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Droplet impact and freezing on cold surfaces is a widely encountered multi-physical phenomenon involving droplet deformation and the liquid–solid phase change. Due to its complexity in nature, it is challenging to simulate the three-dimensional (3D) droplet impact and freezing process. Furthermore, due to the limitation of experimental techniques, it is not easy to experimentally investigate the impact of liquid droplets on ultra-cold superhydrophobic surfaces, which is crucial in some applications. Thus, in the present work, a 3D lattice Boltzmann (LB) method is developed to simulate the droplet impact and freezing on an ultra-cold superhydrophobic surface, in which an enhanced cascaded LB method is used to solve the multiphase flow field, and a multi-relaxation-time scheme is applied to solve the liquid–solid phase change model. The previous experimental results are numerically reproduced, proving that the present model can satisfactorily describe the droplet impact and solidification. The surface temperatures have no significant influence on droplet spreading. However, during the droplet retraction, a rim of ice first appears near the three-phase contact line, and then, the droplet bottom will completely solidify into ice. The occurrence of solidification at the bottom of the droplet will lead the droplet to break at a lower impact velocity, which can only be observed at a high Weber number on the room-temperature superhydrophobic surface. In addition, the effects of surface temperatures and Weber numbers on the evolution of spreading factors and space-averaged heat flux are also quantitatively analyzed in detail. [ABSTRACT FROM AUTHOR]

Aircraft icing is a fairly common phenomenon, which may occur during take-off, landing and flight of the aircraft. In order to ensure flight safety, it is necessary to carry out research on aircraft anti-icing technology. Here, we demonstrate a facile method to prepare icephobic coatings that can be applied to aircraft anti-icing systems by epoxy-silicone composite resin and polytetrafluoroethylene particles. Studies have shown that this icephobic coating not only has good superhydrophobicity, abrasion resistance and aging resistance, but also has excellent anti-icing function. Supercooled droplet impact and delayed icing test results show that the icephobic surface can completely repel supercooled (− 2 °C) water droplets at − 10 °C (rebound within ~ 12 ms), while delaying the freezing process for ~ 718 s. After 10 times of mechanical deicing, the coating still maintained a low ice adhesion strength (~ 112.4 kPa) and consistent wettability. In addition, the icing state of the developed coating was evaluated by used the icing wind tunnel to simulate the icing environment of the aircraft during natural flight, and the results showed that it can significantly reduce the thickness of ice accumulation. The above properties of this icephobic surface provide a new idea for aircraft anti-icing technology. [ABSTRACT FROM AUTHOR]

Previous studies have pointed out that adding a single protrusion on the superhydrophobic surface can effectively reduce the contact time of droplets, which is of practical importance in applications like anti-icing, self-cleaning, and anti-frost. However, the droplet impact dynamics and the mechanism for contact time reduction are still far from completely understood. Therefore, in this paper, via a three-dimensional pseudopotential lattice Boltzmann model coupled with a modified curved boundary scheme (which satisfies mass conservation), the droplet impact dynamics is simulated in a wide range of Weber numbers (0 < We ≤ 67.7), protrusion size (10 ≤ W ≤ 30), and protrusion shape (triangle, square, and circle), with particular interest in understanding their effects on the contact time. We demonstrate that the variation of contact time depends on the bouncing type as well as the retraction way. Among three possible bouncing types observed in the simulation, including non-break bouncing, two droplets bouncing, and three droplets bouncing, two droplets bouncing has less contact time and could be facilitated by increasing We and using triangle protrusion. However, with increasing of W or using square protrusion, the bouncing type may change from two droplets bouncing to three droplets bouncing, and the deformation of fragments may become definitely different, leading to a long contact time. In addition, a transition from twice-retraction to once-retraction can be obtained by increasing We or making the protrusion shape sharp. When the fragments resulting from droplet splitting only retract once on the bottom wall, the contact time can be effectively reduced. [ABSTRACT FROM AUTHOR]

In recent years, the pseudopotential multiphase lattice Boltzmann method (LBM) has been widely applied in the numerical simulations of complex multiphase flow. However, numerical stability at high Weber (We) and Reynolds (Re) numbers seriously restricts its application. In the present work, the pseudopotential multiphase LBM is developed by introducing the entropic stabilizers to the cascaded collision operator, and thus, the numerical stability is effectively enhanced. The relaxation rates for different order moments are all determined by fluid viscosities and the maximum entropy condition instead of being user-defined. Furthermore, the surface tension and contact angle can be adjusted in a wide range, which extends the application of the pseudopotential multiphase model. The accuracy and capability of the present model to simulate the complex multiphase flow are validated by reproducing the droplet impact on the flat or textured superhydrophobic surfaces. In addition, a droplet impact on the superhydrophobic surface at We = 1280 and Re = 18000 is simulated, in which the Weber and Reynolds numbers have significantly increased. This strongly demonstrates that the present model can enhance the numerical stability in the simulation of large density ratio multiphase flows at simultaneously high Weber and Reynolds numbers, which means the present model can further extend the pseudopotential multiphase LBM to more realistic scientific and technical applications. [ABSTRACT FROM AUTHOR]

