Effect of Surface Hydrophilicity and Hydrophobicity on Droplet Behavior in Tiny Rectangular Flow Channels

The effective management of gas–liquid two-phase flow, emerging within the microchannels of proton exchange membrane fuel cells (PEMFCs) during operations, is crucial for improving energy conversion efficiency. In this study, the influence of surface wettability is examined for hydrophilic and hydrophobic conditions through a visualization-based experimental setup focused on single-droplet dynamics. The impact of key parameters on droplet behavior is systematically explored, while the mechanisms underlying the observed flow patterns are elucidated and the coupling among governing physical factors is clarified. The results show that, under comparable conditions, hydrophobic surfaces exhibit larger advancing contact angles and greater contact-angle hysteresis. At low Reynolds numbers, they also display higher receding contact angles. In addition, droplets on hydrophobic surfaces present consistently smaller infiltration diameters than those on hydrophilic ones, indicating a stronger tendency to detach under imposed flow conditions.