Kyo Ohgi’s research while affiliated with Yamaguchi University and other places

The ability of a gas dissolving device to improve the DO condition of water is evaluated using the oxygen transfer rate. Usually the oxygen transfer rate is measured in mixing-type treatment, where air bubbles are released in the water tank. This method, however, has some disadvantages, such as that it cannot be used for compressed-type gas dissolving devices and that it requires the evaluation of the overall gas transfer coefficient. The present study proposes a convenient method of evaluating the oxygen transfer rate which is applicable to gas dissolving devices of both compressed and pressure-free types, applicable to water with an arbitrary DO concentration, and does not require the evaluation of the overall gas transfer coefficient. Evaluation of DO improvement is done using the equivalent DO increment, devised to eliminate the influence of the DO concentration of the water before treatment. The value of the oxygen transfer rate is represented as the value at a temperature of 20 degrees Celsius. Laboratory experiments to check the method have shown that the proposed method of measurement is valid.

Experimental results are given for the vertical motion of water in the water chambers for wave energy converter aligned along the wave propagation direction in order to avoid the impulsive wave forces. This paper mainly focuses on the property of the amplitude of the vertical motion of the water surface in the chambers. The amplification has been investigated by dimensionless parameters of wave period to resonance period ratio of the U-shaped oscillation, T/Tr, chamber size to wave length ratio, l/L, water depth to wave length ratio, h/L, amplitude of up-down motion of water particles to draft of the front wall ratio, ζ/D. It has been shown that l/L should be less than 0.1 and as T/Tr approaches unity the up-down of the water in the chambers is amplified. Also, the structure of the walls which form the water chambers has been examined roughly. It is deduced that the chambers set on both sides of the hull of a single-point moored floating vessel is preferable to those set along a fixed structure such as breakwaters. Copyright © 2013 by the International Society of Offshore and Polar Engineers (ISOPE).

湖沼や海域の水質改善，特にDO改善を目的として著者らが開発中の液膜式気体溶解技術の概要を述べ，そのDO改善性能に関する室内実験の結果を検討する．本方式は，処理対象水を気泡液膜の構成要素にして液相中の気体濃度の勾配を大きくすることにより気体溶解を効率的に行う．また管内の浅い部分で曝気してエアリフト効果を利用して深部の水のDO改善を行うため稼働に必要なエネルギーが小さい．室内実験の結果から装置内にハニカムを装着することの影響を評価した．また，酸素溶解能力およびエネルギー効率の最適条件について調べ，管内径に対して最適の空気流量があること，h型管の水平部の水面からの高さを抑える方が有利であること，エネルギー効率は空気流量が小さいほど有利であることなどを明らかにした．