This paper develops a new model for the nonisotropic dissipation rate tensor ε_ij to close the Reynolds-stress transport equations. The previous models of ε_ij are all algebraic, based on a hypothesis of either the isotropic relationship of the dissipation tensor or the one-to-one relationship of the dissipation anisotropy tensor with that for the Reynolds stresses. However, the recent direct simulation data of the turbulent boundary layer and channel flow have revealed the strongly nonisotropic nature of the dissipation process, which differs considerably from that of the Reynolds-stress components. The present model provides nonisotropic dissipation-rate components through the solutions of approximated transport equations for ε_ij, and hence, the conventional prescription of an ad hoc value of ε_ij is not needed. The proposed model is tested by direct comparisons with the reported full simulation data to validate the performance of the model predictions.

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A forced reattachment of the shear layer separated from cylinder can be realized by setting up a small cylinder in the shear layer near the main cylinder. The properties of the reattachment jet on the rear face of the cylinder have been experimentally investigated. We found that the critical conditions of the forced reattachment coincide with that of a turbulent wall jet along a circular cylinder and a jet on a circular cylinder immersed in uniform flow. The properties of the reattachment jet are similar to those of the turbulent wall jet along the circular cylinder; the velocity distributions of both are nearly equal. The near wake behind the reattachment jet is almost stagnant and the lift acting on the cylinder is proportional to the momentum coefficient of the jet.

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The hydrodynamic forces generated by water-square cylinder interaction have been investigated experimentally. A square cylinder model of 50mm side length and 200mm span length, and five kinds of end-plates of 100, 200, 300, 400, 500mm width were used. The cylinder supported by two end-plates was oscillated horizontally in standing water by mechanical oscillation machinery. The force was measured by means of a quartz force transducer. Period parameters ranging from 0.2 to 3.0 and Reynolds numbers from 5000 to 40000 were covered in the investigation. The results have shown that the force amplitude coefficients based on the acceleration of two-dimensional square cylinder are obtained at end-plate dimensions of greater than 10 times the square cylinder side length, and the force amplitude coefficients and the force wave forms depend on the period parameter but not on the Reynolds number.

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Fully-developed and unsteady flows are dealt with in a curved duct of a rectangular cross-section (aspect ratio = 2, curvature ratio = 8). It is simulated by the MAC method how the flow patterns will evolve under the condition of pressure gradients C suddenly given in the streamwise direction or kept constant. The results are as follows; a pair of stable vortices is obtained at C < 6.90 × 10⁴. At C = 6.90 × 10⁴, the vortex pair begins to fluctuate periodically. It is confirmed that the Hopf bifurcation occurs from steady flow to periodic flow. At about C = 6.93 × 10⁴, the single pair of vortices changes to two pairs of vortices which return shortly through asymmetric vortices. At about C = 30 × 10⁴, asymmetric vortices are obtained after symmetric vortices break down. It is shown that time-dependent flows are predominant over the intermediate Dean numbers in curved ducts.

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The efficiency of the water turbine is calculated using the static pressure measured on the side wall near the draft tube exit. The pressure decided from the water level just behind the draft tube exit is used if the pressure tap is not installed. Then, in this study, the open channel flow around the draft tube exit is researched experimentally using a model. The main results are obtained as follows. (1) The flow patterns in the open channel can be classified into four types. (2) The condition of the water level rise increasing to the downstream was clarified. (3) The difference between the static pressure head on the draft tube wall near the exit and the water level in the middle of open channel near the draft tube was given. Its maximum value reaches 0.12 V²_m/2g for low water levels and wide open channels.

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Vorticity fields were experimentally given with respect to a large-scale coherent vortex in a fully developed turbulent boundary layer. Three vorticity components, vorticity vectors, and enstrophy were obtained from the ensemble-averaged velocity components measured through conditional samplings. The vorticity vector maps showed that the large-scale vortex had a horseshoe like structure inclining downstream at an angle of about 50 deg. with respect to the wall. The normal and spanwise scales of the coherent vortex were about 1.0δ. At the legs of the large-scale vortex composed of a pair of vortex tubes, the contribution of the longitudinal and normal vorticity components exceeded that of the spanwise component. The enstrophy had the maximum value of Y/δ≒0.1 at the bottom of its legs.

