Carbon dioxide is regarded as one of the greenhouse gases. The methods of recovering, fixing and sequestering carbon dioxide are being developed in many parts of the world. Concerning the carbon dioxide recovering method, in Japan, the electric power industry initiated research on carbon dioxide recovery methods well ahead of other industries. Tokyo Electric Power Company (TEPCO) has been tackling the environmental problems such as air pollution caused by SO_x and NO_x in view of their managerial importance. Also, we are implementing effective countermeasures for carbon dioxide mitigation. In this paper, we will introduce mainly TEPCO research on the carbon dioxide removal technology.

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CO₂sequestration in ocean posseses a characteristic of multi-phase flow where CO₂ clathrate-hydrate is formed at the interface between liquid CO₂ and seawater in high pressure condition in ocean. The present report describes following three items of multi-phase flow in CO₂ sequestration in ocean which are dissolution of liquid CO₂ droplets at intermediate sea depth and formation of liquid CO₂ pool at a seabed deeper than 3000m. The first one is an experiment of liquid CO₂ dynamic behavior affected by hydrate-clathrate, which are CO₂ injection from a nozzle, formation of CO₂ pool and propagation of hydrate-clathrate film induced by the nucleation. The second one is measurement of liquid CO₂ droplet dissolution rate in the pressurized water flow with clathrate on the surface, which is important in dissolution of liquid CO₂ droplets at intermediate sea depth. Effects of flow velocity, temperature and pressure on the dissolution rate were clarified. Further, the dissolution behavior of liquid CO₂ droplets dispersed in the sea water has been numerically simulated, where the effects of released droplet size and ambient CO₂ concentration have large effect on the dissolution behavior due to the CO₂ clathrate-hydrate. The last one is an experiment of dissolution of liquid CO₂ pool which simulates liquid CO₂ stored at a seabed and dissolves into an undercurrent flow. The measured surface concentration was applied to the estimation of time-scale for dissolution, where the mass transfer coefficient was obtained from the actual conditions of deep ocean data.

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The increasing of the CO₂ concentration in the atmosphere might be induced by consumption of fossil fuel and destruction of tropical forests. In the research field of global warming, clarification of the global circulation mechanism of CO₂ is one of the important targets. Now, many kinds of option to reduce global warming have been proposed and researched. CO₂ sequestration into the ocean is one of hopeful methods from a view point of feasibility. CO₂ transfer mechanism between the atmosphere and the ocean in the North Pacific Ocean and the CO₂ circulation in the ocean are discussed, which has been surveyed in NOPACCSproject of MITI. Still more, the new method which can dissolve CO₂ in shallow sea-water and transport the solution to the deep sea-water is discussed. The method is an utilization of a gas lift effect by CO₂ bubbles in the pipeline inverse J shape.

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Theoretical studies of processes for dissolution of CO₂at 500-2000m depth in the ocean have revealed a potential of this method as a way to reduce the CO₂emissions to the atmosphere, and thus reduce the impacts of such emissions on the global climate and environment. However, complexities associated with the mass transfer of liquid CO₂from droplets via hydrate films to dissolution in seawater, as well as the dynamics of buoyant dropletplumes, influenced also by the increase in seawater density due to dissolution of CO₂, precludes firm conclusions to be drawn about the vertical distribution of CO₂in the water column following injection. Numerical model results indicate that the fate of disposed CO₂is strongly dependent on droplet size. If small droplets can be created and maintained, open ocean outlets may become a practical disposal technique. However, the pH of water peeling off from the plume is so low that marine life outside the plume would be adversely affected.

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For next-generation nuclear reactors, hybrid safety systems which consist of active and passive safety systems have been planned. Steam generators using U bend pipelines with upper and lower horizontal pipes will be used as one of the passive safety systems. Liquid is generated due to condensation of steam in pipelines if these pipelines are used as condensers. It is supposed that flow patterns in the horizontal parts of these pipelines are different from those in horizontal pipes without U bend. An experimental study was carried out using a U bend pipeline with upper and lower horizontal pipe which has a lower tank and a water supply section at midway of lower horizontal pipe. Flow patterns were observed at four parts, and their maps were compared with those in the previous studies.

