Enhancement and Guidance of Coalescence-Induced Jumping of Droplets on Superhydrophobic Surfaces with a U-Groove

Coalescence-induced droplet jumping has received considerable attention owing to its potential to enhance performance in various applications. However, the energy conversion efficiency of droplet coalescence jumping is very low and the jumping direction is uncontrollable, which vastly limits the application of droplet coalescence jumping. In this work, we used superhydrophobic surfaces with a U-groove to experimentally achieve a high dimensionless jumping velocity V-j* approximate to 0.70, with an energy conversion efficiency eta approximate to 43%, about a 900% increase in energy conversion efficiency compared to droplet coalescence jumping on flat superhydrophobic surfaces. Numerical simulation and experimental data indicated that a higher jumping velocity arises from the redirection of in-plane velocity vectors to out-of-plane velocity vectors, which is a joint effect resulting from the redirection of velocity vectors in the coalescence direction and the redirection of velocity vectors of the liquid bridge by limiting maximum deformation of the liquid bridge. Furthermore, the jumping direction of merged droplets could be easily controlled ranging from 17 to 90 degrees by adjusting the opening direction of the U-groove, with a jumping velocity V-j* >= 0.70. When the opening direction is 60 degrees, the jumping direction shows a deviation as low as 17 degrees from the horizontal surface with a jumping velocity V-j* approximate to 0.73 and corresponding energy conversion efficiency 7 approximate to 46%. This work not only improves jumping velocity and energy conversion efficiency but also demonstrates the effect of the U-groove on coalescence dynamics and demonstrates a method to further control the droplet jumping direction for enhanced performance in applications.

Automated summary

This study experimentally achieved a high dimensionless jumping velocity and energy conversion efficiency on superhydrophobic surfaces with a U-groove, demonstrating a significant improvement compared to conventional droplet coalescence jumping on flat surfaces. The redirection of velocity vectors and control of jumping direction through the U-groove show potential for enhanced performance in applications.