-wire anemometer. The flow visualization with dye technique and a numerical analysis with Navier-Stokes equation were performed to clearly grasp the flow field around the thin plate. A horseshoe vortex was formed around the thin plate, and its two streamwise legs approached each other just behind the trailing edge. These vortices induced a strong downwash and drew the fluids with large velocity toward the flat wall. A velocity peak was thereby generated behind the thin plate. A pair of tornado-type vortices was observed on the trailing edge surface of the thin plate. The fluids near the flat wall were sucked up by these vortices and released at a height in the mean flow region.

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The flow of a non-tumbling nematic liquid crystal through a planar 4 : 1 contraction was simulated using the Leslie-Ericksen (L-E) continuum theory ; this theory accounts for fluid anisotropy and elastic stresses resulting from spatial distortion of the "director", which is a vector field describing average local molecular orientation. Calculations were performed for a wide range of Ericksen numbers (ratio of viscous to elastic stress), as well as for the limiting case of the Transversely Isotropic Fluid (TIF), in which elastic terms are absent. The recirculating eddy at the salient corner is larger for the L-E fluid than for the Newtonian fluid, extending to the reentrant corner for Eγ=1 and decreasing slightly in size with increasing Ericksen number. The anchoring effect of elastic stresses is such that the eddy for Eγ=1000 is still larger than that for the TIF, while the flow field throughout the domain for the TIF is essentially the same as that for the Newtonian fluid. Director orientation changes with Ericksen number, but the flow field away from the recirculating eddy is relatively insensitive to director orientation up to Eγ=1000.

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Experiments on two equal spheres falling freely in quiescent glycerol are carried out in order to discuss the effectiveness of Oseen's reflection method. The width of the test tank with a square cross section is 100 times the sphere diameter. The experiments show that the free-fall motion of two equal spheres at low Reynolds numbers is classified into four types according to the angle between the center line of two spheres and the vertical line. These motions are not predicted using Stokes' theory. However the numerical results obtained using Oseen's reflection method show good agreement with the experimental results.

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Systematic experiments were carried out in order to determine the energy losses due to dividing and combining flows through an orifice set on a side wall of a square duct, for several orifice diameter duct width ratios d/h and velocity ratios U₁/U₂ or U₂/U₁. For dividing flow, the loss coefficient ζ_d and the pressure difference coefficient B_d can be simply expressed by a quadratic curve of U₂/U₁ independent of the diameter d, while for combining flow, the loss coefficient ζ_c and the pressure difference coefficient B_c can also be expressed by a quadratic curve of U₁/U₂, but they clearly depend on d.

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An experimental investigation is conducted in order to determine the discharge coefficients for a water jet discharged into the surrounding air from a standard orifice located on the side wall of a square duct. Six different orifice diameters are tested. Experiments are made for a wide range of Reynolds and Weber numbers, and an empirical equation is obtained for the discharge coefficients, which reproduces the experimental results accurately. The efflux angle is deduced from the momentum theorem which takes into account the loss coefficients in the duct due to dividing flow, and it agrees well with the measurements.

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A numerical analysis has been performed on developing turbulent flow in a rectangular duct of aspect ratio 2.25 : 1, two of whose long-side walls were roughened. Roughness elements with trapezoidal cross section were located along the strearmwise direction. In the calculation, an algebraic stress model was adopted in order to predict Reynolds stresses precisely, and a boundary-fitted coordinate system was introduced to briefly set the boundary conditions. Calculated results were compared with the experimental data available. As a result of this calculation, it was found that the present method could predict streamwise velocity and secondary flow well. The intensity of the secondary flow near the longitudinal roughness element was greater than that in the corner region. This phenomenon strongly suggests that a duct with a longitudinal roughness element is applicable for promoting heat and mass transfer without increasing pressure drop.

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Spinning disk boundary layer provides a flow field convenient for a swept wing boundary layer transition study. In order to examine the randomization process in crossflow dominant three-dimensional (3-D) boundary-layer transition region experimental investigation is performed and two kinds of traveling disturbances with frequencies differing by more than an order of magnitude are detected for the first time. The properties of these disturbances is measured using a rotatable paralle hot wire probe. Results showed that the low frequency disturbance seems to be due to the unsteady crossflow instability (primary instability), while the high frequency one to be inflexional instability (high frequency, secondary instability) and coincides with the structure visualized by smoke visualization technique.

