Numerical Investigation of Friction Behavior in Microchannels with Hydrophobic Surface Properties Using VOF Model

Abstract

This study numerically investigates the frictional behavior of microchannels with regularly structured, microscale, column-shaped surface roughness, focusing on how variations in geometrical parameters affect shear stress under laminar flow. Simulations were conducted using the volume of fluid (VOF) model in ANSYS Fluent. Contact angle measurements across five surface models ranged from 78.04 degrees to 137.07 degrees, with the highest shear stress reduction (34.79%) observed in the S10W10H30Q25 model, which also had the highest contact angle. Roughness height had a nonlinear effect: while H = 3 mu m models showed higher shear stress, increasing the height to 20 mu m reduced it, but further increase to 30 mu m caused it to rise again. Nineteen microchannel models were evaluated to assess the effect of groove width (W) under constant roughness spacing (S). Results showed that increasing W generally reduced the drag-reducing effect. The greatest reduction (38.13%) occurred in the S10W5H30Q11 model. Additionally, 14 models were analyzed with constant roughness height (H = 30 mu m) and fixed W values to investigate the effect of spacing (S) between roughness elements. A nonlinear relationship between S and shear stress was observed in all groups, with optimal performance again found in the S10W10H30Q25 model (9.76 Pa). The results demonstrate that four geometric parameters-contact angle, roughness height, roughness width, and roughness spacing-significantly and often nonlinearly influence friction in microchannel flows. Identifying the optimal combination of these parameters is critical for designing low-friction, high-efficiency microfluidic systems.