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The effects of periodic disturbance on a turbulent separating air flow in a two-dimensional diffuser have been investigated at the Reynolds number of 42000. The disturbance was generated by the external speaker and introduced from the walls of the asymmetric diffuser through a porous plug. With varying disturbance amplitude and frequency, the percent downstream flow, the pressure recovery coefficient, as well as the streamwise- and the normal velocity components, were measured. The results indicated the significant suppression of separation and the improvement of pressure recovery. This was mainly due to the periodic suction and injection from the wall but due to neither the change of the turbulence structure upstream of the incipient detachment point nor the excitation of instability in the separated shear layer.

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The objective of this paper is to gain insight into the coherent structures of turbulent mixing layers. To achieve this purpose, we have performed a direct simulation of a three-dimensional mixing layer by using a pseudospectral method. The results are reported for the case of initial velocity fields with periodic excitation. From these results, we have obtained the following conclusions: 1) streamwise vortices (ribs) are involved in spanwise coherent vortex, and persist in the core region; and 2) ribs, which are involved in the spanwise vortex, connect in the core region as a vortical tube.

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This paper deals with a horizontal sloshing of a liquid metal by means of an unsteady electromagnetic force which is generated by the interaction between a steady vertical magnetic field and a horizontal forced electric current. Two typical cases are considered. One is the case in which the electric current is supplied by an alternting electric field. The other is the case in which the total current flowing in the fluid is AC. The frequency characteristics of the displacement and of the phase lag in both cases are obtained by the linear analysis. Experiments using mercury are conducted. The amplitude of the surface wave is measured using a laser displacement sensor near the sidewalls. The results by experiment show good agreement with the analytical results.

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The flow behavior of water-based ferrofluids in a two-dimensional channel is experimentally examined under the action of magnetic fields having various intensities, and using two kinds of concentrations of ferrofluids, various channel aspect ratios and channel heights. Moreover, various factors governing such flows are clarified by making use of dimensional analysis, and then an empirical formula for pipe friction coefficient is derived.

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Micropolar electrically conducting fluids are electromagnetic fluids such as magnetic fluid, electrically conducting fluid and electrically polarized fluid. The present paper precisely shows how electromagnetic momentum, electromagnetic angular momentum and electromagnetic energy are converted into mechanical energy in micropolar electrically conducting fluids. Gibbs equation is derived using the basic equations and the Maxwell stress tensor obtained in a previous paper. Furthermore, Bernoulli's theorem is generalized for the micropolar polarized fluid and ferrofluid, and it is shown that the new Bernoulli's theorem includes Bernoulli's theorem for magnetic fluid derived by Rosensweig.

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A capsule dropping in an open tube suffers from aerodynamic drag. First. detailed measurements on the velocity of the capsule are carried out to ascertain the validity of a simple theory on drag. Next, an experiment for compensating the drag by a ponderomotive force is performed by the use of a linear motor.

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A new complete set of basic equations for viscoelastic conducting magnetic fluids with internal rotation are derived by the thermodynamical method wherein free energy and dissipation function are used on the basis of kinematical balance equations in the polar theory. The basic equations and the constitutive equations obtained here are useful if the volume concentration of ferromagnetic particles in the magnetic fluids is increased. New constitutive equations for magnetization and polarization are obtained. The magnetization is related to the magnetic field, its change in time and the angular velocity of suspended particles. Furthermore, it is shown that the electromagnetic pressure is independent of the dissipative parts of magnetization and polarization.

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The liquid sloshing phenomenon accompanying solidification was studied experimentally. The influence of vertical vibration on the convection flow by cooling the central inner cylindrical wall was investigated. The solidification rate of melting paraffin in the vibrating and cooling field was also measured quantitatively. The experiment revealed that the free surface wave motion disturbed the natural convection and decreased the rate of solidification. Possible control of the solidification rate by vibrating the container with the suitable input frequency or amplitude was also suggested.

