| WU Weimin,ZHENG Jiayi,WANG Fang.Numerical Study of Enhanced Droplet Merging and Bouncing by Groove Structure[J],53(2):193-200 |
| Numerical Study of Enhanced Droplet Merging and Bouncing by Groove Structure |
| Received:November 02, 2022 Revised:April 13, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.02.019 |
| KeyWord:fluted structure superhydrophobic surfaces droplet merging droplet bounce enhancement finite element method simulation |
| Author | Institution |
| WU Weimin |
MIIT Key Laboratory of Thermal Control of Electronic Equipment, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing , China |
| ZHENG Jiayi |
MIIT Key Laboratory of Thermal Control of Electronic Equipment, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing , China |
| WANG Fang |
MIIT Key Laboratory of Thermal Control of Electronic Equipment, School of Energy and Power Engineering, Nanjing University of Science and Technology, Nanjing , China |
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| Abstract: |
| In recent years, the phenomenon of droplet agglomeration and bouncing, which is a characteristic of superhydrophobic surfaces, has received close attention from scholars. The results of the study have important industrial applications in enhancing heat transfer, anti-icing and frost protection and surface self-cleaning. The construction of various groove structures on superhydrophobic surfaces is highly effective in enhancing droplet merging and bouncing and improving surface energy conversion efficiency.In order to improve the bouncing speed and energy conversion rate of droplet self-bounce, the effect of groove structure on droplet merging bounce phenomenon was studied. The effects of droplet size on the droplet momentum, total droplet kinetic energy, dimensionless bounce velocity, bounce velocity and surface energy conversion rate in different directions of droplet merging, and bouncing on V-shaped and rectangular troughs were investigated by numerical simulations with deionized water as the working medium for the same trough width W and the ratio of trough depth to trough width H/W=1, 1.5 and 2. The simulations were based on a two-dimensional model of two-phase laminar flow with a pair of spherical droplets of equal diameter bouncing together on a superhydrophobic surface with a fluted structure. The phase field method was used to calculate the problem. The simulation results showed that the combined bouncing between droplets inside and outside the groove consisted of four processes:droplet contact, liquid bridge generation, three-phase line contraction and droplet bouncing off the surface. When the ratio of groove width to groove depth was the same, the droplet bounce speed and surface energy conversion rate increased and then decreased with the droplet radius. At this point, the combined bounce velocity of the rectangular trough droplets was 0.318 m/s and the dimensionless bounce velocity was 0.562. The combined bounce velocity of the V-shaped trough droplets was 0.355 m/s and the dimensionless bounce velocity was 0.627. Both rectangular and V-shaped grooves broke the capillary-inertial scalar law for super-sparse horizontal surfaces. And the optimal droplet combined bounce radius was 0.25 mm when the width to height ratio was 1.5. For rectangular grooves, when the ratio of groove width to groove depth was 1 and 2, the optimal droplet merging bounce radius was 0.2 mm. At this point the droplet bounces was 0.329 m/s and 0.301 m/s respectively, with dimensionless velocities of 0.52 and 0.47. The V-shaped groove was better than the rectangular groove in enhancing droplet bounce. For rectangular grooves and V-shaped grooves, the surface energy conversion rate reached a maximum of 27.87% and 30.66% for both with a width to height ratio of 1.5. The notch structure enhanced the droplet merging and bouncing with optimal bounce radius and notch aspect ratio. The droplet bounce speed and surface energy conversion rate increased and then decreased with the radius ratio, reaching a peak at a radius ratio of 1. V-shaped grooves improved droplet bounce efficiency by approximately 12% compared with rectangular grooves. In conclusion, the reaction force of the merged droplet hitting the side wall of the V-shaped groove makes the droplet side flap be inhibited by the side wall surface earlier than that of the rectangular groove and backflow occurs, thus enhancing its energy conversion efficiency and reducing the oscillation loss and viscous dissipation of the droplet. |
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