Delayed Frost Growth on Nanoporous Microstructured Surfaces Utilizing Jumping and Sweeping Condensates

Abstract

Self-propelled jumping of condensate droplets (dew) enables their easy and efficient removal from surfaces and is essential for enhancing the condensation heat transfer coefficient and for delaying the frost growth rate on supercooled surfaces. Here, we report the droplet-jumping phenomenon using nanoporous vertically aligned carbon nanotube (VA-CNT) microstructures grown on smooth silicon substrates and coated with poly-(1H, 1H, 2H, 2H-perfluorodecylacrylate) (pPFDA). We also report dropletsweeping phenomenon on horizontally mounted surfaces, concluding that the frost surface coverage area and the frost growth rates observed with the droplet-sweeping phenomenon are much lower than those that are observed with the droplet-jumping phenomenon alone. We also investigate the fundamentals of droplet-jumping and the frost growth phenomena using line-shaped, hollow-cylindrical, and cylindrical microstructures, comparing the frost surface coverage area and the ice-bridging times during condensation-frosting, prolonged condensation-frosting, and direct-frosting. We find that the closely spaced thin line-shaped microstructures and hollow-cylindrical microstructures are optimal for frost coverage reduction because of their ability to exhibit droplet-jumping and droplet-sweeping phenomena. We observe that adding nonuniform roughness on top of the microstructures leads to jumping-associated droplet-sweeping on supercooled surfaces. Here, we report the evaporation of an already frozen droplet because of freezing of a supercooled condensate droplet in its close vicinity, enabling the Cassie−Baxter state frost growth and enhancing defrosting efficiency. Finally, we discuss the dynamic defrosting behavior of the pPFDA-coated VA-CNT microstructures, concluding that the small gaps (spacings) between the microstructures not only enable dewetting transitions of droplets but also promote the Cassie−Baxter state frost formation.

Tailoring silicon for dew water harvesting panels

“…According to prior studies, the coexistence of jumping and sweeping behaviors requires rigorous conditions (Qu et al, 2015;Chu et al, 2016), which often occurs on the surfaces with complicated nanostructures (Wen et al, 2017;Mohammadian et al, 2020;Peng et al, 2019;Mukherjee et al, 2019). In jumping, the motion direction of resulting droplet is perpendicular to the substrate (Yan et al, 2019), while the sweeping motion, which requires an in-plane velocity, will be easily prevented in this case (Qu et al, 2015).…”

Droplet Dynamics and Freezing Delay on Nanoporous Microstructured Surfaces at Condensing Environment

“…Other ceramic membranes grafted and coated by perfluorosilane showed promising results [56][57][58][59]. In condensate condition, self-cleaning of superhydrophobic surfaces by self-propelled droplet jumping and sweeping have also been demonstrated by several studies [30,32,[60][61][62]. Oberli et al studied condensation of water onto physically-decorated substrates and its associated impact on the freezing of macroscopic droplets on them [39].…”

“…More recently, superhydrophobic surfaces have also shown some promise in delay of icing with potential applications in power lines, wind turbines, photovoltaic panels, and other infrastructures [18][19][20][21][22][23]. Some other anti-icing performances exhibited by the superhydrophobic surfaces include lowering ice adhesion strength, repelling freezing rain droplets, and delaying frost formation [13,[24][25][26][27][28][29][30]. However, under harsh environmental conditions like low temperatures and high humidity, these surfaces lose their superhydrophobicity and fail to exhibit those anti-icing features [31][32][33][34].…”

“…Therefore, most of the superhydrophobic surfaces lose their water repelling and anti-icing features in low temperature and high humidity conditions, due to nucleation and growth of the condensate droplets. This sometimes leads to potential enhanced formation of frost depending on the temperature [30,40,41]. The subsequent freezing of the condensate droplets mechanically anchors them to surface roughness and leads to enhanced ice/frost build up on them, with increased adhesion strength [42,43].…”

Active prevention of snow accumulation on cameras of autonomous vehicles

“…Therefore, sticking efficiency of the snow grains decreases with wind velocity. Previously, passive methods of mitigation of ice and snow have been extensively investigated by developing surface coatings that are mostly focused on reducing ice adhesion strength or delaying freezing [42][43][44]. However, these coatings lack durability and/or scalability and have mostly focused on mitigation of icing.…”