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Mean flow quantities have been investigated experimentally for the turbulent boundary layer developing over an equivalent smooth-mesh rough wall. The roughness Reynolds number defined as ratio of the roughness height to the viscous length is about 4 which corresponds to the fluid dynamical smoothness. Measurements were made within Reynolds number range of about 2200 to 6000. Mean velocity profile nondimensionalized by outer variables shows a similarity within all Reynolds numbers tested, but the present mean velocity profile increases in the inner layer compared with the smooth wall flow. The value of the local skill friction coefficient evaluated using five different methods was slightly lower than the value for smooth wall flow. For the present mesh wall flow, both logarithmic velocity and velocity defect laws are applicable, and the inclination of logarithmic linear part, namely Karman constant, is the same as for smooth wall boundary layer.

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A stochastic model which is used for simulating the time evolution of material line stretching in homogeneous turbulence is developed. Although the present model is similar to the Lagrangian random flight model, turbulent velocity is calculated for the Eulerian grid points considering space correlation in addition to time correlation. Scales of turbulence are estimated from turbulent energy (k) and dissipation rate (ε). Deformation of material line in two-dimensional homogeneous turbulence is simulated by using this model and the result shows that spatial scale of turbulence affects on the distortion of material line.

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Computations of 2-dimensional homogeneous isotropic turbulence by the spectral method and the higher-order finite difference scheme (FDS) have been conducted with the grids of 128×128 and 64×64. The energy spectrum obtained by the FDS is compared with that obtained by the spectral method to investigate the effect of discretization. From these studies, the following conclusions are obtained. (1) As for the discretization of the nonlinear term, with the 128×128 grids, the energy spectrum obtained by the 5th-order upwind FDS coincides with that obtained by the spectral method up to the cutoff wave number, while the 3rd-order upwind FDS shows deflection. (2) With the 64×64 grids, the 5th-order upwind FDS is still valid for DNS, while the 6th-order central FDS requires the use of dealiasing operation or energy-conserving form for the nonlinear term. (3) With the nonlinear term discretized by the 5th-order upwind FDS, the 4th-order FDS is adequate for the diffusion term.

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With artificially introduced periodic disturbances, the behavior of ring vortices in an axisymmetric jet has been experimentally studied using flow visualization and a hot-film anemometer. The excitation frequency is varied in the range of 0∼12 Hz, while the amplitude is kept constant at a=0.5 mm. The Reynolds number is about 6000. It is shown that the influence of excitation frequencies on the initial growth of the ring vortex structure is appreciable. When the excitation frequency is nearly equal to one-half of the natural rolling-up frequency of ring vortices, the ring vortices are symmetric and grow in size. Consequently, the turbulence intensity at the jet centerline is the most amplified. When the excitation frequency is equal to the rolling-up frequency, a vortex-pairing event occurs at a fixed streamwise location.

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A new self-induced sloshing was recently discovered in a rectangular tank having a submerged plane jet. The upward jet entered the tank from a bottom-centered inlet and impinged vertically on a free surface. At a certain water depth and inlet velocity condition, a first-mode sloshing was observed. The frequency of oscillation was nearly equal to an eigenvalue of fluid without a steady circulating flow in the tank. In order to investigate the governing parameters of the oscillation, the tank geometries were systematically changed. The time required for fluctuation to travel from the inlet to the free surface was found to be one of the most important parameters. The sloshing growth mechanism is considered to be strongly related to the traveling time of the jet fluctuation.

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A direct numerical simulation was conducted for temporally developing three-dimensional round jets, assuming periodicity in all directions of rectilinear coordinates. Two cases of nearly axi-symmetric and helical perturbations superposed on a thin round mixing layer were taken as the initial flow conditions. Subsequent evolutions of jets depending on the two initial perturbations are described, especially for coherent structures. In the case of the nearly axi-symmetric perturbation, discrete ring like rolls and streamwise ribs connecting the rolls are generated, and increases in enstrophy and helicity are primarily due to the streamwise vortex in the roll. In the case of the helical perturbation, the generation of structures is earlier than in the nearly axi-symmetric case, and rates of increase in enstrophy and helicity are lower because of the long-lived coherent structure of elongated vortices between rolls.

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Pure tones are unexpectedly generated from slits or gaps between a window and a pole or a damper when wind is strong. We named this type of pure tone a whistle tone. We previously showed that whistle tones are generated by air jet flow from a rectangular slit. The velocity field and its time variation characteristics were investigated in detail to clarify the relationship between them and the generation of the whistle tones. The results are as follows : (1) the frequencies of the whistle tones coincide with those of the velocity fluctuation, and (2) the scale of the turbulence of the jet or the range of the intense velocity fluctuation has the scale comparable with the exit area of the slit used.

