As a first step to clarifying the mechanism of scale effects on cavitation erosion, cavitation-induced shock pressure pulses were carefully investigated around four similar flat hydrofoils, from 53mm to 160mm in a chord length C, under a so-called"true similar conditions"of the same flow velocity, incidence and cavitation number as well as almost the same nuclei distribution in the test water, within the subcavitation region. Under these similar conditions, no marked scale effects on the mean pressure are recognized. When C is large, very large U-shaped vortex cavitation bubbles grow and predominantly collapse, resulting in very high locally concentrated pressure pulses on the foil surface. On the other hand, a large number of moderate pressure pulses attack the surface in a smaller C.

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In order to understand the oscillatory phenomenon of Hartmann-Sprenger tube flow an experiment using a two-dimensional tube was carried out, in which synchronous shadowphotography was applied to visualize the flow field changing periodically. At the same time, the pressure distribution in the flow field near the end closer to the nozzle, of the open tube, was obtained. From these exprimental results, the flow pattern during the oscillation was examined in detail and the necessary conditions for starting and maintaining a stable oscillatory flow in an H-S tube were established.

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From the standpoint of engineering, and industry or space engineering, it is important to clarify the basic interference characteristics of underexpanded jets issuing from several pipes towards the atmosphere. In this paper, the interference characteristics of three parallel underexpanded jets, with intervals between each jet axis four times the pipe inner diameters, were studied. In particular, the flow visualizations of both mean and instantaneous flows with time were conducted by the schlieren and shadowgraph methods. Moreover, the length of pseudo-shock waves, the mean pressure and velocity distributions along the vertical axes, and the equivelocity diagrams within a vertical section to the jet aces were investigated in detail. As result, it was found that three parallel jet flows could be classified into 4 patterns for mean Mach numbers, ranging from 1 to 2, at the pipe exit.

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In recent years, there has been considerable improvement the field of computational fluid dynamics (CFD) owing to the development of supercomputers. Instead of the inviscid flow computations the Navier-Stokes computations have been extended with the recent improvements of CFD. The Navier-Stokes computations are charaterized by calculating the energy losses at design and offdesign conditions for turbomachinery components. In the present paper, the FDM-FEM Zonal Approach code was used to compute the two-dimensional turbine cascade flows. The comparison of the computational results with the cascade wind tunnel test results shows excellent agreement in flow patterns nd also in energy losses.

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Turbulent jets discharged from a circular nozzle along both a convex wall and a flat plate are measured in order to reveal a streamwise curvature effect on the structure of a three-dimensional wall jet. In our previous paper⁽¹⁾, we reported differences between these two flows in the wall static pressure, the turbulence intensities, the Reynolds stresses and the mean streamwise vorticity. The present paper describes characteristics in the intermittent region, such as intermittency, skewness and flatness factors, as well as the volume flux. Distributions of all these quantities suggest that there is substantial difference between turbulence structures in the vertical and spanwise directions. Comparing with a flat plate case, some typical features of the wall jet along a convex wall are disclosed. (1) Both the center and width of the intermittent region become smaller in the vertical direction when these are normalized by the local half-width. (2) The skewness and flatness factors of streamwise velocity fluctuations are greater in the outer part of the intermittent region. (3) The entrainment becomes quite considerable in the central portion of the flow; this leads to the increase of the total volume flux.

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A Reynolds stress model is applied to a fully-developed turbulent flow in a curved circular pipe. Numerical results are compared with the authors' experimental data. Computed velocity is in moderate agreement with the experimental result over the cross section, and the Reynolds stress model is available to the velocity field prediction. Reynolds stress components depend on the axial flow distribution, and the calculated turbulence intensity qualitatively resembles the measured distribution.

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A distance-adjustable plane plate, parallel to the reservoir bottom, was placed a position upstream of the die entry. We investigated experimentally the influence of the plane plate on the unstable flow of viscoelastic fluids and the flow rate. The results are summarized as follows: (1) when the jet shows unstable flow, the inflow angles are not symmetrical to the die axis, (2) the flow rate is larger for a moderate plate distance than that in the absence of the plate and (3) when the die entry flow is controlled by the plate, the critical shear rate of the unstable onset can be increased.

