| Project/Area Number |
06650254
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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 |
Thermal engineering
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| Research Institution | Kyushu University |
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Principal Investigator |
OHTA Haruhiko Kyushu University, Department of Engineering, Assistant Professor, 工学部, 助教授 (50150503)
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| Co-Investigator(Kenkyū-buntansha) |
YOSHIDA Suguru Kyushu University, Department of Engineering, Professor, 工学部, 教授 (30037741)
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| Project Period (FY) |
1994 – 1995
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| Project Status |
Completed (Fiscal Year 1995)
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| Budget Amount *help |
¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1995: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1994: ¥1,600,000 (Direct Cost: ¥1,600,000)
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| Keywords | Microgravity / Boiling / Nucleate boiling / Pool boiling / Microlayr / プール沸騰 / 圧力損失 |
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| Research Abstract |
Experiments in nucleate pool boiling under microgravity were conducted by using ethanol. The transparent heating surface with sensors for the measurement of local surface temperature and liquid film thickness underneath a growing bubble was introduced. The surface is made of sapphire glass, and the structure of back-side heating by transparent ITO film heater realizes the observation of liquid-vapor behaviors at the base of attached bubble and simultaneously the accurate evaluation of local surface heat flux. A new method was developed for the measurement of liquid film thickness by using a set of thin electrodes coated directly on the heating surface. The sensor of 4mm square and 0.1 mum thickness was introduced to measure instantaneously the microlayr thickness of 1 to 10 mum order. Measurements were performed under pressure 0.01 to 0.02 MPa, liquid subcooling 0 to 27 K,heat flux up to 90000 W/m^2.
The following are clarified. i) In microgravity at low heat flux region, there exists two opposite trends of heat transfer enhancement and deterioration depending on whether dry patches emerge or not in the microlayr. ii) In the discrete bubble region, the local heat transfer coefficients underneath a large bubble are significantly influenced by the gravity level, while the coefficient averaged over the entire heating surface is quite insensitive. iii) At high heat flux, underneath a large coalesced bubble in microgravity, small single bubbles emerge from the heating surface and collapse at the surface of macrolayr. The heat transfer is dominated mainly by the nucleate boiling in the macrolayr, and it remains almost constant despite the change of gravity level.
The results give the interpretation of existing experimental results in the past three decades, in which the average heat transfer coefficients in microgravity increase or decrease depending on the experimental manner and conditions adopted, and assumes the values not far different from the terrestrial ones.
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