Superhydrophobicity in the fight against ice

The build-up of ice on the wings and propellers of an aircraft, drone or wind turbine results in reduced lift or increased consumption. Ice formation may be actively and passively combated. It’s recently been shown that making the surface superhydrophobic in certain weather conditions can counteract this ice formation.

Ice build-up is a problem in many sectors and has consequences for the operation of all kinds of systems in various sectors, ranging from aviation to wind energy. Superhydrophobic surfaces could offer a solution here. A recent experimental study of the wettability effects on the dynamic process of ice accretion at the surface of a drone propeller showed that making that surface superhydrophobic under certain weather conditions can prevent this ice formation.

The figure below shows the effect that a superhydrophobic surface versus a hydrophilic surface has on the ice formation on the drone's propeller.  With a hydrophobic surface there is less ice accretion. This is due to the fact that the drops partially bounce off. The ice that still forms shakes off the propeller more quickly than on a hydrophilic surface. 

Top: hydrophilic surface, bottom: hydrophobic surface

Superhydrophobic surfaces can be obtained in various ways, including through coatings or femtosecond laser texturing.

Type of surface and conditions

An important factor in the approach to ice formation using hydrophobic surfaces is to take into account the type of surface and the conditions. Superhydrophobicity is obtained by making small surface structures. If there has been a period of high humidity and falling temperature beforehand, there may have been a deposit of frost that negates this superhydrophobicity. This is shown in the figure below with the bouncing drop. Once the surface is covered with ice, the hydrophobic character is lost. Falling drops can therefore freeze. In addition, this surface structure increases the surface area, which means that the ice can adhere more strongly and is therefore more difficult to remove mechanically. One possible course of action is to remove the ice by heating. A larger surface could lead to greater heat dissipation.  

A superhydrophobic surface (a) with (c) and without (b) frost under the impact of a drop. As long as the surface is free of ice, the drop jumps off, but if there is frost, the drop freezes.  

Ice adhesion increases linearly with surface area/number of microstructures

Sirris is also investigating how surfaces can be protected against icing, and how to monitor icing if it can cause undesirable and dangerous situations in certain applications. As part of the COOCK project Fighting Icing and the H2020 Newskin project, we’re monitoring the state of the art and carrying out comparative tests ourselves with a new ice spray test set-up that’s capable of testing large surfaces with different types of ice formation. This new ice-testing facility was built in our large climate chamber at our site in Antwerp.

Ice spray array and ice test in Sirris’ climate chamber

Want to know more about the possibilities with superhydrophobic surfaces? Then please contact us!

This blog has been written within the framework of the Surfacescript and Fighting Icing COOCK projects.

Sources

An experimental study of surface wettability effects on dynamic ice accretion process over an UAS propeller model, Y. Liu et al, Aerospace Science and Technology 73, p. 164 (2018)

Frost formation and ice adhesion on superhydrophobic surfaces, K.K. Varanasi et al, Applied Phys. Letters 97, 234102 (2010)