The governing equations of a cluster of bubbles are derived by taking account of the thermal effects of the internal gas and the three-dimensional translational motion and deformation of each bubble. The equations are applied to the nonlinear oscillations of multiple interacting bubbles. The frequency response curves are obtained for two typical arrangements of bubbles with the same radii. The present results are compared with the results of polytropic analysis in which the thermal effects are evaluated using the effective polytropic index and the effective viscosity. It is shown that the heat transfer inside the bubble is important in investigating the nonlinear bubble oscillations : The polytropic relation for the internal gas does not hold when the nonlinearity of the radial oscillation becomes strong. Both radial and surface oscillations are affected by the translational motion of each bubble. It is also shown that the subharmonic oscillation of interacting bubbles occurs more easily than that of an isolated bubble due to the bubble-bubble interaction.

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The collapse and rebound of a nonspherical gas bubble near a plane rigid wall are investigated using the boundary element method combined with the finite volume method. The temperature gradient of the internal gas is taken into account in the analysis. It is shown that the bubble collapse is accelerated by the heat transfer inside the bubble : Jetvelocity becomes higher than that predicted by the adiabatic model. Thermal damping is important in investigating the characteristics of the rebounding bubble. It is also shown that the temperature distribution inside the bubble is strongly dependent on the degree of deformation of the bubble. When the jet is produced on the bubble wall, the internal temperature gradient at the side farthest from the rigid wall becomes very steep. This steep gradient increases the liquid temperature to a level higher than that for the single bubble.

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A vortex method is used to simulate several flow fields, such as high Reynolds number flows around bluff bodies, jet flows, and the backward-facing step flows. This method has some advantages : it does not require construction of a complex mesh, the algorithm is simple, numerical viscosity is not inherently included, and numerical results agree well with experimental and other numerical results. However, a few models, which do not satisfy the solenoidal condition, have been used in three-dimensional flow problems. The aims of the present paper are to derive a basic equation concerning the vortex method from the three-dimensional Navier-Stokes equations and to determine the relationship between the vortex method and the Navier-Stokes equations. The basic equation is derived as a simple integral form of the vorticity ; the present equation shown that the evolution of vorticity field is obtained by taking the sum of the two effects : stretching of vorticity and viscosity, which are obtained individually. The solenoidal condition is also discussed in detail the initial approximate vorticity field must be solenoidal.

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In the previous paper, the fundamental integral form of a vortex method in a three-dimensional fluid flow was derived from Navier-Stokes equations. Using this integral form, we attempt to (1) clarify the theoretical background of discrete vortex methods, such as the vortex stick method and the vortex element method, which have been used in many flow problems, and (2) propose a new type of vortex element which satisfies the solenoidal condition, i.e., a Gaussian ring-type. The velocity field of two vortons of a Gaussian element and a proposed Gaussian ring-type element are obtained and a numerical calculation is carried out to show their features clearly.

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Cavity breakdown on a hydrofoil in the transient region between subcavitation and supercavitation causes violent vibrations which are serious obstacles to the reliability and strength design of hydraulic machinery. By the use of high-speed photographs and three-component load cells, this paper clarifies the cavity aspects and the characteristics of fluid forces from noncavitation to supercavitation in the nonseparation, separation and stall regions. The following three results were obtained at cavity breakdown. (i) In the separation or the stall region, several vortex-cavity strings stretched from the end of still-existent sheet cavity on the hydrofoil to the downstream direction and encircled the breakdown cavity cluster. (ii) The fluctuating lift coefficient reached up to about 15% and the fluctuating drag coefficient up to 20% compared with the time mean lift and drag coefficient, respectively. (iii) The center of pressure shifted toward the trailing edge from about 30% chord during noncavitation or subcavitation to 40% chord.

