In this study, a new computational modeling of the gas-surface interaction is proposed to explain experimental results of the scattering of gas molecules from solid surfaces, especially engineering surfaces. The characteristic feature of the model is to settle the collision layer and the adserbed gas layer, involving surface molecules and adsorbed molecules, respectively. Incident molecules experience force due to the gas-solid potential gradient, and change their trajectories which is computed by the molecular dynamics method. The gas molecules are scattered from the surfaces after collisions with surface or adsorbed molecules. The examined characteristics are compared with the experimental results : flux distributions, TOF spectra and the average energy of scattered molecules.

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The present study focuses attention on a three-dimensional Lennard-Jones system in a thermodynamic equilibrium to discuss the divergence processes, the relationships between time intervals and divergence times, and the influences of the time intervals on transport coefficients, under various conditions of number densities and temperatures. The main results obtained here are as follows : the velocities of molecules in the system increase gradually with time, and then the system diverges exponentially suddenly at a specific time ; the time interval-divergence time relationships can be expressed approximately as linear functions if the log-log scale is used, and the system diverges more easily as the temperature or the number density increases ; as long as such sufficiently small time intervals that the system does not diverge are used, the values of transport coefficients and thermodynamical quantities are approximately independent of the values of time intervals.

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The distribution of erosion rate on the target influences the distribution of film growth rate on the substrate. Correlation between the two distributions is examined experimentally in the pressure range of 0.3-10 Pa and for the mass flow rates of 0.5 and 5 sccm. The erosion and growth rates are measured by use of a microbalance. It is found that the pressure has a large effect on the distributions of the erosion and growth rates whereas the mass flow rate has little effect. At a low pressure, the flow pattern in the chamber is reflected in the distributions of erosion and growth rates. Correlation between the two distributions is clearly found at any pressure.

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This paper presents an anisotropic dissipation term modeling for the Reynolds stress transport equation, and presents a comparison with Direct Numerical Simulation (DNS) data for three different flow systems. In the present model, the anisotropic tensor of the dissipation term is evaluated using three algebraic expressions, e^S_ij, e^R_ij and e^W_ij. e^S_ij represents the effects of only fluctuating velocity, and constitutes the anisotropic tensor of Reynolds stress. The term e^R_ij includes the effects of the mean velocity gradient tensor in addition to that of fluctuating velocity. e^W_ij is analogous to the wall term in the redistribution term for Reynolds stress equations, and reproduces near-wall behavior of the dissipation term. The present model predicts the anisotropic tensor of the dissipation term with good accuracy with respect to diagonal components. However, for non-diagonal components, the predictions are not accurate enough for all systems. Some improvements are necessary for expression of model functions.

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The equation of motion for a cluster of solid spheres moving in fluid at low Reynolds numbers is developed taking into consideration of hydrodynamic interaction among the spheres. The hydrodynamic forces of the spheres in the equation of motion are estimated using their relative velocities. The relative velocities are assumed to be represented by superposing Oseen's flow field around each sphere. When the inertia term is negligible in the equation of motion for the spheres, it is shown that the analytical solutions are easily obtained for free-fall motions of solid spheres in fluid. In order to discuss the effectiveness of the above-described method, experiments for two equal spheres falling freely in quiescent glycerol are carried out. The numerical results show good agreement with the experimental results.

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The fluid flow through woven screens in a circular pipe was measured to evaluate the resistance coefficient of those screens. Three kinds of screens, stainless steel, brass and polyethylene, made of round wire forming a square mesh, were used in this study. The Reynolds number based on the pipe diameter was kept constant at 9×10⁴. Results show that after the flow passes through the three kinds of screens, the velocity profiles show three different patterns due to the coefficient of porosity. In particular, the velocity profile for the polyethylene screen is different from those for the stainless and the brass screens. The resistance coefficient K vs the wire diameter Reynolds number can be classified into three categories according to the patterns of the velocity profile. The value of K for the polyethylene screen is larger than those of both the stainless and brass screens because the streamwise gradient of the streamline through the polyethylene screen shows the maximum value. The use of average velocity U_e/β and pore spacing l as a characteristic velocity and scale enables a more general correlation between the resistance coefficient and the Reynolds number.

