1995 Fiscal Year Final Research Report Summary
Marangoni convection and single crystal growth : effect of the sign of temperature coefficient of surface tension
| Project/Area Number |
06452341
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| Research Category |
Grant-in-Aid for General Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Research Field |
化学工学一般
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
IMAISHI Nobuyuki Institute of Advanced Material Study, Professor, 機能物質科学研究所, 教授 (60034394)
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| Co-Investigator(Kenkyū-buntansha) |
AKIYAMA Yasunobu Institute of Advanced Material Study, Research Associate, 機能物質科学研究所, 助手 (10231846)
SATO Tsuneyuki Institute of Advanced Material Study, Associate Professor, 機能物質科学研究所, 助教授 (80170760)
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| Project Period (FY) |
1994 – 1995
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| Keywords | Marangoni Convection / Surface Tension / Microgravity / Potassium Hydroxide / Potassium Nitrate / Multi roll Cell |
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| Research Abstract |
For the sake of producing high quality single crystals of oxides and semi-conductors, it is necessary to understand the details of the melt convection phenomena. Among convection mechanisms, the buoyancy flow is rather well understood, but the fundamentals of the thermocapillary flow (the Marangoni convection) and the buoyancy-Marangoni mixed flow is not well understood. The Marangoni flow is also takes a very important role in liquid flows under micro-gravity conditions.
In this research, in order to get more information on the Marangoni convections, we placed experimental and numerical simulations to investigate the Marangoni and Marangoni-buoyancy mixed convections in small liquid bridges of molten sodium nitrate (NaNO) and sodium hydroxide (NaOH), whose surface tension shows a very peculiar temperature dependency. The results are summarized as followings.
1) Surface tension (sigma) of molten NaOH was measured by means of the maximum bubble pressure method in the temperature range 600-823K.It shows a maximum at T^*=725 K.Between the melting temperature (about 600K) and T^*, sigma_T (=*sigma/*T) is positive, but at higher temperatures above T^*, it becomes negative.
2) The Marangoni convection in liquid bridge of molten NaOH at temperatures below T^* shows surface movement from cold point to hotter point. The observed velocity distributions are well explained by the numerical simulations.
3) The Marangoni convection of molten NaOH above T^* flows from hot point to colder, as is commonly observed in the normal liquids.
4) The Marangoni convections at temperatures around T^* exhibit multi(3^-4) roll cell patterns.
5) The effect of buoyancy on convection is negligible if the liquid bridge is placed upright, but becomes important if the liquid bridge is placed horizontally. This was confirmed by an experiment with NaNO_3 liquid bridge and also by 3-dimensional numerical simulations.
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Research Products
(10 results)