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High-polymer aqueous solutions show various interesting phenomena in their liquid motions, i.e., non-Newtonian viscosity, Toms effect, Johnson effect, effect on jet breakup, elastic effects and so on. Visualization and observation of the polymer chain orientation or alignment under external stress in a fluid flow region will be very important issues in the basic research for the clarification of these phenomena. In this report, polyethylene oxide is used as the polymer additive, and steady Couette flow region is formed with a rotating disk and a fixed wall. The sample is a thin piece of ice adhered on the end of a round brass model, which is supercooled by liquid air and fixed into the rotating disk keeping the end of the surface flush with the disk surface. The ice sample is dehydrated by the freeze-drying method and observed using a microscope. Polymer molecules build up a network structure in the bundle of polymer chains, and this network state changes with flow shear rate, molecular weight and the concentration of polymer.

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Numerical simulations are performed using the two dimensional compressible Navier-Stokes equations to investigate the dynamic stall phenomena of the NACA 0012 airfoil oscillating near the static stall angle. The airfoil oscillates in pitch about an axis at the 0.25 chord. The Mach number is 0.3. The Reynolds number is 4×10⁶. The TVD scheme, which avoids excessive numerical diffusivity, is employed in the discretized convective term. An implicit time discretization is adopted for computational efficiency. Numerical errors caused by using the diagonal matrix method are reduced by Newton iterations at each time step. The effect of the conservation in time on the unsteady grid is investigated. The hysteresis loops of the unsteady lift and pitching moment during dynamic stall are compared with the experimental data of McCroskey-Pucci.

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In the present paper, coherent structures of the supersonic mixing layer are investigated by direct numerical simulations of a spatialy developing free shear layer, We examined numerical results of the velocity components, u, v, w simulated by Fouillet and Lesieur : Reynolds number Re=δ_ω0ΔU/ν=1500, Mach number =1(M₁=1 and M_c=0.3), (U₁+U₂)/2=0.7, U₁-U₂=0.6, and the hyperbolic-tangent velocity profile is perturbed by weak three-dimensional white noise. We find that the coherent structures in the supersonic mixing layer at M_c=0.3 are three dimensional and have rib structures with strong vorticities of ω_y and ω_x similar to those in the incompressible mixing layer. The helical pairing structures found in the rib structure generate a coherent 'upwash' and 'downwash' fluid motion in the supersonic mixing layer. The regions corresponding to high rates of dissipation are found in the rib structures.

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A proper finite difference method based on the gradient/convective form of the equation of motion of incompressible fluid is discussed. The gradient form discretized on the staggered grid has essentially the same conservation properties as those of the divergence/momentum-conservative form or the quadratic-conservative form under some conditions. First, the mass continuity should be numerically satisfied. Second, the numerical consistency between the mass continuity and the momentum convection should be satisfied. The gradient form evaluated at midpoints between velocity points in the direction of convection, rather than directly calculated at velocity points, meets this requirement. In this paper, through mathematical description of the above-mentioned features, the performance of the higher-order finite difference method for the gradient form is demonstrated.

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The conventional SOR method includes a recursive reference, so it is not suitable for modern vector-parallel computers. It is difficult to avoid the recursive reference, especially in the case where are SOR method with unstructured computational grids is used. In this paper, the multi-color method, which avoids the recursive reference, is expanded to the unstructured computational grids as the expansion multi-color method. When we use the irregular mesh in the GSMAC method, the increasing of iteration is caused especially in the domain of fine grids. In order to resolve this problem, the selective simultaneous relaxation method which corresponds on an error criterion of the equation of continuity is presented. Unsteady flows in a two-dimensional lid-driven square cavity at Re=1000 are numerically investigated to verify the present numerical method.

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A simplified tracer gas technique which enables the performance evaluation of a local exhaust suction hood is proposed by detecting the high-concentration region of tracer gas (CO₂) flowing from a point source placed in the suction field. In this technique, the high-concentration region of the gas can be easily distinguished from the background field because of the nondiffusible property of CO₂. When the velocity of gas from a nondirectional point source is lower than that of the suction flow field, streamlines of the flow field can be traced as a narrow high-concentration region. With faster tracer gas flowing from the directional point source, the performance of various hood types can be evaluated by introducing some parameters indicating the shape characteristics of the high-concentration region. In the industrial practice, the suitability of the hood for a certain kind of pollutant is easily checked by monitoring the gas concentration at the points on the side plane of the hood opening. By testing three different hood performances using this technique, the "dominant region" of each hood that was proposed by authors was confirmed.

