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Visualization of convective boiling heat transfer in single microchannels with different shaped cross-sections.

Author(s) : YEN T. H., SHOJI M., TAKEMURA F., et al.

Type of article: Article

Summary

Convective boiling in transparent single microchannels with similar hydraulic diameters but different shaped cross-sections was visualized, along with simultaneous measurement of the local heat transfer coefficient. Two types of microchannels were tested: a circular Pyrex glass microtube (210 µm inner diameter) and a square Pyrex glass microchannel (214 µm hydraulic diameter). A 100-nm-thick semi-transparent ITO/Ag thin film sputtered on the outer wall of the microchannel was used for direct joule heating of the microchannel. The flow field visualization showed semi-periodic variation in the flow patterns in both the square and circular microchannels. Such variation was because the confined space limited the bubble growth in the radial direction. In the square microchannel, both the number of nucleation bubbles and the local heat transfer coefficient increased with decreasing vapour quality. The corners acted as active nucleation cavities, leading to the higher local heat transfer coefficient. In contrast, lack of cavities in the smooth glass circular microchannel yielded a relatively smaller heat transfer coefficient at lower vapour quality. Finally, the heat transfer coefficient was higher for the square microchannel because corners in the square microchannel acted as effective active nucleation sites. [Reprinted with permission from Elsevier. Copyright, 2006].

Details

  • Original title: Visualization of convective boiling heat transfer in single microchannels with different shaped cross-sections.
  • Record ID : 2007-1015
  • Languages: English
  • Source: International Journal of Heat and Mass Transfer - vol. 49 - n. 21-22
  • Publication date: 2006/10

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