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This paper deals with effects of waveforms on predicting performances of a radial turbine for turbochargers under pulsating flows. The extensive unsteady tests were conducted with several pulse shapes and pressure amplitudes over a pulse frequency range from 10 to 70 Hz produced by a disk-type pulse generator rig. Five kinds of pulse shapes were simulated for exhaust gas flows from diesel engines. The time-mean method and the quasi-steady flow analysis were carried out to predict the turbine characteristics by using the steady flow turbine performance. As the results, the following points are made clear. For most turbine running conditions, the quasi-steady flow analysis is satisfactorily valid regardless of whether the turbine is effected by the waveform, amplitude and frequency. It is considered that the turbine under pulsating flow conditions works along the curves of steady flow performances except for windage states. The time-mean method predicts the power output fairly well, but grossly overestimates the mass flow rates according to the waveforms.

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Hot-wire series response equations were derived for the measurement of turbulent flow by an X-probe from the generalized hot-wire response equation at an arbitrary angle. Based on the experimental results for a circular free jet, the turbulence velocities of the jet were shown not to be completely included inside the convergence domain of Taylor's series response equations for an X-probe. Assuming a normal distribution for the turbulence velocities of the jet, the validity of the correction of the effect of the yaw factor on the measured values of the Reynolds stresses was discussed based on the numerical experiment. The optimum number of terms of the series response equations to obtain the most accurate Reynolds stresses was also numerically determined.

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The effects of the tube-bundle rectifier of two different arrangements, staggered and side-by-side, on pressure drop across the rectifier are studied experimentally. Although it was expected that the pressure drop coefficient K of the staggered matrix has a much larger value than that of the side-by-side matrix, a new phenomenon in which the coefficient K varies in accordance with not only their arrangement, but also Reynolds number and length of the tube was found.

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Meiginger's equation for a jet fan cannot be applied to the case in which jet fans operate against air flow to reduce its velocity in a tunnel. This operating mode is used during fire accident in the tunnel. The equation for the mode is shown in this paper and is examined through the model experiments. The efficiency and diffusion of jets equipped with a deflector flap for the normal tunnel ventilation mode are also examined through the model experiments including flow visualization. Application of the flap is recommended.

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The inertial effective length of centrifugal impeller flow channel is defined based on a two-dimensional unsteady potential flow analysis. It is shown that the effective length is not dependent on the average flow rate, impeller rotation and the time dependence of the flow rate. Theoretical values are given for logarithmic impellers. The effects of the mode of circumferential flow distribution are also studied. Making use of the nature of the effective length, simple experiments are carried out to experimentally determine the effective length. It is found that the agreements between theoretical and experimental values are fair and discussions are made on the real flow effects found in the experiments.

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This paper presents an extension of the double linearization theory to study the effects of the mean angle of attack, camber and thickness on the unsteady aerodynamic response of a rotating supersonic annular cascade with oscillating blades. The numerical results compared with the strip theory prediction are presented to demonstrate some features of three-dimensional effects. The effect of spanwise nonuniformity in the angle of attack, camber and thickness on the unsteady aerodynamic force distribution is suppressed by the three-dimensional effect. The three-dimensional effect on the overall unsteady aerodynamic work is, in general, small for a supersonic annular cascade.

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The lifting-surface analysis for the axially symmetric flow and on the other, the lifting-line analysis for the axially non-symmetric flow are presented by singularity method for the super-cavitating circular ring hydrofoils. Main contents are enumerated as follows (1) Comparing the simultaneous integral equations in two limiting cases of large and small aspect ratios with the corresponding ones in two and three dimensional super-cavitating hydrofoils respectively, certain inherent features to the axially symmetric flows are clarified in relation to the aspect ratio and cavity length. Confirmations are made for the present analysis by comparing the predicted pressure distribution and normal forces with the experimental ones. (2) In case of the axially non-symmetric flows, the lifting-line analysis based on the semi-axially symmetric approximation is shown to be most reliable of the three proposed methods. Therefore the circumferential distributions of the local cavity length and local circulation and also the overall lift, induced drag and cavity drag are examined in relation to the aspect ratio and cavitation number through numerical examples.