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Oil column separation in which a tensile wave and the consequent rupture of an oil column can be observed provides intriguing information with cavitation study. In order to investigate the phenomena in more detail from this viewpoint, it is essential to secure a means to precisely measure transiently changing flowrates in column separation. The present paper has aimed to achieve this object ; the method is based on detecting pressure differences kinematically induced in an unsteady pipe flow. Instead of a conventional pressure difference transducer, two independent pressure gauges are used to pick up the pressure differences with high fidelity. Theoretically predicted step-like flowrates until the column rejoining have been successfully measured, showing the usefulness of the method. It is also pointed out that the algorithm adovocated by ZHAO et al. to conveniently transform sampled pressure difference data to flowrate can give unreasonable results when the transient is fast.

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The purpose of the study is to present new data on critical heat flux (CHF) for flow boiling of water in small diameter tubes. The experiment was conducted with atmospheric-pressure water in small-diameter tubes with inner diameter D of 2.2, 4.0 and 6.0 mm, and the length-to-diameter ratio L/D ranging from 5 to 50. CHF was measured as a function of mass velocity ranging from 0 to 13000 kg/(m²·s) at a given inlet water temperature, and the effects of tube diameter and L/D were investigated. The highest CHF attaind in this experiment was 63 MW/m² in a tube with D=2.2 mm and L/D=5. The experimental results were compared with several existing CHF correlations. Some of them showed good agreement with the present data in a limited region either at high quality or under subcooled conditions.

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We have already studied droplet vaporization on a hot surface with flame-sprayed ceramic coating at atmospheric pressure. The present study extended the earlier work and experiment were carried out at pressures up to 10 MPa. The vaporization behavior of the droplet in the pressure vessel prepared for optical observation was investigated, and lifetime curves for some pure liquids were measured. The result showed that the ceramic-coated surface had a wide temperature range in which nucleate boiling was observed in the spreading liquid, and the droplet vaporized in quite a short time at any subcritical ambient pressure. The lifetimes in this region depended on pressure, and the optimum pressure yielding the minimum lifetime was found.

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Theoretical and experimental studies were performed to investigate the effect of fin geometry on the condensation of HCFC-123 on a horizontal finned tube. Approximate expressions of the heat transfer coefficient for a newly proposed high-performance fin was developed. Experiments were conducted to obtain row-by-row heat transfer data during condensation of downward-flowing HCFC-123 vapor in in-line bundles of horizontal two-dimensional fin tubes. Two conventional low-fin tubes and two finned tubes with fin shapes close to the newly proposed ones were tested. The highest heat transfer performance, about 85% higher than the conventional 26-fpi tube, was obtained using one of the new tubes. Predictions of the previously developed theoretical model compared well with experimental data for all the tubes at a low vapor velocity and a low to medium condensate inundation rate.

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An experimental study of condensation of refrigerants HCFC 22, HFC 134a and HCFC 123 inside a horizontal smooth tube is presented. The test condenser is a double-tube counter-flow type, where the refrigerant flows inside the inner tube and the cooling water flows counter-currently in the outer annulus. The inner tube made of copper is of 6.0 m length and 8.4 mm inner diameter. The measured values for the frictional pressure drop are correlated as Φ_v=1+0.5[G/√(gdρ_v(ρ_L-ρ_V)])^0.75X_tt^0.35, where Φ_V and X_tt are Lockhart-Martinelli parameters, G is the total mass velocity, g is the gravitational acceleration, d is the inner diameter, and ρ_V and ρ_L are the densities of vapor and liquid, respectively. The static pressure drop calculated using this correlation equation agrees with the measured values within the error of 0∼-5%.

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The local heat transfer coefficients of refrigerants HCFC22, HFC134a and HCFC123 condensing inside a horizontal smooth tube are measured in the ranges of total mass velocity of 90 to 400 kg/(m²·s) and heat flux of 3 to 33 kW/m². Based on the turbulent liquid film theory and Nusselt's theory, an empirical equation for the heat transfer coefficient is proposed in the form of Nu=(Nu²_F+Nu²_B)^1/2, where Nu_F expresses the effect of vapor shear stress and Nu_B the effect of gravity force. This equation correlates the experimental results within an error of ±20%

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In order to clarify phenomena such as the solidification of soil containing seawater in the ground freezing technique, a horizontal copper cylinder was set in a porous medium saturated with an aqueous solution, and the porous medium, whose size was sufficiently large compared with the cylinder, was solidified by cooling the cylinder. Such a solidification process with natural convection caused by the temperature and concentration gradients in the liquid and mushy regions was studied analytically and experimentally. From the comparison of the analytical results with the experimental ones, the present analysis was found to be useful to simulate this solidification process. By the analysis, the characteristic of the solidification process, especially, the influence of grain size of the porous medium on the solidification phenomenon, was clarified.