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An analysis of rheological properties of magnetic fluids is made for the case of a steady simple shear flow in a strong magnetic field perpendicular to the shearing plane. It is assumed that the particles in the magnetic fluid take a linear, and closely contact each other to make clusters. By applying Galerkin's method, nemerical calculation is made to obtain an approximate solution of the governing equation for the orientational distribution function of the cluster. The numerical results explain well the rheological properties of magnetic fluids.

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In the same way as mentioned in the previous paper, rheological properties of magnetic fluids are investigated for the case of a steady simple shear flow in a strong magnetic field parallel to the shearing plane. It is clarified that the apparent viscosity of magnetic fluids increases with particle numbers forming a cluster and effective diameter of the particle. The increment, however, is not so significant as that in case of a normal magnetic field. Furthermore, it is shown that the behaviour of magnetic fluids as non-Newtonian fluid is complicated due to a distinctive difference of the orientational distribution of the cluster.

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This paper describes the characteristics of leak flow from the rectangular slit simulating the through-wall fatigue crack in pipe related to the Leak-Before-Break (LBB) concept, which is considered applicable to a part of nuclear power plants. The following three items are discussed experimentally and analytically: (1) the leak flow rate from narrow and short slits for the initially saturated water at high pressures and high temperatures, (2) the influence of surface roughness on leak flow rate, and (3) the pressure distribution and exit pressure in rectangular slits.

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The turbine efficiency of a twin-scroll-type variable geometry turbocharger was improved by optimizing the nozzle passage configurations. Then, velocity measurements at the vaneless nozzle outlets divided by a wall were performed with a laser two-focused velocimeter. It was defermined that the flow of the primary scroll nozzle outlet leaks to the secondary scroll. This leaked flow could be suppressed by a reduction of the distance between the tip of the dividing wall and the inlet of the turbine impeller. Further, the turbine efficiency could be improved by making the incline of the secondary scroll nozzle passage approach a radial direction.

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In recent years, scroll machinery has been put into practice as compressors, taking advantage of their high efficiency and low vibration. Based on geometrical relationships of involute teeth of a scroll expander, equations of volume, pressure and output torque are derived. Moreover, practical losses which occur in the scroll expander are analyzed theoretically. The interference of teeth at the end of the suction process decreases pressures in expansion chambers, which lessens the torque and the suction flow rate of the expander. The interference of teeth at the beginning the discharge process prevents a sudden drop of the pressure in the discharge chamber and recovers the under-expansion loss. Leakages through axial clearances increase the flow rate of the expander and decreases torque greatly. An experimental scroll expander showed reasonable performance and recorded its maximum efficiency of 75%.

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The aerodynamic performance of high-specific-speed mixed flow compressors was studied. The specific speed, N_s, was 450 to 550 (m³/min)^1/2 (rpm) (m^-3/4), with approximately a 2.0 pressure ratio per stage. The meridional flow path from the outlet of the mixed flow impeller was inclined in the axial direction and entered into a curved diffuser. A theoretical flow analysis and performance test were carried out. Distributions of the flow velocity, temperature probe. The flow, including the boundary layer, was surveyed. The mixed flow impellers showed high efficiency and handled a flow rate of about three times as much as that of conventional centrifugal impellers. This development contributes tremendously to reducing the compressor size. A 200000m³/h multi stage compressor of this design is in operation.

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The effect of the thermal conductivity of the condenser material on the dropwise condensation heat-transfer has been studied analytically. By taking account of the contribution of the droplet resistance in the individual dropsize class to the thermal resistance in the transient dropwise condensation, the authors derive a fundamental differential equation describing the constriction resistance phenomenon caused by the inhomogeneity of the surface heat flux. It is found from the nondimensionalized form of the fundamental equation that the constriction resistance can be determined by a Biot number defined with the interfacial heat-transfer coefficient, the departing drop radius and with the surface thermal conductivity, in addition to a few characteristic parameters. By applying the so-called equilibrium region of small drops as the drop-size distribution, this equation is solved numerically so that the effects of these parameters on the heat-transfer coefficient are presented.

