Effect of wall roughness on fluid flow inside a microchannel

Microfluidics is a promising technology, although the governing physical mechanisms are still not quite understood due to the difficulties arising in measuring at such small scales. This work intends to bring some insight on the influence of surface phenomena in microscale flows by proposing a different method to quantify such influence. In this new method, detailed velocity measurements are performed to evaluate the influence on the flow of the surface phenomena instead of using measured bulk flow properties . For that Micro-PIV is used to characterize the flow kinematics inside a DantecDynamics® microchannel (with hydraulic diameter of 637 µm) that possesses rather rough walls (relative roughness of 1.6%) and a very irregular cross-section shape. Two-dimensional velocity profiles were measured in 61 horizontal planes to define the three- dimensional laminar flows (Re � 50). Integration of the velocity profiles yielded volumetric flow rates with a maximum deviation of 3% from the measured volume of fluid discharged as function of time, which gives the magnitude of the bias error of the experimental technique. Effects of walls roughness were quantified by comparing Poiseuille numbers obtained from experimental velocity profiles against those obtained from CFD predictions for the same operating conditions but with hydrodynamically smooth walls, according to the new method proposed herein. Those Poiseuille numbers differed 11% , for an estimated uncertainty of 4.5%, demonstrating the need to account for wall roughness in microflows.