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Three-dimensional viscous flows around a single-rotation high-speed propeller are investigated by solving compressible Navier-Stokes equations. An implicit finite difference code based on a high accuracy TVD scheme with a Baldwin-Lomax model of turbulence has been developed and applied. Computations are successfully carried out at cruise and take-off conditions with particular emphasis on grid resolution effects. The solutions clearly capture a leading edge vortex as well as a shock wave so that physical characteristics of the flow field are made clear. Numerical results are compared with the experimental data. Computed surface flow patterns show good agreement with oil flow visualization results. The present results show that the Navier-Stokes approach is capable of accurately simulating viscous phenomena around the propeller while the Euler analysis cannot, and that the propeller flow field is unexpectedly complicated because of the thin, highly swept blade.

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Steady characteristics of an aerofoil in a two-dimensional supersonic shear flow are analyzed by the singularity method. First, on the assumption of small disturbances, a fundamental solution, which represents a supersonic source, is introduced from an equation for perturbed pressures. The solution is composed of two terms; one contains the same Dirac's delta function as in a uniform supersonic flow and the other represents the interference between a source and vorticities in a shear flow. The thin aerofoil theory is applied in order to analyze characteristics of an aerofoil having a thickness distribution. The strength of sources at a point on an upper or lower surface of the aerofoil is determined not only by the gradient of the shape of the aerofoil but also by the interference between sources distributed on the upstream part of the surface from the point and vorticities in a shear flow. In a shear layer, a jet and a wake, lift and drag forces acting on a lens aerofoil and a flat plate are calculated. The results show that a local vorticity at a flat plate are calculated. The results show that a local vorticity at a position of an aerofoil plays an important role for characteristics of the aerofoil.

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The characteristics of the centrifugal impellers with splitter blades were derived from flow measurements within the impeller passages shown in the first report. The effects of the splitter blades on the characteristics of an unshrouded and a shrouded impeller were investigated in comparison with the impellers removed splitter blades. In the impeller with splitter blades, the pressure difference between the suction and the pressure surface of the passage tends to be smaller, and the absolute circumferential velocity and the total pressure at the impeller exit become considerably larger than that in the impeller removed splitter blades. By the addition of splitter blades, the static pressure at the impeller exit increases in the unshrouded impeller, and decresases in the shrouded impeller.

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A series of experiments was carried out on four compressors to study the chacteristics of high subsonic vaned diffusers. The pressure ratio of these compressors are 1.9, 3 and 4. The performance difference between air-foil vane and wedge vane diffusers with the same throat area was examined by the data from a compressor of pressure ratio 3. The critical Mach number for the choke limit, and the inlet semiopened-space area ratio at the stall limit were investigated by the data of pressure ratio 1.9, 3 and 4 compressors.

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The performance of the spiral grooves on a rotor of a turbomolecular pump is analyzed by obtaining the solution of the Boltzmann equation by use of the Monte Carlo direct simulation method. The flow in the grooves is three-dimensional in the transition regime. Also, the mass flux is measured under nearly the same conditions as those used in the theory. The computed mass flux is 23-27% smaller than that of the measured data. The difference may be ascribable to the assumption such as was used in the theory that the gap between the rotor and casing is constant.

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A proportional seat valve with a mechanical position feedback slot has the capabilities of a wide range of flow rate control and quick-response control for fluid power systems. However, it is unstable in the case of rotational speed control of a hydraulic motor with an inertia load. The reasons for this is that the valve works sensitively against the load pressure changes. This paper presents an improved seat valve with a balance spool and shows the stabilized dynamic characteristics. The valve controls flow rates of 70 L/min at pressure difference of 10MPa within 20ms by PWM switching pilot valve. Furthermore, it is shown that a set of computer-controlled 4-seat valves will offer freedom of pressure or flow rate control to a conventional full bridge hydraulic circuit.