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The purpose of this paper is to investigate the characteristics of direcct-contact condensation heat transfer. The jet of Freon vapor (R11 and R113) was injected against a uniform water stream in the vertical tube of inside diameter D=30mm. The temperature distribution in the vertical direction was measured for water flow rate Q_w=5∼20×^-6m³/s, Freon liquid flow rate Q_f=0∼2.17×10^-6m³/s and temperature difference ΔT=T_s-T_w=5∼35K. The results of experiment on the heat-transfer characteristics clarified the relation between the height of effective heat-exchange region, H and the ratio of heat-exchange quantity to its critical value, φ/φ_c.

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Pressure and fluid oscillations with steam injection into pool water were discussed from the view point of the conversion of thermal energy into mechanical work. When the change of fluid state moves clockwise in the p-V diagram, the oscillation sustains since the thermal energy changes into positive work. The equations defining the mechanical work at the condensation oscillations were presented. The oscillation threshold determined by the condition that mechanical work became zero, coincided with the values derived by the linear oscillation theory. The changes of pressure and specific volume during chugging were also shown with one dimensional simulation analysis. The p-V diagrams at various chugging modes were presented with the movement of steam water interface, and the conversion efficiency of thermal energy to mechanical work was also discussed.

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An experimental study has been conducted to investigate the low limit of film boiling in subcooled water. Test specimens selected for the present experiments were a silver cylinder (20mm in diameter and 70mm long) and a silver sphere (30mm in diameter), whose heat transfer surfaces were coated with a thin refractory paint. The heated specimen was plunged into the subcooled water under atmospheric pressure. The subcooling was varied from 0 to 85 K, and the coating thickness ranges between 0 and 29μm. In the uncoated cylinder the minimum film boiling temperature T_min and heat effect of subcooling on T_min while the q_min increased with higher subcooling. The paint coating produced a much greater enhancement in T<min> for the subcooled boiling than that for the saturated boiling.

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Experimental work was carried out to obtain information concerned with the optimum conditions for the melting of frost on a heat exchanger. An ice particles layer representing frost was melted on a heated base with fins consisting of copper plates. The size ratio of the length between the fins to the height of a fin L/H ranged from 0.33 to 1.33. It was demonstrated that the heat flux supplied to melt the ice particles layer produces a large heat loss compared with the melting of the ice plate. This behavior is mainly attributable to the fact that the ice particles layer is a porous media. The ratio of the net heat flux for the melting to the supplied heat flux Q_m/Q_t is dependent on the density of ice particles layer, the supplied heat flux, the environmental temperature (initial temperature of the ice particle layer) and the size ratio of the fin.

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A numerical study is presented for the laminar flow and the heat transfer on the smooth heated surface opposite a single porous-type roughness element on the insulated wall in a parallel plate duct. The calculation was performed for the dimensionless height of an element H=0.357-0.642, the Reynolds number Re=100-1500 and the Darcy number Da=0.000025-0.025. The recirculation flow was generated behind the porous-type roughness element for low Da numbers and aided the increase of local heat transfer. The characteristics were compared with the numerical results for an abrupt contraction and expansion flow due to a single solid-type roughness element in a flow passage.

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The heat transport characteristics of a thermosyphon are experimentally investigated using R 113, methanol and water as the working fluid. The condensation heat transfer at the cooling section shows a trend similar to the Nusslelt's prediction for its temperature difference, while the measured values are considerably lower when the upward vapor velocity is high, as in the case of water. Based on the characteristics in heat transfer at the cooling and heating sections, non-dimensional expressions are derived for relating the heat transfer at the cooling and heating sections, non-dimensional expressions are derived for relating the heat transport rate of thermosyphons to the temperature difference between the heating and cooling sections.

