Quantitative Study of the Relationship Between a Superhydrophobic Surface with Convex Structures and the Jumping Velocity of Coalescence-Induced Droplets

Coalescence-induced droplet jumping on superhydrophobic surfaces is valuable for engineering applications such as enhanced condensation heat transfer, self-cleaning, and anti-icing, which has attracted extensive attention. Some studies have reported that superhydrophobic surfaces with convex structures can achieve greater droplet jumping velocities, and all of these studies focus on the jumping dynamics and energy conversion. However, the relationship between the geometric parameters and the jumping velocity remains ambiguous, and quantitative conclusions about the design of surfaces with convex structures are lacking. Therefore, an improved volume-of-fluid (VOF) method is used to simulate the jumping behavior of droplets on surfaces. The repelling effect caused by the mutual contribution of the Laplace pressure and superhydrophobicity enhances droplet jumping. This changes the dynamic characteristics of the liquid bridge and reduces the contact area between the liquid and the solid. Then, orthogonal regression analysis is applied, which reveals the functional relationship between the convex structure and the jumping velocity. The height (parallel to the normal direction of the surface) of the geometric structure has the greatest influence (60.139%); whereas, the length‒height interaction (3.704%), where the length is parallel to the surface, has the least influence. This work provides the theoretical foundations and method references for the design of special surfaces, which are intended to serve as a guide for designing the optimal combination of the substrate and the different structures to enhance droplet jumping.