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The vapor-liquid-equilibrium and thermodynamic properties of aqueous mixtures of 2, 2, 2-trifluoroethanol have been studied as a function of composition based on the experimental results of bubble pressures, saturated liquid densities and PVTX properties for seven mixtures in the temperature range from 310 K to 420 K at pressures up to 200 MPa. The composition dependence of bubble pressures, saturated liquid densities, excess molar volumes, isothermal compressibilities and isobaric expansivities is reported. The behavior of these properties is discussed on the basis of the inter molecular forces.

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An experimental investigation was made into the absorption of carbon dioxide, CO₂, from concurrently flowing CO₂-laden air into a thin water film in a horizontal duct. We proposed three physical models, CAL1∼CAL3, to explain mass transfer across a sheared non wavy and wavy gas-liquid interface into the flowing thin liquid film. If gas flow was laminar and the flow pattern was smooth surface flow, experimental values agreed well with the estimation by a laminar flow model, CAL1. If the gas flow was turbulent and flow pattern was two-dimensional wave flow, the experimental value agreed well with the estimation using CAL2, in which the film thickness was evaluated using the correlation of the interfacial shear stress. If the flow pattern was pebble wave or ripple flow, CAL3 estimated the experimental values accurately, for gas flow which was turbulent and where the turbulence in the liquid film was also taken into consideration.

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A numerical and an experimental study was carried out to investigate the enhancement of heat transfer within a thermally developing region, by placing a square rod in the vicinity of the lower channel wall. A numerical analysis based on SIMPLE reveals the details of the complex unsteady flow pattern and the corresponding distribution of mass transfer rate. Exhaustive local mass transfer measurements were made using a naphthalene sublimation technique, varying the distance between the square rod and lower channel wall for the Reynolds numbers ranging from 8.27×10³ to 2.205×10⁴. Performance evaluation based on equal pumping power showed substantial augmentation of heat transfer in a thermally developing region upon placing a square rod close to the wall with an orientation angle of 60°.

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This report presents experimental results on the distribution of the heat-transfer coefficient along a large flat plate in the high-temperature region of spray cooling. The results show that the heat-transfer characteristics of spray cooling in the high-temperature region can be divided into the impinging and the wall regions. In the impinging region, with increasing distance from the stagnation point of the spray flow, the local heat-transfer coefficient decreases rapidly with the decrease of the local droplet-flow rate and the minimum temperature of the high-temperature region increases due to the propagation of the wetting front. However, in the wall region, the local heat-transfer coefficient approaches a constant value dependent on the total droplet-flow rate, and the minimum temperature is independent of the distance from the stagnation point.

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This paper describes one of the new package cooling concepts using a phase-changing-material (PCM), to be applied for the development of high-density packaging. A low-cost alloy, composed of Bi/Pb/Sn/In, the melting points of each of the elements of which are less than 70°C, was used as the PCM. Experiments were conducted using this alloy and thermal network method was applied for the analysis of phase-changing phenomena. It was confirmed that the surface temperature of the opposite side of the substrate could be fixed at the PCM's melting temperature for several minutes by thermal absorption effect while the PCM phase changed from its original solid state into the liquid state. It has also been confirmed, in the present work, that thermal network method could be used as a personal computer base engineering tool for the thermal design of a package with a PCM.

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When a temperature drop exists across a point contact which is formed by pressing a metal whisker against a metal plate, the thermoelectric voltage can be measured, even though the entire electric circuit is made from the same metal. This phenomenon is a result of the characteristic thermoelectric power (TEP), which depends on the electron tunneling effect through a several-angstroms-thick oxide layer at the point contact. In this study, the experimental values and theoretical values of the TEP are compared. There is a possibility of producing a new type of thermal probe using this point contact apparatus.

