Visualization experiments of convective boiling in transparent single micro conduits with the same hydraulic diameter but different cross sections are carried out with simultaneous measurement of local heat transfer coefficients and pressure losses. Two different cross sections with the same similar hydraulic diameters are applied: A circular microtube of 210μm in diameter and a square microchannel of 214μm × 214μm cross section. ITO/Ag thin film of 100 nm is sputtered on the outer surface of the conduits for the direct joule heating. The convective boiling shows some periodic variation of different flow patterns in both square and circular conduits. These flow patterns include bubbly, plug, slug, annular and capillary flows. The capillary flow pattern is the independent liquid droplets moving in the flow direction and very rarely observed in conventional tubes. The reason of such variation of flow patterns is that confined spaces limit the bubble growth in radial direction. So the nucleation bubble grows in both upstream and downstream and makes the flow pattern varies radically. The square microchannel conduit has more simple flow pattern variation, more nucleation bubbles and larger local heat transfer coefficients at lower vapor quality. It is due to that corners of the square microchannel act as helps nucleation cavities. Corners also promotes the formation of liquid film and the contact line between liquid and wall, which can stabilize the flow field. Local heat transfer coefficients decrease with increasing local vapor qualities. Local heat transfer coefficients increase with increasing boiling number but have their maximum value when boiling number reaches critical value. Such peculiar heat transfer characteristics can also be explained by the visualization results.
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ASME 3rd International Conference on Microchannels and Minichannels
June 13–15, 2005
Toronto, Ontario, Canada
Conference Sponsors:
- Nanotechnology Institute
ISBN:
0-7918-4185-5
PROCEEDINGS PAPER
Visualization of Convective Boiling Heat Transfer in Single Micro-Conduits With Different Shapes of Cross Sections
Tzu-Hsiang Yen,
Tzu-Hsiang Yen
National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
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Masahiro Shoji,
Masahiro Shoji
National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
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Fumio Takemura,
Fumio Takemura
National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
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Yuji Suzuki,
Yuji Suzuki
University of Tokyo, Tokyo, Japan
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Nobuhide Kasagi
Nobuhide Kasagi
University of Tokyo, Tokyo, Japan
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Tzu-Hsiang Yen
National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Masahiro Shoji
National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Fumio Takemura
National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan
Yuji Suzuki
University of Tokyo, Tokyo, Japan
Nobuhide Kasagi
University of Tokyo, Tokyo, Japan
Paper No:
ICMM2005-75228, pp. 131-137; 7 pages
Published Online:
November 11, 2008
Citation
Yen, T, Shoji, M, Takemura, F, Suzuki, Y, & Kasagi, N. "Visualization of Convective Boiling Heat Transfer in Single Micro-Conduits With Different Shapes of Cross Sections." Proceedings of the ASME 3rd International Conference on Microchannels and Minichannels. ASME 3rd International Conference on Microchannels and Minichannels, Part B cont’d. Toronto, Ontario, Canada. June 13–15, 2005. pp. 131-137. ASME. https://doi.org/10.1115/ICMM2005-75228
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