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An experimental investigation on the forced convection boiling of binary mixtures of refrigerants R11 and R114 is reported. Local heat transfer coefficients in a horizontal tube were measured for each pure fluid and three compositions of mixtures. In the boiling-dominant region the large degradation of heat transfer coefficients due to mixture effects could be recognized, but in the convection-dominant region there was little effect except for the change of fluid properties. A correlation is proposed for heat transfer coefficients, where the mixture effects are taken into account only for nucleat boiling.

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For the development of an air-cooled heat exchanger, mist cooled heat transfer on horizontal circular tubes exposed to the horizontal crossflow is discussed. Analytical and experimental studies were performed on the droplet collision on the tube, and the wetting conditions based on the droplets deposition and their fluidity. Heat transfer was clarified including a comparison with results in a vertical spray flow.

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A numerical investigation was made on fully developed laminar forced convective heat transfer in curved rectangular ducts rotating at a constant angular velocity about an axis through the center of curvature of ducts. Thermal boundary conditions of fluid flow are assumed to be subject to uniform wall heat flux. Navier-Stokes and energy equations are solved by the finite difference method for air. The case for the negative rotation of a duct is considered. Velocity and temperature fields are obtained for various rotation rates and Re numbers. It is found that an additional pair of vortices appears in the vicinity of the inner wall under the influence of Coriolis force and in the vicinity of the outer wall under the influence of centrifugal force. The friction factors and Nusselt numbers are also obtained. The numerical results in regard to the friction factors are in good agreement with experimental results obtained by other researchers.

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The heat transfer performance of coaxial straight heat pipes in high-speed rotation has been analyzed. The parameters are the geometry of the pipe, the kind of working fluid, the mass of the working fluid charged in the pipe, the rotation rate and the heat load. As a result of the analysis, the distribution of film thickness in the pipe, the Nusselt number of the evaporator and condenser section, and the dryout conditions at the end of the evaporator section were found. The Nusselt number from the present analysis is compared with the experiment by Ohtsuka et al. The predictions are is good agreement with the experimental data in the condenser section, but are about 80 100% lower in the evaporator section.

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The effective use of wall radiation can enhance heat transfer of high-temperature heat exchangers for Stirling engines. A heat exchanger consisting of flattened U-tubes with a staggered arrangement is equipped with radiation plates and radiating porous media. Both the radiation plates inserted between the tubes and the porous media installed downstream of the tube bundle are heated by high-temperature combustion gas through convection, , and these heat the tubes by wall radiation, working as a kind of extended surface. The radiation effect is predicted to enhance the heat transfer coefficients at the outer tube surface by about 50%, which depends on the emissivities and the combustion gas temperatures. This heat transfer performance is also compared with that of a round U-tube bundle.

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A general method of solution using the boundary element method (BEM) is developed for multi dimensional inverse problems of heat conduction. A concrete formulation is presented for the one-dimensional problem in which the surface temperature and the surface heat flux are sought from the temperature measured at two interior points. By solving the Beck's problem, the stability of the calculation is studied, and the result is compared with that of the method based on the Duhamel theorem. A simple two-dimensional problem is also dealt with in an attempt to show the applicability of the present method.

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In the present study, measurements of the thermal conductivity of solid materials with high conductivity such as metals were carried out by"a transient hot wire method of comparison"previously reported by the authors in which half of a specimen was exchanged with a reference material. A thin ribbon hot wire was employed for electrical insulation between the hot wire and the specimen. Three methods were developed for electrical insulation between the hot wire and the specimen. Consequently, it was found that the materials with high conductivity to about 100 W/(mK) can be roughly measured by the hot wire method.

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An experimental study was performed on the effective thermal conductivity of screen wicks saturated with a liquid. A planar heat pipe was employed to determine the effective thermal conductivity, and its value was calculated from the heat transfer coefficient in the condenser of the heat pipe positioned horizontally. A comparison of the existing correlations with the present experimental data indicated that the effective thermal conductivity of screen wicks could be predicted by Maxwell's equation derived for the case where wick materials (or screens) were dispersed in working liquids. It was also found that, in predicting the effective thermal conductivity by Maxwell's equation, the thickness and porosity of multilayer screen wicks had to be estimated accurately by taking account of the intermeshing between screen layers.