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Incompressible flows around an inclined circular cylinder have been calculated by the finite difference method. The third-order upwind scheme is used to simulate high Reynolds number flow, and a no turbulence model is employed in this study. Computations are carried out at Reynolds number of 2000 and the yaw angle is changed from 0 to 60 degrees in order to observe its effect on the flow. Moreover, the effects of the boundary layer generated by the side wall are also investigated. The calculated pressure distributions around the cylinder are compared with experiment, and the agreement is satisfactory. The results of this computation show details of the flow especially in the wake region, and it is found that the yaw angle and the boundary layer on the side wall greatly affect the location of the separation point and, therefore, the wake structure.

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Using the branch model in which the side branch bifurcates at a right angle from the trunk, the effect of the shape of the side branch and the flow conditions have been experimentally studied on the variation of wall shear stress in laminar steady flow. The experiment has been carried out on three branch models which have different curvatures at the upstream corner and the same sharp square edge at the downstream corner. The wall shear stress along the proximal wall of the side branch sinusoidally varies downstream, and the gradient of wall shear stress along the proximal wall becomes markedly large. The high wall shear stress which arises around the upstream corner of the side branch is strongly related to the secondary helical flow from the trunk into the side branch. This variation strongly depends on the curvature at the upstream corner and the flow distribution ratio of the side branch to the trunk.

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Oscillatory laminar flow in the inlet region of a circular curved pipe, with a curvature ratio of 11.7, has been investigated by the flow visualization method. The experiments were carried out under the conditions of the Womersley numbers α=5.5∼18 and the Dean number D=300. The velocity was measured using a tracer technique and the instantaneous velocity distributions were obtained at four selected phases in one cycle. The flow mechanism has been made clear in the region from the upper stream tangent to the curved pipe. The flow in the curved pipe is closely related to the flow in the upper stream tangent, and the velocity distribution changes drastically with the phase at the inlet region. The inlet length of oscillatory flow is less than that of steady flow and becomes shorter as α increases.

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When a compression wave propagates along a constant-area straight tube and reaches its open end, an impulsive wave is emitted outward from the exit toward the surrounding area. Assuming a compression waveform as an arctangent curve, the magnitude of an impulsive wave is obtained explicitly in terms of the pressure rise and length of the compression wave. The variation of pressure with time at the exit and the magnitude of an impulsive wave obtained from the present method agree well with the numerical results solved by the TVD scheme.

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As a fundamental consideration in hydraulic valve dynamics, transient laminar flow through a pipe orifice has been studied via numerical analysis. In the previous report the authors performed time-dependent calculation from the initial stationary state under a suddenly imposed pressure gradient, and pointed out that the dynamic behavior is characterized by two time constants. The present report treats the transient flow starting from an initial steady flow. Effects of the recirculating flow and the stretched contraction flow region are investigated in comparison with the previous result.

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Solid spherical shells of mm-order diameter can be applied to lightweight structural materials, buoyant catalytic agents, high-performance solid fuels, and artificial organs. The sequential spherical shell generator in liquid-liquid-gas systems comprised of a cylindrical container containing two immiscible liquids and a gas injection nozzle at the center of the bottom. By controlling the gas flow and the temperature field of the two-layer liquids, liquid spherical shells were formed at the interface between the two immiscible liquids and were solidified during the upward motion. For the stable production, it is necessary to correctly estimate the thermal fluid flow and to control the temperature field in the two-layer liquids with high accuracy. To develop the sequential solid spherical shell generator, natural convection heat transfer in the irnmiscible two-layer liquids in the cylindrical container was studied. By solving the incompressible Navier-Stokes equations and the energy equations for the upper and lower liquids, the flow patterns and thermal field of the two-layer liquids were quantitatively investigated. The suitable conditions for the sequential production of solid spherical shells were explored.

