1989 Fiscal Year Final Research Report Summary
Hydraulic Criteria of a Bubble-Pump System for Destratification
| Project/Area Number |
63850117
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| Research Category |
Grant-in-Aid for Developmental Scientific Research
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| Allocation Type | Single-year Grants |
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| Research Field |
Hydraulic engineering
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| Research Institution | University of Tokyo |
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Principal Investigator |
TAMAI Nobuyuki Univ.of Tokyo, Dept.of Civil Eng, Prof., 工学部, 教授 (90010818)
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| Co-Investigator(Kenkyū-buntansha) |
KADOYA Daiji Kawasa Heavy Indust., Steel Struc., Div. Chief, 鉄構機器事業部, 研究開発課課長
ARITA Masamitsu Tokyo Denki Univ., Dept. Construc. Eng., Assoc. Prof., 理工学部, 助教授 (90130294)
KAWAHARA Yoshihisa Univ.of Tokyo, Dept. of Civil Eng., Assist Prof., 工学部, 講師 (70143823)
ASAEDA Takashi Saitama Univ., Dept. Construc. Foundation, Assoc. Prof., 工学部, 助教授 (40134332)
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| Project Period (FY) |
1988 – 1989
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| Keywords | Destratification / Bubble-Pump System / Reservoir / Eutrophication / Pumping Efficiency / エネルギ-効率 |
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| Research Abstract |
Low concentrain of oxygen frequently appears in a deep layer of a man-made reservoir due to search vertical exchange under thermal stratification. Low oxygen water mass accelerates phosphorus in micro pores of muddy bed to resolute again and then results in entrophication of reservoir water. Feasible technical methods are sought for destratification of water body on use of a large scale air-bubble.
Shape of a large, single bubble is spherical in the upper surface and the bottom is nearly flat. The rising velocity is explained in terms of air volume released and the prediction through a potential theory agreed well with experimental results. A circulation zone generated by a structure similar to a vortex ring entrains surrounding fluid into the wake zone of a bubble and then transport it upward. Transported volume by a single bubble is observed to be about 25 times of the volume of a bubble.
In a second phase a bubble-pump system used a cylinder is analyzed. The vertical velocity in a cylinder is upward in accordance with the rise of a bubble. But after a bubble leaves the top of a cylinder, the vertical velocity reduces and turns into downward. The highest efficiency is obtained when a next bubble is released just before this change in the direction of velocity takes place. Time variation of the vertical velocity in a cylinder is theoretically estimated with good accordance with experimental results. The horizontal scale of the spreading of lifted heavier water is explained as a function of the densimetric Froude number at the outlet of a cylinder and the submergence of a cylinder. A buffl plate set above an outlet of a cylinder is effective to change the direction of a rising negative buoyant jet but has scarse effect in gaining better efficiency of the pumping rate of a deeper water body.
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