Condensation droplet sieve

Abstract

Large droplets emerging during dropwise condensation impair surface properties such as anti-fogging/frosting ability and heat transfer efficiency. How to spontaneously detach massive randomly distributed droplets with controlled sizes has remained a challenge. Herein, we present a solution called condensation droplet sieve, through fabricating microscale thin-walled lattice structures coated with a superhydrophobic layer. Growing droplets were observed to jump off this surface once becoming slightly larger than the lattices. The maximum radius and residual volume of droplets were strictly confined to 16 μm and 3.2 nl/mm2 respectively. We reveal that this droplet radius cut off is attributed to the large tolerance of coalescence mismatch for jumping and effective isolation of droplets between neighboring lattices. Our work brings forth a strategy for the design and fabrication of high-performance anti-dew materials.

Wetting state transitions of individual condensed droplets on pillared textured surfaces

“…On a hydrophilic surface, droplet condensation routinely forms a film (filmwise condensation), [18][19][20] whereas, on a micro/nanotextured superhydrophobic surface, the condensate forms discrete droplets (dropwise condensation). 16,[18][19][20][21] Because of the extremely low affinity with water, when small droplets of the order of micrometers merge on the superhydrophobic surface, jumping could be triggered and the droplets can quickly detach from the surface to increase the condensation heat transfer coefficient, resulting in an improvement in heat transfer performance of 5-7 times as compared to its filmwise counterpart. [18][19][20][21][22][23] In this regard, superhydrophobic surfaces seem to be desirable materials to increase heat transfer efficiency.…”

“…16,[18][19][20][21] Because of the extremely low affinity with water, when small droplets of the order of micrometers merge on the superhydrophobic surface, jumping could be triggered and the droplets can quickly detach from the surface to increase the condensation heat transfer coefficient, resulting in an improvement in heat transfer performance of 5-7 times as compared to its filmwise counterpart. [18][19][20][21][22][23] In this regard, superhydrophobic surfaces seem to be desirable materials to increase heat transfer efficiency. After Boreyko et al first discovered the spontaneous dewetting of merged droplets on two-tier micro/ nanotextured superhydrophobic surfaces, 24 many features of the superhydrophobic materials for condensation have been developed.…”

“…30,31 Despite the broad context of the optimization of superhydrophobic surfaces for dropwise condensation, there are challenges to be overcome. The nucleation energy barrier on a superhydrophobic surface is significantly higher than that on a hydrophilic surface, 18,21,32 which is unfavorable for capturing moisture, especially in the early stages of nucleation. Moreover, typical hydrophobic coatings on superhydrophobic materials can degrade over time, the contact angle could degrade in the environment and the suspended Cassie wetting state could change to the unwanted sticky Wenzel wetting state, 18,33,34 which highly diminishes the droplet removal efficiency.…”

Advances in Microscale Droplet Generation and Manipulation

“…Superhydrophobic flat surfaces have been explored widely for many applications related to drag reduction, self-cleaning, water harvesting, heat-transfer enhancement, and anti-icing. − Similarly, the superhydrophobic mesh with submillimeter pores can be used for applications related to separating oil and water, harvesting moisture, agricultural spraying, repelling rain, , and capturing bubbles . The mesh surface has an inherent structuring which, in combination with the nanostructured surface, leads to several interesting phenomena, such as leaky behavior, where fluid can easily pass through the holes of the sieve.…”

Dropwise Condensate Comb for Enhanced Heat Transfer

“…Condensation heat transfer is common in everyday life and industrial contexts − and has been implemented in a broad range of applications, , including power generation, fog harvesting, water desalination, , thermal management, and air-conditioning. , It is necessary to enhance condensation heat transfer efficiency in order to save resources and capital expenditure in various industrial fields, as well as alleviate water and energy shortage. The major advantage of dropwise condensation (when it is compared with filmwise condensation where a continuous film of condensate is formed on the cold surface) is that it promotes droplet departure by self-propelling, , jumping off, and gravity-induced shedding, − in addition to negating the insulating effect of the condensate layer between vapor and the solid surface. − In comparison with filmwise condensation, the condensation heat transfer coefficient could be enhanced up to an order of magnitude by dropwise condensation. , Therefore, dropwise condensation is beneficial for enhancing condensation heat transfer by physically removing the condensate rapidly away from the vapor phase. − …”