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Direct numerical simulations of Taylor-Couette flows were conducted using a spectral method to clarify a wave-number selection mechanism in the axial direction. For initial conditions, one or two axial modes are superposed on the Couette flow and the growth rate is carefully examined. The calculated relationship between the critical Reynolds number and the critical wavelength for the onset of Taylor vortex flow coincides with the previously reported experiment and linear stability analysis. From this study, we have obtained the following conclusions. (1) In the case that the growth rate of initial disturbance λ is smaller than that of λ/2, the vortex which has axial wavelength λ changes its wavelength to λ/2. (2) In the case of initial fluctuation energy with two different modes, selection of axial mode depends on the total amplitude of initial fluctuation and the relative intensity of each mode. (3) Initially, axial fluctuation energies of two different modes develop independently. As these energies reach some critical amplitude, axial wave-number selection occurs and axial fluctuation energy of nonselected mode decays exponentially. (4) Circumferential fluctuation energy of nonselected mode does not decay exponentially but remains constant.

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This paper describes the basic issues in parallel computation of computational fluid dynamics (CFD) which are analyzed with a parallel computer. The parallel computer used is a cellular array processor called the AP 1000, operated by Fujitsu Parallel Computing Research Facilities. This paper is concerned with the adaptation of a Poisson equation solver, based on the successive over-relaxation method (SOR), to parallel computation. The convergence and relaxation factors of the SOR and the Red-Black SOR are examined. The optimum relaxation factor of the SOR decreases in the parallel computation ; while a high value of relaxation factor can be retained in the Red-Black SOR. Consequently, the Red-Black SOR is found to be a more effective solver in parallel computation. The present paper deals with parallel computation by means of the MAC. SMAC and HSMAC methods applied to a cavity flow. The computed field is decomposed into several domains. Each domain is assigned to one processor. With the methods tested, a high efficiency could be obtained by the present algorithms.

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Numerical simulations for every flow require enormous computing time during iterations. In order to solve this problem several techniques have been proposed, as for example, a multigrid technique. A method using fuzzy reasoning is one such technique. We studied the possibility of accelerating computation with fuzzy reasoning in 2D incompressible laminar flow calculations. In order to obtain qualitatively correct velocity distributions some rules were constructed on the basis of human reasoning. Viscous and obstacle effects were introduced. In addition the recognition of the wall was programmed in order to find the separation point and the backward region. It was found that our procedure can realize a considerable acceleration in the calculation of channel flows which have some convexities and back-step flows.

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We measured the velocity distributions of laminar round jets discharged into stagnant air by the LDV system. Using particles of smoke, we developed a measuring scheme to evaluate the velocity field exactly. We have measured the velocity field not only in the axial direction but also in the radial direction which has never been previously measured. In addition, we have suceeded in measuring the velocity field in the jet pipe. From this experiment, we have established the condition that the centerline velocity of jets is accelerated by gravitational force. To confirm the experimental results, we have carried out the numerical analyses using a code which we developed. The results of the numerical analyses supported those from the experiments.

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The numerical simulation results of tracer gas diffusion from a continuous point source in an unstable boundary layer were obtained and compared with wind tunnel experiment results. The flow fields were predicted by the k-ε model. The obtained turbulent kinetic energy showed good agreement with that from wind tunnel experiments when the buoyancy term of the dissipation equation was eliminated and the wall functions including universal functions were used. Then the predicted turbulent kinetic energy was divided into directional turbulence intensities using algebraic equations and an eddy viscosity concept. Using estimated turbulence intensities, tracer gas diffusion was simulated by a Lagrangian particle dispersion model. Predicted mean concentration profiles showed good agreement when turbulence intensities were obtained from algebraic equations. The Lagrangian time scale T_L was estimated from the flow calculation results, T_L=(k/ε)/C_1ψ, and compared with analytically obtained profiles. The model constant C_1ψ=2, the same value as in the neutral boundary layer, was obtained for the simulation of the tracer gas diffusion in an unstable boundary layer.

