Over the past decades, pool boiling on various wetting surfaces has been intensively investigated to enhance boiling heat transfer and critical heat flux. In this study, to enhance the two thermal performances simultaneously, we developed hydrophilic micro/nanotextured surfaces with hydrophobic patterns. Using a silicon substrate, well-arrayed microtextures and randomly arrayed nanotextures were fabricated hierarchically using micro/nanoelectromechanical system processes. The top of the microtextures was coated locally with hydrophobic characteristics using specific self-assembled monolayer coating methods. Based on experimental data, we postulate that the critical heat flux was enhanced by the capillary-induced flow between microtextures and that nanotextures with superhydrophilicity contribute to the delay of the critical heat flux by better wetting the dried area. Owing to the hydrophobicity at the top of the micropillars, the nucleate site density and boiling heat transfer increased.

For decades, numerous researchers have evaluated dynamic contact angles to understand the interfacial behaviors of moving contact lines. However, owing to the limitations of visualization techniques based on light rays, experiments for dynamic contact angles have typically been conducted in high solid–liquid interaction cases (e.g., hydrophilic surfaces with oil fluids). Currently, in research and industrial fields, there is a continuous need for research on dynamic contact angles in low solid–liquid interaction cases (e.g., hydrophobic surfaces with aqueous fluids); therefore, in this study, we used synchrotron x-ray imaging with high temporal (∼1000 fps)/spatial (∼1.1 μm/pixel) resolutions to precisely measure the dynamic contact angles of various aqueous fluids (distilled water, water–ethanol 5% mixture, and water–ethanol 10% mixture) in hydrophobic minitubes (D = 1.580, 1.023 mm) and microtubes (D = 0.796 mm). Based on the visualization data, we analyzed the dynamic/static contact angles and pressure drops at the moving contact lines according to the fluid properties and tube diameters. This study proposes that the contact angle hysteresis, dynamic contact angles, and pressure drop at the moving contact lines in hydrophobic capillary tubes can be estimated using modified equations and correlations.

For decades, numerous researchers have evaluated dynamic contact angles to understand the interfacial behaviors of moving contact lines. However, owing to the limitations of visualization techniques based on light rays, experiments for dynamic contact angles have typically been conducted in high solid–liquid interaction cases (e.g., hydrophilic surfaces with oil fluids). Currently, in research and industrial fields, there is a continuous need for research on dynamic contact angles in low solid–liquid interaction cases (e.g., hydrophobic surfaces with aqueous fluids); therefore, in this study, we used synchrotron x-ray imaging with high temporal (∼1000 fps)/spatial (∼1.1 μm/pixel) resolutions to precisely measure the dynamic contact angles of various aqueous fluids (distilled water, water–ethanol 5% mixture, and water–ethanol 10% mixture) in hydrophobic minitubes (D = 1.580, 1.023 mm) and microtubes (D = 0.796 mm). Based on the visualization data, we analyzed the dynamic/static contact angles and pressure drops at the moving contact lines according to the fluid properties and tube diameters. This study proposes that the contact angle hysteresis, dynamic contact angles, and pressure drop at the moving contact lines in hydrophobic capillary tubes can be estimated using modified equations and correlations.