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A quantitative analysis of countercurrent flow limitation (CCFL) or flooding was successfully carried out using the existing experimental data for the vertical rectangular channels, adopting the criterion that the CCFL condition is determined by maximizing the falling water mass velocity with respect to the thickness of the falling water film for the whole flow channel, without any additional conditions. It was found that significant factors were the flow pattern, that is, which walls were wet, interfacial friction factor between liquid and gas based on the relative velocity, wall friction factors for laminar, transition and turbulent flow of liquid and gas, and aspect ratio of rectangular channels. Thus it was clarified that the analytical results give good predictions of the existing experimental data of an air-water system for vertical rectangular channels of 33 and 66 mm in channel width, 2.3 to 12.3 mm in channel gap, and 362 and 782 mm in channel length under atmospheric pressure.

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A coaxial jet diffusion flame is often used to experimentally analyze the phenomena in turbulent diffusion combustion and to examine the modeling technique for them. In this flame, however, a low turbulence region is inevitably formed in the periphery, which becomes a disadvantage in its use as a research object. In the present study, another coaxial air jet of high velocity was added to usual coaxial jet diffusion flames between the central fuel jet and the surrounding air flow. In this flame, called a triple jet diffusion flame, large turbulence is generated in the peripheral region of the flame by controlling the high-velocity air. In this report, the characteristics and usefulness of the flame are clarified by experiments and numerical simulations.

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A hot water cycle is proposed as one of the most effective technologies for power generation utilizing heat sources of low temperatures and excess energy from conventional power plants, stored as heat. Due to the preferable heat-exchange characteristics for heat recovery, the effectiveness of the hot water cycle plant will be about 68% higher than that of a typical steam cycle plant. The advantages of applying total flow turbines to the hot water cycle are discussed as well. This paper summarizes the analysis and optimization of hot water cycle application.

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This paper deals with solidification and flow characteristics of high-density polyethylene plastics as polymer plastics in a narrow annular cavity cooled on an inner circular tube. The experiments are carried out with various parameters (plastics temperature, flow velocity of the plastics and cooling surface temperature). The obtained results show that the solidification layer formation of polymer plastics is affected by flow behavior and viscosity of molten polymer plastics. The useful dimensionless equations for predicting the amount of polymer plastics and the time of finishing the injection of the polymer plastics into the cavity are derived as a function of Reynolds number, cooling temperature ratio and Stefan number.

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In the previous study, we clarified various fundamental characteristics, such as radiation temperature, radiosity coefficient, emissivity and reflectivity, of 3 kinds of infrared radiometers to measure temperature distribution on a non metal surface, on which gray-body approximation is applicable. However, gray-body approximation is not always applicable to all material surfaces. For instance, its approximation is not appropriate on metal surfaces owing to the effect of the directive and spectral properties. Therefore, in the present study, applicability of pseudo-gray-body approximation on a metal surface enclosed by black body walls at constant temperature was studied and analyzed to establish a simpler and more general measurement technique using an infrared radiometer.

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Since a conventional air cleaner equipment generally uses more than 6.6 kV ionized voltage for dust charging and 3.5 kV electric voltage as a dust collector, ozone which are discussed with respect to be detrimental to human health are generating. This paper presents a new air cleaner equipment which utilizes low electric voltage to efficiently collect floating dusts in air without generating ozone effects.

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The combustion behavior of single fuel droplets of water-in-'A' heavy oil emulsions was observed in an electric furnace in order to elucidate the dominant factor for the occurrence of microexplosions. The tests were carried out by changing the following parameters : the size of water droplets in the emulsified fuels having the same water content, the ratio of water to 'A' heavy oil, and the power of surfactants in the emulsions. The results reveal that it is not the ratio of water to 'A' heavy oil, but the size of water droplets in the emulsified fuels which plays the most important role in microexplosions and surfactants my be the factor disturbing the occurrence of microexplosions by the effect of stabilizing the emulsified fuels. These phenomena are very similar to 'The Vaporizing Behavior of the Oil Droplet of Water-in-Oil Emulsions on the Hot Surface' reported previously by the authors.

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Cyclic variations of CO and CO₂ emission were investigated in relation to in-cylinder pressure in a small two-stroke engine. High-speed exhaust gas sampling of 200 Hz was carried out at the exhaust port. The results obtained show that the time resolution of gas sampling was insufficient to account for the cycle-resolved fluctuations observed, but was sufficient to show cyclic variation of emissions. The concentrations of CO and CO₂ were measured with regard to the in-cylinder pressure and IMEP. The misfiring effect was examined from the time variations of CO and CO₂ concentrations. The cyclic variation of the ratio of CO to CO₂ and IMEP showed the same periodic pattern under light load condition.

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