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Aerodynamic sound radiated from the low-Mach-number turbulent wake of a circular cylinder has been numerically predicted by the following two-step approach. First, the three-dimensional unsteady incompressible Navier-Stokes equations are solved by the large eddy simulation (LES)technique using a streamline upwind finite-element method. The far-field sound pressure. is then calculated from the fluctuating surface pressure on the cylinder, based on Curle's equation. A sophisticated method has been proposed for computing the SRL radiated from the entire span of the cylinder using the surface pressure fluctuation obtained in a small spanwise computational domain. The method takes the effects of random phase shift of the surface pressure fluctuation into account. The predicted SRL is compared with the measured value. Fairly good agreement has been achieved between the predicted and measured SRL's for the peak spectrum intensity and the frequency dependency of the sound pressure level up to about ten times higher than the peak frequency.

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Pure tones are unexpectedly generated from slits such as a gap between a window and a pole or a damper when wind is strong. We named this type of pure tone as a whistle tone. As the first stage of this study we made clear that the whistle tone was generated by air jet flow from a rectangular slit. The geometry of the slit and the velocity of the jet flow had important effects on the generation of discrete frequency noise (DFN). Those parameters to cause the generation of DFN were limited within certain ranges. The frequency of whistle noise was linearly related to the jet velocity, which means that the mechanism of the generation of whistle noise is different from that of screech noise and the tone caused by an interaction between the jet and a solid body in the jet stream.

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Although analytical and experimental studies on the bending propulsion mechanism of fish or cetaceans have been carried out by many researchers, the reasons for high speed and high efflciency of the bending propulsion motion have not been clarified, probably because the dynamic interaction between mechanism and fluid has not been taken into account. In this study, we investigate the characteristics of the force acting on a three-joint bending propulsion mechanism using the analytical method proposed for a coupled system of the mechanism and the fluid. It is found that the inertial force due to the added mass of fluid which produces the forward thrust is dominant when the propulsive displacement in one period of the bending motion is small, and the lift force which produces the drag becomes large when the propulsive displacement becomes large.

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Although analytical and experimental studies on the bending propulsion mechanism of fish or cetaceans have been carried out by many researchers, the reasons for high speed and high efficiency of the bending propulsion motion have not been clarified, probably because the dynamic interaction between mechanism and fluid has not been taken into account. In this study, we investigate the characteristics of the energy consumption and propulsive efficiency of a three-joint bending propulsion mechanism using the analytical method proposed for a coupled system of the mechanism and the fluid. It is found that the propulsive efficiency has a maximum value of 45% when the propulsive distance in one period of the motion has a certain value and when all phase differences between joints are approximately 60 degrees.

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Flow around Savonius rotors was simulated by solving 2-d Navier-Stokes equations. The equations were discretized by finite volume method for space and fractional step method for time. Convection terms were specially discretized by an upwinding scheme for unstructured grid. Only rotating rotors were simulated in this report. The values of parameters were as follows : Reynolds number, 10⁵ ; overlap ratio, 0 and 0.16 ; tip speed ratio, 0.25-1.75. Results showed good agreement with experimental data for the following points : optimum tip speed ratio is 0.75-1.0 ; overlapping is effective in increasing power coefficient. Moreover, simulated flow fields showed that vortex shed-ding occurs not only at the tips of the bucket but also at the back of the bucket.

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A full three-dimensional lifting surface theory based on the double linearization concept is developed for a rotating annular cascade model operating at axial supersonic velocity. It is assumed that each blade vibrates with infinitesimal displacement amplitude under small mean loading. Vibration modes normal and parallel to the blade chord are considered. Numerical results are presented to investigate the mean loading effects on the aerodynamic instability of the blade motion. It is found that the bending motion can be unstable due to the presence of mean loading. Some numerical results compared with strip theory predictions demonstrate significant three-dimensional effects on the unsteady aerodynamic force.

