1998 Fiscal Year Final Research Report Summary
Multi-Dimensional Flow Characteristics of Bubbly Flows.
| Project/Area Number |
08458119
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
エネルギー学一般・原子力学
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| Research Institution | TOKYO INSTITUTE OF TECHNOLOGY |
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Principal Investigator |
ARITOMI Masanori Tokyo Institute of Technology, Research Laboratory for Nuclear Reactors, 原子炉工学研究所, 教授 (60101002)
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| Co-Investigator(Kenkyū-buntansha) |
TAKAHASHI Minoru Tokyo Institute of Technology, Research Laboratory for Nuclear Reactors, 原子炉工学研究所, 助教授 (90171529)
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| Project Period (FY) |
1996 – 1998
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| Keywords | Multiphase flow / Babbly flow / Ultrasonic pulse / Doxpler effect / Velocity profile / Void fraction profile / Turbulence intersity / Flow arround bubbles |
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| Research Abstract |
(1) A measurement system using Doppler effect of ultrasonic pulse and data processing has been developed. The proposed measurement system can measure instantaneous mixture velocity profiles of bubbly flows in the channel. By treating statistically the measured instantaneous mixture velocity profiles, the velocity profiles of both phases, the void fraction profile and turbulence intensity of the liquid phase in the channel and the liquid velocity field surrounding a bubble can be obtained.
(2) Flow structure in fully developed bubbly flows is governed by the flow profile of a liquid continuous phase which is flatter than that of liquid single phase flows. Since bubbles go up due to the difference between buoyancy and interfacial shear stress, the relative velocity between both phases are almost constant in the channel.
(3) Void fractions in the channel are almost constant except for those near the wall.
(4) The two-phase multiplier of turbulence in bubbly flows is defined as a ratio of tur
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bulence intensity in bubbly flows to that in water single phase flows. The exist of bubbles has both effects of turbulence promotion and dispassion. For void fraction less than 0.3%, the dispassion effect is superior than the promotion effect. In the case of void fraction larger than 0.5%, the promotion effects becomes greater with an increase in void fraction.
(5) The liquid flow field surrounding bubbles can be classified into three regions ; a boundary layer, a transition region and a main flow region. The boundary layer is strongly dependent on the bubble rising motion and the flow is not influenced with changes in air and water flow rates. The transition regions influenced by both effect of the bubble motion and the main liquid flow. Velocity fluctuation is high in this region because the mixing of these two effects exists. The main flow region is located far from bubbles and the bubble motion does not affect the flow.
(6) The boundary layer thickness is dependent strongly on the bubble diameter and slightly on the distance between bubbles and its empirical correlation is proposed. The distance from the bubble surface to this region changes according to both bubble Reynolds number and the average void fraction and its empirical correlation is also proposed. Less
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