Effects of rough elements on mixing in microchannels

For incompressible fluids, no discernible differences exist between microscale and macroscale flows. However, surface roughness has emerged as a significant factor influencing mass transport phenomena at the microscale due to the substantial increase in the surface-to-volume ratio. In this work, we establish a model of a cross-shaped micromixer with structural roughness elements using the finite-element software Comsol. A comprehensive study is conducted to assess the effects of roughness parameters on mixing performance. Our findings indicate that the roughness height can improve mixing quality compared to smooth channels, which is attributed to the extrusion of roughness on the working medium at a low Reynolds number (Re) of 1 and the increase of lateral velocity at high Re = 50. When the roughness height is increased from 2 to 20 μm, the maximum mixing quality is increased by about 7.4 and 32.8% at Re = 1 and 50, respectively. Furthermore, narrowing the roughness pitch enhances the perturbation frequency of microfluidics, thus facilitating the mixing process. When the pitch is reduced from 200 to 20 μm, the maximum mixing quality at Re = 1 and 50 increases by about 1.9 and 13.8%, respectively. This paper provides new insights into the influence of microrough structures on mixing.