Macrotextures-induced jumping relay of condensate droplets

Abstract

Self-propelled droplet jumping plays a crucial role in numerous applications such as condensation heat transfer, self-cleaning, and water harvesting. Compared to individual droplet jumping, the coalescence-induced droplet jumping in a domino manner has attracted more attention due to its potential for the high performance of droplet mobility and heat transfer. However, there is an apparent gap in the current literature regarding the demonstration of the advantage of this preferred droplet transport in a well-controlled way. In this study, we report the attainment of droplet jumping relay by designing a nanosheet-covered superhydrophobic surface with V-shaped macrogrooves (Groove-SHS). We find that the macrogroove arrays can significantly modify the droplet dynamics in the presence of a non-condensable gas (NCG) by coupling rapid droplet growth and efficient droplet removal by jumping relay. The condensate droplets formed through the NCG diffusion layer on top of the cones and between the grooves serve as more efficient conduits for heat transfer. The droplets with higher mobility formed on the bottom of the grooves can undergo a series of coalescence which results in the preferred droplet jumping relay. Such a droplet jumping relay can induce a considerable vibration for triggering the removal of droplets on top of the cones. The condensation performance of the Groove-SHS is increased by 60% compared to that of the flat superhydrophobic surface due to the synergistic effect of rapid droplet growth and efficient droplet removal facilitated by the integration of the droplet jumping relay. The mechanisms revealed in this work pave the way for dropwise condensation enhancement.

Tunable Wetting Patterns on Superhydrophilic/Superhydrophobic Hybrid Surfaces for Enhanced Dew‐Harvesting Efficacy

“…On the SHPo background, spherical water droplets are randomly distributed on the surface (Figure b), demonstrating a dropwise condensation behavior. When adjacent condensate droplets coalesce, the coalesced droplet can depart from the surface, either by way of random sweeping of droplets off the surface or via coalescence‐induced jumping if the released surface energy overcomes the adhesion of the droplet to the surface; alternatively, coalescence may result in the formation of a big droplet that stays immobile on the surface (Figure c). Since there is a surface energy gradient between the SHPo background and the SHPi triangular patterns, immobile droplets on the SHPo region can be readily absorbed by the nearby SHPi patterns (Figure d), facilitating the continuous growth of water film on the triangular patterns.…”

Advances in Dropwise Condensation: Dancing Droplets

“…In addition to the condensation enhancement on the superhydrophobic surfaces as mentioned above, several other potential strategies and surfaces have recently been proposed to enhance condensation by manipulating droplet behaviors [5,27,28,30,64,68,[100][101][102][103][104][105]. For example, a hybrid structured surface with wettability contrast was proposed to spatially control nucleation, where droplets preferentially form on the hydrophilic region [27].…”

“…Some emerging strategies and surface design provide the potential to achieve condensation enhancement by using macrotextures or low-cost commercial materials [68,100,103,104,[115][116][117]. The plain hybrid surfaces, consisting of plain hydrophilic and hydrophobic regions, were proposed to achieve dropwise-filmwise condensation for reducing the droplet departure size [ On such a hybrid surface (Figure 10a), the growing droplets in the hydrophobic regions are removed when they grow large enough to contact with the liquid film in the hydrophilic regions, resulting in a smaller removal size than that of gravitydriven departure.…”

“…(c) A hydrophilic copper tube surface with interval fluorocarbon-coated hydrophobic bumps [103]. (d) A superhydrophobic surface covered with macrogroove arrays [104].…”

“…experimentally demonstrated on the vertical hydrophilic copper tube with hydrophobic fluorocarbon-coated bumps, which is better than both the conventional filmwise and dropwise condensation while avoiding the durability issues of ultrathin hydrophobic coatings. Recently, a structured surface with macrogroove arrays was proposed to improve droplet jumping dynamics in the presence of NCG by coupling rapid droplet growth and efficient droplet jumping relay (Figure 10d) [104].The droplets formed on top of the cones and the bottom of the grooves play different roles during condensation process. Specifically, the cones can promote droplet formation and growth by breaking through the limitation of NCG layer.…”