The reverse osmosis (RO) method is a method obtaining the fresh water by using semi permeable RO membrane. However, the RO method has to give continuous operation at high pressure in seawater desalination plants. In the present study, in order to improve the efficiency of RO desalination under low pressure conditions, the water treatment system is proposed by using microbubbles in salt water disposal. Microbubbles are very small air bubbles with diameters of the order of less than several tens microns, and our proposed microbuble generator was developed in our previous study. The RO desalination efficiency can be improved by microbubble generation in salt water in contrast to the method with no microbubbles, and the efficiency of desalination is significantly improved by microbubbles with a high electrical potential. The effect of the microbubbles on the rate of osmosis was also investigated by measurements of the electric conductivity and the shrinkage rate of microbubbles. The electrical conductivity of salt water decreases with increasing the electrical property of the gas-water interface (ζ- potential) of microbubbles. Furthermore, microbubbles with a high electrical potential of high number density in salt water can exist in salt water because the rising velocity and the shrinkage rate of microbubbles become smaller with increasing the high electrical potential of microbubbles.

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First we have developed the Lattice Boltzmann method based on the fluctuation hydrodynamics which is applicable to a flow problem of a particle suspension. In this method, we have introduced the viscosity-modifying method, instead of the velocity-scaling method, in which the modified viscosity is used for generating the random forces in the lattice Boltzmann simulation. This viscosity-modifying method has been seen to be available for a magnetic particle suspension. Then we have applied this method to a two-dimensional Poiseuille flow of a magnetic suspension between the two parallel walls in order to investigate the behavior of magnetic particles in a non-uniform applied magnetic field situation. From the results of the snapshots, the pair correlation function between the magnetic pole and the magnetic particles and the averaged local particle velocity and magnetization distributions, it is seen that the behavior of magnetic particles drastically changes due to which factor dominates the phenomenon much more significantly among the magnetic particle-particle interaction, the non-uniform applied magnetic field strength and the translational and rotational Brownian motion.

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We have investigated the negative magneto-rheological effect of a dispersion composed of spindle-like hematite (α-Fe₂O₃) particles by means of the experimental method. The spindle-like hematite particles were synthesized by aging a solution of FeCl₃ and KH₂PO₄ for 72 hours at 373K. The particle size distribution was determined by a digital image analysis method from the electronic microscope observation of the particles. In the present study we have considered a glycerol-water-based dispersion in order to clarify the influences of the shear rate and the magnetic field strength on the negative magneto-rheological effect. The measurement of the viscosity was carried out using the rotational-type rheometer in an external magnetic field generated by the Helmholtz coils. The main results obtained here are summarized as follows. The viscosity of hematite/glycerol-water dispersions relative to that for no applied magnetic field case decreases with increasing magnetic field strength: that is, the negative viscosity certainly occurs, as theoretically predicted. Moreover, this negative magneto-rheological effect tends to decrease with increasing shear rate, which also qualitatively agrees with the theoretical prediction.

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We have developed the basic equation of the orientational distribution function of oblate spheroidal hematite particles that conduct the rotational Brownian motion in a simple shear flow under an applied magnetic field. An oblate spheroidal hematite particle has an important characteristic that it is magnetized in a direction normal to the particle axis. Since a dilute dispersion is addressed in the present study, we have taken into account only the friction force (torque) with neglecting the hydrodynamic interactions among particles. This basic equation has been numerically solved in order to investigate the dependence of the orientational distribution on the magnetic field strength, shear rate and rotational Brownian motion, and also the relationship between the orientational distribution and the transport coefficients such as viscosity and diffusion coefficient. The results obtained here are summarized as follows. If the magnetic field is more dominant, the particle inclines such that the oblate surface aligns in the magnetic field direction. If the Peclet number increases and the shear flow becomes more dominant, the particle inclines such that the oblate surface tildes in the shear flow direction. The viscosity due to the magnetic torque increases as the magnetic field becomes strong, since the magnetic torque due to an applied magnetic field becomes more dominant. Moreover, the viscosity increases more significantly for a larger aspect ratio or for a more oblate hematite particle. In another sedimentation phenomenon (not a simple shear flow) where the particle sediments under a magnetic field applied in the sedimentation direction, the particle comes to sediment more significantly with the oblate surface aligning in the sedimentation direction as an applied magnetic field increases.