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A model of the reaction rate in a turbulent premixed flame, based on the local three eddy scales of turbulence (TEST Reaction Model), is proposed to predict time averaged profiles of the velocities, temperatures and species concentration in combustion systems dominated by an intense turbulence. The fundamental features of the model consist of a combustion reaction in the dissipating eddies of the Kolmogorov scale, sticking on the surfaces of Taylor's microscale eddies, and propagating flames within the microscale eddies. The mixing and flame spread in a large scale flow field are dominated by the length scale derived from the k-εturbulence model.

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This study was carried out to clarify the effects of a radiation energy convertor (porous medium) employed in a fluidized bed combustor. The effects of a porous medium were investigated for various conditions which include the bed temperature, stable combustion state, combustion load, excess air ratio and energy conservation rate. In order to clarify these effects in detail city gas was used as the combustion fuel. The experimental results reveal that a higher bed temperature and wide stable combustion range can be obtained by installing a porous medium. Especially, the required combustion loads can be reduced to 50-70% of that needed when a porous medium is not used under the conditions that the bed temperature and excess air ratio are maintained uniformly. This combustion technology may be applied for developing a combustion system of extremely low calorific fuels such as high water content materials.

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A combustion process showing a slow temperature rise was realized in an intense radiation field by burning a lean combustible mixture in a cylindrical combustion chamber lined with a refractory in which a permeable plate was placed at the upstream and downstream ends, respectively. It was found by the measurement of the temperature and composition of gas along with the ion current and by high-speed schlieren photography, that a laminar flame was attached to the lower part of the red-hot refractory surface and that it spread towards the upper central portion, even if the mixture strength was below the lean flammable limit. The flame becomes convex toward the unburnt mixture due to some instability resulting in a kind of cellular structure. The flickering of the flame due to the wavy motion of the flame base and the cellular structure is the cause of the slow temperature rise.

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Experiments were performed to make clear the effects of the equivalence ratio and the turbulence characteristics on the combustion of a propane-air homogeneous mixture. A turbulent flame propagating nearly axisymmetrically in the swirling flow was produced in a disc-type combustion chamber. The burning velocity S_r, the burning zone thickness δ_r of turbulent flames and the laminar burning velocity S_L, were measured under various conditions. The main results obtained are as follows: (1) Both S_r and S_L depend on the equivalence ratio and have a maximum value under the condition of slightly rich mixture, (2) the value of δ_r increases with the increase of S_r/S_L, (3) the ratio of the burn duration of main combustion stage to the total burn duration decreases and the ratio of the early combustion stage increases with the increase of turbulence intensity, but those are almost independent of the equivalence ratio.

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A combustion evaluation concept is introduced on the basis of the spray droplet size distributions in order to determine the optimum atomizing condition for combustion efficiency. The Combustion Index CI to predict the combustibilities is then defined using the dimensionless parameter Stk (Stokes number) which analyzes the trajectories of spray droplets. This is a very useful prediction method to evaluate the combustibilities of CWMs. However the application to various liquids appears to be invalid, since the droplet size distributions of typical fuel oils are different from those of CWM. The major objective of this study is to apply this prediction method to"more homogeneous"liquid. The atomizing tests for fuel oil are carried out varying the air/fuel ratio and liquid flow rate. Based on the results, the CI developed for CWM is then modified to predict the optimum atomizing condition for fuel oil. The predicted results are verified by heavy oil combustion tests.

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The purpose of this study is to investigate flame propagation phenomena through a stratified charge. The stratified charge consists of two or three of two or three propane-air mixtures of different equivalence ratios. Mixtures are arranged in series with a constant volume bomb which has particular slide valves. Changing the composition of the stratified charge, we measured the duration of combustion and the concentration of unburned hydrocarbon. The results are as follows: lean mixtures, the combustion of which are unstable by themselves, can be burned stable by the stratification. If the overall equivalence ratios of stratified charges are the same, a homogeneous charge has a faster flame propagation speed than any other stratified charge. And on this condition, the duration of combustion and unburned hydrocarbon in crease in proportion to the degree of stratification.

