Bekir Doğan, Ünsal Aybek
Surface hydrophobicity plays an important role in modifying the interfacial interaction between fluid and solid boundaries, which may lead to reduced wall shear stress and pressure losses in internal flows. In this study, the influence of surface hydrophobicity on frictional pressure drop in laminar pipe flow was investigated using computational fluid dynamics simulations supported by experimental contact angle measurements. Experiments were conducted using a goniometer to determine the static contact angles of three commonly used metallic surfaces: iron (Fe), aluminum (Al), and copper (Cu). The measured contact angles were approximately 78°, 95°, and 105°, respectively, indicating different levels of surface wettability. A three-dimensional laminar flow model was developed for a circular pipe with a diameter of 4 mm and a length of 400 mm. The hydrophobic effects were represented in the computational fluid dynamics simulations by introducing partial slip boundary conditions through user-defined functions. Numerical simulations were performed for Reynolds numbers of 500, 1000, 1500, and 2000, resulting in a total of 12 simulation cases. The results demonstrate that increasing surface hydrophobicity leads to a measurable reduction in pressure drop due to the decrease in wall shear resistance associated with partial slip behavior. Among the investigated surfaces, the copper surface, which exhibited the highest contact angle, showed the lowest pressure losses. The findings highlight the potential of hydrophobic surface characteristics in reducing flow resistance in small-scale internal flow systems and provide insight into the relationship between experimentally measured wettability and numerical slip modeling. These results may contribute to the design and optimization of compact fluid transport systems, micro/mini-scale flow devices, and thermal engineering applications where frictional pressure losses are critical.