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This study aims at reducing secondary flow and associated losses in total pressure in axial-flow turbines. Boundary layer fences were attached to the casing wall of an annular nozzle cascade. Hot-wire and pneumatic measurements were carried out downstream of the cascade for 7 different protruding heights of the fences. The optimum height of the fences was approximately 1/4 of the inlet boundary layer thickness. The optimum fences reduced the passage-mass-averaged loss by 14 percent from the unfenced blading value. This reduction resulted from local loss reductions within and near the blade wake, which compensated for the installation of the fences. The maximum underturning, induced by the secondary vortices, was markedly attenuated with the use of optimum fences.

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This paper discribes the characteristics and approximation of a radial turbine for exhaust gas turbochargers under steady and unsteady flow conditions. The experiments were carried out at several velocity amplitudes and pulse frequency ranges with sinusoidal waveforms. The approximation was conducted on the assumption of a one-dimensional equivalent nozzle considering the ratio of velocity amplitude. As a result, the following is clarified. For most turbines under unsteady flow conditions, the time-mean mass flow rate becomes less than the steady one at the same turbine expansion ratios as the ratio of velocity amplitude becomes large. Approximated results of mass flow rate using the equivalent nozzle show good agreement in the characteristics of both steady and unsteady flow conditions in consideration of windage states.

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Recently, lever-type water supply valves have been used in many applications. They can be opened and closed quickly and are easy to operate. On the other hand, water hammers are often created when the valve is closed quickly. We devised a spring-type shock absorber with venturi tube for a water hammer. The aim of this paper is to describe characteristics of the water hammer and shock absorber by experiment and numerical simulation. From the computer simulation, we determine the characteristics of the water hammer and shock absorber, including not only the pressure displacement but also the flow velocity and piston displacement inside the shock absorber.

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An experimental study was made on the suction characteristics of a water ring vacuum pump sucking dry air at a water ring temperature in the range of 10-40°C. The characteristics were considerably influenced by the temperature of the ring water. However, by properly considering the vapour pressure of the ring water, it was possible to derive a characteristic curve applicable to the ring water at any tested temperature between 10 and 40°C.

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Basic experimental studies were performed with the objective of developing a jet pump which may be used for new nuclear reactors. Three jet pump scale models were tested to investigate efficiency and cavitation performance, especially the difference between room-temperature and high-temperature. Comparisons of test results with the derived theoretical model clarified the behavior of important parameters governing the characteristics and suggested a further increase in the efficiency. Under high temperature, efficiency showed a slight decrease. Oscillations in differential pressures were observed in the range of flow ratios higher than efficiency peak points. The oscillations, however, were decreased at high temperature compared with those at room temperature.

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The motion behavior of a rotor for a spherical valve plate has been measured in a bent-axis-type axial piston pump. The behavior of the rotor is represented in two-dimensional polar form and by the minimum film thickness between the rotor and the spherical valve plate. In the case of a pressurizing suction port, (1) the attitude angle of the rotor and the azimuth angle of the rotor increase as the operating conditions become severe, (2) the minimum film thickness is related to bearing modulus, and (3) the behavior of the rotor is quasi-static motion. In the case of a reducing suction port, the minimum film thickness increases as the pump delivery pressure increases.

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In order to investigate the basic features of transportation gases, an analytical study of the combined phenomena of molecular diffusion and natural convection of two-component gases in a reverse-U-shaped tube is performed. One dimensional basic equations for continuity and conservation of momentum are numerically solved to obtain the mole fraction change and the onset time of natural circulation in the reverse-U-shaped tube. The numerical calculation is carried out in the ranges of 3.0×10⁸≤Gγ_TSc²≤2.5×10¹⁰, 1.4×10⁸≤Gγ_cSc²≤8.5×10¹⁰ and β_c'(X_Bmax-X_Bmin)≤0.1029. In addition to this, the relationship between the onset time of natural circulation and the Grashof number ratio (R_Gr=Gγ_T/Gγ_c) is expressed by t^*_in=2.199R_Gr²-2.987R_Gr+1.0272 when the R_Gr is lower than 0.66.

