Behavior of Thin Liquid Film underneath a Coalesced Bubble in Nucleate Boiling at High Heat Flux
| Project/Area Number |
09650244
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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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, Dept.Energy and Mechanical Engineering, 工学部, 助教授 (50150503)
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| Project Period (FY) |
1997 – 1998
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| Project Status |
Completed (Fiscal Year 1998)
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| Budget Amount *help |
¥2,500,000 (Direct Cost: ¥2,500,000)
Fiscal Year 1998: ¥500,000 (Direct Cost: ¥500,000)
Fiscal Year 1997: ¥2,000,000 (Direct Cost: ¥2,000,000)
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| Keywords | Nucleate boiling / Pool boiling / Microlayer / Coalesced bubble / Evaporation / Liquid film thickness / 液膜厚さ / 沸騰 / バーンアウト / 限界熱流束 |
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| Research Abstract |
The relation between the liquid-vapor behavior and heat transfer is investigated in detail for the flattened bubble generated between narrow gaps. In the experiments, a transparent heating surface was introduced to make the heating, the observation of liquid-vapor behavior from underneath and the acquisition of heat transfer data simultaneously possible. The test section of the narrow gap was installed to realize the upward flow in the gravity field and was connected to test loop to prescribe the inlet condition without ambiguity. The experiments was conducted by the use of distilled water at pressure : P= 0.1 -0.1 8MPa, temperature : t_p= 100ﾟC, inlet subcooling : DELTAT_<sub, in>= 5 -8K, averaged value of heat flux supplied q_o=*3.2 chi 10^5W/m^2, inlet liquid velocity : u_<in>= 0.06m/s. Gravity level was changed to vary the bubble rising velocity, In the narrow gap, extension of dry patches and rivulets of residual microlayers were recognized underneath a flattened bubble. The perio
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ds covered by the flattened bubble and quenched by the bulk liquid flow were iterated on the heating surface. in the case of slow bubble rising velocity, the surface temperature is maintained at high value owing to the reduced frequency of surface quenching. And the heat flux is enhanced due to the increased surface superheat, while only the deterioration is observed in the values of heat transfer coefficient. In the extremely narrow gap, the flow of flattened bubbles becomes unstable and the flattened bubbles with complicated profiles moves vigorously towards the various direction on the heating surface. As a result, the frequency in the iteration of dry patch extension and of re-wetting is markedly decreased and the heat transfer deterioration is prevented to some extent. In the present research, it was clarified in nucleate boiling the existence of two conflicting trends of heat transfer enhancement by the decreased thickness of microlayer due to evaporation and of heat transfer deterioration by the extending dry patches in the microlayer. Less
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Report
(3 results)
Research Products
(1 results)