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In a high-speed electrohydraulic servo control system, servo valves are mainly used to drive actuators, and the limit of the response of the system is dependent on the servo valves. The aim of this study is to develop an ultra high-speed servo valve with the spool displacement of 30 micrometers and the bandwidth over 5kHz. Piezoelectric devices have the potential to drive valves in quick response. However, as is well known, the devices have the disadvantage of hysteresis between applied voltage and output force. In this study, commercially available multilayered piezodevices, are used to drive the spool of the valve directly. The hysteresis is removed by introducing an inverse hysteresis element implemented on microcomputers and operated in real time. In this case, we developed an element to operate at the sampling frequency of 50kHz. In addition, we develop a method to drive piezoelectric ceramic devices at high speed, and improve damping characteristics of the spool valve. As a result, a servo valve with the bandwidth over 5kHz is successfully developed.

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Analytical and experimental investigations have been performed to examine the characteristics of transient freezing heat transfer in water-saturated porous media. The equation of momentum included Forchheimer's extension as the resistance to flow in the porous media. Three different sizes of glass, iron and copper beads were used as the porous media in this study. The temperature of the cold wall was -10°C. Comparisons of the analytical results with the experimental ones are made, and the effects of superheat and the bead diameter and the physical properties of a porous medium have been discussed for transient freezing heat transfer.

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Experiments were perfomed to study the effect of surface inclination on condensation heat transfer from downward-facing horizontal surfaces. A smooth surface and two low-finned surfaces with a length of 50mm were tested for condensation of R-113. The angle of inclination from the horizontal φ ranged from 0 to 90 deg. For the smooth surface, the heat tranfer coefficient α first decreased with the increasing of φ, then took a minimum near 5 deg, and then increased monotonically with further increasing φ. For the low-finned surfaces, α increased sharply with φ in the range of 0 to 30 deg, and then increased moderately with further increasing φ. The heat tranpfer coefficient for the better performing finned surface was 2.5, 9 and 12 times the smooth surface value for φ=0, 10 and 90 deg., respectively.

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Two-phase compression heat pump cycles have been studied from the theoretical point of cycle analysis to clarify the optimum liquid injection conditions as a first and basic step for developing higher-performance high-temperature heat pump systems, which recover the heat from a 150°C heat source and supply a 300°C-thermal output. In the case where the working fluid is water, the COP is improved by utilizing a two-phase compressios process and an optimum gas-liquid ratio brings about the maximum value of COP. The two-phase injection cycle, in which the liquid partially extracted from the outlet of the condenser and the gas separated in the economizer are injected into an intermediate point of the compression process, can effectively improve the COP and reduce the discharge superheating.

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The local and average coefficients of heat transfer from a rotating cylinder in a uniform flow were measured by Mach-Zehnder interferometer with visual observation of flow pattern. The experiments covered the range of rotating and cross-flow Reynolds numbers (Red) from 0 to 3000. The following results were obtained. Heat transfer is not influenced by natural convection at Red > 1000. Average heat transfer coefficients of rotating cylinder are equal to the case of static cylinder in a uniform flow, when cross-flow Reynolds number is over 1000 and cross-flow Rynolds number is above rotating Reynolds number (Rer). Heat transfer from a cylinder is most declined at Rer = 2Red, and the cross-flow Reynolds number is below 1000.

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This study has been conducted to clarify the mechanism of heat transfer enhancement in a convective field with ionic wind. Experiments were performed in an air channel-flow in which equally spaced positive wire-electrodes were set in parallel to the primary flow direction. The ionic wind was induced by applying electric field to bring about a corona discharge. The visualization of the flow patterns by using smoke-tracer method and the measurements on velocity profiles, friction factor, and heat transfer coefficient were systematically carried out. By combination of the primary flow with the ionic winds, the pairs of counter-rotating longitudinal vortex rolls were created over the wall surface. Heat transfer augmentation utilizing the combined flow was achieved especially in the laminar flow range, being accompanied with an increase in the pressure drop. On the basis of the results, the mechanism of heat transfer enhancement was discussed.