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Jet flows have been applied in a number of fields in order to control flow separation. Over the last decade, several studies have been carried out on the production of synthetic jets. However, there are still a large number of unknown quantities, including details of the structure and the formation mechanism of such jets. The present study attempts to clarify some of the fundamental flow characteristics of free synthetic jets, based on experiments and numerical simulations. Experimental velocity measurements and flow visualizations are performed using the hot-wire anemometer and the smoke wire method, respectively. It is found that both the temporal change in flow pattern and time-averaged velocity distribution at the centerline depend on K=ReU/S² (the ratio of the Reynolds number to the square of the Stokes number). The unsteady downstream flow characteristics are discussed, in addition to the relation between the formative point of the synthetic jet and the value of K. Furthermore, the flow pattern and the unsteady flow characteristics of the synthetic jet are compared with those of a continuous jet.

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The influence of airfoil profile and wing-tip plate on wing in ground effect has been clarified by means of wind tunnel experiment. The aerodynamic force has been directly measured by the three-components force transducer, and the flow field has been measured by the particle image velocimetry (PIV). The characteristic of the aerodynamic force by the wing in ground effect was qualitatively as same as that of previous study. It is found from PIV measurement that the wing-tip vortex exists near the wing-tip without wing-tip plate. When the wing-tip plate is attached, the wing-tip vortex is away from the wing compared with that of no wing-tip plate. In addition, when the wing approaches the ground, the stagnation point of the leading edge moves in the downstream position, and the location of the stagnation point depends on the curvature of leading edge.

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The conventional Galerkin finite element solution is mesh-dependent, and its discretization for Poisson's equation can not satisfy the conservation law over a nodal domain when unstructured linear meshes are used. This research tries to solve these problems by introducing a new concept of the virtual nodal domain(Vnd) for a linear quadrilateral element, and distributing the source term to a nodal algebraic equation in proportion to the area of the Vnd. The Vnd is evaluated using a second-order flux existing within a linear element. We proofed that the total Vnd of the four nodes equals to the area of the element, which guarantees that our scheme is also elementally conservative. Numerical simulation of heat conduction with both Dirichlet and Neumann boundary conditions shows that the accuracy has been improved obviously comparing with the conventional Galerkin FEM for unstructured quadrilateral meshes, especially for bad quality elements. Our scheme can be introduced into any commercial FEM code quite easily.

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An experimental investigation was made on a turbulent boundary layer near the trailing edge on a long flat plate with a blunt trailing edge. The flow was controlled by an additional splitter plate attached to the trailing edge along the wake center line. The length of the splitter plate, l, was varied from 0.3 to 3 times the trailing edge thickness, h. Measurement of fluctuating velocity was made under the freestream zero pressure gradient. Almost independent of the installation of the splitter plate, the turbulent intensity and the Reynolds shear stress in the inner layer decreased when approaching the trailing edge of the flat plate (x/h=0), compared with that in the fully-developed turbulent boundary layer under the zero pressure gradient. The only exception was the distribution at x/h=0 near the wall in the case without the splitter plate (l/h=0), where the degree of the decrease in u_rms/U_e was relatively small, and v_rms/U_e and -uv / U_e² were larger than those of the zero pressure gradient. The effect of l/h on turbulent quantities was shown just upstream of the trailing edge upon close comparison, and was classified into two groups: l/h<1 and l/h≧1. The tendency of the turbulent energy production terms approaching x/h=0 coincided with the decrease in the streamwise turbulent intensity and in the Reynolds shear stress.

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In the present study, we investigate a self-excited oscillatory phenomenon of a two-dimensional confined jet with a rectangular-cross-section cylinder as a downstream target. More specifically, in order to reveal the effects of a kinematic parameter the Reynolds number Re and various geometric parameters upon the jet-oscillation frequency f_D, we conduct experiments at Re < 5000 in water and in air by an ultrasonic velocity profiler and a hot-wire anemometer, respectively. As a result, we specify the effects of Re and four non-dimensional geometric parameters upon f_D, which is non-dimensionalised as the Strouhal number St. As the four geometric parameters, we consider (1) the streamwise target size, (2) the channel breath, (3) the cross-streamwise target size and (4) the target distance in non-dimensional forms with a length scale of the jet's breadth. It is found that the Re effect is negligible. This guarantees a wide-range workability as flowmeters. All the results can be summarised in an empirical formula describing the relation of St with the four geometric parameters.

