An experimental study in the fully developed two-dimensional channel flow was performed to investigate the possibility of a spanwise discontinuity of wall roughness as a device to generate secondary currents associated with longitudinal vortex. A k-type rough wall, which consists of an array of two-dimensional rectangular roughness elements, is placed to make spanwise discontinuity of wall roughness. Mean velocity and turbulent intensity were measured with hot-wire anemometers and crossed wire probes. Velocity vector plot in a cross streamwise plane clearly shows that the discontinuity of wall roughness is able to generate secondary currents. And, the secondary currents are associated with longitudinal vorticity. The contours of the longitudinal momentum flux are consistent with the distribution of secondary currents. Transport to the near-wall by the downwash is greater than the upward transport by the upwash. Transport of momentum toward the wall due to secondary currents is quite large compared to that caused by turbulence.

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An electric conducting fluid flow in a cylinder driven by a rotating magnetic field is numerically studied. A time-averaged Lorentz force term is derived on the condition that the skin effect can be neglected and then it is incorporated into the Navier-Stokes equation as a body force term. The axisymmetric velocity profile of basic flow for an infinitely long cylinder case depends only on the Hartmann number. A set of steady disturbance equations was successfully solved using the HSMAC method. For various cases of the basic flow i.e. the Hartmann numbers, the corresponding critical rotational Reynolds numbers for the onset of secondary flow were obtained instead of using the conventional magnetic Taylor number. The numerical results reveal that the critical Reynolds number takes its minimum at a certain Hartmann number. On the other hand, for a case of finite length cylinder, the no-slip condition at the flat walls generates the Bödewadt-like boundary layers and consequently the flow structure is changed significantly.

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In modern analytical chemistry, it is crucial to save an analysis time and a cost. Acoustic levitation technique is well suited for a sample pre-treatment because the surface tension and density are properties that determine the viability of the method and it avoids a sample contamination and a sorption process by container walls, but suffers from an evaporation and loss of solvents. On the other hand, it is widely known an acoustic streaming is generated around a levitated droplet and complex flow also appears in a droplet. The purpose of present study is to investigate the interaction between internal / external flow and mass transport of an acoustically levitated droplet. The internal and external flow structure of a levitated droplet were measured by using Particle Image Velocimetry(PIV) technique. Also, we have measured the flow structure of the water, ethanol and water-ethanol mixture droplet. The evaporation process and surface temperature of the levitated droplet were measured with the high speed camera and radiation thermometer. In the case of the water droplet, the circular vortex was observed in it, and toroidal vortex was generated below it. In the case of the ethanol, two toroidal vortices were observed in it, and two toroidal vortices also were generated below and above it. In addition, circular rotating vortices were observed near the ethanol droplet surface. The experimental value of the evaporation process was quantitatively good agreement with the theoretical prediction that considers the forced convection. It is indicated that the flow field near the droplet surface affected the rate of the mass transfer of an acoustically levitated droplet.

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Surface tension is a dominant force in gas-liquid flows within micro/nano spaces, such as gas-liquid flows of micro-electro-mechanical systems, nano-in-print processes, and resin coating processes. We developed a surface tension model for a particle method to simulate gas-liquid flows within micro/nano spaces; the inter-particle force between particles was defined to simulate interactions at gas-liquid and liquid-solid interfaces. The inter-particle force was given by the derivation of potential energy and was related to the surface tension by Bakker's equation. The surface tension was modeled as volume force in the Navier-Stokes equation, and the volume force was changed in proportion to the curvatures of interfaces. The surface tension model was verified for pressure in a drop, oscillation of a square drop, and wall adhesion. The predicted pressure in a drop quantitatively agreed well with those given by the Young-Laplace equation. The oscillation of a square drop was qualitatively simulated. In the wall-adhesion verification, effects of different contact angles on drop deformations were quantitatively simulated. We clarified that our new surface tension model was useful for simulating gas-liquid interfaces.

