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Journal Articles

Lifetime estimation of microbubble in mercury

Naoe, Takashi; Hasegawa, Shoichi; Bucheeri, A.; Futakawa, Masatoshi

Journal of Nuclear Science and Technology, 45(12), p.1233 - 1236, 2008/12

 Times Cited Count:4 Percentile:31.93(Nuclear Science & Technology)

Cavitation damage is a critical issue in high power mercury targets for pulsed spallation neutron sources. Cavitation is induced by pressure wave which is caused by rapid thermal expansion of mercury. Microbubble injection into the mercury target has studied to mitigate the cavitation damage. Bubble condition: distribution and size, will affect the mitigation effect. It is important to estimate bubble lifetime to determine the bubble distribution and injection region because the microbubbles are disappeared by dissolution and diffusion. In this study, since mercury is an opaque liquid, a shrinking behavior of helium microbubbles in contact with an acrylic wall were observed and their lifetime was measured. The actual lifetime of microbubble suspended in the liquid was estimated from the observed bubbles. The lifetime of microbubble in mercury is longer than that in water.

Journal Articles

Microbubble formation at a nozzle in liquid mercury

Bucheeri, A.; Kogawa, Hiroyuki; Naoe, Takashi; Futakawa, Masatoshi; Haga, Katsuhiro; Maekawa, Katsuhiro*

Journal of Nuclear Science and Technology, 45(6), p.525 - 531, 2008/06

 Times Cited Count:2 Percentile:18.72(Nuclear Science & Technology)

A mercury target for pulsed neutron sources is being developed in JAEA. Cavitation will be induced by pressure waves which are caused by high intense proton beam injection into the target. Microbubbles with 50 to 200 $$mu$$m in diameter injected in mercury are plausibly effective to mitigate cavitation. The mitigation is dependent on the conditions of bubble size and population. It is important to understand bubble formation behavior in mercury to develop microbubble injection method. CFD simulations were carried out to investigate the bubble formation behavior in mercury. Bubbles in stagnant mercury were visualized with X-ray to observe the formation behavior of bubbles at a micro-gas-nozzle and compared with the simulation results. It was found that high surface tension makes the bubble to grow around the outer surface of the nozzle in stagnant and makes it larger until its effect becomes small in the flow. The bubble diameter in stagnant increases with increasing the contact angle.

Journal Articles

Wettability effect on bubble formation at orifice type nozzle

Bucheeri, A.; Kogawa, Hiroyuki; Naoe, Takashi; Futakawa, Masatoshi; Maekawa, Katsuhiro*

Jikken Rikigaku, 7(4), p.331 - 336, 2007/12

A mercury target system will be installed in Japan Proton Accelerator Complex (J-PARC). High intense proton beams injected into the target will induce cavitation by pressure waves. Injection of microbubbles with 50 to 200 $$mu$$m in diameter into mercury may be effective to reduce cavitation damage. Bubble generation in mercury is difficult because of its poor wettability. Therefore, we artificially change wetting condition in water to simulate bubble formation in poor wetting conditions. Experimentally, visualization of bubble growth at an orifice type nozzle of 100 $$mu$$m in diameter was done by a high-speed CCD camera. Wetting condition on the orifice surface was worsen by coating it with a water-repellent. Computational Fluid Dynamics simulation was carried out under stagnant water to understand the effect of wettability on bubble formation from the orifice nozzle. It was found that the bubble diameter depends on contact angle and it increases as wetting become worse.

Oral presentation

Numerical study on gas bubble formation in stagnant and flowing mercury

Bucheeri, A.; Kogawa, Hiroyuki; Naoe, Takashi; Futakawa, Masatoshi; Maekawa, Katsuhiro*

no journal, , 

A high-power liquid mercury target system for spallation neutron source is being developed in Japan Atomic Energy Agency. Cavitation will be induced by pressure waves which are caused by high intense proton beam injection into mercury. Injection of microbubbles in mercury with 50 to 200$$mu$$m in diameter may be effective to mitigate the cavitation. The effectiveness is dependent on bubble size and population. To investigate the behavior of bubble formation in mercury from a nozzle and develop microbubbles injection technique, numerical simulation on bubble injection in stagnant and flowing mercury were carried out using a Computational Fluid Dynamics (CFD) code. The simulation in stagnant showed that bubble grew around the outer wall of the nozzle. Bubble computed under flowing condition was smaller than that in stagnant due to the drag and shearing fources induced by mercury flow.

Oral presentation

A Method of fabrication meso-nozzle for bubbling

Osone, Ryuji; Bucheeri, A.; Kurishita, Hiroaki*; Kato, Masahiro*; Yamasaki, Kazuhiko*; Maekawa, Katsuhiro*; Naoe, Takashi; Futakawa, Masatoshi

no journal, , 

Liquid mercury target system for high power spallation neutron sources is being developed. When high intensity proton beams are injected into the target, pressure waves are generated by the thermal shock in mercury and pitting damage will be imposed on the target vessel. Bubble injection into mercury is effective to mitigate the pressure waves. In this work, we propose a method of fabricating meso-nozzle for bubble injection. The method is based on powder metallurgy by inserting thin glass fibers into a metal powder matrix to create a green compact, followed by sintering at a temperature between the melting points of the powder and the fiber. SUS316L and molybdenum powders were used as the nozzle matrix materials. In order to investigate optimum sintering condition, experiments were performed at different combination of pressing load and sintering temperature. We found that in molybdenum high relative density and straight hole with circlar cross section were obtained.

Oral presentation

Fabrication of bubbler nozzle for micro-bubble injection in liquid mercury

Bucheeri, A.; Kurishita, Hiroaki*; Kato, Masahiro*; Naoe, Takashi; Kogawa, Hiroyuki; Futakawa, Masatoshi; Maekawa, Katsuhiro*

no journal, , 

Mercury target system for high power spallation neutron sources is being developed. Proton beam will be injected into the target. Pressure waves will be generated and cavitation damage will be imposed on the target vessel. Injection of microbubbles may be effective to act as a cushion against pressure waves. Numerical simulations were carried out to investigate the optimum generation of microbubbles taking into account; wettability, bubbler size, gas flow rate, and liquid flowing velocity. It was found that orientation with respect to flowing liquid and bubbler geometry are essential parameters. The fabrication method uses Mo and 316L SS powders and glass fibers of 100 $$mu$$m in diameter. Sintering at a temperature between melting point causes glass to evaporate leaving a hole and densify the powder. Green compacts were prepared at various compressive loads and then subjected to sintering. The hole exhibited straightness and a circular cross-section, and was free from powder and glass.

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