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In conjunction with the experimental studies, the analytical studies have been undertaken aimed at deeper and accurate understanding of the heat transfer enhancement phenomena by applying ionic wind in a channel flow. The positive wire-electrodes were set in parallel to the primary flow direction, and an electric field was applied. A theoretical analysis was performed on electric, flow, and temperature fields taking account of the interactions among them. By comparing the experimental results with the analytical results, the flow combined with the longitudinal vortex motions was clearly defined in relation to the applied voltage, the primary flow velocity, and the wire-spacing. The mechanism of heat transfer enhancement was found to correspond positively to the combined flow. The characteristics of heat transfer were also observed to be in connection with the arrangement of wire-electrodes such as the wire-spacing in spanwise and the wire-offset ratio in the channel height direction.

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An experimental study has been performed on critical heat flux (CHF) of boiling in closed end vertical tubes. Characteristics quite different from those of CHF in ordinary boiling systems have been found, relating to the matters such as the axial location where temperature excursion starts, a considerable time lag in the onset of CHF, and complicated behavior of local wall temperature at CHF. The paper also presents a physical model capable of explaining the appearance of such peculiar phenomena.

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Three-dimensional flow generated in the multicellular natural convection field of a vertical slot is visualized by aluminum tracer particles and the dye-injection method through the transparent side wall of hot water bath and an insulating side wall. The experiment reveals that the three-dimensional spiral flow in the secondary flow cell moves toward the insulating side wall, but the spiral flow along the circumference of the secondary flow cell moves in the opposite direction. Moreover, it is also revealed that the tertially flow cell stays still at the central cross section of the vertical slot.

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This paper deals with the effects of midheight cooling on natural convection and entropy generation in a porous layer heated from below. A porous screen, which is called as thermal screen in this paper, is adopted for the intermediate cooling with fluid flowing through internal passages formed within its solid matrix. It is shown from a numerical and analytical examination that the midheight cooling, reducing nonuniformity in horizontal temperature distributions, can control convective patterns and the associated heat transfer rate. Also, it is found that the midheight cooling can reduce the net entropy generation through the whole layer for certain convection regimes, and that the additional increase in the entropy generation due to convection is evaluated in terms of the porous Rayleigh number and the temperature level of the thermal screen.

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In order to certify one of the models for augmenting boiling heat transfer that was proposed in the previous paper, basic experiments and analyses were performed by using an air bubble in a mixture of silicone oil and ethanol as a working fluid to clarify the bubble-breakup effect of an electric field. From the experiments and analyses, it was clarified that the analytical shape of a deformed bubble in the electric field agreed well with that obtained by the experiments, and the breakup of a bubble was related to the EHD-coupled Taylor instability of the deformed bubble.

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A thin wire is installed just upstream of the throat in a convergent-divergent nozzle in order to decrease pressure undershoot (that is, the degree of the thermal nonequilibrium) at the throat. To study the effect of the wire diameter (0.3 to 1.5mm) on the nozzle performance, experiments have been carried out using initially subcooled hot water under inlet pressures of 0.47, 0.62 and 0.77MPa, and inlet subcoolings of 6, 12, and 19K. The one-dimensional void fraction is measured. Moreover, the measured pressure profiles and void fractions are compared with those calculated using the code "MINI-TRAC". The results are summarized as follows: (1) The greater the inlet subcooling or the lower the inlet pressure, the greater the improvement (using the method of a wire installation) of the nozzle performance. (2) The difference of the wire diameter has little effect on the nozzle performance. The pressure profiles for the nozzle with the wire agree with those calculated from the code "MINI-TRAC". (3) The one-dimensional void fraction profile can be obtained using real-time neutron radiography and image processing.