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The velocity field around a symmetrical wedge is measured with two LDVs. The data analysis of the velocity, vorticity and energy distributions is executed by using a new FFT spectrum method which can easily eliminate FM-AM modulations of the fluctuating velocity compared with the phase-average method. The analysis of these distributions based on the steady and unsteady velocity components clearly illustrates the mechanism of a Karman vortex formation in a cycle. Namely, an unsteady vortex generates just at the back of the wedge and moves in the wake. It interacts with the stationary flat vortices produced on the upper and lower, stationary but separated shear layers, supplying velocity energy to the upper vortex and removing it from the lower vortex. Consequently, the actual Karman vortex formation exhibits four stages. In the first stage the upper stationary vortex expands to the downstream direction, in the second stage it slightly rolls around the lower vortex, in the third stage it is cut off near its middle portion and in the final stage it sheds a Karman vortex.

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It is well known that self-excited flow cscillation can occur in a duct downstream of a sudden area change when the line pressure is high enough to produce transonic or supersonic flow. The mechanism of the flow oscillation has not yet been well established. The experiment was carried out using the duct of rectangular cross section to visualize the flow pattern. The numerical method was also used to simulate the steady flow pattern in the duct. The flow pattern during the oscillation, as well as the steady flow pattern, is obtained by Mach-Zehnder interferometry, shadowphotography, and the numerical technique.

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Near-wall bursting has been detected in a fully developed turbulent square-duct flow both by the VITA technique and by quadrant analysis. Discrepancy between these detection schemes is shown, and its possible cause is discussed. Dependence of bursting frequencies and contribution rates to the Reynolds shear stress on threshold parameters is also investigated at the wall bisector, z/H=0.5, and the vicinity of the duct corner, z/H=0.2. In the case of quadrant analysis the bursting frequency at z/H=0.2 is found to be higher than at z/H=0.5 for large threshold values, while in the case of the VITA technique they are nearly identical. It is shown that the contribution rate of ejection at z/H=0.2 is higher than at z/H=0.5, but that of sweep at z/H=0.2 is lower than at z/H=0.5. In addition, a plot of the measured Reynolds shear stress is presented on the wall bisector, and its difference between a square duct and two-dimensional channel is demonstrated.

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Near-wall velocity measurement has been performed at y⁺=2.6 in a fully developed turbulent square-duct flow in order to evaluate fluctuating wall skin friction. Turbulence structures, which induce high wall shear rates, have been identified using simultaneous flow visualization. It is shown that quasi-streamwise vortical structures play a dominant role in the high-friction generation, and that they can be classified into the 'cyclonic' or 'anticyclonic' vortex, which is tilted toward the spanwise direction with its vorticity parallel or antiparallel, respectively, to the mean shear vorticity. The generation of high wall shear rates is often seen on the sweep sides of the cyclonic and anticyclonic streamwise vortices. In addition to the experiments, the long-wavelength instability of a spanwise vortex filament in a background shear has been investigated using the Biot-Savart law with a suitable cutoff in order to demonstrate the generation mechanism of streamwise vortices. It is found that the unstable modes lead to the generation of streamwise vorticity, and that the most unstable mode has a spanwise wavelength of the order of 100 wall units in the near-wall region.

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A simple and low-storage finite-element method for three-dimensional incompressible non-Newtonian flow is presented. The present method employs the rational Runge-Kutta scheme for time integration and simultaneous relaxation method of velocity and pressure for the incompressible condition. In order to reduce computational storage, coefficient matrices are calculated by simple integration formulas which are applicable to large systems. Flow of power-law fluids through an axisymmetric abrupt contruction is calculated to confirm the present method. The present method is stable in numerical simulation of power-law fluids, and the numerical results agree with other numerical results.

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Structures of supersonic radial flow in a disk MHD channel have been investigated by experiments and numerical calculations. Total pressure profiles across the channel height and static pressure distributions along the radial direction on both surfaces of a disk MHD channel were measured in the absence of the MHD effect. Furthermore, three-dimensional time-dependent calculations by means of the MUSCL-type TVD scheme were carried out. Measurements and calculations have shown that the working gas flow becomes asymmetric in the height direction due to some pseudo shock waves, and a large region of flow separation exists downstream of the channel.

