Enhanced Pool Boiling Heat Transfer Using Layer-by-layer Assembly of Nanoparticulate Thin Film
Date Issued
2011
Date
2011
Author(s)
Chen, Dong-Fu
Abstract
The purpose of this research is to enhance the boiling heat transfer capacity in a pool boiling system by changing surface wettability using layer-by-layer (LbL) assembly method, which was applied to a copper surface. To observe the effect of the wettability, the present study measured the contact angle of water and 99.5% ethanol on the plain surface.
After coating process, the contact angle of water varied from 43° to 134°. The contact angle of ethanol is 14° on the uncoated surface and 45° on the hydrophobic, respectively. On the hydrophilic surface, however, the contact angle is below 10°. In contrast with the uncoated surface, the ethanol spread and then evaporated fast on the hydrophilic surface. However, it became a liquid droplet on the hydrophobic surface.
In the pool boiling experiments using water and ethanol, for the hydrophilic surface, it was found that the critical heat flux would be enhanced, and the heat transfer coefficient would be promoted on the hydrophobic surface. Moreover, hydrophobic surfaces became vapor-blanketed at 50 kW/m2 using water as working fluid. It indicated that the hydrophobic surface would decrease the heat transfer coefficient at low heat flux. The heat transfer characteristics during the boiling process of ethanol on the uncoated surface and on the hydrophilic surface were similar. For a high wettable liquid, hydrophilic surface would not affect the boiling heat transfer. The results in the present work suggested that using hydrophobic surface for a heat transfer enhancement.
Subjects
Heat transfer enhancement
Pool boiling
Thin-film coating
Type
thesis
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