Understanding the Role of Superhydrophobicity on Heat Transfer Enhancement During Dropwise Condensation in Humid Air Flow

Superhydrophobic surfaces have been extensively studied to enhance heat transfer during moisture condensation. However, the existing literature presents conflicting results, with some studies reporting enhanced performance while others observe a decline compared to hydrophilic surfaces. Furthermore, the effect of air velocity has been marginally addressed. In this work, superhydrophobic aluminum surfaces (advancing contact angle of 160°, contact angle hysteresis <1°) are fabricated by chemical etching followed by fluorosilane coating. Condensation tests are performed at constant air temperature (28 °C), while varying relative humidity (70%, 90%), dew-to-wall temperature difference (7–13 K) and air velocity (0.4–6 m s−1). It is found that, compared to the hydrophilic untreated surface, superhydrophobic surfaces do not offer any advantage at low air velocities (0.4 and 1 m s−1), while a condensation heat transfer coefficient increased by 30%–40% is achieved at high air velocities (4 and 6 m s−1). The performance is attributed to a more efficient droplet removal mechanism and enhanced vapor mass transfer through the non-condensable gas layer, which is also associated with droplet-induced vorticity, as confirmed by video analysis. The results clarify the operating conditions under which superhydrophobic surfaces are advantageous for applications of condensation from humid air, including dehumidification.