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A new Cartesian grid system approach is proposed for the numerical simulation of two-dimensional compressible viscous flows around an arbitrary shape body. The grid system is constructed of patched blocks which is composed of the nested-spacing regular grid. The numerical procedure is based on the method of lines. For the spatial discretization, the neighboring-point local collocation method is developed and introduced for the grid points near the body, and the 2nd-order central difference method is used for the points far from the body. The 2-stage Runge-Kutta method (RK 2) is used for the time integration scheme. For the unsteady solution the nesting time step technique is combined with RK 2. Numerical results are obtained for subsonic steady and unsteady flows around a circular cylinder and compared with the other results. The results for transonic and supersonic steady flows over NACA 0012 are compared with the GAMM workshop ones. The present approach is confirmed to be applicable for the arbitrary shape body, and the computational cost is about 50% that of the conventional boundary-fitted grid approach.

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Previous experimental data concering to the terminal scour depth by clear-water scour around a circular bridge pier are examined thoroughly. The effects of the pier size D, the flow velocity U, the water depth h_o and the sand grain size d_s on the terminal scour depth are investigated. For the case of h_o/D≤1.2, which is a considerable effect on the scour, the main results obtained are as follows. The terminal scour depth Z_s/D is represented by a function of three dimensionless factors, the sediment number N_s=U/[(σ/p-1)gd_s]^0.5, the water depth h_o/D and the sediment Reynolds number Re_d=Ud_s/ν, where σ/p is the ratio of solid density to fluid density, and is formulated as Z_s/D=0.09N_s^0.24(h_o/D)^0.60Re_d^0.12. This equation agrees well with the former experimental data within ±7 %.

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An original flying hot-wire (FHW) method was developed to measure an extremely low-velocity region in a recirculating flow. This method moves the hot-wire probe in the spanwise Z-direction. The method can measure three components of the mean velocity and six components of the Reynolds stress using an X-array hot-wire probe. The probe moves at a constant velocity, and detects the velocity W in addition to a biasing velocity W_b. The sensitivity of the yaw and pitch angles is important to maximize the accuracy of the velocity data. This paper proposes a newly developed velocity reduction method for the FHW system using an X-array hot-wire probe. The accuracy of the velocity data is estimated by numerical simulation and experiments. The estimated error in the mean velocities is less than 3.5%, if the probe is fabricated and installed in the tunnel with care.

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This paper proposes a calibration technique for a flying hot-wire method that uses with an X-array hot-wire probe. The flying hot-wire system moves the hot-wire probe in the spanwise Z-direction of the flow field. The calibration of yaw and pitch angle sensitivities of the probe is of utmost importance to this system. After careful calibration, the system is applied to a three-dimensional flow to obtain three components of the mean velocity and six components of the Reynolds stress. The mean velocities and the Reynolds shear stresses downstream of a pair of vortex generators embedded in a two-dimensional boundary layer show the same profiles as those obtained with an ordinary X-array hot-wire probe. In one traverse, the flying hot-wire system can measure 60 points of six components of the Reynolds stress with good accuracy.

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In a thermal convection field constrained by right and left insulated walls, stable multiple solutions easily exist. In the case of a two-dimensional cavity with aspect ratio of 1.5, whose upper wall is cooled and lower wall is heated at a constant temperature, the two modes of thermal convection cell pattern are stable at Rayleigh number Ra of 2.0 × 10⁵. That is, one-cell-mode and two-cell-mode. However, as Ra increases to 3.5 × 10⁵, both modes become unstable, and appear in similar probability. The objective of this work is to demonstrate the possibility of controlling convection patterns under unstable conditions. We found that estimation using artificial neural network is effective to increase the probability of obtaining a desired mode, even in the slightly higher Ra of 2.5×10⁵.

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Gas-liquid two-phase flow in an inclined tube is frequently encountered in various kinds of pipelines transporting thermal energy using steam and water as a thermal medium. However, fundamental experimental data on annular two-phase flow in an inclined pipeline are very few compared with those on two-phase flow in a vertical pipeline. In this paper, experimental data on hold-up, frictional pressure drop of an annular two-phase flow and flow pattern in an inclined tube of 26 mm diameter are presented and the effects of the inclination angle are examined. The inclination angles measured from the horizontal were 0, 15, 30, 45° and 60°. Superficial velocities of air and water ranged from 10 m/s to 50 m/s and from 0.006 m/s to 0.20 m/s, respectively. As a result, it was clarified that the transition j_G from froth to annular flow decreases as the inclination angle increases, the L-M curve for frictional pressure drop can be applied to the case of large inclination angle, the distribution of probability density function has exhibits a unique shape for each flow pattern independent of the inclination angle, and the relation between two-phase friction multiplier and hold-up varies with the inclination angle.