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The direct-injection stratified-charge engine has the advantages of higher thermal efficiency and less CO and NO_x emission levels than conventional spark ignition engines. However, its actual utilization is prevented by high unburned hydrocarbon emission levels during light-load operations. In order to reduce the unburned hydrocarbon emissions, the effects of intensification of local premixing by radial fuel injection were examined experimentally using a pancake-type constant volume bomb. Unburned hydrocarbon emission levels by this"locally homogenized DISC system"with radial fuel injection were shown to be lower than those of tangential fuel injection cases. Moreover, the emission levels were discussed by comparing them with unburned hydrocarbon levels of premixed turbulent combustion.

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The influence of injection characteristics on the performance of a direct-injection diesel engine driven by water to gas oil emulsified fuel was investigated. As result, it was confirmed that although the spray characteristics such as atomization, drop-size distribution and dispersion for emulsified spray deteriorate in comparison with those for gas oil spray, sufficient improvements in the specific fuel consumption, smoke density and NO_x concentration can be expected using the emulsified fuel. It was also found that when a low pressure and low injection rate are used with emulsified fuel, the specific fuel consumption, smoke density and NO_x concentration are lower than those for a high pressure and high injection rate with gas oil.

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The soot emission from diesel engines generally increases with the shortening of the ignition lag. However, the mechanism of this phenomenon in the combustion chamber is obscure and difficult to follow. The objective of this investigation is to observe and analyze the in-chamber soot formation process under varied ignition lag with simultaneous photography of the direct flame image and laser shadowgraph. In the experiment, the qualitative measurement of the soot concentration was carried out by subtracting the laser light extinction through a non-firing chamber from that through a firing chamber. It was found that the soot concentration in the divided chamber showed a maximum immediately after the start of combustion, and reduced rapidly. With a shortening of the ignition lag, the maximum soot concentration in the divided chamber increased while the apparent soot formation rate decreased.

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The relations between induction swirl and flows from the inlet valve of a diesel engine were examined using a water model and a rig which is an apparatus for estimating swirl veiocity. The results obtained are as follows. (1) One-sided flows flom the inlet valve based on biased flows in the inlet port and on the shrouded valve cause swirl geneation to occur to a large extent. (2) The direction of flows around the inlet valve hardly changes with valve lift in the rig tests, but in the dynamic water model it changes to some extent during large valve lift by affecting the inlet port shapes. (3) According to the dynamic effect of the intake, swirl velocities obtained from the water model are larger than those of the fig tests.

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The validity of the method for numerically predicting the three-dimensional unsteady flow characteristics in the intake port has been examined by comparing the numerical results with the experimental ones under steady conditions. Although the data for the comparison are not sufficient, it seems that the calculation has simulated comparatively well the general characteristics of the flow at the intake valve outlet. From the comparison between the swirl ratio calculated from the flow characteristics at the valve outlet and the swirl ratio calculated from the flow characteristics at the valve outlet. Furthermore, an investigation has been made into the effect of the helical port configuration on the induction swirl intensity and the volumetric efficiency. The effect of the configuration of the valve head and helical part both on the swirl intensity and on the volumetric efficiency has been demonstrated with regard to the helical port.

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With the aim of application to the measurement of ammonia concentration, an ammonia converter was constructed using commercially available platinum catalyst. The dependences of the ammonia converter efficiency on reaction temperature and ammonia concentration were investigated by measuring the concentration of the converted nitric oxide. The results have shown that the catalyst used almost completely oxidizes ammonia into nitric oxide at temperatures above 600°C in the tested range of ammonia concentration. In addition, the combination of the ammonia converter and a chemiluminescent NO_x analyzer was found to be able to measure ammonia concentration in an ammonia-nitric oxide mixture with a precision within 3% by making a correction due to oxygen concentration.

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