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Both mass transfer in the gas phase and heat transfer in the liquid phase are examined experimentally for gravity-controlled condensation of ethanol and water vapor mixtures on a vertical surface. Some flow patterns of the condensate are observed in relation to the measured concentration of condensate and the heat flux. The departure from the smooth-film-wise condensation is considered to be related to the local fluctuation of surface tension over the condensate film. For the gas-phase mass transfer, the laminar boundary layer theory, applied taking into consideration the increased mass flux, is approximately valid even for the case of drop-wise condensation.

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Close-contact-melting heat-transfer characteristics, including natural convection in the liquid region in cylindrical capsules were studied theoretically. Elucidation of such heat-transfer mechanism is of great importance from the view-point of cost-effective ice storage and heat storage systems employing the latent heat-of-fusion thermal energy storage (TES) concept. The Growth Ring Method (GRM) was used as a numerical tool to handle the moving interface between the liquid and solid regions. The computed isotherms, streamlines and stored heat fractions were clarified in detail. In particular, a special attention was focused on the role of natural convection in the upper liquid region. Hitherto, no exact numerical analysis has been made to clarify the contribution of natural convection.

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There is a possibility that flow induced by the gradient of wall temperature can occur in a container filled with a rarefied gas. Simulation of this type of flow is important in material technology, such as chemical vapor deposition or in the design of thermal devices effectively utilizing this phenomenon. The objective of the present study is to clarify the possibility of modeling this type of flow by the direct simulation Monte Carlo method.

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In the present report, the effect of liquid properties on the effective thermal diffusivity of the oscillation-controlled heat transport tube (the so-called dream pipe) is investigated. First, a slip flow model is presented to investigate the fundamental mechanism and the governing quantities of this phenomena. Results of the analyses show that cascade heat transport between the stagnant boundary layer and the core liquid, which is caused by phase shift between the radial conduction heat-flux and the oscillation, is the fundamental mechanism of the phenomena. Next, it is found that the effective thermal diffusivity reaches a maximum at a value of the thermal diffusivity of the liquid because the phase shift increases with increasing thermal diffusivity. Finally, it is shown that water is one of the desirable operating liquids of the heat transport tube of this type.

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Experimental studies have been carried out on heat-transfer enhancement and flow-drag reduction in a tube by means of wire coil insert. Heat-transfer rate and pressure-drop data of tubes with wire coil inserts have been taken under various experimental conditions of wire coil diameter and pitch, water flow rate and heating-surface temperature. The performance of these tubes with wire coil inserts has been evaluated concerning the increase of heat-transfer rate and flow resistance. The useful nondimensional correlations of heat-transfer rate and flow-resistance factor have been derived as functions of Reynolds number and wire coil pitch-to-diameter ratio.

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Heat transfer downstream of a backward-facing step was controlled using a jet discharged flow from a slit in the duct wall opposite the step. The local heat transfer coefficients were measured for various jet locations, jet velocities and duct expansion ratios. The reattachment region moves upstream and the heat transfer coefficients, which are maximum, increase with jet velocity. The coefficients also increase with the expansion ratio, but to a lesser extent. With appropriate change of the downstream coordinate, the many heat coefficient profiles under various conditions may be normalized to produce a single characteristic curve. The average heat transfer over the peak in each case can be expressed as a function of its maximum.

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In the present study, we propose empirical formulas concerning heat transfer and pressure loss characteristics for pin-fin arrays, which are made of thin pins of square cross section arranged in a rectangular form. The effect of the pin pitches in the flow direction and transverse direction were evaluated and the critical Reynolds numbers, at which the transition from steady laminar flow to oscillating flow begins, were determined from the experimental data obtained by utilizing the modified single blow transient heat transfer test method and flow visualization.

