The capillary-induced flow underneath nucleate bubbles is visualized on microtextured surfaces via synchrotron x-ray imaging.

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.

The primary moisture separator—a key component in the PWR nuclear power plant—determines the quality of supplied steam to a turbine. Investigating its characteristics is important because supplying steam with excessive droplet entrainment results in damages to pipes, valves, and turbines in power plant circuits. In this numerical study, the particle tracking method in the Eulerian–Lagrangian methodology is used to investigate the characteristics of a primary moisture separator. Various swirl vanes with different bending angles, vane quantities, and vane locations are chosen to investigate the effect of design parameters on characteristics of the primary moisture separator. Additionally, the water droplet size is considered to vary from 0.01 to 50 $\mathsf{\mu }$m in this study. The pressure drop between the inlet and outlet, the steam quality at the orifice outlet, and the particle collection ratio are discussed in this paper. The results show that steam quality increases as the bending angle decreases, and increasing the number of swirl vanes increases both the pressure drop and the steam quality.

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.