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

Self Cite

Coalescence-induced droplet jumping has great prospects in many applications. Nevertheless, the applications are vastly limited by a low jumping velocity. Conventional methods to enhance the droplet coalescence jumping velocity are enabled by protruding structures with superhydrophobic surfaces. However, the jumping velocity improvement is limited by the height of protruding structures. Here, we present rationally designed limitation structures with superhydrophobic surfaces to achieve a dimensionless jumping velocity, V j * ≈ 0.64. The mechanism of enhancing the jumping velocity is demonstrated through the study of numerical simulations and geometric parameters of limitation structures, providing guidelines for optimized structures. Experimental and numerical results indicate that the mechanism consists of the combined action of the velocity vectors' redirection and the Laplace pressure difference within deformed droplets trapped in limitation structures. On the basis of previous research on the mechanisms of protruding structures and our study, we successfully exploited those mechanisms to further improve the jumping velocity by combining the limitation structure with the protruding structure. Experimentally, we attained a dimensionless jumping velocity of V j * ≈ 0.74 with an energy conversion efficiency of η ≈ 48%, breaking the jumping velocity limit. This work not only demonstrates a new mechanism for achieving a high jumping velocity and energy conversion efficiency but also sheds lights on the effect of limitation structures on coalescence hydrodynamics and elucidates a method to further enhance the jumping velocity based on protruding structures.

Section: Experimental Methodsmentioning

confidence: 72%

“…The model has been verified in our previous studies. 18,43 Velocity vectors, the pressure distribution, the instantaneous upward velocity V up , and the instantaneous upward acceleration A up were studied through numerical simulations.…”

Section: ■ Experimental Methodsmentioning

confidence: 99%

Laplace Pressure Difference Enhances Droplet Coalescence Jumping on Superhydrophobic Structures

Liu

Zhao

et al. 2022

Self Cite

“…Previous research studies have shown that the radius ratio of two droplets has a significant effect on the efficiency of droplet coalescence-induced jumping, and the efficiency of droplet jumping is highest when the radius ratio is close to 1. ,,, Therefore, the ability to produce droplets of uniform size by condensation on the sample surface is crucial to improve the efficiency of droplet jumping. In addition, the relative position between the droplet and the surface structure also affects the efficiency of droplet jumping.…”

Section: Resultsmentioning

confidence: 99%

Coalescence-Induced Droplet Jumping on Honeycomb Bionic Superhydrophobic Surfaces

Gao

Yang

et al. 2022

Condensation-induced jumping of droplets on superhydrophobic surfaces has received extensive attention because of its great potential for applications in areas such as condensation enhancement and self-cleaning. However, the jumping efficiency of droplets on flat superhydrophobic surfaces is very low, and there is no reliable means of achieving efficient droplet jumping on large scales, which greatly limits its application. To this end, we developed a class of honeycomb bionic superhydrophobic surfaces (HBSS) that enable reliable and efficient droplet jumping on a large scale for the first time and performed experimental and simulation studies on droplet condensation and jumping on this kind of surface. Condensation experiments show that condensate droplets on HBSS can be effectively positioned under the influence of gravity and the uniformity of the droplet diameter is ensured, laying the foundation for achieving efficient jumping. The shape and geometric parameters of HBSS have a significant impact on the droplet jumping efficiency, and the maximum dimensionless jumping velocity of droplet jumping was experimentally measured to be 0.747, corresponding to an efficiency of about 45.25%. Combining with the results of simulation calculations, we found that the surface structure of HBSS can promote more of the excess surface energy to net upward kinetic energy along an extremely efficient and simple pathway (direct conversion), thus achieving an energy conversion efficiency of over 45%.

“…Recently, Liu et al reported tunable droplet jumping with energy efficiency up to 46%, but it requires the complex fabrication of three-dimensional sub-millimeter features of a U groove on a semicircular plate. 32 Until now, tuning the jumping direction of the coalescence-induced jumping drop with high energy conversion efficiency remains challenging.…”

Section: ■ Introductionmentioning

confidence: 99%

“…Lately, meticulously designed surface structures, such as L-shaped macrostructure, asymmetric grooves, and inclined strings, have been applied in adjusting the jumping direction with energy conversion efficiency of around 30%. Recently, Liu et al reported tunable droplet jumping with energy efficiency up to 46%, but it requires the complex fabrication of three-dimensional sub-millimeter features of a U groove on a semicircular plate . Until now, tuning the jumping direction of the coalescence-induced jumping drop with high energy conversion efficiency remains challenging.…”

Section: Introductionmentioning

confidence: 99%

High-Efficiency Directional Ejection of Coalesced Drops on a Circular Groove

Liu

et al. 2022

Coalescence-induced drop jumping has received significant attention in the past decade. However, its application remains challenging as a result of the low energy conversion efficiency and uncontrollable drop jumping direction. In this work, we report the high-efficiency coalescenceinduced drop jumping with tunable jumping direction via rationally designed millimeter-sized circular grooves. By increasing the surface-droplet impact site area and restricting the oscillatory deformation, the energy conversion efficiency of the jumping droplet reaches 43.5%, 600% as high as the conventional superhydrophobic surfaces. The droplet jumping direction can be tuned from 90°to 60°by varying the principal curvature of the circular groove, while the energy conversion efficiency remains unchanged. We show through theoretical analysis and numerical simulations that the directional jumping mainly originates from reallocation of droplet momentum enabled by the asymmetric liquid bridge impact. Our study demonstrates a simple yet effective method for fast, efficient, and directional droplet removal, which warrants promising applications in jumping droplet condensation, water harvesting, anti-icing, and self-cleaning.