Transient Heat Transfer to Rolling or Sliding Drops on Inclined Heated Superhydrophobic Surfaces

This presentation examines the time resolved heat transfer to drops rolling or sliding along inclined, heated non-wetting surfaces. Results were experimentally obtained using IR imaging for a smooth hydrophobic surface and post as well as rib structured superhydrophobic surfaces of varying solid fraction (0.06 - 0.5). Tests were performed at varying inclination angle (10, 15, 20, and 25°), drop volume (12, 20, 30, and 40 <!--[if gte msEquation 12]>μL), and surface temperature (50, 65, and 80 °C). Rib structured superhydrophobic surfaces were explored for drops moving parallel and perpendicular to the rib structures. The findings indicate that transient heat transfer is predominantly influenced by the surface’s solid fraction and the velocity of the drops, with a secondary dependence on drop volume. Surfaces with low solid fraction show a significant reduction in initial heating rate (up to 80% reduction) to the drop, when compared with that of the smooth surface. The drop velocity depends on surface solid fraction and inclination angle, with drop volume exerting smaller influence. Rib structured surfaces impact heat transfer by enhancing heat transfer rate for drops that move along the rib direction compared with drops that move perpendicular to the ribs. The difference is likely due to increased drop velocity that exists for the parallel rib orientation. Correlations that enable prediction of the heat transfer to rolling drops on superhydrophobic surfaces are presented that show excellent collapse of the experimental data.