Experimental investigation of surface wettability induced runback water flow and heat transfer behavior

Aircraft icing is a serious threat to flight safety, therefore, active anti-icing systems are widely utilized in the aviation industry. In order to reduce the energy consumption of anti-icing systems, passive anti-icing methods combined with superhydrophobic surfaces are of interest. However, the passive protection of superhydrophobic surfaces is not as effective as expected when applied to aircraft anti-icing, which involves high speed and high humidity condition. The flow and heat transfer of runback water is an issue of fundamental importance for understanding of the aircraft anti-icing processes. In order to understand the mechanism of passive anti-icing on superhydrophobic surface, this study experimentally investigated the runback water flow and heat transfer behavior on airfoil with different surface wettabilities in a straight-flow spray wind tunnel. It was found that the runback water film was more likely to break up and form the rivulets when the wettability is more hydrophobic, with the breakup location closing to the leading edge, and the wetted surface area became smaller, therefore reducing ice accumulation. The water droplets on superhydrophobic surface shed away easily to make the surface have no runback water, which enables low energy consumption for the dry anti-icing method. The coupled analysis of the flow and heat transfer behavior indicated that surface wettability altered the runback water patterns, leading to changes in the convective heat transfer coefficient and heat transfer area, ultimately affecting the overall heat transfer process. In addition, the droplet erosion resistance of superhydrophobic surfaces prepared by two methods were tested and compared in this study.