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A molecular tagging technique utilizing evanescent wave illumination was developed to investigate the motion of a caged fluorescent dye in the vicinity of the microchannel wall surface in electroosmotic and pressure-driven flows. A line pattern in a buffer solution was written by a pulsed UV laser and the uncaged dye was excited by the evanescent wave with total internal reflection inside the glass wall using an objective lens. The velocities calculated by the measured displacement of the near-wall tagged region were compared with the results of molecular tagging using volume illumination, which represents the bulk flow information. Concerning electroosmotic flow, the micro-PIV technique using a confocal microscope system was applied to the microchannel rinsed by the caged fluorescein beforehand in comparison with a pure glass-PDMS microchannel to examine the effect of dye adsorption to the wall on the electroosmotic mobility. The electroosmotic mobility obtained by evanescent wave molecular tagging (EWMT) showed close to the micro-PIV measurement result near the glass wall for the rinsed case and the uncaged dye at the almost constant velocity remained in the depthwise illumination region. On the other hand, the dye velocity in pressure-driven flow by EWMT increased rapidly with respect to time. The uncaged dye convected to the streamwise direction dispersed toward the wall due to the concentration gradient of the dye, which was confirmed by the numerical simulations.

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Direct numerical simulation was performed for a spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel. A rib was placed on either an inner- or outer-wall of the straight part nearby curved-channel inlet for controlling the flow and thermal fields. Outer-wall was heated at the constant temperature and inner-wall was cooled similarly. In the simulation, fully developed flow and temperature computed by the straight channel was given to the inlet of curved channel domain. The frictional Reynolds number was assigned at 150, and the Prandtl number was given 0.71. When a rib was attached to the inner-wall, heat transfer in the upstream region of curved channel was enhanced effectively. On the other hand, placing a rib on the outer-wall caused an enhancement of heat transfer in the relatively downstream region of curved part, suggesting active heat transport of the large-scale vortices. Consequently, the inner-rib case affected more greatly on heat transfer than the outer-rib case. Mean velocity vector and power spectrum analysis implied that development of coherent structures near the outer-wall were controlled by a rib. It was found that inner-rib restrained large-scale vortex, while outer-rib promoted growth and power of large-scale vortex.

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A novel numerical simulation procedure has been proposed for prediction of local urban climatological phenomena. Buildings and skyscrapers in the urban area were modeled as a collection of porous blocks of prescribed permeability and porosity. A new set of the governing equations based on the volume averaging theory has been derived in which the velocity vector, Exner function, potential temperature and the mass fraction of water are dependant variables. A numerical integration scheme similar to SIMPLE has been developed to solve the set of the equations. Sample calculation results reveal interesting climatological phenomena, associated with the local urban climate.

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One of the important factors of cell performance in polymer electrolyte fuel cell (PEFC) is moisture control in gas diffusion layer (GDL). It is necessary to clarify the mass transfer characteristics in GDL. The oxygen diffusion coefficient in GDL is measured with a galvanic battery type oxygen absorber. Particularly, measurement in high accuracy of oxygen diffusion coefficient in GDL becomes important. In the previous study, the measurement of the effective oxygen diffusivity in the microporous GDL using the galvanic cell type oxygen absorber was proposed. In addition, the measurement of the effective oxygen diffusivity in the microporous GDL containing moisture was proposed and shown to be an effective technique for measurement of the effective oxygen diffusivity in microporous media. However, because the diffusion resistance of dry GDL is small, the error margin of tens of percent existed in the result of a measurement of the oxygen diffusivity. In the present study, the objective of this study is high precision measurement of the oxygen diffusion coefficient in GDL by specifying the error factors and improving them.

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Since lean premixed combustion in gas turbine combustors undergoes in elevated pressure condition, it is important to know NO_X formation characteristics under elevated pressure. Generally, effects of pressure on NO_X formation characteristics are evaluated by using pressure coefficient on conventional systems. However, the value of pressure coefficient distributes widely from -0.2 to 0.5. This difference in the pressure coefficient stems from differences in experimental conditions and formation processes of NO_X. As a result, effects of pressure on different NO_X formation mechanisms have not been elucidated yet because of difficulties of temperature control of combustion region. In this study, to clarify the effects of pressure on the prompt NO_X formation process is set as the objective. Experimental measurements and numerical simulation with detailed elementary reactions are conducted. The temperature controllable premixed flat flame burner is fabricated in the elevated pressure combustion chamber, and measurement of NO_X concentration is conducted in the chamber. Both the experimental and numerical results clearly show that the pressure does not affect to the prompt NO_X formation.

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The purpose of this research is to include the phenomenon that occurs because of “Wrinkle (Stretch)” which naturally generates to the flame surface under a rich condition that promotes the burning speed. This happens in a gasoline fuel combustion that is heavier than air. In the present study, the unstable flame was formed due to the imbalance of the mass diffusion and the temperature diffusion of the fuel was modeled. The laminar burning speed model was developed by considering the stretch. The model has shown the capability to reproduce the heat generation (heat release rate) at high accuracy in comparison with experimental data. The simulation was carried out for both homogeneous and the stratification combustion and validated with experimental data. Considering the flame stretch made 3-D combustion simulation tool high accuracy from lean to rich fuel mixture condition.

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