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Journal Articles

Pulsed pressure induced cavitation erosion in mercury narrow channel under flowing conditions

Naoe, Takashi; Kogawa, Hiroyuki; Tanaka, Nobuatsu*; Futakawa, Masatoshi

Advanced Experimental Mechanics, 4, p.17 - 21, 2019/08

We have introduced the following two techniques to mitigate the pressure wave-induced cavitation damage in the mercury target. One is the gas microbubble injection into the flowing mercury, and the other is the double-walled structure with a narrow gap channel at the proton beam entrance portion of the mercury vessel. The latter is expected to mitigate the cavitation damage due to the high-speed liquid flow ($$sim$$ 4 m/s) and the narrow gap boundary (2 mm). To quantitatively investigate the effect of double-walled structure on cavitation damage, cavitation damage tests were conducted by parametrically changing mercury flow velocity and gap width of the channel wall. The results showed that the damage evaluated as a surface roughness was reduced by increasing the flow velocity. By contrast, the effect of gap width on cavitation damage was hardly observed under flowing conditions.

Journal Articles

Evaluation growing and collapsing behaviors of cavitation bubbles under flowing condition

Kawamura, Shunsuke; Naoe, Takashi; Ikeda, Tsubasa*; Tanaka, Nobuatsu*; Futakawa, Masatoshi

Advanced Experimental Mechanics, 4, p.33 - 37, 2019/08

A mercury enclosure vessel made of stainless steel is used as a spallation target in the pulsed spallation neutron source at J-PARC. It is severely damaged by the cavitation induced with pressure waves in association with the pulsed proton beam injection. A double-walled structure with a narrow mercury channel was adopted in the front end of the target vessel to reduce the cavitation damage. It has been experimentally demonstrated that the cavitation damage could be mitigated in the narrow channel but its mechanism has been unclarified yet. In this study, we investigated the cavitation from growing to collapsing through visualizing the spark-induced cavitation bubbles under flow field using a high-speed video camera. Furthermore, we measured the wall vibration due to the cavitation bubble collapse with changing flow velocity parametrically. It was found that the microjet collided perpendicular to the wall in the stagnant flow condition while it collided with an inclined angle from the perpendicular direction, suggesting that the collision pressure on the wall was reduced by flowing.

Journal Articles

A Large-scale numerical simulation of bubbly and liquid film flows in narrow fuel channels

Takase, Kazuyuki; Yoshida, Hiroyuki; Ose, Yasuo*; Akimoto, Hajime

Proceedings of 2005 ASME International Mechanical Engineering Congress and Exposition (CD-ROM), 8 Pages, 2005/11

no abstracts in English

Journal Articles

Numerical analysis of a water-vapor two-phase film flow in a narrow coolant channel with a three-dimensional rectangular rib

Takase, Kazuyuki; Yoshida, Hiroyuki; Ose, Yasuo*; Tamai, Hidesada

JSME International Journal, Series B, 47(2), p.323 - 331, 2004/05

no abstracts in English

Journal Articles

Heat transfer characteristics in narrow vertical rectangular channels heated from both sides

