Impact dynamics and maximum spreading of water droplets on cold surfaces with different wettabilities

The effect of surface wettability on the dynamic behaviors and maximum spreading of water droplets onto supercooled surfaces has been investigated experimentally at Weber numbers ranging from 77 to 198 and for a total of fourteen surfaces at temperatures ranging from −35.3 to −9.7 °C. These surfaces cover a wide range of wettabilities with static contact angles ranging from 60.7° to 138.7°. Compared to the surface temperature, surface wettability plays a more critical role in terms of maximum spreading factor (βmax) and maximum spreading time (tmax). The results also show that the dynamic contact angle at the maximum spreading mainly depends on the surface wettability and barely varies with surface temperature. In addition, the maximum spreading factor and the maximum spreading time both increase with decreasing the static contact angle, while they are almost independent of the surface temperature, suggesting the potential applicability of models developed at room temperature to cold surfaces. Based on the energy balance method, this study proposes an improved model for maximum spreading factor by replacing the conventional correlation of maximum spreading time, tmax=83D0V0, with a more accurate one, tmax=(βmax−1)D0V0 to modify the viscous dissipation. This improved model demonstrates good agreement with experimental values and a better prediction performance compared to other models in the literature, with a mean error of 2.2%.