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One-dimensional flow model for a pseudo-shock wave in a constant-area duct is presented where the boundary layer at the initial section of the pseudo-shock region is considered. The conservation equations of mass, momentum and energy across the pseudo-shock are treated one-dimensionally by assuming an appropriate mean flow over a given cross section of the flow. For given conditions upstream of the pseudo-shock, the characteristic properties through the pseudo-shock such as the downstream Mach number and the static and stagnation pressure ratios across the pseudo-shock calculated using the present model agree well with the previous experimental results.

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In this paper, we propose a technique of suppressing aerofoil flutter using sound waves. Acoustic equipment is used to carry out the technique of active sound control that is known as anti-sound. Firstly, Theodorsen's method was applied to analyze the aerodynamic forces when an aerofoil is oscillating in an airstream with sound-wave disturbances. It is shown that sound waves do affect the maximum energy input in heaving and pitching oscillations. Secondly, we fabricated flutter equipment which has two degrees of freedom of aerofoil oscillation : heaving and pitching oscillations. The acoustic equipment consists of an amplifier, delay equipment and a loudspeaker. The loudspeaker is driven by the amplified and phase shifted-signals from the strain gauge used to measure the heaving or pitching oscillation of the aerofoil. We measured the energy input from the airstream and the relation of amplitude ratio and phase lag for heaving and pitching oscillations with increasing airstream velocity up to flutter speed. It is shown that the effective sound wave for suppressing the aerofoil flutter depends on the amplitude ratio between heaving and pitching oscillations.

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Spanwise coherent structure of surface pressure fluctuation on a circular cylinder is studied experimentally in order to obtain quantitative information for understanding the generation mechanism of aerodynamic sound from the cylinder at Reynolds numbers between 5 × 10³ and 1.4 × 10⁵. Spanwise distribution of the coherence function between surface pressures is kept as high as up to several diameters for the frequency components of the so-called orderly structure, or the Karman vortex shedding frequency and its harmonics, while the coherence function for the turbulent frequency component decays rapidly spanwise to half-diameter. Spanwise coherence function of the surface pressure is calculated as an exponential function of spanwise spacing and Reynolds number. The correlation length of the flow structure is found to be inversely proportional to Re^1/2.

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One-dimensional unsteady Euler equations are solved for the investigation of the flow field induced by a train entering a tunnel. The effect of the moving train is included in the basic equations as an area change in time. The equations are discretized by the finite difference method, and the calculations are performed for trains with various speeds, cross-sectional areas and nose area gradients. Effects of these parameters on the strength of a compression wave and the maximum pressure gradient are studied. Computed strength of the compression wave shows good agreement with the theoretical 1-D analysis and the axisymmetric numerical simulation. The one-dimensional flow model is validated through the comparison of computed pressure gradient with multidimensional numerical simulations.

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A new method of evaluation of adhesion tension that does not require measurement of the contact angle, which is conventionally used for definition of adhesion tension, is proposed. In this method, adhesion tension can be derived from a function of size and surface tension of sessile drops which are easily, obtained without requiring a high-precision experimental technique for contact angle measurement. In order to derive the function of adhesion tension, potential theory is applied to it with approximating the sessile drop configuration as an ellipsoidal solid. It is confirmed that the method proposed here is appropriate for practical use, since the error of adhesion tension determined with this method is less than 1.5% compared with the solution given by Laplace formula.

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Numerical simulations of linear and nonlinear wave phenomena are described in this paper. Both third-order upwind-difference and second-order central-difference methods are used to approximate the convection terms. Interaction of the wave properties in these numerical schemes is discussed to develop the appropriate discretization of the convection terms in the case of nonlinear wave problems. The results show that the controls of the numerical viscosity in the third-order upwind-difference are effective to solve the Navier-Stokes equations for nonlinear wave phenomena.