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Two kinds of photosensors, composed of a red-or green-light-emitting diode and a phototransistor, with optical fiber are applied to measure the temperature profile appearing on a temperature-sensitive liquid-crystal film. By the preliminary experiment the photosensors are found to be useful to precisely measure the surface temperature of the liquid-crystal film. Then the handy photosensors are successfully applied to measure the local heat transfer of a thin metallic-foil heater with liquid-crystal film under impingement cooling by a circular jet. The heat transfer results fit very well with the empirical equation proposed by Goldstein et. al.

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The purpose of this study is to investigate the effects of repeated transverse rib roughness on forced convection evaporation in a narrow vertical channel. Five channels which have the same cross section measuring 2mm by 50mm (aspect ratio 25) and have different rib heights (e=0.6 and 1.0) and rib spacings (P=7, 10, 15, 20mm) were investigated. Experiments were conducted using R12 as a working fluid for vertical upward flow at mass velocities between 50 and 130kg/m²s and mass qualities between 0.2 and 0.8. Comparison of these data indicates that the heat transfer coefficient has a tendency to increase with reducing rib spacing and to decrease with reducing rib height. The highest heat transfer coefficient, which is obtained by the channel with P=7mm and e=1mm, is about three times higher than the smooth channel. This ribbed channel was also found to be best in these five channels under the same pumping power condition.

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The solutions of steady flow of a viscous fluid, of which the viscosity, the conductivity and the density depend on the temperature, between two plane walls (a solid wall and a permeable one), with a constant suction or injection, are found theoretically in the similar form, in which the governing equations are reduced to an ordinary differential system. For the injection case, the solution is found uniquely, but for the suction case, the solution can be found uniquely or threefold, and reverse flow can arise beyond a critical Reynolds number. The extent of the Reynolds number range, where there are three kinds of solutions, becomes narrow for the case in which the viscosity decreases with increasing temperature and becomes wide for the opposite case. It is explained theoretically that, for the injection case, the thermal boundary layer arises near the solid wall. However, for the suction case, it can arise near the solid wall or/and the suction wall. For the suction case, there can exist a peculiar case in which either wall is regarded as adiabatic. The stabilities of these steady solutions are studied with respect to the two-dimensional disturbances. It is found that for the injection case, the solutions are always stable, but for the suction case, only one of the three kinds of solutions is unstable while the others are stable.

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A latent heat thermal storage system using a packed bed is one of the most attractive recovery methods of periodically generated waste heat in industrial processes. The thermal performance of the system depends largely on that of a single spherical capsule containing phase change material (PCM). In this study, PCMs were investigated as materials to recover and store heat for the temperature range between 500 and 1100K. Some inorganic salts and metals were selected from the point of view of higher latent heat, chemical stability, nontoxicity, inexpensiveness. Heat storage and release experiments of single capsules under the condition of predominant convective heat transfer were carried out. The results were favorably simulated by a mathematical model derived from enthalpy balance. For obtaining constant-temperature gas, metallic PCMs were more advantageous than inorganic salts because of higher thermal conductivity.

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Among the many solar-powered energy conversion systems, a recuperated closed Brayton cycle (CBC) is the most promising one. Several investigated aspects can be mentioned in the present study: a first assessment of a reference 25kWe system, the simulation studies related to various operating conditions and the heat rejection studies related to the transfer of the Brayton cycle waste heat to the radiating area. In addition, particular attention is being paid to the significance of the reduction of system mass required for radiation of waste heat from a closed Brayton cycle to space. Conceptually, the radiator area can be reduced by rejecting the heat from a radiator at higher temperature level than that of the waste heat of CBC, Operating a kind of heat pump by using a fraction of generated power. The optimum radiator area is obtained. As a consequence, for high temperature ratios of the radiator-to waste on the order greater than 5, the total radiator area is reduced remarkably and the required mass addition by the inclusion of the heat pump is estimated.

