Groundwater contamination due to chlorinated hydrocarbons like trichloroethylene and tetrachloroethylene has been a great environmental issue in Japan. Because these substances are volatile and little soluble in water, and can exist in unsaturated zone as vaporized, dissolved and undiluted non-aqueous phases, they migrate as gas-water-liquid three phase flow in subsurface. Recently, the air sparging coupled with the soil vapor extraction as the physical remediation technologies has been applied to a site contaminated with chlorinated hydrocarbons. The air sparging technology facilitates the contaminant volatilization with air injected into saturated zone and the soil vapor extraction technology extracts the contaminant in soil and injected gas. Therefore, in order to establish these technologies, it is indispensable to understand the mechanism of gas-water two phase flow in subsurface.

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Possibility of CO₂ underground disposal in Japan was studied by some authors. Summaries of the results were introduced first. Then, capacity of the disposal amount was estimated for geologically classified reservoir types. The result indicated that enough capacity existed in Japan. Finally an example simulation study to investigate distribution of CO₂ injected from surface into the reservoir was explained.

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This paper presents some numerical results for the motion of a discrete particle and the effects of the governing three parameters on the particle behaviors in the flow field of a Burgers vortex which is considered to be closely related to the small scale vortex of Kolmogorov microscale in turbulence. As a qualitative approach, the governing equation is based on Basset-Boussinesq-Oseen equation⁽¹⁾ without external forces and historical force. There are four kinds of typical particle characteristic behaviors, and the corresponding characteristic regimes have been obtained. For the light particle, the lighter the particle is, the faster it reaches the vortex center, and there is a value of the critical unit Stokes numberSt₀cγ, in case of the unit Stokes number St<St₀cγ, the particle oscillation can be observed and makes the reaching time much longer with the increase of St₀, and the reaching time is nearly independent of D. While St₀<St₀cγ, the particle oscillation can not be observed, however, a maximum in the reaching time appears. The value of St₀cγ decreases with the increase of σ, and when σ is greater than some value, St₀cγ, disappears. The time of particle oscillation lasts so long that it makes a very intensive effect on the surrounding fluid flow, and it will be helpful to understand turbulent dissipation.

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High critical-power fuel assemblies are needed for boiling water reactors to increase the thermal safety margin of the reactor core. There are seven spacers supporting the fuel rods in a BWR fuel assembly, and it is well known that the critical power is affected by the spacer geometry. Studies of spacer geometry are therefore important to the development of high critical-power fuel assemblies.
Recently, Morooka et al. reported that a twisted tape increased the critical power. The purpose of this study was to clarify the mechanism by which the twisted tape improves critical power by measuring the film flow rate on the fuel rod under air-water conditions. The test data demonstrate that the twisted tape increases the film flow rate in the annular dispersed flow regime. It is thought likely that a swirling flow is generated downstream of the twisted tape and that droplet deposition is promoted by the swirl. We believe this is why the twisted tape increases critical power.

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In order to provide a technical basis for preventing the blockage of heterogeneous slurry pipelines, the unsteady characteristics of slurry transport were studied. Our experiments were carried out using a test pipeline of about 130m long and 50mm in diameter. The flow rate, the solid concentration and the pressures were measured in the pipeline, in terms of responses to a stepwise charge of solid particles. It became clear how behavior of slurry changed in the pipeline if it changed with the feed rate of solid particles and how the phenomenon of the pipe blockage happened. Various information and data were obtained from these experiments, which will be useful in planning and in operating heterogeneous slurry pipelines.

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A measurement system using Doppler method of ultrasound pulses has been developed in order to clarify multi-dimensional flow characteristics of bubbly flows. The measurement system can measure an instantaneous velocity profile of mixture. Since the statistical process of the measured velocity profiles gives information of velocity profiles of both gas and liquid phases, a void fraction profile, turbulence intensity of liquid phase for bubbly flow in a channel, a liquid velocity profile around a bubble and so on. In this paper, the measurement system is discussed and typical results are introduced.

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