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A direct numerical simulation of three-dimensional homogeneous isotropic turbulence by the spectral method and the higher-order finite difference scheme (FDS) has been conducted with 64×64×64 and 96×96×96 grids. The energy spectrum obtained by the FDS is compared with that obtained by the spectral method and that obtained by the experiment 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 64×64×64 grids, the energy spectrum obtained by the 5th-order upwind FDS coincides with those obtained by the spectral method and the experiment up to the cutoff wave number, while the 3rd-order upwind FDS shows deviation from those obtained by the spectral method and the experiment. (2) With the 64×64×64 grids, the 6th-order central FDS with the skew-symmetric form is valid for DNS, while the 6th-order central FDS with the convective form overestimates the energy in the region around the cutoff wave number. (3) With the nonlinear term discretized by the 5th-order upwind FDS or 6th-order central FDS with the skew-symmetric from, the 4th-order FDS is suitable for the viscous term.

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We study numerically a finite difference method (FDM) on 2-dimensional curved surfaces. A 2-dimensional surface is discretized by piecewise linear triangles, to form what is called a triangulated surface. We present a technique for discretization of Poisson's equation on triangulated surfaces. Our technique is examined for Laplace's equation on a flat domain and on a spherical domain, and the results are compared, and found to be in good agreement, with those obtained by known FDMs. The most remarkable feature of our technique is a coordinate-free property, i. e. the only data necessary to carry out a FDM are the lengths of bonds of a triangulated surface.

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Void fractions and pressure drops were measured for gas-liquid flows in five kinds of horizontal narrow flat channels with a width of 10 mm and channel clearances of 0.2∼2.0 mm. Four kinds of aqueous ethanolic solutions were used to examine the influences of surface tension 6 and viscosity μ of liquid on flow characteristics. The void fractions increased with a decrease in σ, μ and channel clearance. Under low liquid velocity conditions, the pressure drops were affected by the surface tension, and it was found that Chisholm's equation for the Lockhart-Martinelli correlation could not be applied to channels with relatively large clearances.

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In this study, condensation heat transfer experiments were performed in order to verify a condensation heat transfer model coupled with a three-dimensional two-phase flow analysis. In the heat transfer model, the liquid film flow rate on the heat transfer tubes was calculated by a mass balance equation and the liquid film thickness was calculated from the liquid film flow rate using Nusselt's laminar flow model and Fujii's equation for steam velocity effect. In the experiments, 112 horizontal staggered tubes with an outer diameter of 16 mm and length of 0.55 m were used. Steam and spray water were supplied to the test section, and inlet quality was controlled by the spray water flow rate. The temperature was 100°C and the pressure was 0.1 MPa. The overall heat transfer coefficients were measured for inlet quality of 13-100%. From parameter calculations for the falling liquid film ratio from the upper tubes to the lower tubes, the calculated overall heat transfer coefficients agreed with the data to within ±5% at the falling liquid film ratio of 0.7.

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The effects on the local heat transfer and pressure coefficients of a slat downstream of a backward-facing step were investigated. The inclinations of the slat placed on the wall opposite the step were varied in the range of θ = 10∼60° for both slat lengths of 20 mm and 30 mm, with the aim of augmenting and controlling the heat transfer characteristics. The reattachment region of the main flow shifted upstream due to the increase of the amount of circulating bubbles formed behind the slat when the inclination angle was increased, which enhanced the heat transfer in the recirculating region. These tendencies are marked with a large expansion ratio. It was also found that the performance ratio η (the ratio of averaged heat transfer with a slat to that without a slat under the condition of equivalent pumping power) is larger than unity.

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Heat transfer efficiency of annular-type heat pipes is investigated experimentally and theoretically, for the evaporating section and condensation section respectively. The heat transfer coefficients of evaporating liquid film are obtained under several conditions of the annular gap, charged volume rate of the working fluid, wall superheating and rotational speed. It is shown that the results of theoretical analysis for condensation heat flux agree well with experimental results, and also that the taper angle of the condensation wall greatly influences on the heat transfer efficiency.

