A combined active/passive scheme for enhancing the mixing efficiency of microfluidic devices

The straight microchannels used in conventional microfluiclic devices yield a poor mixing performance because the fluid flow is restricted to the low Reynolds number regime, and hence mixing takes place primarily as a result of diffusion. In an attempt to improve the mixing efficiency of pressure-driven microfluidic flows, the current study applies periodic velocity perturbations to the species flows at the microchannel inlet and incorporates a wavy-wall section within the mixing channel. Numerical simulations are performed to analyze the respective effects on the mixing efficiency of the geometric amplitude of the wavy surface, the length of the wavy-wall section, and the Strouhal number of the periodic velocity perturbations. Overall, the results reveal that the mixing performance is improved by increasing the geometric wave amplitude or length of the wavy-wall section and by applying a Strouhal number in the range 0.33-0.67. (C) 2008 Elsevier Ltd. All rights reserved.