Heat Transfer to Stationary and Rolling Droplets on Carbon Nanotube Superhydrophobic Surfaces

Superhydrophobic (SH) surfaces reduce liquid–solid contact and can greatly alter heat transfer characteristics compared to smooth or hydrophilic surfaces. While previous work has studied heat transfer to stationary droplets or droplets sliding on inclined SH surfaces, heat transfer to droplets on nanostructured carbon nanotube (CNT) SH surfaces remains largely unexplored experimentally. This study presents experimental measurements of heat transfer to water droplets—both stationary and rolling or sliding—on level and inclined heated SH surfaces nano-textured with CNT forests. Experiments were performed by releasing droplets of controlled volume (20–50 µL) onto SH surfaces inclined at 0–10 degrees and maintained at a constant temperature (≈80 °C). An infrared camera captured droplet temperatures over time as they rested on or rolled down the surfaces. Image processing software then enabled calculation of heating effectiveness as a function of CNT height, CNT diameter, droplet volume, and inclination angle. Preliminary results show approximately a 45% reduction in heat effectiveness for level CNT surfaces and a 75% reduction for inclined (10°) surfaces compared to low solid fraction (0.09) microstructured SH surfaces.[RJ1] High variability exists in heating effectiveness for both stationary and dynamic droplets, likely due to the high area density of imperfections present on the surfaces. Average heat effectiveness appears similar for surfaces with differing CNT heights and/or diameters. These findings advance understanding of dynamic thermal transport on SH surfaces and have implications for heat exchanger design, condensation, and self-cleaning applications.