Droplet impacts on solid surfaces are key elements in technical applications, such as semiconductor cleaning, rapid spray cooling and ink-jet printing. There exist varieties of physical parameters proposed that control the droplet impact although they are not thoroughly explored; hence, dynamics of the droplet after the impact are yet fully understood. In this study, we experimentally observed the high-speed droplet impact on acrylic surfaces in a vacuum chamber with a high-speed photography, in order to clarify the effects of both the ambient gas pressure around the droplet and the impact velocity. The results show that the splash does not occur under the reduced ambient gas pressure even when the impact velocity becomes much higher than in the conventional experiments, in the range of the present experimental conditions.

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Acoustic levitation method is one of levitation techniques and describes some nonlinear behaviors such as the deformation of droplet interface. The purpose of this paper is to clarify the interaction between the flow behavior generated by the ultrasonic wave and the transport phenomena at the droplet interface. The following results were experimentally obtained: in the case of volatile fluids, a pair of the toroidal vortex was observed in the vicinity of droplet interface. As the saturated vapor pressure of droplet increases, the size of the circular vortex decreases. By measuring the change of surface area and surface temperature of the levitated droplet, the heat transfer coefficient was estimated. In the case of the droplet with the circular vortex, the heat transfer coefficient was larger than that obtained from the Ranz-Marshall correlation. Then, the thickness of thermal-boundary layer was calculated by using the heat transfer coefficient. The range of thickness was from 0.2 mm to 0.6 mm. We estimated the correlation between the flow structure and boundary layer around a droplet by using above mentioned result. By comparing the thickness of boundary layer, we concluded that the Stokes layer was inside the diffusion boundary layer. Thus, physical properties of the surrounding atmosphere were affected by the evaporation behavior. In the case of the droplets with the evaporation, the result suggested that the kinematic viscosity variation of gas phase around the droplet affected the flow structure.

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An air cavity is formed behind a spherical particle plunging into a liquid bath. The residual bubble attached to the sphere has an important effect on the performance of CaO particle used for desulfurization of melted iron. Based on the water model with the same kinematic viscosity as the melted iron, the behavior of air cavity was observed for the spheres coated by two kinds of water repellent preparations. In this report, the volume of residual bubble was theoretically estimated for the quasi-static immersion of sphere as a reference condition. First the critical depth at which the axi-symmetric meniscus breaks is obtained by using Laplace equation. Then the bubble volume was obtained from a simple energy minimum principle in which we considered the effect of the interfacial energy including the wetting behavior and the liquid potential energy. The calculated volumes can approximate fairly well the measured results for two kinds of contact angles of 115° and 162°.

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For introducing the use of fine bubbles (FB) in industrial applications, it is important to understand their properties and the mechanisms of the effect in order to utilize them effectively. However, it is difficult to observe FB directly because of their small size. We measured the electrochemical properties of water containing FB in order to examine the effect of FB on ions macroscopically. The conductivity of the FB water generated from purified water was lower than that of the purified water. In particular, the decrease in the conductivity of the FB water supports the hypothesis that ions are closely involved in the generation mechanism of FB. We also analyzed the effect of FB water on the nutrient uptake of soybean seedlings. For the uptake experiment, we used radio isotope elements (¹³⁷Cs, ²²Na, ³²P) at different pH conditions. As a result, we have found the increased uptake of ¹³⁷Cs and ²²Na and the decreased uptake of ³²P compared with distilled water. There was no correlation between pH value and the effect of FB water. Transpiration rate was not significantly different between FB water and distilled water. Although questions still remain in the elements efficiency in ions (anion or cation), these results suggest a possible influence of fine bubbles on the plant activity to uptake nutrient ions.

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Snow characteristics are changed by climate or region. For the efficient development of a snow blower, stable and quantitative performance evaluation method is required. We try to reproduce the snow removal work using Discrete Element Method (DEM). In this study, we have improved the snow characteristic model for fallen snow simulation. It is possible to reproduce fallen snow by constraint of motion of a single particle and limit for potential force.

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This paper presents a prediction method about pressure drop in tight lattice fuel bundles. Pressure drop of fuel bundle is one of the important parameters to evaluate the core performance. Friction coefficient and spacer loss coefficient depend on the fuel shape. In previous study, these coefficients were evaluated based on experimental data or an experimental correlation. However, the experiments need a lot of time and cost. Therefore, the purpose of this study is to predict pressure drop of fuel bundle without experiments. In this study, friction coefficient and spacer loss coefficient under single phase flow condition were evaluated using CFD analysis and total pressure drop under two phase flow condition were predicted using these coefficients. The predicted results were compared with the experimental results of 3 types of tight lattice fuel bundle. It was found from comparison results that the prediction accuracy of this method was about 10% and this accuracy was the almost same as that of previous method.

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VOF numerical simulations were conducted for a three-fluid dam break problem to investigate the scaling effect on mixing and stratification processes of three immiscible fluids by gravity. Two liquids (silicone oil and salt water) were initially separated with a vertical partition plate and filled in a rectangle container. Computational fluid dynamics analysis was conducted with Star CCM+ version 9.02. The contact angle affects the interfacial motion significantly in a relatively small-scale domain, while the interfacial tension affects it in a relatively large-scale domain.

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Various oscillation phenomena such as transition between meander and non- meander paths of western boundary current such as the Kuroshio exist in the oceanic general circulation. These phenomena are considered to be related to nonlinear rhythmic phenomena such as synchronization and stochastic resonance. Thus, we investigate the responses of oceanic double-gyre to external wind forcing with and without noise using a 1.5 layer quasi-geostrophic model, and considered the possibility of nonlinear rhythmic phenomena in oceanic general circulation.

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