Mixing enhancement of electrokinetically-driven non-Newtonian fluids in microchannel with patterned blocks

A numerical investigation is performed into the mixing characteristics of electrokinetically-driven non-Newtonian fluids in microchannels containing patterned blocks. In performing the simulations, the rheological behavior of the fluid is described using a power-law model. Two different types of patterned blocks are considered, namely rectangular and wavy. The effects of the geometry parameters of the patterned blocks and the flow behavior index in the power-law model on the mixing efficiency within the microchannel are systematically explored. The results show that the rectangular patterned blocks yield a better mixing performance than the wavy patterned blocks. However, for both types of block, the mixing efficiency can be improved by increasing the width and length of the blocks and extending the total length of the block region. In addition, the results show that the flow behavior index in the power-low model has a significant effect on the mixing performance. Specifically, the volumetric flow rate increases with a decreasing flow behavior index, and therefore results in a poorer mixing performance. It is shown that a heterogeneous patterning of the zeta potential on the upper surfaces of the rectangular and wavy blocks prompts the formation of local flow recirculations, and therefore improves the mixing efficiency. In addition, it is shown that the mixing performance improves with an increasing magnitude of the heterogeneous surface zeta potential. Overall, the results show that the mixing efficiency of non-Newtonian fluids with a low flow behavior index can be improved by utilizing blocks with an appropriate geometry, applying a heterogeneous distribution of the surface zeta potential, and increasing the magnitude of the zeta potential. (C) 2012 Elsevier B.V. All rights reserved.