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Rapid quenching of thin horizontal platinum wires falling at a constant speed was studied experimentally with pure water and ethanol as quenching liquids. The transient boiling curve obtained from the cooling curve had two local minimum-heat-flux points, M1 and M2. Measurement of the liquid-solid contact and observation of the boiling pattern showed that a marked liquid-solid contact began at the first (higher wall superheat) minimum-heat-flux point, M1. The heat transfer results indicated that the M1 point corresponded to the minimum vapor film thickness for stable film boiling. The effects of liquid subcooling and falling velocity on the avarage vapor film thickness and the wall superheat at the M1 point were clarified. The wall superheat at the M2 point was almost constant for each liquid irrespective of liquid subcooling and falling velocity.

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This paper deals with cold energy release characteristics of a fine capsulated latent-heat storage material-water mixture as a latent-heat-storage material having a low melting point of the core material (pentadecane, C₁₅H₃₂, freezing point 283.1 K). A direct-contact heat exchange method for an air-fine capsulated latent heat storage material-water mixture was selected to investigate the cold energy release characteristics from the mixture layer including the solidified core latent-heat-storage materials. The temperature effectiveness, the sensible-heat release time and the latent-heat release time were measured as experimental parameters. Useful nondimensional correlation equations for those parameters were derived in terms of nondimensional level of the mixture layer dimension, Reynolds number for air flow, Stefan number and heat capacity ratio.

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In order to control the response of a capsule-type thermal energy storage system, a new method using a bypass is introduced. The bypass is set so as to connect the inlet to the outlet directly, to obtain the required temperature by mixing low and high temperature fluids. The bypass works simply using a proportionally controlled 3-way valve. Then the performance of a storage tank is defined by the amount of energy released to obtain the required temperature. Finally the performance map is shown as a function of the required temperature and flow rate.

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The infrared absorption spectra of N₂O and CO₂ molecular clusters formed in a supersonic free jet expansion were measured at various source gas pressures and solvent densities. The infrared absorption spectra of N₂O and CO₂ were measured at different positions in the vicinity of the condensate and compared with the monomer and cluster spectra. These spectra are compared with the vibrational spectra of clustering molecules calculated using the molecular dynamics method. The results show that the measured spectra have a distinct difference between the large-size (L) and the small-size (S) clusters. In the case of N₂O, L clusters were observed in a wide range of spatial position, but S clusters were formed in a limited region from the condensate. In the case of CO₂, L clusters were replaced by S clusters at higher pressures. The distance from the condensate at which the S clusters were observed depended on the pressure, and the clustering region of the L clusters was proportional to approximately the cubic power of the mean free path.

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Direct conversion from methane to methanol is one of the key technologies for more efficient utilization of fossil fuels, because low-quality or low-temperature heat sources corresponding to 100°C can be used and regenerated in the reforming of methanol to hydrogen, whose exergy loss through the combustion process is by far the lowest among hydrocarbon fuels. In this study, direct conversion from methane to methanol has been successfully realized using a methane/oxygen gas mixture, with a newly developed nonequilibrium plasma of pulsed silent discharges under atmospheric pressure at 373 K. Major products are methanol, water, carbon monoxide, and a small amount of carbon dioxide and formaldehyde. Effects of initial oxygen concentration, residence time and strength of electric field on the methanol synthesis have been clarified. Methanol is significantly formed only when the applied electric field is raised above that for electrical breakdown of oxygen gas, about 21.3 kV/cm, and the high selectivity of 32% for methanol formation has been attained at low initial oxygen concentrations of about 5%. Furthermore, we have also confirmed the possibility of methanol formation using a methane/water-vapor mixture, by the same method. The time-dependent changes of emission intensity for CH radicals have shown that streamer-type discharges are essential for the effective formation of radical species and thus methanol formation.

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A large-capacity [100 kW-class] molten Carbonate fuel cell (MCFC) stack was operated for over 5000 hours by CRIEPI/IHI under the New Sunshine Program. The stack was manufactured by IHI/NEDO, and consisted of 102 cells which were 1 m² in size and had rectangular shape and Co-flow internal gas manifold. In the initial stage, the stack achieved over l00 kW electric power generation with small cell-to-cell variation and demonstrated high performance similarly to the [10 kW-class] stack operated under an collaborative research agreement with CRIEPI and IHI. On the other hand, slow voltage decrease and increase phenomena were observed, and thermal deformation occurred in the tall stack. Also, an increase of inside shorting current calculated by gas analysis was observed. This may be caused by cathode NiO dissolution and deposition.

