1995 Fiscal Year Final Research Report Summary
Study on Cavitation Generation and Acoustic Transient in Liquid Nitrogen
| Project/Area Number |
06650185
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| Research Category |
Grant-in-Aid for General Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Research Field |
Fluid engineering
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| Research Institution | Hokkaido University of Education |
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Principal Investigator |
TOMITA Yukio Faculty of Education, Hokkaido University of Education ; Professor, 教育学部函館校, 教授 (00006199)
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| Co-Investigator(Kenkyū-buntansha) |
TSUBOTA Makoto Institute of Fluid Science, Tohoku Univercity ; Associate Professor, 流体科学研究所, 助教授 (10197759)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Cavitation / Bubble / Liquid Nitrogen / Acoustic Transient / Shock Wave / Laser / Plasma / Phase Ghange |
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| Research Abstract |
A single bubble was produced by focusing a pulsed ruby laser into subcooled liquid nitrogen at various applied pressures. Highly spherical cavitation bubbles were successfully generated by using an annular laser beam adjusted through a double-stage lens array. When the laser energy exceeds a threshold energy, the optical breakdown takes place, following by a series of high-speed phenomena such as the plasma formation, acoustic transients including shock wave emission and vapor bubble generation. The dynamics of these phenomena, especially the initial behavior and subsequent motion of the bubbles, are investigated by means of high speed photography. It is found that very weak pressure dependency is found for the threshold conditions of bubble generation. On the other hands, it is also a bubble is generated strongly reflecting from the plasma formation which occurs along with the optical axis. Therefore initial bubble shape is nonspherical, but its volume varies similarly with time for different input energies. The liquid inertia is dominant during the bubble growth, whereas the thermal effect becomes significant in the collapse process, yielding the retardation of the bubble motion. The latter feature is primarily associated with the saturated vapor pressure inside a bubble and influenced by other thermodynamic effects which is confirmed by investigating the period of the bubble motion. A considerable instability takes place over the bubble surface immediately after the bubble rebound, mainly due to the Taylor instability coupled with thermal instability.
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