2014 Fiscal Year Annual Research Report
バブルダイナミクスに及ぼす表面性状効果を利用する最適沸騰面に関する研究
| Project/Area Number |
26889044
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| Research Institution | Kyushu University |
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Principal Investigator |
SHEN Biao 九州大学, カーボンニュートラル・エネルギー国際研究所, 学術研究員 (80730811)
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| Project Period (FY) |
2014-08-29 – 2016-03-31
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| Keywords | boiling heat transfer / wettability / superhydrophilicity / superhydrophobicity / bubble dynamics / dissolved air / Marangoni convection / subcooled boiling |
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| Outline of Annual Research Achievements |
This project aims to develop an enhanced boiling surface based on clear understanding of the mechanics of bubble formation and growth under the influence of surface wettability and physical structures. Towards this objective, a superbiphilic surface has been fabricated. A copper substrate was first coated with a superhydrophilic TiO2 layer (with contact angle nearing 0°, via continuous UV irradiation). Then, superhydrophobic patterns (with contact angle>150°), made by drop coating of mixed solution of halloysite nanotubes modified by P(FA-C8-co-DOPAm), was deposited onto the TiO2 surface to provide sites for controlled bubble generation. High speed visualization revealed fundamentally different bubble behaviors under subcooled conditions on such a surface with varying degrees of degassing: (i) the presence of dissolved air in the water contributes to frequent bubble growth and separation from the surface even below the nominal saturation temperature; (ii) under more thorough degassing, bubbles continue to be attached to the surface without departure. The results suggest that dissolved air facilitates bubble growth, of which significant heat transfer enhancement ensues as a result.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We have achieved most of the research goals for FY2014. Specifically, a superbiphilic surface with alternating superhydrophilic (contact angle close to 0°) and superhydrophobic (contact angle>150°) patterns was successfully made, which shows decent durability for boiling applications. In addition, we have carried out a detailed visualization study of bubble behavior on such a surface using a high speed camera. The results demonstrate the interesting role that dissolved air plays in bubble nucleation and growth on mixed wettability surfaces. Based on the experimental observation, numerical simulation of the evolution of an air-vapor mixture bubble is under development, which will provide basis for realizing the research target set for FY2015 as regards surface design optimization for boiling applications.
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| Strategy for Future Research Activity |
In FY2015, a non-contact Mach-Zehnder interferometric measurement of the Marangoni flow surrounding growing bubbles on a superbiphilic surface will be carried out, which promises critical insights regarding the various subprocesses involved in boiling heat transfer. As a result, a refined model of bubble dynamics will be established to provide reliable parameters for an optimized design of a supernucleating surface.
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Research Products
(4 results)
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[Journal Article] Bubble activation from a hydrophobic spot at “negative“ surface superheats in subcooled boiling2015
Author(s)
Shen, B., Suroto, B.J., Hirabayashi, S., Yamada, M., Hidaka, S., Kohno, M., Takahashi, K. and Takata, Y.
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Journal Title
Applied Thermal Engineering
Volume: 88
Pages: 230
DOI
Peer Reviewed / Int'l Joint Research
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[Presentation] Formation of air-rich bubbles on a superbiphilic surface in subcooled boiling2015
Author(s)
Shen, B., Yamada, M., Orejon, D., Suroto, B.J., Hidata, S., Kohno, M., Takahashi, K., Takata, Y.
Organizer
9th International Conference on Boiling and Condensation Heat Transfer
Place of Presentation
Boulder, CO., USA
Year and Date
2015-04-26
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