Natural dropwise condensation of humid air on engineered flat surfaces: An experimental study

This study investigates the natural dropwise condensation of humid air on various surfaces, with different material and textures. A comparative study is performed between micro and nanotextured surfaces, for the first time. The present study finds that microtextured superhydrophobic substrates can outperform nanotextured by two to three times for moist air condensation. This is attributed to the higher heat transfer area despite a higher contact angle hysteresis. The present study also proposes a novel correlation from over 700 experimental results for the condensation heat transfer coefficient considering relative humidity, humid air temperature, surface temperature, apparent contact angle, contact angle hysteresis, and inclination angle. Contact angle and its hysteresis were found to have optimal values in maximizing the heat transfer coefficient. Inclination angle and relative humidity were also substantial factors, with the vertical orientation outperforming the horizontal by up to 20 %, and relative humidity found to linearly affect the heat transfer coefficient. These findings offer valuable insights into humid air dropwise condensation, particularly relevant for dehumidification and atmospheric water harvesting systems whose advancement relies heavily on condensation heat transfer coefficients.