Materials decorated by the hierarchical micro-nanostructures similar to lotus leaf surface topographies are firmly considered to possess the substantial anti-icing functions, showing icing-delay and low ice adhesion. Here, the aim of this work is to verify the anti-icing capacity in the actual icing environment containing supercooled airflow. This study, therefore, develops both routes to fabricate the hierarchical micro-nanostructure and single nanostructure superhydrophobic surfaces, and first evaluates their anti-icing capacity based on the routine measuring strategies in laboratory. Also, the potential application environment is modeled and used to verify their anti-icing performance for further guiding rational design of surface structures of anti-icing materials. Due to the double-scale effect, the hierarchical micro-nanostructure can induce more air pockets to produce the higher hydrophobicity and anti-icing capacity based on the big reference droplets (diameter > 2 mm) and even static water. However, the verified results in the potential application environment demonstrate that the hierarchical micro-nanostructure exhibits the inferior anti-icing performance, comparing with the single nanostructure. The icing area on the single nanostructure surface is almost half of that on the hierarchical micro-nanostructure surface, also causing a reduction of ≈26 g in icing mass. [ABSTRACT FROM AUTHOR]

Based on the high icing-delay performance and low ice adhesion strength, the anti-icing potential of superhydrophobic surfaces has been well investigated over the past years. The aim of this work was to verify the deicing capacity of superhydrophobic surfaces under the conditions of wind and thermal fields, expecting to promote its engineering applications. We took various wetting surfaces ranging from hydrophilic to superhydrophobic as research objects, and discussed the deicing properties of these sample surfaces based on the wind and thermal fields. The results indicated that under the condition of wind field, the micro-nanoscale hierarchical structured superhydrophobic surface exhibited a remarkable deicing property (no matter what the freezing temperature was), due to the time required for blowing away ice on the surface being least. However, the specific micro-nanoscale hierarchical structures on the superhydrophobic surface also induced a poorly melting ice property owing to the lower heat transfer efficiency caused by trapped air pockets. Furthermore, the superhydrophobic surface displayed a robust durability under the condition of 30 icing/deicing cycles. Therefore, we believe that the wind field deicing is an ideal choice as the assistant deicing approach considered in the practical applications of the anti-icing superhydrophobic surfaces. [ABSTRACT FROM AUTHOR]

The aim of this paper is to report a facile strategy of planting a layer of petal shaped nanostructures on the surface of array micro-patterns, and producing the excellent superhydrophobicity and anti-icing property. In this work, the superhydrophobic surfaces were prepared by modifying petal shaped nanostructures (constructed by chemical etching in alkaline solution) planted on array micro-patterns (constructed by lithography process with the electrochemical etching under the neutral solution condition) on aluminum substrate with fluoroalkylsilane (FAS-17). Meanwhile, we further studied the effects of chemical etching process parameters on morphology and superhydrophobicity, and on this basis explored the anti-icing potential under the condition of icing wind tunnel. The results indicated that the process parameters including NaOH concentration of 0.05 M, etching time of 5 min, and the subsequent boiling time of 40 min were of benefit to producing the ideal nanostructure morphology and geometric dimension, and the resultant surface displayed an excellent superhydrophobicity with the apparent contact angle of 165° and the sliding angle being almost equal to zero (cannot be measured). Furthermore, the as-superhydrophobic surface generated a tremendous anti-icing potential, greatly preventing the icing accumulation at − 10 °C under the condition of icing wind tunnel, and exhibiting a lower ice adhesion strength comparing with a market mature production of superhydrophobic coating. [ABSTRACT FROM AUTHOR]

Here we presented an ultra water-repellent surface with the ternary composite structures, expecting to provide an inspiration to the application research. Our strategy is to design macro ridge structures on the superhydrophobic surface, which is prepared by modifying the composite micro-nanoscale hierarchical structures with FAS-17. The effect of micro-nanoscale hierarchical structures on the non-wettability were firstly analyzed and examined for achieving a perfect unity of microstructures and property. On this basis, we designed the macro ridge structures and obtained the final sample surface, which could not only display a strong superhydrophobicity with the apparent contact angle reaching 161° and the contact angle hysteresis reducing to 1.5°, but also exhibit the capacity to compel the impact water droplet to bounce off within an extreme short time (5.5 ms). [ABSTRACT FROM AUTHOR]

Aircraft icing seriously threatens flight safety. The widely used electrothermal anti/de-icing technology has high energy consumption and poor performance. The bionic superhydrophobic surface has anti-icing potential, which can be combined with electric heater technology to achieve energy savings and efficiency improvement. In the previous research, we developed a superhydrophobic coating with mechanochemical robustness for aircraft anti-icing and proved its excellent anti-icing performance. This research combines this coating with the graphene electric heater to obtain a coupling system and explores its anti-icing effect under aviation conditions through the ice wind tunnel test. The results showed that the coating significantly improves the anti-icing properties, delaying the icing process for 10 s, saving the anti-icing energy consumption by 21% compared with graphene heating alone, and increasing the deicing efficiency by 250%. When the coating protection area reaches 30% chord, it can achieve a 'dry' anti-icing state, and this coupling system saves energy by 60% compared with wire heating. Furthermore, The 'honeycomb structure' coating is better in anti-icing effect, and the 'island structure' coating has stronger anti-icing stability. The hydrophobicity of the coating is less affected by the high-speed droplet impact, so it has a long life expectancy in the active anti-icing mode. This study can provide new ideas for solving the problem of aircraft icing. [Display omitted] • Micro-nano structure coating is coupled with graphene heater for ice tunnel tests. • Increasing 250% efficiency and saving 60% energy at 6 ℃ surface. • 30% of the coating area can achieve ideal 'dry' anti-icing state. • 'Honeycomb structure' better in effect and 'island structure' better in stability. • Active anti-icing mode is more conducive to maintaining a longer coating life. [ABSTRACT FROM AUTHOR]