Void fraction behavior in the vicinity of the surface in microbubble emission boiling
In subcooled boiling under certain conditions of subcooling and velocity of the liquid, the heat flux does not decrease with increasing of the surface temperature in transition boiling regime, but increases steeply. In this phenomenon a lot of minute bubbles are emitted from the surface accompanying extraordinary loud sound. Therefore, the authors call this phenomenon microbubble emission boiling, abbreviated as MEB. The high heat flux in MEB far exceeding CHF should be considered a result of violent growing and collapsing behavior of coalescent bubbles in that region, which strongly introduces subcooled liquid to the heated surface. This bubble behavior generates a high pressure in the vicinity of the surface. In this study, a measurement of the pressure fluctuation in the liquid near the surface was performed synchronously with a recording of the bubble motion by use of a void probe set close to the surface. In high liquid subcooling conditions (S-MEB I), the void probe signal in the vicinity of the surface shows regular cyclic behavior synchronous with the pressure waveform. The peak frequency of the power spectrum of the void signal increases with increasing of the heat flux as well as that of the pressure fluctuation. Under a medium subcooling condition (S-MEB II), there appear three different modes in the void signal in sequence. The one looks random and does not synchronize with the pressure waveform. Another is very systematic and similar to the signal in high liquid subcooling. The other shows a constant void fraction of a high value, indicating the surface to be covered with a thick vapor blanket. The time fraction of the second mode increases gradually with increasing the heat flux. The peak frequency of the power spectrum of the void signal under this condition does not change much with the heat flux.
- Research Organization:
- Tohoku Univ., Aobaku, Sendai (JP)
- OSTI ID:
- 20026809
- Resource Relation:
- Conference: 5th ASME/JSME Thermal Engineering Joint Conference, San Diego, CA (US), 03/14/1999--03/19/1999; Other Information: 1 CD-ROM. Operating system required: Windows i386(tm), i486(tm), Pentium (R) or Pentium Pro, MS Windows 3.1, 95, or NT 3.51, 8 MB RAM, MacIntosh and Power MacIntosh with a 68020 or greater processor, System software version 7.1, 3.5 MB RAM (5 MB for PowerMac) 6 MB available hard-disk space, Unix; PBD: 1999; Related Information: In: Proceedings of the 5th ASME/JSME thermal engineering joint conference, [3600] pages.
- Country of Publication:
- United States
- Language:
- English
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