Visualization of Kinetic Parameters of a Droplet Nucleation Boiling on Smooth and Micro-Pillar Surfaces with Inclined Angles

Yi-Nan Zhang, Guo-Qing Huang, Lu-Ming Zhao and Hong-Xia Chen ()
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Yi-Nan Zhang: The Energy Power and Mechanical Engineering Department, North China Electric Power University, Beijing 102206, China
Guo-Qing Huang: The Energy Power and Mechanical Engineering Department, North China Electric Power University, Beijing 102206, China
Lu-Ming Zhao: The Energy Power and Mechanical Engineering Department, North China Electric Power University, Beijing 102206, China
Hong-Xia Chen: The Energy Power and Mechanical Engineering Department, North China Electric Power University, Beijing 102206, China

Energies, 2025, vol. 18, issue 15, 1-21

Abstract: The evaporation dynamics of droplets on smooth and inclined micro-pillar surfaces were experimentally investigated. The surface temperature was increased from 50 °C to 120 °C, with the inclination angles being 0°, 30°, 45°, and 60° respectively. The dynamic parameters, including contact area, nucleation density, bubble stable diameter, and droplet asymmetry, were recorded using two high-speed video cameras, and the corresponding evaporation performance was analyzed. Experimental results showed that the inclination angle had a significant influence on the evaporation of micro-pillar surfaces than smooth surfaces as well as a positive correlation between the enhancement performance of the micro-pillars and increasing inclination angles. This angular dependence arises from surface inclination-induced tail elongation and the corresponding asymmetry of droplets. With definition of the one-dimensional asymmetry factor ( ε ) and volume asymmetry factor ( γ ), it was proven that although the asymmetric thickness of the droplets reduces the nucleation density and bubble stable diameter, the droplet asymmetry significantly increased the heat exchange area, resulting in a 37% improvement in the evaporation rate of micro-pillar surfaces and about a 15% increase in its enhancement performance to smooth surfaces when the inclination angle increased from 0°to 60°. These results indicate that asymmetry causes changes in heat transfer conditions, specifically, a significant increase in the wetted area and deformation of the liquid film, which are the direct enhancement mechanisms of inclined micro-pillar surfaces.

Keywords: droplet; evaporation; micro-pillar surfaces; visualization; asymmetry factors; enhancement mechanism (search for similar items in EconPapers)
JEL-codes: Q Q0 Q4 Q40 Q41 Q42 Q43 Q47 Q48 Q49 (search for similar items in EconPapers)
Date: 2025
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