Colloids and Surfaces A: Physicochem. Eng. Aspects 374 (2011) 142–153 Contents lists available at ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa Numerical analysis of mixed electroosmotic/pressure driven flow of power-law fluids in microchannels and micropumps Mohammad Hadigol ∗ , Reza Nosrati, Mehrdad Raisee Department of Mechanical Engineering, Faculty of Engineering, University of Tehran, Tehran, Iran article info Article history: Received 13 August 2010 Received in revised form 14 October 2010 Accepted 28 October 2010 Available online 5 November 2010 Keywords: Finite volume scheme Power-law fluid Microfluidics Mixed electroosmotic/pressure driven flow abstract Mixed electroosmotic/pressure driven (EO/PD) flow of power-law fluids in microchannels and microp- umps is analyzed using a numerical scheme based on the finite volume formulation. Effects of the fluid behavior index (n), zeta potential and electric double layer (EDL) thickness are investigated on character- istics of pure EO and mixed EO/PD flow of power-law fluids in microchannels and micropumps. Results show that the velocity profile becomes more plug-like as the fluid behavior index, decreases. Concerning EO micropumping of power-law fluids, it was found that higher volumetric flow rates can be expected in EO micropumping of pseudoplastic fluids (n < 1). It was observed that increase in zeta potential or decrease in EDL thickness results in higher pressure rise and volumetric flow rate of EO micropumping of pseudoplastic fluids, while these changes do not have considerable effects on pressure rise and the volumetric flow rate of EO micropumping of dilatant fluids (n > 1). Moreover, pressure rise of power-law fluid in a closed system (zero net flow rate) under the influence of EO forces was studied and it was revealed that a higher pressure rise can be generated as the fluid behavior index decreases. © 2010 Elsevier B.V. All rights reserved. 1. Introduction In recent years, micro-electro-mechanical systems (MEMS) have been the topic of extensive research due to increasing demands for transport of biofluids through lab-on-a-chip based microsystems in biomedical and biotechnological applications. MEMS-fluidics is classified as MEMS devices which involve fluid transportation. Microchannels and micropumps, as the significant parts of MEMS-fluidics, have characteristic dimensions in range of micrometer. These devices are not simply scale-down version of the conventional ones because the fluid behavioral at microscale can be significantly different compare to macroscale. For exam- ple, electrokinetic and surface tension effects become dominate at microscale. A good understanding of fluid flows in these microscale channels and pumps can contribute to the design of more efficient and accurate MEMS devices [1–8]. While in most conventional applications liquid flows are derived by applying a pressure difference along the flow direction, impos- ing an electric field to liquid carrying free charges is a practical method for transporting liquids in micro- and nanochannels. The former method is known as PD flow, whilst the latter one is the ∗ Corresponding author at: Department of Mechanical Engineering, Faculty of Engineering, University of Tehran, P.O. Box: 11365/4563, Tehran, Iran. Tel.: +98 21 88337123; fax: +98 21 88013029. E-mail address: Hadigol@ut.ac.ir (M. Hadigol). EO flow. EO flow enables variety of micro- and nano-fluidic sys- tems such as pumps, mixers, and valves, which can be utilize in biology, medicine, biochips and other high level technologies. EO flow enjoys numerous advantages, including ease of fabrication and control, no need for moving parts, high reliability, and no noise. Comprehensive reviews of EO micropumping can be found in Laser and Santiago [9]. Biofluids, which exhibit non-Newtonian fluid flow behavior, are often used in MEMS-fluidics. Due to the importance of Bio-MEMS and lab-on-a-chip technologies, many researchers have recently focused on non-Newtonian fluid behavior of biofluids in electroki- netically driven flows. For example, Das and Chakraborty [10] obtained an analytical solution, describing the transport character- istics of a non-Newtonian fluid flow in a rectangular microchannel, under the sole influence of electrokinetic effects. As an illustrative case study, they analyzed the flow behavior of a blood sample. Zhao et al. [11] analyzed EO flow of power-law fluids in a slit microchannel by introducing exact and approximate analytical expressions for the shear stress, effective viscosity and velocity profile distribution. Akgul and Pakdemirli [12] presented analytical and numerical solutions for EO flow of a third grade fluid between micro-parallel plates. They analyzed influences of non-Newtonian parameter, Joule heating effect, viscosity index and electrokinetic effect on the velocity and temperature profiles. Berli and Olivares [13] introduced a theoretical description of the electrokinetic flow of non-Newtonian fluids through slit and cylindrical microchan- nels. Tang et al. [14] reported a numerical study of the flow behavior 0927-7757/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.colsurfa.2010.10.045