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The effects of thermal conductivity of fins on the heat-transfer characteristics of offset fins in low-Reynolds-number region are studied. Three-dimensional forced convection flow is solved numerically considering heat conduction in fins, and the results are compared with experimental results. It was found that : (1) heat-transfer coefficient on SUS fins in water is less than that on aluminum fins. This is caused by the fact that the thermal boundary layer which developed on the bottom surface relaxes the temperature gradient in the fluid perpendicular to the fin surface, as well as by the fact that the heat conduction characteristics of SUS fins is poor. (2) Analytical results of pressure drop and heat-transfer coefficients agree very well with those obtained by experiment, which shows the validity of the present analyses.

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A new enhancement technique was developed for natural-convection heat transfer from a horizontal heated plate. The technique aims to increase the heat-transfer rate. For this purpose, rectangular grids of which the upper faces were exposed to an ambient fluid were installed on the heated plate. The grids inhibit the buoyant flow from the edges to the center of the heated plate and promote cellular motion within the grid. These two actions increase the heat-transfer coefficients of the heated plate, in particular, in the central portion of the grid. The maximum and the average heat-transfer coefficients within the grids were increased by 40% and 20%, respectively, compared to those for the smooth plate, when the grids with appropriate size and height were used. Further increase in the heat-transfer coefficients will be feasible by adopting high-conductivity grids.

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Experiments were performed to determine the effect of saline water concentration on the melting heat-transfer characteristics of a horizontal ice cylinder immersed in quiescent saline water. The ambient saline water concentration ranged from 0.5 to 3.5 wt% in salinity for ambient temperature ranging from 1.8 to 24.0°C. The measurements show that the flow patterns around the ice cylinder are strongly dependent on the saline water concentration, which considerably affect the local heat-transfer coefficients along the ice cylinder.

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A new heat flux model that is able to explain the two thermal conduction terms in the prediction-based heat flux equation of multilayer insulation (discussed in the first report) is proposed. Based on the new model, the expansion and applicability of the equation to various parameters of multilayer insulation are examined in detail. The prediction equation was derived for various parameters and the predicted heat flux values were evaluated. The treated parameters were : the mesh size of the net, the number of layers of net inserted between films, film thickness, single- vs double-aluminized films, the winding method for the multilayer insulation, the layer density, and the hot and cold boundary temperatures. Predicted values for the various parameters coincided well with measured values.

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Th effects of various parameters on heat flux between room temperature and liquid nitrogen temperature through multilayer insulation (MLI) are examined using the prediction equations and experimental results. The investigated parameters were : the winding method of multilayer insulation, hot boundary temperature, mesh size of the net, number of layers of net inserted between films, direction of layer installation, film thickness, and use of single-vs. double-aluminized films. To accomplish good thermal performance, laminated winding, larger mesh size, a layer of net inserted between films, thinner film (light weight), and double-aluminized film are needed. The optimum number of layers for different parameters is also discussed. It is found that the optimum number of layers is in the range of 30 to 60 layers in many cases.

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The present study aims to obtain a fundamental understanding of the mechanism of instabilities arising on a flame front propagating in a disk-shaped constant-volume chamber, by visualizing the flame front with Schlieren photography. The ignition was performed at the center or at a point on the periphery of the chamber to observe the effects of wall configuration. The mixtures selected were hydrogen-air, methane-air and propane-air with various equivalence ratios. As a result, it is found that the instabilities occur when the Lewis number of the unburned mixture is less than unity for the hydrogen-air and propane-air flames. This shows that instability is caused by the so-called "preferential diffusive instability". However, in the methane-air flame, for which the Lewis number is always near unity, an instability with very regular cells appears when the flame approaches the wall for any value of the equivalence ratio. This instability may be interpreted as a "hydrodynamic instability" affected by the presence of the wall.

