Hydrodynamic Behaviour and Influence of Channel Wall Roughness and Hydrophobicity in Microchannels

The sometimes contradictory results available for fluid flow in micropipes show that much is yet to be verified in micro fluid dynamics. In this study the influence of channel wall roughness and of channel wall roughness and of channel wall hydrophobicity on adiabatic flow in circular microchannels is investigated, varying in diameter from 70 μm to 326 μm. The hydrodynamic behaviour of water in smooth tubes down to 30 μm inner diameter (ID) is also ascertained. Within the current experimental accuracy it is found that the classical Hagen-Poiseuille law for friction factor vs. Reynolds number is respected for all diameters measured and Re > 300. With degassed water, no effect of slip flow conditions due to hydrophobic channel walls even at 70 μm ID was noted, which might suggest that the slip flow phenomenon is associated with local desorption of dissolved gases on the hydrophobic surface, as reported elsewhere in the literature. For roughened glass channels, an increase in friction factor above 64/Re was observed only at the smallest diameter measured, 126 μm. For all experiments, no anticipated transition to turbulent flow was observed (2000 < Re_tr < 3000).