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Thermal puffer type SF₆ Gas Circuit Breaker (GCB) has the advantage in reducing operating energy. However, its efficient design needs a detail understanding of the fluid-plasma interaction phenomena associated with the gas blast characteristics. In the fluid-plasma interaction process, turbulence mixing between the high temperature arc plasma core and the surrounding fluid plays a dominant role. Therefore the main aim of this paper is to study the fluid-plasma interaction phenomena based on three dimensional compressible turbulent viscous flow analyses using a High-Order LES turbulence model along with arc plasma model. The first part of this work deals with basic fluid-plasma interaction phenomena around a converging-diverging type nozzle installed with two electrodes inside to generate thermal arc plasma in the nozzle flow field. In the second part of this work, pressure rise mechanism in a thermal puffer type GCB and related physical behavior is analyzed. The results led to an understanding, that basically fluid-plasma interaction results in sudden expansion of the hot gas which in turn led to the pressure rise in the tank and the transport of thermal and pressure energy is carried out through two different modes, namely the convection and the acoustic mode.

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The discharging flow rate from safety or relief valves is restricted with the minimum flow area between disk and seat. The flow rate is usually smaller than the calculation with the minimum flow area due to the vena contraction. The discharging flow rate of water was measured at different valve lifts and seat configurations. The water flow rate was affected with the lift and seat configuration due to the different formation of vena contraction. The air and air-water two-phase discharging flow rate were also measured and compared with the non-equilibrium or slip flow model. The air flow rate was affected not only with the vena contraction but also with the delay of expansion. The two-phase flow rate was affected with the slip velocity between air and water. It was suggested that the vena contraction of two-phase flow was mitigated with the oscillatory flow behavior. The two-phase discharging flow rate was well correlated with the simple pressure loss equation. The single and two-phase discharging behavior was carefully observed by using the transparent disk.

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The discharging flow rate from safety or relief valves is restricted with the minimum flow area between disk and seat. The flow rate is usually smaller than the calculation with the minimum flow area due to the vena contraction. The non-equilibrium flashing flow model directly using the steam table was proposed to obtain the critical mass flux at the vena contraction. The more precious prediction can be available compared to the previous model using the approximation of steam condition. The discharging flow rate of flashing water through the simple contraction between disk and seat was measured at the different inlet subcooling or two-phase quality. The comparison of the experimental results with the non-equilibrium model indicated the significant non-equilibrium in the flashing flow at the vena contraction in spite of the disk material. The subcooled liquid and two-phase discharging behavior was carefully observed by using the transparent disk. The observation also supported the significant non-equilibrium. The two-phase discharging flow rate was well correlated with the simple pressure loss equation.

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The objective of this study is to understand the effect of cavitation inside the injection nozzle on spray atomization for various nozzle geometries and injection conditions. In this paper, pressure measurement and observation of flow pattern including cavitation inside the nozzle hole were carried out for various injection conditions and saturated vapor pressure of test fuel using by transparent nozzle which was made of acrylic and magnified 25 times. As results of these experiments, with increase in saturated vapor pressure of test fuel under the same injection pressure, cavitation develops toward the downstream of the injection nozzle hole similar to the conditions of high injection pressure with the same test fuel. The strong relationship between pressure distribution and cavitation region inside the nozzle was obtained for both experimental parameters. In addition, there was not much difference in patterns of pressure distribution and liquid jet between both experimental parameters under the same cavitation number. It is concluded that the cavitation region, pressure distribution inside the nozzle and width of liquid jet are able to be arranged by use of cavitation number.

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The efficiency index η, (i.e., the ratio between heat transfer enhancement and drag increase from a smooth channel), is discussed in a channel with a delta wing-type vortex generator (VG) installed on the wall in laminar and turbulent flow. In this report, the effect of Prandtl number Pr on η is mainly discussed by use of the equation obtained in the preceding report to estimate various effects on the heat transfer enhancement. From the results of direct numerical simulation, η decreases slightly in the turbulent flow with Pr, while it increases noticeably in the laminar flow. In the laminar flow, since there is no background turbulence in the smooth channel, the fluctuation generated by VG directly enhances the heat transfer, which is greater at high Pr where the thermal diffusion effect is weakened. In addition, the increase of convective heat transfer near the wall has an important effect on the good efficiency. In the turbulent flow, on the other hand, the efficiency index slightly decreases with Pr since the turbulence generated by VG is not strongly dependent on the Prandtl number. The influence of the notched hole beneath the wing is discussed from the numerical results.

