Condensation and freezing of droplets on superhydrophobic surfaces

Superhydrophobic coatings are reported as promising candidates for anti-icing applications. Various studies have shown that as well as having ultra water repellency the surfaces have reduced ice adhesion and can delay water freezing. However, the structure or texture (roughness) of the superhydrophobic surface is subject to degradation during the thermocycling or wetting process. This degradation can impair the superhydrophobicity and the icephobicity of those coatings. In this review, a brief overview of the process of droplet freezing on superhydrophobic coatings is presented with respect to their potential in anti-icing applications. To support this discussion, new data is presented about the condensation of water onto physically decorated substrates, and the associated freezing process which impacts on the freezing of macroscopic droplets on the surface.     

Investigation on Preparation and Anti-icing Performance of Superhydrophobic Surface on Aluminum Conductor

Aluminum is widely used in transmission lines, and the accumulation of ice on aluminum conductor may inflict serious damage such as tower collapse and power failure.In this study, super-hydrophobic surface (SHS) on aluminum conductor with micro-nanostructure was fabricated using the preferential etching principle of crystal defects.The surface microstructure and wettability were investigated by scanning electron microscope and contact angle measurement, respectively.The icing progress was observed with a self-made icing experiment platform at different environment temperature.The results showed that, due to jumping and rolling down of coalesced droplets from SHS of aluminum conductor at low temperature, the formation of icing on SHS could be delayed.Dynamic icing experiment indicated that SHS on aluminum conductor could restrain the formation of icing in certain temperature range, but could not exert influence on the accumulation of icing.This study offers new insight into understanding the anti-icing performance of actual aluminum conductor.     

可控阵列微纳结构超疏水铜表面冰霜传质特性

金属表面粗糙结构及其润湿性对其露、霜、冰的相变及传质现象有重要影响.通过电火花微加工和化学氧化法,本文首先实现了铜片表面微米、纳米阵列结构的可控制备.针对条纹,方柱和四棱锥三种典型微米结构特征,对比研究了单级粗糙结构和二级复合结构超疏水表面的润湿性、结露、结霜、结冰及其融化过程.微纳复合结构可有效增强超疏水性,减少霜晶形核和生长速度,同时还能大幅度延缓结冰的时间,多次冷热循环处理后,表面仍能保持较好的防霜抗冰性能.通过经典形核理论,Brown凝并,一维传热及传质理论,综合分析了冰霜在这种表面的传质特性.     

可控阵列微纳结构超疏水铜表面冰霜传质特性

金属表面粗糙结构及其润湿性对其露、霜、冰的相变及传质现象有重要影响. 通过电火花微加工和化学氧化法,本文首先实现了铜片表面微米、纳米阵列结构的可控制备. 针对条纹,方柱和四棱锥三种典型微米结构特征,对比研究了单级粗糙结构和二级复合结构超疏水表面的润湿性、结露、结霜、结冰及其融化过程. 微纳复合结构可有效增强超疏水性,减少霜晶形核和生长速度,同时还能大幅度延缓结冰的时间,多次冷热循环处理后,表面仍能保持较好的防霜抗冰性能. 通过经典形核理论,Brown 凝并,一维传热及传质理论,综合分析了冰霜在这种表面的传质特性.     

超疏水铝导线的制备及其防覆冰性能研究

Aluminum is widely used in transmission lines,and the accumulation of ice on aluminum conductor may inflict serious damage such as tower collapse and power failure.In this study,super-hydrophobic surface (SHS) on aluminum conductor with micro-nanostructure was fabricated using the preferential etching principle of crystal defects.The surface microstructure and wettability were investigated by scanning electron microscope and contact angle measurement,respectively.The icing progress was observed with a self-made icing experiment platform at different environment temperature.The results showed that,due to jumping and rolling down of coalesced droplets from SHS of aluminum conductor at low temperature,the formation of icing on SHS could be delayed.Dynamic icing experiment indicated that SHS on aluminum conductor could restrain the formation of icing in certain temperature range,but could not exert influence on the accumulation of icing.This study offers new insight into understanding the anti-icing performance of actual aluminum conductor.     

Measurements of 220 GHz atmospheric opacity on Mt. Fuji with a radiometer/radome system

We measured atmospheric opacity at 220 GHz at the summit of Mt. Fuji (alt. 3776 m) about one year in order to explore a feasibility of submillimeter-wave astronomical observations. For this purpose, a 220 GHz radiometer system enclosed in a radome (51×51×62 cm³) has been developed. The 220 GHz opacity was lower than 0.06 for a significant fraction ( 45 %) of time from November 1994 to March 1995. Diurnal variation of the opacity at the summit of Mt. Fuji is so small that continuous observation at submillimeter-wave is possible through day and night. Yearly variation of the opacity is studied from water vapor pressure data measured at the weather station for the past 3 years. To prevent accumulation of ice and snow on the Gore-Tex membrane in the radome, the outer membrane was supplied with a thermal flux of 0.63 kW m^–2 and the adjacent metal radome surfaces were supplied with a flux of 0.9 kW m^–2. We evaluate from the 220 GHz transmission data that this heat flux is sufficient to keep the membrane on the radome free of ice and snow during 83 % of the time in 5 winter months. The summit of Mt. Fuji appears to be a promising site for submillimeter-wave observations.     

离子液体/聚偏氟乙烯纳米纤维的防结冰性能

通过静电纺丝方法制备了掺杂离子液体([BMIM][PF₆])的聚偏氟乙烯(PVDF)纳米纤维. 研究结果表明, [BMIM][PF₆]与PVDF具有相互作用, 并可促进PVDF形成β相晶体. 在溶剂挥发后, 离子液体存在于PVDF纳米纤维的表面. 纳米纤维中的离子液体含量对复合纳米纤维的表面形态和润湿性具有显著影响. 通过离子液体的引入, 可有效推迟水滴在纳米纤维表面的结冰时间, 降低水滴的结晶温度, 并且降低冰黏附强度. 研究结果显示含有10%[BMIM][PF₆]的PVDF纳米纤维疏水性最高, 并具有优异的防结冰性质.     

Silane decorated metallic nanorods for hydrophobic applications

A novel technique to modify a metallic surface for anti-icing applications is presented. An oblique angle deposition (OAD) technique has been used to fabricate metallic nanorods of Aluminum and Tungsten on a glass substrate. A conformal coating of a silane has been applied using a molecular vapor deposition technique. The resulting surface has shown a static contact angle of 134° with the water droplet. SEM, AFM and XPS have been used to study the surface modification. This is a highly promising approach for anti-icing applications due to its scalability at a very low cost.