Sudo, Yukio; *; Kaminaga, Masanori

JSME Int. J., Ser. II, 33(4), p.743 - 748, 1990/00

no abstracts in English

Oral presentation

Current status of pulsed spallation neutron source at J-PARC

Takada, Hiroshi

no journal, , 

At the Japan Proton Accelerator Research Complex, a pulsed spallation neutron source provides neutrons with high-intensity and narrow pulse width to promote a variety field of materials science by injecting high power proton beam of 3-GeV, 1 MW at repetition rate of 25 Hz. The core components of the spallation neutron source are a mercury target, liquid hydrogen moderators and a reflector with beryllium and iron. Their sizes and arrangement were optimized to get superior neutronics performance for 100% para-hydrogen as the moderator material. Since the lifetime of the mercury target vessel made from SS316L steel is determined by the pitting damage induced by the pressure wave generated at the pulsed proton beam injection, mitigating the pitting damage is the most critical issue to achieve 1 MW operation for long time. So far, gas micro-bubbles injection technique and a target front structure to get faster mercury flow in narrow channel were employed for mitigating the pitting damage in the mercury target vessel. A pitting damage of 25 $$mu$$m was observed on the target front after 670 MWh operation with an average power of 406 kW. In 2018, it is planned to observe the target front of the newly manufactured target after operation with a power of 300 to 500 kW. Further developments of the narrow channel structure of the target front will be carried out. It is also planned to make post irradiation examination to study radiation damage of the target vessel in other facility of Japan Atomic Energy Agency.

Oral presentation

Visualization of cavitation growing and collapsing behaviors in narrow channel

Kawamura, Shunsuke; Naoe, Takashi; Ikeda, Tsubasa; Tanaka, Nobuatsu*; Futakawa, Masatoshi

no journal, , 

A mercury enclosure vessel made of stainless steel is used as a spallation target in the pulsed spallation neutron source at J-PARC. It is severely damaged by the cavitation induced with pressure waves in association with the pulsed proton beam injection. A double-walled structure with a narrow mercury channel was adopted in the front end of the target vessel to reduce the cavitation damage. It has been experimentally demonstrated that the cavitation damage could be mitigated in the narrow channel but its mechanism has been unclarified yet. In this study, we investigated the cavitation from growing to collapsing through visualizing the spark-induced cavitation bubbles under flow field using a high-speed video camera. Furthermore, we measured the wall vibration due to the cavitation bubble collapse with changing flow velocity parametrically. It was found that the microjet collided perpendicular to the wall in the stagnant flow condition while it collided with an inclined angle from the perpendicular direction, suggesting that the collision pressure on the wall was reduced by flowing.

Oral presentation

Flow effect on cavitation bubble behaviors in narrow channel

Kawamura, Shunsuke; Naoe, Takashi; Tanaka, Nobuatsu*; Futakawa, Masatoshi

no journal, , 

In the mercury target for the pulsed spallation neutron source at J-PARC, cavitation damage at the beam window of the mercury target vessel is a key factor to decide lifetime of target because the damage degrade the vessel structural integrity. A double-walled structure with a narrow channel was adopted to the vessel for expecting to reduce cavitation damage. In this study, the cavitation bubble behaviors of the growth and collapse under water flow field were investigated to determine the effective factor for mitigating cavitation damage in narrow channel. We measured the equivalent diameter and wall vibration due to the cavitation bubble collapse with parametrically changing flow velocity. It was found that the maximum equivalent diameter of the cavitation bubble and the response vibrational acceleration of the wall are decreased with the increasing velocity. As the results, it was found that cavitation bubble collapse pressure was affected by flowing condition in the narrow channel.

Oral presentation

Effect of wall boundary on growing and collapsing behaviors of cavitation bubble

Kawamura, Shunsuke; Naoe, Takashi; Tanaka, Nobuatsu*; Futakawa, Masatoshi

no journal, , 

A mercury target for spallation neutron source has been in operation at the J-PARC. When the high-intense proton beams hits the mercury to produce spallation neutrons, pressure waves are generated due to the abrupt heat deposition of mercury. Mercury enclosure vessel made of stainless steel with a thin wall thickness of 3 mm is severely damaged by pressure wave-induced cavitation erosion. Recently a double-walled structure with narrow gap channel at the front part of the vessel has been developed to mitigate the cavitation damage. In this study, we observed experimentally the growth and collapse behavior of cavitation bubbles in the narrow channel by using a technique of spark discharge in water and a high-speed video camera. Furthermore, the effects of flow velocity and gap width on collapsing pressure were investigated with focusing on the ratio of the projection radius to the gap width. The relationship between the narrow gap and the collapsing pressure will be discussed.

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