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The similarity between turbulent heat transfer and Reynolds stress is investigated using the equations written in Lagrange description. The correlation between pressure gradient fluctuation in the flow direction and wall-normal velocity [term (B)] depresses the Reynolds stress, which makes the turbulent Prandtl number Prt less than unity. Based on the trajectories of fluid particles, an algebraic equation was theoretically derived to correlate the term (B) to Prt. Using the database of the trajectories calculated by DNS, the change of Prt with regard to (B) was actually estimated from the equation. The slight decrease of (B) causes the dramatic reduction of Prt in the log-law region, while the change of Prt in the near-wall region is hardly recognized. This is caused by the fact that the Reynolds stress or turbulent heat transfer in the log-law region are influenced by the fluid particles coming from further positions compared with the near-wall region.

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Pulse tube cryocoolers are more attractive than other small cryocoolers because they have no moving parts in the expander and thus have higher reliability. However, Stirling type pulse tube cryocooler needs further improvement on regenerator. The entrance areas at the regenerator ends of the typical pulse tube cryocooler are smaller than the cross-sectional area of the regenerator matrix. So, the working gas flow in the regenerator has non-uniform velocity distribution with the expansion and contraction flow. They cause the excessive pressure loss and reheat loss. In this study, the effect of the regenerator entrance shape on the performance of compact pulse tube cryocooler was examined experimentally. Additionally, the analytical method for losses in the regenerator using experimental data is suggested. Experimentally and analytically, the effect of after-cooler end at the regenrator has been bigger than that of cold-head end.

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The effective thermal conductivity of metal hydride (MH) is greatly influenced by the void fraction of packed bed. So, we investigated metal hydride packed-bed change caused by repetition of hydrogen absorption and discharge. This paper includes two experiments; one is the measurement of the particle breakup, and the other is the direct visualization of volume change of metal hydride bed. The particle breakup makes the diameter of particle become uniform gradually, decreases the degree of circularity and increases the surface roughness. The volume change of metal hydride bed was clearly shown by the visualization experiment. The results shows that it became impossible to pack metal hydride densely under the influence of the foregoing particle change and that the total volume increased. When the particle breakup and the increase in the volume almost stopped, the cycles of expansion and contraction were repeated at the void fraction beyond 60%.

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An LDV system was employed to measure three components of velocity at a mid-flame point on the centerline of a propane-air flame of equivalence ratio 1.10 on a 26 mm-diameter Bunsen burner with fully developed turbulent pipe flow upstream at a Reynolds number of 6700. The LDV measurement volume was 1mm below the leading electrode of a four-element electrostatic probe that provided the velocity and direction of motion of flame-front in the turbulent flame brush. It was found that when the coordinate system was rotated about a vertical axis to the plane of the flame-front velocity vector, most of the burnt-gas motion following flame-front passage remained largely in this plane. The sequence of LDV data for gas motion in the burnt gas consistently showed movement beginning first in a direction opposite to that of flame-front front passage, then gradually rotating until finally becoming in the direction of flame-front passage, completing a turn of 180 degrees. This behavior is explained qualitatively by considering a momentum conservation and of the nature of the LDV measurements. Histories of gas-acceleration vectors in the burnt gas were derived from the LDV data, demonstrating the turbulent fluctuations that are imposed on this systematic behavior.

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Lean premixed combustion is one of the most efficient techniques to reduce nitrogen oxide (NOx) emission. However, a lean premixed combustor has narrow stable combustion range compared with a diffusion combustor and has a risk of flashback. Flashback of the flame into the nozzle causes serious damage to a combustor. In this study, we present characteristics of flame propagating in a premixed burner with swirling flow in order to investigate unsteady flame behavior in a gas turbine premixer. During flashback, the flame propagating upstream was visualized with a high-speed camera. Moreover, we established the technique to measure the instantaneous flow fields of unburned fuel-air mixture in a swirling premixed burner using stereo Particle Image Velocimetry (stereo-PIV). As a result, characteristics of flame behavior propagating upstream were examined. In addition, it was found that a low velocity region existed near the flame tip. We clarified the existence of the vortex core of swirling flow near the center axis with precession movement.