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The heat transfer performance of the actual heat exchangers obtained from the experimental results of the test Stirling engine is presented. The heater for the test engine has 120 heat transfer tubes that consist of a bare-tube part and a fin-tube part. These tubes are located around the combustion chamber and heated by the combustion gas. The cooler is the shell and tube-type heat exchanger and is cooled by the water. It is shown that the experimental results of heat transfer performance of the heater and cooler of the test Stirling engine have a good agreement with the calculated results by the correlation that is induced by our previous heat transfer study under the periodically reversing flow condition. Then our correlation is confirmed to be applicable for the evaluation of the heat transfer coefficient and the thermal design of the heat exchangers for the Stirling engine.

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A new heat transfer system has been developed on the basis of the effective energy conversion method between flowing gas enthalpy and thermal radiation. The basic concept consists of two porous media separated by a solid wall. A high temperature gas flows in the porous medium toward the receding direction from the separating wall, and the flowing gas enthalpy is effectively converted into radiant energy emitted in the upward direction on the heating side. On the other hand, on the cooling side, the reversed conversion from the radiant energy into the enthalpy increase of working gas takes place, where the working gas flows toward the approaching direction to the separating wall as well as to the receding direction from the wall. Consequently, both the analytical and experimental results show that the new heat transfer system exhibits a much higher overall heat transmission coefficient, which is evaluated from the net radiation flux and the effective temperatures being capable to emit equivalent radiation fluxes from both porous media, than that of conventional gas-gas heat exchangers.

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A new methane-steam reforming system for a fuel cell has been developed on the basis of the effective energy conversion method between flowing gas enthalpy and thermal radiation. The basic concept consists of a porous medium (heating side) and a porous catalyst (cooling side) which are separated by a solid wall. A combustion gas, which is used for heating the system, flows in the porous medium toward the receding direction from the separating wall, and the flowing gas enthalpy is effectively converted into radiant energy emitted in the upward direction. Conversely, a methane-steam mixture is supplied to the cooling side, and the radiant energy is effectively converted into endothermic reaction heat for the production of hydrogen in the porous catalyst. Consequently, the experimental results show that the compactness of the proposed reforming system can be improved, compared with conventional tubular reformers, to a considerable extent.

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The structure and transient behavior of a radiation-controlled flame both in and behind a highly porous medium, which has a finite length along the flow direction, have been clarified in detail through numerical calculation on the basis of the rigorous treatment of the radiative transfer and of the simplified one-dimensional flame theory. The results have disclosed that the flame is sustained in the region from about the middle to the upstream end of the porous medium over a wide mixture velocity range from about one-fifth to several times as high as the burning velocity of the ordinary gas phase flame because of the energy feedback by radiation. In addition, the flame is held at the downstream end of the porous medium under the condition of the mixture velocity below the burning velocity of the ordinary flame. Further, the radiation plays an important role in the transient phenomena for the flame propagation in both the upward and downward directions in the porous medium.

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Unsteady motions of two-dimensional reactive flows have been simulated to investigate the body-force effect on hydrodynamic flame instability. The numerical model contains compressibility, viscosity, heat conduction, molecular diffusion, chemical reaction, and convection. We have calculated the evolution of a disturbed flame and numerically reproduced that the disturbance on the flame grows exponentially in time, as predicted by the linear theory. The growth rate of disturbance depending on its wave number was obtained and the critical wave number for neutral stability was determined. The disturbances having small wave number rather than the critical one are unstable: i.e., long wave disturbances are unstable. The body-force has great influence on the flame instability: the growth rate of disturbance increases and the unstable region becomes wide for body-force in the direction of the hot burned gas, and the growth rate decreases and the unstable region becomes narrow for the other case. Moreover, the cellular structure of the flame front as observed in the experiment is reproduced in the simulation.

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We examined the possibility whether the indirect heating by radiant tubes in an annealing process at steel industry can be replaced with the direct flame heating without oxidation of the surface. The energy and capital savings are expected by this new-concept technology. The possibility of its practical application has been proved although the successful operating conditions are sensitive to the controlling factors. To realize this concept, the residual oxygen concentration in a flame must be lower than 0.1%(v/v), and the volume ratios of CO/CO₂ and H₂/H₂O in the flame should be over 0.4 and 0.09, respectively.

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