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In integrated coal gasification combined cycle power generation (IGCC) systems, ammonia in the gasified fuel is passed through a hot/dry gas cleanup facility into the gas turbine. The ammonia is converted to nitrogen oxides in the combustion process in the gas turbine. Therefore ammonia removal from coal-gasified fuel would effectively reduce NO_x emissions in IGCC systems. We're defined the optimum NO/NH₃ ratio, the optimum concentration of added O₂ and the influence of CO and H₂ in the coal-gasified fuel on NH₃ decomposition and NO reduction by experiments using a tubular flow reactor and numerical analysis based on reaction kinetics. The main results are as follows : (1) The optimum NO/NH₃ ratio is about 1 to maximize NH₃ decomposition and NO reduction. (2) The NH₃ decomposition ratio depends only on H₂, and decreases rapidly with increasing H₂ concentration. (3) The NO reduction ratio decreases with increasing H₂ concentration. (4) This method is effective for decreasing TFN by up to 60% minimizing the total concentration of remaining NH₃ and NO in air-blown coal-gasified fuel.

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A methane-air premixed flame with an equivalence ratio of 1.25 was simulated with a model including 91 pairs of elementary reactions occurring among 29 species. In this first work, the structure of a representative transversal section of the flame is presented and the mechanisms of combustion at the inner and outer cones are discussed in detail. CH₄ and O₂ in the mixture both react with H atoms, but the reaction between CH₄ and H occurs preferentially to that between O₂ and H at the fuel side of the inner cone. This results in a lack of oxygen atoms at the position where CH₄ breaks into CH₃ radicals and the reactions belonging to the C₂ route proceed with higher velocities than those belonging to the C₁ route. The consumption of O₂, being posterior to the consumption of CH₄, produces O atoms at the center of the inner cone. These O atoms, though not abundant, are sufficient to oxidize the last stable product of the C₂ route, C₂H₂, preventing soot production. The diffusion of H atoms from the flame front to low-temperature regions and the subsequent production of OH radicals were found to be essential to the stability of both inner and outer cones, by triggering the combustion chain reactions.

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In order to measure flow velocity in the swirl and radial directions of a cylinder of an engine in practical use by means of a laser Doppler anemometer (LDA) through a small measuring window on the cylinder head, a back-scattering fringe mode LDA is used. It, however, could not measure the velocity component in the axial direction of the cylinder. The single incidence-beam reference-mode LDA is developed to measure the velocity component along the optical axis of the LDA and applied to measure the fluctuating flow velocity in the axial direction of the cylinder. Ensemble-averaged mean velocity and fluctuation intensity of the velocity as measured by the LDA show good agreement with those measured by the conventional fringe-mode LDA. Based on these results, it can be concluded the reference-mode LDA is applicable to measurements of the flow velocity in the axial direction of the cylinder through the small window on the cylinder head.

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This paper describes in detail the experimental and theoretical results of a new type of Stirling engine with a pendulum-type displacer (PDSE) that is suspended by a hinge shaft and swings in a displacer space. The main features of PDSE are its simplicity, ease of outside gas sealing, and lower mechanical friction than that of the conventional-type Stirling engine. However, gas leakage inside the displacer is larger than that of the conventional type. The power required to induce a pendulum-type displacer motion, which consists of flow loss powers of multiple fin gas passage and regenerator wire mesh, is analyzed using a simple equation. It has been clarified that the calculated theoretical power output agreed well with the experimental power output. It has also been clarified that the measured Nusselt number of the regenerator agreed with that of a previous study. It is hoped that PDSE can be employed to utilize naturai heat energy sources in the future.

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Natural-convection heat transfer from uniformly heated horizontal cylinders to air was investigated experimentally for a bank of cylinders in staggered arrangement. The heat transfer coefficients for seven cylinders, arranged in a vertical array, were measured for varying cylinder spacings in the horizontal and vertical directions. A correlation equation for evaluating average heat transfer coefficients was deduced for banks of cylinders. It was shown that this equation was also applicable to cylinder banks in an in-line arrangement.

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