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When diesel fuel was evaporated on a high temperature wall in a combustion chamber, a deposit was formed on the wall. Deposit formation on the wall of the combustion chamber affected a decrease of thermal conductivity. However, it is difficult to investigate directly a behavior of a diesel deposit in a diesel engine. Therefore it is necessary to develop the measurement technique for understanding the behavior of the deposit in the combustion chamber. In this study, an engine head of a small DI diesel engine was drilled in order to insert a plug for sampling of the deposit in the combustion chamber, and the deposit on the surface of the plug was collected. By using the measurement system developed, effects of wall temperature of the cylinder head and excess air ratios on the deposit formation were investigated. Moreover, thermal resistance of a PM deposit layer was estimated using a simplified engine head wall model. As the results, deposit mass in the lower wall temperature was larger than that in the higher wall temperature under the condition of the same excess air ratio. It was also clear that the deposit mass in the lower excess air ratio was larger than that in the higher excess air ratio under the condition of the same wall temperature. According to estimation of thermal resistance of the PM deposit layer, it was clarified that thermal resistance of the deposit layer with around 10μm thickness was higher than that of aluminum diecast aroy with 5mm thickness.

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Gas diffusion layers (GDLs) coated with a hydrophobic microporous layer (MPL) have been commonly used to improve water management properties of polymer electrolyte fuel cells (PEFCs). In the present study, a novel hydrophilic and hydrophobic double MPL coated GDL was developed to achieve further enhancement of the PEFC performance under both low and high humidity conditions. Under low humidity conditions, a thin hydrophilic layer using titanium dioxide coated on the hydrophobic MPL is effective to conserve the humidity of the membrane electrode assembly (MEA), while a hydrophobic intermediate MPL between the hydrophilic layer and the carbon paper substrate prevents removal of water in the hydrophilic layer. This results in a significant enhancement of the ability of the MPL to prevent drying-up of the MEA. Under high humidity conditions, the double MPL coated GDL with appropriate pore diameter, thickness, and hydrophilic and hydrophobic properties is also effective to reduce flooding on the cathode catalyst layer, resulting in the higher PEFC performance compared with that for a hydrophobic MPL coated GDL.

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An experimental study on fuel sprays for direct injection gasoline engines was carried out in order to evaluate spray velocity characteristics. Tested injectors were swirl and outwardly opening type ones, and formed sprays into a pressure chamber in which the pressure was set to 0.1 MPa and 1.1 MPa. The spray velocity was measured by two components laser Doppler anemometry and was processed by a time-dividing method which divided the phase-matched spray information into five distinct time periods. By the increase in back pressure, the spray development was limited in axial direction for the swirl type injector, while spray developing direction was not changed for the outwardly opening type injector. Under high back pressure condition, the axial velocity fluctuation for the swirl type injector was larger than that of radial component, while the axial velocity fluctuation for the outwardly opening type injector was comparable with that of radial component. Strong correlation of axial and radial velocity fluctuations was observed except for the condition of the swirl type injector with high back pressure.

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The adhesion type micro-manipulator tip was proposed and studied. The adhesion force is thermally controlled by supplying and evaporating liquid water film on the tip end. The force between the tip and small glass ball was measured with a movable coil type analog volt meter in micro-Newton level. The capillary tip indicates the adhesion force of 10 μN level in wet state of below 90°C, and 1μN level of dry state of over 100°C. Theoretically estimated capillary force between two spheres with various meniscus amount covers the measured values. The wet state of the tip can control with sub-second time constant, which is enough speed for manual operation of micro manipulation. In the manipulation test of small glass beads, pick up and release operation was conducted with high probability and beads arrangement along an M shape was demonstrated.

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Stirling engines have been used frequently for the explanations of the environmental and energy saving education, because they have excellent characteristics which are high thermal efficiency, multi-fuel capability and low pollution. Since Stirling engines work relatively in the range of low gas pressure compared with the internal combustion engines, the models of Stirling engines have been used as teaching materials in the thermal energy education. However, the principle of Stirling cycle is difficult to understand. For this reason, CG animation multi-media content dealing with the operation principle of the Stirling engine was developed for the sake of promoting the understanding of its principle to students. This content was pretested in a teaching training for the teachers of elementary school, junior high school and high school and evaluated by questionnaire. The questionnaire result showed that the most teachers realized the animation contents were very good to understand the principle of the Stirling engine.

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