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This paper discusses the predictions of both emission characteristics of NO_x for various kinds of coals in single-stage combustion and NO_x reduction due to two-stage combustion upon pulverized coal combustion using the authors' method of numerical simulation reported previously. The analyses have been compared with the experiments of single-stage combustion for various kinds of coals in the laboratory of the Central Research Institute of the Electric Power Industry and our results agree fairly well with their experimental data in the laboratory. The best conditions also can be predicted with sufficient accuracy on the position of injection port as well as the injection air flow rate for over fired air in two-stage combustion.

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The effect of the atomizing pressure of fuel on thermal NO_x formation has been studied in a practical combustion system (kerosene flow rate : 14.4 kg/h) with liquid fuel pressure atomizer. The experimental results indicated that about 30% reduction in NO_x formation can be obtained when atomizing pressure is decreased from 1.37 MPa to 0.40 MPa. The decrease in atomizing pressure decreased NO_x formation by approximately 20% as compared with the standard condition in atomizing pressure at various ranges of fuel consumption rate. The results are explained in terms of decrease of the mean flame temperature caused by increasing Sauter mean diameter due to decreasing atomizing pressure. In this case, it is confirmed that both the particulates and total hydrocarbon emissions were at negligible levels in the exhaust flow ; consequently, the combustion efficiency was not affected by this simple technique for suppressing NO_x formation.

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To measure the fuel vapor concentration in an unsteady evaporating spray, the exciplex-forming method, which produces spectrally separated fluorescence from the liquid and vapor phase, was applied in this study. Two experiments were conducted to investigate the qualitative and quantitative applicability of the technique in a high-temperature and high-pressure atmosphere during the fuel injection period. In one experiment, we examined the thermal decomposition of TMPD (NNN' N'-tetramethyl-P-phenylene-diamine) dopant in a high-temperature and high-pressure atmosphere during a period of time shorter than 10 ms. In the other, we calibrated the relationship between fluorescence intensity and vapor concentration of TMPD at different temperatures. Then, the distributions of fuel vapor concentration in diesel sprays were measured.

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We developed a new technique for analyzing droplet and vapor behavior in an evaporating diesel spray. This technique is based on the principle of laser light attenuation caused by ultraviolet light absorption by the fuel vapor and visible light scattering by the fuel droplets in an α-methylnaphthalene diesel spray. This new technique has been applied to an evaporating diesel spray under high pressure injection into a model combustion chamber which has a variety of cavity diameters, injection angles, nozzle projections and top clearances. It is found that with an increase in the injection pressure, the mixture formation in the piston cavity and the top clearance are seem to be improved with an optimal combination of the cavity diameter, injection angle, nozzle projection and top clearance values.

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The characteristics of unburned HC from a prechamber were studied using a small sized single cylinder engine and a constant-volume combustion rig. It is thought that HC in exhaust gas is unburned fuel from a crevice volumes between a liner and a piston and between a liner and a head. When the compression ratio is higher, a ratio of the crevice volume to the combustion chamber is higher and HC increases. When the crevice volume reduces, the thermal efficiency improves because unburned fuel HC and CO reduce. When a hole angle of the prechamber is made larger, HC decreases. The flame jet from the larger hole angle can reach the liner wall. When the swirl intensity decreases, the thermal efficiency improves and NO_x decreases, but HC increases. The flame jet is disturbed by the swirl and the flame propagates to the liner wall.

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Cooke-Yarborough cycle (CY) machines are composed of several Stirling cycle (ST) machines and have some possibility as future external-combustion engines and/or thermally actuated heat pumps. This paper treats a CY machine with two displacers and one power piston, which is suitable for practical application. The method of CY machine analysis has been newly developed and applied to some examples. Analytical consideration shows that the CY machine is internally divided into a ST engine and a ST refrigerator in the same manner as a Vuilleumier cycle (VM) machine. The performance of the CY machine is almost equivalent to that of the VM machine under the specifications adopted in this paper, although these machines are considerably different in their pressure variation. The CY machine operates at its highest capacity when the power piston reciprocates with a delay of 90 degrees in the phase angle against the two displacers.

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