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The flow patterns of the air-water two-phase flow in horizontal and horizontal-downward declined pipes were studied experimentally in order to obtain basic information on the flow characteristics of gas-liquid two-phase flows in hilly-terrain pipelines. It is one of the special characteristics of the flow pattern in these hilly-terrain pipelines that the developing and/or unsteady flow patterns occupy almost whole pipes. Flow pattern maps were presented through a new classification and definition. The concept of “basic and auxiliary flow patterns” was introduced. The flow state was expressed by the combination of a basic flow pattern and some auxiliary flow patterns. The flow behavior greatly changes along hilly-terrain pipelines. It is impossible to predict the flow patterns with existing flow pattern maps for single pipes.

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On dropwise condensation, it has been well known that behavior of condensate droplets on a condensing surface have an effect on the heat transfer considerably. Therefore, it is very important to make clear what the shape of a stationary single droplet on a horizontal flat plate (Teflon plate). We will discuss the shape of a single droplet using CCD camera, and compare the experimental results with its calculated results. From these results, we can easily estimate the shape of a single droplet corresponding with its weight.

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This paper provides an experimental understanding of liquid film characteristics to examine flooding mechanisms in the countercurrent annular two-phase flow in a vertical tube. The experiments are performed in an air-water system with a large diameter tube, 50mm or 100mm in diameter. Time variations of liquid film thicknesses at four different elevations along the tube are measured, and their power spectra are used to examine interfacial wave characteristics. At the top region of the tube periodic wave with a frequency of about 45Hz is observed at a low gas flow rate condition. Increasing gas flow rate, the periodic wave disappears and the continuous spectra indicating a chaotic aspect is observed in the power spectrum profile. At the bottom of the tube the spectra indicate the continuous feature even at a low gas flow rate condition. As the gas flow rate increases, a power of the spectra increases due to large amplitude waves produced by interaction between the gas and liquid flows. The frequency of maximum power spectra shifts slightly to the low frequency region, but the profile does not change significantly before flooding. At the just before flooding, however, the profile become more flat in the high frequency region. The probability density of interfacial velocity increases in the large velocity region at just before flooding than at low gas flow rate condition. As the gas flow rate increases, the wave number of large amplitude tends to be small.

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技術革新を担う重要な研究課題の一つとして新素材開発とその応用面開発が挙げられる。近年材料科学の分野では、素形材料 (あるいは構造材料) に対して機能材料、さらには、知能材料の概念が広く認識されるに至り、その開発研究が進められてきている。流体材料に関してみても、水や空気、油といったいわば素形材料に相当するものに対して、電磁場の作用により機能性を発現させることのできる流体として、磁性流体やER流体の研究が進められてきている。さらに、より高度な機能性を付与したり、多機能化を進めることにより流体の知的の制御を行おうとする研究も開始されている。この意味からも混相流体は、重要な役割を演じるものと期待されている。
本稿では、機能性流体の代表例として磁性流体を取り上げ、その基礎から応用にわたる研究の道筋を4回シリーズで解説することにする。第1回目は、混相流体的な側面から磁性流体をとらえて磁性微粒子を含む流体の特性について、第2回目では磁性流体の力学の基礎を、第3回目では磁場の作用下での各種の流れの特性について、第4回目には磁性流体の応用面について解説することにする。

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In under-developing countries as China, coal is mainly used as an energy source, considerable amount of which is for daily living use. However it is very difficult to equip a desulphurizer to each personal furnace. The air pollution problem there is now serious and is becoming an environmental problem on earth. If clean coal can be obtained at a coal field, the air pollution problem can be cleared. Recently, column floatation has been paid much attention as a prospective technique to remove minerals including inorganic sulphur from coal at a coal field. In this article, the prospective aspects of the column floatation as a coal cleaning process at a coal field is described putting special emphasis on the possible application in under developing countries. The floatation mechanisms are also illustrated on the basis of recent data of column floatation. It was shown that the coal recovery and ash rejection strongly depend on hydrophobicity of coal particles and that a surrounding flow of each bubble plays a roll in catching particles regardless of its hydrophobicity for the case of high gas feed.

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